CMOS image sensor

Abstract

The invention discloses a CMOS (Complementary Metal-Oxide-Semiconductor Transistor) image sensor, which is characterized in that a mesh structure is reasonably arranged, the light receiving areas of color filters with different colors in different areas of a chip light receiving area are adjusted, and the widths of meshes in different areas of the light receiving area are adjusted at the same time; the problem of chromatic aberration of a central area and an edge area of a chip light receiving area and the problem of optical crosstalk between pixels of different colors can be solved at the same time, and the imaging quality is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more particularly to CMOS image sensors. Background Technology

[0002] Image sensors are the core components of camera equipment, converting light signals into electrical signals to achieve image capture. Taking CMOS image sensors (CIS) as an example, they are widely used in various fields due to their advantages of low power consumption and high signal-to-noise ratio.

[0003] Taking back-side illumination (BSI) CIS as an example, in the existing manufacturing process, logic devices, pixel devices, and metal interconnect structures are first formed in the semiconductor substrate. Then, a carrier wafer is bonded to the front side of the semiconductor substrate, and the back side of the semiconductor substrate is thinned. Subsequent CIS processes are then formed on the back side of the semiconductor substrate, such as forming a grid-like grid on the back side of the semiconductor substrate of the pixel device, and forming a color filter matrix in the grid between the grids.

[0004] Taking front-side illumination (FSI) CIS as an example, in the existing manufacturing process, logic devices, pixel devices, and metal interconnect structures are first formed in the semiconductor substrate, and then a grid-like grid is formed on the surface of the metal interconnect structure. Color filter matrices are formed in the grid between the grids.

[0005] In traditional image sensor chips, the color filter areas defined by the mesh structure in the central and edge regions of the chip are the same. When externally incident light reaches the light-receiving area of ​​the image sensor chip, the light is directly incident near the center of the light-receiving area, resulting in stronger illumination. At the edges of the light-receiving area, the light is obliquely incident, resulting in weaker illumination. This leads to differences in the ratio of blue to green wavelengths (BG ratio) and the ratio of red to green wavelengths (RG ratio) received at the center and edges of the light-receiving area. The BG and RG ratios at the edges are greater than those at the center, resulting in significant color shading between the center and edges, greatly affecting the image sensor's imaging quality. Furthermore, the mesh structure typically contains oxides to refract or reflect light into the photosensitive pixels. However, the wider the mesh structure, the easier it is for light to pass through the oxide layer from one pixel area to adjacent pixel areas, easily causing optical crosstalk between pixels of different colors, which also affects the image sensor's imaging quality. Summary of the Invention

[0006] Based on the problems described above, this invention proposes a CMOS image sensor structure.

[0007] The light receiving area includes a central area near the center of the light receiving area and an edge area away from the center of the light receiving area. Both the central area and the edge area further include: multiple pixels and multiple color filters corresponding to them, each color filter including a first color filter and a second color filter, wherein the first color filter and the second color filter are different; a mesh is disposed around the multiple color filters to isolate adjacent color filters; the mesh width between adjacent first and second color filters in the edge area is smaller than the mesh width between adjacent first and second color filters in the central area, thereby reducing light crosstalk between different color pixel areas; wherein the light receiving area of ​​the first color filter in the edge area is smaller than the light receiving area of ​​the first color filter in the central area, or the light receiving area of ​​the second color filter in the edge area is larger than the light receiving area of ​​the second color filter in the central area, thereby reducing the color difference between the edge area and the central area.

[0008] Optionally, the first color filter is a red or blue color filter, and the second color filter is a green color filter.

[0009] Optionally, when the light-receiving area of ​​the first color filter in the edge region is smaller than the light-receiving area of ​​the first color filter in the middle region, the grid width between adjacent first color filters in the edge region is greater than the grid width between adjacent first color filters in the middle region.

[0010] Optionally, the light-receiving area of ​​the first color filter in the edge region is smaller than the light-receiving area of ​​the second color filter in the edge region.

[0011] Optionally, the light-receiving area of ​​the second color filter in the edge region is the same as the light-receiving area of ​​the second color filter in the middle region.

[0012] Optionally, when the light-receiving area of ​​the second color filter in the edge region is greater than the light-receiving area of ​​the second color filter in the middle region, the light-receiving area of ​​the second color filter in the edge region is greater than the light-receiving area of ​​the first color filter in the edge region.

[0013] Optionally, the light-receiving area of ​​the first color filter in the edge region is the same as the light-receiving area of ​​the first color filter in the middle region.

[0014] Optionally, when the light-receiving area of ​​the second color filter in the edge region is greater than the light-receiving area of ​​the second color filter in the middle region, the grid width between adjacent second color filters in the edge region is less than the grid width between adjacent second color filters in the middle region.

[0015] Optionally, when the light-receiving area of ​​the second color filter in the edge region is greater than the light-receiving area of ​​the second color filter in the middle region, the grid width between adjacent second color filters in the edge region is greater than or equal to the grid width between adjacent second color filters in the middle region.

[0016] Optionally, the grid comprises an oxide material. Optionally, the oxide comprises a metal oxide or silicon oxide. Optionally, the grid further comprises a metallic material.

[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The image sensor of this invention, through a rational arrangement of the mesh structure, can simultaneously solve the color difference problem in the central and edge areas of the chip's light-receiving area, as well as the optical crosstalk problem between pixels of different colors, significantly improving image quality. By setting the light-receiving area of ​​the first color filter (such as a red or blue filter) in the edge area to be smaller than that of the first color filter in the central area, or by setting the light-receiving area of ​​the second color filter (such as a green filter) in the edge area to be larger than that of the second color filter in the central area, the technical problem that the BG and RG ratios at the edge positions are greater than those in the central area is solved, reducing color difference between different areas of the image sensor chip. Furthermore, based on the above, the mesh width between adjacent different color filters in the edge area (such as between a blue filter and a green filter, or between a red filter and a green filter) is set to be smaller than the mesh width between adjacent different color filters in the central area, thereby simultaneously solving the optical crosstalk problem between pixels of different colors or between color filters. Attached Figure Description

[0018] The accompanying drawings, which form part of this specification, are used to further understand the invention. The drawings illustrate embodiments of the invention and, together with the specification, serve to explain the principles of the invention.

[0019] Figure 1 This is a top view showing the layout of the light receiving area of ​​the image sensor in Embodiment 1 of the present invention.

[0020] Figure 2 for Figure 1 A magnified view of a portion of the image.

[0021] Figure 3 For along Figure 2 Schematic diagram of the cross-sectional structure in the AA and BB directions.

[0022] Figure 4a , 4b This is a magnified view of the local layout of the central and edge regions of the image sensor in Embodiment 2 of the present invention.

[0023] Figure 5 This is a magnified view of the local layout of the central and edge regions of the image sensor in Embodiment 3 of the present invention. Detailed Implementation

[0024] The following detailed description is exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the present invention. Example 1

[0026] Figures 1 to 3 This is a schematic diagram of the image sensor structure in Embodiment 1 of the present invention.

[0027] See Figure 1 A top view shows an image sensor comprising a light-receiving area L, with a plurality of pixels P disposed within the light-receiving area. The pixels P are arranged in a two-dimensional matrix along a first direction X and a second direction Y in the XY plane. The light-receiving area L includes a central area Z1 and an edge area Z2, wherein the central area Z1 is closer to the center point C of the light-receiving area L, and the edge area Z2 is farther from the center point C of the light-receiving area L. The central area Z1 is closer to the center C of the light-receiving area L than the edge area Z2. (Appendix) Figure 1 In the image, both the central region Z1 and the edge region Z2 consist of four pixels forming a pixel array unit.

[0028] See appendix Figure 2 , 3 In this embodiment, the image sensor includes a substrate, a dielectric structure 103, a color filter 106, grids 100a and 100b, and a lens 107.

[0029] An isolation structure 101 and photosensitive areas 102 are formed in the substrate. The photosensitive areas 102 are arranged in a two-dimensional array along a first direction X and a second direction Y, corresponding one-to-one with the aforementioned pixel P. Each photosensitive area 102 has a photosensitive structure (not shown), which includes optoelectronic devices such as photodiodes. Multiple photosensitive structures correspond one-to-one with multiple photosensitive areas. The isolation structure 101 is located between adjacent photosensitive areas 102 and surrounds the photosensitive areas to isolate each adjacent photosensitive area to prevent optical crosstalk and electrical crosstalk between adjacent photosensitive areas. The material of the isolation structure 101 includes a dielectric material, which includes one or more combinations of silicon oxide, silicon nitride, silicon carbide, silicon carbide, silicon oxynitride, aluminum oxide, aluminum nitride, tantalum oxide, hafnium oxide, silicon carbide nitride, and silicon carbide nitride.

[0030] The substrate is made of silicon. In this invention, the image sensor can be a front-illuminated (FSI) or back-illuminated (BSI) image sensor. Taking a back-illuminated image sensor as an example, the substrate also includes a circuit structure (not shown) located below, wherein the circuit structure includes electronic components, including transistors, and wiring structures.

[0031] A dielectric structure 103 is formed on a substrate. The dielectric structure includes one or more dielectric layers, the material of which includes one or more combinations of silicon oxide, hafnium oxide, silicon nitride, and aluminum oxide. The dielectric structure is a transparent material so that light can pass through it to reach the photosensitive area. The dielectric structure also serves as an insulator to prevent electrical crosstalk and provides planarization.

[0032] Color filters 106 are formed on the medium structure 103. In this embodiment, multiple color filters correspond one-to-one with multiple photosensitive areas 102. Of course, the correspondence between color filters and photosensitive areas can also be in other ways. Consistent with the arrangement of the photosensitive areas 102, the color filters are arranged in a two-dimensional array along the first direction X and the second direction Y. The color filters 106 may include a first color filter (red), a blue color filter, and a second color filter (green), and may also include combinations of other color filters. In this embodiment, the color filters are arranged in a Bayer pattern. See also... Figure 2, taking the pixel units in the central region Z1 and the edge region Z2 as an example where each includes 4 pixels, the color filters in the central region Z1 and the edge region Z2 both include 2 green color filters G1 or G2, 1 blue color filter B1 or B2, and 1 red color filter R1 or R2. The 4 color filters in the central region Z1 and the edge region Z2 are both distributed in a "field" shape. Among them, the two green color filters G1 or G2 are distributed diagonally. The green color filter G1 or G2 and the blue color filter B1 or B2 are distributed along the second direction Y. The green color filter G1 or G2 is also distributed with the red color filter R1 or R2 along the first direction X. The blue color filter B1 or B2 and the red color filter R1 or R are distributed diagonally.

[0033] The mesh grids 100a and 100b are formed on the dielectric structure 103, and the mesh grids 100a and 100b are arranged around and between multiple color filters for isolating adjacent color filters. In some embodiments, the mesh grids 100a and 100b may or may not overlap with the isolation structure 101 in the third direction Z. In this embodiment, the mesh grids 100a and 100b include an oxide 105 for refracting or reflecting the obliquely incident light into the photosensitive structure in the photosensitive region to improve the light collection efficiency. The oxide material includes silicon oxide or metal oxide. In some embodiments, the mesh grids 100a and 100b may further include a metal layer 104, and the metal layer 104 absorbs light to prevent optical crosstalk between adjacent color filters.

[0034] Appendix Figure 2 , 3 In the figure, the light receiving area S22 of the green color filter G2 in the edge region Z2 is larger than the light receiving area S12 of the green color filter G1 in the central region Z1. Refer to Appendix Figure 1 , the light receiving area of the green color filter can increase as the distance from the center point C of the light receiving region increases. The light receiving area of the color filter is defined as the area of the color filter surrounded by the mesh grid 100 in the XY plane. Further, the light receiving area S22 of the green color filter G2 in the edge region Z2 is also larger than the light receiving area S21 of the blue color filter B2 or the light receiving area S23 of the red color filter R2 in the edge region Z2. In addition, the light receiving area S21 of the blue color filter B2 in the edge region Z2 may be the same as the light receiving area S11 of the blue color filter B1 in the central region Z1, and the light receiving area S23 of the red color filter R2 is equal to the light receiving area S13 of the red color filter R1 in the central region Z1. In addition, the light receiving areas S11, S12, and S13 of the color filters in the central region Z1 may be all equal.

[0035] Meanwhile, the mesh widths W21 and W22 between the blue filter B2 or the red-green filter R2 and the green filter G2 in the edge region Z2 are smaller than the mesh widths W11 and W12 between the corresponding blue filter B1 or the red filter R1 and the green filter G1 in the central region Z1, i.e., W21 < W11 and W22 < W12. In some embodiments of this example, the mesh widths between the filters in the central region Z1 can be equal.

[0036] See appendix Figure 3 Lens 107 is formed on grids 100a, 100b and color filter 106, with each lens 107 corresponding to a color filter 106. Lens 107 has an arc-shaped protruding structure that can converge light into the photosensitive structure of photosensitive area 102.

[0037] In traditional image sensors, the color filter areas defined by the mesh structure in the central and edge regions of the chip are the same. When externally incident light reaches the light-receiving area L of the image sensor chip, the light is directly incident and has a stronger intensity near the center C of the light-receiving area L, while the light at the edge of the light-receiving area L is obliquely incident and has a weaker intensity. This results in different ratios of blue to green wavelengths (BG ratio) and red to green wavelengths (RG ratio) at the center and edge of the light-receiving area of ​​the image sensor chip. The BG and RG ratios at the edge are both greater than those at the center, leading to a significant color shading between the center and edge, which greatly affects image quality. Furthermore, in the oxide-containing mesh structure, the wider the mesh structure, the easier it is for light to pass through the oxide layer from one pixel area to adjacent pixel areas. This can easily cause optical crosstalk between pixels of different colors, which also affects the image quality of the image sensor.

[0038] The image sensor used in this embodiment can simultaneously solve the color difference problem in the central and edge areas, as well as the optical crosstalk problem between pixels of different colors. In this embodiment, the light-receiving area of ​​the green filter increases with the distance from the center C of the light-receiving area L of the image sensor. As mentioned above, the light-receiving areas S22 and S23 of the green filter G2 in the edge area Z2 are greater than the light-receiving areas S12 and S13 of the green filter G1 in the central area Z1. Thus, the technical problem that the BG and RG ratios at the edge positions are greater than those in the central area is solved, reducing the color difference between different areas of the image sensor chip. Furthermore, based on the above, the mesh width between adjacent color filters of different colors in the edge region Z2 (such as between blue filter B2 and green filter G2, and between red filter R2 and green filter G2) is set to be smaller than the mesh width between adjacent color filters of different colors in the center region Z1 (such as between blue filter B1 and green filter G1, and between red filter R1 and green filter G1), thereby simultaneously solving the problem of optical crosstalk between different color pixels or color filters. Example 2

[0039] Figure 4a , 4b This is a magnified view of the local layout of the central and edge regions of the image sensor in Embodiment 2 of the present invention.

[0040] Referring to Figure 4, in this embodiment, the color filters of different colors are arranged in a 2×2 array, where the four color filters in adjacent 2×2 arrays have the same color. However, the above is only an example; the color filters of the same color can also be arranged in other array forms, such as 3×3, 4×4, 2×3, etc. The photosensitive area, color filters, and lenses are arranged in a one-to-one correspondence.

[0041] The light-receiving area of ​​the green filter increases with the distance from the center C of the light-receiving area L of the image sensor. For example, the light-receiving area S42 of the green filter G2 in the edge region Z2 is larger than the light-receiving area S32 of the green filter G1 in the center region Z1. Furthermore, the light-receiving area S42 of the green filter G2 in the edge region Z2 is also larger than the light-receiving area S41 of the blue filter B2 or the light-receiving area S43 of the red filter R2 in the edge region Z2. In addition, the light-receiving area S41 of the blue filter B2 in the edge region Z2 is the same as the light-receiving area S31 of the blue filter B1 in the center region Z1, and the light-receiving area S43 of the red filter R2 is equal to the light-receiving area S33 of the red filter R1 in the center region Z1. Furthermore, the light-receiving areas S31, S32, and S33 of the filters in the center region Z1 can all be equal.

[0042] Meanwhile, the mesh widths W41 and W42 between the blue filter B2 and the red-green filter R2 and the green filter G2 in the edge region Z2 are smaller than the mesh widths W31 and W32 between the corresponding blue filter B1 and the red filter R1 and the green filter G1 in the center region Z1, i.e., W41 < W31 and W42 < W32. In some embodiments of this example, see the appendix. Figure 4a In edge region Z2, the mesh widths W44 and W45 between adjacent green filters G2 are smaller than the mesh widths W34 and W35 between adjacent green filters G1 in center region Z1, i.e., W44 < W34 and W45 < W35. In some embodiments of this example, conversely, see attached... Figure 4b The mesh widths W44 and W45 between adjacent green filters G2 in the edge region Z2 can also be greater than or equal to the mesh widths W34 and W35 between adjacent green filters G1 in the center region Z1, i.e., W44 ≥ W34 and W45 ≥ W35. This is mainly because the optical crosstalk between pixels of the same color is relatively small. In some embodiments of this example, the mesh width of the center region Z1 can be uniform.

[0043] The other components in this embodiment are the same as those in Embodiment 1, and will not be described again here.

[0044] Consistent with Example 1, this example addresses the technical issue of the BG / RG ratio being greater at the edge than in the center by increasing the light-receiving area of ​​the green filter in the edge region, thereby reducing color difference between different areas of the image sensor chip. Furthermore, based on the above, the mesh width between adjacent color filters in the edge region Z2 is reduced, thus simultaneously resolving the optical crosstalk problem between different color pixels or color filters. Example 3

[0045] Figure 5 This is a magnified view of the local layout of the central and edge regions of the image sensor in Embodiment 3 of the present invention.

[0046] See Figure 5 In this embodiment, the color filters of different colors are arranged in a 2×2 array, where the four color filters in adjacent 2×2 arrays have the same color. However, the above is only an example, and the color filters of the same color can also be arranged in other array forms, such as 3×3, 4×4, 2×3, etc. The photosensitive area, color filters, and lenses are arranged in a one-to-one correspondence.

[0047] The light-receiving area of ​​the blue or red color filter decreases as the distance from the center C of the light-receiving area L of the image sensor increases. For example, the light-receiving area S61 or S63 of the blue color filter B2 or red color filter R2 in the edge region Z2 is smaller than the light-receiving area S51 or S53 of the blue color filter B1 or red color filter R1 in the center region Z1, i.e., S61 < S51 or S63 < S53. Further, the light-receiving area S61 or S63 of the blue color filter B2 or red color filter R2 in the edge region Z2 can be smaller than the light-receiving area S62 of the green color filter G2 in the edge region Z2, i.e., S61 < S62 or S63 < S62. Moreover, the light-receiving area S62 of the green color filter G2 in the edge region is the same as the light-receiving area S52 of the green color filter G1 in the center region. Furthermore, the light-receiving areas S51, S52, and S53 of the color filters in the center region Z1 can all be equal.

[0048] Appendix Figure 5In the edge region Z2, the light-receiving area S61 of the blue filter B2 is the same as the light-receiving area S63 of the red-green filter R2, meaning that the reduction in the light-receiving area S61 of the blue filter B2 and the light-receiving area S63 of the red-green filter R2 relative to the corresponding filter in the center region is the same. In other embodiments of this example, the reduction in the light-receiving area S61 of the blue filter B2 and the light-receiving area S63 of the red-green filter R2 relative to the corresponding filter in the center region may be different. For example, only the light-receiving area S61 of the blue filter B2 in the edge region may be reduced while the light-receiving area S63 of the red-green filter R2 remains unchanged; or only the light-receiving area S63 of the red-green filter R2 may be reduced while the light-receiving area S61 of the blue filter B2 may remain unchanged; or both may be reduced while the light-receiving areas S61 and S63 are different.

[0049] Meanwhile, the mesh width W61 or W62 between the blue filter B2 or the red / green filter R2 and the green filter G2 in the edge region Z2 is smaller than the mesh width W51 or W52 between the corresponding blue filter B1 or the red filter R1 and the green filter G1 in the central region Z1, i.e., W61 < W51 or W62 < W52. However, the mesh width W63 between adjacent blue filters B2 or the mesh width W65 between adjacent red filters R2 in the edge region Z2 is greater than the mesh width W53 between adjacent blue filters B1 or the mesh width W55 between adjacent red filters R1 in the central region Z1, i.e., W63 > W53 or W65 > W55. In some embodiments of this example, the mesh width of the central region Z1 can be the same for all filters.

[0050] The other components in this embodiment are the same as those in Embodiment 1, and will not be described again here.

[0051] This embodiment addresses the technical issue that the BG / RG ratio at the edge is greater than that in the center region by reducing the light-receiving area of ​​the red or blue filter in the edge area, thereby reducing color difference between different regions of the image sensor chip. Furthermore, by reducing the mesh width between adjacent color filters in the edge region Z2, the optical crosstalk problem between different color pixels or filters is simultaneously resolved.

[0052] The basic concepts have been described above. It is clear that the detailed disclosure above is merely illustrative and does not constitute a limitation of the present invention. Although not explicitly stated herein, various modifications, improvements, and corrections may be made to the present invention by those skilled in the art. Such modifications, improvements, and corrections are suggested in this invention and therefore remain within the spirit and scope of the exemplary embodiments of the present invention.

[0053] It should be understood that the embodiments described in this invention are merely illustrative of the principles of the invention. Other modifications may also fall within the scope of this invention. Therefore, alternative configurations of the embodiments of this invention are considered as examples and not limitations, and are regarded as consistent with the teachings of this invention. Accordingly, the embodiments of this invention are not limited to those explicitly described and illustrated herein.

Claims

1. An image sensor, comprising: The light receiving area includes a central area, which is close to the center of the light receiving area, and an edge area, which is far from the center of the light receiving area; Both the central region and the edge region further include: Multiple pixels and multiple corresponding color filters, wherein the color filters include a first color filter and a second color filter, and the first color filter and the second color filter are different. A grid is disposed around the plurality of color filters to isolate adjacent color filters; The mesh width between adjacent first color filters and second color filters in the edge region is smaller than the mesh width between adjacent first color filters and second color filters in the center region, thereby reducing optical crosstalk between different color pixel regions; The light-receiving area of ​​the first color filter in the edge region is smaller than that of the first color filter in the middle region. Alternatively, the light-receiving area of ​​the second color filter in the edge region is larger than that of the second color filter in the middle region, thereby reducing the color difference between the edge region and the center region.

2. The image sensor according to claim 1, characterized in that, The first color filter is either a red or blue filter, and the second color filter is a green filter.

3. The image sensor according to claim 1, characterized in that, When the light-receiving area of ​​the first color filter in the edge region is smaller than the light-receiving area of ​​the first color filter in the middle region, the grid width between adjacent first color filters in the edge region is greater than the grid width between adjacent first color filters in the middle region.

4. The image sensor according to claim 3, characterized in that, The light-receiving area of ​​the first color filter in the edge region is smaller than the light-receiving area of ​​the second color filter in the edge region.

5. The image sensor according to claim 4, characterized in that, The light-receiving area of ​​the second color filter in the edge region is the same as that of the second color filter in the middle region.

6. The image sensor according to claim 1, characterized in that, When the light-receiving area of ​​the second color filter in the edge region is greater than the light-receiving area of ​​the second color filter in the middle region, the light-receiving area of ​​the second color filter in the edge region is greater than the light-receiving area of ​​the first color filter in the edge region.

7. The image sensor according to claim 6, characterized in that, The light-receiving area of ​​the first color filter in the edge region is the same as that of the first color filter in the middle region.

8. The image sensor according to claim 1, characterized in that, When the light-receiving area of ​​the second color filter in the edge region is greater than the light-receiving area of ​​the second color filter in the middle region, the grid width between adjacent second color filters in the edge region is less than the grid width between adjacent second color filters in the middle region.

9. The image sensor according to claim 1, characterized in that, When the light-receiving area of ​​the second color filter in the edge region is greater than the light-receiving area of ​​the second color filter in the middle region, the grid width between adjacent second color filters in the edge region is greater than or equal to the grid width between adjacent second color filters in the middle region.

10. The image sensor according to claim 1, characterized in that, The grid contains an oxide material.

11. The image sensor according to claim 10, characterized in that, The oxide includes metal oxides or silicon oxide.

12. The image sensor according to claim 11, characterized in that, The grid also contains metallic material.

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