Image sensor forming method and image sensor thereof

Abstract

The present invention provides a method for forming an image sensor and its associated image sensor. The method comprises: forming a metal grid structure above a pixel area; forming island structures between adjacent metal grids; and depositing a microlens material to cover the metal grid structure and the island structures, thereby forming embedded convex microlenses between adjacent metal grids. By forming the metal grid and the island structures within the metal grid, the present invention forms the convex microlenses in a single step, simplifying the manufacturing process. The metal grid surrounding the microlenses reduces light crosstalk, enhances optical response, and improves signal-to-noise ratio.

Description

Technical Field

[0001] The present invention relates to the field of image processing, and in particular to an image sensor forming method and an image sensor thereof. Background Art

[0002] CMOS image sensors offer advantages such as simple manufacturing, easy integration with other devices, small size, light weight, low power consumption, and low cost. Consequently, with technological advancements, CMOS image sensors are increasingly replacing CCD image sensors in various electronic products. Currently, CMOS image sensors are widely used in digital still cameras, camera phones, digital video cameras, medical imaging devices (such as gastroscopes), and automotive cameras. CMOS image sensor products can be categorized as FSI (front-side illumination) and BSI (back-side illumination).

[0003] The image sensor directs incident light onto the image sensor through a microlens, which improves light collection efficiency and is a major factor in determining the characteristics of the image sensor.

[0004] Microlenses are typically fabricated in dedicated OCF factories. There are two common methods for producing microlenses: hot reflow and reverse etching. The hot reflow process heats the columnar photoresist above its glass transition temperature, molten into a molten state. Surface tension on the photoresist causes it to automatically form hemispherical microlenses. Since melted photoresist tends to stick together, adjacent molten photoresist sheets, upon contact, fail to form a lens-like surface. This results in an abnormal microlens structure, hindering the full utilization of incident light and causing background noise. Therefore, the hot reflow process requires a certain spacing between the molten photoresist sheets, ultimately resulting in a low fill factor for the image sensor. The reverse etching process adds a further step to the hot reflow process, etching the material beneath the photoresist back to the shape of the molten hemispherical sheet. This results in a nearly gapless microlens, which improves the image sensor's fill factor. However, the currently commonly used thermal reflow process and reverse etching process need to be processed in a dedicated color filter foundry (OCF FAB), which requires additional logistics time and complex processing technology, resulting in increased costs.

[0005] Therefore, how to reduce the process flow, reduce the transportation process in the preparation process, save time and cost, and at the same time try to reduce the optical crosstalk of the image sensor and improve the performance of the image sensor has always been a problem that technicians in this field have been concerned about. Summary of the Invention

[0006] The object of the present invention is to provide an image sensor forming method and an image sensor thereof, so as to reduce the process flow, reduce the transportation process, save time and cost, and improve the performance of the image sensor.

[0007] Based on the above considerations, the present invention provides a method for forming an image sensor, the method at least comprising:

[0008] forming a metal grid structure above the pixel area;

[0009] An island structure is formed between adjacent metal grids;

[0010] A microlens material is deposited to cover the metal grid structure and the island structure, and an embedded convex microlens is formed between adjacent metal grids.

[0011] Optionally, the method includes at least the following steps:

[0012] Providing a semiconductor substrate, wherein a device layer is provided on a surface of the semiconductor substrate, wherein the device layer includes a pixel region and a peripheral circuit region located around the pixel region;

[0013] forming a top metal layer on the surface of the device layer, and forming a metal grid structure on the top metal layer above the pixel area and a metal interconnect structure on the top metal layer above the peripheral circuit area through a photolithography and etching process;

[0014] Depositing a top dielectric layer to cover and fill the top metal layer, and forming an island structure between adjacent metal grids through a photolithography and etching process;

[0015] A microlens material is deposited on the surface of the structure formed in the above steps to form embedded convex microlenses between adjacent metal grids.

[0016] Optionally, the height of the island structure is greater than the height of the metal grid.

[0017] Optionally, the island structure includes a frustum, a cylinder or a cone.

[0018] Optionally, the cross-sectional shape of the island structure includes a circle, a triangle or a polygon.

[0019] Optionally, the method further comprises the step of depositing an etch stop layer on the surface of the device layer before forming the top metal layer on the surface of the device layer.

[0020] Optionally, the method further comprises the step of forming a passivation layer on the surface of the convex microlens.

[0021] Optionally, the method further includes the step of forming an anti-reflection layer on the surface of the passivation layer.

[0022] Optionally, the method further includes the step of depositing a filter layer on the surface of the convex microlens to form a color image sensor.

[0023] Optionally, the method for forming embedded convex microlenses between adjacent metal grids further includes: etching the microlens material so that the convex microlenses are completely embedded between the adjacent metal grids or partially embedded between the adjacent metal grids.

[0024] Optionally, the forming method is applied to the preparation of a front-illuminated image sensor, the preparation of a back-illuminated image sensor, or the preparation of a fingerprint recognition image sensor.

[0025] The present invention further provides an image sensor, the image sensor comprising at least:

[0026] a metal mesh structure located above the pixel area;

[0027] embedded convex microlenses located between adjacent metal grids;

[0028] Wherein, an island structure is provided at the center of the convex microlens.

[0029] Optionally, the image sensor includes at least:

[0030] A semiconductor substrate, wherein a device layer is provided on a surface of the semiconductor substrate, wherein the device layer includes a pixel region and a peripheral circuit region located around the pixel region;

[0031] A top metal layer located on the surface of the device layer, wherein the top metal layer located above the pixel area is a metal grid structure, and the top metal layer located above the peripheral circuit area is a metal interconnect structure; and a convex microlens located between adjacent metal grids, wherein an island structure is provided at the center of the convex microlens.

[0032] Optionally, the height of the island structure is greater than the height of the metal grid.

[0033] Optionally, the cross-sectional shape of the island structure includes a circle, a triangle or a polygon.

[0034] Optionally, the island structure includes a frustum, a cylinder or a cone.

[0035] Optionally, the device layer is covered with an etch stop layer.

[0036] Optionally, the material of the microlens includes any one or more combinations of silicon nitride, silicon oxide, silicon oxynitride, and polyimide.

[0037] Optionally, the image sensor further includes a passivation layer covering the surface of the convex microlens.

[0038] Optionally, the image sensor further includes an anti-reflection layer covering the surface of the passivation layer.

[0039] Optionally, the convex microlenses are completely embedded between the adjacent metal grids.

[0040] Optionally, the convex microlens is partially embedded between adjacent metal grids.

[0041] Optionally, the image sensor further includes a filter layer located on the surface of the convex microlens to form a color image sensor.

[0042] Optionally, the image sensor is applied to a front-illuminated image sensor system, a back-illuminated image sensor system, or a fingerprint recognition image sensor system.

[0043] The image sensor forming method and the image sensor thereof of the present invention have the following beneficial effects:

[0044] 1) A photomask is used to form a metal grid from the metal layer, and island structures are formed within the metal grid. Microlens material is then deposited, resulting in a single-step formation of convex microlenses. This process does not involve a reflow step, reducing the manufacturing process. Furthermore, the entire image sensor is fabricated in the wafer fab, eliminating the need for shipping to an OCF facility, thus saving shipping costs.

[0045] 2) The microlens is surrounded by a metal grid, forming an embedded microlens, which can reduce light crosstalk, improve optical response and improve signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Other features, objects and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments when read with reference to the accompanying drawings.

[0047] Figures 1-6 A schematic diagram of the process of forming an image sensor provided by the present invention;

[0048] Figure 7 This is a schematic structural diagram of the image sensor provided by the present invention.

[0049] In the drawings, the same or similar reference numerals denote the same or similar devices (modules) or steps throughout different drawings. DETAILED DESCRIPTION

[0050] To solve the above-mentioned problems in the prior art, the present invention provides an image sensor forming method and an image sensor thereof, so as to reduce the process flow, reduce the transportation process, save time and cost, improve the optical response of the image sensor and improve the signal-to-noise ratio.

[0051] In the following detailed description of preferred embodiments, reference will be made to the accompanying drawings, which form a part of the present invention. The accompanying drawings illustrate, by way of example, specific embodiments that can implement the present invention. The illustrative embodiments are not intended to be exhaustive of all embodiments according to the present invention. It will be understood that other embodiments may be utilized, and structural or logical modifications may be made, without departing from the scope of the present invention. Therefore, the following detailed description is not restrictive, and the scope of the present invention is defined by the appended claims.

[0052] The present invention is further described below with reference to specific embodiments.

[0053] This embodiment provides a method for forming an image sensor, the method at least comprising:

[0054] forming a metal grid structure above the pixel area;

[0055] An island structure is formed between adjacent metal grids;

[0056] A microlens material is deposited to cover the metal grid structure and the island structure, and an embedded convex microlens is formed between adjacent metal grids.

[0057] Reference Figures 1 to 6 , a method for forming an image sensor is described in detail.

[0058] like Figure 1 As shown, step 1 is performed, providing a semiconductor substrate (not shown). The semiconductor substrate is provided with a device layer 10. The device layer 10 includes a pixel region 101 and a peripheral circuit region 102 located around the pixel region 101. In this embodiment, the pixel region 101 is exemplified by adjacent pixel units 1011 and 1012. The pixel unit includes a photodiode as well as a transfer transistor, a reset transistor, a source follower transistor, a row select transistor (not shown), etc. In this embodiment, an etch stop layer 11 is also provided on the device layer 10 to protect the pixel unit during subsequent etching processes.

[0059] like Figure 2 and Figure 3 As shown, step 2 is performed) to form a top metal layer 12 on the surface of the device layer 10. Through a photolithography and etching process, the top metal layer 12 located above the pixel area 101 forms a metal grid structure 121, and the top metal layer 12 located above the peripheral circuit area 102 forms a metal interconnect structure 122.

[0060] like Figure 4 and Figure 5 As shown, step 3 is performed, a top dielectric layer 13 is deposited to cover and fill the top metal layer 12, and an island structure 131 is formed between adjacent metal grids through a photolithography and etching process.

[0061] The island structure can be a truncated cone, cylinder, cone, or other three-dimensional structure. The cross-sectional shape of the island structure can be circular, triangular, polygonal, or other regular or irregular shapes. The height of the island structure and the height of the metal grid can be set as needed. Preferably, the height of the island structure is greater than the height of the metal grid to facilitate the formation of convex microlenses.

[0062] like Figure 6 As shown, step 4 is performed to deposit a microlens material 14 on the surface of the structure formed in the above steps to form embedded convex microlenses 141 between adjacent metal grids.

[0063] In order to better form the embedded convex microlens, the microlens material can also be etched by etching so that the convex microlens 141 is completely embedded between adjacent metal grids 121 or partially embedded between adjacent metal grids 121, such as Figure 7 The convex microlens 141 is surrounded by a metal grid, forming an embedded microlens, which can reduce light crosstalk, enhance optical response and improve signal-to-noise ratio.

[0064] After forming the convex microlenses, a passivation layer can be formed on the surface of the convex microlenses to protect the convex microlens material. An anti-reflection layer can also be formed on the surface of the passivation layer to reduce light reflection from the microlens surface and improve the optical performance of the microlenses. After forming the convex microlenses, a filter layer can also be deposited on the surface of the microlenses to form a color image sensor.

[0065] The present invention further provides an image sensor, the image sensor comprising at least:

[0066] a metal mesh structure located above the pixel area;

[0067] embedded convex microlenses located between adjacent metal grids;

[0068] Wherein, an island structure is provided at the center of the convex microlens.

[0069] Specifically, such as Figure 7 As shown, the image sensor includes at least: a semiconductor substrate (not shown), with a device layer 10 disposed on the surface of the semiconductor substrate. The device layer 10 includes a pixel region 101 and a peripheral circuit region 102 located around the pixel region 101; a top metal layer disposed on the surface of the device layer 10, wherein the top metal layer above the pixel region 101 is a metal grid structure 121, and the top metal layer above the peripheral circuit region 102 is a metal interconnect structure 122; and convex microlenses 141 disposed between adjacent metal grids 122, wherein an island structure 131 is disposed at the center of each convex microlens 141. In this embodiment, the pixel region is exemplified by adjacent pixel units 1011 and 1012.

[0070] The island structure can be a truncated cone, cylinder, cone, or other three-dimensional structure. The cross-sectional shape of the island structure can be circular, triangular, polygonal, or other regular or irregular shapes. The height of the island structure and the height of the metal grid can be set as needed. Preferably, the height of the island structure is greater than the height of the metal grid to facilitate the formation of convex microlenses.

[0071] Preferably, the device layer 10 is further covered with an etching stop layer 11 to protect the pixel units in a subsequent etching process.

[0072] The convex microlenses can be completely embedded between adjacent metal grids or partially embedded between adjacent metal grids. Figure 7 As shown, the convex microlens 141 is partially embedded between adjacent metal grids 121. The convex microlens is surrounded by metal grids to reduce light crosstalk, increase optical response, and improve signal-to-noise ratio.

[0073] The material of the convex microlens is a transparent material or a semi-transparent material, including any one or more combinations of silicon nitride, silicon oxide, silicon oxynitride, polyimide, etc., and can be set as needed without limitation here.

[0074] A passivation layer can be placed on top of the convex microlens to protect it. An anti-reflection layer can also be formed on the surface of the passivation layer to reduce light reflection from the microlens surface and improve the optical performance of the microlens. A filter layer can also be formed on the surface of the convex microlens to form a color image sensor.

[0075] It should be noted that the image sensor forming method and image sensor provided by the present invention can be applied to the preparation of outer lenses of front-illuminated image sensors, back-illuminated image sensors, or the preparation of inner lenses in fingerprint recognition image sensors.

[0076] The image sensor formation method and image sensor provided by the present invention utilize a photomask to form a metal grid within the pixel region without increasing costs. Dielectric layer deposition and back-etching processes are then used to create island structures, followed by deposition of microlens material to form the microlenses. The entire process does not involve a reflow process, reducing the number of manufacturing steps. Furthermore, the entire image sensor is fabricated in the wafer fab, eliminating the need for shipping to an optical fiber fabrication facility (OCF), saving shipping costs. The metal grid surrounding the microlenses creates an embedded microlens, reducing light crosstalk, enhancing optical response, and improving signal-to-noise ratio.

[0077] This embodiment is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, in any case, the embodiments should be regarded as exemplary and non-restrictive. In addition, it is obvious that the word "comprising" does not exclude other elements and steps, and the wording "a" does not exclude pluralities. Multiple elements stated in a device claim may also be implemented by one element. Words such as first and second are used to indicate names and do not indicate any particular order.

Claims

1. A method for forming an image sensor, characterized in that: The method comprises at least: forming a metal grid structure above the pixel area; Depositing a top dielectric layer to cover and fill the metal grid structure, and forming an island structure between adjacent metal grids through a photolithography and etching process; A microlens material is deposited on the surface of the structure formed in the above steps to cover the metal grid structure and the island structure, and an embedded convex microlens is formed between adjacent metal grids in one step.

2. The method for forming an image sensor according to claim 1, wherein: The method comprises at least the following steps: Providing a semiconductor substrate, wherein a device layer is provided on a surface of the semiconductor substrate, wherein the device layer includes a pixel region and a peripheral circuit region located around the pixel region; forming a top metal layer on the surface of the device layer, and forming a metal grid structure on the top metal layer above the pixel area and a metal interconnect structure on the top metal layer above the peripheral circuit area through a photolithography and etching process; An island structure is formed between adjacent metal grids; A microlens material is deposited on the surface of the structure formed in the above steps to form embedded convex microlenses between adjacent metal grids.

3. The method for forming an image sensor according to claim 1 or 2, wherein: The height of the island structure is greater than the height of the metal grid.

4. The method for forming an image sensor according to claim 1 or 2, wherein: The island structure includes a frustum, a cylinder or a cone.

5. The method for forming an image sensor according to claim 1 or 2, wherein: The cross-sectional shape of the island structure includes a circle, a triangle or a polygon.

6. The method for forming an image sensor according to claim 2, wherein: The method further comprises the step of depositing an etch stop layer on the surface of the device layer before forming a top metal layer on the surface of the device layer.

7. The method for forming an image sensor according to claim 1 or 2, wherein: The method further comprises the step of forming a passivation layer on the surface of the convex microlens.

8. The method for forming an image sensor according to claim 7, wherein: The method further comprises the step of forming an anti-reflection layer on the surface of the passivation layer.

9. The method for forming an image sensor according to claim 1, wherein: The method further comprises the step of depositing a filter layer on the surface of the convex microlens to form a color image sensor.

10. The method for forming an image sensor according to any one of claims 1 or 2, wherein: The method for forming embedded convex microlenses between adjacent metal grids further includes: etching the microlens material so that the convex microlenses are completely embedded between the adjacent metal grids or partially embedded between the adjacent metal grids.

11. The method for forming an image sensor according to claim 1, wherein: The forming method is applied to the preparation of a front-illuminated image sensor, a back-illuminated image sensor or a fingerprint recognition image sensor.

12. An image sensor prepared by the method according to claim 1, characterized in that: The image sensor comprises at least: a metal mesh structure located above the pixel area; embedded convex microlenses located between adjacent metal grids; Wherein, an island structure is provided at the center of the convex microlens.

13. The image sensor according to claim 12, wherein: The image sensor at least comprises: a semiconductor substrate, a device layer is provided on the surface of the semiconductor substrate, and the device layer comprises a pixel area and a peripheral circuit area located around the pixel area; A top metal layer located on the surface of the device layer, wherein the top metal layer located above the pixel area is a metal grid structure, and the top metal layer located above the peripheral circuit area is a metal interconnect structure; and a convex microlens located between adjacent metal grids, wherein an island structure is provided at the center of the convex microlens.

14. The image sensor according to claim 12, wherein: The height of the island structure is greater than the height of the metal grid.

15. The image sensor according to claim 12, wherein: The cross-sectional shape of the island structure includes a circle, a triangle or a polygon.

16. The image sensor according to claim 12, wherein: The island structure includes a frustum, a cylinder or a cone.

17. The image sensor according to claim 13, wherein: The device layer is covered with an etching stopper layer.

18. The image sensor according to claim 12, wherein: The material of the microlens includes any one or more combinations of silicon nitride, silicon oxide, silicon oxynitride, and polyimide.

19. The image sensor according to claim 12, wherein: The image sensor further includes a passivation layer covering the surface of the convex microlens.

20. The image sensor according to claim 19, wherein The image sensor further includes an anti-reflection layer covering a surface of the passivation layer.

21. The image sensor according to any one of claims 12 to 19, wherein: The convex microlenses are completely embedded between the adjacent metal grids.

22. The image sensor according to any one of claims 12 to 19, wherein: The convex microlens is partially embedded between the adjacent metal grids.

23. The image sensor according to any one of claims 12 to 19, wherein: The image sensor further includes a filter layer located on the surface of the convex microlens to form a color image sensor.

24. The image sensor according to any one of claims 12 to 19, wherein: The image sensor is applied to a front-illuminated image sensor system, a back-illuminated image sensor system or a fingerprint recognition image sensor system.

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