Patent Publication Number: US-2022238585-A1

Title: Polarizers For Image Sensor Devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/907,788, titled “Polarizers for Image Sensor Devices,” filed Jun. 22, 2020, which is a continuation of U.S. patent application Ser. No. 16/521,181, titled “Polarizers for Image Sensor Devices,” filed on Jul. 24, 2019, which is a continuation of U.S. patent application Ser. No. 15/964,288, titled “Polarizers for Image Sensor Devices,” filed on Apr. 27, 2018, which claims the benefit of U.S. Provisional Patent Application No. 62/586,277, titled “Polarizers for Image Sensor Devices,” filed on Nov. 15, 2017, each of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Semiconductor image sensors are used to sense radiation, such as light. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors are used in various applications such as digital still camera or mobile phone camera applications. These devices utilize an array of pixels (which can include photodiodes, transistors, and other components) in a substrate to absorb (e.g., sense) radiation that is projected toward the substrate and convert the sensed radiation into electrical signals. A back side illuminated image sensor device is one type of image sensor device that can detect light from the back side. 
    
    
     
       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 may be arbitrarily increased or reduced for clarity of illustration and discussion. 
         FIG. 1  is a cross-sectional view of a backside illuminated image sensor device, according to some embodiments. 
         FIG. 2  is a top view of a composite grid structure with color filters, according to some embodiments. 
         FIG. 3  is a flow chart of a method for forming a polarization grating structure in a composite grid structure of a backside illuminated image sensor device, according to some embodiments. 
         FIGS. 4-6  are cross-sectional views of a partially fabricated backside illuminated image sensor device during formation of a polarization grating structure, according to some embodiments, 
         FIGS. 7A-D  are top views of polarization grating structures with grating elements oriented in different polarization angles, according to some embodiments. 
         FIG. 8  is a cross-sectional view of a partially fabricated backside illuminated image sensor device after deposition of a passivation layer, according to some embodiments. 
         FIG. 9  is a cross-sectional view of a backside illuminated image sensor device with a polarization grating structure, according to some embodiment. 
         FIGS. 10-13  are top views of composite grid structures with polarization. grating structures in different arrangements, according to some embodiments. 
     
    
    
     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 “nominal” as used herein refers to a desired, or target, value of a characteristic or parameter for a component or a process operation, set during the design phase of a product or a process, together with a range of values above and/or below the desired value. The range of values can be due to slight variations in manufacturing processes or tolerances. 
     The term “substantially” as used herein indicates the value of a given quantity varies by ±5% of the value. 
     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). 
     Semiconductor image sensor devices are used to sense electromagnetic radiation, such as light (e.g., visible light). Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors can be used in various applications, such as digital still camera or mobile phone camera applications. These devices utilize an array of pixels (which can include photodiodes, transistors, and other components) in a substrate to absorb (e.g., sense) radiation that is projected toward the substrate. The absorbed radiation can be converted by the photodiodes (in the pixel) into electrical signals, such as charge or current, that can be further analyzed and/or processed by other modules of the image sensor device. 
     One type of image sensor device is a back side illuminated image sensor device. 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 photodiodes. 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 photodiodes of the image sensor device. The composite grid structure can be made in part from an oxide or another dielectric material which is transparent to visible light. 
     Further, the image sensor can also be equipped with external polarizers in order to collect polarization information from incident light. Polarization information can be used in applications such as photography and filming. However, since the polarizers are external and not integrated to the composite grid structure, a distance between the polarizers and the image sensor can be substantial—e.g., relative to the size of the back side illuminated image sensor device. This configuration can impact the final product&#39;s size and can restrict size reduction efforts. Further, in order to obtain information on different polarization conditions, the external polarizer can rotate, or spin, which can impact polarization data acquisition time. 
     Various embodiments in accordance with this disclosure provide a method to integrate one or more polarizers in a composite grid structure of a back side illuminated image sensor device. In some embodiments, the polarizers are integrated into the composite grid structure by replacing one or more color filters of the composite grid structure with a polarizing grating structure (grid polarizer) within the composite grid structure. In some examples, the polarizing grating structure can provide polarization information for incident light along the following polarization angles: 0°, 45°, 90°, and/or 135°. However, these directions are not limiting and other polarization angles are possible. According to some embodiments, the pitch between the elements (grating elements) of the polarizing grating structure can range from about 100 nanometers (nm) to about 500 nm (e.g., from 100 nm to 500 nm), and the width of each grating element can range from about 20 nm to about 300 nm (e.g., from 20 nm to 300 nm). The aforementioned ranges are optimized based on the wavelength of the incident light. In some embodiments, the grating elements of the polarizing grating structure include a same material as the composite grid structure. In some embodiments, the grating elements of the polarizing grating structure include a different material from the composite grid structure. 
       FIG. 1  is a simplified cross-sectional view of a back side illuminated image sensor device  100 , according to some embodiments of the present disclosure. Back side illuminated image sensor device  100  includes a semiconductor layer  102  with radiation-sensing areas  104 . Semiconductor layer  102  can include a silicon material doped with a p-type dopant, such as boron. Alternatively, semiconductor layer  102  can include silicon doped with an n-type dopant, such as phosphorous or arsenic. Semiconductor layer  102  can also include other elementary semiconductors, such as germanium or diamond. Semiconductor layer  102  can optionally include a compound semiconductor and/or an alloy semiconductor. Further, semiconductor layer  102  can include an epitaxial layer, which may be strained for performance enhancement. Semiconductor layer  102  can include a silicon-on-insulator (SOI) structure. 
     Semiconductor layer  102  has a front side (also referred to herein as a “bottom surface”)  106  and a back side (also referred to herein as a “top surface”)  108 . Semiconductor layer  102  has a thickness that can range from about 100 μm to about 3000 μm (e.g., from 100 μm to 3000 μm). 
     Radiation-sensing regions  104  are formed in semiconductor layer  102 . Radiation-sensing regions  104  are configured to sense radiation, such as incident light rays impinging semiconductor layer  102  from back side  108 . Each of the radiation-sensing regions or radiation-sensing regions  104  include a photodiode that can convert photons to charge, according to some embodiments of the present disclosure. In some embodiments of the present disclosure, radiation-sensing regions  104  can include photodiodes, transistors, amplifiers, other similar devices, or combinations thereof. Radiation-sensing regions  104  may also be referred to herein as “radiation-detection devices” or “light-sensors.” 
     For simplicity, two radiation-sensing regions  104  are illustrated in  FIG. 1 , but additional radiation-sensing regions  104  can be implemented in semiconductor layer  102 . By way of example and not limitation, radiation-sensing regions  104  can be formed using an ion implant process on semiconductor layer  102  from front side  106 . Radiation-sensing regions  104  can also be formed by a dopant diffusion process. 
     Radiation-sensing regions  104  are electrically isolated from each other with isolation structures  110 . Isolation structures  110  can be trenches etched into semiconductor layer  102  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, isolation structures  110  on back side  108  of semiconductor layer  102  have an anti-reflective coating (ARC)  112 . ARC  112  is a liner layer that can prevent incoming light rays from being reflected away from radiation-sensing areas/pixels  104 . ARC  112  can include a high-k material (e.g., a material with a k-value lower 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  112  can be deposited using a sputtering process, a chemical vapor deposition (CVD)-based process, an atomic layer deposition (ALD)-based techniques, or any other suitable deposition technique. In some embodiments of the present disclosure, the thickness of ARC  112  can range from about 10 Å to about 500 Å (e.g., from 10 Å to 500 Å). 
     Back side illuminated image sensor device  100  also includes a capping layer  114  formed over semiconductor layer  102 , such as over ARC  112 , as illustrated in  FIG. 1 . In some embodiments of the present disclosure, capping layer  114  can provide a planar surface on which additional layers of back side illuminated image sensor device  100  can be formed. Capping layer  114  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  114  can be deposited using CVD or any other suitable deposition technique. In some embodiments of the present disclosure, the thickness of capping layer  114  can range between about 500 Å and about 2000 Å (e.g., from 500 Å to 2000 Å). 
     Further, back side illuminated image sensor device  100  includes a composite grid structure  116  formed over capping layer  114 . According to some embodiments of the present disclosure, composite grid structure  116  includes cells  118  arranged in columns and rows, where each cell  118  is aligned to a respective radiation-sensing area  104 . As mentioned above, cells  118  can receive a red, green, or blue color filter  120 . 
       FIG. 2  is a top view of composite grid structure  116 , according to some embodiments. The arrangement of color filters  120  in composite grid structure  116  can be based on a Bayern pattern. For example, composite grid structure  116  can include 50% green color filters 25% red color filters and 25% blue color filters, where every other cell  118  of composite grid structure  116  is filled with a different color filter  120 . However, this is not limiting and neighboring cells  118  can be occupied (e.g., filled) by the same-color color filter. 
     Referring to  FIG. 1 , cells  118  of composite grid structure  116  can be formed by depositing a bottom layer  122  and a top dielectric layer  124  and selectively etching away portions of the bottom layer and top dielectric layer to form cells  118 . By way of example and not limitation, composite grid structure  116  can be formed as follows: bottom layer  122  and top dielectric layer  124  can be blanket deposited on capping layer  114 ; and one or more photolithography and etch operations can be used to pattern bottom layer  122  and top dielectric layer  124  to form the sidewalls of cells  118 . The photolithography and etch operations can be performed so that each cell  118  of composite grid structure  116  is aligned to respective radiation-sensing regions  104  of semiconductor layer  102 . In some embodiments, the sidewall height of each cell  118  of composite grid structure  116  can range from about 200 nm to about 1000 nm (e.g., from 200 nm to 1000 nm). 
     Bottom layer  122  of cell  118  can be made of titanium, tungsten, aluminum, or copper. However, bottom layer  122  of cells  118  may not be limited to metals and may include other suitable materials or stack of materials that can reflect and guide incoming visible light towards radiation-sensing areas  104 . In some embodiments of the present disclosure, bottom layer  122  of cells  118  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  122  of each cell  118  can range from about 100 Å to about 3000 Å (e.g., from 100 Å to 3000 Å). 
     Top dielectric layer  124  can include one or more dielectric layers, In some embodiments, top dielectric layer  124  can protect previously-formed layers of back side illuminated image sensor device  100  (e.g., bottom layer  122  and capping layer  114 ). Top dielectric layer  124  can allow incoming light to pass through and reach radiation-sensitive areas  104 . Top dielectric layer  124  can be made of a transparent material or materials. In some embodiments of the present disclosure, top dielectric layer  124  can include SiO 2 , Si 3 N 4 , SiON, or any other suitable transparent dielectric material. Top dielectric layer  124  can be deposited by CVD or ALD and can have a deposited thickness range from about 1000 Å to about 3000 Å (e.g., from 1000 Å to 3000 Å), according to some embodiments. In some embodiments, composite grid structure  116  includes more than two layers, such as a first layer of tungsten, a second layer of plasma-enhanced oxide (PEOX) over the first layer, and a third layer of silicon oxynitride over the second layer. 
     Cells  118  also include a passivation layer  126 , which is interposed between color filter  120  and the sidewalk materials of cells  118  (e.g., bottom layer  122  and top dielectric layer  124 ), By way of example and not limitation, passivation layer  126  can be conformally deposited by a CVD-based or an ALD-based deposition technique. Passivation layer  126  can be formed from a dielectric material, such as SiO 2 , Si 3 N 4 , or SiON, and can have a thickness between about 50 Å to about 3000 Å (e.g., from 50 Å to 3000 Å). 
     According to some embodiments, the top surface of color filters  120  can be aligned to the top surface of passivation layer  126  on top dielectric layer  124 . Alternatively, color filters  120  can be over the top surface of passivation layer  126  on top dielectric layer  124 . For example and explanation purposes, the top surface of color filters  120  will be described as being aligned to the top surface of passivation layer  126  on top dielectric layer  124 . 
     After cells  118  of composite grid structure  116  receive their respective color filters  120 , a transparent material layer  128  can be formed over composite grid structure  116  and color filters  120 . Transparent material layer  128  can be in contact with passivation layer  126  if the top surface of color filters  120  is aligned to the top surface of passivation layer  126  over top dielectric layer  124 , according to some embodiments. Alternatively, in some embodiments, transparent material layer  128  may not be in contact with passivation layer  126  if the top surface of color filters  120  is above the top surface of passivation layer  126  over top dielectric layer  124 . In some examples, transparent material layer  128  forms a micro-lens  130  over each cell  118  of composite grid structure  116 . Micro-lenses  130  are aligned with respective radiation-sensing areas  104  and are formed so they cover the top surface of color filters  120  within the boundaries of cell  118  (e.g., within the sidewalk of each cell  118 ). 
     Micro-lenses  130 , due to their curvature, are thicker than other areas of transparent material layer  128  (e.g., areas between micro-lenses  130  above top dielectric layer  124 ). For example, transparent material layer  128  is thicker over color filter  120  (e.g., where micro-lens  130  are formed) and thinner in areas between micro-lenses  130  (e.g., above top dielectric layer  124 ) 
     Referring to  FIG. 1 , back side illuminated image sensor device  100  can also include an interconnect structure  132 . Interconnect structure  132  can include patterned dielectric layers and conductive layers that form interconnects (e.g., wiring) between radiation-sensing regions  104  and other components (not shown in  FIG. 1 ). Interconnect structure  132  may be, for example, one or more multilayer interconnect (MLI) structures  134  embedded in an interlayer dielectric (ILD) layer  136 . According to some embodiments of the present disclosure, MLI structures  134  can include contacts/vias and metal lines. For purposes of illustration, multiple conductive lines  138  and vias/contacts  140  are shown in  FIG. 1 . The position and configuration of conductive lines  138  and vias/contacts  140  can vary depending on design and are not limited to the depiction of  FIG. 1 . Further, interconnect structure  132  can include sensing devices  142 . Sensing devices  142  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)  104  and configured to read an 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  132  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, and/or other semiconductor devices. As a result, interconnect structure  132  can include front end of the line (FEOL) and middle of the line (MOL) layers. Furthermore, interconnect structure  132  can be attached via a buffer layer (not shown in  FIG. 1 ) to a carrier substrate (not shown in  FIG. 1 ) that can provide support to the structures fabricated thereon (e.g., interconnect layer  132 , semiconductor layer  102 , 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, fabrication of back side illuminated image sensor device  100  can include forming semiconductor layer  102  on a silicon substrate (e.g., silicon wafer) and subsequently forming interconnect structure  132  over front side  106  of semiconductor layer  102 . Interconnect structure  132  can undergo multiple photolithography, etch, deposition, and planarization operations before it is completed. Once interconnect structure  132  is formed, a carrier substrate (as discussed above) can be attached to the top of interconnect structure  132 . For example, a buffer layer can act as an adhesion medium between the carrier substrate and interconnect structure  132 , The silicon substrate can be turned upside down, and the silicon substrate can be mechanically grinded and polished until back side  108  of semiconductor layer  102  is exposed. The isolation structures on back side  108  of semiconductor layer  102  can be subsequently formed to further electrically isolate radiation-sensing areas or pixels  104 . Capping layer  114 , along with the composite grid structure  116 , can be formed on back side  108  of semiconductor layer  102 . 
     Composite grid structure  116  can be formed so that each of its cells  118  is aligned to respective radiation-sensing areas or pixels  104 . Alignment of composite grid structure  116  and radiation-sensing areas, or pixels,  104  can be achieved with photolithographic operations based on, for example, alignment marks present on back side  108  of semiconductor layer  102 . The formation of composite grid structure  116  can include the deposition and subsequent patterning of bottom layer  122  and top dielectric layer  124  using photolithography and etch operations to form cells  118 . Passivation layer  126  is subsequently deposited over the exposed surfaces of bottom layer  122  and top dielectric layer  124 . Color filters  120  can fill cells  118 , and transparent material layer  128  can be deposited thereon to form micro-lenses  130 . Fabrication of back side illuminated image sensor device  100  is not limited to the operations described above and additional or alternative operations can be performed. 
     According to some embodiments,  FIG. 3  is a flow chart of a method  300  for forming one or more polarizing grating structures (grid polarizers) within the composite grid structure of an image sensor. For example purposes, method  300  will be described in the context of back side illuminated image sensor device  100  of  FIG. 1 . The polarizing grating structure can have any of the following polarization directions: 0°, 45°, 90°, or 135°. However, these directions are not limiting and other polarization directions are possible. Method  300  is not limited to back side illuminated image sensor devices and may be extended to other types of image sensor devices, such as 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. 
     According to some embodiments, method  300  can form grating elements in cells  118  of composite grid structure  116 . The grating elements can be oriented towards a polarization angle that can range from 0° to 135° at increments of 45° (e.g., 0°, 45°, 90°, and 135°). Method  300  is not limited to the operations described below. Other fabrication operations can be performed between the various operations of method  300  and are omitted merely for clarity. 
     In referring to  FIG. 3 , method  300  begins with operation  302 , where a layer stack is formed over a semiconductor layer. in some examples, the layer stack can include more than 2 layers.  FIG. 4  shows a partially fabricated image sensor, such as back side illuminated image sensor device  100  of  FIG. 1 , according to method  300 . In  FIG. 4 , and according to operation  302 , a layer stack  401 ), which includes bottom layer  122  and top dielectric layer  124 , is formed over semiconductor layer  102 . As discussed above, bottom layer  122  can include titanium, tungsten, aluminum, or copper. However, bottom layer  122  is not 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  104  of semiconductor layer  102 . By way of example and not limitation, bottom layer  122  can be formed using a sputtering process, a plating process, an evaporation process, a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, or any suitable deposition method. Further, the thickness of bottom layer  122  can range from about 100 Å to about 3000 Å (e.g., from 100 Å to 3000 Å). Bottom layer  122  is not deposited directly on semiconductor layer  102 . According to some embodiments, bottom layer  122  is deposited over capping layer  114 . In some embodiments, bottom layer  122  may be deposited on an adhesion/barrier layer  115  disposed between bottom layer  122  and capping layer  114 , as shown in  FIG. 4 . 
     According to operation  302 , and referring to  FIG. 4 , top dielectric layer  124  of layer stack  400  can be deposited over bottom layer  122 . In some embodiments, top dielectric layer  124  can be a stack of one or more dielectric layers. In some embodiments, top dielectric layer  124  allows incoming visible light to pass through. In other words, top dielectric layer  124  is made of a transparent material, or materials, that function as an anti-reflective material. In some embodiments, top dielectric layer  124  is made of SiO 2 , Si 3 N 4 , SiON, SiC, a polymer, or other suitable transparent dielectric material(s). Top dielectric layer  124  can be deposited by CVD or ALD and have an as-deposited thickness that ranges from about 1000 Å to about 3000 Å (e.g., from 1000 Å to 3000 Å). Alternatively, top dielectric layer  124  can be spin-coated on bottom layer  122 . 
     In referring to  FIG. 3 , method  300  continues with operation  304  and the formation of one or more polarization grating structures with grating elements therein within a composite grid structure, such as composite grid structure  116 . In some embodiments, the formation of the one or more polarization grating structures is performed concurrently with the formation of the composite grid structure, such as composited grid structure  116 . For example, referring to  FIG. 4 , a photoresist (PR) layer or a hard mask (HM) layer can be deposited over layer stack  400 . The PR or HM layer is subsequently patterned so that patterned structures  402  and  404  are formed over layer stack  400 . Patterned structures  402  can have a pitch P 1  that ranges from about 100 nm to about 500 nm (e.g., from 100 nm to 500 nm) and can be used to form the grating elements of the polarization grating structures. The range of pitch P 1  ensures that the width of each grating element can range from about 20 nm to about 300 nm (e.g., from 20 nm to 300 nm), as discussed above. Patterned structures  404  can have a pitch P 2  greater than pitch P 1  (e.g., P 2 &gt;P 1 ) and can be used to form the sidewalk of cells  118  of composite grid structure  116 . By way of example and not limitation, four patterned structures  402  and  404  respectively are shown in  FIG. 4 . However, additional patterned structures  402  and  404  are possible across layer stack  400 , according to some embodiments. Further, patterned structures  402 , which are responsible for the formation of the grating elements of polarization grating structures, can be formed with their length at an angle with respect to patterned structures  404 , which are responsible for the formation of cells  118  in composite grid structure  116 . In some embodiments, the angle between patterned structures  402  and  404  coincides with a polarization angle of visible light. In some embodiments, the polarization angle can range from 0° to 135° in increments of 45°. 
     For example purposes, formation of grating elements will be described with patterned structures  402  being parallel to patterned structures  404  (e.g., resulting in grating elements with a polarization angle of 0°). Based on the disclosure herein, other orientation angles, as discussed above, can be implemented. These orientation angles are within the spirit and scope of this disclosure. 
     Patterned structures  402  and  404  are used as a mask layer so that a subsequent etch process can selectively remove layer stack  400  between patterned structures  402  and  404  to form composite grid structure  116 . In some embodiments, the etch process can use a different etch chemistry for top dielectric layer  124  and bottom layer  122 . In some embodiments, the etch process is end pointed; for example, it can be automatically terminated when capping layer  114  is exposed. Additionally, the etch process can be timed or can be a combination of timed and end-pointed etch processes. In some examples, the etch process is anisotropic so that the etched features have nominally vertical sidewalls. Further the etch process can have high selectivity towards top dielectric layer  124  and bottom layer  122 .  FIG. 5  is an example structure of  FIG. 4  after the etch process of operation  304  described above. 
     Once the etch process is complete, patterned structures  402  and  404  can be removed with a wet etch chemistry. The resulting etched structures e.g., grating elements  600  and the sidewalls of cells  118  are shown in  FIG. 6 . In some embodiments, the height of grating elements  600  is between about 200 nm and about 1000 nm (e.g., from 200 nm to 1000 nm), their width is between about 20 nm and about 300 nm (e.g., from 20 mu to 300 nm), and their pitch is between about 100 nm to about 500 nm (e.g., from 100 nm to 500 nm). In the example of  FIG. 6 , grating elements  600  of polarization grating structure  610  are aligned parallel (e.g., at 0° polarization angle) to the sidewalk of cells  118  of composite grid structure  116  as shown for example in  FIG. 7 a   , which is a top view of polarization grating structure  610  within a cell  118  at 0° polarization angle. According to  FIG. 6 , polarization grating structure  610  can be part of composite grid structure  116 . In other words, polarization grating structure  610  can be formed in a cell  118  of composite grid structure  116 . As discussed above, grating elements  600  can be aligned to different angles with respect to the sidewalk of cells  118  so that polarization grating structure  610  can detect light with additional polarization angles. By way of example and not limitation,  FIGS. 7( a )-( d )  are top views of exemplary polarization grating structures  610  with grating elements  600  oriented in different angles with respect to the sidewalk of cell  118  (e.g., 0°, 45°, 90°, or 135°). As discussed above, these angles can coincide with respective polarization angles of incident light. 
     Further, cells  118  of composite grid structure  116  and polarization grating structure  610  are substantially aligned to radiation-sensing regions  104  of semiconductor layer  102 . Further, additional polarization grating structures are possible across composite grid structure  116 . 
     In referring to  FIG. 8 , after the formation of grating elements  600  and cells  118 , passivation layer  126  is conformally deposited over the sidewalk of cells  118  and grating elements  600 . By way of example and not limitation, passivation layer  126  can be deposited by a CVD-based or an ALD-based deposition method. Passivation layer  126  can be formed from a dielectric material, such as SiO 2 , Si 3 N 4 , or SiON and can have a thickness between about 50 Å to about 3000 Å (e.g., from 50 Å to 3000 Å). 
     Referring to  FIG. 3 , method  300  continues with operation  306  where a gap between grating elements  600  of polarization grating structure  610  is filled with a color filter, air, a dielectric material, or a combination thereof. In some embodiments, the dielectric material is a transparent/anti-reflective material made of SiO 2 , Si 3 N 4 , SiON, SiC, or a polymer. 
     In operation  308 , cells  118  of composite grid structure  116  are filled with one or more color filters  120 , as shown in  FIG. 9 . In some embodiments, color filters  120  can be red, green, or blue. In the example of  FIG. 9 , the gap between grating elements  600  is filled with air.  FIGS. 10 through 13  show exemplary arrangements of color filters  120  and polarization grid structures  610  with different polarization angles in composite grid structure  116 , according to some embodiments. The examples of  FIGS. 10-13  are not limiting and additional arrangements are possible and within the spirit and the scope of this disclosure, For example, in a Bayern pattern where the composite grid structure 116 can include 50% green color filters, 25% red color filters, and 25% blue color filters some of the green color filters can be replaced by polarization grating structures. 
     In referring to  FIG. 9 , a micro-lens  130  can be formed over each cell  118  and polarization grating structure  610 . Micro-lens  130  focuses the incoming light rays into respective cells  118  of composite grid structure  116  towards radiation-sensing regions  104  of semiconductor layer  102 . 
     The present disclosure is directed to a method that describes the formation of a polarization grating structure (e.g., polarizer) as part of a composite grid structure of a back side illuminated image sensor device. In some embodiments, the polarization grating structure can be integrated into the composite grid structure by replacing one or more color filters of the composite grid structure with the polarizing grating structure (grid polarizer), In some embodiments, the polarizing grating structure can provide polarization information of the incident light along the following polarization directions: 0°, 45°, 90°, and/or 135°. The aforementioned polarization directions are not limiting and other polarization directions are possible. According to some embodiments, the pitch between grating elements of polarizing grating structure can range from about 100 nm to about 500 nm (e.g., from 100 nm to 500 nm), and the width of each grating element can range from about 20 nm to about 300 nm (e.g., from 20 nm to 300 nm). The grating elements of the polarizing grating structure can be made of the same material as the composite grid structure. Integration of the polarizers into the composite grid structure of a sensor device can offer several benefits, including: compact design for the image sensor, absence of moving parts, and faster acquisition of light polarization information. (e.g., polarization information for all polarization angles is collected simultaneously), 
     In some embodiments a semiconductor image sensor device includes a semiconductor layer with one or more sensing regions configured to sense radiation; a grid structure, over the semiconductor layer, with one or more cells respectively aligned to the one or more sensing regions; and a polarizing grating in the one or more cells of the grid structure configured to polarize the light incoming to the semiconductor image sensor. 
     In some embodiments a semiconductor image sensor includes one or more polarizing grating structures with grating elements aligned to a light polarization angle, where the one or more polarization grating structures are disposed in cells defined by a grid structure; a semiconductor layer with sensing regions configured to sense radiation entering the semiconductor layer from the grid structure, where the semiconductor layer is disposed below the grid structure so that each of the cells of the grid structure is aligned to a sensing region of the semiconductor layer; and a micro-lens over each cell of the grid structure. 
     In some embodiments a method to form an image sensor includes depositing a layer stack over a semiconductor layer with radiation-sensing regions, where the layer stack includes a bottom layer and a top anti-reflective layer. The method further includes, patterning the layer stack to form a grid structure with cells and a polarization grating structure within a cell, where the polarization grating structure comprises grating elements oriented to a light polarization angle. The method also includes filling the grating structure between the grating elements with air or a dielectric material and filling the cells that do not contain a polarization grating structure with a color filter. 
     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.