Patent Publication Number: US-10763289-B2

Title: Light blocking layer for image sensor device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. Non-Provisional patent application Ser. No. 15/966,885, filed on Apr. 30, 2018 and titled “Light Blocking Layer for Image Sensor Device,” which claims the benefit of U.S. Provisional Patent Application No. 62/586,294, filed on Nov. 15, 2017 and titled “Light Blocking Layer for Image Sensor Device.” The entire contents of both applications are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Semiconductor image sensors are used to sense visible or non-visible radiation; such as, for example, visible light, infrared light, etc. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors are used in various applications such as digital still cameras, mobile phones, tablets, goggles, etc. Arrays of pixels featured in CMOS and CIS devices can sense incoming radiation that is projected toward the sensor and convert it into electrical signals. 
    
    
     
       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 common practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features can be arbitrarily increased or reduced for clarity of illustration and discussion. 
         FIG. 1  is a flow chart of a method for forming an image sensor device, according to some embodiments of the present disclosure. 
         FIG. 2  is cross-sectional view of a back side illuminated image sensor device, according to some embodiments of the present disclosure. 
         FIG. 3  is a top view of a composite grid structure configured to receive color filters, according to some embodiments of the present disclosure. 
         FIG. 4  is a cross-sectional view of magnified top portion of a back side illuminated image sensor device, according to some embodiments of the present disclosure. 
         FIG. 5  is cross-sectional view of a back side illuminated image sensor device after the deposition of a light blocking material layer, according to some embodiments of the present disclosure. 
         FIG. 6  is a cross-sectional view of magnified top portion of a back side illuminated image sensor device after the deposition of a light blocking material layer, according to some embodiments of the present disclosure. 
         FIG. 7  is a cross-sectional view of magnified top portion of a back side illuminated image sensor device after etching a light blocking material layer, according to some embodiments of the present disclosure. 
         FIG. 8  is a cross-sectional view of a back side illuminated image sensor device after etching a light blocking material layer, according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components 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 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 are disposed between the first and second features, such that the first and second features are not in direct contact. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” 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. 
     The term “about” as used herein indicates the value of a given quantity that can vary based on a particular technology node associated with the subject semiconductor device. Based on the particular technology node, the term “about” can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value). 
     As used herein, the term “substantially” indicates that the value of a given quantity varies by ±1% to ±5% of the value. 
     In a back side illuminated image sensor device, color filters and micro-lenses are positioned on the back side of a substrate (e.g., on an opposite side of the substrate&#39;s circuitry), so that the image sensor device can collect light with minimal or no obstructions. As a result, back side illuminated image sensor devices are configured to detect light from the back side of the substrate, rather than from a front side of the substrate where the color filters and micro-lenses of the image sensor device are positioned between the substrate&#39;s circuitry and the pixels. Compared to front side illuminated image sensor devices, back side illuminated image sensor devices have improved performance under low light conditions and higher quantum efficiency (QE) (e.g., photon to electron conversion percentage). 
     Image sensor devices use color filters to capture color information from incident light rays. For example, the image sensor devices through the use of color filters can detect the red, green, and blue (RGB) regions of the visible light spectrum. A composite grid structure, which can be filled with color filter material, can be used to position the color filter material above pixels of the image sensor device. The composite grid structure can include, for example, an oxide or any other dielectric material that is transparent to visible light. 
     During normal operation, incoming natural light enters the color filter of the image sensor device from different directions. For example, incoming light rays can have incident angles that range from normal (e.g., 90°) to about 0° (grazing angles) with respect to a horizontal top surface of the color filter. “Stray” light rays, which impinge the color filter at grazing incident angles between about 0° and about 45°, artificially amplify the amount of light collected by the color filter and result in an artificial increase of the pixel&#39;s QE. This artificial increase of the pixel&#39;s QE from stray light rays is referred to as “crosstalk” and is an undesired phenomenon. The composite grid structure, which contains the color filter, is transparent to visible light and cannot be used to block stray light rays. 
     Various embodiments in accordance with the present disclosure provide a method to form a light blocking material layer (or structure) that can prevent light rays from entering the color filter at grazing incident angles. Light rays that enter the color filter at grazing incident angles can also be referred to as “stray” light rays. In some embodiments of the present disclosure, the light blocking material layer can reflect the incoming light. Alternatively, the light blocking material layer can absorb the incoming light. In some embodiments of the present disclosure, the light blocking material layer is formed using a self-aligned process so that the light blocking material layer is selectively formed in areas where light rays with grazing incident angles may enter the color filter. Such areas can be, for example, areas of the composite grid structure between the micro-lenses. In some embodiments of the present disclosure, the light blocking material layer is a metal—such as tungsten, aluminum, or copper—or a metal alloy. In other embodiments of the present disclosure, the light blocking material layer can be a dielectric such as silicon oxide, silicon oxy-nitride, or silicon carbide. Alternatively, the light blocking material layer can include an infrared (IR) color filter material that can absorb the visible light and allow IR to pass through. According to some embodiments of the present disclosure, the light blocking material layer enhances the light-guiding capability of the composite grid structure. 
     According to some embodiments of the present disclosure,  FIG. 1  describes a method  100  for forming a light block layer that can block stray light rays from entering the color filters of an image sensor device. The formation of the light blocking layer can therefore prevent or minimize “crosstalk” in the image sensor device (e.g., a back side illuminated image sensor device). For example purposes, method  100  will be described in the context of a back side illuminated image sensor device, Method  100  however, may not limited to back side illuminated image sensor devices and can be applied to other types of image sensor devices, (e.g., front side illuminated image sensor devices) that share similar material layers and/or geometries. These other types of image sensor devices are within the spirit and scope of the present disclosure. 
     Referring to  FIG. 1 , method  100  begins with operation  102 , where a light blocking material layer is deposited over a transparent material layer which forms micro-lenses on a composite grid structure of an image sensor device.  FIG. 2  is a simplified cross-sectional view of a back side illuminated image sensor device  200 , according to some embodiments of the present disclosure. Back side illuminated image sensor device  200  includes a semiconductor layer  202  with radiation-sensing areas  204 . By way of example and not limitation, semiconductor layer  202  includes a silicon material doped with a p-type dopant, such as boron. Alternatively, semiconductor layer  202  can include silicon that is doped with an n-type dopant, such as phosphorous or arsenic. Semiconductor layer  202  can also include other elementary semiconductors, such as germanium or diamond. Semiconductor layer  202  can optionally include a compound semiconductor and/or an alloy semiconductor. Further, semiconductor layer  202  can include an epitaxial layer, which may be strained for performance enhancement. Semiconductor layer  202  can include a silicon-on-insulator (SOI) structure. 
     The semiconductor layer  202  has a front side (also referred to as a bottom surface)  206  and a back side (also referred to as a top surface)  208 . The semiconductor layer  202  has a thickness that can range from about 100 μm to about 3000 μm. 
     Radiation-sensing regions or pixels  204  are formed in the semiconductor layer  202 . As disclosed herein, the terms “radiation-sensing regions” and “pixels” may be used interchangeably. Pixels  204  are configured to sense radiation, such as incident light rays impinging semiconductor layer  202  from back side  208 . Each of the radiation-sensing regions or pixels  204  can include a photodiode that can convert photons to electric charge, according to some embodiments of the present disclosure. In some embodiments of the present disclosure, pixels  204  can include photodiodes, transistors, amplifiers, other similar devices, or combinations thereof. Pixels  204  may also be referred to herein as “radiation-detection devices” or “light-sensors.” 
     For simplicity, two pixels  204  are illustrated in  FIG. 2 , but additional pixels  204  can be implemented in semiconductor layer  202 . By way of example and not limitation, pixels  204  can be formed using an ion implant process on semiconductor layer  202  from front side  206 . Pixels  204  can also be formed by a dopant diffusion process. 
     Pixels  204  are electrically isolated from each other with shallow trench isolation (STI) structures  210  and deep trench isolation (DTI) structures  211  STI structures  210  and DTI structure  211  are trenches etched into semiconductor layer  202  and filled with a dielectric material, such as silicon oxide, silicon nitride, silicon oxynitride, fluorine-doped silicate glass (FSG), a low-k dielectric material (e.g., a material with a k value lower than  3 . 9 ), and/or a suitable insulating material. According to some embodiments of the present disclosure, DTI structures  211  on back side  208  of semiconductor layer  202  have an anti-reflective coating (ARC)  212 . ARC  212  is a liner layer that can prevent incoming light rays from being reflected away from radiation-sensing areas/pixels  204 . ARC  212  can include a high-k material (e.g., a material with a k-value higher than 3.9), such as hafnium oxide (HfO 2 ), tantalum pentoxide (Ta 2 O 5 ), zirconium dioxide (ZrO 2 ), aluminum oxide (Al 2 O 3 ), or any other high-k material. ARC  212  can be deposited using sputtering, a chemical vapor deposition (CVD)-based process, an atomic layer deposition (ALD)-based process, or any other suitable deposition process or method. In some embodiments of the present disclosure, the thickness of ARC  212  can range from about 10 Å to about 500 Å. 
     Back side illuminated image sensor device  200  also includes a capping layer  214  formed over the semiconductor layer  202 , such as over the ARC  212 , as illustrated in  FIG. 2 . In some embodiments of the present disclosure, capping layer  214  can provide a planar surface on which additional layers of back side illuminated image sensor device  200  can be formed. Capping layer  214  can include a dielectric material, such as silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), silicon oxy-nitride (SiON), or any other suitable dielectric material. Further, capping layer  214  can be deposited using CVD or any other suitable deposition technique. In some embodiments of the present disclosure, the thickness of capping layer  214  can range between about 500 Å and about 2000 Å. 
     Further, back side illuminated image sensor device  200  includes a composite grid structure  216  formed over capping layer  214 . According to sonic embodiments of the present disclosure, composite grid structure  216  includes cells  218  arranged in columns and rows, where each cell  218  is aligned to a respective radiation-sensing area  204 . As mentioned above, cells  218  can receive a red, green, or blue color filter  220 . 
       FIG. 3  is a top view of composite grid structure  216 , according to some embodiments of the present disclosure. Each cell  218  of composite grid structure  216  includes (e.g., is filled with) color filter  220 . By way of example, a red, a green, or a blue color filter can occupy more than one cell  218 . For example, in  FIG. 3 , four cells (e.g., adjacent cells)  218  include (e.g., are filled with) the same color filter  220 . For example in  FIG. 3 , four cells  218  are filled with a black shading, four cells  218  are filled with a gray shading, and four cells  218  are filled with a hashed shading, etc.; where each shading can correspond to a different color filter  220 . The number of cells  218  that include the same color filter  220 , as depicted in  FIG. 3 , is exemplary and not limiting. Therefore, the group of cells  218  that include the same color filter  220  can be larger or smaller (e.g., two, six, etc.). 
     Referring to  FIG. 2 , cells  218  of composite grid structure  216  can be formed by depositing a bottom layer  222  and a top dielectric layer  224  and selectively etching away portions of the metal layer and dielectric layer to form cells  218 . By way of example and not limitation, composite grid structure  216  can be formed as follows: bottom layer  222  and top dielectric layer  224  can be blanket deposited on capping layer  214 . One or more photolithography and etch operations can be used to pattern bottom layer  222  and top dielectric layer  224  to form the sidewalls of cells  218 . The photolithography and etch operations can be performed so that each cell  218  of composite grid structure  216  is aligned to respective pixels  204  of semiconductor layer  202 . In some embodiments, the sidewall height of each cell  188  of composite grid structure  216  can range from about 200 nm to about 1000 nm. 
     Bottom layer  222  of cell  218  can include titanium, tungsten, aluminum, or copper. However, bottom layer  222  of cells  218  may not be limited to metals, and can include other suitable materials or stack of materials that can reflect and guide incoming visible light towards radiation-sensing areas  204 . In some embodiments of the present disclosure, bottom layer  222  of cells  218  is formed using a sputtering process, a plating process, an evaporation process, or any other suitable deposition method. According to some embodiments of the present disclosure, the thickness of bottom layer  222  of each cell  218  can range from about 100 Å to about 3000 Å. 
     Top dielectric layer  224  can include one or more dielectric layers. In some embodiments of the present disclosure, top dielectric layer  224  can protect previously formed layers of back side illuminated image sensor device  200  (e.g., bottom layer  222  and capping layer  214 ). Top dielectric layer  224  can allow incoming light to pass through and reach radiation-sensitive areas (or pixels)  204 , Top dielectric layer  224  can include a transparent material or materials. In some embodiments of the present disclosure, top dielectric layer  224  can include SiO 2 , Si 3 N 4 , SiON, or any other suitable transparent dielectric material. Top dielectric layer  224  can be deposited by CND or ALI) and can have a deposited thickness range from about 1000 Å to about 3000 Å, according to some embodiments of the present disclosure. 
     Cells  218  can also include a passivation layer  226 , which is interposed between color filter  220  and the sidewalls of cells  218  (e.g., bottom layer  222  and top dielectric layer  224 ). In some embodiments of the present disclosure, passivation layer  226  can be conformally deposited by a CVD-based or an ALD-based deposition technique at a thickness range between about 50 Å and about 3000 Å. Passivation layer  226  can be formed from a dielectric material, such as SiO 2 , Si 3 N 4 , or SION. 
     According to some embodiments of the present disclosure, the top surface of color filters  220  can be aligned to the top surface of passivation layer  226  on top dielectric layer  224 . Alternatively, color filters  220  can be formed above the top surface of passivation layer  226  on top dielectric layer  224 . For example and explanation purposes, the top surface of color filters  220  will be described as being aligned to the top surface of passivation layer  226  on top dielectric layer  224 . 
     Referring to  FIG. 2 , after cells  218  of composite grid structure  216  receive their respective color filters  220 , a transparent material layer  228  can be formed over composite grid structure  216  and color filters  220 . Transparent material layer  228  can be in contact with passivation layer  226  if the top surface of color filters  220  is aligned to the top surface of passivation layer  226  over top dielectric layer  224 . Alternatively, transparent material layer  228  may not be in contact with passivation layer  226  if the top surface of color filters  220  is above the top surface of passivation layer  226  over top dielectric layer  224 . .in some examples, transparent material layer  228  forms a micro-lens  230  over each cell  218  of composite grid structure  216 . Micro-lenses  230  are aligned with respective radiation-sensing areas  204  and are formed so they cover the top surface of color filters  220  within the boundaries of cell  218  (e.g., within the sidewalis of each cell  218 ). 
     Micro-lenses  230 , due to their curvature, are thicker than other areas of transparent material layer  228  (e.g., areas between micro-lenses  230  above top dielectric layer  224 ). For example, transparent material layer  228  is thicker over color filter  220  (e.g., where micro-lens  230  is formed) and thinner in areas between micro-lenses  230  (e.g., above top dielectric layer  224 ). Referring to  FIG. 4 , which is a magnified view of a top portion of back side illuminated image sensor device  200  of  FIG. 2 , transparent material layer  228  is thicker over color filter  220  (e.g., where micro-lens  230  is formed) and thinner in areas between micro-lenses  230  (e.g., over top dielectric layer  224 ). Transparent material layer  228  has a thickness T 1  at micro-lenses  230  region over color filter  220 , and a thickness T 2  between adjacent micro-lenses  230  over top dielectric layer  224 . 
     Referring to  FIG. 2 , back side illuminated image sensor device  200  can also include an interconnect structure  232 . Interconnect structure  232  can include a plurality of patterned dielectric layers and conductive layers that form interconnects (e.g., wiring) between pixels  204  and other components not shown in  FIG. 1  of back side illuminated image sensor device  200 . The interconnect structure  232  may, for example be, one or more multilayer interconnect (MLI) structures  234  embedded in an interlayer dielectric (ILD) layer  236 . According to some embodiments of the present disclosure, MLI structures  234  can include contacts/vias and metal lines. For purposes of illustration, a plurality of conductive lines  238  and vias/contacts  240  are shown in  FIG. 2 . The position and configuration of conductive lines  238  and vias/contacts  240  can vary depending on design needs and is not limited to the depiction of  FIG. 2 . Further, interconnect structure  232  can include sensing devices  242 . Sensing devices  242  can be, for example, an array of field effect transistors (FETs) and/or memory cells that are electrically connected to respective radiation-sensing areas (or pixels)  204  and configured to read the electrical signal produced in those areas as a result of a light-to-charge conversion process. 
     In some embodiments of the present disclosure, interconnect structure  232  can be a top layer of a partially-fabricated integrated circuit (IC) or of a fully-fabricated IC that can include multiple layers of interconnects, resistors, transistors, or other semiconductor devices. Furthermore, interconnect structure  232  can be attached via a buffer layer (not shown in  FIG. 2 ) to a carrier substrate (not shown in  FIG. 1 ) that can provide support to the structures fabricated thereon (e.g., interconnect structure  232 , semiconductor layer  202 , etc.). The carrier substrate can be, for example, a silicon wafer, a glass substrate, or any other suitable material. 
     In some embodiments of the present disclosure, a method to fabricate back side illuminated image sensor device  200  can include forming semiconductor layer  202  on a silicon substrate (e.g., silicon wafer) and subsequently forming interconnect structure  232  over front side  206  of semiconductor layer  202 . Interconnect structure  232  can undergo multiple photolithography, etch, deposition, and planarization operations before it is completed. Once interconnect structure  232  is formed, a carrier substrate, as discussed above, can be attached to the top of interconnect structure  232 . For example, a buffer layer can act as an adhesion medium between the carrier substrate and interconnect structure  232 . The silicon substrate can be turned upside down, and the silicon substrate can be mechanically grinded and polished until back side  208  of semiconductor layer  202  is exposed. DTI structures  211  on back side  208  of semiconductor layer  202  can be subsequently formed to further electrically isolate radiation-sensing areas or pixels  204 , according to some embodiments. Capping layer  214 , along with the composite grid structure  216 , can be formed on back side  208  of semiconductor layer  202 . 
     Composite grid structure  216  can be formed so that each of its cells  218  is aligned to respective radiation-sensing areas or pixels  204 . Alignment of composite grid structure  216  and radiation-sensing areas, or pixels  204  can be achieved with photolithographic operations based on, for example, alignment marks present on back side  208  of semiconductor layer  202 . The formation of composite grid structure  216  can include the deposition and subsequent patterning of bottom layer  222  and top dielectric layer  224  using photolithography and etch operations to form cells  218 . Passivation layer  226  is subsequently deposited over the exposed surfaces of bottom layer  222  and top dielectric layer  224 . Color filters  220  can fill cells  218 , and transparent material layer  228  can be deposited thereon to form micro-lenses  230 . Fabrication of back side illuminated image sensor device  200  is not limited to the operations described above and additional or alternative operations can be performed. 
     In referring to  FIG. 2 , transparent material layer  228  of back side illuminated image sensor device  200  can be the transparent material layer described in operation  102 ; and the composite grid structure  216  of back side illuminated image sensor device  200  can be the composite grid structure of operation  102 . As discussed above, transparent material layer  228  can form micro-lenses  230  that are aligned to respective color filters  220  of back side illuminated image sensor device  200 , In some embodiments of the present disclosure, micro-lenses  230  are designed to focus and guide incoming light rays through color filters  220  to respective pixel, or radiation-sensitive areas,  204 . 
       FIG. 5  shows back side illuminated image sensor device  200  after the deposition of a. light blocking material layer  500  according to operation  102 . According to some embodiments of the present disclosure, light blocking material layer  500  is blanket deposited on transparent material layer  228 , In some embodiments of the present disclosure, light blocking material layer  500  covers the entire surface of transparent material layer  228  including areas where micro-lenses  230  are formed and areas therebetween (e.g., over top dielectric layer  224  of composite grid structure  216  between cells  218 ). Additionally, light blocking material layer  500  can include an infrared oR) color filter material that can absorb visible light. According to some embodiments of the present disclosure, light blocking material layer  500  can include a dielectric, such as silicon nitride, silicon oxy-nitride, silicon carbide, or any other suitable material. Alternatively, light blocking material layer  500  can include a reflective material, such as tungsten, copper, aluminum, a metal alloy, or any other suitable material. 
     Deposition of light blocking material layer  500  can be performed by a physical vapor deposition (PVD), CVD, ALD, plasma-assisted CVD, plasma-assisted ALD, evaporation, focused ion beam induced deposition, electron-beam assisted deposition, a spin-coating process, or any other suitable deposition technique. In some embodiments of the present disclosure, after the deposition of light blocking material layer  500 , an optional chemical mechanical planarization (CMP) process can be used to planarize and smoothen the top surface of light blocking material layer  500 . 
     Referring to  FIG. 6 , which is a magnified top portion of  FIG. 5 , the as-deposited (or planarized) light blocking material layer  500  has a thickness T 3  that is larger than the thickness T 4  of micro-lens  230  above the level of transparent material layer  228 . If T 3  is less than T 4  (e.g., T 3 &lt;T 4 ), the CMP process cannot adequately planarize the surface of light blocking material layer  500  without damaging micro-lens  230 , and/or a subsequent etch step will not be able to recess light blocking material layer  500  in a desired manner. In some embodiments, the ratio of T 3  to T 4  is equal to or greater than one (e.g., T 3 /T 4 &gt;1) 
     In referring to  FIG. 1  and operation  104 , an etch operation is used to recess/remove light blocking material layer  500  from a portion of the top surface of micro-lenses  230 . The etch operation can be terminated when the etched/recessed blocking material layer  500  is limited to portions of transparent material layer  228  between micro-lenses  230 .  FIG. 7  shows the recessed blocking material layer  500  on transparent material layer  228  after the etch process of operation  104 . According to some embodiments of the present disclosure, the resulting recessed thickness T 5  of light blocking material layer  500  can range from about 5% to about 50% of thickness T 1  of micro-lens  230 . In other words, the thickness ratio between T 5  and T 1  can range from about 0.05 to about 0.5 (e.g., 0.05&lt;T 5 /T 1 &lt;0.5). If the T 5 /T 1  ratio is less than 0.05, blocking material layer  500  will not effectively block light rays entering micro-lenses  230  at grazing angles (e.g., between 0° and about 45°). On the other hand, if the T 5 /T 1  ratio is greater than 0.5, blocking material layer  500  will block light rays entering micro-lenses  230  at angles larger than about 45°, which will result in fewer light rays entering the sensor device. According to some embodiments of the present disclosure, the thickness ratio T 5 /T 1  is determined based on the thickness T 1  of micro-lens  230  and the type of material for light blocking material layer  500 . For example, light blocking material layer  500  can be made from a dielectric (e.g., silicon nitride, silicon oxy-nitride, silicon carbide, or any other suitable material) and can have a different recessed thickness T 5  from light blocking material layer  500  being made from a metal (e.g., tungsten, copper, aluminum, or any other suitable material) or from light blocking material layer  500  being made from a light absorbing material that includes an IR color filter. Alternatively, in some embodiments of the present disclosure, the selection of light blocking material layer  500  can be made based on geometrical characteristics of back side illuminated image sensor device  200 , such as the thickness T 4  of micro-lens  130  and the desired recessed thickness T 5  of light blocking material layer  500 . 
     According to some embodiments of the present disclosure, the etch process is an anisotropic etch. For example, an etch process that is directional with a high etch rate towards a single direction. Further, the etch process has a high selectivity towards light blocking material layer  500 . For example, the etch selectivity ratio between light blocking material layer  500  and transparent material layer  228  can be more than 5:1 (e.g., 10:1). The etch process can be a dry etch or a wet etch with appropriate selectivity (e.g., more than 5:1). Additionally, the etch process can be timed for example, the etch process can be terminated after a predetermined amount of time based on the as-deposited thickness T 3  (shown in  FIG. 6 ) and the type of light blocking material layer  500 . 
     As described above, method  100  does not include operations that do not require a photolithography mask or photolithography operations to form light blocking material layer  500  between micro-lenses  230 . For example, the recessed light blocking material layer  500  can be self-aligned to portions of transparent material layer  228  between micro-lenses  230 . Therefore, the recessed thickness T 4  can be adjusted depending on (i) the type of material of light blocking material layer  500  and (ii) the thickness T 1  of micro-lenses  230 . 
       FIG. 8  is a cross-sectional view of back side illuminated image sensor device  200  after etching light blocking mated al layer  500 , according to some embodiments of the present disclosure. For example, light ray  800 —which is incoming to back side illuminated image sensor device  200  at a grazing angle θ—is reflected from light blocking material layer  500 , according to some embodiments of the present disclosure. In some embodiments of the present disclosure, incoming ray  800  is absorbed by light blocking material layer  500 . Contrary to light ray  800 , light ray  802 —which is incoming at a normal angle to back side illuminated image sensor device  200 —is allowed to enter color filter  220 . Therefore, light blocking material layer  500  can mitigate crosstalk from light rays incoming at grazing incident angles. 
     The present disclosure is directed to an exemplary fabrication method that can be used to form a self-aligned light blocking material layer on a back side illuminated image sensor device. The light blocking material layer can block or absorb light rays incoming to the back side illuminated image sensor device at grazing incident angles. In some embodiments of the present disclosure, the light blocking material layer can be formed using a self-aligned process that does not require the use of a photolithography mask or photolithography operations. For example, the light blocking material layer can be formed over an image sensor device and subsequently etched so that the light blocking material layer remains in areas where light rays incoming at grazing incident angles enter the color filter. In other words, the etch process takes advantage of the local topography of the micro-lenses to form a self-aligned light blocking layer on the areas between adjacent micro-lenses. Such areas can be, for example, areas of the composite grid structure between the micro-lenses (between cells  218  of  FIG. 2 ). In some embodiments of the present disclosure, the light blocking material layer can be a metal—such as, tungsten, aluminum, or copper—or a metal alloy. In other embodiments of the present disclosure, the light blocking material layer can be a dielectric, such as silicon oxide, silicon oxy-nitride, or silicon carbide. Alternatively, the light blocking material layer can include an IR color filter material that allows IR to pass through. An  1 R color filter material can be, for example, a polymer. As a result, the light blocking material layer can enhance the back side illuminated image sensor device&#39;s light-guiding capability. 
     In some embodiments of the present disclosure, an image sensor includes a semiconductor layer with a top surface and a bottom surface, where the semiconductor layer includes one or more sensing regions configured to sense radiation that enters the semiconductor layer from the top surface. The image sensor further includes a grid structure with one or more cells respectively aligned to the one or more sensing regions; a transparent material layer disposed over the grid structure, where the transparent material layer forms a micro-lens over each of the one or more cells; and a light blocking material layer disposed on the transparent material layer between the micro-lenses. 
     In some embodiments of the present disclosure, a semiconductor image sensor includes a grid structure with one or more cells disposed over a semiconductor layer configured to sense radiation received by the grid structure, where the semiconductor layer is disposed on a multilayer interconnect structure. The semiconductor image sensor further includes a color filter in each of the one or more cells, micro-lenses formed over the one or more cells of the grid structure, and a light blocking layer disposed between the micro-lenses. Further, the light blocking layer is thinner than the micro-lenses. 
     In some embodiments of the present disclosure, a method to manufacture a semiconductor image sensor includes forming a semiconductor layer over a multilayer interconnect structure, where the semiconductor layer includes one or more sensing regions configured to sense radiation received by the semiconductor layer. The method further includes forming, on the semiconductor layer, a grid structure with one or more cells respectively aligned to the one or more sensing regions, disposing a transparent layer over the grid structure to form a micro-lens that is aligned with each of the one or more cells, and forming a light blocking layer between adjacent micro-lenses. Further, forming the light blocking layer includes depositing the light blocking layer over the transparent layer and etching the light blocking layer to remove the light blocking layer over the micro-lens. 
     It is to be appreciated that the Detailed Description section, and not the Abstract of the Disclosure, is intended to be used to interpret the claims. The Abstract of the Disclosure section may set forth one or more but not all exemplary embodiments contemplated and thus, are not intended to be limiting to the subjoined claims. 
     The foregoing disclosure 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 will 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 will 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 without departing from the spirit and scope of the subjoined claims.