Patent Publication Number: US-11658196-B2

Title: Semiconductor image sensor

Description:
PRIORITY DATA 
     This application is a continuation of U.S. patent application Ser. No. 16/706,189, filed on Dec. 6, 2019, entitled of “SEMICONDUCTOR IMAGE SENSOR”, which is a continuation of U.S. patent application Ser. No. 15/928,748, filed on Mar. 22, 2018, entitled of “SEMICONDUCTOR IMAGE SENSOR”, which claims priority of U.S. Provisional Patent Application Ser. No. 62/579,474 filed Oct. 31, 2017, the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     Digital cameras and other imaging devices employ images sensors. Image sensors convert optical images to digital data that may be represented as digital images. An image sensor includes an array of pixel sensors and supporting logic circuits. The pixel sensors of the array are unit devices for measuring incident light, and the supporting logic circuits facilitate readout of the measurements. One type of image sensor commonly used in optical imaging devices is a back side illumination (BSI) image sensor. BSI image sensor fabrication can be integrated into conventional semiconductor processes for low cost, small size, and high integration. Further, BSI image sensors have low operating voltage, low power consumption, high quantum efficiency, low read-out noise, and allow random access. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG.  1    is a top view of a portion of a semiconductor image sensor according to aspects of the present disclosure in one or more embodiments. 
         FIG.  2    is a cross-sectional view of a portion of a semiconductor image sensor taken along a line A-A′ of  FIG.  1    according to aspects of the present disclosure in one or more embodiments. 
         FIG.  3    is a cross-sectional view of a portion of a semiconductor image sensor according to aspects of the present disclosure in one or more embodiments. 
         FIG.  4    is a cross-sectional view of a portion of a semiconductor image sensor according to aspects of the present disclosure in one or more embodiments. 
         FIG.  5    is a cross-sectional view of a portion of a semiconductor image sensor according to aspects of the present disclosure in one or more embodiments. 
         FIG.  6    is a flow chart representing a method for manufacturing a semiconductor image sensor according to aspects of the present disclosure. 
         FIG.  7 A through  7 H  illustrate a series of cross-sectional views of a portion of a semiconductor image sensor at various fabrication stages constructed according to aspects of the present disclosure in one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of elements and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper”, “on” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     As used herein, the terms such as “first”, “second” and “third” describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another. The terms such as “first”, “second” and “third” when used herein do not imply a sequence or order unless clearly indicated by the context. 
     As used herein, the terms “approximately,” “substantially,” “substantial” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can refer to a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, two numerical values can be deemed to be “substantially” the same or equal if a difference between the values is less than or equal to ±10% of an average of the values, such as less than or equal to ±5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, “substantially” parallel can refer to a range of angular variation relative to 0° that is less than or equal to 10°, such as less than or equal to 5°, less than or equal to 4°, less than or equal to ±3°, less than or equal to ±2°, less than or equal to ±1°, less than or equal to ±0.5°, less than or equal to ±0.1°, or less than or equal to ±0.05°. For example, “substantially” perpendicular can refer to a range of angular variation relative to 90° that is less than or equal to 10°, such as less than or equal to ±5°, less than or equal to ±4°, less than or equal to ±3°, less than or equal to ±2°, less than or equal to ±1°, less than or equal to ±0.5°, less than or equal to 0.1°, or less than or equal to ±0.05°. 
     BSI image sensor includes an array of pixel sensors. Typically. BSI image sensors include an integrated circuit having a semiconductor substrate and light-sensing devices such as photodiodes corresponding to the pixel sensors arranged within the substrate, a back-end-of-line (BEOL) metallization of the integrated circuits disposed over a front side of the substrate, and an optical stack including color filters and micro-lens corresponding to the pixel sensors disposed over a back side of the substrate. As the size of BSI image sensors decrease, BSI image sensors face a number of challenges. One challenge with BSI image sensors is cross talk between neighboring pixel sensors. As BSI image sensors become smaller and smaller, distance between neighboring pixel sensors becomes smaller and smaller, thereby increasing the likelihood of cross talk. Another challenge with BSI image sensors is light collection. Also as image sensors become smaller and smaller, the surface area for light collection becomes smaller and smaller, thereby reducing the sensitivity of pixel sensors. This is problematic for low light environments. Therefore, it is in need to reduce cross talk and to increase absorption efficiency of the pixel sensors such that performance and sensitivity of BSI image sensors is improved. 
     The present disclosure therefore provides a pixel sensor of a BSI image sensor including a reflective grid buried in the isolation structure used to provide isolation between neighboring light-sensing devices. In some embodiments, the present disclosure provides a hybrid isolation disposed in the substrate, and the hybrid isolation includes the reflective grid. The reflective structure serves as a light guide or a mirror that light are reflected back to the light-sensing device. In other words, light is directed and reflected to the pixel sensor instead of entering to the neighboring pixel sensors. Accordingly, cross talk is reduced, and thus performance and sensitivity of the pixel sensors are both improved. 
       FIG.  1    is a top view of a portion of a semiconductor image sensor  100  according to aspects of the present disclosure in one or more embodiments, and  FIG.  2    is a cross-sectional view of a portion of the semiconductor image sensor  100  taken along a line A-A′ of  FIG.  1    according to aspects of the present disclosure in some embodiments. In some embodiments, the semiconductor image sensor  100  is a BSI image sensor  100 . As shown in  FIGS.  1  and  2   , the BSI image sensor  100  includes a substrate  102 , and the substrate  102  includes, for example but not limited to, a bulk semiconductor substrate such as a bulk silicon (Si) substrate, or a silicon-on-insulator (SOI) substrate. The substrate  102  has a front side  102 F and a back side  102 B opposite to the front side  102 F. The BSI image sensor  100  includes a plurality of pixel sensors  110  typically arranged within an array, and each of the pixel sensors  110  includes a light-sensing device such as a photodiode  112  disposed in the substrate  102 . In other words, the BSI image sensor  100  includes a plurality of photodiodes  112  corresponding to the pixel sensors  110 . The photodiodes  112  are arranged in rows and columns in the substrate  102 , and configured to accumulate charge (e.g. electrons) from photons incident thereon. Further, logic devices, such as transistors  114 , can be disposed over the substrate  102  on the front side  102 F and configured to enable readout of the photodiodes  112 . The pixel sensors  110  are disposed to receive light with a predetermined wavelength. Accordingly, the photodiodes  112  can be operated to sense visible light of incident light in some embodiments. 
     In some embodiments, a plurality of isolation structures  120  is disposed in the substrate  102  as shown in  FIG.  2   . In some embodiments, the isolation structure  120  includes a deep trench isolation (DTI) and the DTI structure can be formed by the following operations. For example, a first etch is performed from the back side  102 B of the substrate  102 . The first etch results in a plurality of deep trenches (not show) surrounding and between the photodiodes  112  of the pixel sensors  110 . An insulating material such as silicon oxide (SiO) is then formed to fill the deep trenches using any suitable deposition technique, such as chemical vapor deposition (CVD). In some embodiments, sidewalls and bottoms of the deep trenches are lined by a dielectric layer  122 , such as a coating  122  and the deep trenches are then filled up by an insulating structure  124 . The coating  122  may include a low-n material, which has a refractive index (n) less than color filter formed hereafter. The low-n material can include SiO or hafnium oxide (HfO), but the disclosure is not limited to this. In some embodiments, the insulating structure  124  filling the deep trenches can include the low-n insulating material. In some embodiments, a planarization is then performed to remove superfluous insulating material, thus the surface of the substrate  102  on the back side  102 B is exposed, and the DTI structures  120  surrounding and between the photodiodes  112  of the pixel sensors  110  are obtained as shown in  FIG.  2   . 
     More importantly, a portion of the insulating structure  124  is then removed and thus a plurality of recesses (not shown) may be formed in each DTI structure  120 . Next, a conductive material such as tungsten (W), copper (Cu), or aluminum-copper (AlCu), or other suitable material is formed to fill the recess. Accordingly, a conductive structure  126  is formed over the insulating structure  124  as shown in  FIG.  2   . The conductive structure  126 , the insulating structure  124  and the dielectric layer  122  construct a hybrid isolation  128  surrounding each photodiode  112  of the pixel sensor  110 . In other words, a hybrid isolation  128  including the dielectric layer  122 , the insulating structure  124  and the conductive structure  126  is provided and disposed in the substrate  102  according to some embodiments. In some embodiments, a thickness T 2  of the hybrid isolation  128  is less than a thickness T 1  of the substrate  102 . In some embodiments, the dielectric layer  122  covers at least sidewalls of the conductive structure  126 . Further, the dielectric layer  122  covers sidewalls and a bottom surface of the insulating structure  124 . 
     In some embodiments, an anti-reflective coating (ARC)  116  is disposed over the substrate  102  on the back side  102 B, and a passivation layer  118  is disposed over the ARC  116 . In some embodiments, the ARC  116  and the dielectric layer  122  include the same material and can be formed at the same time. Thus a substantially flat and even surface is obtained on the back side  102 B of the substrate  102  as shown in  FIG.  2   . 
     A back-end-of-line (BEOL) metallization stack  130  is disposed over the front side  102 F of the substrate  102 . The BEOL metallization stack  130  includes a plurality of metallization layers  132  stacked in an interlayer dielectric (ILD) layer  134 . One or more contacts of the BEOL metallization stack  130  is electrically connected to the logic device  114 . In some embodiments, the ILD layer  134  can include a low-k dielectric material (i.e., a dielectric material with a dielectric constant less than 3.9) or an oxide, but the disclosure is not limited to this. The plurality of metallization layers  132  may include a metal such as copper (Cu), tungsten (W), or aluminum (Al), but the disclosure is not limited to this. In some embodiments, another substrate (not shown) can be disposed between the metallization structure  130  and external connectors such as a ball grid array (BGA) (not shown). And the BSI image sensor  100  is electrically connected to other devices or circuits through the external connectors, but the disclosure is not limited to this. 
     Referring to  FIGS.  1  and  2   , in some embodiments, a plurality of color filters  150  corresponding to the pixel sensors  110  is disposed over the substrate  102  on the back side  102 B. Further, another insulating structure  140  is disposed between the color filters  150 . In some embodiments, the insulating structure  140  includes a grid structure and the color filters  150  are located within the grid. Thus the insulating structure  140  surrounds each color filter  150 , and separates the color filters  150  from each other as shown in  FIGS.  1  and  2   . The insulating structure  140  can include materials with a refractive index less than the refractive index of the color filters  150  or less than a refractive index of Si, but the disclosure is not limited to this. Further, the conductive structure  126  is disposed between the insulating structure  124  and the insulating structure  140 , as shown in  FIGS.  1  and  2   . 
     Each of the color filters  150  is disposed over each of the corresponding photodiodes  112 . The color filters  150  are assigned to corresponding colors or wavelengths of lights, and configured to filter out all but the assigned colors or wavelengths of lights. Typically, the color filters  150  assignments alternate between red, green, and blue lights, such that the color filters  150  include red color filters  150 /R, green color filters  150 /G and blue color filters  150 /B, as shown in  FIG.  1   . In some embodiments, the red color filters  150 /R the green color filters  150 /G and the blue color filters  150 /B are arranged in a Bayer or other mosaic pattern, but the disclosure is not limited to this. 
     In some embodiments, a micro-lens  160  corresponding to each pixel sensor  110  is disposed over the color filter  150 . It should be easily understood that locations and areas of each micro-lens  160  correspond to those of the color filter  150  or those of the pixel sensor  110  as shown in  FIG.  2   . 
     In some embodiments, the insulating structures  124  and the dielectric layers  122  of the hybrid isolations  128  form an isolation grid  120  in the substrate  102 , and the isolation grid  120  provides electrical isolation between neighboring pixel sensors  110 . In other words, the isolation grid  120  separates the plurality of pixel sensors  110  including the photodiodes  112  from each other. In some embodiments, a depth D I  of the isolation grid  120  is less than the thickness T 1  of the substrate  102 , as shown in  FIG.  2   . In some embodiments, the conductive structures  126  of the hybrid isolations  128  form a reflective grid  126  disposed over the isolation grid  120  on the back side  102 B of the substrate  102 . In some embodiments, the depth D I  of the isolation grid  120  is less than the thickness T 1  of the substrate  102 , and a depth D R  of the reflective grid  126  is less than the depth D I  of the isolation grid  120 . It should be noted that depth D R  of the reflective grid  126  is related to a pitch P of the pixel sensor  110 . For example but not limited to, the depth D R  of the reflective grid  126  can be greater than 0.1 micrometer (μm) and less than the depth D I  of the isolation grid  120  when the pitch P of the pixel sensor  110  is about 0.9 μm. In some embodiments, the depth D R  of the reflective grid  126  can be greater than 0.2 μm and less than the depth D I  of the isolation grid  120  when the pitch P of the pixel sensor  110  is about 0.7 μm. In some embodiments, the insulating structures  140  between the color filters  150  form a low-n grid  140  over the substrate  102  on the back side  102 B. Thus, the low-n grid  140  separates the color filters  150  from each other. As shown in  FIG.  2   , the reflective grid  126  is disposed between the low-n grid  140  and the isolation grid  120 . Further, the low-n grid  140  overlaps the reflective grid  126  and the isolation grid  120  from a plan view, in some embodiments. 
     Due to the low refractive index, the low-n grid  140  serves as a light guide to direct or reflect light to the color filters  150 . Consequently, the low-n structure  140  effectively increases the amount of the light incident into the color filters  150 . Further, due to the low refractive index, the low-n grid  140  provides optical isolation between neighboring color filters  150 . The reflective grid  126  serves as a light guide or a mirror, and reflects light to the photodiode  112 . Consequently, the reflective grid  126  effectively increases the amount of light to be absorbed by photodiode  112  and thus provides optical isolation between neighboring pixel sensors  110 . On the other hands, the isolation grid  120  including the dielectric layer  122  and the insulating structure  124  provides electrical isolation between the neighboring pixel sensors  110 . In other words, the isolation grid  120  separates the plurality of pixel sensors  110  including the photodiodes  112  from each other thereby serving as a substrate isolation grid and reducing cross-talk. 
       FIG.  3    is a cross-sectional view of a portion of a semiconductor image sensor  200  according to aspects of the present disclosure in one or more embodiments. It should be easily understood elements the same in the BSI image sensor  100  and the BSI image sensor  200  can include the same material and/or formed by the same operations, and thus those details are omitted in the interest of brevity. In some embodiments, the semiconductor image sensor  200  is a BSI image sensor  200 . In some embodiments, a top view of the BSI images sensor  200  can be similar as shown  FIG.  1   , but the disclosure is not limited to this. As shown in  FIG.  3   , the BSI image sensor  200  includes a substrate  202 , and the substrate  202  has a front side  202 F and a back side  202 B opposite to the front side  202 F. The BSI image sensor  200  includes a plurality of pixel sensors  210  typically arranged within an array. A plurality of photo-sensing devices such as photodiodes  212  corresponding to the pixel sensors  210  is disposed in the substrate  202 . The photodiodes  212  are arranged in rows and columns in the substrate  202 . In other words, each of the pixel sensors  210  includes a photo-sensing device such as the photodiode  212 . Further, logic devices, such as transistors  214 , are disposed over the front side  202 F of the substrate  202  and configured to enable readout of the photodiodes  212 . 
     A plurality of isolation structures  220  is disposed in the substrate  202  as shown in  FIG.  3   . In some embodiments, the isolation structure  220  includes a DTI structure and the DTI structure can be formed by operations as mentioned above. Therefore, those details are omitted in the interest of brevity. In some embodiments, sidewalls and bottoms of the deep trenches are lined by a dielectric layer  222 , such as a coating  222  and the deep trenches are then filled up by an insulating structure  224 . As mentioned above, the coating  222  may include a low-n material, which has a refractive index (n) less than color filter formed hereafter. The low-n material can include SiO or hafnium oxide (HfO), but the disclosure is not limited to this. In some embodiments, the insulating structure  224  filling the deep trenches can include the low-n insulating material. A planarization is then performed to remove superfluous insulating material, thus the surface of the substrate  202  on the back side  202 B is exposed, and the DTI structures  220  surrounding and between the photodiodes  212  of the pixel sensors  210  are obtained as shown in  FIG.  3   . 
     More importantly, a portion of the insulating structure  224  is then removed and thus a recess (not shown) may be formed in each DTI structure  220 . Next, a conductive material such as W, Cu, or AlCu, or other suitable material is formed to fill the recess. Accordingly, a conductive structure  226  is formed over the insulating structure  224 . The conductive structure  226 , the insulating structure  224  and the dielectric layer  222  construct a hybrid isolation  228  surrounding each photodiode  212  of the pixel sensor  210 . In other words, a hybrid isolation  228  including the dielectric layer  222 , the insulating structure  224  and the conductive structure  226  is provided and disposed in the substrate  202  according to some embodiments. In some embodiments, a thickness T 2  of the hybrid isolation  228  is substantially equal to a thickness T 1  of the substrate  202 . In some embodiments, the dielectric layer  222  covers at least sidewalls of the conductive structure  226 . Further, the dielectric layer  222  covers sidewalls and a bottom surface of the insulating structure  224 . 
     In some embodiments, an ARC  216  is disposed over the substrate  202  on the back side  202 B, and a passivation layer  218  is disposed over the ARC  216 . In some embodiments, the ARC  216  and the dielectric layer  222  include the same material and can be formed at the same time. Thus a substantially flat and even surface is obtained on the back side  202 B of the substrate  202  as shown in  FIG.  3   . 
     A BEOL metallization stack  230  is disposed over the front side  202 F of the substrate  202 . As mentioned above the BEOL metallization stack  230  includes a plurality of metallization layers  232  stacked in an ILD layer  234 . One or more contacts of the BEOL metallization stack  230  are electrically connected to the logic device  214 . In some embodiments, another substrate (not shown) can be disposed between the metallization structure  230  and external connectors such as a ball grid array (BGA) (not shown). And the BSI image sensor  200  is electrically connected to other devices or circuits through the external connectors, but the disclosure is not limited to this. 
     Referring to  FIG.  3   , in some embodiments, a plurality of color filters  250  corresponding to the pixel sensors  210  is disposed over the pixel sensors  210  on the back side  202 B of the substrate  202 . Further, another insulating structure  240  is disposed between the color filters  250 . In some embodiments, the insulating structure  240  includes a grid structure and the color filters  250  are located within the grid. Thus the insulating structure  240  surrounds each color filter  250 , and separates the color filters  250  from each other as shown in  FIG.  3   . The insulating structure  240  can include materials with a refractive index less than the refractive index of the color filters  250  or a material with a refractive index less than a refractive index of Si, but the disclosure is not limited to this. Further, the conductive structure  226  is disposed between the insulating structure  224  and the insulating structure  240 , as shown in  FIG.  3   . 
     As mentioned above, each of the color filters  250  is disposed over each of the corresponding photodiodes  212 . The color filters  250  are assigned to corresponding colors or wavelengths of lights, and configured to filter out all but the assigned colors or wavelengths of lights. Typically, the color filters  250  assignments alternate between red, green, and blue lights, such that the color filters  250  include red color filters, green color filters and blue color filters. In some embodiments, the red color filters, the green color filters and the blue color filters are arranged in a Bayer or other mosaic pattern, but the disclosure is not limited to this. In some embodiments, a micro-lens  260  corresponding to each pixel sensor  210  is disposed over the color filter  250 . It should be easily understood that locations and areas of each micro-lens  260  correspond to those of the color filter  250  or those of the pixel sensor  210  as shown in  FIG.  3   . 
     In some embodiments, the insulating structures  224  and the dielectric layers  222  of the hybrid isolations  228  form an isolation grid  220  in the substrate  202 , and the isolation grid  220  provides electrical isolation between neighboring pixel sensors  210 . In other words, the isolation grid  220  separates the plurality of pixel sensors  210  including the photodiodes  212  from each other. In some embodiments, a depth D I  of the isolation grid  220  is less than the thickness T 1  of the substrate  202 , as shown in  FIG.  3   . In some embodiments, the conductive structures  226  of the hybrid isolations  228  form a reflective grid  226  disposed over the isolation grid  220  on the back side  202 B of the substrate  202 . In some embodiments, a depth D I  of the isolation grid  220  is substantially equal to the thickness T 1  of the substrate  202 , and a depth D R  of the reflective grid  226  is less than the depth D I  of the isolation grid  220 . As mentioned above, the depth D R  of the reflective grid  226  is related to a pitch P of the pixel sensor  210 . In some embodiments, the insulating structures  240  between the color filters  250  form a low-n grid  240  over the substrate  202  on the back side  202 B. Thus, the low-n grid  240  separates the color filters  250  from each other. As shown in  FIG.  3   , the reflective grid  226  is disposed between the low-n grid  240  and the isolation grid  220 . Further, the low-n grid  240  overlaps the reflective grid  226  and the isolation grid  220  from a plan view, in some embodiments. 
     Due to the low refractive index, the low-n grid  240  serves as a light guide to direct or reflect light to the color filters  250 . Consequently, the low-n structure  240  effectively increases the amount of the light incident into the color filters  250 . Further, due to the low refractive index, the low-n grid  240  provides optical isolation between neighboring color filters  250 . The reflective grid  226  serves as a light guide or a mirror, and reflects light to the photodiode  212 . Consequently, the reflective grid  226  effectively increases the amount of light to be absorbed by photodiode  212  and thus provides optical isolation between neighboring pixel sensors  210 . On the other hands, the isolation grid  220  including the dielectric layer  222  and the insulating structure  224  provides electrical isolation between the neighboring pixel sensors  210 . In other words, the isolation grid  220  separates the plurality of pixel sensors  210  including the photodiodes  212  from each other thereby serving as a substrate isolation grid and reducing cross-talk. 
       FIG.  4    is a cross-sectional view of a portion of a BSI image sensor  300  according to aspects of the present disclosure in one or more embodiments. It should be easily understood elements the same in the BSI image sensors  100 / 200  and the BSI image sensor  300  can include the same material and/or formed by the same operations, and thus those details are omitted in the interest of brevity. In some embodiments, the semiconductor image sensor  300  is a BSI image sensor  300 . In some embodiments, a top view of the BSI images sensor  300  can be similar as shown  FIG.  1   , but the disclosure is not limited to this. As shown in  FIG.  4   , the BSI image sensor  300  includes a substrate  302 , and the substrate  302  has a front side  302 F and a back side  302 B opposite to the front side  302 F. The BSI image sensor  300  includes a plurality of pixel sensors  310  typically arranged within an array. A plurality of photo-sensing devices such as photodiodes  312  corresponding to the pixel sensors  310  is disposed in the substrate  302 . The photodiodes  312  are arranged in rows and columns in the substrate  302 . In other words, each of the pixel sensors  310  includes a photo-sensing device such as the photodiode  312 . Further, logic devices, such as transistors  314 , are disposed over the front side  302 F of the substrate  302  and configured to enable readout of the photodiodes  312 . 
     A hybrid isolation  328  is disposed in the substrate  302  as shown in  FIG.  4   . In some embodiments, the hybrid isolation  328  can be formed by operations for forming DTI structure, but the disclosure is not limited to this. For example, a first etch is performed from the back side  302 B of the substrate  302 . The first etch results in a plurality of deep trenches (not show) surrounding and between the photodiodes  312 . In some embodiments, sidewalls and bottoms of the deep trenches are lined by a dielectric layer  322 , such as a coating  322 . The coating  322  may include a low-n material, which has a refractive index less than color filter formed hereafter. Next, a conductive material such as W, Cu, AlCu, or other suitable material is formed to fill the trenches. Accordingly, a conductive structure  326  is disposed in each deep trench. The conductive structure  326  and the dielectric layer  322  construct the hybrid isolation  328 . In other words, a hybrid isolation  328  including the dielectric layer  322  and the conductive structure  326  is provided and disposed in the substrate  302  according to some embodiments. In some embodiments, a thickness T 2  of the hybrid isolation  328  is substantially equal to a thickness T 1  of the substrate  302 . Further, the dielectric layer  322  covers sidewalls and a bottom surface of the conductive structure  326 , as shown in  FIG.  4   . 
     In some embodiments, an ARC  316  is disposed over the substrate  302  on the back side  302 B, and a passivation layer  318  is disposed over the ARC  316 . In some embodiments, the ARC  316  and the dielectric layer  322  include the same material and can be formed at the same time. Thus a substantially flat and even surface is obtained on the back side  302 B of the substrate  302  as shown in  FIG.  4   . 
     A BEOL metallization stack  330  is disposed over the front side  302 F of the substrate  302 . As mentioned above, the BEOL metallization stack  330  includes a plurality of metallization layers  332  stacked in an ILD layer  334 . One or more contacts of the BEOL metallization stack  330  are electrically connected to the logic device  314 . In some embodiments, another substrate (not shown) can be disposed between the metallization structure  330  and external connectors such as a ball grid array (BGA) (not shown). And the BSI image sensor  300  is electrically connected to other devices or circuits through the external connectors, but the disclosure is not limited to this. 
     Referring to  FIG.  4   , in some embodiments, a plurality of color filters  350  corresponding to the pixel sensors  310  is disposed over the pixel sensors  310  on the back side  302 B of the substrate  302 . Further, an insulating structure  340  is disposed between the color filters  350 . In some embodiments, the insulating structure  340  includes a grid structure and the color filters  350  are located within the grid. Thus the insulating structure  340  surrounds each color filter  350 , and separates the color filters  350  from each other as shown in  FIG.  4   . The insulating structure  340  can include materials with a refractive index less than the refractive index of the color filters  350  or a material with a refractive index less than a refractive index of Si, but the disclosure is not limited to this. 
     As mentioned above, each of the color filters  350  is disposed over each of the corresponding photodiodes  312 . The color filters  350  are assigned to corresponding colors or wavelengths of lights, and configured to filter out all but the assigned colors or wavelengths of lights. Typically, the color filters  350  assignments alternate between red, green, and blue lights, such that the color filters  350  include red color filters, green color filters and blue color filters. In some embodiments, the red color filters, the green color filters and the blue color filters are arranged in a Bayer or other mosaic pattern, but the disclosure is not limited to this. In some embodiments, a micro-lens  360  corresponding to each pixel sensor  310  is disposed over the color filter  350 . It should be easily understood that locations and areas of each micro-lens  360  correspond to those of the color filter  350  or those of the pixel sensor  310  as shown in  FIG.  4   . 
     In some embodiments, the dielectric layers  322  of the hybrid isolations  328  form an isolation grid  320  in the substrate  302 , and the isolation grid  320  provides electrical isolation between neighboring pixel sensors  310 . In some embodiments, a depth D I  of the isolation grid  320  is substantially equal to the thickness T 1  of the substrate  302 , as shown in  FIG.  4   . In some embodiments, the conductive structures  326  of the hybrid isolations  328  form a reflective grid  326  disposed in the substrate  302 . In some embodiments, a depth D I  of the isolation grid  320  is substantially equal to the thickness T 1  of the substrate  302 , and a depth D R  of the reflective grid  326  is less than the depth D I  of the isolation grid  320 . As mentioned above, the depth D R  of the reflective grid  326  is related to a pitch P of the pixel sensor  310 . In some embodiments, the insulating structures  340  between the color filters  350  form a low-n grid  340  over the substrate  302  on the back side  302 B. As shown in  FIG.  4   , the reflective grid  326  is disposed between the low-n grid  340  and the isolation grid  320 . Further, the low-n grid  340  overlaps the reflective grid  326  from a plan view, in some embodiments. 
     Due to the low refractive index, the low-n grid  340  serves as a light guide to direct or reflect light to the color filters  350 . Consequently, the low-n structure  340  effectively increases the amount of the light incident into the color filters  350 . Further, due to the low refractive index, the low-n grid  340  provides optical isolation between neighboring color filters  350 . The reflective grid  326  serves as a light guide or a mirror, and reflects light to the photodiode  312 . Consequently, the reflective grid  326  effectively increases the amount of light to be absorbed by photodiode  312  and thus provides optical isolation between neighboring pixel sensors  310 . On the other hands, the isolation grid  320  including the dielectric layer  322  provides electrical isolation between the neighboring pixel sensors  310 . In other words, the isolation grid  320  separates the plurality of pixel sensors  310  including the photodiodes  312  from each other thereby serving as a substrate isolation grid and reducing cross-talk. 
       FIG.  5    is a cross-sectional view of a portion of a BSI image sensor  400  according to aspects of the present disclosure in one or more embodiments. It should be noted that the same elements in the BSI image sensor  400  and the BSI image sensor  100 / 200 / 300  can include the same material and/or formed by the same operations, and thus those details are omitted in the interest of brevity. In some embodiments, the semiconductor image sensor  400  is a BSI image sensor  400 . In some embodiments, a top view of the BSI images sensor  400  can be similar as shown  FIG.  1   , but the disclosure is not limited to this. As shown in  FIG.  5   , the BSI image sensor  400  includes a substrate  402 . The substrate  402  has a front side  402 F and a back side  402 B opposite to the front side  402 F. The BSI image sensor  400  includes a plurality of pixel sensors  410  typically arranged within an array, and each of the pixel sensors  410  includes a light-sensing device such as a photodiode  412  disposed in the substrate  402 . In other words, the BSI image sensor  400  includes a plurality of photodiodes  412  corresponding to the pixel sensors  410 . The photodiodes  412  are arranged in rows and columns in the substrate  402 , and configured to accumulate charge (e.g. electrons) from photons incident thereon. Further, logic devices, such as transistors  414 , can be disposed over the substrate  402  on the front side  402 F and configured to enable readout of the photodiodes  412 . The pixel sensors  410  are disposed to receive light with a predetermined wavelength. Accordingly, the photodiodes  412  can be operated to sense visible light of incident light in some embodiments. 
     A plurality of isolation structures  420  is disposed in the substrate  402  as shown in  FIG.  5   . In some embodiments, the isolation structure  420  includes a DTI structure, and the DTI structure can be formed by operations as mentioned above, therefore those details are omitted for brevity. In some embodiments, sidewalls and bottoms of the deep trenches are lined by a dielectric layer  422 , such as a coating  422  and the deep trenches are then filled up by an insulating structure  424 . The coating  422  may include a low-n material, which has a refractive index (n) less than color filter formed hereafter. In some embodiments, the insulating structure  424  filling the deep trenches can include the low-n insulating material. A planarization is then performed to remove superfluous insulating material, thus the surface of the substrate  402  on the back side  402 B is exposed, and the DTI structures  420  surrounding and between the photodiodes  412  are obtained. 
     In some embodiments, a portion of the insulating structure  424  is then removed and thus a recess (not shown) may be formed in each DTI structure  420 . Next, a conductive material is formed to fill the recess. Accordingly, a conductive structure  426  is formed over the insulating structure  424  as shown in  FIG.  5   . The conductive structure  426 , the insulating structure  424  and the dielectric layer  422  construct a hybrid isolation  428 . In other words, a hybrid isolation  428  including the dielectric layer  422 , the insulating structure  424  and the conductive structure  426  is provided and disposed in the substrate  402  according to some embodiments. In some embodiments, a depth or a thickness T 2  of the hybrid isolation  428  is less than the thickness T 1  of the substrate  402 . However, in some embodiments the depth or the thickness T 2  of the hybrid isolation  428  can be substantially equal to the thickness T 1  of the substrate  402 . Such hybrid isolation  428  can be similar as the hybrid isolation  228  shown in  FIG.  3   , therefore those details are omitted in the interest of brevity. In those embodiments, the dielectric layer  422  covers at least sidewalls of the conductive structure  426 . Further, the dielectric layer  422  covers sidewalls of the insulating structure  424  and a bottom surface of the insulating structure  424 . 
     However, in some embodiments, the conductive structure  426  can be formed to fill the deep trenches directly after forming the dielectric layer  422 . Consequently, a hybrid isolation  428  including the dielectric layer  422  and the conductive structure  426  can be obtained as shown in  FIG.  5   . In those embodiments, the dielectric layer  422  covers not only the sidewalls of the conductive structure  426  but also the bottom surface of the conductive structure  426 . Such hybrid isolation  428  can be similar as hybrid isolation  328  shown in  FIG.  4   , therefore those details are omitted in the interest of brevity. 
     In some embodiments, an ARC  416  is disposed over the substrate  402  on the back side  402 B, and a passivation layer  418  is disposed over the ARC  416 . In some embodiments, the ARC  416  and the dielectric layer  422  include the same material and can be formed at the same time. Thus a substantially flat and even surface is obtained on the back side  402 B of the substrate  402  as shown in  FIG.  5   . 
     As mentioned above, a BEOL metallization stack  430  is disposed over the front side  402 F of the substrate  402 . The BEOL metallization stack  430  includes a plurality of metallization layers  432  stacked in an ILD layer  434 . One or more contacts of the BEOL metallization stack  430  are electrically connected to the logic device  414 . In some embodiments, another substrate (not shown) can be disposed between the metallization structure  430  and external connectors such as a ball grid array (BGA) (not shown). And the BSI image sensor  400  is electrically connected to other devices or circuits through the external connectors, but the disclosure is not limited to this. 
     Referring to  FIG.  5   , in some embodiments, a plurality of color filters  450  corresponding to the pixel sensors  410  is disposed over the pixel sensors  410  on the back side  402 B of the substrate  402 . Further, a hybrid isolation  440  is disposed between the color filters  450  in some embodiments. In some embodiments, the hybrid isolation  440  includes a grid structure and the color filters  450  are located within the grid. Thus the hybrid isolation  440  surrounds the color filter  450 , and separates the color filters  450  from each other as shown in  FIG.  5   . The hybrid isolation  440  can include layers with a refractive index less than the refractive index of the color filters  450 . In some embodiments, the composite structure  440  can include a composite stack including at least a conductive structure  442  and an insulating structure  444  disposed over the conductive structure  442 . In some embodiments, the conductive structure  442  can include W, Cu, or AlCu, and the insulating structure  444  includes a material with a refractive index less than the refractive index of the color filter  450  or a material with a refractive index less than a refractive index of Si, but the disclosure is not limited to this. 
     Each of the color filters  450  is disposed over each of the corresponding photodiodes  412 . The color filters  450  are assigned to corresponding colors or wavelengths of lights, and configured to filter out all but the assigned colors or wavelengths of lights. Typically, the color filters  450  assignments alternate between red, green, and blue lights, such that the color filters  450  include red color filters, green color filters and blue color filters. In some embodiments, the red color filters, the green color filters and the blue color filters are arranged in a Bayer mosaic pattern, but the disclosure is not limited to this. In some embodiments, a micro-lens  460  corresponding to each pixel sensor  410  is disposed over the color filter  450 . It should be easily understood that locations and areas of each micro-lens  460  correspond to those of the color filter  450  or those of the pixel sensor  410  as shown in  FIG.  5   . 
     In some embodiments, the hybrid isolation  428  including the insulating structures  424 , the dielectric layers  422  and the conductive structures  426  is disposed in the substrate  402 . The insulating structures  424  and/or the dielectric layers  422  of the hybrid isolation  428  provide electrical isolation between neighboring pixel sensors  410 . In other words, insulating structures  424  and/or the dielectric layers  422  of the hybrid isolation  428  serve as a substrate isolation grid separating the plurality of pixel sensors  410  including the photodiodes  412  from each other, and thus reducing cross-talk. A depth T 2  of the hybrid isolation  428  can be equal to or less than the thickness T 1  of the substrate  402 , as shown in  FIG.  5   . In some embodiments, the conductive structures  426  of the hybrid isolation  428  form a reflective grid. In some embodiments, a depth D R  of the reflective grid  426  can be equal to or less than the depth T 2  of the hybrid isolation  428 . As mentioned above, the depth D R  of the reflective grid  426  is related to a pitch P of the pixel sensor  410 . Additionally, the dielectric layers  422  and/or the insulating structures  424  form an isolation grid  420 , and the reflective grid  426  is disposed between the isolation grid  420  and the hybrid isolation  440  including the conductive structure  442  and the insulating structure  444 , as shown in  FIG.  5   . Further, the hybrid isolation  440  overlaps the hybrid isolation  428  from a plan view. 
     Due to the low refractive index, the hybrid isolation  440  serves as a light guide to direct or reflect light to the color filters  450 . Consequently, the hybrid isolation  440  effectively increases the amount of the light incident into the color filters  450 . Further, due to the low refractive index, the hybrid isolation  440  provides optical isolation between neighboring color filters  450 . The conductive structure  426  of the hybrid isolation  428  serves as a light guide or a mirror, and reflects light to the photodiode  412 . Consequently, the conductive structure/reflective grid  426  effectively increases the amount of light to be absorbed by photodiode  412  and thus provides optical isolation between neighboring pixel sensors  410 . On the other hands, the isolation grid  420  (including the conductive structure  424  and the dielectric layer  422  of the hybrid isolation  428 ) provides electrical isolation between the neighboring pixel sensors  410 . 
     Please refer to  FIG.  6    and  FIGS.  7 A- 7 H .  FIG.  6    shows a flow chart representing method for forming a semiconductor image sensor according to aspects of the present disclosure, and  FIGS.  7 A- 7 H  are a series of cross-sectional views of a semiconductor image sensor at various fabrication stages constructed according to aspects of the present disclosure in one or more embodiments. In the present disclosure, a method of manufacturing a semiconductor image sensor  50  is also disclosed. In some embodiments, a semiconductor image sensor structure  600  can be formed by the method  50 . The method  50  includes a number of operations and the description and illustration are not deemed as a limitation as the sequence of the operations. The method  50  includes a number of operations ( 502 ,  504 ,  506 ,  508 , and  510 ). Additionally, it should be noted that elements the same in  FIGS.  2  and  7 A- 7 H  are designated by the same numerals, and can include the same materials, thus those details are omitted in the interest of brevity. 
     In operation  502 , a substrate  602  is provided or received. As mentioned above, the substrate  602  has a front side  602 F and a back side  602 B opposite to the front side  102 F. The semiconductor image sensor  600  includes a plurality of pixel sensors  610  typically arranged within an array, and each of the pixel sensors  610  includes a light-sensing device such as a photodiode  612  disposed in the substrate  602 . Further, logic devices, such as a transistor  614 , can be disposed over the substrate  602  on the front side  602 F and configured to enable readout of the photodiodes  612 . The pixel sensors  610  are disposed to receive light with a predetermined wavelength. As mentioned above, the photodiodes  612  can be operated to sense visible light of incident light in some embodiments. 
     In some embodiments, a BEOL metallization stack  630  is disposed over the front side  602 F of the substrate  602 . The BEOL metallization stack  630  includes a plurality of metallization layers  632  stacked in an ILD layer  634 . One or more contacts of the BEOL metallization stack  630  is electrically connected to the logic device  614 . In some embodiments, another substrate (not shown) can be disposed between the metallization structure  630  and external connectors such as a ball grid array (BGA) (not shown). And the BSI image sensor  600  is electrically connected to other devices or circuits through the external connectors, but the disclosure is not limited to this. 
     In operation  504 , a first etch is performed from the back side  602 B of the substrate  602 . The first etch results in a plurality of deep trenches  613  surrounding and between the photodiodes  612  of the pixel sensors  610 , as shown in  FIG.  7 A . 
     In operation  506 , a plurality of hybrid isolation structures  620  is formed in the deep trenches  613 . In some embodiment, the forming of the hybrid isolation structures  620  further includes following operations. Referring to  FIG.  7 B , sidewalls and bottoms of the deep trenches  613  are lined by a dielectric layer  622 , such as a coating  622 . In some embodiments, the coating  622  may include a low-n material, which has a refractive index (n) less than color filter formed hereafter. The low-n material can include SiO or HfO, but the disclosure is not limited to this. 
     Referring to  FIG.  7 C , an insulating material  624  such as SiO is then formed to fill the deep trenches  613  using any suitable deposition technique, such as CVD. In some embodiments, the insulating structure  624  filling the deep trenches can include the low-n insulating material. 
     Referring to  FIG.  7 D , in some embodiments, the insulating material  624  is then recessed from the back side  602 B of the substrate  602 . Consequently, a plurality of DTI structures  620  surrounding and between the photodiodes  612  of the pixel sensors  610  are obtained as shown in  FIG.  7 D . Further, a plurality of recesses  615  is formed in each DTI structure  620 . 
     Referring to  FIG.  7 E , Next, a conductive material  626  such as W, Cu, or AlCu, or other suitable material is formed to fill the recesses  613 . Accordingly, a conductive structure  626  is formed over the insulating structure  624  as shown in  FIG.  7 E . Referring to  FIG.  7 F , a planarization then can be performed to remove the superfluous conductive material  626 , such that top surfaces of the insulating materials  624  are exposed from the back side  602 B of the substrate  602 . Accordingly, the conductive structure  626 , the insulating structure  624  and the dielectric layer  622  construct the hybrid isolations  628  surrounding each photodiode  612  of the pixel sensor  610 . In some embodiments, an ARC and a passivation layer (not shown) can be disposed over the insulating material  624 . Thus a substantially flat and even surface is obtained on the back side  602 B of the substrate  602 . 
     In operation  508 , an insulating structure  640  including a grid structure is formed over the back side  602 B of the substrate  602 , as shown in  FIG.  7 G . In some embodiments, the insulating structure  640  can include materials with a refractive index less than the refractive index of the color filters to be formed or less than a refractive index of Si, but the disclosure is not limited to this. 
     In operation  510 , a plurality of color filters  650  are disposed within the grid of the insulating structure  640 . Thus the insulating structure  640  surrounds each color filter  650 , and separates the color filters  650  from each other as shown in  FIG.  7 H . Further, the conductive structures  626  are disposed between the insulating structures  624  and the insulating structure  640 , as shown in  FIG.  7 H . In some embodiments, a plurality of micro-lenses  660  corresponding to each pixel sensor  610  is disposed over the color filters  650 . It should be easily understood that locations and areas of each micro-lens  660  correspond to those of the color filter  650  or those of the pixel sensor  610  as shown in  FIG.  7 H . 
     Accordingly, the present disclosure therefore provides a BSI image sensor including at least a hybrid isolation disposed in the substrate. The hybrid isolation includes at least a conductive structure and a dielectric layer. In some embodiments, the hybrid isolation includes an insulating structure under the conductive structure. Further, the insulating structures and/or the dielectric layers form an isolation grid providing electrical isolation between neighboring pixel sensors, while the conductive structures form a reflective grid providing optical isolation between neighboring photodiodes. And a low-n structure or another hybrid isolation providing optical isolation between neighboring color filters can be formed over the substrate on the back side. Accordingly, cross-talk between neighboring pixel sensors and signal-to-noise ratio (SNR) are reduced. Further, quantum efficiency and angular response are improved. Consequently, the sensitivity of the BSI image sensor is improved. 
     In some embodiments, a BSI image sensor is provided. The BSI image sensor includes a substrate including a front side and a back side opposite to the front side, a plurality of pixel sensors, an isolation grid disposed in the substrate and separating the plurality of pixel sensors from each other, a reflective grid disposed over the isolation grid on the back side of the substrate, an a low-n grid disposed over the back side of the substrate and overlapping the reflective grid from a top view. In some embodiments, a width of the low-n grid is greater than a width of the reflective grid. 
     In some embodiments, a BSI image sensor is provided. The BSI image sensor includes a substrate, a pixel sensor, and a hybrid isolation surrounding the pixel sensor in the substrate. The hybrid isolation includes a conductive structure and a first insulating structure disposed in the substrate. In some embodiments, a thickness of the conductive structure is greater than a thickness of the first insulating structure. 
     In some embodiments, a BSI image sensor is provided. The BSI image sensor includes a substrate including a front side and a back side opposite to the front side, a pixel sensor, a color filter corresponding to the pixel sensor and disposed over the substrate on the back side, a first insulating structure disposed in the substrate and surrounding the pixel sensor, a first conductive structure disposed in the substrate and over the first insulating structure on the back side of the substrate and surrounding the pixel sensor, a second insulating structure surrounding the color filter on the back side of the substrate, and a second conductive structure surrounding the color filter on the back side of the substrate. In some embodiments, the first conductive structure and the second conductive structure are between the first insulating structure and the second insulating layer. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein.