Image sensor with light balance structure and method thereof

Abstract

The invention relates to an image sensor with a light balance structure and a method thereof. An image sensor is described. The image sensor includes a plurality of pixel cells arranged to form an image sensor array disposed in or on a semiconductor substrate, a proximal metal layer, and a light balancing structure. Each pixel cell included in the plurality of pixel cells includes one or more photodiodes disposed between a first side and a second side of the semiconductor substrate, the second side being opposite the first side. The proximal metal layer is included in an interconnect stack disposed proximate to the second side of the semiconductor substrate. The light balancing structure is disposed between the second side of the semiconductor substrate and the proximal metal layer. The light balancing structure includes a plurality of discrete segments optically aligned with pixel cells of a first type included in the plurality of pixel cells.

Description

Technical Field

[0001] The present disclosure generally relates to image sensors, and more particularly but not exclusively, to complementary metal oxide semiconductor image sensors. Background Art

[0002] Image sensors are a type of semiconductor device that have become ubiquitous and are now widely used in digital cameras, mobile phones, security cameras, and medical, automotive, and other applications. As image sensors are integrated into a wider range of electronic devices, there is a desire to enhance the functionality, performance metrics, etc. of the image sensors in as many ways as possible (e.g., resolution, power consumption, dynamic range, size, etc.) through both device architecture design and image acquisition processing.

[0003] Typical image sensors operate in response to image light incident on the image sensor that is reflected from an external scene. The image sensor includes a pixel array having photosensitive elements (e.g., photodiodes), which absorb a portion of the incident image light and generate image charge immediately after absorbing the image light. The image charge generated by the pixels can be measured as an analog output image signal on a column bit line, which varies as a function of the incident image light. In other words, the amount of image charge generated is proportional to the intensity of the image light, and the image charge is read out as an analog image signal from the column bit line and converted to a digital value to generate a digital image (i.e., image data) representing the external scene. Summary of the Invention

[0004] One aspect of the present disclosure discloses an image sensor including: a plurality of pixel units arranged to form an image sensor array disposed in or on a semiconductor substrate, wherein each pixel unit included in the plurality of pixel units includes one or more photodiodes disposed within the semiconductor substrate between a first side and a second side of the semiconductor substrate, wherein the first side is opposite the second side; a proximal metal layer included in an interconnect stack disposed proximate to the second side of the semiconductor substrate; and a light balance structure disposed between the second side of the semiconductor substrate and the proximal metal layer, wherein the light balance structure includes a plurality of discrete segments optically aligned with a first type of pixel unit included in the plurality of pixel units.

[0005] Another aspect of the present disclosure discloses a method for forming an image sensor, which includes: etching an interlayer dielectric to form a plurality of trenches positioned above a first type of pixel unit included in a plurality of pixel units, wherein each pixel unit included in the plurality of pixel units includes one or more photodiodes disposed within a semiconductor substrate, and the semiconductor substrate includes a first side and a second side opposite to the first side; depositing a metal material to fill the plurality of trenches to form a light balance structure, wherein the light balance structure includes a plurality of discrete segments corresponding to the plurality of trenches filled with the metal material, and the plurality of discrete segments are optically aligned with the first type of pixel unit included in the plurality of pixel units; depositing an intermetallic dielectric layer on the light balance structure formed within the interlayer dielectric; etching the intermetallic dielectric layer to form a plurality of second trenches; and depositing the metal material to fill the plurality of second trenches to form a proximal metal layer included in an interconnect stack, wherein the light balance structure is disposed between the second side of the semiconductor substrate and the proximal metal layer.

[0006] Another aspect of the present disclosure discloses a multicolor image pixel, which includes: a group of four pixel units arranged in a 2×2 array, the group of four pixel units including a red pixel unit, two green pixel units adjacent to the red pixel unit, and a blue pixel unit adjacent to the two green pixel units, and wherein each pixel unit included in the group of four pixel units includes at least four photodiodes disposed within a semiconductor substrate; a proximal metal layer included in an interconnect stack coupled to the semiconductor substrate; and a discrete segment of a light balance structure optically aligned with the red pixel unit included in the group of four pixel units, wherein the discrete segment is further disposed between the semiconductor substrate and the proximal metal layer. Description of the Drawings

[0007] The non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, in which like reference numerals refer to like components throughout the various views, unless otherwise specified. Not all instances of an element must be labeled, so as not to clutter the drawings when appropriate. The figures are not necessarily to scale; instead, emphasis is placed on illustrating the described principles.

[0008] FIG. 1 illustrates a top view of a repeating unit for a conventional image sensor.

[0009] Figure 2A FIG. 15 illustrates a top view of a 2×2 pixel unit array of an image sensor including a light balance structure according to an embodiment of the present disclosure.

[0010] Figure 2BIllustrated is a cross-sectional view of an image sensor including a light balancing structure according to an embodiment of the present disclosure.

[0011] Figure 2C The present invention is described in detail according to an embodiment of the present invention. Figure 2B An enlarged portion of the cross-sectional view illustrated in FIG.

[0012] Figure 2D Illustrated is an enlarged top view of an image sensor including a light balancing structure according to an embodiment of the present disclosure.

[0013] Figure 3A Illustrated is a top view of an image sensor including a light balancing structure according to an embodiment of the present disclosure.

[0014] Figure 3B The present invention is described in detail with reference to an embodiment of the present invention. Figure 3A A top view of an image sensor of a light balancing structure further comprising one or more dummy segments.

[0015] Figure 4 An exemplary method for fabricating a light-balancing structure included in an image sensor according to an embodiment of the present disclosure is illustrated.

[0016] Figure 5 According to an embodiment of the present disclosure, Figures 2A to 4 A functional block diagram of an imaging system of an image sensor with a light balancing structure described in an exemplary embodiment of FIG.

[0017] Throughout the several views of the drawings, corresponding reference characters indicate corresponding components. Those skilled in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, to help improve understanding of the various embodiments of the present invention, the dimensions of some of the elements in the various figures may be exaggerated relative to other elements. In addition, common and well-known elements that are useful or necessary in commercially feasible embodiments are generally not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. DETAILED DESCRIPTION

[0018] An embodiment of an apparatus, system, and / or method related to an image sensor with a light balancing structure is described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. However, those skilled in the art will recognize that the techniques described herein may be practiced without one or more of the specific details or may be practiced using other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring some aspects.

[0019] References throughout this specification to "one embodiment", "an embodiment", "one example" or "an example" mean that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" throughout the specification are not necessarily all referring to the same embodiment. Additionally, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0020] Throughout this specification, several terms are used. These terms will assume their ordinary meaning in the art to which they pertain, unless specifically defined otherwise herein or the context in which they are used clearly implies otherwise. It should be noted that in this document, element names and symbols may be used interchangeably (e.g., Si and silicon); however, both have the same meaning.

[0021] FIG. 1 illustrates a top view of a repeating unit for a conventional image sensor, the repeating unit including one red pixel (R pixel), two green pixels (e.g., Gr pixel and Gb pixel), and one blue pixel (B pixel), the pixels together forming a full-color image pixel of the conventional image sensor. During operation, each of the pixels included in the repeating unit can generate an image charge in response to incident light, and the image charge can be read out (e.g., as a voltage signal) to generate an image of an external scene. However, it has been found that optical crosstalk can asymmetrically affect the readout of two adjacent green pixels, such that there is a non-negligible deviation (e.g., GrGb difference) between the signal associated with the Gr pixel and the signal associated with the Gb pixel. It has further been found that the GrGb difference varies based on the relative position of a given pixel within the pixel array forming the conventional image sensor. More specifically, it has been found that the chief ray angle (CRA) of a given pixel can be related to the GrGb difference, and the CRA also varies based on the relative position of the given pixel within the pixel array. For example, the amount of light incident on adjacent Gr and Gb pixels located near the edge of the pixel array (e.g., where the CRA is highest) can cause the corresponding signals read out from the adjacent Gr and Gb pixels to deviate by 25% or more (e.g., a GrGb difference of 25% or more), which negatively affects the performance of the conventional image sensor.

[0022] In addition, it should be understood that particular embodiments of the present disclosure (e.g., embodiments of an image sensor utilizing an architecture such as that Figures 2A to 2D illustrated in ) are particularly sensitive to crosstalk that asymmetrically affects adjacent green pixels, because the adjacent green pixels can be used as image or phase detection pixels that compare Gr and / or Gb imaging signals for various functions (e.g., phase or distance detection for accurate autofocus). Thus, there is a need to address the asymmetric optical crosstalk that can affect an image sensor.

[0023] One way to address the asymmetric optical crosstalk of a conventional image sensor is to determine the readout differences between each Gr / Gb pixel pair and develop a compensation look-up table stored, for example, on a one-time programmable memory. In other words, additional circuit elements may be included in a conventional image sensor, and the additional circuit elements may be configured to compensate for the asymmetric optical crosstalk. However, due to the limitations of on-chip memory, this compensation is implemented by optically compensating by dividing the entire pixel array into a finite number of regions of interest (ROIs), where individual pixels within a given one of the ROIs share a common compensation factor. However, the compensation look-up table does not address the root cause of the asymmetric optical crosstalk, nor does it compensate for the asymmetric optical crosstalk present within the finite number of ROIs. For example, a given one of the ROIs contains multiple full-color pixels, and each full-color pixel contains adjacent Gr and Gb pixels that individually encounter different degrees of asymmetric optical crosstalk, meaning that the GrGb differences cannot be averaged. Additional differences such as die-to-die differences, lot-to-lot differences, device differences associated with processing differences, etc., on a given wafer of an image sensor die further complicate the resolution of the asymmetric optical crosstalk. In addition, even a minor change to a known pixel layout (e.g., a change to the color filter layer or other elements of the optical stack) will require re-measurement to determine the readout differences of the Gr / Gb pixel pairs, resulting in adjusted values for the compensation table.

[0024] Although the compensation look-up table method is inefficient, it can be used in combination with embodiments of the present disclosure, which are directed to more directly addressing the asymmetric optical crosstalk problem by targeting at least one of the main contributing factors of the asymmetric optical crosstalk. Specifically, it has been found that longer wavelength light (e.g., red light that propagates through a red pixel is longer in wavelength than green light that propagates through a green pixel and blue light that propagates through a blue pixel) is one of the main contributing factors to the asymmetric optical crosstalk of adjacent green pixels. It has been determined that red light can penetrate deeper into the substrate (e.g., relative to green light or blue light) to such an extent that the red light can be reflected from underlying elements of the image sensor and subsequently asymmetrically redirected to a nearby photodiode of an adjacent pixel (e.g., a photodiode associated with a green pixel adjacent to a given red pixel). For example, it has been found that red light can be reflected from a first metal or "metal 1" layer and redirected as optical crosstalk along a specific direction towards a photodiode associated with a non-red pixel (e.g., a green pixel), which can affect the sensitivity of adjacent green pixels. The first metal or "metal 1" layer may be a metal layer disposed relatively close to the semiconductor substrate in which the photodiode is formed.

[0025] In addition, it has been found that the asymmetric optical crosstalk adjacent to the green pixels is inconsistent across the pixel array. In other words, based on the relative positions of the adjacent green pixels on the image sensor die, the adjacent green pixels can experience different levels of optical crosstalk associated with adjacent red pixels. Specifically, a correlation has been found between the principal ray angle of the incident light and the asymmetric optical crosstalk of the adjacent green pixels, which will be discussed in more detail later in this disclosure. Other factors found to affect the asymmetric optical crosstalk include the underlying isolation structure, especially when the underlying isolation structure provides regions for pixel control circuitry that is positioned non-uniformly relative to the adjacent green pixels, and reflection differences across the image sensor die.

[0026] Accordingly, embodiments of the present disclosure are directed to specifically addressing asymmetric optical crosstalk by utilizing a light balancing structure disposed between the "Metal 1" layer and the plurality of photodiodes of a given image sensor. In embodiments of the present disclosure, the light balancing structure can be configured to reduce or eliminate asymmetric optical crosstalk by reflecting long wavelength light (e.g., red light) in a manner that reduces and / or balances the amount of crosstalk incident on the photodiodes associated with the shorter wavelength light (e.g., adjacent green pixels or pixel units of a given repeating unit). In other words, embodiments of the light balancing structure disclosed herein can address one or more of the aforementioned contributing factors of asymmetric optical crosstalk by redirecting light in a manner that balances the optical crosstalk to two or more pixels or pixel units (e.g., adjacent green pixels and / or adjacent pixel units of a given repeating unit).

[0027] In addition, by being disposed between the "Metal 1" layer and the first type of pixel or pixel unit (e.g., a red pixel or pixel unit), the light balance structure further suppresses the "Metal 1" layer from reflecting longer wavelength light and causing asymmetric optical crosstalk. Embodiments of the light balance structure disclosed herein are defined by a plurality of discrete segments. In some embodiments, the plurality of discrete segments may be further arranged to address other contributing factors of asymmetric optical crosstalk (e.g., principal ray angle, isolation structure location and / or pixel control circuitry location, reflection differences across the image sensor die, processing differences across the image sensor die and / or wafer, etc.). In other words, although the plurality of discrete segments defining the light balance structure may be configured to redirect most of the longer wavelength light (e.g., red light) back to the photodiode associated with the longer wavelength light (e.g., a red pixel or red pixel unit) to reduce overall optical crosstalk, in some embodiments, the plurality of discrete segments may be further configured to cancel or otherwise mitigate other contributing factors of asymmetric optical crosstalk and / or otherwise balance the crosstalk between green pixels adjacent to the red pixel to reduce non-uniformity of light sensitivity. For example, a portion of the red light may be intentionally redirected by the light balance structure towards one or more of the adjacent green pixels or pixel units in a given repeating unit such that the adjacent green pixels or pixel units have a similar amount of crosstalk. The degree of redirection (or lack of redirection) provided by the light balance structure may then be adjusted across the image sensor die (e.g., by adjusting one or more of the relative position with respect to the center of the pixel or pixel unit, the size, shape, orientation, etc. of the individual segments included in the plurality of discrete segments defining the light balance structure) to compensate for differences in asymmetric optical crosstalk that vary based on the corresponding position of a given pixel or pixel unit in the pixel array.

[0028] Figures 2A to 2DIllustrative views of an image sensor 200 including a light balancing structure 239 in accordance with embodiments of the present disclosure. The image sensor 200 includes an objective lens 298 (e.g., one or more optical elements) to focus or otherwise redirect light to be incident on an image sensor array formed by a plurality of instances of a 2×2 pixel cell array 290. Each instance of the 2×2 pixel cell array 290 includes a plurality of pixel cells 230 (e.g., red pixel cells 230-R including 230-R1, 230-R2, and 230-R3, green pixel cells 230-G including 230-G1 and 230-G2, and blue pixel cells 230-B) formed in or on a semiconductor substrate 201. The semiconductor substrate 201 has a first side 202 and a second side 203 opposite the first side 202. Each pixel cell included in the plurality of pixel cells 230 is at least partially defined by pixels of a similar color included in a plurality of pixels 225 (e.g., red pixels 225-R, green pixels 225-G, or blue pixels 225-B). Individual pixels included in the plurality of pixels 225 are separated from each other by an isolation structure 208 (e.g., one or more dielectric or oxide materials such as silicon dioxide), which may include a deep trench isolation structure 210 and / or a shallow trench isolation structure 212. Individual pixels included in the plurality of pixels 225 further include corresponding photodiodes (e.g., first photodiode 215-1, second photodiode 215-2, third photodiode 215-3, fourth photodiode 215-4, fifth photodiode 215-5, sixth photodiode 215-6, seventh photodiode 215-7, eighth photodiode 215-8, etc.) included in a plurality of photodiodes 215 (e.g., pinned photodiodes having doped regions with a charge carrier type opposite to the majority charge carrier type of the semiconductor substrate 201 such that the outer perimeter of the doped region forms a PN junction or a PIN junction of the photodiode). Each pixel cell included in the plurality of pixel cells 230 further includes at least one color filter (e.g., red color filter 219-R, green color filter 219-G, or blue color filter 219-B) included in a plurality of color filters 219. The color filters included in the plurality of color filters 219 are at least partially separated from each other by a metal grid structure 217 (e.g., aluminum, copper, tungsten, or other metals arranged in a grid to laterally surround the plurality of color filters 219). Each pixel cell included in the plurality of pixel cells 230 further includes one or more microlenses (e.g., molded plastic or polymer materials to form an optical structure that focuses or otherwise directs incident light onto the plurality of photodiodes 215) included in a plurality of microlenses 235.

[0029] In Figures 2A to 2DIn the illustrated embodiment, the semiconductor substrate 201 may correspond to a part or all of a semiconductor wafer (e.g., a silicon wafer). In some embodiments, the semiconductor substrate 201 comprises or is otherwise formed of: silicon, silicon germanium alloy, germanium, silicon carbide alloy, indium gallium arsenide alloy, any other alloy formed of group III-V compounds, combinations thereof, one or more epitaxial layers of the foregoing materials, or a bulk substrate thereof. More specifically, the semiconductor substrate 201 may correspond to any semiconductor material or combination of materials that can be doped or otherwise configured to include the plurality of photodiodes 215 included in the image sensor array of the image sensor 200. For example, in some embodiments, the semiconductor substrate 201 may correspond to one or more epitaxial layers (e.g., P- or N-doped silicon) formed on a carrier wafer. In this embodiment, the plurality of photodiodes 215 may be formed in the one or more epitaxial layers corresponding to the semiconductor substrate 201, and the carrier wafer may be removed or otherwise thinned during fabrication. In one embodiment, the semiconductor substrate 201 is formed of an intrinsic or non-intrinsic silicon material having regions that are sufficiently doped to form the plurality of photodiodes 215.

[0030] The image sensor 200 further includes pixel transistors 265 (e.g., pixel control circuitry, such as transfer transistors including floating diffusion regions, reset transistors, row select transistors, source follower transistors, other transistors, other circuit system elements, such as memory elements or combinations thereof) disposed adjacent to the second side 203 of the semiconductor substrate 201. The pixel transistors 265 may include source / drain regions (e.g., doped regions of the semiconductor substrate 201), gate electrodes (e.g., polysilicon), and gate dielectrics (e.g., silicon dioxide, hafnium dioxide, other insulating materials, or combinations thereof).

[0031] As Figures 2A to 2DAs illustrated, the image sensor 200 further includes an interconnect stack 250 disposed adjacent to the second side 203 of the semiconductor substrate 201. The interconnect stack includes a proximal metal layer 254 (e.g., a "metal 1" layer) and one or more non-proximal metal layers (e.g., non-proximal metal layer 256, which corresponds to a "metal 2" layer and / or additional non-proximal metal layers not illustrated, such as a "metal 3" layer, a "metal 4" layer, etc.). The proximal metal layer 254 includes a metal contact M1, and the non-proximal metal layer 256 includes a metal contact M2. Note that the proximal metal layer 254 may include vias 245 (e.g., one or more vertical interconnects that are conductive) coupling the metal contact M1 of the proximal metal layer 254 to the pixel transistor 265. The metal contacts M1 and M2 (e.g., Al, Au, Cu, W, Ti, other metals, metal alloys, polysilicon, other conductive materials, or combinations thereof) are disposed within an intermetal dielectric 253 (e.g., an inorganic oxide (such as silicon dioxide), a nitride (such as silicon nitride), spin-on glass, or other materials, such as an organic polymer) and an intermetal dielectric 255 (e.g., an inorganic oxide (such as silicon dioxide), a nitride (such as silicon nitride), spin-on glass, or other materials, such as an organic polymer), respectively. The image sensor 200 further includes a light balancing structure 239 disposed within an interlayer dielectric 251 between the second side 203 of the semiconductor substrate 201 and the interconnect stack 250. The light balancing structure 239 includes a plurality of discrete segments 240 (e.g., 240-1, 240-2, 240-3, 240-4, 240-5, 240-6, 270-7, 240-8, 240-9, 240-10, 240-11, 240-12, 240-13, 240-14, etc., which are labeled as Figures 2B to 2C "M0" in some views) to mitigate asymmetric optical crosstalk. It should be understood that the light balancing structure 239 may have the same composition as the metal contacts of the proximal metal layer 254 and / or the non-proximal metal layer 256 (e.g., a titanium liner filled with tungsten).

[0032] It should be understood that Figures 2A to 2D the views presented may omit certain features of the image sensor 200 to avoid obscuring the details of the present disclosure. In other words, not all elements of the image sensor 200 may be labeled, illustrated, or otherwise shown throughout the present disclosure Figures 2A to 2D or in other figures. It should be further understood that in some embodiments, the image sensor 200 may not necessarily include all of the elements shown.

[0033] Figure 2AA top view (e.g., along the x-y plane according to coordinate system 299) of an example of a 2×2 pixel unit array 290 of an image sensor 200 including a light balance structure 239 according to an embodiment of the present disclosure is illustrated. The 2×2 pixel unit array 290 includes an isolation structure 208, a plurality of pixels 225 (e.g., blue pixel 225-B, green pixel 225-G, and red pixel 225-R), a plurality of pixel units 230 (e.g., blue pixel unit 230-B, green pixel unit 230-G including 230-G1 and 230-G2, and red pixel unit 230-R), a plurality of microlenses 235, and a light balance structure 239 formed of a plurality of discrete segments including discrete segment 240-1. It should be understood that in some embodiments, the 2×2 pixel unit array 290 may correspond to the smallest repeating unit and / or the full-color image pixel of the image sensor 200.

[0034] The plurality of pixel units 230 are arranged in a plurality of rows and a plurality of columns to form the 2×2 pixel unit array 290. The 2×2 pixel unit array 290 includes one red pixel unit 230-R, one blue pixel unit 230-B, and two green pixel units 230-G1 and 230-G2. As illustrated, the plurality of pixels 225 together form the plurality of pixel units 230, wherein individual pixels included in the plurality of pixels 225 are at least partially separated from each other by the isolation structure 208 (e.g., see Figure 2CThe shallow trench isolation structure 212 and / or the deep trench isolation structure 210 illustrated therein may individually or jointly correspond to the isolation structure 208). Each pixel unit included in the plurality of pixel units 230 includes a 2×2 array of pixels of the same color included in the plurality of pixels 225. For example, the blue pixel unit 230-B is formed by a 2×2 array of blue pixels 225-B, the red pixel unit 230-R is formed by a 2×2 array of red pixels 225-R, and the green pixel units 230-G1 and 230-G2 are each formed by a 2×2 array of green pixels 225-G. Since each pixel unit included in the plurality of pixel units 230 in the example exactly includes four pixels included in the plurality of pixels 225, the plurality of pixel units 230 may generally be referred to as "4C" pixel units. However, it should be understood that in other embodiments, the plurality of pixel units 230 may include more or fewer pixels per pixel unit (e.g., each pixel unit included in the plurality of pixel units 230 may include 1 pixel, 2 pixels, 8 pixels, 16 pixels, or any other amount of pixels included in the plurality of pixels 225) per pixel unit. In the illustrated embodiment, each pixel unit included in the plurality of pixel units 230 includes a microlens included in the plurality of microlenses 235 (e.g., there is a one-to-one ratio between the pixel units included in the plurality of pixel units 230 and the microlenses included in the plurality of microlenses 235). However, in other embodiments, different arrangements of microlenses may be utilized (e.g., there is a one-to-one ratio, a two-to-one ratio, or other ratio between the pixels included in the plurality of pixels 225 and the microlenses included in the plurality of microlenses 235).

[0035] As Figure 2AAs illustrated, the 2×2 pixel cell array 290 includes blue pixel cells 230-B, red pixel cells 230-R, and two green pixel cells 230-G1 and 230-G2. As previously discussed, longer wavelength light (e.g., red light) propagating through a first type of pixel cell (e.g., red pixel cell 230-R) included in the plurality of pixel cells 230 can be reflected or otherwise contribute to asymmetric optical crosstalk incident on a second type of pixel cell (e.g., green pixel cells 230-G1 and 230-G2) included in the plurality of pixel cells 230. The light balancing structure 239 is then positioned to be optically aligned (e.g., optically communicate) with the first type of pixel cell to redirect the longer wavelength light back to the first type of pixel cell and / or an adjacent or neighboring pixel cell in the second type of pixel cell. For example, the discrete segment 240-1 is positioned to redirect at least some of the red light propagating through the red pixel cell 230-R back to the red pixel cell 230-R to reduce overall optical crosstalk, and can also further redirect some of the red light propagating through the red pixel cell 230-R to one or both of the green pixel cells 230-G1 and 230-G2 to further reduce the asymmetric optical crosstalk between the green pixel cells 230-G1 and 230-G2. It should be appreciated that depending on the position of the discrete segment 240-1, the amount of red light redirected to the green pixel cells 230-G1 and 230-G2 (e.g., the second type of pixel cell adjacent to one of the first type of pixel cells) can be varied to mitigate the asymmetric optical crosstalk (e.g., the green pixel cell 230-G2 can receive more redirected red light relative to the green pixel cell 230-G1 or vice versa to balance the amount of optical crosstalk received by the two neighboring green pixel cells 230-G1 and 230-G2). In the illustrated embodiment, the discrete segment 240-1 included in the light balancing structure 239 does not completely cover the red pixel cell 230-R. For example, although the discrete segment 240-1 extends over each pixel included in the red pixel cell 230-R (e.g., the discrete segment 240-1 extends over at least four pixels included in the red pixel cell 230-R), there is a lateral separation distance 275 (e.g., 275-A, 275-B, 275-C, and 275-D) between the perimeter boundary of the discrete segment 240-1 and the corresponding perimeter boundary of the red pixel cell 230-R. The discrete segment 240-1 can be further configured based on its relative position within the pixel array on the die of the image sensor 200. For example, the distance from the perimeter boundary of the pixel cell (e.g., the array edge) along a vertical or horizontal direction can be used to configure the specific position of the discrete segment 240-1.In the same or other embodiments, the discrete segment 240-1 can be configured by adjusting the size, shape, orientation, lateral area, and / or position of the discrete segment 240-1 relative to the red pixel unit 230-R (e.g., based on the lateral separation distance 275, such as one or more of 275-A, 275-B, 275-C, and 275-D) to compensate for one or more contributing factors to the asymmetric optical crosstalk to the neighboring green pixel units 230-G1 and 230-G2 (e.g., chief ray angle, isolation structure position, and / or pixel control circuitry position, reflection differences across the image sensor die, processing differences across the image sensor die and / or wafer, etc.), the one or more contributing factors varying with respect to the position on the image sensor 200. In some embodiments, depending on the relative position of the red pixel unit 230-R relative to the center of the image sensor 200, the discrete segment 240-1 can extend over more or fewer pixels (e.g., one pixel, two pixels, or three pixels) in a given pixel unit (e.g., see. Figure 2D , 3A and 3B).

[0036] In Figure 2A the illustrated embodiment, the first lateral area of the discrete segment 240-1 included in the optical balance structure 239 is smaller than the second lateral area of the optically aligned microlenses included in the plurality of microlenses 235. In the same or other embodiments, the first lateral area of the discrete segment 240-1 is greater than the third lateral area of a given one of the optically aligned red pixels in the red pixel 225-R but smaller than the fourth lateral area of the red pixel unit 230-R. It should be understood that the lateral areas discussed herein (e.g., the first lateral area, the second lateral area, the third lateral area, and the fourth lateral area) are with respect to the x-y plane of the coordinate system 299. It should be further understood that when viewed from a top view (e.g., as Figure 2A illustrated), the elements are at different z positions of the coordinate system 299 but are otherwise optically aligned. For example, although the red pixel unit 230-R, the discrete segment 240-1, and one of the plurality of microlenses 235 are each located in a different plane (e.g., different z positions), Figure 2AShow the foregoing elements in optical alignment or otherwise in optical communication such that light can propagate from one of the plurality of microlenses 235 through the red pixel unit 230-R until reaching the discrete segment 240-1. Thus, it should be understood that references to terms such as "lateral area" or "separation distance" etc. are with reference to a planar projection or a similar view (e.g., a planar projection onto the x-y plane based on the coordinate system 299). For example, the separation distance 275 is a lateral distance on the x-y plane of the coordinate system 299 and not a corresponding vertical separation distance (e.g., along the z-axis of the coordinate system 299, which can be seen in Figure 2B ).

[0037] In some embodiments, Figure 2A the illustrated view shows the multi-color image pixels of an image sensor. For example, the red pixel unit 230-R, the green pixel units 230-G1 and 230-G2, and the blue pixel unit 230-B can together form an example of a multi-color image pixel included in a pixel array of an image sensor. The multi-color image pixel includes a group of four pixel units arranged in a 2×2 array. The group of four pixel units includes a red pixel unit (e.g., 230-R), two green pixel units adjacent to the red pixel unit (e.g., 230-G1 and 230-G2), and a blue pixel unit adjacent to the two green pixel units (e.g., 230-B). Each pixel unit included in the group of four pixel units includes at least four photodiodes disposed within a semiconductor substrate (e.g., see Figures 2B to 2C ). The multi-color image pixel further includes a proximal metal layer (e.g., the proximal metal layer 254 as illustrated in Figures 2B to 2C ) included in an interconnect stack (e.g., the interconnect stack 250) coupled to the semiconductor substrate (e.g., the semiconductor substrate 201). The multi-color image pixel further includes a discrete segment (e.g., 240-1) of a light balance structure (e.g., the light balance structure 239 illustrated in Figures 2B to 2C ) optically aligned with the red pixel unit included in the group of four pixel units. The discrete segment is further disposed between the semiconductor substrate and the proximal metal layer. In some embodiments, the discrete segment is positioned above the red pixel unit by at least partially based on the relative position of the red pixel unit in the pixel array on the image sensor, and the discrete segment is adapted to mitigate the asymmetric optical crosstalk of the two green pixel units.

[0038] Figure 2BCross-sectional view of an image sensor 200 including a light balancing structure 239 according to an embodiment of the present disclosure (e.g., along the x-z plane indicated by the coordinate system 299). As illustrated, the image sensor 200 is formed of a plurality of instances of a 2×2 pixel unit array 290 arranged in a number of rows and a number of columns to form an image sensor array, which is further illustrated in Figure 2D Return reference Figure 2B , a plurality of pixel units 230 (e.g., 230-R1, 230-R2, 230-R3, and other unlabeled pixel units) are disposed in or on a semiconductor substrate 201. Each pixel unit included in the plurality of pixel units 230 includes one or more photodiodes included in a plurality of photodiodes 215 disposed between a first side 202 and a second side 203 of the semiconductor substrate 201. The image sensor 200 further includes a proximal metal layer 254 included in an interconnect stack 250 disposed adjacent to the second side 203 of the semiconductor substrate 201.

[0039] The light balancing structure 239 is disposed between the second side 203 of the semiconductor substrate 201 and the proximal metal layer 254. As previously discussed, the light balancing structure 239 includes a plurality of discrete segments 240 optically aligned with a first type of pixel unit (e.g., red pixel units 230-R including 230-R1, 230-R2, and / or 230-R3) included in the plurality of pixel units 230, including 240-1, 240-2, 240-3, 240-4, and 240-5. It should be understood that the plurality of discrete segments 240 of the light balancing structure 239, including 240-1, 240-2, 240-3, 240-4, and 240-5, are labeled "M0" to indicate that the light balancing structure 239 may correspond to a "metal 0" layer, which may be formed using the same materials and manufacturing processes as the metal layers included in the interconnect stack 250 (e.g., the proximal metal layer 254 and one or more non-proximal metal layers 256). In other words, the light balancing structure 239 is advantageously compatible with existing processes used for back-end-of-line processing.

[0040] In Figure 2B the illustrated embodiment, the plurality of discrete segments 240 do not individually extend beyond the first type of pixel unit. For example, the plurality of discrete segments 240 are only disposed between the first type of pixel unit (e.g., red pixel units 230-R) and the proximal metal layer 254. It should be understood that restricting the lateral area of the plurality of discrete segments 240 can provide the benefit of maintaining sufficient space for forming other device components (e.g., providing sufficient space for the metal contacts and / or vias of the proximal metal layer 254 to contact the pixel transistors 265 and / or other components of the image sensor 200).

[0041] In an embodiment, an individual segment included in the plurality of discrete segments 240 may be configured to be electrically floating or coupled to a ground reference voltage (e.g., see Figure 2B for the discrete segment 240-1 illustrated therein). As previously discussed, the pixel transistor 265 includes one or more transistors (e.g., pixel control circuitry) disposed proximate the second side 203 of the semiconductor substrate 201. Metal contacts (e.g., the metal contact labeled "M1") (e.g., metal traces or segments) disposed within the proximal metal layer 254 may then be directly or indirectly electrically coupled to the one or more transistors included in the pixel transistor 265 (e.g., via the vias 245). Thus, in some embodiments, the plurality of discrete segments 240 do not provide signal routing or otherwise directly facilitate the transfer of photo-generated charge from the plurality of photodiodes 215 to the proximal metal layer 254. Instead, the plurality of discrete segments 240 reflect incident red light that has propagated through the red pixel units included in the plurality of pixel units 230 to mitigate asymmetric optical crosstalk. It should be appreciated that grounding or floating the plurality of discrete segments 240 of the light balancing structure may provide the benefit of mitigating the effect of the plurality of discrete segments 240 on the readout of the plurality of pixel units 230.

[0042] As Figure 2B illustrated, the image sensor 200 is configured to produce an image of the external scene 291 via the objective lens 298. However, as previously discussed, asymmetric optical crosstalk may have an adverse effect on the performance of the image sensor 200 (e.g., the quality of the produced image, autofocus, etc.). Specifically, light 295 may be reflected from the proximal metal layer 254 in a manner that causes asymmetric crosstalk, such as illustrated by the reflected light ray 295R1. To mitigate the crosstalk difference to adjacent green pixel units (e.g., diagonally adjacent Gr and Gb green pixel units) due to the incident light angle, the image sensor 200 includes a light balancing structure 239 that includes a plurality of discrete segments 240 that are optically aligned with each respective first type of pixel unit 230 (e.g., red pixel units 230-R, such as 230-R1, 230-R2, 230-R3, etc.) and positioned to direct the light 295 to adjacent green pixel units, such as illustrated by the reflected light ray 295R2, where the light varies according to the separation distance 275 (e.g., Figure 2A 275-A, 275-B, 275-C, and 275-D illustrated therein) with respect to the red pixel unit 230-R in order to minimize the difference (e.g., GrGb difference) between adjacent green pixel units.

[0043] However, it has been found that the degree of asymmetric optical crosstalk varies based on the relative position of a given pixel or pixel unit included in a plurality of pixel units 230 on the die of the image sensor 200, and thus the performance of the optical balance structure 239 can be improved by adjusting the positions of the plurality of discrete segments 240 (e.g., 240-1, 240-2, 240-3, 240-4, 240-5) based on their relative positions within the pixel array of the image sensor 200. It has been found that one way to correlate the differences in asymmetric optical crosstalk is based on the principal ray angle of the light, which corresponds to the angle at which the light is incident on the image sensor 200. Specifically, reference is made to the angle at which light passing through the center of the objective lens 298 is incident on a given pixel or pixel unit included in the plurality of pixel units 230. Axis 297 represents the normal to any planar surface of the image sensor 200 (e.g., the first side 202, the second side 203, or any other surface of the image sensor 200 parallel to the x-y plane of the coordinate system 299). In the illustrated embodiment, axis 297 intersects the center "X" of the objective lens 298, which is centrally aligned with the image sensor array of the image sensor 200 formed by a plurality of instances of the 2×2 pixel unit array 290. It should be understood that axis 297 indicates the position where the principal ray angle with respect to the imaging plane of the image sensor 200 is the lowest. However, as the light is incident on the image sensor 200 away from the lateral center, the principal ray angle increases proportionally. Thus, the principal ray angle of a given pixel or pixel unit included in the plurality of pixel units 230 increases as the position of the given pixel or pixel unit moves towards the perimeter of the image sensor 200. Therefore, the principal ray angle θ1 associated with the position of the red pixel unit 230-R1 is less than the principal ray angle θ2 associated with the position of the red pixel unit 230-R2. Similarly, the principal ray angle associated with the position of the red pixel unit 230-R3 is greater than the principal ray angles associated with the positions of the red pixel units 230-R1 and 230-R2. In other words, a first type of pixel unit (e.g., the red pixel unit 230-R) has an associated principal ray angle based on its relative pixel position within the image sensor 200, which in turn affects the asymmetric optical crosstalk. Thus, in some embodiments, the individual segments included in the plurality of discrete segments 240 of the optical balance structure 239 are arranged based on the associated principal ray angle. For example, the size, shape, orientation, lateral area, relative position (e.g., relative to the center of a given pixel or pixel unit), etc. of the individual segments included in the plurality of discrete segments 240 can be adjusted based on the associated principal ray angle.

[0044] Figure 2C Illustrating an embodiment in accordance with the present disclosure Figure 2BAn enlarged cross-sectional view of the image sensor 200 illustrated in the figure. As illustrated, the 2×2 pixel unit array 290 includes at least a first type of pixel unit (e.g., the red pixel unit 230-R) and a second type of pixel unit (e.g., the green pixel unit 230-G). Each pixel unit included in the plurality of pixel units further includes an optically aligned photodiode included in the plurality of photodiodes 215, an optically aligned color filter included in the plurality of color filters 219, and an optically aligned microlens included in the plurality of microlenses 235. For example, two photodiodes (e.g., 215-1 and 215-2) included in the red pixel unit 230-R are optically aligned with one of the plurality of microlenses 235 (i.e., the leftmost microlens included in the plurality of microlenses 235 in the illustrated view) and one of the plurality of color filters included in the plurality of color filters 219 (i.e., the red color filter 219-R to the left of the green color filter 219-G).

[0045] The image sensor 200 further includes a light balancing structure 239 disposed between the plurality of photodiodes 215 and the proximal metal layer 254 of the interconnect stack 250. It should be further understood that in some embodiments, individual segments of the plurality of segments M0 included in the light balancing structure 239 are confined to a lateral region defined by a first type of pixel unit (e.g., red pixel unit 230-R) included in the plurality of pixel units 230. For example, the discrete segments 240-1 and 240-2 do not extend beyond the pixel region associated with the red pixel unit 230-R defined by the isolation structure 208. In other words, in some embodiments, individual segments of the plurality of discrete segments 240 included in the light balancing structure 239 do not optically communicate with non-red pixel units included in the plurality of pixel units 230. In some embodiments, individual segments of the plurality of discrete segments 240 are electrically floating or coupled to ground. For example, the discrete segment 240-1 is directly or indirectly coupled to ground or a reference voltage (e.g., through one or more metal contacts and / or vias included in the interconnect stack 250). In another example, the discrete segment 240-2 is coupled to a component disposed in or on the semiconductor substrate 201 of the image sensor 200 through a via 246, and the component is coupled to ground or a reference voltage. For example, a well 266 that has been grounded or otherwise coupled to a reference voltage or other components of the image sensor 200 (e.g., a conductive fill of the shallow trench isolation structure 212) can be coupled to the discrete segment 240-2. In contrast, one or more transistors included in the pixel transistor 265 can be coupled to a metal contact (e.g., a metal trace or segment labeled "M1") included in the proximal metal layer 254 through a via 245. In some embodiments, the via 245 and one or more individual segments of the plurality of discrete segments 240 included in the light balancing structure 239 are disposed in the same dielectric layer (e.g., the interlayer dielectric 251), which can reduce fabrication complexity, cost, and time. Thus, in some embodiments, at least one of the vias 245 and at least a portion of the plurality of discrete segments 240 included in the light balancing structure 239 can extend through a common plane 279. In some embodiments, the common plane 279 is parallel to the first side 202 and / or the second side 203 of the semiconductor substrate 201. As previously discussed, in some embodiments, the proximal metal layer 254 and the plurality of discrete segments 240 of the light balancing structure 239 can include the same metal material to facilitate processing compatibility and simplification.

[0046] Figure 2D Illustrated is an embodiment in accordance with the present disclosure that includes Figures 2A to 2DAn enlarged top view of an image sensor 200 of the optical balance structure 239 illustrated therein. The illustrated view shows a plurality of instances of a 2×2 pixel unit array 290, the 2×2 pixel unit array including one pixel unit included in a first type of pixel unit (e.g., a red pixel unit 230-R labeled by "R"), two pixel units included in a second type of pixel unit (e.g., green pixel units 230-G labeled by "Gr" and "Gb"), and one pixel unit included in a third type of pixel unit (e.g., a blue pixel unit 230-B labeled by "B"), the pixel units being arranged in a plurality of rows and a plurality of columns to form an image sensor array of the image sensor 200. In the illustrated view, the plurality of pixel units 230 are 4C pixel units, the 4C pixel units each exactly including four pixels, as indicated by the dashed lines. For example, each blue pixel unit 230-B includes four blue pixels 225-B. Similarly, each red pixel unit 230-R includes four red pixels 225-R and each green pixel unit 230-G includes four green pixels 225-G. In addition, it should be understood that each pixel included in the plurality of pixels 225 includes at least one photodiode included in a plurality of photodiodes 215 (e.g., the red pixel unit 230-R marked includes four photodiodes, including photodiodes 215-7 and 215-8; one photodiode per pixel included in the red pixel unit 230-R).

[0047] In the illustrated embodiment, according to an embodiment of the present disclosure, a plurality of discrete segments (e.g., 240-7 to 240-14) are arranged or otherwise configured to mitigate asymmetric optical crosstalk. One way to configure the plurality of discrete segments 240 to mitigate asymmetric optical crosstalk is to optically align each individual segment included in the plurality of discrete segments 240 of the optical balance structure 239 with a corresponding one of the first type of pixel units (e.g., the red pixel unit 230-R), such that the individual segment redirects light back to one or more photodiodes associated with the corresponding one of the first type of pixel units. Another way to configure the plurality of discrete segments 240 to mitigate asymmetric optical crosstalk is to arrange or otherwise configure the individual segments based on the associated principal ray angle associated with a corresponding one of the first type of pixel units. For example, in the illustrated view, "X" indicates the lateral center of the image sensor 200, at which the principal ray angle of a corresponding one of the first type of pixel units included in the plurality of pixel units 230 is zero. The principal ray angle of a corresponding one of the first type of pixel units included in the plurality of pixel units 230 increases as the corresponding one of the first type of pixel units moves away from the lateral center of the image sensor 200. As previously discussed, it has been found that the asymmetric optical crosstalk difference is at least partially based on, or otherwise associated with, the principal ray angle. Therefore, configuring the individual segments based on the associated principal ray angle of a corresponding one of the first type of pixel units can further mitigate asymmetric optical crosstalk.

[0048] Accordingly, it should be appreciated that the plurality of discrete segments 240 of the light balance structure 239 can be configured to have one or more features that are shifted in proportion to the principal ray angle of a pixel or pixel cell with a given optical alignment. The one or more features of the plurality of discrete segments 240 can include the size of an individual segment, the shape of an individual segment, the orientation of an individual segment, the lateral area of an individual segment, the position of an individual segment relative to the center of a corresponding (e.g., optically aligned) pixel cell in the first type of pixel cell, and combinations thereof. Thus, in some embodiments, adjacent segments included in the plurality of discrete segments 240 can have at least one of different sizes, different shapes, different orientations, different lateral areas, different positions relative to the center of the first type of pixel cell, or combinations thereof. In one example, the discrete segment 240-11 is adjacent to the discrete segment 240-12, which has a different orientation (e.g., the discrete segment 240-12 is rotated counterclockwise by approximately 45° relative to the discrete segment 240-11). In another example, the discrete segments 240-12 and 240-13 have different shapes (e.g., a rectangular shape and a circular shape, respectively). In another example, the discrete segment 240-11 has a different shape, size, and / or lateral area relative to the discrete segment 240-10 that is adjacent to the discrete segment 240-11. In another example, the discrete segments 240-11 and 240-10 have different positions relative to the optically aligned first type of pixel cells included in the plurality of pixel cells 230. For example, the center of the discrete segment 240-11 marked by the black circle is located at the midpoint between two pixels included in the corresponding optically aligned pixel cell. In contrast, the center of the discrete segment 240-10, also marked by the black circle, is not located at the midpoint between two pixels included in the corresponding optically aligned pixel cell and is not aligned with the optical center of the pixel cell.

[0049] In some embodiments, the center-to-center distance between an individual segment included in a plurality of discrete segments 240 of the light balance structure 239 and a corresponding optically aligned pixel unit included in a first type of pixel unit (e.g., red pixel unit 230-R) is arranged such that the center-to-center distance increases radially toward the perimeter of the image sensor 200. For example, in the illustrated embodiment, discrete segment 240-7 is closest to the center of the image sensor 200 marked by "X" and thus has a lower principal ray angle relative to the principal ray angles of other discrete segments included in the plurality of discrete segments 240 (e.g., 240-8, 240-9, 240-10, 240-11, etc.). Thus, the center of discrete segment 240-7 marked by the black circle is approximately located at the center of the optically aligned pixel unit included in the first type of pixel unit (e.g., the center of the optically aligned pixel unit indicated by the dashed line dividing the optically aligned pixel unit into a 2×2 pixel array intersects the center of discrete segment 240-7). In other words, there is a zero or near-zero center-to-center distance between the center of discrete segment 240-7 and the center of the optically aligned pixel unit. In contrast, other first type pixel units included in the plurality of pixel units 230 have a larger center-to-center distance that increases radially toward the perimeter boundary 285 of the image sensor 200. For example, the center-to-center distance between discrete segment 240-9 and the optically aligned pixel unit increases (e.g., the center of discrete segment 240-9 is shifted to the left to the center of the corresponding optically aligned pixel unit). In another example, the center-to-center distance between discrete segment 240-11 and the pixel unit optically aligned with discrete segment 240-11 is greater than the center-to-center distance between discrete segment 240-9 and the pixel unit optically aligned with discrete segment 240-9 because the pixel unit optically aligned with discrete segment 240-11 has a larger principal ray angle than the pixel unit optically aligned with discrete segment 240-9. More generally, in some embodiments, the center-to-center distance between an individual segment included in a plurality of discrete segments 240 and a corresponding optically aligned pixel unit included in a first type of pixel unit is based on the associated principal ray angle.

[0050] In another example, the discrete segment 240-7 of the light balance structure 239 may be referred to as a first segment that is optically aligned with a first pixel unit included in a first type of pixel unit, and any other discrete segment included in the light balance structure 239 (e.g., discrete segments 240-8, 240-9, 240-10, 240-11, 240-12, 240-13, 240-14, and / or other unlabeled discrete segments) may be referred to as a second segment that is optically aligned with a second pixel unit included in the first type of pixel unit. In some embodiments, the first segment is optically centered relative to the first pixel unit and the second segment is optically eccentric relative to the second pixel unit. In the same embodiment, the first principal ray angle of the first pixel unit is less than the second principal ray angle of the second pixel unit. In the same or other embodiments, the first segment is disposed between four photodiodes included in the first pixel unit and the proximal metal layer (see, for example, when viewed in the context of Figure 2D and based on Figure 2B and 2C , where the proximal metal layer corresponds to Figure 2B and 2D as illustrated in Figure 2B and 2D ). In the same or other embodiments, the second segment is disposed between two or fewer photodiodes included in the second pixel unit and the proximal metal layer (e.g., when the second segment corresponds to, for example, discrete segment 240-11 and the proximal metal layer corresponds to Figure 2B and 2D as illustrated in Figure 2B and 2D ). It should be understood that in the illustrated embodiments, each pixel unit included in the plurality of pixel units 230 includes a 2×2 array of four photodiodes (e.g., see pixel unit 230-R having four outlined photodiodes including photodiodes 215-7 and 215-8). In some embodiments, the first segment included in the plurality of discrete segments 240 of the light balance structure 239 is disposed between at least two of the four photodiodes of the 2×2 array of photodiodes included in the optically aligned pixel unit and the proximal metal layer (e.g., Figure 2B and 2Dbetween the proximal metal layer 254 illustrated in [the figure]. In the same or other embodiments, the first segment has a first lateral area that is larger than the corresponding lateral area of an individual photodiode included in a 2×2 array of four photodiodes. In the same or other embodiments, the first lateral area of the first segment is larger than the second lateral area of the second segment. In some embodiments, the lateral area of the plurality of discrete segments 240 may radially decrease as the individual segments included in the plurality of discrete segments move closer to the perimeter boundary 285 of the image sensor 200. In the same or other embodiments, the amount of displacement of an individual segment included in the plurality of discrete segments relative to the optical center of an optically aligned pixel cell increases as the distance between the center of the optically aligned pixel cell and the perimeter boundary 285 of the image sensor 200 decreases.

[0051] It should be appreciated that the configuration of the plurality of discrete segments 240 included in the light balance structure 239 discussed in the various embodiments of the present disclosure may individually or in combination provide reduced asymmetric optical crosstalk for a common type of adjacent pixel or pixel cell (e.g., a second type of pixel cell that may correspond to a green pixel cell). In other words, each of the first type of pixel cells is adjacent to two or more of the second type of pixel cells, and the plurality of discrete segments 240 are configured to reduce asymmetric optical crosstalk when reading out two or more of the second type of pixel cells that are adjacent to each other. More generally, it should be appreciated that the plurality of discrete segments 240 have an asymmetric or non-uniform arrangement to configure the light balance structure 239 to reduce asymmetric optical crosstalk from light propagating through the first type of pixel towards the second type of pixel.

[0052] Figure 3AFIG. illustrates a top view (e.g., along the x-y plane based on the coordinate system 399) of an image sensor 300 including a light balance structure according to an embodiment of the present disclosure, the light balance structure including a plurality of discrete segments 340. The image sensor 300 includes a plurality of instances of a 2×2 pixel unit array 390, the 2×2 pixel unit array including a red pixel unit 330-R, two green pixel units 330-G, and one blue pixel unit 330-B. Each pixel unit included in the plurality of pixel units 330 corresponds to a 4C pixel unit of a 2×2 array having four pixels (e.g., each green pixel unit 330-G includes four green pixels 325-G, each red pixel unit 330-R includes four red pixels 325-R, and each blue pixel unit 330-B includes four blue pixels 325-B). The light balance structure including a plurality of discrete segments 340 (e.g., 340-1, 340-2, 340-3, 340-4, 340-5, 340-6, 340-7, 340-8, 340-9, 340-10, 340-11, 340-12, 340-13, and 340-15) is configured to mitigate asymmetric optical crosstalk. More generally, it should be understood that the image sensor 300 is similar in many respects to Figures 2A to 2D the image sensor 200 illustrated in Figure 3A and may include the same or similar features. Figures 2A to 2D One difference between the image sensor 300 of Figures 2A to 2D and the image sensor 200 illustrated in Figure 3A is the arrangement of the plurality of discrete segments. However, it should be understood that the configuration of the plurality of discrete segments 240 included in the light balance structure 239 illustrated in

[0053] may be arranged similar to the plurality of discrete segments 340 included in the light balance structure illustrated in Figure 3A (or vice versa).

[0053] The plurality of discrete segments included in Figure 3AThe plurality of discrete segments 340 in the light balancing structure illustrated in FIG. 3 are arranged in an asymmetric or non-uniform manner, which may be based at least in part on the chief ray angles of the optically aligned pixel cells included in the plurality of pixel cells 330. In the illustrated embodiment, it should be noted that the plurality of discrete segments closest to the perimeter boundary 385 of the image sensor 300 are arranged to extend to the edge of the optically aligned pixel cells. For example, each of the discrete segments 340-1, 340-2, 340-3, 340-4, 340-5, 340-6, 340-10, 340-11, 340-12, 340-13, 340-14, and 340-15 are positioned to extend laterally to the edge of the optically aligned pixel cells in the first type of pixel cells (e.g., red pixel cells 330-R). However, it should be understood that elements in a common row or column do not necessarily share a common orientation. For example, discrete segments 340-11 and 340-12 are adjacent to each other and are located along a common row but are oriented differently. Specifically, discrete segment 340-11 is rotated 90 degrees relative to discrete segment 340-12. Additionally, it should be appreciated that in the illustrated embodiment, the outermost discrete segments included in the plurality of discrete segments (i.e., 340-1, 340-2, 340-3, 340-4, 340-5, 340-6, 340-10, 340-11, 340-12, 340-13, 340-14, and 340-15) each extend over only two pixels included in the optically aligned first type pixel cells (which are included in the plurality of pixel cells 330).

[0054] Figure 3B The present invention is described in detail with reference to an embodiment of the present invention. Figure 3A A top view of an image sensor 300 of a light balancing structure including a plurality of discrete segments 340 and further including one or more dummy segments. It should be understood that Figure 3B The configuration of the image sensor 300 illustrated in FIG. 3 may further include Figures 2A to 2D In other words, according to an embodiment of the present disclosure, Figures 3A to 3B Possible configurations of image sensors that may be included in image sensor 200 are shown.

[0055] In some embodiments, the image sensor 300 includes a second side of the semiconductor substrate and a proximal metal layer (eg, Figures 2A to 2D 2 and 3. In the same or other embodiments, the plurality of dummy segments 341 and / or 342 may have the same structure as that included in the image sensor 300. Figure 3BThe multiple discrete segments 340 in the optical balance structure have the same composition and are vertically arranged (e.g., in the z direction indicated by the coordinate system 399). For example, in the illustrated embodiment, the multiple discrete segments 340, the multiple dummy segments 341, and the multiple dummy segments 342 are arranged on a common transverse plane according to the coordinate system 399. In some embodiments, individual dummy segments included in the multiple dummy segments 341 or 342 are optically aligned with at least one of the second type of pixel units or the third type of pixel units. For example, the multiple dummy segments 341 are optically aligned with the blue pixel units 330-B (e.g., the third type of pixel units), and the multiple dummy segments 342 are optically aligned with the green pixel units 330-G (e.g., the second type of pixel units). It should be understood that according to embodiments of the present disclosure, the multiple dummy segments 341 and / or 342 are optional. In other words, in some embodiments of the present disclosure, either or both of the multiple dummy segments 341 and 342 may be omitted. Instead, it should be understood that in some embodiments, the multiple dummy segments 341 and / or 342 may provide advantageous processing effects, such as reducing "dishing" that may occur during the chemical mechanical planarization step in the formation process of the multiple discrete segments 340.

[0056] In some embodiments, the Figure 3A and 3B multiple discrete segments 340 in the optical balance structure have an asymmetric or non-uniform arrangement (e.g., when configuring the size, shape, orientation, etc. of individual discrete segments based on the principal ray angles of the optically aligned pixel units included in the multiple pixel units 330). In the same or other embodiments, the multiple dummy segments 341 and / or 342 may have a uniform arrangement. For example, individual dummy segments included in the multiple dummy segments 341 are optically centered with respect to the corresponding optically aligned pixel units included in the third type of pixel units (e.g., the blue pixel units 330-B).

[0057] Figure 4 FIG. 400 illustrates an exemplary method 400 for fabricating an optical balance structure included in an image sensor according to an embodiment of the present disclosure. The method 400 is a possible way to fabricate the optical balance structure 239 illustrated in Figures 2A to 2D and the optical balance structure (which includes multiple discrete segments 340) illustrated in Figures 3A - 3B that can be included in the image sensors 200, 300, and 505. It should be further understood that the method 400 can be similarly used to fabricate Figure 3BThe multiple dummy segments 341 and 342 illustrated therein. It should be understood that the numbered boxes of method 400, including boxes 405, 410, 415, 420, 425, and 430, can occur in any order and even in parallel. Additionally, according to embodiments of the present disclosure, several boxes can be repeated, added, or removed in method 400.

[0058] Method 400 and conventional semiconductor device processing and microfabrication techniques known to those skilled in the art can be used to fabricate Figures 2A to 3B and Figure 5 the embodiments of the present disclosure illustrated therein. It should be further understood that conventional semiconductor device processing and microfabrication techniques can include, but are not limited to, lithography, ion implantation, chemical vapor deposition, physical vapor deposition, thermal evaporation, sputter deposition, reactive ion etching, plasma etching, wafer bonding, chemical mechanical planarization, and the like. It should be understood that the described techniques are merely illustrative and not exhaustive, and other techniques can be utilized to fabricate one or more components of various embodiments of the present disclosure.

[0059] Box 405 illustrates depositing an interlayer dielectric (e.g., silicon dioxide) adjacent to the second side of the semiconductor substrate. The semiconductor substrate can be a semi-fabricated substrate and thus includes a plurality of photodiodes, isolation structures, floating diffusion regions, and transistors formed therein and / or thereon. A silicon dioxide layer (e.g., Figure 2C the interlayer dielectric 251 illustrated therein) can be deposited on top of the second side of the semiconductor substrate (e.g., the second side 203 of the semiconductor substrate 201) via chemical vapor deposition, physical vapor deposition, thermal oxidation, or other means known to those skilled in the art. After depositing the interlayer dielectric, chemical mechanical planarization (CMP) can be utilized to planarize the interlayer dielectric to form a planar surface.

[0060] Box 410 shows etching the interlayer dielectric to form a plurality of trenches positioned above a first type of pixel unit (e.g., a red pixel unit 230-R included in Figures 2A to 2D the plurality of pixel units 230) included in a plurality of pixel units. In some embodiments, each pixel unit included in the plurality of pixel units includes one or more photodiodes disposed within the semiconductor substrate. In the same or other embodiments, the semiconductor substrate includes a first side and a second side opposite the first side (e.g., Figures 2A to 2DThe first side 202 and the second side 203 of the semiconductor substrate 201 illustrated in []. The plurality of trenches can be formed using photolithography and subsequent etching. For example, a first photoresist layer can be deposited over the interlayer dielectric and patterned to form openings positioned over the first type of pixel units. Then, etching (e.g., plasma etching or other known etching techniques) can be used to form the plurality of trenches, which removes the material of the interlayer dielectric aligned with the openings to form the plurality of trenches. It should be understood that an after-etch cleaning can be used to subsequently remove the first photoresist layer after the etching to form the plurality of trenches.

[0061] Block 415 illustrates depositing a metal material to fill the plurality of trenches to form a light balance structure (e.g., Figures 2A to 2D the light balance structure 239 illustrated in [] and / or a light balance structure formed by Figures 3A to 3B the plurality of discrete segments 340 illustrated in []. In some embodiments, prior to depositing the metal material, a portion of the plurality of trenches can be widened to have an appropriate size for the light balance structure. For example, a first portion of the plurality of trenches can be filled to form vias for one or more components that can be contacted to ground, while a second portion coupled to the first portion can form the plurality of discrete segments of the light balance structure. It should be further understood that in some embodiments, the deposited metal material can include more than one material (e.g., a liner material and a fill material). In one embodiment, the liner material is first deposited into the plurality of trenches to line each trench included in the plurality of trenches. For example, the liner material can correspond to titanium. Subsequently, the plurality of trenches lined with the liner material are filled with a fill material (e.g., tungsten) to form the light balance structure. In other words, in some embodiments, the light balance structure includes a first metal (e.g., a fill material such as tungsten) at least partially surrounded by a second metal (e.g., a liner material such as titanium). In some embodiments, the light balance structure includes a plurality of discrete segments corresponding to the plurality of trenches filled with the metal material. In the same or other embodiments, the plurality of discrete segments included in the light balance structure are optically aligned with the first type of pixel units included in the plurality of pixel units to reduce asymmetric optical crosstalk that would otherwise affect the second type of pixel units adjacent to the first type of pixel units included in the plurality of pixel units.

[0062] In some embodiments, the interlayer dielectric is etched in block 410 to form openings positioned over the first type of pixel units included in the plurality of pixel units (e.g., including Figures 2A to 2DThe process of the multiple trenches above the red pixel units 230 - R among the multiple pixel units 230 further includes etching the interlayer dielectric to form multiple contact trenches that land on one or more pixel components (e.g., the contact areas of the gates, sources, and drain regions of pixel transistors and / or the contact areas of floating diffusion regions). The trench width of an individual trench for the light balance structure may be greater than the trench width of an individual trench for the contacts. Subsequently, in block 415, a metal material may be deposited to fill the multiple trenches to form the light balance structure while filling the multiple contact trenches to form contacts to various pixel components. In such embodiments, the multiple trenches for the light balance structure and the multiple contact trenches for forming contacts to pixel components may be formed in the same process, thereby improving processing efficiency and reducing manufacturing costs.

[0063] In some embodiments, the metal material may be deposited by chemical vapor deposition, physical vapor deposition, or other means known to those skilled in the art. It should be understood that additional processing may be further utilized to deposit the metal material. The additional process may include forming a second photoresist layer on the interlayer dielectric with appropriately widened openings as needed, etching to widen the multiple trenches to form a second portion of the multiple trenches, and etching or otherwise cleaning the interlayer dielectric to remove the second photoresist layer. After depositing the metal material, chemical mechanical planarization may be utilized to planarize the light balance structure.

[0064] Block 420 shows depositing an intermetal dielectric layer on the light balance structure (e.g., Figure 2C the intermetal dielectric 253 illustrated in Figure 2C formed within the interlayer dielectric. For example, a silicon dioxide layer (e.g., Figure 2C the intermetal dielectric 253 illustrated in

[0065] Figure 2C can be deposited on top of the light balance structure and the interlayer dielectric 251 (e.g.,

[0065] the light balance structure 239 and the interlayer dielectric 251 illustrated in Figure 2C by chemical vapor deposition, physical vapor deposition, thermal oxidation, or other means known to those skilled in the art. After depositing the intermetal dielectric, chemical mechanical planarization (CMP) can be utilized to planarize the intermetal dielectric to form a planar surface.

[0065] Block 425 illustrates etching the intermetal dielectric layer to form a plurality of second trenches. In some embodiments, individual trenches included in the plurality of second trenches are aligned with respect to components of the image sensor (e.g., to couple pixel transistors 265 or otherwise facilitate readout of the plurality of photodiodes). It should be understood that in some embodiments, lithography and subsequent etching may be used to form the plurality of second trenches. For example, a third photoresist layer may be deposited over the intermetal dielectric and the third photoresist layer may be patterned to form an opening positioned over or otherwise aligned with respect to components of the image sensor. The plurality of second trenches may then be formed using etching (e.g., plasma etching or other known etching techniques), which removes the material of the intermetal dielectric aligned with the opening to form the plurality of second trenches. It should be understood that an after-etch clean may be used to subsequently remove the third photoresist layer after performing the etching to form the plurality of second trenches.

[0066] Block 430 shows depositing a metal material to fill the plurality of second trenches to form metal contacts of a proximal metal layer included in an interconnect stack (e.g., metal contacts M1 of proximal metal layer 254 included in interconnect stack 250 illustrated in Figure 2C ). In embodiments of the present disclosure, a light balancing structure is disposed between a second side of the semiconductor substrate and the proximal metal layer. In some embodiments, the proximal metal layer may have a composition common or identical to that of the light balancing structure. Thus, in some embodiments, the metal material may include a liner material and a fill material and may then be processed using similar techniques. In other words, the formation of the light balancing structure and the interconnect stack may be compatible and use similar processing techniques as previously discussed.

[0067] Figure 5 is a functional block diagram of an imaging system 500 including an image sensor 505 according to embodiments of the present disclosure that includes Figures 2A to 4 a light balancing structure (e.g., the light balancing structure 239 illustrated in Figures 2A to 2D and the light balancing structure including a plurality of discrete segments 340 illustrated in Figures 3A to 3B ) as described in the exemplary embodiments. The image sensor 505 may have a structure corresponding to the exemplary image sensor 200 illustrated in Figures 2A to 2D and the image sensor 300 illustrated in Figures 3A to 3B , and may use Figure 4fabricated by the method 400 illustrated therein. For example, according to an embodiment of the present disclosure, the image sensor 505 includes a light balance structure to mitigate asymmetric optical crosstalk. The imaging system 500 includes an image sensor 505 configured to generate an electrical signal or an image signal in response to incident light 596, an objective lens 598 having an adjustable optical power to focus on one or more points of interest within an external scene 591, and a controller 572 configured to control the operation of the image sensor 505 and the objective lens 598 in particular. The image sensor 505 is Figures 2A to 2D the exemplary image sensor 200 illustrated therein and Figures 3A to 3B a possible implementation of the image sensor 300 illustrated therein. The image sensor 505 is a simplified schematic diagram showing a semiconductor substrate 501, a plurality of color filters 519, and a plurality of microlenses 535, wherein a plurality of photodiodes 515 are disposed within respective portions of the semiconductor substrate 501. The controller 572 includes one or more processors 574, a memory 576, control circuitry 578, readout circuitry 580, and functional logic 582.

[0068] The controller 572 includes logic and / or circuitry configured to control the operation of various components of the imaging system 500 (e.g., before, after, and during an in-situ stage of image and / or video acquisition). The controller 572 can be implemented as hardware logic (e.g., an application specific integrated circuit, a field programmable gate array, a system-on-a-chip, etc.), software / firmware logic executed on a general purpose microcontroller or microprocessor, or a combination of hardware and software / firmware logic. In one embodiment, the controller 572 includes a processor 574 coupled to a memory 576 that stores instructions executed by the controller 572, the processor 574, and / or one or more other components of the imaging system 500. When executed, the instructions can cause the imaging system 500 to perform operations associated with any one or combination of the various functional modules, logic blocks, or circuitry of the imaging system 500, including the control circuitry 578, the readout circuitry 580, the functional logic 582, the image sensor 505, the objective lens 598, and any other elements of the imaging system 500 (illustrated or otherwise). The memory is a non-transitory computer-readable medium that can include, but is not limited to, a volatile (e.g., RAM) or non-volatile (e.g., ROM) storage system readable by the controller 572. It should be further understood that the controller 572 can be a monolithic integrated circuit, one or more discrete interconnected electrical components, or a combination thereof, which can be formed on one or more substrates coupled together. Additionally, in some embodiments, one or more electrical components can be coupled together to collectively serve as the controller 572 for coordinating the operation of the imaging system 500.

[0069] The control circuitry 578 can control the operating characteristics of an array formed by a plurality of photodiodes 515 (e.g., exposure duration, when to capture a digital image or video, etc.). In some embodiments, the control circuitry 578 can be configured to provide a ground reference voltage to a plurality of discrete segments included in the optical balance structure of the image sensor 505. The readout circuitry 580 reads or otherwise samples the analog signals from the individual photodiodes (e.g., reads the electrical signals generated by each of the plurality of photodiodes 515 in response to incident light to generate an image signal for capturing an image frame, etc.) and can include amplifier circuitry, analog-to-digital (ADC) circuitry, an image buffer, or others. In the illustrated embodiment, the readout circuitry 580 is included in the controller 572, but in other embodiments, the readout circuitry 580 can be separate from the controller 572. The functional logic 582 is coupled to the readout circuitry 580 to receive the image data, thereby demosaicking the image data and generating one or more image frames. In some embodiments, the electrical signals and / or the image data can be manipulated or otherwise processed by the functional logic 582 (e.g., applying post-image effects such as cropping, rotation, red-eye removal, brightness adjustment, contrast adjustment, or others).

[0070] References throughout this specification to "one example" or "one embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one example" or "in one embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Additionally, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0071] Spatial relative terms (such as "beneath," "below," "upper," "lower," "above," "over," "top," "bottom," "left," "right," "center," "middle," etc.) may be used herein for ease of description to describe the relationship of one element or feature to another (other) element or feature illustrated in the figures. It will be understood that the spatial relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is rotated or flipped, an element described as "beneath" or "below" or "lower" than another element or feature will then be oriented "above" the other element or feature. Thus, the exemplary terms "below" and "beneath" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and thus the spatial relative descriptors used herein can be interpreted accordingly. Additionally, it will also be understood that when an element is referred to as being "between" two other elements, the element can be the only element between the two other elements, or there can be one or more intervening elements.

[0072] Throughout this specification, several technical terms are used. These terms will assume their ordinary meaning in the field to which they belong, unless specifically defined herein or the context in which they are used will clearly imply otherwise. It should be noted that in this document, element names and symbols may be used interchangeably (e.g., Si and silicon); however, both have the same meaning.

[0073] The processes explained above can be implemented using software and / or hardware. The described techniques may constitute machine-executable instructions embodied within a tangible or non-transitory machine (e.g., a computer) readable storage medium, which when executed by a machine (e.g., Figure 5 controller 572 thereof) will cause the machine to perform the described operations. Additionally, the processes may be embodied within hardware such as, for example, an application specific integrated circuit (“ASIC”), a field programmable gate array (FPGA), or others.

[0074] A tangible machine readable storage medium includes any mechanism that provides (i.e., stores) information in a non-transitory form that can be accessed by a machine (e.g., a computer, a network device, a personal digital assistant, a manufacturing tool, any device having a set of one or more processors, etc.). By way of example, a machine readable storage medium includes recordable / non-recordable media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.).

[0075] The above description of the illustrated examples of the invention, which includes what is described in the abstract of the invention, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Although specific examples of the invention have been described herein for illustrative purposes, as will be recognized by those of ordinary skill in the art, various modifications can be made within the scope of the invention.

[0076] These modifications can be made in view of the above detailed description. The terms used in the appended claims should not be construed as limiting the invention to the specific examples disclosed in this specification. Rather, the scope of the invention will be determined entirely by the appended claims, which are to be construed in accordance with the established principles of claim interpretation.

Claims

1. An image sensor, comprising: a plurality of pixel cells arranged to form an image sensor array disposed in or on a semiconductor substrate, wherein each pixel cell in the plurality of pixel cells includes one or more photodiodes disposed within the semiconductor substrate between a first side and a second side of the semiconductor substrate, wherein the first side is opposite the second side; a proximal metal layer included in an interconnect stack disposed proximate the second side of the semiconductor substrate; and A light balancing structure is disposed between the second side of the semiconductor substrate and the proximal metal layer, wherein the light balancing structure includes a plurality of discrete segments optically aligned with a first type of pixel cells included in the plurality of pixel cells. 2 . The image sensor of claim 1 , wherein individual segments included in the plurality of discrete segments are coupled to ground.

3. The image sensor according to claim 2 further includes one or more transistors disposed near the second side of the semiconductor substrate, wherein metal contacts disposed within the proximal metal layer are electrically coupled to the one or more transistors through one or more through-holes; wherein at least one of the one or more through-holes is disposed in the same dielectric layer as at least a portion of the light balancing structure.

4. The image sensor of claim 1 , wherein the first type of pixel cells have associated chief ray angles based on relative pixel positions within the image sensor, and individual segments included in the plurality of discrete segments are arranged based on the associated chief ray angles.

5. The image sensor of claim 4, wherein a center-to-center distance between the individual segments included in the plurality of discrete segments and corresponding optically aligned pixel cells included in the first type of pixel cells is based on the associated chief ray angles.

6. The image sensor of claim 1 , wherein the center-to-center distances between individual segments included in the plurality of discrete segments and corresponding optically aligned pixel cells included in the first type of pixel cells are arranged such that the center-to-center distances increase toward a perimeter of the image sensor.

7. The image sensor of claim 1, wherein adjacent segments included in the plurality of discrete segments have at least one of different sizes, different shapes, different orientations, different lateral areas, or different locations relative to a center of a pixel cell of the first type.

8. An image sensor according to claim 1, wherein the plurality of pixel cells further include pixel cells of a second type different from the first type of pixel cells, wherein each of the first type of pixel cells is adjacent to two or more of the second type of pixel cells, and wherein the plurality of discrete segments have an asymmetric or non-uniform arrangement to configure the light balancing structure to reduce asymmetric optical crosstalk from light propagating through the first type of pixels toward the second type of pixels. 9 . The image sensor of claim 8 , wherein the first type of pixel cells corresponds to red pixel cells and wherein the second type of pixel cells corresponds to green pixel cells.

10. The image sensor of claim 1 , wherein the plurality of pixel cells include a first pixel cell, the first pixel cell including a 2×2 array of four photodiodes, and wherein a first segment included in the plurality of discrete segments is disposed between the proximal metal layer and at least two photodiodes included in the 2×2 array of four photodiodes.

11. The image sensor of claim 10, wherein the first segment has a first lateral area that is larger than a corresponding lateral area of ​​an individual photodiode included in the 2x2 array of four photodiodes.

12. The image sensor of claim 1 , wherein the plurality of pixel cells further include a second type of pixel cells and a third type of pixel cells, each having a color different from that of the first type of pixel cells, and wherein the plurality of segments included in the light balancing structure are optically aligned with neither the second type of pixel cells nor the third type of pixel cells.

13. The image sensor of claim 12, further comprising a plurality of dummy segments disposed between the second side of the semiconductor substrate and the proximal metal layer, wherein individual dummy segments included in the plurality of dummy segments are optically aligned with at least one of the second type of pixel cells or the third type of pixel cells. 14 . The image sensor of claim 13 , wherein the plurality of discrete segments have a non-uniform arrangement and the plurality of dummy segments have a uniform arrangement, and wherein the plurality of discrete segments and the plurality of dummy segments are arranged on a common transverse plane.

15. An image sensor according to claim 1, wherein the first type of pixel cell includes a first pixel cell and a second pixel cell, wherein the plurality of discrete segments include a first segment optically aligned with the first pixel cell and a second segment optically aligned with the second pixel cell, wherein the first segment is disposed between four photodiodes included in the first pixel cell and the proximal metal layer, and wherein the second segment is disposed between two or fewer photodiodes included in the second pixel cell and the proximal metal layer.

16. An image sensor according to claim 1, wherein the first type of pixel cell includes a first pixel cell and a second pixel cell, wherein the plurality of discrete segments include a first segment optically aligned with the first pixel cell and a second segment optically aligned with the second pixel cell, wherein the first segment is optically centered relative to the first pixel cell, and wherein the second segment is optically decentered relative to the second pixel cell, and wherein a first principal ray angle of the first pixel cell is less than a second principal ray angle of the second pixel cell.

17. The image sensor of claim 1, wherein both the proximal metal layer and the plurality of discrete segments of the light balancing structure comprise the same metal material.

18. A method for forming an image sensor, comprising: etching an interlayer dielectric to form a plurality of trenches positioned over a first type of pixel cell included in a plurality of pixel cells, wherein each pixel cell included in the plurality of pixel cells includes one or more photodiodes disposed within a semiconductor substrate, the semiconductor substrate including a first side and a second side opposite the first side; Depositing a metal material to fill the plurality of trenches to form a light balancing structure, wherein the light balancing structure includes a plurality of discrete segments corresponding to the plurality of trenches filled by the metal material, the plurality of discrete segments being optically aligned with the first type of pixel cells included in the plurality of pixel cells; depositing an intermetallic dielectric layer on the light balancing structure formed in the interlayer dielectric; etching the intermetal dielectric layer to form a plurality of second trenches; and The metal material is deposited to fill the plurality of second trenches to form a proximal metal layer included in an interconnect stack, wherein the light balancing structure is disposed between the second side of the semiconductor substrate and the proximal metal layer.

19. A multi-color image pixel comprising: a group of four pixel cells arranged in a 2×2 array, the group of four pixel cells comprising a red pixel cell, two green pixel cells adjacent to the red pixel cell, and a blue pixel cell adjacent to the two green pixel cells, wherein each pixel cell included in the group of four pixel cells comprises at least four photodiodes disposed within a semiconductor substrate; a proximal metal layer included in an interconnect stack coupled to the semiconductor substrate; and Discrete segments of a light-balancing structure are optically aligned with the red pixel cells included in the group of four pixel cells, wherein the discrete segments are further disposed between the semiconductor substrate and the proximal metal layer.

20. The multi-color image pixel of claim 19, wherein the multi-color image pixel is included in an image sensor, wherein the discrete segments are adapted to mitigate asymmetric optical crosstalk of the two green pixel cells by positioning the discrete segments above the red pixel cells based at least in part on the relative positions of the red pixel cells in a pixel array of the image sensor.

Images