Patent Publication Number: US-2023143387-A1

Title: Distance measuring system

Description:
TECHNICAL FIELD 
     The present disclosure relates to an imaging device and an electronic device. 
     BACKGROUND ART 
     In recent years, an imaging device has adopted a method of detecting a phase difference using a pair of phase difference detection pixels as an autofocus function. As such an example, an imaging element disclosed in Patent Document 1 below can be mentioned. In the technique disclosed in Patent Document 1, both an effective pixel that captures an image of a subject and a phase difference detection pixel that detects a phase difference as described above are separately provided on a light receiving surface. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: JP 2000-292685 A 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the technology disclosed in Patent Document 1, when a captured image of a subject is acquired, it is difficult to use information obtained by the phase difference detection pixel as information similar to information from the imaging pixel. Therefore, interpolation is performed on an image of a pixel corresponding to the phase difference detection pixel using information from effective pixels around the phase difference detection pixel to generate a captured image. That is, in the technology disclosed in Patent Document 1, since the phase difference detection pixel is provided to perform the phase difference detection, it is difficult to avoid deterioration of the captured image due to a loss of information of the captured image corresponding to the phase difference detection pixel. 
     Therefore, the present disclosure proposes an imaging device and an electronic device capable of avoiding deterioration of a captured image while improving accuracy of phase difference detection. 
     Solutions to Problems 
     According to the present disclosure, there is provided an imaging device including: a semiconductor substrate; and a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which each of the plurality of imaging elements includes: a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; an element separation wall surrounding the plurality of pixels and provided so as to penetrate the semiconductor substrate; an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels; and a first separation portion provided in a region surrounded by the element separation wall to separate the plurality of pixels, the first separation portion is provided so as to extend in a thickness direction of the semiconductor substrate, and a first diffusion region containing impurities of a second conductivity type opposite to the first conductivity type is provided in a region positioned around the first separation portion and extending in the thickness direction of the semiconductor substrate. 
     According to the present disclosure, there is provided an imaging device including: a semiconductor substrate; and a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which each of the plurality of imaging elements includes: a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; a pixel separation wall that separates the plurality of pixels; and an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels, the pixel separation wall is provided so as to extend from the light receiving surface to a middle of the semiconductor substrate along a thickness direction of the semiconductor substrate, and a region positioned on a side opposite to the light receiving surface with respect to the pixel separation wall in the thickness direction of the semiconductor substrate contains impurities of a second conductivity type opposite to the first conductivity type. 
     According to the present disclosure, there is provided an electronic device including: an imaging device including: a semiconductor substrate; and a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which each of the plurality of imaging elements includes: a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; an element separation wall surrounding the plurality of pixels and provided so as to penetrate the semiconductor substrate; an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels; and a first separation portion provided in a region surrounded by the element separation wall to separate the plurality of pixels, the first separation portion is provided so as to extend in a thickness direction of the semiconductor substrate, and a first diffusion region containing impurities of a second conductivity type opposite to the first conductivity type is provided in a region positioned around the first separation portion and extending in the thickness direction of the semiconductor substrate. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an explanatory diagram illustrating a planar configuration example of an imaging device  1  according to an embodiment of the present disclosure. 
         FIG.  2    is an explanatory diagram (part  1 ) illustrating a part of a cross-section of an imaging element  100  according to the first embodiment of the present disclosure. 
         FIG.  3    is an explanatory diagram (part  2 ) illustrating a part of a cross-section of the imaging element  100  according to the first embodiment of the present disclosure. 
         FIG.  4    is an explanatory diagram illustrating a plane of the imaging element  100  according to the first embodiment of the present disclosure. 
         FIG.  5    is a transparent perspective view of the imaging element  100  according to the first embodiment of the present disclosure. 
         FIG.  6    is an explanatory diagram illustrating a configuration example of a light shielding portion  204  according to the first embodiment of the present disclosure. 
         FIG.  7    is an explanatory diagram illustrating a configuration example of a light shielding portion  204  according to a modified example of the first embodiment of the present disclosure. 
         FIG.  8    is an explanatory diagram illustrating a plane of an imaging element  100  according to a second embodiment of the present disclosure. 
         FIG.  9    is an explanatory diagram illustrating a plane of an imaging element  100  according to a third embodiment of the present disclosure. 
         FIG.  10    is an explanatory diagram (part  1 ) illustrating a plane of an imaging element  100  according to a fourth embodiment of the present disclosure. 
         FIG.  11    is an explanatory diagram (part  2 ) illustrating a plane of the imaging element  100  according to the fourth embodiment of the present disclosure. 
         FIG.  12    is an explanatory diagram (part  3 ) illustrating a plane of the imaging element  100  according to the fourth embodiment of the present disclosure. 
         FIG.  13    is an explanatory diagram illustrating a plane of an imaging element  100  according to a fifth embodiment of the present disclosure. 
         FIG.  14    is an explanatory diagram illustrating a plane of an imaging element  100  according to a sixth embodiment of the present disclosure. 
         FIG.  15    is an explanatory diagram illustrating a plane of an imaging element  100  according to a seventh embodiment of the present disclosure. 
         FIG.  16    is an explanatory diagram illustrating a configuration example of a light shielding portion  204  according to the seventh embodiment of the present disclosure. 
         FIG.  17    is an explanatory diagram (part  1 ) illustrating a part of a cross-section of an imaging element  100  according to an eighth embodiment of the present disclosure. 
         FIG.  18    is an explanatory diagram (part  1 ) illustrating a plane of the imaging element  100  according to the eighth embodiment of the present disclosure. 
         FIG.  19    is an explanatory diagram (part  2 ) illustrating a plane of the imaging element  100  according to the eighth embodiment of the present disclosure. 
         FIG.  20    is an explanatory diagram (part  2 ) illustrating a part of a cross-section of the imaging element  100  according to the eighth embodiment of the present disclosure. 
         FIG.  21    is an explanatory diagram (part  3 ) illustrating a part of a cross-section of the imaging element  100  for each color according to the eighth embodiment of the present disclosure. 
         FIG.  22    is an explanatory diagram (part  3 ) illustrating a plane of the imaging element  100  according to the eighth embodiment of the present disclosure. 
         FIG.  23    is an explanatory diagram (part  4 ) illustrating a part of a cross-section of the imaging element  100  according to the eighth embodiment of the present disclosure. 
         FIG.  24    is an explanatory diagram (part  4 ) illustrating a plane of the imaging element  100  according to the eighth embodiment of the present disclosure. 
         FIG.  25    is an explanatory diagram (part  5 ) illustrating a part of a cross-section of the imaging element  100  according to the eighth embodiment of the present disclosure. 
         FIG.  26    is a process cross-sectional view for explaining a part of the manufacturing process of the imaging element  100  according to the eighth embodiment of the present disclosure. 
         FIG.  27    is an explanatory diagram illustrating a plane of an imaging element  100  according to a ninth embodiment of the present disclosure. 
         FIG.  28    is an explanatory diagram (part  1 ) illustrating a part of a cross-section of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  29    is an explanatory diagram illustrating a part of a cross-section of an imaging element  100  according to a comparative example of the ninth embodiment of the present disclosure. 
         FIG.  30    is an explanatory diagram (part  2 ) illustrating a part of a cross-section of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  31    is an explanatory diagram (part  3 ) illustrating a part of a cross-section of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  32    is an explanatory diagram (part  4 ) illustrating a part of a cross-section of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  33    is an explanatory diagram (part  5 ) illustrating a part of a cross-section of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  34    is an explanatory diagram (part  6 ) illustrating a part of a cross-section of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  35    is an explanatory diagram (part  7 ) illustrating a part of a cross-section of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  36    is an explanatory diagram (part  2 ) illustrating a plane of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  37    is a process cross-sectional view (part  1 ) for explaining a part of the manufacturing process of the imaging device  1  according to the ninth embodiment of the present disclosure. 
         FIG.  38    is a process cross-sectional view (part  2 ) for explaining a part of the manufacturing process of the imaging device  1  according to the ninth embodiment of the present disclosure. 
         FIG.  39    is an explanatory diagram (part  1 ) illustrating a plane of an imaging element  100  according to a tenth embodiment of the present disclosure. 
         FIG.  40    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  according to the tenth embodiment of the present disclosure. 
         FIG.  41    is an explanatory diagram illustrating a part of a cross-section of an imaging element  100  according to a comparative example of a tenth embodiment of the present disclosure. 
         FIG.  42    is a graph illustrating a relationship between a slit width and a protruding portion width according to a tenth embodiment of the present disclosure. 
         FIG.  43    is a process cross-sectional view (part  1 ) for explaining a part of the manufacturing process of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  44    is a process cross-sectional view (part  2 ) for explaining a part of the manufacturing process of the imaging element  100  according to the ninth embodiment of the present disclosure. 
         FIG.  45    is an explanatory diagram (part  2 ) illustrating a plane of an imaging element  100  according to a tenth embodiment of the present disclosure. 
         FIG.  46    is an explanatory diagram (part  3 ) illustrating a plane of an imaging element  100  according to the tenth embodiment of the present disclosure. 
         FIG.  47    is an explanatory diagram (part  4 ) illustrating a plane of the imaging element  100  according to the tenth embodiment of the present disclosure. 
         FIG.  48    is an explanatory diagram (part  5 ) illustrating a plane of the imaging element  100  according to the tenth embodiment of the present disclosure. 
         FIG.  49    is an explanatory diagram (part  6 ) illustrating a plane of the imaging element  100  according to the tenth embodiment of the present disclosure. 
         FIG.  50    is an explanatory diagram (part  7 ) illustrating a plane of the imaging element  100  according to the tenth embodiment of the present disclosure. 
         FIG.  51    is an explanatory diagram (part  1 ) illustrating a plane of an imaging element  100  according to an eleventh embodiment of the present disclosure. 
         FIG.  52    is an explanatory diagram illustrating a plane of an imaging element  100  according to a comparative example of the eleventh embodiment of the present disclosure. 
         FIG.  53    is a process cross-sectional view for explaining a part of the manufacturing process of the imaging element  100  according to the eleventh embodiment of the present disclosure. 
         FIG.  54    is an explanatory diagram (part  2 ) illustrating a plane of the imaging element  100  according to the eleventh embodiment of the present disclosure. 
         FIG.  55    is an explanatory diagram (part  3 ) illustrating a plane of the imaging element  100  according to the eleventh embodiment of the present disclosure. 
         FIG.  56    is an explanatory diagram (part  4 ) illustrating a plane of the imaging element  100  according to the eleventh embodiment of the present disclosure. 
         FIG.  57    is an explanatory diagram (part  5 ) illustrating a plane of the imaging element  100  according to the eleventh embodiment of the present disclosure. 
         FIG.  58    is an explanatory diagram (part  1 ) illustrating a plane of an imaging element  100  according to a twelfth embodiment of the present disclosure. 
         FIG.  59    is an explanatory diagram (part  1 ) illustrating both surfaces and a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  60    is an explanatory diagram illustrating a relationship between a slit width, a condensing characteristic, and a pixel characteristic of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  61    is an explanatory diagram (part  2 ) illustrating both surfaces and a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  62    is an explanatory diagram (part  3 ) illustrating a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  63    is an explanatory diagram (part  4 ) illustrating a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  64    is an explanatory diagram (part  5 ) illustrating a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  65    is an explanatory diagram (part  6 ) illustrating both surfaces and a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  66    is an explanatory diagram (part  7 ) illustrating a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  67    is an explanatory diagram (part  8 ) illustrating both surfaces of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  68    is an explanatory diagram (part  9 ) illustrating both surfaces and a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  69    is an explanatory diagram (part  10 ) illustrating both surfaces and a cross-section of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  70    is an explanatory diagram (part  11 ) illustrating both surfaces of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  71    is an explanatory diagram (part  12 ) illustrating both surfaces of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  72    is a process cross-sectional view for explaining a part of the manufacturing process of the imaging element  100  according to the twelfth embodiment of the present disclosure. 
         FIG.  73    is an explanatory diagram (part  1 ) illustrating a plane of an imaging element  100  according to a thirteenth embodiment of the present disclosure. 
         FIG.  74    is an explanatory diagram illustrating a plane of an imaging element  100  according to a comparative example of the thirteenth embodiment of the present disclosure. 
         FIG.  75    is an explanatory diagram (part  2 ) illustrating a plane of the imaging element  100  according to the thirteenth embodiment of the present disclosure. 
         FIG.  76    is an explanatory diagram (part  3 ) illustrating a plane of the imaging element  100  according to the thirteenth embodiment of the present disclosure. 
         FIG.  77    is an explanatory diagram (part  4 ) illustrating a plane of the imaging element  100  according to the thirteenth embodiment of the present disclosure. 
         FIG.  78    is an explanatory diagram (part  5 ) illustrating a plane of the imaging element  100  according to the thirteenth embodiment of the present disclosure. 
         FIG.  79    is an explanatory diagram (part  1 ) illustrating a plane of an imaging element  100  according to another embodiment of the present disclosure. 
         FIG.  80    is an explanatory diagram (part  1 ) illustrating a part of a cross-section of an imaging element  100  for each structure according to another embodiment of the present disclosure. 
         FIG.  81    is an explanatory diagram (part  2 ) illustrating a plane of an imaging element  100  according to another embodiment of the present disclosure. 
         FIG.  82    is an explanatory diagram (part  2 ) illustrating a part of a cross-section of an imaging element  100  for each structure according to another embodiment of the present disclosure. 
         FIG.  83    is an explanatory diagram (part  3 ) illustrating a plane of an imaging element  100  according to another embodiment of the present disclosure. 
         FIG.  84    is an explanatory diagram (part  4 ) illustrating a plane of an imaging element  100  according to another embodiment of the present disclosure. 
         FIG.  85    is an explanatory diagram illustrating a cross-section of a two-layer stacked structure to which the imaging device  1  according to the embodiment of the present disclosure can be applied. 
         FIG.  86    is an explanatory diagram illustrating a cross-section of a three-layer stacked structure to which the imaging device  1  according to the embodiment of the present disclosure can be applied. 
         FIG.  87    is an explanatory diagram illustrating a cross-section of a two-stage pixel structure to which the imaging device  1  according to the embodiment of the present disclosure is applicable. 
         FIG.  88    is an explanatory diagram illustrating a plane of an imaging element  100  according to an embodiment of the present disclosure. 
         FIG.  89    is an explanatory diagram illustrating planes of a plurality of imaging elements  100  according to an embodiment of the present disclosure. 
         FIG.  90    is an explanatory diagram illustrating an example of a schematic functional configuration of a camera. 
         FIG.  91    is a block diagram illustrating an example of a schematic functional configuration of a smartphone. 
         FIG.  92    is a diagram illustrating an example of a schematic configuration of an endoscopic surgery system. 
         FIG.  93    is a block diagram illustrating an example of functional configurations of a camera head and a CCU. 
         FIG.  94    is a block diagram illustrating an example of a schematic configuration of a vehicle control system. 
         FIG.  95    is an explanatory diagram illustrating an example of installation positions of a vehicle exterior information detection unit and an imaging unit. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each of the following embodiments, the same parts are denoted by the same reference numerals, and redundant description will be omitted. 
     In addition, in the present specification and the drawings, a plurality of components having substantially the same or similar functional configurations may be distinguished by attaching different numbers after the same reference numerals. However, in a case where it is not particularly necessary to distinguish each of a plurality of components having substantially the same or similar functional configuration, only the same reference numeral is attached. In addition, similar components of different embodiments may be distinguished by adding different characters after the same reference numerals. However, in a case where it is not necessary to particularly distinguish each of similar components, only the same reference numeral is assigned. 
     In addition, the drawings referred to in the following description are drawings for facilitating the description and understanding of an embodiment of the present disclosure, and shapes, dimensions, ratios, and the like illustrated in the drawings may be different from actual ones for the sake of clarity. Furthermore, the imaging device illustrated in the drawings can be appropriately modified in design in consideration of the following description and known techniques. Furthermore, in the description using the cross-sectional view of the imaging device, the vertical direction of the stacked structure of the imaging device corresponds to a relative direction in a case where the light receiving surface into which the light incident on the imaging device enters is upward, and may be different from the vertical direction according to the actual gravitational acceleration. 
     The dimension expressed in the following description means not only a mathematically or geometrically defined dimension but also a dimension including an allowable difference (error/distortion) in the operation of the imaging device and the manufacturing process of the imaging device. Furthermore, “substantially the same” used for specific dimensions in the following description does not mean only a case of mathematically or geometrically completely matching, but also a case of having a difference (error/distortion) to an allowable extent in the operation of the imaging device and the manufacturing process of the imaging device. 
     Furthermore, in the following description, “electrically connecting” means connecting a plurality of elements directly or indirectly via other elements. 
     Furthermore, in the following description, “sharing” means that one other element (for example, an on-chip lens or the like) is used together between elements different from each other (for example, a pixel or the like). 
     Note that the description will be given in the following order. 
     1. Schematic configuration of imaging device 
     2. Background of creation of embodiments according to present disclosure by present inventors 
     3. First Embodiment
         3.1 Cross-sectional configuration   3.2 Planar configuration   3.3 Modified example       

     4. Second Embodiment 
     5. Third Embodiment 
     6. Fourth Embodiment 
     7. Fifth Embodiment 
     8. Sixth Embodiment 
     9. Seventh Embodiment 
     10. Eighth Embodiment 
     11. Ninth Embodiment 
     12. Tenth Embodiment 
     13. Eleventh Embodiment 
     14. Twelfth Embodiment 
     15. Thirteenth Embodiment 
     16. Summary 
     17. Application example to camera 
     18. Application example to smartphone 
     19. Application example to endoscopic surgery system 
     20. Application example to mobile body 
     21. Supplement 
     1. Schematic Configuration of Imaging Device 
     First, a schematic configuration of an imaging device  1  according to an embodiment of the present disclosure will be described with reference to  FIG.  1   .  FIG.  1    is an explanatory diagram illustrating a planar configuration example of an imaging device  1  according to an embodiment of the present disclosure. As illustrated in  FIG.  1   , an imaging device  1  according to an embodiment of the present disclosure includes a semiconductor substrate  10  made of, for example, silicon, a pixel array unit  20  in which a plurality of imaging elements  100  is arranged in a matrix on the semiconductor substrate  10 , and a peripheral circuit unit provided so as to surround the pixel array unit  20 . Furthermore, the imaging device  1  includes, as the peripheral circuit unit, a vertical drive circuit unit  21 , a column signal processing circuit unit  22 , a horizontal drive circuit unit  23 , an output circuit unit  24 , a control circuit unit  25 , and the like. Hereinafter, details of each block of the imaging device  1  will be described. 
     (Pixel Array Unit  20 ) 
     The pixel array unit  20  includes a plurality of imaging elements  100  two-dimensionally arranged in a matrix along the row direction and the column direction on the semiconductor substrate  10 . Each imaging element  100  is an element that performs photoelectric conversion on incident light, and includes a photoelectric conversion unit (not illustrated) and a plurality of pixel transistors (for example, metal-oxide-semiconductor (MOS) transistors) (not illustrated). Then, the pixel transistor includes, for example, four MOS transistors of a transfer transistor, a selection transistor, a reset transistor, and an amplification transistor. Furthermore, in the pixel array unit  20 , for example, the plurality of imaging elements  100  is two-dimensionally arranged according to the Bayer array. Here, the Bayer array is an array pattern in which the imaging elements  100  that generate charges by absorbing light having a green wavelength (for example, a wavelength of 495 nm to 570 nm) are arranged in a checkered pattern, and the imaging elements  100  that generate charges by absorbing light having a red wavelength (for example, a wavelength of 620 nm to 750 nm) and the imaging elements  100  that generate charges by absorbing light having a blue wavelength (for example, a wavelength of 450 nm to 495 nm) are alternately arranged in the remaining portion for each line. Note that a detailed structure of the imaging element  100  will be described later. 
     (Vertical Drive Circuit Unit  21 ) 
     The vertical drive circuit unit  21  is formed by, for example, a shift register, selects a pixel drive wiring  26 , supplies a pulse for driving the imaging element  100  to the selected pixel drive wiring  26 , and drives the imaging element  100  in units of rows. That is, the vertical drive circuit unit  21  selectively scans each imaging element  100  of the pixel array unit  20  sequentially in the vertical direction (vertical direction in  FIG.  1   ) in units of rows, and supplies a pixel signal based on a signal charge generated according to the amount of light received by a photoelectric conversion unit (not illustrated) of each imaging element  100  to the column signal processing circuit unit  22  described later through a vertical signal line  27 . 
     (Column Signal Processing Circuit Unit  22 ) 
     The column signal processing circuit unit  22  is arranged for each column of the imaging elements  100 , and performs signal processing such as noise removal for each pixel column on the pixel signals output from the imaging elements  100  for one row. For example, the column signal processing circuit unit  22  performs signal processing such as correlated double sampling (CDS) and analog-digital (AD) conversion in order to remove fixed pattern noise unique to pixels. 
     (Horizontal Drive Circuit Unit  23 ) 
     The horizontal drive circuit unit  23  is formed by, for example, a shift register, sequentially selects each of the column signal processing circuit units  22  described above by sequentially outputting horizontal scanning pulses, and causes each of the column signal processing circuit units  22  to output a pixel signal to the horizontal signal line  28 . 
     (Output Circuit Unit  24 ) 
     The output circuit unit  24  performs signal processing on the pixel signals sequentially supplied from each of the column signal processing circuit units  22  described above through the horizontal signal line  28 , and outputs the pixel signals. The output circuit unit  24  may function as, for example, a functional unit that performs buffering, or may perform processing such as black level adjustment, column variation correction, and various digital signal processing. Note that buffering refers to temporarily storing pixel signals in order to compensate for differences in processing speed and transfer speed when pixel signals are exchanged. Furthermore, the input/output terminal  29  is a terminal for exchanging signals with an external device. 
     (Control Circuit Unit  25 ) 
     The control circuit unit  25  receives an input clock and data instructing an operation mode or the like, and outputs data such as internal information of the imaging device  1 . That is, the control circuit unit  25  generates a clock signal or a control signal serving as a reference of operations of the vertical drive circuit unit  21 , the column signal processing circuit unit  22 , the horizontal drive circuit unit  23 , and the like on the basis of the vertical synchronization signal, the horizontal synchronization signal, and the master clock. Then, the control circuit unit  25  outputs the generated clock signal and control signal to the vertical drive circuit unit  21 , the column signal processing circuit unit  22 , the horizontal drive circuit unit  23 , and the like. 
     2. Background of Creation of Embodiments According to Present Disclosure by Present Inventors 
     Next, before describing the details of the embodiment according to the present disclosure, the background in which the present inventors have created the embodiment according to the present disclosure will be described. 
     Meanwhile, the present inventors have intensively studied providing phase difference detection pixels on the entire surface of the pixel array unit  20  of the imaging device  1  (all-pixel phase difference detection) in order to further improve an autofocus function while avoiding deterioration of a captured image, that is, to improve accuracy of phase difference detection. Under such circumstances, it has been studied to provide an imaging element that functions as one imaging element at the time of imaging and functions as a pair of phase difference detection pixels at the time of phase difference detection on the entire surface of the pixel array unit  20  (dual photodiode structure). In such all-pixel phase difference detection, since the phase difference detection pixels are provided on the entire surface, the accuracy of phase difference detection can be improved, and further, since imaging can be performed by all the imaging elements, deterioration of the captured image can be avoided. 
     Furthermore, in order to improve the accuracy of the phase difference detection in the all-pixel phase difference detection, the present inventors have conceived that an element for physically and electrically separating the phase difference detection pixels is provided in order to prevent the outputs of the pair of phase difference detection pixels from being mixed at the time of phase difference detection. In addition, the present inventors have conceived that an overflow path is provided between a pair of phase difference detection pixels in order to avoid deterioration of a captured image in all-pixel phase difference detection. Specifically, at the time of normal imaging, when the charge of any one pixel of the phase difference detection pixels is about to be saturated, the charge is transferred to the other pixel via the overflow path, whereby saturation of one pixel can be avoided. Then, by providing such an overflow path, the linearity of the pixel signal output from the imaging element can be secured, and deterioration of the captured image can be prevented. 
     That is, on the basis of the viewpoint as described above, the present inventors have created an embodiment according to the present disclosure that makes it possible to avoid deterioration of a captured image while improving the accuracy of phase difference detection. Hereinafter, details of embodiments according to the present disclosure created by the present inventors will be sequentially described. 
     3. First Embodiment 
     3.1 Cross-Sectional Configuration 
     First, a cross-sectional configuration of an imaging element  100  according to a first embodiment of the present disclosure will be described with reference to  FIGS.  2  and  3   .  FIGS.  2  and  3    are explanatory diagrams illustrating a part of a cross-section of the imaging element  100  according to the present embodiment, and specifically, correspond to cross-sections obtained by cutting the imaging element  100  at different positions along the thickness direction of the semiconductor substrate  10 . 
     As illustrated in  FIGS.  2  and  3   , the imaging element  100  according to the present embodiment includes an on-chip lens  200 , a color filter  202 , a light shielding portion (light shielding film)  204 , a semiconductor substrate  10 , and transfer gates  400   a  and  400   b , similarly to the comparative example. Furthermore, in the present embodiment, the semiconductor substrate  10  includes a pair of pixels  300   a  and  300   b  each including a photoelectric conversion unit  302 . In addition, the semiconductor substrate  10  has a protruding portion (an example of a first separation portion)  304  separating the pair of pixels  300   a  and  300   b , and includes an element separation wall  310  surrounding the pixels  300   a  and  300   b  and a diffusion region  306  provided around the protruding portion  304  and the element separation wall  310 . Hereinafter, a stacked structure of the imaging element  100  according to the present embodiment will be described, but in the following description, description will be made in order from the upper side (light receiving surface  10   a  side) to the lower side in  FIGS.  2  and  3   . Note that  FIG.  2    corresponds to a cross-section obtained by cutting the imaging element  100  at a position where the above-described protruding portion  304  is cut, and  FIG.  3    corresponds to a cross-section obtained by cutting the imaging element  100  at a position where a region (slit  312 , see  FIG.  4   ) between the protruding portions  304  facing each other is cut. 
     As illustrated in  FIGS.  2  and  3   , the imaging element  100  includes one on-chip lens  200  that is provided above the light receiving surface  10   a  of the semiconductor substrate  10  and condenses incident light on the photoelectric conversion unit  302 . The imaging element  100  has a structure in which a pair of pixels  300   a  and  300   b  is provided for one on-chip lens  200 . That is, the on-chip lens  200  is shared by the two pixels  300   a  and  300   b . Note that the on-chip lens  200  can be formed of, for example, a silicon nitride film (SiN), or a resin material such as a styrene resin, an acrylic resin, a styrene-acrylic copolymer resin, or a siloxane resin. 
     Then, the incident light condensed by the on-chip lens  200  is emitted to each of the photoelectric conversion units  302  of the pair of pixels  300   a  and  300   b  via the color filter  202  provided below the on-chip lens  200 . The color filter  202  is any of a color filter that transmits a red wavelength component, a color filter that transmits a green wavelength component, and a color filter that transmits a blue wavelength component. For example, the color filter  202  can be formed of, for example, a material in which a pigment or a dye is dispersed in a transparent binder such as silicone. 
     Furthermore, a light shielding portion  204  is provided on the light receiving surface  10   a  of the semiconductor substrate  10  so as to surround the color filter  202 . Since the light shielding portion  204  is provided between the adjacent imaging elements  100 , it is possible to perform light shielding between the imaging elements  100  in order to suppress crosstalk between the adjacent imaging elements  100  and further improve accuracy in phase difference detection. The light shielding portion  204  can be formed of, for example, a metal material or the like containing tungsten (W), aluminum (Al), copper (Cu), titanium (Ti), molybdenum (Mo), nickel (Ni), or the like. 
     Moreover, for example, in the semiconductor substrate  10  of the second conductivity type (for example, P type), the photoelectric conversion unit  302  having the impurity of the first conductivity type (for example, N type) is provided for each of the pixels  300   a  and  300   b  adjacent to each other. As described above, the photoelectric conversion unit  302  absorbs the light L having the red wavelength component, the green wavelength component, or the blue wavelength component incident through the color filter  202 , and generates a charge. Then, in the present embodiment, the photoelectric conversion unit  302  of the pixel  300   a  and the photoelectric conversion unit  302  of the pixel  300   b  can function as a pair of phase difference detection pixels at the time of phase difference detection. That is, in the present embodiment, the phase difference can be detected by detecting a difference between pixel signals based on charges generated by the photoelectric conversion unit  302  of the pixel  300   a  and the photoelectric conversion unit  302  of the pixel  300   b.    
     Specifically, the photoelectric conversion unit  302  changes the amount of charge to be generated, that is, the sensitivity, depending on the incident angle of light with respect to its own optical axis (axis perpendicular to the light receiving surface). For example, the photoelectric conversion unit  302  has the highest sensitivity when the incident angle is 0 degrees, and the sensitivity of the photoelectric conversion unit  302  has a line-symmetric relationship with respect to the incident angle with the incident angle having 0 degrees as the object axis. Therefore, in the photoelectric conversion unit  302  of the pixel  300   a  and the photoelectric conversion unit  302  of the pixel  300   b , light from the same point is incident at different incident angles, and charges of amounts corresponding to the incident angles are generated, so that a shift (phase difference) occurs in the detected image. That is, the phase difference can be detected by detecting a difference between the pixel signals based on the charge amount generated by the photoelectric conversion unit  302  of the pixel  300   a  and the photoelectric conversion unit  302  of the pixel  300   b . Therefore, such a difference (phase difference) between the pixel signals is detected as a difference signal in a detection unit (not illustrated) of the output circuit unit  24 , for example, a defocus amount is calculated on the basis of the detected phase difference, and an image forming lens (not illustrated) is adjusted (moved), whereby autofocus can be realized. Note that, in the above description, it has been described that the phase difference is detected as a difference between the pixel signals of the photoelectric conversion unit  302  of the pixel  300   a  and the photoelectric conversion unit  302  of the pixel  300   b . However, in the present embodiment. However, the present invention is not limited thereto, and for example, the phase difference may be detected as a ratio between the pixel signals of the photoelectric conversion unit  302  of the pixel  300   a  and the photoelectric conversion unit  302  of the pixel  300   b.    
     Furthermore, in the present embodiment, the two photoelectric conversion units  302  are physically separated by the protruding portion  304 . The protruding portion  304  includes a trench (not illustrated) provided as a penetrating deep trench isolation (DTI) so as to penetrate the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 , and a material embedded in the trench and made of an oxide film such as a silicon oxide film (SiO), a silicon nitride film, amorphous silicon, polycrystalline silicon, a titanium oxide film (TiO), aluminum, or tungsten or a metal film. In the imaging element  100 , at the time of phase difference detection, in a case where the pixel signals output from the pair of pixels  300   a  and  300   b  are mixed with each other and color mixing occurs, accuracy of phase difference detection deteriorates. In the present embodiment, since the protruding portion  304  penetrates the semiconductor substrate  10 , the pair of pixels  300   a  and  300   b  can be physically separated effectively. As a result, the occurrence of color mixing can be suppressed, and the accuracy of phase difference detection can be further improved. 
     Furthermore, in a case where the imaging element  100  is viewed from the light receiving surface  10   a  side, a slit  312  (see  FIG.  4   ) corresponding to a space between the two protruding portions  304  is provided in the vicinity of the center of the imaging element  100 . Furthermore, in the region of the slit  312  (an example of a region positioned around the protruding portion  304  and extending in the thickness direction of the semiconductor substrate  10 ) in the semiconductor substrate  10 , the impurity of the second conductivity type (for example, the P type) is diffused via the protruding portion  304  by conformal doping, and the diffusion region  306  (an example of the first diffusion region) is formed (specifically, as will be described later, the diffusion region  306  is also formed around the element separation wall  310 ). In order to further improve the accuracy of phase difference detection, the diffusion region  306  can electrically separate the pair of pixels  300   a  and  300   b  so as not to cause color mixing. Furthermore, in the present embodiment, since the protruding portion  304  penetrates the semiconductor substrate  10 , the diffusion region  306  can be formed deep (here, the depth is a distance to the back surface  10   a  and the front surface  10   b  of the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 ) in the semiconductor substrate  10  by conformal doping via the protruding portion  304 . Therefore, in the present embodiment, since the desired diffusion region  306  can be formed with high accuracy, the pair of pixels  300   a  and  300   b  can be effectively electrically separated. As a result, the occurrence of color mixing can be suppressed, and the accuracy of phase difference detection can be further improved. Details of the region of the slit  312  will be described later. 
     Furthermore, in the present embodiment, as illustrated in  FIG.  3   , an impurity of the first conductivity type (for example, N type) is introduced by ion implantation below the diffusion region  306  (on the front surface  10   b  side) provided in the slit  312 , whereby the diffusion region  320  is formed. Specifically, the impurity of the first conductivity type is ion-implanted into the lower region in the diffusion region  306  described above, and a hole is formed in the diffusion region  306 , thereby forming the diffusion region  320 . Then, the diffusion region  320  functions as an overflow path capable of exchanging charges generated between the pixels  300   a  and  300   b . Specifically, at the time of normal imaging, when the charge of one pixel of the pixels  300   a  and  300   b  is about to be saturated, the charge is transferred to the other pixel via the overflow path, whereby the saturation of one pixel can be avoided. Then, by providing such an overflow path, the linearity of the pixel signal output from the imaging element  100  can be secured, and deterioration of the captured image can be prevented. Further, in the present embodiment, instead of forming the diffusion region  320  by ion implantation, a gate (not illustrated) may be provided between the transfer gates  400   a  and  400   b  on the front surface  10   b  of the semiconductor substrate  10 . In this case, by adjusting the voltage applied to the gate, the pair of pixels  300   a  and  300   b  may be electrically separated at the time of phase difference detection, and a channel serving as an overflow path may be formed in a region on the front surface  10   b  side of the slit  312  at the time of normal imaging. 
     Furthermore, in the present embodiment, an element separation wall  310  surrounding the pixels  300   a  and  300   b  and physically separating the adjacent imaging elements  100  is provided in the semiconductor substrate  10 . The element separation wall  310  includes a trench (not illustrated) provided so as to penetrate the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 , and a material embedded in the trench and made of an oxide film such as a silicon oxide film, a silicon nitride film, amorphous silicon, polycrystalline silicon, a titanium oxide film, aluminum, or tungsten, or a metal film. That is, the protruding portion  304  and the element separation wall  310  may be formed of the same material. Note that, in the present embodiment, since the element separation wall  310  and the protruding portion  304  have the same configuration, they can have a form in which they are integrated with each other, and thus can be formed simultaneously. As a result, according to the present embodiment, since the protruding portion  304  can be formed simultaneously with the element separation wall  310 , an increase in the process steps of the imaging element  100  can be suppressed. 
     Furthermore, in the present embodiment, the charges generated in the photoelectric conversion unit  302  of the pixel  300   a  and the photoelectric conversion unit  302  of the pixel  300   b  are transferred via the transfer gates  400   a  and  400   b  of the transfer transistors (one type of the pixel transistors described above) provided on the front surface  10   b  positioned on the opposite side of the light receiving surface  10   a  of the semiconductor substrate  10 . The transfer gates  400   a  and  400   b  can be formed of, for example, a metal film. Then, the charge may be accumulated in, for example, a floating diffusion portion (charge accumulation portion) (not illustrated) provided in a semiconductor region having the first conductivity type (for example, N type) provided in the semiconductor substrate  10 . Note that, in the present embodiment, the floating diffusion portion is not limited to being provided in the semiconductor substrate  10 , and may be provided, for example, on another substrate (not illustrated) stacked on the semiconductor substrate  10 . 
     Furthermore, on the front surface  10   b  of the semiconductor substrate  10 , a plurality of pixel transistors (not illustrated) other than the above-described transfer transistors, which are used for reading out charges as pixel signals, and the like, may be provided. Furthermore, in the present embodiment, the pixel transistor may be provided on the semiconductor substrate  10 , or may be provided on another substrate (not illustrated) stacked on the semiconductor substrate  10 . 
     3.2 Planar Configuration 
     Next, a planar configuration of the imaging element  100  according to the first embodiment of the present disclosure will be described with reference to  FIG.  4   .  FIG.  4    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  taken along line A-A′ illustrated in  FIG.  3   . 
     As illustrated in  FIG.  4   , in the present embodiment, the pixels  300   a  and  300   b  adjacent to each other are separated by a protruding portion  304  formed integrally with the element separation wall  310 . Specifically, when the imaging element  100  is viewed from above the light receiving surface  10   a , the element separation wall  310  has two protruding portions (an example of a first separation portion)  304  protruding along the column direction toward the center O of the imaging element  100  and facing each other. Here, in a case where the imaging element  100  is viewed from the light receiving surface  10   a  side, a region between the two protruding portions  304  positioned in the vicinity of the center of the imaging element  100  is referred to as a slit  312 . In the region of the slit  312 , as described above, impurities of the second conductivity type (for example, P type) are diffused via the protruding portion  304  by conformal doping, and the diffusion region  306  is formed so as to surround the protruding portion  304 . As described above, in order to further improve the accuracy of phase difference detection, the diffusion region  306  can electrically separate the pair of pixels  300   a  and  300   b  so as not to cause color mixing. Furthermore, in the present embodiment, the impurity of the second conductivity type is diffused via the element separation wall  310  by conformal doping, and the diffusion region  306  is formed along the element separation wall  310 . 
     Furthermore, the two protruding portions  304  are provided at the center of the imaging element  100  in the row direction when the imaging element  100  is viewed from above the light receiving surface  10   a , and protruding lengths (lengths in the column direction) are substantially the same. As described above, the two protruding portions  304  are provided so as to penetrate the semiconductor substrate  10 . Note that, in the present embodiment, the width of the protruding portion  304  is not particularly limited as long as the pair of pixels  300   a  and  300   b  can be separated. 
     Furthermore, the protruding portion  304  and the element separation wall  310  according to the present embodiment described above have a form as illustrated in  FIG.  5    which is a transparent perspective view of the imaging element  100  according to the present embodiment. That is, the protruding portion  304  and the element separation wall  310  according to the present embodiment are provided so as to penetrate the semiconductor substrate  10 . Furthermore, the slit  312  is provided in the vicinity of the center of the imaging element  100  between the two protruding portions  304 . 
     As described above, in the present embodiment, since the slit  312  is provided in the vicinity of the center O of the imaging element  100 , scattering of light by the protruding portion  304  is suppressed. Therefore, according to the present embodiment, light incident on the center O of the imaging element  100  can be incident on the photoelectric conversion unit  302  without being scattered. As a result, according to the present embodiment, since the imaging element  100  can more reliably capture light incident on the center O of the imaging element  100 , deterioration of imaging pixels can be avoided. 
     Furthermore, in the present embodiment, as described above, for example, the impurity of the first conductivity type is introduced into the region on the front surface  10   b  side of the slit  312  by ion implantation, and a channel serving as an overflow path can be formed. Therefore, according to the present embodiment, since the overflow path can be formed at the time of normal imaging while separating the pair of pixels  300   a  and  300   b  at the time of phase difference detection, deterioration of the captured image can be avoided while improving the accuracy of phase difference detection. 
     Furthermore, in the present embodiment, since the diffusion region  306  can be formed by introducing impurities into the region of the slit  312  via the protruding portion  304  by conformal doping, use of ion implantation can be avoided. Therefore, according to the present embodiment, since the ion implantation is not used, it is possible to avoid introduction of impurities into the photoelectric conversion unit  302 , and it is possible to avoid reduction and damage of the photoelectric conversion unit  302 . Further, using conformal doping, it is possible to repair crystal defects while uniformly diffusing impurities by applying a high temperature. As a result, according to the present embodiment, it is possible to suppress a decrease in sensitivity and a decrease in dynamic range of the imaging element  100 . 
     Note that, in the present embodiment, when the imaging element  100  is viewed from above the light receiving surface  10   a , the element separation wall  310  may have two protruding portions (an example of the first separation portion)  304  protruding along the row direction toward the center O of the imaging element  100  and facing each other. Furthermore, in this case, the two protruding portions  304  may be provided at the center of the imaging element  100  in the column direction when the imaging element  100  is viewed from above the light receiving surface  10   a.    
     As described above, according to the present embodiment, at the time of phase difference detection, since the diffusion region  306  that electrically separates the pair of pixels  300   a  and  300   b  from the protruding portion  304  that physically separates the pair of pixels  300   a  and  300   b , the diffusion region  320  that electrically separates the pair of pixels  300   a  and  300   b , and the like are provided. Thus, it is possible to avoid deterioration of the captured image while improving the accuracy of phase difference detection. Specifically, in the present embodiment, the pair of pixels  300   a  and  300   b  can be effectively separated by the protruding portion  304  and the diffusion region  306 . As a result, the occurrence of color mixing can be suppressed, and the accuracy of phase difference detection can be further improved. Furthermore, in the present embodiment, since the overflow path is provided, when the charge of any one pixel of the pixels  300   a  and  300   b  is about to be saturated at the time of normal imaging, saturation of one pixel can be avoided by transferring the charge to the other pixel via the overflow path. Therefore, according to the present embodiment, by providing such an overflow path, the linearity of the pixel signal output from the imaging element  100  can be secured, and deterioration of the captured image can be prevented. 
     Furthermore, in the present embodiment, since the diffusion region  306  can be formed by diffusing impurities into the region of the slit  312  via the protruding portion  304  by conformal doping, use of ion implantation can be avoided. Therefore, according to the present embodiment, since the ion implantation is not used, it is possible to avoid introduction of impurities into the photoelectric conversion unit  302 , and it is possible to avoid reduction and damage of the photoelectric conversion unit  302 . Further, using conformal doping, it is possible to repair crystal defects while uniformly diffusing impurities by applying a high temperature. As a result, according to the present embodiment, it is possible to suppress a decrease in sensitivity and a decrease in dynamic range of the imaging element  100 . 
     Furthermore, in the present embodiment, since the protruding portion  304  penetrates the semiconductor substrate  10 , the diffusion region  306  can be formed in a deep region in the semiconductor substrate  10  by conformal doping via the protruding portion  304 . Therefore, in the present embodiment, since the desired diffusion region  306  can be formed with high accuracy, the pair of pixels  300   a  and  300   b  can be effectively electrically separated. As a result, the occurrence of color mixing can be suppressed, and the accuracy of phase difference detection can be further improved. Furthermore, according to the present embodiment, since the element separation wall  310  and the protruding portion  304  have the same form, the protruding portion  304  can be formed simultaneously with the element separation wall  310 , and an increase in process steps of the imaging element  100  can be suppressed. 
     In addition, in the present embodiment, since the slit  312  is provided at the center O of the imaging element  100 , scattering of light by the protruding portion  304  is suppressed, and light incident on the center O of the imaging element  100  can be incident on the photoelectric conversion unit  302  without being scattered. As a result, according to the present embodiment, since the imaging element  100  can more reliably capture light incident on the center O of the imaging element  100 , deterioration of imaging pixels can be avoided. 
     3.3 Modified Example 
     In the present embodiment, the light shielding portion (light shielding film)  204  can be modified as follows. Therefore, a detailed configuration of the light shielding portion  204  will be described with reference to  FIGS.  6  and  7   .  FIG.  6    is an explanatory diagram illustrating a configuration example of the light shielding portion  204  according to the present embodiment, and  FIG.  7    is an explanatory diagram illustrating a configuration example of the light shielding portion  204  according to a modified example of the present embodiment. Note that, in  FIGS.  6  and  7   , the view illustrated in the lower part corresponds to a cross-section obtained by cutting the imaging element  100  along line A-A′ illustrated in  FIG.  3   , and the view illustrated in the upper part corresponds to a cross-section obtained by cutting the imaging element  100  along line B-B′ illustrated in  FIG.  3   . 
     In the present embodiment, for example, as illustrated in  FIG.  6   , in a case where the imaging element  100  is viewed from above the light receiving surface  10   a , the light shielding portion (light shielding film)  204  may be provided on the element separation wall  310  along the element separation wall  310 . 
     Furthermore, in the modified example of the present embodiment, for example, as illustrated in  FIG.  7   , when the imaging element  100  is viewed from above the light receiving surface  10   a , the light shielding portion (light shielding film)  204  may be not only provided on the element separation wall  310  along the element separation wall  310 , but also provided on the protruding portion  304  (an example of the first separation portion) along the protruding portion  304 . 
     4. Second Embodiment 
     In the embodiment of the present disclosure, in a case where the imaging element  100  is viewed from above the light receiving surface  10   a , the protruding lengths (lengths in the column direction) of the two protruding portions  304  are not limited to being substantially the same, and may be different from each other. Therefore, a second embodiment of the present disclosure in which protruding lengths are different from each other will be described with reference to  FIG.  8   .  FIG.  8    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  taken along line A-A′ illustrated in  FIG.  3   . 
     As illustrated in  FIG.  8   , in the present embodiment, when the imaging element  100  is viewed from above the light receiving surface  10   a , the element separation wall  310  has two protruding portions (an example of a first separation portion)  304  protruding along the column direction toward the center O (not illustrated) of the imaging element  100  and facing each other. Further, the protruding lengths of the two protruding portions  304  are different from each other. 
     Note that, in the present embodiment, the two protruding portions  304  may protrude along the row direction toward the center O (not illustrated) of the imaging element  100 . Furthermore, in the present embodiment, the two protruding portions  304  are not limited to be provided so as to face each other, and for example, one protruding portion may be provided. In this case, in the region between the protruding portion  304  and the portion of the element separation wall  310  facing the protruding portion  304 , the impurity of the second conductivity type (for example, P-type) is diffused via the protruding portion  304  and the element separation wall  310  by conformal doping, and the diffusion region (an example of the first diffusion region)  306  is formed. 
     5. Third Embodiment 
     In the embodiment of the present disclosure, the two protruding portions  304  are not limited to being provided at the center of the imaging element  100  in the row direction when the imaging element  100  is viewed from above the light receiving surface  10   a , and may be provided at a position shifted by a predetermined distance from the center of the imaging element  100  in the row direction. Therefore, a third embodiment of the present disclosure in which the two protruding portions  304  are provided at positions shifted by a predetermined distance from the center of the imaging element  100  in the row direction will be described with reference to  FIG.  9   .  FIG.  9    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  taken along line A-A′ illustrated in  FIG.  3   . 
     As illustrated in  FIG.  9   , in the present embodiment, similarly to the first embodiment, the element separation wall  310  has two protruding portions (an example of a first separation portion)  304  facing each other and protruding along the column direction when the imaging element  100  is viewed from above the light receiving surface  10   a . Furthermore, in the present embodiment, the protruding portions  304  are provided at positions shifted by a predetermined distance from the center of the imaging element  100  in the row direction. In the present embodiment, the predetermined distance is not particularly limited. 
     Furthermore, in the present embodiment, the two protruding portions  304  are not limited to the form illustrated in  FIG.  9   . For example, in the case of the two protruding portions (an example of the first separation portion)  304  protruding along the row direction, the two protruding portions may be provided at positions shifted by a predetermined distance from the center of the imaging element  100  in the column direction. In addition, the present embodiment may be combined with the second embodiment described above, and thus the protruding lengths of the two protruding portions  304  may be different from each other. 
     6. Fourth Embodiment 
     Meanwhile, in a case where the plane size of the imaging element  100  is large, there is a possibility that the pair of pixels  300   a  and  300   b  cannot be sufficiently separated in the protruding portion  304  and the diffusion region  306 . Therefore, in such a case, it is conceivable to further provide the additional wall  308  and the like between the two protruding portions  304  in order to ensure sufficient separation of the pair of pixels  300   a  and  300   b . Hereinafter, such an embodiment will be described as a fourth embodiment of the present disclosure with reference to  FIGS.  10  to  12   .  FIGS.  10  to  12    are explanatory diagrams illustrating a plane of the imaging element  100  according to the present embodiment, and specifically correspond to a cross-section of the imaging element  100  taken along line A-A′ illustrated in  FIG.  3   . 
     First, as illustrated in  FIG.  10   , in the present embodiment, as in the first embodiment, the element separation wall  310  has two protruding portions (an example of a first separation portion)  304  facing each other and protruding along the column direction when the imaging element  100  is viewed from above the light receiving surface  10   a . Furthermore, in the present embodiment, a plurality of rectangular additional walls  308  is arranged in a dot shape between these protruding portions  304  (slits  312 ). Similarly to the protruding portion  304 , the additional wall  308  is provided so as to penetrate the semiconductor substrate  10 . In addition, although not illustrated in  FIG.  10   , a diffusion region  306  formed by introducing an impurity of the second conductivity type (for example, P type) by conformal doping via the additional wall  308  is also provided around the additional wall  308 . 
     In the present embodiment, by providing the plurality of additional walls  308  between the two protruding portions  304  (slits  312 ) and providing the diffusion region  306  also around the additional walls  308 , it is possible to further ensure sufficient separation of the pair of pixels  300   a  and  300   b . Furthermore, in the present embodiment, by providing the additional wall  308  in a dot shape, scattering of light by the additional wall  308  is suppressed, and light incident on the center O (not illustrated) of the imaging element  100  can be incident on the photoelectric conversion unit  302  without being scattered. As a result, according to the present embodiment, since the imaging element  100  can more reliably capture light incident on the center O of the imaging element  100 , deterioration of imaging pixels can be avoided. 
     In the present embodiment, the cross-section of the additional wall  308  is not limited to the rectangular shape as illustrated in  FIG.  10   , and the number of additional walls  308  is not limited to two as illustrated in  FIG.  10   , and may be one or three or more. 
     As illustrated in  FIG.  11   , in the present embodiment, one additional wall  308   a  may be disposed between the two protruding portions  304  (slits  312 ), and the additional wall  308   a  may be used as the back surface DTI. The back surface DTI is formed by forming a trench penetrating from the light receiving surface  10   a  (back surface) side of the semiconductor substrate  10  to the middle of the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10  and embedding an oxide film or the like in the trench. In this case, a channel serving as the overflow path is formed by introducing impurities into a region on the front surface  10   b  side of the additional wall  308   a  through which the additional wall  308   a  does not penetrate. 
     In the present embodiment, the cross-section of the additional wall  308   a  is not limited to the rectangular shape as illustrated in  FIG.  11   , and the number of additional walls  308   a  is not limited to two as illustrated in  FIG.  11   , and may be one or three or more. 
     Furthermore, in a case where the plane size of the imaging element  100  is large, there is a possibility that the pair of pixels  300   a  and  300   b  cannot be sufficiently separated in the diffusion region  306 . Therefore, in such a case, in order to ensure sufficient separation of the pair of pixels  300   a  and  300   b , as illustrated in  FIG.  12   , a diffusion region  306   a  (an example of a first diffusion region) formed by introducing an impurity of the second conductivity type (for example, P-type) by ion implantation may be provided between the two protruding portions  304  (slits  312 ). 
     7. Fifth Embodiment 
     Further, in the embodiment of the present disclosure, the protruding portion  304  may be formed of a material different from the element separation wall  310 . Hereinafter, such an embodiment will be described as a fifth embodiment of the present disclosure with reference to  FIG.  13   .  FIG.  13    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  taken along line A-A′ illustrated in  FIG.  3   . 
     As described above, the protruding portion  304  and the element separation wall  310  are made of a material including an oxide film such as a silicon oxide film, a silicon nitride film, amorphous silicon, polycrystalline silicon, a titanium oxide film, aluminum, or tungsten, or a metal film. Therefore, in the present embodiment, as illustrated in  FIG.  13   , the protruding portion  304  and the element separation wall  310  may be formed of materials selected from the above-described materials and different from each other. 
     More specifically, for example, the element separation wall  310  is formed of a silicon oxide film, and the protruding portion  304  is formed of a titanium oxide film having a high refractive index with a small difference in refractive index from silicon forming the semiconductor substrate  10 . In this way, scattering of light by the protruding portion  304  can be suppressed, and light incident on the center O (not illustrated) of the imaging element  100  can be incident on the photoelectric conversion unit  302  without being scattered. As a result, according to the present embodiment, since the imaging element  100  can more reliably capture light incident on the center O of the imaging element  100 , deterioration of imaging pixels can be avoided. Note that, in the present embodiment, the protruding portion  304  is not limited to being formed of a titanium oxide film, and for example, other materials may be used as long as the material has a small difference in refractive index from the material forming the semiconductor substrate  10 . 
     8. Sixth Embodiment 
     Furthermore, the embodiment of the present disclosure is not limited to providing the two protruding portions  304 , and two or more protruding portions  304  may be provided. Hereinafter, such an embodiment will be described as a sixth embodiment of the present disclosure with reference to  FIG.  14   .  FIG.  14    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  taken along line A-A′ illustrated in  FIG.  3   . 
     As illustrated in  FIG.  14   , in the present embodiment, when the imaging element  100  is viewed from above the light receiving surface  10   a , the element separation wall  310  includes two protruding portions (an example of a first separation portion)  304  protruding along the column direction toward the center of the imaging element  100  and facing each other, and two protruding portions (an example of a second separation portion)  324  protruding along the row direction toward the center of the imaging element  100  and facing each other. The four protruding portions  304  and  324  are provided so as to penetrate the semiconductor substrate  10 . 
     Furthermore, in the present embodiment, although not illustrated in  FIG.  14   , impurities of the second conductivity type (for example, P-type) are introduced into a space (slit  312 ) between the two protruding portions  304  facing each other and a space (slit  312 ) between the two protruding portions  324  facing each other by conformal doping via the protruding portions  304  and  324 , and the diffusion region  306  (an example of a first diffusion region and an example of a second diffusion region) can be formed. Furthermore, also in the present embodiment, the diffusion region  320  that is formed by introducing impurities of the first conductivity type (for example, N type) by ion implantation and functions as an overflow path is formed below the diffusion region  306  provided in the slit  312  (on the front surface  10   b  side). 
     In the case of  FIG.  14   , the inside of the imaging element  100  is separated into four pixels  300   a ,  300   b ,  300   c , and  300   d  by such four protruding portions  304 . In this case, a phase difference in both the row direction and the column direction can be detected by one imaging element  100 . Note that the present embodiment is not limited to the four protruding portions  304  and  324 , and four or more (for example, eight or the like) protruding portions may be provided. 
     9. Seventh Embodiment 
     Furthermore, in the embodiment of the present disclosure, a pixel separation wall  334  including a back surface DTI that separates the pair of pixels  300   a  and  300   b  may be provided. Hereinafter, such an embodiment will be described as a seventh embodiment of the present disclosure with reference to  FIG.  15   .  FIG.  15    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  taken along line A-A′ illustrated in  FIG.  3   . 
     As illustrated in  FIG.  15   , in the present embodiment, a pixel separation wall (an example of a separation portion)  334  including a back surface DTI is provided between the pair of pixels  300   a  and  300   b . As described above, the back surface DTI is formed by forming a trench penetrating from the light receiving surface  10   a  (back surface) side of the semiconductor substrate  10  to the middle of the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10  and embedding an oxide film or the like in the trench. In this case, in the thickness direction of the semiconductor substrate  10 , a region on the front surface  10   b  side of the pixel separation wall  334  through which the pixel separation wall  334  does not penetrate becomes an overflow path. Alternatively, in the present embodiment, an overflow path may be formed by introducing an impurity of the first conductivity type into the region by ion implantation. Note that, in the present embodiment, the pixel separation wall  334  may or may not be in contact with the element separation wall  310 , and is not particularly limited. Furthermore, in the case of not being in contact with each other, a diffusion region (not illustrated) is provided which is formed by introducing an impurity of the second conductivity type (for example, P type) by conformal doping via the element separation wall  310  or ion implantation between the pixel separation wall  334  and the element separation wall  310 , and electrically separates the pair of pixels  300   a  and  300   b  from each other. 
     As described above, according to the present embodiment, by providing the pixel separation wall  334  including the back surface DTI that physically separates the pair of pixels  300   a  and  300   b  at the time of phase difference detection, it is possible to effectively physically separate the pair of pixels  300   a  and  300   b . As a result, it is possible to suppress the occurrence of color mixing and further improve the accuracy of phase difference detection. Furthermore, in the present embodiment, when the charge of any one of the pixels  300   a  and  300   b  is about to be saturated at the time of normal imaging due to the overflow path positioned in the region on the front surface  10   b  side of the pixel separation wall  334 , the charge is transferred to the other pixel via the overflow path, so that the saturation of the one pixel can be avoided. Then, according to the present embodiment, by providing such an overflow path, the linearity of the pixel signal output from the imaging element  100  can be secured, and deterioration of the captured image can be prevented. 
     Furthermore, in the present embodiment, a pixel separation wall  334  formed by introducing an impurity of the second conductivity type (for example, P-type) by ion implantation may be provided between the pair of pixels  300   a  and  300   b . Also in such a modified example, the pixel separation wall  334  formed by ion implantation is formed in such a form as to penetrate from the light receiving surface  10   a  (back surface) side of the semiconductor substrate  10  to the middle of the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . In the modified example, in the thickness direction of the semiconductor substrate  10 , a region on the front surface  10   b  side of the pixel separation wall  334  through which the pixel separation wall  334  does not penetrate is an overflow path. Then, the overflow path may be formed by preventing impurities from being implanted into the region on the front surface  10   b  side of the pixel separation wall  334  at the time of ion implantation for forming the pixel separation wall  334 , or may be formed by introducing impurities of the first conductivity type into the region by ion implantation. Note that, also in this modified example, the pixel separation wall  334  may or may not be in contact with the element separation wall  310 , and is not particularly limited. 
     As described above, according to this modified example, by providing the pixel separation wall  334  formed by ion implantation, it is possible to effectively electrically separate the pair of pixels  300   a  and  300   b . As a result, it is possible to suppress the occurrence of color mixing and further improve the accuracy of phase difference detection. Furthermore, in the present embodiment, when the charge of any one of the pixels  300   a  and  300   b  is about to be saturated at the time of normal imaging due to the overflow path positioned in the region on the front surface  10   b  side of the pixel separation wall  334 , the charge is transferred to the other pixel via the overflow path, so that the saturation of the one pixel can be avoided. Then, by providing such an overflow path, the linearity of the pixel signal output from the imaging element  100  can be secured, and deterioration of the captured image can be prevented. 
     Furthermore, in the present embodiment, the light shielding portion (light shielding film)  204  can be modified as follows. Therefore, a detailed configuration of the light shielding portion  204  will be described with reference to  FIG.  16   .  FIG.  16    is an explanatory diagram illustrating a configuration example of the light shielding portion  204  according to the present embodiment. Note that, in  FIG.  16   , the view illustrated in the lower part corresponds to a cross-section obtained by cutting the imaging element  100  along line A-A′ illustrated in  FIG.  3   , and the view illustrated in the upper part corresponds to a cross-section obtained by cutting the imaging element  100  along line B-B′ illustrated in  FIG.  3   . 
     In the present embodiment and the modified example, for example, as illustrated in the upper part of  FIG.  16   , when the imaging element  100  is viewed from above the light receiving surface  10   a , the light shielding portion (light shielding film)  204  may be provided on the element separation wall  310  along the element separation wall  310 , and may have two protruding portions  206  protruding along the column direction toward the center O of the imaging element  100  and facing each other. Alternatively, in the present embodiment and the modified example, the light shielding portion  204  may be provided along the element separation wall  310  and may not have the protruding portion  206 . 
     10. Eighth Embodiment 
     In the embodiment of the present disclosure, one additional wall  308   b  may be used as the front surface DTI. Hereinafter, such an embodiment will be described as an eighth embodiment of the present disclosure with reference to  FIGS.  17  to  21   .  FIG.  17    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the imaging element  100  along the thickness direction of the semiconductor substrate  10 .  FIG.  18    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  taken along line C-C′ illustrated in  FIG.  17   .  FIG.  19    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  taken along line D-D′ illustrated in  FIG.  17   .  FIG.  20    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along line E-E′ illustrated in  FIG.  17   .  FIG.  21    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  for each color according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . 
     As illustrated in  FIGS.  17  to  20   , in the present embodiment, one additional wall  308   b  is disposed between the two protruding portions  304  (slits  312 ), and the additional wall  308   b  is used as the front surface DTI. As illustrated in  FIG.  20   , the front surface DTI is formed by forming a trench extending from the front surface  10   b  side, which is the opposite surface of the light receiving surface  10   a  of the semiconductor substrate  10 , to the middle of the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10  and embedding an oxide film or the like in the trench. The length of the additional wall  308   b  in the thickness direction of the semiconductor substrate  10  can be adjusted by adjusting the depth of the trench. In the case of the front surface DTI, a channel serving as the overflow path may be formed by introducing impurities into a region on the back surface  10   a  side of the additional wall  308   b  through which the additional wall  308   b  does not penetrate. 
     That is, the additional wall  308   b  is provided so as to extend from the front surface  10   b , which is a surface of the semiconductor substrate  10  opposite to the light receiving surface  10   a , to the middle of the semiconductor substrate  10  along the thickness direction (substrate thickness direction) of the semiconductor substrate  10 . As a result, the length of the additional wall  308   b  in the substrate thickness direction becomes shorter than the lengths of the two protruding portions  304  in the substrate thickness direction. Therefore, since the end surface (surface on the light receiving surface  10   a  side) of the additional wall  308   b  is separated from the light receiving surface  10   a , scattering of incident light near the light receiving surface  10   a  by the additional wall  308   b  can be suppressed. In addition, it is possible to reduce the volume of the additional wall  308   b  on the light receiving surface  10   a  side as compared with the case where the additional wall  308   b  is formed by the full trench, and it is possible to reliably suppress scattering of incident light near the light receiving surface  10   a  by the additional wall  308   b.    
     Here, for example, in the examples of  FIGS.  2  to  5   , the incident light is scattered by the two protruding portions  304  arranged in the vicinity of the center of the imaging element  100  of the light receiving surface  10   a , and this may cause color mixing deterioration, and sensitivity decrease suppression may be insufficient. In this case, although it is possible to suppress incident light scattering by lengthening the slits  312  of the two protruding portions  304 , the effect of conformal doping using the two protruding portions  304  is reduced, and the saturation charge amount Qs is reduced. Therefore, as described above, by forming the additional wall  308   b  as the front surface DTI, the additional wall  308   b  is eliminated in the vicinity of the center of the imaging element  100  on the light receiving surface  10   a  side, and incident light scattering is suppressed. As a result, color mixing, a decrease in sensitivity, a decrease in saturation charge amount, and the like can be suppressed. 
     Furthermore, as illustrated in  FIG.  21   , in the present embodiment, the depth (trench depth) of the trench for forming the additional wall  308   b  may be adjusted according to the wavelength of incident light in each of the imaging elements  100  of RGB (Red, Green, Blue), that is, the photoelectric conversion depth. In the R pixel, since photoelectric conversion occurs in the deep part, the trench depth is set shallow. For example, the trench depth is a trench depth Z R =3200 nm (50% of light having the wavelength of 700 nm is absorbed). In the B pixel, since photoelectric conversion occurs in the shallow part, the trench depth is set to be deep. For example, the trench depth is a trench depth Z R =350 nm (50% of light having the wavelength of 450 nm is absorbed). In the G pixel, since photoelectric conversion occurs in the deep part with the Blue ratio and the shallow part with the Red ratio, the trench depth is set between the trench depth of the R pixel and the trench depth of the B pixel. For example, the trench depth is the trench depth Z G =1000 nm (50% of light having the wavelength of 550 nm is absorbed). 
     As described above, the trench depth, that is, the length of the additional wall  308   a  in the substrate thickness direction may be determined according to the wavelength of the incident light incident on the light receiving surface  10   a . This can minimize scattering of incident light for each color. As a result, it is possible to suppress the incident light scattering according to the wavelength of the incident light. Thus, it is possible to reliably suppress color mixing, sensitivity reduction, saturation charge amount reduction, and the like. 
     Further, in the present embodiment, the additional wall  308   b  can be modified as follows. Therefore, a detailed configuration of the additional wall  308   b  will be described with reference to  FIGS.  22  to  25   .  FIG.  22    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction (direction orthogonal to the thickness direction of the semiconductor substrate  10 ).  FIG.  23    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  for each color according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 .  FIG.  24    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction.  FIG.  25    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  for each color according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . 
     As illustrated in  FIG.  22   , in the present embodiment, when viewed from above the light receiving surface  10   a , the width (for example, the length in the row direction) of the central portion of the additional wall  308   b  may be narrower than the width (for example, the length in the row direction) of both ends of the additional wall  308   b . As illustrated in  FIG.  23   , the length in the substrate thickness direction of the central portion of the additional wall  308   b  may be shorter than the lengths in the substrate thickness direction of both ends of the additional wall  308   b.    
     As described above, by reducing the line width of the central portion of the additional wall  308   b  with respect to both ends and reducing the depth of the trench for forming the central portion of the additional wall  308   b  to shorten the length of the central portion of the additional wall  308   b  in the substrate thickness direction, it is possible to separate the central portion of the additional wall  308   b  from the light receiving surface  10   a  while narrowing the end surface of the central portion of the additional wall  308   b , and it is possible to reduce the volume of the additional wall  308   b  on the light receiving surface  10   a  side. Thus, scattering of the incident light near the light receiving surface  10   a  by the additional wall  308   b  can be reliably suppressed. 
     In the examples of  FIGS.  22  and  23   , the width of the central portion of the additional wall  308   b  is narrower than the both ends of the additional wall  308   b , and the length in the thickness direction of the central portion of the semiconductor substrate  10  is shorter than the both ends of the additional wall  308   b . However, the present invention is not limited thereto, and either one of the width and the length may be reduced. Further, the width of the additional wall  308   b  may be shorter than the width of the two protruding portions  304 . 
     As illustrated in  FIG.  24   , in the present embodiment, when viewed from above the light receiving surface  10   a , the width (for example, the length in the row direction) of each of the two protruding portions  304  may be narrower than the width (for example, the length in the row direction) of the additional wall  308   b . In addition, as illustrated in  FIG.  25   , the two protruding portions  304  may be provided so as to extend from the front surface  10   b  of the semiconductor substrate  10  to the middle of the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . At this time, the length of the additional wall  308   b  in the substrate thickness direction may be shorter than the length of each of the two protruding portions  304  in the substrate thickness direction. 
     As described above, in addition to shortening the length of the additional wall  308   b  in the substrate thickness direction, the line width of the two protruding portions  304  is narrowed, and further, the depth of the trench for forming the two protruding portions  304  is shallowed to shorten the length of each protruding portion  304  in the substrate thickness direction. Thus, the end surface of the additional wall  308   b  and the end surfaces of the two protruding portions  304  can be separated from the light receiving surface  10   a , and the volume of the two protruding portions  304  can be reduced in addition to the volume of the additional wall  308   b  on the light receiving surface  10   a  side. Therefore, scattering of incident light near the light receiving surface  10   a  by the additional wall  308   b  and the two protruding portions  304  can be reliably suppressed. 
     In the examples of  FIGS.  24  and  25   , the width of each of the two protruding portions  304  is narrower than the width of the additional wall  308   b , but the present invention is not limited thereto. For example, the width of one of the two protruding portions  304  may be narrower than the width of the additional wall  308   b.    
     Here, a part of the manufacturing process (manufacturing method) of the imaging element  100  will be described with reference to  FIG.  26   .  FIG.  26    is a process cross-sectional view for explaining a part of the manufacturing process of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . 
     As illustrated in  FIG.  26   , in the present embodiment, a mask M 1  such as a photomask is formed on the front surface  10   b  of the semiconductor substrate  10  (see the first diagram from the left in  FIG.  26   ). The mask M 1  is formed, for example, by stacking a photoresist layer on the front surface  10   b  of the semiconductor substrate  10  by a spin coating method or the like and patterning the photoresist layer in accordance with a trench formation pattern. Next, a mask M 2  functioning as a protective layer is formed on the mask M 1 , and a part of the trench T 1  for forming the element separation wall  310  is formed by etching such as dry etching (see the second diagram from the left in  FIG.  26   ). Thereafter, the mask M 2  is removed (see the third diagram from the left in  FIG.  26   ), and etching is further executed to form the trench T 1  for forming the element separation wall  310  and the trench T 2  for forming the additional wall  308   b  (see the fourth diagram from the left in  FIG.  26   ). In a subsequent process, conformal doping or the like is performed, and a material such as an oxide film is embedded in the trench T 1  and the trench T 2 , and the element separation wall  310  and the additional wall  308   b  are formed. Thereafter, the mask M 1  is also removed, and the imaging element  100  having the final structure is formed through a post-process. 
     As described above, according to the present embodiment (including modified examples), it is possible to obtain effects according to other embodiments (including modified examples). That is, deterioration of the captured image can be avoided while improving the accuracy of the phase difference detection. In addition, since the end surface (surface on the light receiving surface  10   a  side) of the additional wall  308   b  is separated from the light receiving surface  10   a , and the volume of the additional wall  308   b  can be further reduced on the light receiving surface  10   a  side, scattering of incident light near the light receiving surface  10   a  by the additional wall  308   b  or the protruding portion  304  can be suppressed. 
     11. Ninth Embodiment 
     In the embodiment of the present disclosure, a diffusion region  306   b  (an example of a first diffusion region) formed by introducing impurities by ion implantation may be provided between the two protruding portions  304  (slits  312 ). Hereinafter, such an embodiment will be described as a ninth embodiment of the present disclosure with reference to  FIGS.  27  to  29   .  FIG.  27    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction.  FIG.  28    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 .  FIG.  29    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  of the comparative example according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . 
     As illustrated in  FIG.  28   , in the present embodiment, ion implantation is performed from both the front surface  10   b  and the back surface  10   a  of the semiconductor substrate  10 . As a result, the diffusion region  306   b  is formed in a shape that expands from the front surface  10   b  of the semiconductor substrate  10  toward the inside of the semiconductor substrate  10  and narrows from the inside of the semiconductor substrate  10  toward the back surface  10   a  of the semiconductor substrate  10 . That is, the diffusion region  306   b  has a first region R 1  that extends from the front surface  10   b  of the semiconductor substrate  10  toward the inside of the semiconductor substrate  10 , and a second region R 2  that narrows from the inside of the semiconductor substrate  10  toward the back surface  10   a  of the semiconductor substrate  10 . The first region R 1  and the second region R 2  are connected. 
     In the example of  FIG.  28   , the central axis of the first region R 1  and the central axis of the second region R 2  are positioned so as to coincide with each other without being shifted, but the present invention is not limited thereto. For example, the central axis of the first region R 1  and the central axis of the second region R 2  may be positioned so as to be shifted in the left-right direction (as an example, a row direction). The same applies to the following configurations illustrated in  FIGS.  30  to  35   . 
     Here, as illustrated in  FIG.  29   , when ion implantation is performed only from the front surface  10   b  of the semiconductor substrate  10 , diffusion greatly spreads in the thickness direction of the semiconductor substrate  10 , and a diffusion region  306   a  that continues to spread from the front surface  10   b  to the back surface  10   a  of the semiconductor substrate  10  is formed. Therefore, the photoelectric conversion region becomes narrow. Therefore, as illustrated in  FIG.  28   , ion implantation is performed from both the front surface  10   b  and the back surface  10   a  of the semiconductor substrate  10 . As a result, the diffusion region  306   b  is formed in a shape that expands from the front surface  10   b  of the semiconductor substrate  10  toward the inside of the semiconductor substrate  10  and narrows from the inside of the semiconductor substrate  10  toward the back surface  10   a  of the semiconductor substrate  10 . As a result, since the diffusion region  306   b  (see  FIG.  28   ) is narrower than the diffusion region  306   a  (see  FIG.  29   ), the photoelectric conversion region can be widened. 
     Furthermore, in the present embodiment, the diffusion region  306   b  can be modified as follows. Therefore, a detailed configuration of the diffusion region  306   b  will be described with reference to  FIGS.  30  to  35   .  FIGS.  30  to  35    are explanatory diagrams illustrating a part of a cross-section of the imaging element  100  according to the present embodiment, and specifically correspond to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . 
     As illustrated in  FIG.  30   , in the present embodiment, the diffusion region  306   b  may be formed such that the first region R 1  and the second region R 2  are separated without being connected. Even in the diffusion region  306   b  having such a shape, the spread of the diffusion region  306   b  can be suppressed, and the photoelectric conversion region can be widened. 
     As illustrated in  FIG.  31   , in the present embodiment, the diffusion region  306   b  may be formed such that the first region R 1  and the second region R 2  are thinner than the first region R 1  and the second region R 2  illustrated in  FIG.  28   . The first region R 1  and the second region R 2  are connected. In the diffusion region  306   b  having such a shape, the spread of the diffusion region  306   b  can be further suppressed as compared with the first region R 1  and the second region R 2  illustrated in  FIG.  28   , and the photoelectric conversion region can be reliably widened. 
     As illustrated in  FIG.  32   , in the present embodiment, the diffusion region  306   b  may be formed such that the impurity concentration in the first region R 1  and the second region R 2  is higher than that in the first region R 1  and the second region R 2  illustrated in  FIG.  28   . The first region R 1  and the second region R 2  are connected. According to such a diffusion region  306   b , potential adjustment (potential design) can be easily performed by changing the impurity concentrations of the first region R 1  and the second region R 2 . 
     As illustrated in  FIG.  33   , in the present embodiment, the diffusion region  306   b  may be formed so that the length (depth) of the first region R 1  in the substrate thickness direction is longer than the length (depth) of the second region R 2  in the substrate thickness direction. The first region R 1  and the second region R 2  are connected. According to such a diffusion region  306   b , potential adjustment (potential design) can be easily performed by changing the length in the substrate thickness direction of each of the first region R 1  and the second region R 2 . Note that the diffusion region  306   b  may be formed such that the lengths in the substrate thickness direction of the first region R 1  and the second region R 2  are different from each other. Moreover, for example, the diffusion region  306   b  may be formed such that the length in the substrate thickness direction of the second region R 2  is longer than the length in the substrate thickness direction of the first region R 1  contrary to the above description. 
     Furthermore, as illustrated in  FIG.  34   , in the present embodiment, the diffusion region  306   b  may be formed such that the first region R 1  is thinner than the second region R 2 . That is, the length of the first region R 1  in the direction orthogonal to the substrate thickness direction is shorter than the length of the first region R 1  in the direction orthogonal to the substrate thickness direction. The first region R 1  and the second region R 2  are connected. According to such a diffusion region  306   b , potential adjustment (potential design) can be easily performed by changing the thickness of each of the first region R 1  and the second region R 2 . Note that the diffusion region  306   b  may be formed such that the thicknesses of the first region R 1  and the second region R 2  are different from each other. Moreover, for example, the second region R 2  may be formed to be thinner than the first region R 1  contrary to the above. 
     As illustrated in  FIG.  35   , in the present embodiment, the diffusion region  306   b  may be formed such that the impurity concentration of the first region R 1  is lower than the impurity concentration of the second region R 2 . The first region R 1  and the second region R 2  are connected. According to such a diffusion region  306   b , potential adjustment (potential design) can be easily performed by changing the impurity concentration of each of the first region R 1  and the second region R 2 . Note that the diffusion region  306   b  may be formed such that the impurity concentration of each of the first region R 1  and the second region R 2  is different. Moreover, for example, the diffusion region  306   b  may be formed such that the impurity concentration of the second region R 2  is lower than the impurity concentration of the first region R 1  contrary to the above description. 
     Ion implantation is performed to form the diffusion regions  306   b  having various shapes as illustrated in  FIGS.  28  and  30  to  35   . At the time of ion implantation, various conditions such as power, implantation time, processing temperature, and electric field are adjusted. By appropriately adjusting these various conditions, it is possible to obtain the diffusion regions  306   b  having various shapes as illustrated in  FIGS.  28  and  30  to  35   . 
     As illustrated in  FIG.  36   , in the present embodiment, one additional wall  308  may be provided between the two protruding portions  304  (slits  312 ). In this case, the diffusion region  306   b  is provided between each of the two protruding portions  304  and one additional wall  308  (two regions). Furthermore, a cross-section of the imaging element  100  taken along line G-G′ illustrated in  FIG.  36    is the same as the cross-section illustrated in  FIG.  28   , and a cross-section of the imaging element  100  taken along line H-H′ illustrated in  FIG.  36    is the same as the cross-section illustrated in  FIG.  34   . In such a configuration, for example, a potential gradient (see a white arrow in  FIG.  36   ) can be formed. As a result, the electric charge can easily roll (move) toward the transfer gates  400   a  and  400   b . That is, potential adjustment (potential design) such as forming a potential gradient can be easily performed by a combination of various shapes of the first region R 1  and the second region R 2  constituting the diffusion region  306   b , a combination of impurity concentrations, or the like. 
     Here, a part of the manufacturing process (manufacturing method) of the imaging device  1  will be described with reference to  FIGS.  37  and  38   .  FIGS.  37  and  38    are process cross-sectional views for explaining a part of the manufacturing process of the imaging device  1  according to the present embodiment. Note that, in  FIGS.  37  and  38   , for the sake of clarity, only a main part of the imaging device  1  related to the present embodiment is illustrated, and illustration of other parts is omitted. 
     As illustrated in the upper part of  FIG.  37   , in the present embodiment, for example, ion implantation is performed on the first semiconductor substrate  10  on which a photodiode, a floating diffusion (both are not illustrated), transfer gates  400   a  and  400   b , an element separation wall  310 , a protruding portion  304 , and the like are formed. At this time, in the example of  FIG.  37   , ion implantation is performed from the front surface  10   b  of the first semiconductor substrate  10 . Thereafter, the first semiconductor substrate  10  and the second semiconductor substrate  11  are bonded via an interlayer insulating film  10 A. Thereafter, chemical mechanical polishing (CMP), a grinder, or the like is used for the first semiconductor substrate  10 , and thinning is performed from the back surface  10   a  of the first semiconductor substrate  10  as illustrated in the middle part of  FIG.  37   . Thereafter, for example, activation annealing or the like is executed, and then ion implantation is executed again on the first semiconductor substrate  10 . At this time, in the example of  FIG.  37   , ion implantation is performed from the back surface  10   a  of the first semiconductor substrate  10 . Thereafter, as illustrated in the lower part of  FIG.  37   , the support substrate  12  is bonded to the first semiconductor substrate  10 , and for example, activation annealing is executed. 
     Next, as illustrated in the upper part of  FIG.  38   , for example, various transistors, signal lines (for example, the pixel drive wiring  26 , the horizontal signal line  28 , and the like), and the like are formed on the second semiconductor substrate  11 . Then, as illustrated in the middle part of  FIG.  38   , a logic substrate  13  is bonded to the second semiconductor substrate  11 . The logic substrate  13  includes, for example, a plurality of circuits such as various circuit units  21  to  25 . Thereafter, CMP, a grinder, or the like is used for the support substrate  12 , and thinning is performed as illustrated in the lower part of  FIG.  38   . 
     As described above, according to the present embodiment (including modified examples), it is possible to obtain effects according to other embodiments (including modified examples). That is, deterioration of the captured image can be avoided while improving the accuracy of the phase difference detection. Furthermore, the diffusion region  306   b  is formed in a shape that expands from the front surface  10   b  of the semiconductor substrate  10  toward the inside of the semiconductor substrate  10  and narrows from the inside of the semiconductor substrate  10  toward the back surface  10   a  of the semiconductor substrate  10 . As a result, since the diffusion region  306   b  (see  FIG.  28   ) is narrower than the diffusion region  306   a  (see  FIG.  29   ), the photoelectric conversion region can be widened. 
     12. Tenth Embodiment 
     Further, in the embodiment of the present disclosure, the protruding portion  304  may be configured by an extension portion  304   a  and a projection portion  304   b . Hereinafter, such an embodiment will be described as a tenth embodiment of the present disclosure with reference to  FIGS.  39  to  41   .  FIG.  39    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction.  FIG.  40    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along line I-I′ illustrated in  FIG.  39   .  FIG.  41    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  according to the comparative example of the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . 
     As illustrated in  FIG.  39   , in the present embodiment, the two protruding portions  304  each have an extension portion  304   a  and a projection portion  304   b . The extension portion  304   a  is connected to the element separation wall  310  and extends in the column direction from the element separation wall  310 . The projection portion  304   b  is provided at an end of the extension portion  304   a  and extends in the row direction. When viewed from above the light receiving surface  10   a , the shape of the extension portion  304   a  and the shape of the projection portion  304   b  are rectangular, and in the example of  FIG.  39   , the protruding portion  304  is T-shaped. Each projection portion  304   b  has opposing surfaces S 1  facing each other. When viewed from above the light receiving surface  10   a , an individual width (for example, a length in the row direction) of each opposing surface S 1  is wider than an individual line width (for example, a length in the row direction) of each extension portion  304   a.    
     According to such a configuration, as illustrated in  FIG.  40   , a diffusion layer (doping layer), that is, the diffusion region  306  is formed only by conformal doping on the wall surface of the element separation wall  310 , and the slit  312  is filled with the diffusion region  306 . This is because the two protruding portions  304  forming the slit  312  are formed straight so as to be orthogonal to the light receiving surface  10   a . That is, this is because the shape of the slit  312  is not a tapered shape but a linear shape. 
     For example, as illustrated in  FIG.  41   , the processed shape of the full trench may be tapered due to the influence of the micro-loading effect at the time of etching. In this case, the region of the slit  312  is not completely filled with the diffusion region  306  only by the conformal doping, and sufficient potential separation may not be performed. As a countermeasure, it is desirable to perform ion implantation into the slit  312 , but this leads to an increase in manufacturing processes. In general, the etching rate can be improved in the case of forming a trench (sparse) having a wide line width as compared with the case of forming a trench (dense) having a narrow line width. Therefore, by providing the projection portion  304   b  in the extension portion  304   a  to constitute the protruding portion  304 , the etching rate can be increased as compared with the case where the protruding portion  304  is constituted only by the extension portion  304   a , and the shape of the slit  312  can be made not a tapered shape but a linear shape. As a result, ion implantation can be omitted, and an increase in the number of manufacturing steps can be suppressed. Furthermore, since the perpendicularity of the slit  312  (perpendicularity of the trench) is improved, the saturation charge amount Qs can be improved as compared with a case where ion implantation is essential, color mixing and the quantum efficiency Qe can be improved, and crystal defect damage can be reduced to improve white spots. 
     Here,  FIG.  42    is a graph illustrating a relationship between the width of the slit  312  and the width of the protruding portion  304  according to the present embodiment. When the line width (the length in the row direction) of the extension portion  304   a  is L 1 , the width (the length in the row direction) of the projection portion  304   b  is L 2  as illustrated in  FIG.  39   , the width (the length in the column direction) of the slit  312  on the back surface  10   a  side of the semiconductor substrate  10  is L 3  as illustrated in  FIG.  41   , and the width (the length in the column direction) of the slit  312  on the front surface  10   b  side of the semiconductor substrate  10  is L 4 , a graph showing the relationship between “L 2 /L 1  (ratio)” and “L 4 -L 3  (difference)” is obtained as illustrated in  FIG.  42   . From this graph, by making the width L 2  of the projection portion  304   b  1.2 times or more the line width L 1  of the extension portion  304   a , the slit  312  is made perpendicular, and a sufficient effect can be obtained at a practical level. In the case of obtaining further perpendicularity, it is desirable that the width L 2  of the projection portion  304   b  be 1.4 times or more the line width L 1  of the extension portion  304   a.    
     Note that it is also possible to move the formation position of the slit  312  in the column direction. In this case, the length (for example, the length in the column direction) of the extension portion  304   a  is adjusted. Such movement of the formation position of the slit  312  is also possible in the following configurations of  FIGS.  45  to  50   . By moving the formation position of the slit  312  and taking the blooming path region to the end instead of the center, for example, the transfer gates  400   a  and  400   b  and the floating diffusion region can be separated from the blooming path region, and the margin for transfer, white spots, and the like can be improved. 
     Here, a part of the manufacturing process (manufacturing method) of the imaging element  100  will be described with reference to  FIGS.  43  and  44   .  FIG.  43    is a process cross-sectional view for explaining a part of the manufacturing process of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the semiconductor substrate  10  taken along line L-L′ illustrated in  FIG.  39   .  FIG.  44    is a process cross-sectional view for explaining a part of the manufacturing process of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the semiconductor substrate  10  taken along line I-I′ illustrated in  FIG.  39   . 
     As illustrated in  FIGS.  43  and  44   , in the present embodiment, a mask M 1  (for example, an inorganic mask such as SiO 2 ) is formed on the back surface  10   a  (or the front surface  10   b ) of the semiconductor substrate  10 . Thereafter, the mask M 2  is formed on the mask M 1 . The mask M 2  is formed, for example, by stacking a photoresist layer on the mask M 1  on the front surface  10   b  of the semiconductor substrate  10  by a spin coating method or the like and patterning the photoresist layer in accordance with a trench formation pattern. Next, trenches for forming the protruding portion  304  and the element separation wall  310  are formed by etching such as dry etching, and the mask M 2  is removed. Then, for example, conformal doping is performed to form the diffusion region  306 . Thereafter, a material such as an oxide film is embedded in each trench, and the protruding portion  304  and the element separation wall  310  are formed. Finally, the mask M 1  is removed, and the imaging element  100  having the final structure is formed through a post-process. 
     Further, in the present embodiment, the protruding portion  304  can be modified as follows. Therefore, a detailed configuration of the protruding portion  304  will be described with reference to  FIGS.  45  to  50   .  FIGS.  45  to  50    are explanatory diagrams illustrating a plane of the imaging element  100  according to the present embodiment, and specifically correspond to a cross-section of the imaging element  100  cut along a plane direction. 
     As illustrated in  FIG.  45   , in the present embodiment, the protruding portion  304  has an extension portion  304   a  and a projection portion  304   b . The extension portion  304   a  is connected to the element separation wall  310  and extends in the column direction from the element separation wall  310 . The projection portion  304   b  is provided at an end of the extension portion  304   a  and extends in the row direction. When viewed from above the light receiving surface  10   a , the shape of the extension portion  304   a  and the shape of the projection portion  304   b  are rectangular, and in the example of  FIG.  45   , the shape of the protruding portion  304  is T-shaped. The projection portion  304   b  has an opposing surface S 1  facing the wall surface of the element separation wall  310 . When viewed from above the light receiving surface  10   a , the width (for example, the length in the row direction) of the opposing surface S 1  of the projection portion  304   b  is longer than the line width (for example, the length in the row direction) of the extension portion  304   a.    
     Further, as illustrated in  FIG.  46   , in the present embodiment, the two protruding portions  304  are formed so as to be bent in the middle and the slit  312  to be inclined. Each of the protruding portions  304  has opposing surfaces S 1  facing each other. When viewed from above the light receiving surface  10   a , the length (for example, the length in the inclination direction) of each of the opposing surfaces S 1  is longer than the line width (for example, the length in the row direction) of each of the two protruding portions  304 . 
     As illustrated in  FIG.  47   , in the present embodiment, the two protruding portions  304  are formed so as to be shifted in the row direction. Each of the protruding portions  304  has opposing surfaces S 1  facing each other. When viewed from above the light receiving surface  10   a , an individual length (for example, a length in the column direction) of each opposing surface S 1  is longer than an individual line width (for example, a length in the row direction) of each protruding portion  304 . 
     As illustrated in  FIG.  48   , in the present embodiment, the two protruding portions  304  each have an extension portion  304   a  and a projection portion  304   b . The extension portion  304   a  is connected to the element separation wall  310  and extends in the column direction from the element separation wall  310 . The projection portion  304   b  is provided at an end of the extension portion  304   a , and is formed in a shape extending in the row direction and the column direction. When viewed from above the light receiving surface  10   a , the shape of the extension portion  304   a  is rectangular, and in the example of  FIG.  48   , the shape of the projection portion  304   b  is L-shaped. Each of the protruding portions  304  has opposing surfaces S 1  facing each other. When viewed from above the light receiving surface  10   a , an individual length (for example, a length in the row direction and a length in the column direction) of each opposing surface S 1  is longer than an individual line width (for example, a length in the row direction) of each extension portion  304   a.    
     Furthermore, as illustrated in  FIG.  49   , in the present embodiment, in addition to the two protruding portions  304 , two additional walls (an example of a separation portion)  308   c  are provided to face each other with the center of the imaging element  100  interposed therebetween. Each additional wall  308   c  has opposing surfaces S 1  facing each other. When viewed from above the light receiving surface  10   a , an individual length (for example, a length in the column direction) of each opposing surface S 1  is longer than an individual line width (for example, a length in the row direction) of each protruding portion  304 . 
     As illustrated in  FIG.  50   , in the present embodiment, the two protruding portions  304  each have an extension portion  304   a  and a projection portion  304   b . In the example of  FIG.  50   , the configuration other than the circular shape of the projection portion  304   b  when viewed from above the light receiving surface  10   a  is the same as the configuration of  FIG.  39   . Note that the shape of the projection portion  304   b  may be various shapes such as an elliptical shape and a trapezoidal shape other than the circular shape. 
     As described above, according to the present embodiment (including modified examples), it is possible to obtain effects according to other embodiments (including modified examples). That is, deterioration of the captured image can be avoided while improving the accuracy of the phase difference detection. In addition, the width (for example, the length in the row direction) of the opposing surface S 1  of the protruding portion  304  is wider than the line width (for example, the length in the row direction) of the extension portion  304   a  of the protruding portion  304 . As a result, the etching rate on the opposing surface S 1  side of the protruding portion  304  can be increased, and the shape of the slit  312  can be made not a tapered shape but a linear shape. As a result, ion implantation can be omitted, and an increase in the number of manufacturing steps can be suppressed. Furthermore, since the perpendicularity of the slit  312  (perpendicularity of the trench) is improved, the saturation charge amount Qs can be improved as compared with a case where ion implantation is essential, color mixing and the quantum efficiency Qe can be improved, and crystal defect damage can be reduced to improve white spots. 
     13. Eleventh Embodiment 
     Furthermore, in the embodiment of the present disclosure, two pixel separation walls (an example of a separation portion)  334   a  may be provided. Hereinafter, such an embodiment will be described as an eleventh embodiment of the present disclosure with reference to  FIGS.  51  and  52   .  FIG.  51    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction.  FIG.  52    is an explanatory diagram illustrating a plane of an imaging element  100  according to a comparative example of the present embodiment, and specifically, corresponds to a cross-section of the imaging element  100  according to the comparative example cut along a plane direction. 
     As illustrated in  FIG.  51   , in the present embodiment, the two pixel separation walls  334   a  are arranged in the column direction so as to face each other with the center of the imaging element  100  interposed therebetween. Each pixel separation wall  334   a  is separated from the element separation wall  310  without contacting the element separation wall  310 , and is further separated from each other. In the example of  FIG.  51   , when viewed from above the light receiving surface  10   a , each pixel separation wall  334   a  has a rectangular shape. 
     The diffusion region  306  includes a first region  306 A and a second region  306 B. The first region  306 A is a region formed by a solid-phase diffusion process for each trench for forming the two pixel separation walls  334   a . The second region  306 B is a region formed by a solid-phase diffusion process for the trench for forming the element separation wall  310 . That is, diffusion from the trench corresponding to the element separation wall  310  on the outer periphery and diffusion from each trench corresponding to the two protruding portions  304  occur independently, so that the diffusion region  306  has the first region  306 A and the second region  306 B. 
     Here, in order to enhance the separation between the two pixels, for example, it is possible to use a method of diffusing boron from doped silicon oxide deposited on the trench sidewall by solid-phase diffusion. In this case, in the structure as illustrated in  FIG.  52   , diffusion from the trench corresponding to the element separation wall  310  on the outer periphery and diffusion from each trench corresponding to the two protruding portions  304  simultaneously occur, and the diffusion region  306  of boron is widely formed. Since the diffusion region  306  is widely formed, the saturation charge amount decreases. Therefore, as described above, by disposing the element separation wall  310  and the two pixel separation walls  334   a  apart from each other and forming the separation structure independently, it is possible to independently perform solid-phase diffusion of the separation structure. Thus, it is possible to suppress a decrease in the saturation charge amount. That is, since diffusion from the trench corresponding to the element separation wall  310  and diffusion from each trench corresponding to the two protruding portions  304  occur independently, the size of the diffusion region  306  can be suppressed, and a decrease in the saturation charge amount can be suppressed. 
     In the present embodiment, for example, boron is diffused by a solid-phase diffusion process (an example of a diffusion process). However, the diffusion process is not limited to the solid-phase diffusion process, and a doping technique such as plasma doping in which doping is performed from a sidewall by heat can also be used. 
     Furthermore, in the example of  FIG.  51   , the two pixel separation walls  334   a  are positioned on the center line passing through the center of the imaging element  100 . However, the present invention is not limited thereto, and for example, the pixel separation walls may be positioned so as to be shifted in the left-right direction (as an example, a row direction) of  FIG.  51   . The same applies to the following configurations illustrated in  FIGS.  54  to  57   . 
     Here, a part of the manufacturing process (manufacturing method) of the imaging element  100  will be described with reference to  FIG.  53   .  FIG.  53    is a process cross-sectional view for explaining a part of the manufacturing process of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along the planar direction. 
     As illustrated in  FIG.  53   , in the present embodiment, individual trenches T 4  for forming the two pixel separation walls  334   a  are formed at internal positions away from the formation positions of the element separation walls  310  (see the first diagram from the left in  FIG.  53   ). Subsequently, a solid-phase diffusion process is used for the trenches T 4 , a solid-phase diffusion layer (for example, a P-type layer), that is, the first region  306 A is formed around each trench T 4 , and then a material such as an oxide film is embedded in the trenches T 4  to form the pixel separation wall  334   a  (see the second diagram from the left in  FIG.  53   ). Next, the trench T 5  for forming the element separation wall  310  is formed in a rectangular shape of a predetermined size surrounding each trench T 4 , a solid-phase diffusion process is used for the trench T 5 , a solid-phase diffusion layer (for example, a P-type layer), that is, the second region  306 B is formed around the trench T 5 , and finally, a material such as an oxide film is embedded in the trench T 5  to form the element separation wall  310  (see the third diagram from the left in  FIG.  53   ). As a result, the diffusion region  306  including the first region  306 A and the second region  306 B is formed. 
     Furthermore, in the present embodiment, the pixel separation wall  334   a  can be modified as follows. Therefore, a detailed configuration of the pixel separation wall  334   a  will be described with reference to  FIGS.  54  to  57   .  FIGS.  54  to  57    are explanatory diagrams illustrating a plane of the imaging element  100  according to the present embodiment, and specifically correspond to a cross-section of the imaging element  100  cut along a plane direction. 
     As illustrated in  FIG.  54   , in the present embodiment, four pixel separation walls  334   a  are provided. Two of the four pixel separation walls  334   a  are arranged in the column direction so as to face each other with the center of the imaging element  100  therebetween, and the other two are arranged in the row direction so as to face each other with the center of the imaging element  100  therebetween. Each pixel separation wall  334   a  is separated from the element separation wall  310  without contacting the element separation wall  310 , and is further separated from each other. In the example of  FIG.  54   , when viewed from above the light receiving surface  10   a , each pixel separation wall  334   a  has a rectangular shape, and each pixel separation wall  334   a  is disposed so as to form a cross shape. 
     Furthermore, as illustrated in  FIG.  55   , in the present embodiment, in addition to the two pixel separation walls  334   a , two pixel separation walls  334   a  having a smaller planar area than those pixel separation walls  334   a  are provided. The pixel separation walls  334   a  having a small area (size) are arranged in the row direction so as to face each other with the center of the imaging element  100  therebetween. Individual parts of the two pixel separation walls  334   a  are positioned in a region between the other two pixel separation walls  334   a . In the example of  FIG.  55   , when viewed from above the light receiving surface  10   a , each pixel separation wall  334   a  has a rectangular shape. 
     Furthermore, as illustrated in  FIG.  56   , in the present embodiment, four pixel separation walls  334   a  are provided. The four pixel separation walls  334   a  are arranged in a dot shape in the column direction passing through the center of the imaging element  100 . Each pixel separation wall  334   a  is separated from the element separation wall  310  without contacting the element separation wall  310 , and is further separated from each other. In the example of  FIG.  56   , when viewed from above the light receiving surface  10   a , each pixel separation wall  334   a  has a rectangular shape, and each pixel separation wall  334   a  is arranged on one straight line. 
     Furthermore, as illustrated in  FIG.  57   , in the present embodiment, the two pixel separation walls  334   a  are each formed in a circular shape when viewed from above the light receiving surface  10   a . In the example of  FIG.  57   , when viewed from above the light receiving surface  10   a , the configuration other than that the shape of each pixel separation wall  334   a  is circular is the same as the configuration of  FIG.  51   . Note that the pixel separation wall  334   a  may have various shapes such as an elliptical shape and a trapezoidal shape in addition to the circular shape. 
     As described above, according to the present embodiment (including modified examples), it is possible to obtain effects according to other embodiments (including modified examples). That is, deterioration of the captured image can be avoided while improving the accuracy of the phase difference detection. Furthermore, by disposing the element separation wall  310  and each pixel separation wall  334   a  apart from each other and forming the separation structure independently, it is possible to independently perform a diffusion process such as solid-phase diffusion of the separation structure. Thus, it is possible to suppress a decrease in the saturation charge amount. 
     14. Twelfth Embodiment 
     In the embodiment of the present disclosure, the pair of protruding portions  304  is not limited to have the substantially same separation distance in the depth direction (height direction), and may have different distances. Therefore, such an embodiment will be described as a twelfth embodiment of the present disclosure with reference to  FIGS.  58  to  60   .  FIG.  58    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction.  FIG.  59    is an explanatory diagram illustrating both surfaces and a cross-section of the imaging element  100  according to the present embodiment, and the cross-section corresponds to a cross-section of the imaging element  100  taken along line M-M′ illustrated in  FIG.  58   .  FIG.  60    is an explanatory diagram illustrating the relationship between the slit width (the length of the gap between the slits), the condensing characteristics, and the pixel characteristics of the imaging element  100  according to the present embodiment. 
     As illustrated in  FIGS.  58  and  59   , in the present embodiment, the pair of protruding portions  304  is formed in a tapered shape in which a separation distance (slit width) therebetween gradually changes in the depth direction. In the example of  FIG.  59   , the distance between the pair of protruding portions  304  gradually increases in the depth direction from the front surface  10   b  toward the back surface (light receiving surface)  10   a  (from the upper surface to the lower surface in  FIG.  58   ) (a&lt;b). As a result, it is possible to secure the protruding amount as a whole while moving the light receiving surface  10   a  side of the pair of protruding portions  304  away from the center. As illustrated in  FIG.  60   , it is possible to reduce scattering of light while maintaining pixel characteristics, and it is possible to eliminate a trade-off between light collection characteristics and pixel characteristics. 
     Here, there is a relationship of b−a=2×(t/tan (θ)). Note that a is the length of the slit  312  on the front surface  10   b  side, b is the length of the slit  312  on the back surface (light receiving surface)  10   a  side, t is the thickness (length in the depth direction) from the front surface  10   b  to the back surface  10   a , and θ is the taper angle of the slit  312  with respect to the front surface  10   b . Even when the taper angle θ is small, a large difference occurs in the slit width from the front surface  10   b  to the back surface  10   a  depending on the thickness t from the front surface  10   b  to the back surface  10   a.    
     In the present embodiment, the pair of protruding portions  304  can be modified as follows. Therefore, a detailed configuration of the pair of protruding portions  304  will be described with reference to  FIGS.  61  to  71   .  FIGS.  61 ,  65 ,  68   , and  69  are explanatory diagrams illustrating both surfaces and a cross-section of the imaging element  100  according to the present embodiment, respectively.  FIGS.  62  to  64  and  66    are explanatory diagrams illustrating a cross-section of the imaging element  100  according to the present embodiment.  FIGS.  67 ,  70   , and  71  are explanatory diagrams illustrating both surfaces of the imaging element  100  according to the present embodiment. 
     As illustrated in  FIG.  61   , in the present embodiment, the pair of protruding portions  304  is formed such that the separation distances from the front surface  10   b  to the back surface  10   a  (from the upper surface to the lower surface in  FIG.  61   ) are substantially the same by a predetermined depth in the depth direction, and gradually widen in the depth direction from the middle in the depth direction (a&lt;b). Note that, as for color mixing deterioration, the trench shape in the light condensing portion is dominant, and thus it is effective if the light condensing portion is changed. 
     As illustrated in  FIG.  62   , in the present embodiment, the pair of protruding portions  304  is formed such that the separation distance between the protruding portions  304  gradually narrows in the depth direction from the front surface  10   b  toward the back surface  10   a  (from the upper surface to the lower surface in  FIG.  62   ), becomes substantially the same by a predetermined depth in the depth direction, and gradually widens in the depth direction from the middle in the depth direction (a=b&gt;c). Note that a&lt;b or a&gt;b may be satisfied. The separation distance on the back surface (light receiving surface)  10   a  side is preferably wide because it is effective for light collection, and the separation distance on the front surface  10   b  side is preferably wide from the viewpoint of potential design. The central separation distance works for Qs, so it is better to be narrow. 
     Further, as illustrated in  FIG.  63   , in the present embodiment, the pair of protruding portions  304  is formed such that the separation distance therebetween changes in multiple stages in the depth direction from the front surface  10   b  toward the back surface  10   a  (from the upper surface to the lower surface in  FIG.  63   ). In the example of  FIG.  63   , the separation distance between the pair of protruding portions  304  changes in two stages in the depth direction, and the separation distance on the front surface  10   b  side is narrower than the separation distance on the back surface  10   a  side (a&lt;b). Therefore, each of the pair of protruding portions  304  has a step. As described above, the separation distance between the pair of protruding portions  304  may be changed not continuously but discontinuously, and may be changed in multiple stages such as three stages or four stages instead of two stages. 
     In addition, as illustrated in  FIG.  64   , in the present embodiment, the pair of protruding portions  304  is formed such that the separation distance between the protruding portions changes in two stages in the depth direction from the front surface  10   b  toward the back surface  10   a  (from the upper surface to the lower surface in  FIG.  64   ) and gradually widens in the depth direction from the middle in the depth direction (a&lt;c&lt;b). In this manner, the intermediate tapered shape illustrated in  FIGS.  61  and  62   , the multistage processed shape illustrated in  FIG.  63   , or the like may be combined. 
     As illustrated in  FIG.  65   , in the present embodiment, one protruding portion  304  is formed such that a separation distance from the element separation wall  310  gradually increases in the depth direction from the front surface  10   b  toward the back surface  10   a  (from the upper surface to the lower surface in  FIG.  65   ) (a&lt;b). 
     As illustrated in  FIG.  66   , in the present embodiment, one protruding portion  304  is formed so as to change in two stages in the depth direction from the front surface  10   b  toward the back surface  10   a  (from the upper surface to the lower surface in  FIG.  66   ). In the example of  FIG.  66   , the separation distance on the front surface  10   b  side is narrower than the separation distance on the back surface  10   a  side (a&lt;b). 
     As illustrated in  FIG.  67   , in the present embodiment, the four protruding portions  304  are formed such that the distance between the pair of protruding portions  304  facing each other gradually increases in the depth direction from the front surface  10   b  toward the back surface  10   a  (a&lt;b). These protruding portions  304  are arranged in a cross shape. 
     As illustrated in  FIGS.  65  to  67   , the intermediate tapered shape illustrated in  FIGS.  61  and  62   , the multistage processed shape illustrated in  FIG.  63   , or the like may be applied to the plurality of protruding portions  304  such as one protruding portion  304  and four protruding portions  304 , or a combination thereof may be applied. 
     As illustrated in  FIG.  68   , in the present embodiment, the pair of protruding portions  304  is formed such that each line width (width in the direction orthogonal to the extension direction) gradually narrows in the depth direction from the front surface  10   b  toward the back surface  10   a  (from the upper surface to the lower surface in  FIG.  68   ) (d&gt;e). The distance between the pair of protruding portions  304  is substantially the same in the depth direction (a=b). 
     As illustrated in  FIG.  69   , in the present embodiment, one protruding portion  304  is formed such that a line width (width in a direction orthogonal to the extension direction) thereof gradually narrows in the depth direction from the front surface  10   b  toward the back surface  10   a  (from the upper surface to the lower surface in  FIG.  69   ) (d&gt;e). The separation distance between the protruding portion  304  and the element separation wall  310  gradually increases along the depth direction from the front surface  10   b  toward the back surface  10   a  (a&lt;b). 
     Furthermore, as illustrated in  FIG.  70   , in the present embodiment, the four pixel separation walls  334   a  are formed such that the line widths thereof gradually narrow in the depth direction from the front surface  10   b  toward the back surface  10   a . These pixel separation walls  334   a  are arranged in a dot shape in the column direction passing through the center of the imaging element  100 . Each pixel separation wall  334   a  is separated from the element separation wall  310  without contacting the element separation wall  310 , and is further separated from each other. 
     As illustrated in  FIG.  71   , in the present embodiment, the four protruding portions  304  are formed such that the line width (width in the direction orthogonal to the extension direction) gradually decreases in the depth direction from the front surface  10   b  toward the back surface  10   a  (d&lt;e). These protruding portions  304  are arranged in a cross shape. A distance between the pair of protruding portions  304  facing each other is substantially the same in the depth direction (a=b). 
     As described above, by widening the gap of the slit  312  (the width of the slit  312 ) on the light receiving surface  10   a  side, scattering by each protruding portion  304  is suppressed, and the condensing characteristic is particularly dominant in the vicinity of the light receiving surface  10   a . Thus, both the condensing characteristic and the pixel characteristic can be achieved. In addition, not only the gap between the slits  312  is widened on the light receiving surface  10   a  side, but also the line width of the protruding portion  304  is narrowed on the light receiving surface  10   a  side. Thus, scattering by the protruding portion  304  can be suppressed, and color mixing can be suppressed. 
     Note that only one of widening the gap of the slit  312  on the light receiving surface  10   a  side and narrowing the line width of the protruding portion  304  may be performed, or both of them may be performed. That is, the configurations illustrated in  FIGS.  61  to  71    may be used alone or in combination. 
     Here, a part of the manufacturing process (manufacturing method) of the imaging element  100  will be described with reference to  FIG.  72   .  FIG.  72    is a process cross-sectional view for explaining a part of the manufacturing process of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section obtained by cutting the semiconductor substrate  10  along the thickness direction of the semiconductor substrate  10 . 
     As illustrated in  FIG.  72   , in the present embodiment, front surface full trench isolation (FFTI) processing is performed on the semiconductor substrate  10  to embed the material. Thereafter, after various steps (omitted), the semiconductor substrate  10  and the bonded substrate  501  are bonded to each other, and thinning is performed. The semiconductor substrate  10  that has been thinned is back-filled, and the color filter  202  and the on-chip lens  200  are stacked. Note that, as the bonded substrate  502 , for example, a logic substrate, a semiconductor substrate, or the like is used. 
     15. Thirteenth Embodiment 
     Furthermore, in the embodiment of the present disclosure, the two transfer gates  400   a  and  400   b , the FD portion (floating diffusion portion)  601 , and the ground portion  602  may be arranged as illustrated in  FIG.  73   . Hereinafter, such an embodiment will be described as a thirteenth embodiment of the present disclosure with reference to  FIGS.  73  and  74   .  FIG.  73    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction.  FIG.  74    is an explanatory diagram illustrating a plane of an imaging element  100  according to a comparative example of the present embodiment, and specifically, corresponds to a cross-section of the imaging element  100  according to the comparative example cut along a plane direction. 
     As illustrated in  FIG.  73   , in the present embodiment, the two transfer gates  400   a  and  400   b  are positioned on one end side (for example, the upper side of  FIG.  73   ) of the cell region surrounded by the element separation wall  310 . The cell region is included in the imaging element  100 . In the example of  FIG.  73   , the cell region is a square. 
     The FD portion  601  is a floating diffusion shared by two adjacent cell regions (see a dotted line region in  FIG.  73   ). The FD portion  601  is positioned on one end side (for example, the upper side of  FIG.  73   ) of the cell region. In the example of  FIG.  73   , the shape of the FD portion  601  is not a regular octagon but an octagon having long sides and short sides. Specifically, the FD portion  601  is horizontally long, and in the FD portion  601 , the length in the direction orthogonal to the extension direction of the protruding portion  304  is longer than the length in the extension direction of the protruding portion  304 . As the FD portion  601 , for example, Poly-Si (polycrystalline Si) is used. 
     The ground portion  602  is a ground portion shared by two adjacent cell regions (see a dotted line region in  FIG.  73   ). The ground portion  602  is positioned on one end side (for example, the lower side of  FIG.  73   ) of the cell region. In the example of  FIG.  73   , the shape of the ground portion  602  is not a regular octagon but an octagon having long sides and short sides. Specifically, the ground portion  602  is horizontally long, and in the ground portion  602 , a length of the protruding portion  304  in a direction orthogonal to an extension direction is longer than a length of the protruding portion  304  in the extension direction. As the ground portion  602 , for example, Poly-Si (polycrystalline Si) is used. The ground portion  602  is at the ground (GND) potential, and functions as, for example, a well contact. 
     Here, as illustrated in  FIG.  74   , when the shape of each of the FD portion  601  and the ground portion  602  is a regular octagon, the width g (the length in the vertical direction in  FIG.  74   ) of the slit  312  is narrower than the width f (the length in the vertical direction in  FIG.  75   ) of the slit  312  illustrated in  FIG.  75   . In  FIG.  74    as described above, the ratio of the width g of the slit  312  to the cell pitch of the cell region (length in the vertical direction in  FIG.  74   ) is increased from the viewpoint of optical factors (improvement in Qe and suppression of color mixing) or further miniaturization. For example, when the width g of the slit  312  illustrated in  FIG.  74    increases, the region (division portion) of the slit  312  approaches the FD portion  601  (for example, N+ diffusion layer) and the ground portion  602  (for example, a P+ diffusion layer). Therefore, the FD portion  601  and the ground portion  602  may interfere with the region of the slit  312 , and an increase in single pixel Qs variation, FD white spot deterioration, and the like may occur. 
     Therefore, in the present embodiment, as illustrated in  FIG.  73   , each of the FD portion  601  and the ground portion  602  has a horizontally long shape. For example, in each of FD portion  601  and ground portion  602 , the length of the protruding portion  304  in the extension direction is shorter than the length of the protruding portion  304  in the direction orthogonal to the extension direction. As a result, the FD portion  601  and the ground portion  602  are separated from the region (division portion) of the slit  312  as compared with  FIG.  74   . Therefore, the influence of the diffusion of the FD portion  601  and the ground portion  602  on the potential of the region of the slit  312  is suppressed. Thus, it is possible to suppress an increase in single pixel Qs variation, FD white spot deterioration, and the like. Furthermore, the shape of each of the transfer gates  400   a  and  400   b , for example, the shape of the slit  312  side in the transfer gates  400   a  and  400   b  can be enlarged, and transfer improvement (improvement of transfer characteristics) and suppression of variation in potential barriers can be realized. 
     In the present embodiment, the ground portion  602  can be modified as follows. Therefore, a detailed configuration of the ground portion  602  will be described with reference to  FIGS.  75  to  78   . Each of  FIGS.  75  to  78    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment, and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction. 
     As illustrated in  FIG.  75   , in the present embodiment, the ground portion  602  is provided at two of the four corners of the cell region. These ground portions  602  are ground portions shared by four adjacent cell regions. In the example of  FIG.  75   , the cells are provided at the lower left and lower right of the four corners of the cell region. Each ground portion  602  is shifted from the FD portion  601  by a half of the cell pitch (length in the left-right direction in  FIG.  75   ) of the cell region. As a result, each ground portion  602  is further away from the region of the slit  312  as compared with  FIGS.  73  and  74   . Therefore, an increase in single pixel Qs variation, FD white point deterioration, and the like can be reliably suppressed. 
     As illustrated in  FIG.  76   , in the present embodiment, the ground portion  602  illustrated in  FIG.  75    is provided rotated by 90 degrees (the other configurations are the same as those of  FIG.  75   ). As a result, each ground portion  602  is further away from the region of the slit  312  as compared with  FIG.  75   . Therefore, it is possible to more reliably suppress an increase in single pixel Qs variation, FD white spot deterioration, and the like. 
     As illustrated in  FIG.  77   , in the present embodiment, the ground portion  602  illustrated in  FIG.  75    is formed in a regular octagon (the other configurations are the same as those of  FIG.  75   ). Even in this case, each ground portion  602  is separated from the region of the slit  312  as compared with  FIG.  74   . Therefore, an increase in single pixel Qs variation, FD white point deterioration, and the like can be reliably suppressed. 
     Furthermore, as illustrated in  FIG.  78   , in the present embodiment, the FD portion  601  illustrated in  FIG.  77    is formed in a regular octagon, and the shapes of the transfer gates  400   a  and  400   b  are the same as those of  FIG.  74    (the other configurations are the same as those of  FIG.  77   ). Even in this case, each ground portion  602  is separated from the region of the slit  312  as compared with  FIG.  74   . Therefore, an increase in single pixel Qs variation, FD white point deterioration, and the like can be reliably suppressed. 
     Note that the FD portion  601  and the ground portion  602  may have the same shape (see  FIGS.  73  to  76  and  78   ) or different shapes (see  FIG.  77   ). Furthermore, the shape of the FD portion  601  or the ground portion  602  may be a shape having long sides and short sides, for example, a vertically and horizontally symmetrical shape (see  FIGS.  73  to  78   ), or a vertically and horizontally asymmetrical shape. 
     Furthermore, the FD portion  601  and the ground portion  602  are arranged in an array (for example, a matrix shape along the row direction and the column direction), but may be arranged at the same pitch as the cell pitch of the cell region, or may be arranged by being shifted from each other by a half pitch. 
     Furthermore, the shape of the FD portion  601  and the ground portion  602  may be, for example, other polygonal shapes or elliptical shapes other than the octagonal shape having the long side and the short side. 
     16. Summary 
     As described above, according to each embodiment of the present disclosure, since the element that separates the pair of pixels  300   a  and  300   b  is provided at the time of phase difference detection, and in addition to the separating element, the element that functions as the overflow path at the time of normal imaging is provided, it is possible to avoid deterioration of the captured image while improving the accuracy of phase difference detection. 
     Note that, in the embodiment of the present disclosure described above, a case where the present disclosure is applied to a back-illuminated CMOS image sensor structure has been described. However, the embodiment of the present disclosure is not limited thereto, and may be applied to other structures. 
     Note that, in the embodiment of the present disclosure described above, the imaging element  100  in which the first conductivity type is N type, the second conductivity type is P type, and electrons are used as signal charges has been described, but the embodiment of the present disclosure is not limited to such an example. For example, the present embodiment can be applied to the imaging element  100  in which the first conductivity type is P-type, the second conductivity type is N-type, and holes are used as signal charges. 
     Furthermore, in the embodiment of the present disclosure described above, the semiconductor substrate  10  is not necessarily a silicon substrate, and may be another substrate (for example, a silicon on insulator (SOI) substrate, a SiGe substrate, or the like). In addition, the semiconductor substrate  10  may have a semiconductor structure or the like formed on such various substrates. 
     Furthermore, the imaging device  1  according to the embodiment of the present disclosure is not limited to an imaging device that detects a distribution of the amount of incident light of visible light and captures the distribution as an image. For example, the present embodiment can be applied to an imaging device that captures a distribution of incident amounts of infrared rays, X-rays, particles, or the like as an image, or an imaging device (physical quantity distribution detection device) such as a fingerprint detection sensor that detects a distribution of other physical quantities such as pressure and capacitance and captures the distribution as an image. 
     Furthermore, the imaging device  1  according to the embodiment of the present disclosure can be manufactured using a method, a device, and conditions used for manufacturing a general semiconductor device. That is, the imaging device  1  according to the present embodiment can be manufactured using an existing semiconductor device manufacturing process. 
     Examples of the above-described method include a physical vapor deposition (PVD) method, a chemical vapor deposition (CVD) method, and an atomic layer deposition (ALD) method. Examples of the PVD method include a vacuum vapor deposition method, an electron beam (EB) vapor deposition method, various sputtering methods (Magnetron sputtering method, radio frequency (RF)-direct current (DC) coupled bias sputtering method, electron cyclotron resonance (ECR) sputtering method, counter target sputtering method, high frequency sputtering method, and the like), an ion plating method, a laser ablation method, a molecular beam epitaxy (MBE) method, and a laser transfer method. Examples of the CVD method include a plasma CVD method, a thermal CVD method, an organic metal (MO) CVD method, and a photo CVD method. Further, other methods include an electroplating method, an electroless plating method, a spin coating method; an immersion method; a cast method; a micro contact printing method; a drop cast method; various printing methods such as a screen printing method, an inkjet printing method, an offset printing method, a gravure printing method, and a flexographic printing method; a stamp method; a spray method; and various coating methods such as an air doctor coater method, a blade coater method, a rod coater method, a knife coater method, a squeeze coater method, a reverse roll coater method, a transfer roll coater method, a gravure coater method, a kiss coater method, a cast coater method, a spray coater method, a slit orifice coater method, and a calendar coater method. Furthermore, examples of the patterning method include chemical etching such as shadow mask, laser transfer, and photolithography, and physical etching using ultraviolet rays, laser, or the like. In addition, examples of the planarization technique include a chemical mechanical polishing (CMP) method, a laser planarization method, a reflow method, and the like. 
     Note that, in the embodiment of the present disclosure described above, the structures of the protruding portions (an example of the separation portion)  304  and  324 , the additional walls (an example of the separation portion)  308 ,  308   a ,  308   b , and  308   c , and the pixel separation walls (an example of the separation portion)  334  and  334   a  have been described, but the structure according to the embodiment of the present disclosure is not limited thereto. Here, various aspects of the structure of each part will be described in detail with reference to  FIGS.  79  to  84   . 
       FIG.  79    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment (modified example), and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction.  FIG.  80    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  for each structure, that is, the semiconductor substrate  10  for each structure according to the present embodiment (modified example), and specifically, corresponds to a cross-section obtained by cutting the semiconductor substrate  10  for each structure along the line J-J′ illustrated in  FIG.  79   . 
     As illustrated in  FIGS.  79  and  80   , the pixel separation wall  334  is formed in any structure of RDTI (back surface DTI), FDTI (front surface DTI), FFTI (front surface FTI: Full Trench Isolation), RFTI (back surface FTI), and RDTI+FDTI. In these structures, the trench T 3  is formed in the thickness direction of the semiconductor substrate  10 . A material such as an oxide film is embedded in the trench T 3 . In the example of  FIG.  80   , the trench T 3  is formed in a tapered shape expanding from the surface of the semiconductor substrate  10  toward the inside, but the present invention is not limited thereto. For example, the trench T 3  may be formed straight so as to be orthogonal (or substantially orthogonal) to the surface of the semiconductor substrate  10 . 
     The RDTI has a structure in which a trench T 3  is formed from the back surface  10   a  (light receiving surface  10   a ) of the semiconductor substrate  10  to the middle of the semiconductor substrate  10 . The FDTI has a structure in which a trench is formed from the front surface  10   b  (the surface opposite to the light receiving surface  10   a ) of the semiconductor substrate  10  to the middle of the semiconductor substrate  10 . The FFTI is a structure formed by penetrating the trench T 3  from the front surface  10   b  to the back surface  10   a  of the semiconductor substrate  10 . The RFTI is formed by penetrating the trench T 3  from the back surface  10   a  to the front surface  10   b  of the semiconductor substrate  10 . The RDTI+FDTI is a method in which the RDTI and the FDTI described above are combined. In the RDTI+FDTI, the trench T 3  extending from the back surface  10   a  and the trench T 3  extending from the front surface  10   b  are connected near the center in the thickness direction of the semiconductor substrate  10 . 
       FIG.  81    is an explanatory diagram illustrating a plane of the imaging element  100  according to the present embodiment (modified example), and specifically corresponds to a cross-section of the imaging element  100  cut along a plane direction.  FIG.  82    is an explanatory diagram illustrating a part of a cross-section of the imaging element  100  for each structure, that is, the semiconductor substrate  10  for each structure according to the present embodiment (modified example), and specifically, corresponds to a cross-section obtained by cutting the semiconductor substrate  10  for each structure along the line K-K′ illustrated in  FIG.  81   . 
     As illustrated in  FIGS.  81  and  82   , the protruding portion  304  is formed in any structure of RDTI, FDTI, FFTI, RFTI, and RDTI+FDTI similarly to the above-described pixel separation wall  334  (see  FIG.  80   ). In these structures, the trench T 3  is formed in the thickness direction of the semiconductor substrate  10 . At this time, as illustrated in  FIG.  82   , the trench T 3  is formed such that the protruding portion  304  is in contact with the element separation wall  310  and is not separated from each other. A material to be an oxide film or the like is embedded in the trench T 3 . In the example of  FIG.  82   , the trench T 3  is formed in a tapered shape expanding from the surface of the semiconductor substrate  10  toward the inside, but the present invention is not limited thereto. For example, the trench T 3  may be formed straight so as to be orthogonal (or substantially orthogonal) to the surface of the semiconductor substrate  10 . 
     Here, as illustrated in  FIG.  79   , as the pixel separation wall  334 , another structure may be used in addition to one pixel separation wall  334  that is not in contact with the element separation wall  310 . For example, as illustrated in  FIG.  83   , a plurality of pixel separation walls  334  may be formed in a line in a dot shape so as not to be in contact with the element separation wall  310 . In the example of  FIG.  83   , the number of pixel separation walls  334  is 6, but the number is not limited. Furthermore, as illustrated in  FIG.  84   , the pixel separation wall  334  may be formed such that both ends thereof are in contact with the element separation wall  310 . Note that, in the examples of  FIGS.  79 ,  83 , and  84   , the pixel separation wall  334  is formed in the column direction, but is not limited thereto, and may be formed in the row direction, for example. 
     In addition, the structures of the RDTI, the FDTI, the FFTI, the RFTI, and the RDTI+FDTI described above can be applied not only to the pixel separation wall  334  and the protruding portion  304  described above but also to the second protruding portion  324 , the pixel separation wall  334   a , the additional walls  308 ,  308   a ,  308   b , and  308   c  according to the respective embodiments described above. 
     Note that, in the embodiment of the present disclosure described above, a case where the present disclosure is applied to a one-layer CMOS image sensor structure has been described. However, the embodiment of the present disclosure is not limited thereto, and may be applied to other structures such as a stacked CMOS image sensor (CIS) structure. For example, as illustrated in  FIGS.  85  to  87   , the embodiments of the present disclosure may be applied to a two-layer stacked CIS, a three-layer stacked CIS, a two-stage pixel CIS, or the like. Application to the two-stage pixel CIS is an example, and application to one-stage pixel is also possible. Here, the structures of the two-layer stacked CIS, the three-layer stacked CIS, and the two-stage pixel CIS will be described in detail with reference to  FIGS.  85  to  87   . 
     (Two-Layer Stacked CIS) 
       FIG.  85    illustrates an example of a two-layer stacked structure to which the embodiment of the present disclosure is applicable.  FIG.  85    is an explanatory diagram illustrating a cross-section of a two-layer stacked structure to which the imaging device  1  according to the embodiment of the present disclosure can be applied. 
     In the structure illustrated in  FIG.  85   , the imaging device  1  is configured by electrically connecting the pixel region (pixel array unit  20 ) and the control circuit unit  25  on the first semiconductor substrate  31  side and the logic circuit (not illustrated) on the second semiconductor substrate  45  side by one through-connection conductor  84  formed on the first semiconductor substrate  31 . That is, in the example of  FIG.  85   , the first semiconductor substrate  31  and the second semiconductor substrate  45  are stacked, and these semiconductor substrates  31  and  45  are electrically connected by the through-connection conductor  84 . Specifically, a through-connection hole  85  that penetrates the first semiconductor substrate  31  from the back surface  31   b  side of the first semiconductor substrate, reaches the uppermost layer wiring  53  of the second semiconductor substrate  45 , and reaches the uppermost layer wiring  40  of the first semiconductor substrate  31  is formed. After the insulating film  63  is formed on the inner wall surface of the through-connection hole  85 , a through-connection conductor  84  that connects the wiring  40  on the pixel region and control circuit unit  25  side and the wiring  53  on the logic circuit side is embedded in the through-connection hole  85 . In  FIG.  85   , since the through-connection conductor  84  is connected to the uppermost layer wiring  40 , the wirings  40  of the respective layers are connected to each other such that the connected uppermost layer wiring  40  becomes a connection end. 
     In the structure illustrated in  FIG.  85   , a photodiode (PD) serving as a photoelectric conversion unit of each pixel is formed in the semiconductor well region  32  of the first semiconductor substrate  31 . Further, a source/drain region  33  of each pixel transistor is formed in the semiconductor well region  32 . The semiconductor well region  32  is formed by introducing p-type impurities, for example, and the source/drain region  33  is formed by introducing n-type impurities, for example. Specifically, the photodiode (PD) and the source/drain region  33  of each pixel transistor are formed by ion implantation from the substrate surface. 
     The photodiode (PD) has an n-type semiconductor region  34  and a p-type semiconductor region  35  on the substrate surface side. A gate electrode  36  is formed on the surface of the substrate constituting the pixel via a gate insulating film, and pixel transistors Tr 1  and Tr 2  are formed by the gate electrode  36  and a pair of source/drain regions  33 . For example, the pixel transistor Tr 1  adjacent to the photodiode (PD) corresponds to a transfer transistor, and its source/drain region corresponds to a floating diffusion (FD). Unit pixels are separated by the element separation region  38 . 
     On the first semiconductor substrate  31 , MOS transistors Tr 3 , Tr 4  constituting a control circuit are formed. The MOS transistors Tr 3  and Tr 4  are formed by an n-type source/drain region  33  and a gate electrode  36  formed via a gate insulating film. Furthermore, a first interlayer insulating film  39  is formed on the surface of the first semiconductor substrate  31 , and a connection conductor  44  connected to a required transistor is formed in the interlayer insulating film  39 . In addition, the multilayer wiring layer  41  is formed of the plurality of layers of wiring  40  via the interlayer insulating film  39  so as to be connected to each connection conductor  44 . 
     In addition, as illustrated in  FIG.  85   , a plurality of MOS transistors constituting a logic circuit separated by the element separation region  50  is formed in the p-type semiconductor well region  46  on the front surface side of the second semiconductor substrate  45 . Each of the MOS transistors Tr 6 , Tr 7 , and Tr 8  has a pair of n-type source/drain regions  47  and a gate electrode  48  formed via a gate insulating film. Furthermore, a first interlayer insulating film  49  is formed on the surface of the second semiconductor substrate  45 , and a connection conductor  54  connected to a required transistor is formed in the interlayer insulating film  49 . Furthermore, a connection conductor  51  penetrating from the surface of the interlayer insulating film  49  to a desired depth in the second semiconductor substrate  45  is provided. Furthermore, an insulating film  52  for insulating the connection conductor  51  and the semiconductor substrate  45  is provided. 
     In addition, the multilayer wiring layer  55  is formed by providing a plurality of layers of wiring  53  in the interlayer insulating film  49  so as to be connected to each of the connection conductors  54  and the connection conductor  51  for electrode extraction. 
     Furthermore, as illustrated in  FIG.  85   , the first semiconductor substrate  31  and the second semiconductor substrate  45  are bonded to each other such that the multilayer wiring layers  41  and  55  face each other. 
     In addition, as illustrated in  FIG.  85   , for example, on-chip color filters  74  of red (R), green (G), and blue (B) are provided on the flattening film  73  corresponding to each pixel, and an on-chip microlens  75  is provided thereon. 
     On the other hand, on the second semiconductor substrate  45  side, an opening  77  corresponding to the connection conductor  51  is provided, and a spherical electrode bump  78  electrically connected to the connection conductor  51  through the opening  77  is provided. 
     (Three-Layer Stacked CIS) 
       FIG.  86    illustrates an example of a three-layer stacked structure to which the embodiment of the present disclosure is applicable.  FIG.  86    is an explanatory diagram illustrating a cross-section of a three-layer stacked structure to which the imaging device  1  according to the embodiment of the present disclosure can be applied. 
     In the structure illustrated in  FIG.  86   , the imaging device  1  has a three-layer stacked structure in which a first semiconductor substrate  211 , a second semiconductor substrate  212 , and a third semiconductor substrate  213  are stacked. Specifically, in the structure illustrated in  FIG.  86   , for example, in addition to the first semiconductor substrate  211  on which a sensor circuit is formed and the second semiconductor substrate  212  on which a logic circuit is formed, the third semiconductor substrate  213  on which a memory circuit is formed is included. Note that the logic circuit and the memory circuit are configured to operate together with input and output of signals to and from the outside. 
     As illustrated in  FIG.  86   , a photodiode (PD)  234  serving as a photoelectric conversion unit of a pixel is formed in the first semiconductor substrate  211 , and a source/drain region of each pixel transistor is formed in the semiconductor well region. Furthermore, a gate electrode is formed on the substrate surface of the first semiconductor substrate  211  via a gate insulating film, and a pixel transistor Tr 1  and a pixel transistor Tr 2  are provided by source/drain regions paired with the gate electrode. Specifically, the pixel transistor Tr 1  adjacent to the photodiode (PD)  234  corresponds to a transfer transistor, and its source/drain region corresponds to a floating diffusion (FD). Furthermore, an interlayer insulating film (not illustrated) is provided on the first semiconductor substrate  211 , and a connection conductor  244  connected to the pixel transistors Tr 1  and Tr 2  is provided in the interlayer insulating film. 
     Furthermore, the first semiconductor substrate  211  is provided with a contact  265  used for electrical connection with the second semiconductor substrate  212 . The contact  265  is connected to a contact  311  of the second semiconductor substrate  212  to be described later, and is also connected to a pad  280   a  of the first semiconductor substrate  211 . 
     On the other hand, a logic circuit is formed on the second semiconductor substrate  212 . Specifically, the MOS transistor Tr 6 , the MOS transistor Tr 7 , and the MOS transistor Tr 8 , which are a plurality of transistors constituting a logic circuit, are formed in a p-type semiconductor well region (not illustrated) of the second semiconductor substrate  212 . Furthermore, in the second semiconductor substrate  212 , a connection conductor  254  connected to the MOS transistor Tr 6 , the MOS transistor Tr 7 , and the MOS transistor Tr 8  is formed. 
     Furthermore, a contact  311  used for electrical connection with the first semiconductor substrate  211  and the third semiconductor substrate  213  is formed on the second semiconductor substrate  212 . The contact  311  is connected to the contact  265  of the first semiconductor substrate  211  and is also connected to the pad  330   a  of the third semiconductor substrate  213 . 
     Further, a memory circuit is formed on the third semiconductor substrate  213 . Specifically, the MOS transistor Tr 11 , the MOS transistor Tr 12 , and the MOS transistor Tr 13 , which are a plurality of transistors constituting a memory circuit, are formed in a p-type semiconductor well region (not illustrated) of the third semiconductor substrate  213 . 
     Furthermore, in the third semiconductor substrate  213 , a connection conductor  344  connected to the MOS transistor Tr 11 , the MOS transistor Tr 12 , and the MOS transistor Tr 13  is formed. 
     (Two-Stage Pixel CIS) 
       FIG.  87    illustrates an example of a two-stage pixel structure to which the embodiment of the present disclosure is applicable.  FIG.  87    is an explanatory diagram illustrating a cross-section of a two-stage pixel structure to which the imaging device  1  according to the embodiment of the present disclosure can be applied. 
     In the structure illustrated in  FIG.  87   , a first substrate  80  is configured by stacking an insulating layer  86  on a semiconductor substrate  11 . The first substrate  80  includes an insulating layer  86  as a part of the interlayer insulating film  87 . The insulating layer  86  is provided in a gap between the semiconductor substrate  11  and a semiconductor substrate  21 A described later. The first substrate  80  includes a photodiode PD ( 83 ), a transfer transistor TR, and a floating diffusion FD. The first substrate  80  has a configuration in which the transfer transistor TR and the floating diffusion FD are provided in a portion on the front surface side (side opposite to light incident surface side, second substrate  20 A side) of the semiconductor substrate  11 . 
     In the structure illustrated in  FIG.  87   , the transfer transistor TR has a planar transfer gate TG. However, the present invention is not limited to such a configuration, and the transfer gate TG may be a vertical transfer gate penetrating the well layer  42 . 
     The second substrate  20 A is formed by stacking an insulating layer  88  on a semiconductor substrate  21 A. The second substrate  20 A includes an insulating layer  88  as a part of the interlayer insulating film  87 . The insulating layer  88  is provided in a gap between the semiconductor substrate  21 A and the semiconductor substrate  81 . The second substrate  20 A includes a readout circuit  22 A. Specifically, the second substrate  20 A has a configuration in which the readout circuit  22 A is provided in a portion on the front surface side (third substrate  30  side) of the semiconductor substrate  21 A. The second substrate  20 A is bonded to the first substrate  80  with the back surface of the semiconductor substrate  21 A facing the front surface side of the semiconductor substrate  11 . That is, the second substrate  20 A is bonded to the first substrate  80  in a face-to-back manner. The second substrate  20 A further includes an insulating layer  89  penetrating the semiconductor substrate  21 A in the same layer as the semiconductor substrate  21 A. The second substrate  20 A includes an insulating layer  89  as a part of the interlayer insulating film  87 . 
     The stacked structure including the first substrate  80  and the second substrate  20 A has an interlayer insulating film  87  and a through-wiring  90  provided in the interlayer insulating film  87 . Specifically, the through-wiring  90  is electrically connected to the floating diffusion FD and a connection wiring  91  to be described later. The second substrate  20 A further includes, for example, a wiring layer  56  on the insulating layer  88 . 
     The wiring layer  56  further includes, for example, a plurality of pad electrodes  58  in the insulating layer  57 . Each pad electrode  58  is made of metal such as copper (Cu) or aluminum (Al), for example. Each pad electrode  58  is exposed on the surface of the wiring layer  56 . Each pad electrode  58  is used for electrical connection between the second substrate  20 A and the third substrate  30  and bonding between the second substrate  20 A and the third substrate  30 . 
     The third substrate  30  is formed by stacking an interlayer insulating film  61  on a semiconductor substrate  81 , for example. As will be described later, the third substrate  30  is bonded to the second substrate  20 A on the front surface side. The third substrate  30  has a configuration in which the logic circuit  82  is provided in a portion on the front surface side of the semiconductor substrate  81 . The third substrate  30  further includes, for example, a wiring layer  62  on the interlayer insulating film  61 . The wiring layer  62  includes, for example, an insulating layer  92  and a plurality of pad electrodes  64  provided in the insulating layer  92 . The plurality of pad electrodes  64  is electrically connected to the logic circuit  82 . Each pad electrode  64  is made of, for example, Cu (copper). Each pad electrode  64  is exposed on the surface of the wiring layer  62 . Each pad electrode  64  is used for electrical connection between the second substrate  20 A and the third substrate  30  and bonding between the second substrate  20 A and the third substrate  30 . 
     Note that, in a case where the technology of the present disclosure is applied to a single-stage pixel (normal CIS), as an example, as illustrated in  FIG.  88   , transistors (for example, CMOS transistors) other than the transfer gates  400   a  and  400   b  can be arranged in the two pixel transistor regions Ra and Rb in the imaging element  100 . The floating diffusion FD is provided at a position adjacent to the transfer gates  400   a  and  400   b . In the example of  FIG.  88   , the pixel transistor regions Ra and Rb are formed so as to sandwich the pixel region Rc including the pixels  300   a  and  300   b . The selection transistor SEL and the amplification transistor AMP are arranged in the pixel transistor region Ra on the left side in  FIG.  88   , and the reset transistor RST is arranged in the pixel transistor region Rb on the right side in  FIG.  88   . The pixel sharing system, the arrangement of the transistors, the embedded structure of the photodiode, and the like according to  FIG.  88    are merely examples, and the present invention is not limited thereto. 
     Furthermore, the imaging element  100  illustrated in  FIG.  88    may be arranged as illustrated in  FIG.  89    (repeated arrangement), and one selection transistor SEL, one amplification transistor AMP, one reset transistor RST, and one FD transfer transistor FDG may be arranged in each of the pixel transistor regions Ra and Rb of each imaging element  100 . The FD transfer transistor FDG is used to switch the conversion efficiency. The arrangement of each transistor may be equal or unequal to each of the pixel transistor regions Ra and Rb. For example, a plurality of amplification transistors AMP may be arranged for four imaging elements  100 , and the amplification transistors AMP can be arranged in parallel. 
     17. Application Example to Camera 
     The technology (present technology) according to the present disclosure can be further applied to various products. For example, the technology according to the present disclosure may be applied to a camera or the like. Therefore, a configuration example of a camera  700  as an electronic device to which the present technology is applied will be described with reference to  FIG.  90   .  FIG.  90    is an explanatory diagram illustrating an example of a schematic functional configuration of a camera  700  to which the technology according to the present disclosure (the present technology) can be applied. 
     As illustrated in  FIG.  90   , the camera  700  includes an imaging device  702 , an optical lens  710 , a shutter mechanism  712 , a drive circuit unit  714 , and a signal processing circuit unit  716 . The optical lens  710  forms an image of image light (incident light) from a subject on an imaging surface of the imaging device  702 . As a result, signal charges are accumulated in the imaging element  100  of the imaging device  702  for a certain period of time. The shutter mechanism  712  opens and closes to control a light irradiation period and a light shielding period for the imaging device  702 . The drive circuit unit  714  supplies a drive signal for controlling a signal transfer operation of the imaging device  702 , a shutter operation of the shutter mechanism  712 , and the like to these. That is, the imaging device  702  performs signal transfer on the basis of the drive signal (timing signal) supplied from the drive circuit unit  714 . The signal processing circuit unit  716  performs various types of signal processing. For example, the signal processing circuit unit  716  outputs the video signal subjected to the signal processing to, for example, a storage medium (not illustrated) such as a memory, or to a display unit (not illustrated). 
     18. Application Example to Smartphone 
     The technology (present technology) according to the present disclosure can be further applied to various products. For example, the technology according to the present disclosure may be applied to a smartphone or the like. Therefore, a configuration example of a smartphone  900  as an electronic device to which the present technology is applied will be described with reference to  FIG.  91   .  FIG.  91    is a block diagram illustrating an example of a schematic functional configuration of a smartphone  900  to which the technology according to the present disclosure (the present technology) can be applied. 
     As illustrated in  FIG.  91   , the smartphone  900  includes a central processing unit (CPU)  901 , a read only memory (ROM)  902 , and a random access memory (RAM)  903 . In addition, the smartphone  900  includes a storage device  904 , a communication module  905 , and a sensor module  907 . Furthermore, the smartphone  900  includes an imaging device  909 , a display device  910 , a speaker  911 , a microphone  912 , an input device  913 , and a bus  914 . Furthermore, the smartphone  900  may include a processing circuit such as a digital signal processor (DSP) instead of or in addition to the CPU  901 . 
     The CPU  901  functions as an arithmetic processing device and a control device, and controls the overall operation in the smartphone  900  or a part thereof according to various programs recorded in the ROM  902 , the RAM  903 , the storage device  904 , or the like. The ROM  902  stores programs, operation parameters, and the like used by the CPU  901 . The RAM  903  primarily stores programs used in the execution of the CPU  901 , parameters that appropriately change in the execution, and the like. The CPU  901 , the ROM  902 , and the RAM  903  are connected to one another by a bus  914 . In addition, the storage device  904  is a device for data storage configured as an example of a storage unit of the smartphone  900 . The storage device  904  includes, for example, a magnetic storage device such as a hard disk drive (HDD), a semiconductor storage device, an optical storage device, and the like. The storage device  904  stores programs and various data executed by the CPU  901 , various data acquired from the outside, and the like. 
     The communication module  905  is a communication interface including, for example, a communication device for connecting to the communication network  906 . The communication module  905  can be, for example, a communication card for wired or wireless local area network (LAN), Bluetooth (registered trademark), wireless USB (WUSB), or the like. Furthermore, the communication module  905  may be a router for optical communication, a router for asymmetric digital subscriber line (ADSL), a modem for various types of communication, or the like. The communication module  905  transmits and receives signals and the like to and from the Internet and other communication devices using a predetermined protocol such as Transmission Control Protocol (TCP)/Internet Protocol (IP). Furthermore, the communication network  906  connected to the communication module  905  is a network connected in a wired or wireless manner, and is, for example, the Internet, a home LAN, infrared communication, satellite communication, or the like. 
     The sensor module  907  includes, for example, various sensors such as a motion sensor (for example, an acceleration sensor, a gyro sensor, a geomagnetic sensor, or the like), a biological information sensor (for example, a pulse sensor, a blood pressure sensor, a fingerprint sensor, and the like), or a position sensor (for example, a global navigation satellite system (GNSS) receiver or the like). 
     The imaging device  909  is provided on the front surface of the smartphone  900 , and can image an object or the like positioned on the back side or the front side of the smartphone  900 . Specifically, the imaging device  909  can include an imaging element (not illustrated) such as a complementary MOS (CMOS) image sensor to which the technology (present technology) according to the present disclosure can be applied, and a signal processing circuit (not illustrated) that performs imaging signal processing on a signal photoelectrically converted by the imaging element. Furthermore, the imaging device  909  can further include an optical system mechanism (not illustrated) including an imaging lens, a zoom lens, a focus lens, and the like, and a drive system mechanism (not illustrated) that controls the operation of the optical system mechanism. Then, the imaging element collects incident light from an object as an optical image, and the signal processing circuit photoelectrically converts the formed optical image in units of pixels, reads a signal of each pixel as an imaging signal, and performs image processing to acquire a captured image. 
     The display device  910  is provided on the surface of the smartphone  900 , and can be, for example, a display device such as a liquid crystal display (LCD) or an organic electro luminescence (EL) display. The display device  910  can display an operation screen, a captured image acquired by the above-described imaging device  909 , and the like. 
     The speaker  911  can output, for example, a call voice, a voice accompanying the video content displayed by the display device  910  described above, and the like to the user. 
     The microphone  912  can collect, for example, a call voice of the user, a voice including a command to activate a function of the smartphone  900 , and a voice in a surrounding environment of the smartphone  900 . 
     The input device  913  is a device operated by the user, such as a button, a keyboard, a touch panel, or a mouse. The input device  913  includes an input control circuit that generates an input signal on the basis of information input by the user and outputs the input signal to the CPU  901 . By operating the input device  913 , the user can input various data to the smartphone  900  and give an instruction on a processing operation. 
     The configuration example of the smartphone  900  has been described above. Each of the above-described components may be configured using a general-purpose member, or may be configured by hardware specialized for the function of each component. Such a configuration can be appropriately changed according to the technical level at the time of implementation. 
     19. Application Example to Endoscopic Surgery System 
     The technology (present technology) according to the present disclosure can be further applied to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgical system. 
       FIG.  92    is a diagram illustrating an example of a schematic configuration of an endoscopic surgery system to which the technology according to the present disclosure (the present technology) can be applied. 
       FIG.  92    illustrates a state in which an operator (doctor)  11131  is performing surgery on a patient  11132  on a patient bed  11133  using an endoscopic surgery system  11000 . As depicted, the endoscopic surgery system  11000  includes an endoscope  11100 , other surgical tools  11110  such as a pneumoperitoneum tube  11111  and an energy device  11112 , a supporting arm device  11120  which supports the endoscope  11100  thereon, and a cart  11200  on which various device for endoscopic surgery are mounted. 
     The endoscope  11100  includes a lens barrel  11101  having a region of a predetermined length from a distal end thereof to be inserted into a body cavity of the patient  11132 , and a camera head  11102  connected to a proximal end of the lens barrel  11101 . In the example depicted, the endoscope  11100  is depicted which includes as a rigid endoscope having the lens barrel  11101  of the hard type. However, the endoscope  11100  may otherwise be included as a flexible endoscope having the lens barrel of the flexible type. 
     The lens barrel  11101  has, at a distal end thereof, an opening in which an objective lens is fitted. A light source device  11203  is connected to the endoscope  11100  such that light generated by the light source device  11203  is introduced to a distal end of the lens barrel by a light guide extending in the inside of the lens barrel  11101  and is irradiated toward an observation target in a body cavity of the patient  11132  through the objective lens. It is to be noted that the endoscope  11100  may be a forward-viewing endoscope or may be an oblique-viewing endoscope or a side-viewing endoscope. 
     An optical system and an imaging element are provided in the inside of the camera head  11102  such that reflected light (observation light) from the observation target is condensed on the imaging element by the optical system. The observation light is photoelectrically converted by the imaging element to generate an electric signal corresponding to the observation light, namely, an image signal corresponding to an observation image. The image signal is transmitted to a camera control unit (CCU)  11201  as RAW data. 
     The CCU  11201  includes a central processing unit (CPU), a graphics processing unit (GPU) or the like and integrally controls operation of the endoscope  11100  and a display device  11202 . Further, the CCU  11201  receives an image signal from the camera head  11102  and performs, for the image signal, various image processes for displaying an image based on the image signal such as, for example, a development process (demosaic process). 
     The display device  11202  displays thereon an image based on an image signal, for which the image processes have been performed by the CCU  11201 , under the control of the CCU  11201 . 
     The light source device  11203  includes a light source such as a light emitting diode (LED), for example, and supplies irradiation light for photographing a surgical site or the like to the endoscope  11100 . 
     An inputting device  11204  is an input interface for the endoscopic surgery system  11000 . A user can perform inputting of various kinds of information or instruction inputting to the endoscopic surgery system  11000  through the inputting device  11204 . For example, the user would input an instruction or a like to change an imaging condition (type of irradiation light, magnification, focal distance or the like) by the endoscope  11100 . 
     A treatment tool controlling device  11205  controls driving of the energy device  11112  for cautery or incision of a tissue, sealing of a blood vessel or the like. A pneumoperitoneum device  11206  feeds gas into a body cavity of the patient  11132  through the pneumoperitoneum tube  11111  to inflate the body cavity in order to secure the field of view of the endoscope  11100  and secure the working space for the surgeon. A recorder  11207  is a device capable of recording various kinds of information relating to surgery. A printer  11208  is a device capable of printing various kinds of information relating to surgery in various forms such as a text, an image or a graph. 
     Note that the light source device  11203  that supplies the endoscope  11100  with the irradiation light at the time of imaging the surgical site can include, for example, an LED, a laser light source, or a white light source including a combination thereof. In a case where the white light source includes a combination of RGB laser light sources, since the output intensity and the output timing of each color (each wavelength) can be controlled with high accuracy, adjustment of the white balance of the captured image can be performed in the light source device  11203 . Furthermore, in this case, by irradiating the observation target with the laser light from each of the RGB laser light sources in a time division manner and controlling the driving of the imaging element of the camera head  11102  in synchronization with the irradiation timing, it is also possible to capture an image corresponding to each of RGB in a time division manner. According to this method, a color image can be obtained even if color filters are not provided for the imaging element. 
     Further, the light source device  11203  may be controlled such that the intensity of light to be outputted is changed for each predetermined time. By controlling driving of the imaging element of the camera head  11102  in synchronism with the timing of the change of the intensity of light to acquire images time-divisionally and synthesizing the images, an image of a high dynamic range free from underexposed blocked up shadows and overexposed highlights can be created. 
     Further, the light source device  11203  may be configured to supply light of a predetermined wavelength band ready for special light observation. In special light observation, for example, by utilizing the wavelength dependency of absorption of light in a body tissue to irradiate light of a narrow band in comparison with irradiation light upon ordinary observation (namely, white light), narrow band observation (narrow band imaging) of imaging a predetermined tissue such as a blood vessel of a superficial portion of the mucous membrane or the like in a high contrast is performed. Alternatively, in special light observation, fluorescent observation for obtaining an image from fluorescent light generated by irradiation of excitation light may be performed. In fluorescent observation, it is possible to perform observation of fluorescent light from a body tissue by irradiating excitation light on the body tissue (autofluorescence observation) or to obtain a fluorescent light image by locally injecting a reagent such as indocyanine green (ICG) into a body tissue and irradiating excitation light corresponding to a fluorescent light wavelength of the reagent upon the body tissue. The light source device  11203  can be configured to supply such narrow-band light and/or excitation light suitable for special light observation as described above. 
       FIG.  93    is a block diagram illustrating an example of functional configurations of the camera head  11102  and the CCU  11201  illustrated in  FIG.  92   . 
     The camera head  11102  includes a lens unit  11401 , an imaging unit  11402 , a driving unit  11403 , a communication unit  11404  and a camera head controlling unit  11405 . The CCU  11201  includes a communication unit  11411 , an image processing unit  11412  and a control unit  11413 . The camera head  11102  and the CCU  11201  are connected for communication to each other by a transmission cable  11400 . 
     The lens unit  11401  is an optical system, provided at a connecting location to the lens barrel  11101 . Observation light taken in from a distal end of the lens barrel  11101  is guided to the camera head  11102  and introduced into the lens unit  11401 . The lens unit  11401  includes a combination of a plurality of lenses including a zoom lens and a focusing lens. 
     The imaging unit  11402  is configured of an imaging element. The number of imaging elements which is included by the imaging unit  11402  may be one (single-plate type) or a plural number (multi-plate type). Where the imaging unit  11402  is configured as that of the multi-plate type, for example, image signals corresponding to respective R, G and B are generated by the imaging elements, and the image signals may be synthesized to obtain a color image. Alternatively, the imaging unit  11402  may include a pair of imaging elements for acquiring right-eye and left-eye image signals corresponding to three-dimensional (3D) display. If 3D display is performed, then the depth of a living body tissue in a surgical region can be comprehended more accurately by the surgeon  11131 . It is to be noted that, where the imaging unit  11402  is configured as that of stereoscopic type, a plurality of systems of lens units  11401  are provided corresponding to the individual imaging elements. 
     Further, the imaging unit  11402  may not necessarily be provided on the camera head  11102 . For example, the imaging unit  11402  may be provided immediately behind the objective lens in the inside of the lens barrel  11101 . 
     The driving unit  11403  includes an actuator and moves the zoom lens and the focusing lens of the lens unit  11401  by a predetermined distance along an optical axis under the control of the camera head controlling unit  11405 . Consequently, the magnification and the focal point of a captured image by the imaging unit  11402  can be adjusted suitably. 
     The communication unit  11404  includes a communication device for transmitting and receiving various kinds of information to and from the CCU  11201 . The communication unit  11404  transmits an image signal acquired from the imaging unit  11402  as RAW data to the CCU  11201  through the transmission cable  11400 . 
     In addition, the communication unit  11404  receives a control signal for controlling driving of the camera head  11102  from the CCU  11201  and supplies the control signal to the camera head controlling unit  11405 . The control signal includes information relating to imaging conditions such as, for example, information that a frame rate of a captured image is designated, information that an exposure value upon imaging is designated and/or information that a magnification and a focal point of a captured image are designated. 
     It is to be noted that the imaging conditions such as the frame rate, exposure value, magnification or focal point may be designated by the user or may be set automatically by the control unit  11413  of the CCU  11201  on the basis of an acquired image signal. In the latter case, an auto exposure (AE) function, an auto focus (AF) function and an auto white balance (AWB) function are incorporated in the endoscope  11100 . 
     The camera head controlling unit  11405  controls driving of the camera head  11102  on the basis of a control signal from the CCU  11201  received through the communication unit  11404 . 
     The communication unit  11411  includes a communication device for transmitting and receiving various kinds of information to and from the camera head  11102 . The communication unit  11411  receives an image signal transmitted thereto from the camera head  11102  through the transmission cable  11400 . 
     Further, the communication unit  11411  transmits a control signal for controlling driving of the camera head  11102  to the camera head  11102 . The image signal and the control signal can be transmitted by electrical communication, optical communication or the like. 
     The image processing unit  11412  performs various image processes for an image signal in the form of RAW data transmitted thereto from the camera head  11102 . 
     The control unit  11413  performs various kinds of control relating to imaging of a surgical region or the like by the endoscope  11100  and display of a captured image obtained by imaging of the surgical region or the like. For example, the control unit  11413  creates a control signal for controlling driving of the camera head  11102 . 
     Further, the control unit  11413  controls, on the basis of an image signal for which image processes have been performed by the image processing unit  11412 , the display device  11202  to display a captured image in which the surgical region or the like is imaged. Thereupon, the control unit  11413  may recognize various objects in the captured image using various image recognition technologies. For example, the control unit  11413  can recognize a surgical tool such as forceps, a particular living body region, bleeding, mist when the energy device  11112  is used and so forth by detecting the shape, color and so forth of edges of objects included in a captured image. The control unit  11413  may cause, when it controls the display device  11202  to display a captured image, various kinds of surgery supporting information to be displayed in an overlapping manner with an image of the surgical region using a result of the recognition. Where surgery supporting information is displayed in an overlapping manner and presented to the surgeon  11131 , the burden on the surgeon  11131  can be reduced and the surgeon  11131  can proceed with the surgery with certainty. 
     The transmission cable  11400  which connects the camera head  11102  and the CCU  11201  to each other is an electric signal cable ready for communication of an electric signal, an optical fiber ready for optical communication or a composite cable ready for both of electrical and optical communications. 
     Here, while, in the example depicted, communication is performed by wired communication using the transmission cable  11400 , the communication between the camera head  11102  and the CCU  11201  may be performed by wireless communication. 
     An example of the endoscopic surgery system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to, for example, the endoscope  11100 , (the imaging unit  11402  of) the camera head  11102 , (the image processing unit  11412  of) the CCU  11201 , and the like) among the configurations described above. 
     Note that, here, the endoscopic surgery system has been described as an example, but the technology according to the present disclosure may be applied to, for example, a microscopic surgery system or the like. 
     20. Application Example to Mobile Body 
     The technology (present technology) according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of mobile body such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility, an airplane, a drone, a ship, and a robot. 
       FIG.  94    is a block diagram illustrating a schematic configuration example of a vehicle control system which is an example of a mobile body control system to which the technology according to the present disclosure can be applied. 
     The vehicle control system  12000  includes a plurality of electronic control units connected to each other via a communication network  12001 . In the example illustrated in  FIG.  94   , the vehicle control system  12000  includes a driving system control unit  12010 , a body system control unit  12020 , a vehicle exterior information detection unit  12030 , a vehicle interior information detection unit  12040 , and an integrated control unit  12050 . Furthermore, as a functional configuration of the integrated control unit  12050 , a microcomputer  12051 , an audio image output unit  12052 , and an in-vehicle network interface (I/F)  12053  are illustrated. 
     The driving system control unit  12010  controls the operation of devices related to the driving system of the vehicle in accordance with various kinds of programs. For example, the driving system control unit  12010  functions as a control device for a driving force generating device for generating the driving force of the vehicle, such as an internal combustion engine, a driving motor, or the like, a driving force transmitting mechanism for transmitting the driving force to wheels, a steering mechanism for adjusting the steering angle of the vehicle, a braking device for generating the braking force of the vehicle, and the like. 
     The body system control unit  12020  controls the operation of various kinds of devices provided to a vehicle body in accordance with various kinds of programs. For example, the body system control unit  12020  functions as a control device for a keyless entry system, a smart key system, a power window device, or various kinds of lamps such as a headlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, or the like. In this case, radio waves transmitted from a mobile device as an alternative to a key or signals of various kinds of switches can be input to the body system control unit  12020 . The body system control unit  12020  receives these input radio waves or signals, and controls a door lock device, the power window device, the lamps, or the like of the vehicle. 
     The vehicle exterior information detection unit  12030  detects information about the outside of the vehicle including the vehicle control system  12000 . For example, the vehicle exterior information detection unit  12030  is connected with an imaging unit  12031 . The vehicle exterior information detection unit  12030  makes the imaging unit  12031  image an image of the outside of the vehicle, and receives the imaged image. On the basis of the received image, the vehicle exterior information detection unit  12030  may perform processing of detecting an object such as a human, a vehicle, an obstacle, a sign, a character on a road surface, or the like, or processing of detecting a distance thereto. 
     The imaging unit  12031  is an optical sensor that receives light, and which outputs an electric signal corresponding to a received light amount of the light. The imaging unit  12031  can output the electric signal as an image, or can output the electric signal as information about a measured distance. In addition, the light received by the imaging unit  12031  may be visible light, or may be invisible light such as infrared rays or the like. 
     The vehicle interior information detection unit  12040  detects information about the inside of the vehicle. The vehicle interior information detection unit  12040  is, for example, connected with a driver state detection unit  12041  that detects the state of a driver. The driver state detection unit  12041 , for example, includes a camera that images the driver. On the basis of detection information input from the driver state detection unit  12041 , the vehicle interior information detection unit  12040  may calculate a degree of fatigue of the driver or a degree of concentration of the driver, or may determine whether the driver is dozing. 
     The microcomputer  12051  can calculate a control target value for the driving force generating device, the steering mechanism, or the braking device on the basis of the information about the inside or outside of the vehicle which information is obtained by the vehicle exterior information detection unit  12030  or the vehicle interior information detection unit  12040 , and output a control command to the driving system control unit  12010 . For example, the microcomputer  12051  can perform cooperative control intended to implement functions of an advanced driver assistance system (ADAS) which functions include collision avoidance or shock mitigation for the vehicle, following driving based on a following distance, vehicle speed maintaining driving, a warning of collision of the vehicle, a warning of deviation of the vehicle from a lane, or the like. 
     In addition, the microcomputer  12051  can perform cooperative control intended for automated driving, which makes the vehicle to travel automatedly without depending on the operation of the driver, or the like, by controlling the driving force generating device, the steering mechanism, the braking device, or the like on the basis of the information about the outside or inside of the vehicle which information is obtained by the vehicle exterior information detection unit  12030  or the vehicle interior information detection unit  12040 . 
     Furthermore, the microcomputer  12051  can output a control command to the body system control unit  12020  on the basis of the vehicle exterior information acquired by the vehicle exterior information detection unit  12030 . For example, the microcomputer  12051  can perform cooperative control intended to prevent a glare by controlling the headlamp so as to change from a high beam to a low beam, for example, in accordance with the position of a preceding vehicle or an oncoming vehicle detected by the vehicle exterior information detection unit  12030 . 
     The audio image output unit  12052  transmits an output signal of at least one of a sound and an image to an output device capable of visually or auditorily notifying information to an occupant of the vehicle or the outside of the vehicle. In the example of  FIG.  94   , an audio speaker  12061 , a display unit  12062 , and an instrument panel  12063  are illustrated as the output device. The display unit  12062  may, for example, include at least one of an on-board display and a head-up display. 
       FIG.  95    is a diagram illustrating an example of an installation position of the imaging unit  12031 . 
     In  FIG.  95   , the vehicle  12100  includes imaging units  12101 ,  12102 ,  12103 ,  12104 , and  12105  as the imaging unit  12031 . 
     The imaging units  12101 ,  12102 ,  12103 ,  12104 , and  12105  are provided, for example, at positions such as a front nose, a side mirror, a rear bumper, a back door, and an upper portion of a windshield in a vehicle interior of the vehicle  12100 . The imaging unit  12101  provided to the front nose and the imaging unit  12105  provided to the upper portion of the windshield within the interior of the vehicle obtain mainly an image of the front of the vehicle  12100 . The imaging units  12102  and  12103  provided at the side mirrors mainly acquire images of the sides of the vehicle  12100 . The imaging unit  12104  provided to the rear bumper or the back door obtains mainly an image of the rear of the vehicle  12100 . The front images acquired by the imaging units  12101  and  12105  are mainly used for detecting a preceding vehicle, a pedestrian, an obstacle, a traffic light, a traffic sign, a lane, or the like. 
     Note that  FIG.  95    illustrates an example of imaging ranges of the imaging units  12101  to  12104 . An imaging range  12111  represents the imaging range of the imaging unit  12101  provided to the front nose. Imaging ranges  12112  and  12113  respectively represent the imaging ranges of the imaging units  12102  and  12103  provided to the sideview mirrors. An imaging range  12114  represents the imaging range of the imaging unit  12104  provided to the rear bumper or the back door. A bird&#39;s-eye image of the vehicle  12100  as viewed from above is obtained by superimposing image data imaged by the imaging units  12101  to  12104 , for example. 
     At least one of the imaging units  12101  to  12104  may have a function of obtaining distance information. For example, at least one of the imaging units  12101  to  12104  may be a stereo camera constituted of a plurality of imaging elements, or may be an imaging element having pixels for phase difference detection. 
     For example, the microcomputer  12051  can determine a distance to each three-dimensional object within the imaging ranges  12111  to  12114  and a temporal change in the distance (relative speed with respect to the vehicle  12100 ) on the basis of the distance information obtained from the imaging units  12101  to  12104 , and thereby extract, as a preceding vehicle, a nearest three-dimensional object in particular that is present on a traveling path of the vehicle  12100  and which travels in substantially the same direction as the vehicle  12100  at a predetermined speed (for example, equal to or more than 0 km/hour). Further, the microcomputer  12051  can set a following distance to be maintained in front of a preceding vehicle in advance, and perform automatic brake control (including following stop control), automatic acceleration control (including following start control), or the like. It is thus possible to perform cooperative control intended for automated driving that makes the vehicle travel automatedly without depending on the operation of the driver or the like. 
     For example, the microcomputer  12051  can classify three-dimensional object data on three-dimensional objects into three-dimensional object data of a two-wheeled vehicle, a standard-sized vehicle, a large-sized vehicle, a pedestrian, a utility pole, and other three-dimensional objects on the basis of the distance information obtained from the imaging units  12101  to  12104 , extract the classified three-dimensional object data, and use the extracted three-dimensional object data for automatic avoidance of an obstacle. For example, the microcomputer  12051  identifies obstacles around the vehicle  12100  as obstacles that the driver of the vehicle  12100  can recognize visually and obstacles that are difficult for the driver of the vehicle  12100  to recognize visually. Then, the microcomputer  12051  determines a collision risk indicating a risk of collision with each obstacle. In a situation in which the collision risk is equal to or higher than a set value and there is thus a possibility of collision, the microcomputer  12051  outputs a warning to the driver via the audio speaker  12061  or the display unit  12062 , and performs forced deceleration or avoidance steering via the driving system control unit  12010 . The microcomputer  12051  can thereby assist in driving to avoid collision. 
     At least one of the imaging units  12101  to  12104  may be an infrared camera that detects infrared rays. The microcomputer  12051  can, for example, recognize a pedestrian by determining whether or not there is a pedestrian in imaged images of the imaging units  12101  to  12104 . Such recognition of a pedestrian is, for example, performed by a procedure of extracting characteristic points in the imaged images of the imaging units  12101  to  12104  as infrared cameras and a procedure of determining whether or not it is the pedestrian by performing pattern matching processing on a series of characteristic points representing the contour of the object. When the microcomputer  12051  determines that there is a pedestrian in the imaged images of the imaging units  12101  to  12104 , and thus recognizes the pedestrian, the audio image output unit  12052  controls the display unit  12062  so that a square contour line for emphasis is displayed so as to be superimposed on the recognized pedestrian. The audio image output unit  12052  may also control the display unit  12062  so that an icon or the like representing the pedestrian is displayed at a desired position. 
     An example of the vehicle control system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to, for example, the imaging unit  12031  and the like among the configurations described above. 
     21. Supplement 
     Although the preferred embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field of the present disclosure can conceive various changes or modifications within the scope of the technical idea described in the claims, and it is naturally understood that these also belong to the technical scope of the present disclosure. 
     Furthermore, the effects described in the present specification are merely illustrative or exemplary, and are not restrictive. That is, the technology according to the present disclosure can exhibit other effects obvious to those skilled in the art from the description of the present specification together with or instead of the above effects. 
     Note that the present technology can also have the following configurations. 
     (1) An imaging device including: 
     a semiconductor substrate; and 
     a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which 
     each of the plurality of imaging elements includes: 
     a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; 
     an element separation wall surrounding the plurality of pixels and provided so as to penetrate the semiconductor substrate; 
     an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels; and 
     a first separation portion provided in a region surrounded by the element separation wall to separate the plurality of pixels, 
     the first separation portion is provided so as to extend in a thickness direction of the semiconductor substrate, and 
     a first diffusion region containing impurities of a second conductivity type opposite to the first conductivity type is provided in a region positioned around the first separation portion and extending in the thickness direction of the semiconductor substrate. 
     (2) The imaging device according to (1), in which 
     two first separation portions are provided, 
     the two first separation portions extend to separate the plurality of pixels and face each other when viewed from above the light receiving surface, and 
     the first diffusion region is provided in a region between the two first separation portions. 
     (3) The imaging device according to (2), in which 
     an overflow path for exchanging saturation charges between the plurality of pixels is provided in a region between the two first separation portions. 
     (4) The imaging device according to (2) or (3), in which 
     each of the two first separation portions is provided so as to penetrate the semiconductor substrate along the thickness direction of the semiconductor substrate. 
     (5) The imaging device according to (2) or (3), in which 
     each of the two first separation portions is provided to extend from the light receiving surface of the semiconductor substrate or a surface of the semiconductor substrate opposite to the light receiving surface to a middle of the semiconductor substrate along the thickness direction of the semiconductor substrate. 
     (6) The imaging device according to any one of (2) to (5), in which 
     the two first separation portions protrude from the element separation wall toward a center of the imaging element and face each other when viewed from above the light receiving surface. 
     (7) The imaging device according to any one of (2) to (6), in which 
     the two first separation portions protrude from the element separation wall along the column direction when viewed from above the light receiving surface. 
     (8) The imaging device according to (7), in which 
     the two first separation portions are provided so as to be positioned at the center of the imaging element in the row direction when viewed from above the light receiving surface. 
     (9) The imaging device according to (7), in which 
     the two first separation portions are provided at positions shifted from the center of the imaging element by a predetermined distance in the row direction when viewed from above the light receiving surface. 
     (10) The imaging device according to any one of (2) to (6), in which 
     the two first separation portions protrude from the element separation wall along the row direction when viewed from above the light receiving surface. 
     (11) The imaging device according to (10), in which 
     the two first separation portions are provided so as to be positioned at the center of the imaging element in the column direction when viewed from above the light receiving surface. 
     (12) The imaging device according to (10), in which 
     the two first separation portions are provided at positions shifted from the center of the imaging element by a predetermined distance in the column direction when viewed from above the light receiving surface. 
     (13) The imaging device according to any one of (2) to (12), in which 
     lengths of the two first separation portions are the same when viewed from above the light receiving surface. 
     (14) The imaging device according to any one of (2) to (12), in which 
     lengths of the two first separation portions are different from each other when viewed from above the light receiving surface. 
     (15) The imaging device according to any one of (2) to (14), further including: 
     two second separation portions extending along a direction different from a direction in which each of the two first separation portions extends, and facing each other when viewed from above the light receiving surface, in which 
     each of the two second separation portions is provided so as to extend in the thickness direction of the semiconductor substrate, and 
     a second diffusion region containing impurities of the second conductivity type is provided in a region between the two second separation portions. 
     (16) The imaging device according to any one of (2) to (15), including 
     one or more additional walls provided between the two first separation portions. 
     (17) The imaging device according to (16), in which 
     the additional wall is provided so as to penetrate the semiconductor substrate. 
     (18) The imaging device according to (16), in which 
     the additional wall is provided to extend from the light receiving surface to a middle of the semiconductor substrate along the thickness direction of the semiconductor substrate. 
     (19) The imaging device according to (16), in which 
     the additional wall is provided to extend from a surface of the semiconductor substrate opposite to the light receiving surface to a middle of the semiconductor substrate along the thickness direction of the semiconductor substrate. 
     (20) The imaging device according to (19), in which 
     a length of the additional wall in the thickness direction is determined according to a wavelength of incident light incident on the light receiving surface. 
     (21) The imaging device according to (19) or (20), in which 
     when viewed from above the light receiving surface, a width of a central portion of the additional wall is narrower than widths of both ends of the additional wall. 
     (22) The imaging device according to any one of (19) to (21), in which 
     a length in the thickness direction of a central portion of the additional wall is shorter than a length in the thickness direction of both ends of the additional wall. 
     (23) The imaging device according to any one of (19) to (22), in which 
     when viewed from above the light receiving surface, a width of both or one of the two first separation portions is narrower than a width of the additional wall. 
     (24) The imaging device according to any one of (19) to (23), in which 
     the two first separation portions are provided to extend from a surface of the semiconductor substrate opposite to the light receiving surface to a middle of the semiconductor substrate along the thickness direction of the semiconductor substrate. 
     (25) The imaging device according to (24), in which 
     a length of the additional wall in the thickness direction is shorter than a length of both or one of the two first separation portions in the thickness direction. 
     (26) The imaging device according to any one of (2) to (25), in which 
     the element separation wall and the two first separation portions are made of the same material. 
     (27) The imaging device according to any one of (2) to (25), in which 
     the element separation wall and the two first separation portions are made of materials different from each other. 
     (28) The imaging device according to any one of (2) to (25), in which 
     the two first protruding portions are made of titanium oxide. 
     (29) The imaging device according to any one of (2) to (28), in which 
     the plurality of imaging elements further includes a light shielding film provided along the element separation wall on the element separation wall when viewed from above the light receiving surface. 
     (30) The imaging device according to (29), in which 
     the light shielding film is provided along the two first separation portions. 
     (31) The imaging device according to any one of (2) to (30), in which 
     the first diffusion region is formed in a shape that expands from the light receiving surface toward the inside of the semiconductor substrate and narrows from the inside of the semiconductor substrate toward a surface of the semiconductor substrate opposite to the light receiving surface. 
     (32) The imaging device according to (31), in which 
     the first diffusion region includes: 
     a first region that expands from the light receiving surface toward the inside of the semiconductor substrate; and 
     a second region that narrows from the inside of the semiconductor substrate toward a surface of the semiconductor substrate opposite to the light receiving surface. 
     (33) The imaging device according to (32), in which 
     the first region and the second region are separated from each other. 
     (34) The imaging device according to (32) or (33), in which 
     lengths in the thickness direction of the first region and the second region are different. 
     (35) The imaging device according to (34), in which 
     a length of the first region in the thickness direction is longer than a length of the second region in the thickness direction. 
     (36) The imaging device according to any one of (32) to (35), in which 
     lengths of the first region and the second region in a direction orthogonal to the thickness direction are different. 
     (37) The imaging device according to (36), in which 
     a length of the first region in a direction orthogonal to the thickness direction is shorter than a length of the second region in a direction orthogonal to the thickness direction. 
     (38) The imaging device according to any one of (32) to (37), in which 
     concentrations of the impurities in the first region and the second region are different from each other. 
     (39) The imaging device according to (38), in which 
     a concentration of the impurities in the first region is lower than a concentration of the impurities in the first region. 
     (40) The imaging device according to any one of (16) to (25), in which 
     the first diffusion region is provided between each of the two first separation portions and at least one additional wall, and 
     the two first diffusion regions have different shapes and are formed in a shape that expands from the light receiving surface toward the inside of the semiconductor substrate and narrows from the inside of the semiconductor substrate toward a surface of the semiconductor substrate opposite to the light receiving surface. 
     (41) The imaging device according to any one of (1) to (40), in which 
     the first separation portion includes: 
     an extension portion connected to the element separation wall; and 
     an opposing surface facing a wall surface of the element separation wall, and 
     when viewed from above the light receiving surface, a width of the opposing surface of the first separation portion is wider than a line width of the extension portion. 
     (42) The imaging device according to (41), in which 
     the first separation portion further includes: 
     a projection portion provided at an end of the extension portion and having the opposing surface. 
     (43) The imaging device according to any one of (2) to (40), in which 
     each of the two first separation portions includes: 
     an extension portion connected to the element separation wall; and 
     opposing surfaces facing each other, and 
     when viewed from above the light receiving surface, a width of each of the opposing surfaces of each of the two first separation portions is wider than a width of each of the line widths of each of the two extension portions. 
     (44) The imaging device according to (43), in which 
     each of the two first separation portions further includes: 
     a projection portion provided at an end of the extension portion and having the opposing surface. 
     (45) The imaging device according to any one of (2) to (44), including: 
     two additional walls provided so as to face each other with the center of the imaging element interposed therebetween when viewed from above the light receiving surface. 
     (46) The imaging device according to any one of (2) to (45), in which 
     each of the two first separation portions is provided at a position separated from the element separation wall. 
     (47) The imaging device according to (46), in which 
     three or more first separation portions are provided. 
     (48) The imaging device according to (47), in which 
     four first separation portions are provided, 
     two of the first separation portions are provided in the column direction so as to face each other with the center of the imaging element interposed therebetween when viewed from above the light receiving surface, and 
     the other two first separation portions are provided in the row direction so as to face each other with the center of the imaging element interposed therebetween when viewed from above the light receiving surface. 
     (49) The imaging device according to (48), in which 
     a size of each of the two first separation portions arranged in the column direction is different from a size of each of the two first separation portions arranged in the row direction. 
     (50) The imaging device according to any one of (2) to (49), in which 
     the first diffusion region includes: 
     a first region formed by a diffusion process on individual trenches for forming the two first separation portions; and 
     a second region formed by a diffusion process on a trench for forming the element separation wall. 
     (51) An imaging device including: 
     a semiconductor substrate; and 
     a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which 
     each of the plurality of imaging elements includes: 
     a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; 
     a pixel separation wall that separates the plurality of pixels; and 
     an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels, 
     the pixel separation wall is provided so as to extend from the light receiving surface to a middle of the semiconductor substrate along a thickness direction of the semiconductor substrate, and 
     a region positioned on a side opposite to the light receiving surface with respect to the pixel separation wall in the thickness direction of the semiconductor substrate contains impurities of a second conductivity type opposite to the first conductivity type. 
     (52) An electronic device including: 
     an imaging device including: 
     a semiconductor substrate; and 
     a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which 
     each of the plurality of imaging elements includes: 
     a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; 
     an element separation wall surrounding the plurality of pixels and provided so as to penetrate the semiconductor substrate; 
     an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels; and 
     a first separation portion provided in a region surrounded by the element separation wall to separate the plurality of pixels, 
     the first separation portion is provided so as to extend in a thickness direction of the semiconductor substrate, and 
     a first diffusion region containing impurities of a second conductivity type opposite to the first conductivity type is provided in a region positioned around the first separation portion and extending in the thickness direction of the semiconductor substrate. 
     (Added) 
     (53) An electronic device including the imaging device according to any one of (1) to (51). 
     (54) The imaging device according to (26) or (27), in which the material includes at least one or more materials selected from the group consisting of silicon oxide, silicon nitride, amorphous silicon, polycrystalline silicon, titanium oxide, aluminum, and tungsten. 
     (55) An imaging device including: 
     a semiconductor substrate; and 
     a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which 
     each of the plurality of imaging elements includes: 
     a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; 
     an element separation wall surrounding the plurality of pixels and provided so as to penetrate the semiconductor substrate; and 
     an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels, 
     the element separation wall includes two first protruding portions protruding toward a center of the imaging element and facing each other when viewed from above the light receiving surface, 
     each of the two first protruding portions is provided so as to penetrate the semiconductor substrate, and 
     a first diffusion region containing impurities of a second conductivity type opposite to the first conductivity type is provided in a region between the two first protruding portions. 
     (56) An imaging device including: 
     a semiconductor substrate; and 
     a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which 
     each of the plurality of imaging elements includes: 
     a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; 
     an element separation wall surrounding the plurality of pixels and provided so as to penetrate the semiconductor substrate; and 
     an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels, 
     the element separation wall includes a first protruding portion protruding toward a center of the imaging element when viewed from above the light receiving surface, 
     the first protruding portion is provided so as to penetrate the semiconductor substrate, and 
     a first diffusion region containing impurities of a second conductivity type opposite to the first conductivity type is provided in a region between the first protruding portion and a portion of the element separation wall facing the first protruding portion. 
     (57) An imaging device including: 
     a semiconductor substrate; and 
     a plurality of imaging elements arranged in a matrix on the semiconductor substrate along a row direction and a column direction, and configured to perform photoelectric conversion on incident light, in which 
     each of the plurality of imaging elements includes: 
     a plurality of pixels provided adjacent to each other in the semiconductor substrate and containing impurities of a first conductivity type; 
     a pixel separation wall that separates the plurality of pixels; and 
     an on-chip lens provided above a light receiving surface of the semiconductor substrate so as to be shared by the plurality of pixels, and 
     the pixel separation wall contains impurities of a second conductivity type opposite to the first conductivity type. 
     REFERENCE SIGNS LIST 
     
         
           1  Imaging device 
           10  Semiconductor substrate 
           10   a  Light receiving surface 
           10   b  Front surface 
           20  Pixel array unit 
           21  Vertical drive circuit unit 
           22  Column signal processing circuit unit 
           23  Horizontal drive circuit unit 
           24  Output circuit unit 
           25  Control circuit unit 
           26  Pixel drive wiring 
           27  Vertical signal line 
           28  Horizontal signal line 
           29  Input/output terminal 
           100  Imaging element 
           200  On-chip lens 
           202  Color filter 
           204  Light shielding portion 
           300   a ,  300   b ,  300   c ,  300   d  Pixel 
           302  Photoelectric conversion unit 
           304 ,  324  Protruding portion 
           304   a  Extension portion 
           304   b  Projection portion 
           306 ,  306   a ,  306   b ,  320  Diffusion region 
           306 A First region 
           306 B Second region 
           308 ,  308   a ,  308   b ,  308   c  Additional wall 
           310  Element separation wall 
           312  Slit 
           334 ,  334   a  Pixel separation wall 
           400   a ,  400   b  Transfer gate 
         R 1  First region 
         R 2  Second region