Abstract:
An image sensor includes an imaging area that includes a plurality of pixels, with each pixel including a photosensitive charge storage region formed in a substrate. A passivation implantation region contiguously surrounds the side wall and bottom surfaces of each trench in the one or more trench isolation regions. A portion of each passivation implantation region is laterally adjacent to a respective charge storage region and resides only in an isolation gap disposed between the respective charge storage region and a respective trench isolation region and does not substantially reside under the charge storage region. Each passivation implantation region is formed by implanting one or more dopants at a low energy into the side wall and bottom surfaces of each trench after annealing the image sensor and prior to filling the trenches with an insulating material.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application 61/120,519 filed on Dec. 8, 2008, which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to image sensors for use in digital cameras and other types of image capture devices, and more particularly to shallow trench isolation regions in image sensors. 
       BACKGROUND 
       [0003]    An electronic image sensor typically captures images using an array of pixels, with each pixel including a light-sensitive photodetector for converting incident light into photo-generated charges. Shallow trench isolation (STI) regions are typically fabricated between adjacent photodetectors or pixels to isolate the photodetectors and reduce crosstalk.  FIG. 1  is a simplified cross-sectional view of a portion of a pixel in accordance with the prior art. Pixel  100  includes photodetector  102  and STI region  104 . In  FIG. 1 , photodetector  102  is configured as a pinned photodiode formed by charge storage region  106  and pinning layer  108 . In general, a photodiode will collect charge generated in, or charge that makes it to, the boundary region  110  provided by the junction  112  between the p-doped charge storage region  106  and the n-doped region (e.g., well or substrate)  114 . 
         [0004]    STI region  104  is fabricated by etching a trench into region  114  and filling the trench with an insulating material. Interface  116  between STI region  104  and region  114  is typically a source for dark current and point defects. To reduce dark current and point defects, interface  116  is conventionally passivated by implanting one or more n-type dopants into the side walls and bottom of the trench. For example, one prior art passivation technique performs two passivation implantation steps after the trench is filled with the insulating layer. The first step implants a dose of phosphorus (e.g., 3×10 12  atoms per square centimeter at 250 kilo-electron volts (keV)) into the side walls and bottom of the trench, and the second step implants at a relatively high energy (e.g., 400 keV) a dose of phosphorus (e.g., 1.5×10 13  atoms per square centimeter) into the side walls and bottom of the trench. 
         [0005]    Unfortunately, the implanted phosphorus dopants of the isolation regions, which may or may not include STI region  104 , spread laterally out into region  114  and under photodetector  102  during implantation and subsequent processing of image sensor  100 . The lateral spreading of the dopants can adversely affect the collection volume of photodetector  102 .  FIG. 2  is a two-dimensional cross-sectional view illustrating doping contours of a photodetector between two implanted isolation regions in accordance with the prior art. The isolation regions are typically disposed on either side of photodetector  102  in a cross-section coming out of the page of  FIG. 1 . Contour lines  200  depict the spreading of dopants from the STI regions adjacent to charge storage region  106 . As can be seen, the dopants spread laterally from the isolation regions and merge under charge storage region  106 . 
         [0006]      FIG. 3  is a graphical view of exemplary junction and depletion edges for charge storage region  106  in  FIG. 1 . Junction  112  is formed between the edge of charge storage region  106  and region  114 . Depletion edge  300  represents the edge of depletion region  110 . The spreading of the dopants in the isolation regions reduce the size of charge storage region  106  and produce a shallow depletion region  110 . The reduced size of depletion region  110  also reduces the quantum efficiency of the image sensor at longer wavelengths. 
       SUMMARY 
       [0007]    An image sensor includes an imaging area that includes a plurality of pixels, with each pixel including a photosensitive charge storage region formed in a substrate. One or more shallow trench isolation (STI) regions are also formed in the substrate. The STI regions can be formed between pixels, between groups of two or more pixels, or outside the imaging area to isolate the pixels from other electronic components in the image sensor. A passivation implantation region contiguously surrounds the side wall and bottom surfaces of each trench in the one or more STI regions. A portion of each passivation implantation region is laterally adjacent to a respective charge storage region and resides in an isolation gap disposed between the respective charge storage region and a respective trench isolation region and in between the photodetectors in the other direction. 
         [0008]    The one or more STI regions are fabricated by depositing and patterning a photoresist layer on the image sensor to form openings where one or more trenches are to be formed. The trench or trenches are formed in the substrate and the image sensor is annealed. One or more dopants are then implanted at a low energy into the side wall and bottom surfaces of each trench to form a passivation implantation region that contiguously surrounds the side wall and bottom surfaces of each trench. In image sensors that include STI regions, the passivation implantation region is also created in between photodetectors. A liner layer of oxide can be formed over the side wall and bottom surfaces of each trench either prior to, or after, implanting the dopant or dopants at a low energy into the side wall and bottom surfaces of each trench. The photoresist layer is then removed and the trench or trenches filled with an insulating material. After the trenches are filled with an insulating material, another layer of photoresist can be deposited on the image sensor and patterned to cover the sites where the photodetectors will be formed. One or more dopants can then be implanted into the STI regions, isolation regions, or FET regions in the pixels. 
       ADVANTAGEOUS EFFECT OF THE INVENTION 
       [0009]    The present invention increases the depletion region of a photodetector, thereby improving the collection efficiency of the photodetector. Therefore, the present invention also increases the quantum efficiency of the pixel and reduces pixel-to-pixel crosstalk between adjacent pixels. And finally, the present invention passivates the STI interface to reduce dark current generation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments of the invention are better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other. 
           [0011]      FIG. 1  is a simplified cross-sectional view of a portion of a pixel in accordance with the prior art; 
           [0012]      FIG. 2  is a two-dimensional cross-sectional view illustrating doping contours of a photodetector between two implanted isolation regions in accordance with the prior art; 
           [0013]      FIG. 3  is a graphical view of exemplary junction and depletion edges for charge storage region  110  in  FIG. 1 ; 
           [0014]      FIG. 4  is a simplified block diagram of an image capture device in an embodiment in accordance with the invention; 
           [0015]      FIG. 5  is a simplified block diagram of image sensor  406  shown in  FIG. 4  in an embodiment in accordance with the invention; 
           [0016]      FIG. 6  is a cross-sectional view of a first pixel structure in an embodiment in accordance with the invention; 
           [0017]      FIGS.7(A)-7(G)  are cross-sectional views of a portion of a pixel that are used to illustrate a method for fabricating shallow trench isolation regions in an embodiment in accordance with the invention; 
           [0018]      FIG. 8  is a two-dimensional cross-sectional view illustrating a doping contour of the first pixel structure shown in  FIG. 6 ; 
           [0019]      FIG. 9  is a graphical view of exemplary junction and depletion edges for charge storage region  802  in  FIG. 8 ; 
           [0020]      FIG. 10  is a one-dimensional doping profile of STI region  722  in  FIG. 7 ; 
           [0021]      FIG. 11  is a cross-sectional view of a second pixel structure in an embodiment in accordance with the invention; and 
           [0022]      FIG. 12  is a two-dimensional cross-sectional view illustrating a doping contour of the second pixel structure shown in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Throughout the specification and claims the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” The term “connected” means either a direct electrical connection between the items connected or an indirect connection through one or more passive or active intermediary devices. The term “circuit” means either a single component or a multiplicity of components, either active or passive, that are connected together to provide a desired function. The term “signal” means at least one current, voltage, or data signal. 
         [0024]    Additionally, directional terms such as “on”, “over”, “top”, “bottom”, are used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration only and is in no way limiting. When used in conjunction with layers of an image sensor wafer or corresponding image sensor, the directional terminology is intended to be construed broadly, and therefore should not be interpreted to preclude the presence of one or more intervening layers or other intervening image sensor features or elements. Thus, a given layer that is described herein as being formed on or formed over another layer may be separated from the latter layer by one or more additional layers. 
         [0025]    And finally, the terms “wafer” and “substrate” are to be understood as a semiconductor-based material including, but not limited to, silicon, silicon-on-insulator (SOI) technology, doped and undoped semiconductors, epitaxial layers or well regions formed on a semiconductor substrate, and other semiconductor structures. 
         [0026]    Referring to the drawings, like numbers indicate like parts throughout the views. 
         [0027]      FIG. 4  is a simplified block diagram of an image capture device in an embodiment in accordance with the invention. Image capture device  400  is implemented as a digital camera in  FIG. 4 . Those skilled in the art will recognize that a digital camera is only one example of an image capture device that can utilize an image sensor incorporating the present invention. Other types of image capture devices, such as, for example, cell phone cameras and digital video camcorders, can be used with the present invention. 
         [0028]    In digital camera  400 , light  402  from a subject scene is input to an imaging stage  404 . Imaging stage  404  can include conventional elements such as a lens, a neutral density filter, an iris and a shutter. Light  402  is focused by imaging stage  404  to form an image on image sensor  406 . Image sensor  406  captures one or more images by converting the incident light into electrical signals. Digital camera  400  further includes processor  408 , memory  410 , display  412 , and one or more additional input/output (I/O) elements  414 . Although shown as separate elements in the embodiment of  FIG. 4 , imaging stage  404  may be integrated with image sensor  406 , and possibly one or more additional elements of digital camera  400 , to form a compact camera module. 
         [0029]    Processor  408  may be implemented, for example, as a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), or other processing device, or combinations of multiple such devices. Various elements of imaging stage  404  and image sensor  406  may be controlled by timing signals or other signals supplied from processor  408 . 
         [0030]    Memory  410  may be configured as any type of memory, such as, for example, random access memory (RAM), read-only memory (ROM), Flash memory, disk-based memory, removable memory, or other types of storage elements, in any combination. A given image captured by image sensor  406  may be stored by processor  408  in memory  410  and presented on display  412 . Display  412  is typically an active matrix color liquid crystal display (LCD), although other types of displays may be used. The additional  110  elements  414  may include, for example, various on-screen controls, buttons or other user interfaces, network interfaces, or memory card interfaces. 
         [0031]    It is to be appreciated that the digital camera shown in  FIG. 4  may comprise additional or alternative elements of a type known to those skilled in the art. Elements not specifically shown or described herein may be selected from those known in the art. As noted previously, the present invention may be implemented in a wide variety of image capture devices. Also, certain aspects of the embodiments described herein may be implemented at least in part in the form of software executed by one or more processing elements of an image capture device. Such software can be implemented in a straightforward manner given the teachings provided herein, as will be appreciated by those skilled in the art. 
         [0032]    Referring now to  FIG. 5 , there is shown a simplified block diagram of image sensor  406  shown in  FIG. 4  in an embodiment in accordance with the invention. Image sensor  406  typically includes an array of pixels  500  that form an imaging area  502 . Image sensor  406  further includes column decoder  504 , row decoder  506 , digital logic  508 , and analog or digital output circuits  510 . Image sensor  406  is implemented as a back or front-illuminated Complementary Metal Oxide Semiconductor (CMOS) image sensor in an embodiment in accordance with the invention. Thus, column decoder  504 , row decoder  506 , digital logic  508 , and analog or digital output circuits  510  are implemented as standard CMOS electronic circuits that are electrically connected to imaging area  502 . 
         [0033]    Functionality associated with the sampling and readout of imaging area  502  and the processing of corresponding image data may be implemented at least in part in the form of software that is stored in memory  410  and executed by processor  408  (see  FIG. 4 ). Portions of the sampling and readout circuitry may be arranged external to image sensor  406 , or formed integrally with imaging area  502 , for example, on a common integrated circuit with photodetectors and other elements of the imaging area. Those skilled in the art will recognize that other peripheral circuitry configurations or architectures can be implemented in other embodiments in accordance with the invention. 
         [0034]      FIG. 6  is a cross-sectional view of a first pixel structure in an embodiment in accordance with the invention. Pixel  500  is implemented as a p-type metal-oxide-semiconductor (pMOS) pixel in the embodiment of  FIG. 6 . Other embodiments in accordance with the invention can implement pixel  500  as an n-type metal-oxide-semiconductor (nMOS) pixel with appropriate reverse conductivity types as recognized by one skilled in the art. 
         [0035]    Pixel  500  includes photodetector  602  that collects and stores charge that is generated in response to light striking photodetector  602 . Transfer gate  604  is used to transfer the integrated charge in photodetector  602  to charge-to-voltage converter  606 . Converter  606  converts the charge into a voltage signal. Source-follower transistor  608  buffers the voltage signal stored in charge-to-voltage converter  606 . Reset transistor  606 ,  610 ,  612  is used to reset charge-to-voltage converter  606  to a known potential prior to pixel readout. And power supply voltage (VSS)  614  is used to supply power to source follower transistor  608  and drain off signal charge from charge-to-voltage converter  606  during a reset operation. 
         [0036]    Photodetector  602  is implemented as a pinned photodiode consisting of n+ pinning layer  616  and p-type charge storage region  618  formed within n-type well  620 . Well  620  is formed within p-type epitaxial layer  622 . Epitaxial layer  622  is disposed on p-type substrate  624 . 
         [0037]    Shallow trench isolation (STI) regions  626  are formed between the pixels, or between groups of two or more pixels, to isolate the pixels or groups of pixels from one another. Interface  628  resides between STI region  626  and pinning layer  616  and well  620  in the embodiment shown in  FIG. 6 . In another embodiment in accordance with the invention, where photodetector  602  is configured as an unpinned photodetector, interface  628  resides between STI region  626  and well  620 . And finally, in yet another embodiment in accordance with the invention, interface  628  is created between STI region  626  and epitaxial layer  622  or some other type of substrate. 
         [0038]    Referring now to  FIGS. 7(A)-7(G) , there are shown cross-sectional views of a portion of a pixel that are used to illustrate a method for fabricating shallow trench isolation regions in an embodiment in accordance with the invention.  FIG. 7(A)  shows the portion of the pixel after a number of initial CMOS fabrication steps have been completed. The pixel at this stage includes an insulating layer  700  formed over substrate  702 . Layer  704  is formed over insulating layer  700 . Insulating layer  700  and layer  704  are configured as layers of silicon dioxide and silicon nitride, respectively, in an embodiment in accordance with the invention. 
         [0039]    A photoresist layer  706  is then deposited and patterned over the image sensor to form openings  708  where STI regions are to be formed (see  FIG. 7(B) ). Box  710  represents a site where a photodetector will eventually be formed. Next, as shown in  FIG. 7(C) , layers  704  and  700  are etched to match the pattern in photoresist  706 . Trenches  712  are then formed by etching the exposed substrate  702  in openings  708  (see  FIG. 7(D) ). Trenches  712  are etched such that isolation gaps  714  (indicated by dashed circles) are created between trenches  712  and site  710 . Isolation gaps  714  are immediately adjacent trenches  712  and do not extend under the charge storage region of the yet to be formed photodetector. Next, photoresist  706  is removed, as shown in  FIG. 7(E) . A liner layer  716  of oxide is then thermally grown on the side wall and bottom surfaces of trenches  712  (see  FIG. 7(F) ) and an anneal process performed on the image sensor. The anneal process reduces any detrimental effects caused by etching epitaxial layer  702  to form trenches  712  and by the formation of the insulating oxide layer  716 . The anneal smoothes out the surfaces of the side walls and bottoms of trenches  712 , relieves stress, and reduces dangling bonds and surface states along the side walls and bottoms of trenches  712 . 
         [0040]    A low energy passivation implantation at different angles (illustrated by the arrows  718 ) is then performed to implant dopants into the side wall and bottom surfaces of trenches  712 . Performing the low energy passivation implantation after the liner layer  716  is grown can minimize lateral spreading of the dopants. In one embodiment in accordance with the invention, a dose of arsenic (1.5×10 13  atoms per square centimeter) is implanted at 40 keV into the side wall and bottom surfaces of trenches  712 . This low-energy implantation forms passivation implantation regions  720  along the side walls of trenches  712  in isolation gaps  714  and along the bottoms of trenches  712  in substrate  702 . 
         [0041]    Next, layer  704  and insulating layer  700  are removed, as shown in  FIG. 7(G) . An insulating layer, such as a silicon dioxide layer, is deposited over the image sensor and selectively removed so that trenches  712  are filled with insulating material and form STI regions  722 . Although not shown in  FIG. 7 , an oxide is typically grown before the next processes are performed. 
         [0042]    Photoresist  724  is then deposited and patterned to cover site  710  where a photodetector will be subsequently formed, as well as other areas that will not be included in a second passivation implantation. The second passivation implantation is performed (illustrated by the arrows  726 ) to implant dopants around and into STI regions  722 . By way of example only, the second passivation implantation is performed in two steps in an embodiment in accordance with the invention, with the first step implanting a dose of arsenic (1.2×10 13  atoms per square centimeter) at 130 keV, and the second step implanting a dose of phosphorus (5×10 12  atoms per square centimeter) at 140 keV. 
         [0043]    Photoresist  724  is then removed and production of the image sensor is now completed using traditional fabrication processes well known in the art. For example, the photodetectors will be formed by implanting dopants into substrate  702 . Since these fabrication processes are well known, the steps will not described in detail herein. 
         [0044]    Although the embodiment of  FIG. 7  is described as implanting particular doses of arsenic and phosphorus into the side wall and bottom surfaces of the trenches for a pMOS pixel, embodiments in accordance with the invention are not limited to these two particular dopants or doses. One or more different types of n-type dopants or different dosage amounts can be implanted into the side walls and bottom surfaces of the trenches in other embodiments in accordance with the invention. Alternatively, for an nMOS pixel, appropriate conductivity types are reversed as will be recognized by one skilled in the art. Thus, when the charge storage regions are doped with an n-type dopant, one or more p-type dopants can be implanted into the side wall and bottom surfaces of the trenches. 
         [0045]    Moreover, other embodiments in accordance with the invention can include additional or alternative fabrication steps. And some of the fabrication steps shown in  FIG. 7  can be performed in a different order. For example, the low-energy implantation can be performed before the liner layer  716  of oxide is formed on the side walls and bottoms of the trenches  712 . 
         [0046]      FIG. 8  is a two-dimensional cross-sectional view illustrating a doping contour of the first pixel structure shown in  FIG. 6 . Contour lines  800  depict lines of constant doping density from passivation implantation regions  720 . As can be seen, the dopants surround the sides of STI regions  722  and isolation gaps  714 . The dopants also spread into substrate  702  or surround the bottom of STI regions  722 . The dopants do not, however, significantly diffuse under charge storage region  802 . This minimal encroachment by the dopants into the depletion region of a photodetector opens up the depletion region and increases collection volume of the photodetector. 
         [0047]      FIG. 9  is a graphical view of exemplary junction and depletion edges for charge storage region  802  in  FIG. 8 . Junction  900  is formed between the edge of charge storage region  802  and a substrate. Depletion edge  902  represents the boundary of depletion region  904 . Both charge storage region  802  and depletion region  904  are larger in size than the prior art charge storage region  106  and depletion region  300  shown in  FIG. 3 . As discussed earlier, the larger charge storage region  802  and depletion region  904  increase the collection volume of the photodetector. 
         [0048]    Moreover, the interface between STI regions  722  and substrate  702  are passivated effectively, thereby reducing dark current.  FIG. 10  is a one-dimensional doping density plot of STI region  722  in  FIG. 7 . The plot is down through the center of the trench. As can be seen, the doping density at the bottom of STI regions  722  is approximately 2×10 18  cm −3  to 3×10 18  cm −3  (see point  1000 ). The doping concentration along the trench side wall is at this same order of magnitude. 
         [0049]    Referring now to  FIG. 11 , there is shown a cross-sectional view of a second pixel structure in an embodiment in accordance with the invention. Pixel  1100  includes transfer gate  604 , charge-to-voltage converter  606 , source follower transistor  608 , reset transistor  606 ,  610 ,  612 , pinning layer  616 , epitaxial layer  622 , substrate  624 , and STI region  626  described in conjunction with  FIG. 6 . Buried n-type layer  1102  is formed within a portion of epitaxial layer  622 . N-type wells  1104 ,  1106  are formed within another portion of epitaxial layer  622 . Well  1106  is contained within pixel  1100  and is disposed laterally adjacent to and abutting photodetector  1108 . 
         [0050]    Region  1110  of epitaxial layer  622  is positioned between buried layer  1102 , photodetector  1108 , and wells  1104 ,  1106 . The doping of the region  1110  is substantially the same as the doping of epitaxial layer  622  in an embodiment in accordance with the invention. Region  1110  effectively produces an “extension” of p-type charge storage region  1112  in photodetector  1108 . This results in a deeper depletion depth and a deeper junction depth for photodetector  1108 . 
         [0051]    Additionally, isolation region  626 , when fabricated pursuant to the method shown in  FIG. 7 , has an interface  628  that is effectively passivated. There is minimal encroachment by the passivation implantation region dopants into the depletion region of photodetector  1108 . In an alternate embodiment in accordance with the invention, wells  1104 ,  1106  abut and make direct contact with buried layer  1102 . U.S. patent application Ser. No. 12/054,505, filed on Mar. 25, 2008 and entitled “A Pixel Structure With A Photodetector Having An Extended Depletion Depth,” incorporated by reference herein, describes in more detail the pixel structure of  FIG.11  and an alternate pixel structure where wells  1104 ,  1106  abut buried well  1102 . 
         [0052]      FIG. 12  is a two-dimensional cross-sectional view illustrating a doping contour of the alternate second pixel structure described in conjunction with  FIG. 11 . In this embodiment, wells  1104 ,  1106  abut and make direct contact with buried layer  1102 . Contour lines  1200  depict the spreading of dopants from the passivation implantation region surrounding STI region  626 . As can be seen, the dopants surround the sides and bottom of STI region  626 . The dopants do not, however, significantly spread under charge storage region  1112 . Additionally, region  1110  (not shown in  FIG. 12 ) effectively produces an extension  1202  of charge storage region  1112  in photodetector  1108  ( 1108  and  1112  not shown in  FIG. 12 ). This extension results in a deeper depletion depth and a deeper junction depth for photodetector  1108 . 
         [0053]    The invention has been described with reference to particular embodiments in accordance with the invention. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. By way of examples only, an image sensor can be implemented as a CMOS image sensor or a charge-coupled device (CCD) image sensor. A bulk wafer overlying the substrate can be used instead of substrate  624  and epitaxial layer  622 . Photodetector  602  ( FIG. 6 ) or photodetector  1108  ( FIG. 11 ) can be implemented using alternate structures or conductivity types in other embodiments in accordance with the invention. Photodetectors  602 ,  1108  can be implemented as an unpinned p-type diode formed in an n-well in a p-type substrate in another embodiment in accordance with the invention. In other embodiments in accordance with the invention, photodetector  602 ,  1108  can include a pinned or unpinned n-type diode formed within a p-well in an n-type substrate. And finally, although a simple non-shared pixel structure is shown in  FIG. 6  and  FIG. 11 , a shared architecture is used in another embodiment in accordance with the invention. One example of a shared architecture is disclosed in U.S. Pat. No. 6,107,655. 
         [0054]    Additionally, even though specific embodiments of the invention have been described herein, it should be noted that the application is not limited to these embodiments. In particular, any features described with respect to one embodiment may also be used in other embodiments, where compatible. And the features of the different embodiments may be exchanged, where compatible. 
       PARTS LIST 
       [0000]    
       
           100  pixel 
           102  photodetector 
           104  shallow trench isolation (STI) region 
           106  charge storage region 
           108  pinning layer 
           110  depletion region 
           112  junction 
           114  substrate 
           116  interface 
           200  contour lines 
           300  junction of charge storage region 
           302  edge of depletion region 
           400  image capture device 
           402  light 
           404  imaging stage 
           406  image sensor 
           408  processor 
           410  memory 
           412  display 
           414  other input/output devices 
           500  pixel 
           502  imaging area 
           504  column decoder 
           506  row decoder 
           508  digital logic 
           510  analog or digital output circuits 
           602  photodetector 
           604  transfer gate 
           606  charge-to-voltage converter 
           608  source follower transistor 
           610  gate of reset transistor 
           612  source/drain of reset transistor 
           614  power supply voltage 
           616  pinning layer 
           618  charge storage region 
           620  well 
           622  epitaxial layer 
           624  substrate 
           626  STI region 
           628  interface 
           700  insulating layer 
           702  substrate 
           704  layer 
           706  photoresist 
           708  openings 
           710  site of to be formed photodetector 
           712  trench 
           714  isolation gap 
           716  liner layer 
           718  arrows representing dopant implantation 
           720  passivation implantation regions 
           722  STI region 
           724  photoresist 
           726  arrows representing dopant implantation 
           800  contour lines 
           802  charge storage region 
           900  junction of charge storage region 
           902  edge of depletion region 
           904  depletion region 
           1000  dopant density at interface 
           1100  pixel 
           1102  buried layer 
           1104  well 
           1106  well 
           1108  photodetector 
           1110  region 
           1112  charge storage region 
           1200  contour lines 
           1202  extension of charge storage region