Image sensor and method for manufacturing the same

Abstract

The technical solution of the present invention discloses an image sensor and a manufacturing method thereof, wherein the image sensor comprises: a semiconductor substrate, wherein discretely arranged photodiodes are formed in the semiconductor substrate; a color filter, which is located on the semiconductor substrate and corresponds to the photodiodes; and a microlens, which is located on the color filter and wherein a photosensitive color-changing material is doped in the microlens. The technical solution of the present invention utilizes the characteristic that the color-changing microlens is dark in strong light to reduce the amount of light entering, thereby improving the overexposure phenomenon of the image and improving the performance of the image sensor.

Description

Technical Field

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

[0002] Image sensors receive light signals from an object and convert them into electrical signals, which can then be transmitted for further processing, such as digitization, and then stored in a storage device such as a memory, optical disk or disk, or for display on a display, printing, etc. Image sensors are commonly used in devices such as digital cameras, camcorders, smartphones, scanners, fax machines, etc.

[0003] The image sensor has a standard dynamic response range. When the incident light intensity is within the standard dynamic response range of the image sensor, the image sensor can form an image normally. If the incident light intensity to the image sensor is higher than the maximum value of the standard dynamic response range of the image sensor, the image will be overexposed, thus affecting the performance of the image sensor and the user experience is not good. Summary of the invention

[0004] The technical problem to be solved by the technical solution of the present invention is that when an existing image sensor is imaging, excessive intensity of incident light will cause overexposure.

[0005] In order to solve the above technical problems, the technical solution of the present invention provides an image sensor, including: a semiconductor substrate, in which discretely arranged photodiodes are formed; a color filter, which is located on the semiconductor substrate and corresponds to the photodiodes; a microlens, which is located on the color filter, and the microlens is doped with a photosensitive color-changing material.

[0006] Optionally, the content of the photochromic material is determined according to the relationship between the dynamic response range of the image sensor and the light intensity.

[0007] Optionally, the microlens is formed of a lens material doped with photosensitive powder, a resin material doped with pyspirocyclic ring, or a silver halide photosensitive material.

[0008] Optionally, the microlens includes a lens layer and a color-changing layer covering the lens layer, and the color-changing layer is formed of a lens material doped with photosensitive powder, a resin material doped with pyrochlore, or a silver halide photosensitive material.

[0009] Optionally, the content of the photosensitive powder in the lens material is 0.8% to 3%.

[0010] Optionally, the lens material is also doped with a light stabilizer and an antioxidant.

[0011] Optionally, the content of the light stabilizer and the antioxidant in the lens material is 0.5 to 5 times the content of the photosensitive powder.

[0012] Optionally, the color-changing layer has a thickness ranging from 40 nm to 80 nm.

[0013] Optionally, the light transmittance decreases by 5% to 10% when the microlens changes color.

[0014] In order to solve the above technical problems, the technical solution of the present invention also provides a method for manufacturing an image sensor, comprising: providing a semiconductor substrate, in which discretely arranged photodiodes are formed; forming a color filter on the semiconductor substrate, wherein the color filter corresponds to the photodiodes; forming a microlens on the color filter, wherein the microlens is doped with a photosensitive color-changing material.

[0015] Optionally, forming the microlens includes: using a lens material doped with photosensitive powder, a resin material doped with pyrochlore, or a silver halide photosensitive material to form the microlens.

[0016] Optionally, forming the microlens includes: forming a lens layer and a color-changing layer covering the lens layer on the color filter, wherein the color-changing layer is formed of a lens material doped with photosensitive powder, a resin material doped with pyrochlore, or a silver halide photosensitive material.

[0017] Optionally, the lens material is also doped with a light stabilizer and an antioxidant.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0019] By utilizing the characteristic of photochromic materials changing color under strong light, the microlenses doped with photochromic materials are darkened when exposed to strong light to reduce the light transmittance, that is, reduce the amount of light entering, thereby improving the overexposure phenomenon of the image. When exposed to normal light or weak light, the microlenses are transparent, allowing light to pass normally, thus not affecting the normal exposure of the image.

[0020] The color-changing microlens is directly formed by conventional process using lens material doped with photochromic material, or a color-changing layer doped with photochromic material is formed on an existing microlens by conventional process. The formation process is simple and easy to implement, and will not affect the manufacturing process of the entire image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figures 1 to 3 It is a structural schematic diagram corresponding to each step of the method for manufacturing an image sensor according to the first embodiment of the present invention;

[0022] Figure 4 and Figure 5 It is a schematic diagram of the state of the microlens of the image sensor of the first embodiment of the present invention under different light irradiation conditions;

[0023] Figure 6 It is a structural schematic diagram corresponding to the steps of the method for manufacturing an image sensor according to the second embodiment of the present invention;

[0024] Figure 7 and Figure 8 Schematic diagram of the state of the microlens of the image sensor of the second embodiment of the present invention under different light irradiation conditions. DETAILED DESCRIPTION

[0025] The existing image sensor at least includes a photosensitive device (such as a photodiode), a color filter and a microlens. The light passes through the microlens and the color filter in turn and is received by the photodiode, which converts the light into an electrical signal. However, when the intensity of the incident light is too large, the image may be overexposed. In order to solve the above technical problems, the inventor proposes an image sensor with a color-changing microlens, which uses the color-changing microlens to appear dark under strong light to reduce the light transmittance, that is, reduce the amount of light entering, thereby improving the overexposure phenomenon. Therefore, the image sensor of the technical solution of the present invention at least includes: a semiconductor substrate, in which discretely arranged photodiodes are formed; a color filter, which is located on the semiconductor substrate and corresponds to the photodiode; a microlens, which is located on the color filter, and the microlens is doped with a photosensitive color-changing material.

[0026] In the following, in conjunction with the drawings and embodiments, the image sensor and the manufacturing method thereof according to the technical solution of the present invention are described in detail by taking a back-illuminated image sensor as an example.

[0027] Embodiment 1

[0028] Please refer to Figure 1 , a semiconductor substrate 10 is provided, in which discretely arranged photodiodes 11 are formed.

[0029] The semiconductor substrate 10 may be a silicon substrate, or the material of the semiconductor substrate 10 may be germanium, silicon germanium, silicon carbide, gallium arsenide or indium gallium. The semiconductor substrate 10 may also be a silicon substrate on an insulator or a germanium substrate on an insulator, or a substrate with an epitaxial layer grown thereon.

[0030] The photodiode 11 is a light-sensing device for converting received light signals into electrical signals. In order to meet the requirement of reducing the total thickness of the semiconductor substrate 10 , the positions of the photodiodes 11 in the semiconductor substrate 10 are generally at substantially the same depth.

[0031] Further, if Figure 1As shown, the photodiodes 11 are isolated by a deep trench isolation structure (DTI) 12 to avoid the problem of photogenerated carrier diffusion between different pixels. A shallow trench isolation structure (STI) 13 is also formed in the semiconductor substrate 10, and its position corresponds to the deep trench isolation structure (DTI) 12, which is used to isolate the device structure (not shown) formed in the semiconductor substrate 10.

[0032] The semiconductor substrate 10 has a first surface 10a and a second surface 10b opposite to each other, and the color filter and the microlens are formed on the first surface 10a of the semiconductor substrate 10. A metal interconnection layer 21 is formed on the second surface 10b of the semiconductor substrate 10, and a metal interconnection structure 21a is formed in the metal interconnection layer 21. The semiconductor substrate 10 can be bonded to a carrier wafer 40 through the metal interconnection layer 21.

[0033] Please continue to refer to Figure 2 , a color filter (Color Filter) 36 is formed on the semiconductor substrate 10 , and the color filter 36 corresponds to the photodiode 11 .

[0034] In a specific implementation, an anti-reflection (ARC) layer 31, a high dielectric constant (High-K) material layer 32 and a dielectric layer 33 may be sequentially formed on the first surface 10a of the semiconductor substrate 10. Then, a color filter isolation structure (CFI) and a color filter 36 are formed on the dielectric layer 33.

[0035] The material of the color filter isolation structure may be a material having an isolation function or a light shielding function, and the color filter isolation structure is used to block incident light to avoid optical crosstalk that affects the imaging effect. In this embodiment, the color filter isolation structure includes a metal grid (Metal Grid) 34 and a protective medium 35 covering the sidewalls and top of the metal grid 34. The protective medium 35 is used to prevent the metal material in the metal grid 34 from diffusing into the color filter 36, thereby affecting the performance of the image sensor.

[0036] The color filter 36 is formed between the color filter isolation structures, and the top of the color filter 36 is flush with the top surface of the color filter isolation structure. The color filter isolation structure is distributed in a grid shape, and each color filter 36 is arranged in an array. The color filter 36 may include a red filter, a green filter, and a blue filter. And corresponding to only forming a color filter 36 of one color on each photodiode 11, the incident light entering the color filter 36 can be filtered by the color filter of one color, and then the incident light irradiated to the surface of the photodiode 11 is monochromatic light, and the photodiode 11 absorbs the monochromatic light and converts the optical signal into an electrical signal.

[0037] Please continue to refer to Figure 3 A microlens 37 is formed on the color filter 36, and the microlens 37 is doped with a photosensitive color-changing material 37a.

[0038] The microlenses 37 correspond to the color filters 36. A microlens 37 is formed on each color filter 36. Since the color filters 36 are arranged in an array, the microlenses 37 are also arranged in an array. The microlenses 37 are used to focus incident light so that the incident light passing through the microlenses 37 can be irradiated onto the photodiode 11 corresponding to the microlens 37.

[0039] In this embodiment, forming the microlens 37 includes: forming the microlens using a lens material doped with a photochromic material. The lens material doped with a photochromic material may be a lens material (e.g., a transparent resin) doped with photosensitive powder (OP powder). Specifically, forming the microlens 37 may include: depositing a lens material doped with OP powder on the color filter 36 and the color filter isolation structure to form a lens material layer; forming a photoresist layer on the lens material layer; exposing and developing the photoresist layer to form a microlens pattern arranged at intervals; using the photoresist layer as a mask, etching the lens material layer along the microlens pattern until the color filter isolation structure is exposed to form microlenses 37 arranged at intervals; and using a reflow process to make the surface of the microlens 37 convex. In other embodiments, a mask with a gradient transmittance may be used so that the exposed photoresist has different thicknesses, and different etching thicknesses are achieved at the edge and center of the microlens 37 during the subsequent etching process, thereby forming a microlens 37 with a convex surface.

[0040] Combine the following Figure 4 and Figure 5 The state of the microlens of the image sensor of this embodiment when exposed to different light is described. Ultraviolet rays are divided into three types according to different wavelengths: UVC with a wavelength below 250nm, UVB with a wavelength within 250nm to 320nm, and UVA with a wavelength within 320nm to 380nm. The wavelength range of visible light is 380nm to 800nm, and the wavelength range of infrared light is 900nm to 1800nm. The photochromic principle of OP powder is: use the energy of UVA to open the photosensitive molecular bond, so that it jumps from a low energy level to a high energy level. That is, it jumps from invisible light to visible light, thereby producing a change in color. When the ultraviolet irradiation is lost, the photosensitive molecular bond is closed, that is, it returns to the original color.

[0041] like Figure 4 As shown in FIG. 1 , under bright light, due to the effect of ultraviolet UVA, the microlens 37 changes color to a dark color (such as gray or gray-black), blocking part of the light from entering, that is, reducing the amount of light entering, so that the amount of light irradiating the photodiode 11 is also reduced, thereby reducing the overexposure phenomenon of the image. Figure 5 As shown, under normal light (Normal Light) or weak light, the microlens 37 is transparent, and light passes through the microlens 37 and the color filter 36 to illuminate the photodiode 11, which will not affect the normal exposure of the image. In this embodiment, the light transmittance of the microlens 37 decreases by 5% to 10% when the microlens 37 changes color, that is, the light transmittance of the microlens 37 under strong light is 90% to 95% of the light transmittance of the microlens 37 under normal light or weak light. The normal light or weak light in this embodiment refers to light whose light intensity is within the dynamic response range of the image sensor, and the strong light refers to light whose light intensity is higher than the maximum value of the dynamic response range of the image sensor.

[0042] It should be noted that this embodiment uses the example of forming a microlens with a lens material doped with photosensitive powder, but is not limited thereto. The microlens may also be formed with a resin material doped with pyrochlore or a silver halide (such as silver chloride, silver bromide, etc.) photosensitive material.

[0043] Among them, the content of photochromic material in the microlens can be determined according to the relationship between the dynamic response range of the image sensor and the light intensity. Generally, the stronger the light intensity of the incident light, the more photochromic material should be doped in order to reduce the overexposure phenomenon. Taking the addition of OP powder in the lens material as an example, the content of the photosensitive powder in the lens material can be 0.8% to 3%, and the photosensitive powder is evenly distributed in the lens material. In addition, when OP powder is added to the lens material, the lens material can also be doped with photostabilizers and antioxidants. Generally, the content of photostabilizers and antioxidants in the lens material can be 0.5 times to 5 times the content of the photosensitive powder.

[0044] This embodiment uses a lens material doped with a photochromic material and utilizes a conventional microlens forming process to directly form a color-changing microlens. The forming process is simple and easy to implement and does not affect the manufacturing process of the image sensor.

[0045] Embodiment 2

[0046] The steps of forming the microlens in the manufacturing method of the image sensor of this embodiment are different from those in the first embodiment. The steps before forming the microlens can be combined with Figure 1 and Figure 2 Refer to the description of the first embodiment.

[0047] Please refer to Figure 6 A microlens 47 is formed on the color filter 36, and a photosensitive color-changing material 47a is doped in the microlens 47.

[0048] The microlenses 47 correspond to the color filters 36. A microlens 47 is formed on each color filter 36. Since the color filters 36 are arranged in an array, the microlenses 47 are also arranged in an array. The microlenses 37 are used to focus incident light so that the incident light passing through the microlenses 47 can be irradiated onto the photodiode 11 corresponding to the microlens 47.

[0049] In this embodiment, forming the microlens 47 includes: forming a lens layer 47b and a color-changing layer 47c covering the lens layer on the color filter 36, wherein the color-changing layer 47c is doped with a photosensitive color-changing material 47a.

[0050] The lens layer 47b may be formed by using a lens material first, and then the color-changing layer 47c may be formed by using a lens material mixed with a photochromic material. The lens material mixed with a photochromic material may be a lens material (such as a transparent resin) mixed with photosensitive powder (OP powder).

[0051] Specifically, forming the lens layer 47b may include: depositing lens material on the color filter 36 and the color filter isolation structure to form a lens material layer; forming a photoresist layer on the lens material layer; exposing and developing the photoresist layer to form a spaced microlens pattern; using the photoresist layer as a mask, etching the lens material layer along the microlens pattern until the color filter isolation structure is exposed to form a spaced lens layer 47b; using a reflow process to make the surface of the lens layer 47b convex. In other embodiments, a mask with a gradient transmittance may be used so that the exposed photoresist has different thicknesses, and different etching thicknesses are achieved at the edge and center of the lens layer 47b during the subsequent etching process, thereby forming a lens layer 47b with a convex surface.

[0052] Forming the color-changing layer 47c may include: depositing a lens material doped with OP powder on the lens layer 47b to form a color-changing material layer; forming a photoresist layer on the color-changing material layer; exposing and developing the photoresist layer to form a microlens pattern arranged at intervals; using the photoresist layer as a mask, etching the color-changing material layer along the microlens pattern to form a color-changing layer 47c arranged at intervals; and using a reflow process to make the surface of the color-changing layer 47c convex. In other embodiments, a mask with a gradient transmittance may be used so that the photoresist after exposure has different thicknesses, and different etching amounts are achieved at the edge and center of the color-changing layer 47c during the subsequent etching process, thereby forming a color-changing layer 47c with a convex surface.

[0053] The lens layer 47b and the color-changing layer 47c may also be formed by a single photolithography process. Specifically, the formation of the microlens 47 may include: sequentially depositing lens material and lens material doped with photosensitive color-changing material 47a on the color filter 36 and the color filter isolation structure to form a lens material layer and a color-changing material layer; forming a photoresist layer on the color-changing material layer; exposing and developing the photoresist layer to form a microlens pattern arranged at intervals; using the photoresist layer as a mask, sequentially etching the color-changing material layer and the lens material layer along the microlens pattern until the color filter isolation structure is exposed to form a color-changing layer 47c and a lens layer 47b arranged at intervals; using a reflow process to make the surface of the color-changing layer 47c and the lens layer 47b convex, thereby forming a microlens 47 with a convex surface. In other embodiments, a mask with a gradient transmittance can be used to make the photoresist have different thicknesses after exposure, so that different thicknesses of etching can be achieved at the edge and center of the color-changing layer 47c and the lens layer 47b during the subsequent etching process, thereby forming a color-changing layer 47c and a lens layer 47b with raised surfaces.

[0054] In this embodiment, the color-changing layer 47c covering the lens layer 47b has a uniform thickness, and the thickness of the color-changing layer 47c may range from 40 nm to 80 nm.

[0055] Combine the following Figure 7 and Figure 8 The state of the microlens of the image sensor of this embodiment when irradiated with different light is described. Figure 7 As shown, under bright light, due to the effect of ultraviolet UVA, the color-changing layer 47c of the microlens 47 changes color to a dark color (for example, gray or gray-black), blocking part of the light from entering, that is, reducing the amount of light entering, so that the amount of light irradiating the photodiode 11 is also reduced, thereby reducing the overexposure phenomenon of the image. Figure 8 As shown, under normal light (Normal Light) or weak light, the lens layer 47b and the color-changing layer 47c of the microlens 47 are both transparent, and light passes through the microlens 47 and the color filter 36 to illuminate the photodiode 11, which will not affect the normal exposure of the image. In this embodiment, the light transmittance of the microlens 47 is reduced by 5% to 10% when the microlens 47 changes color, that is, the light transmittance of the microlens 47 under strong light is 90% to 95% of the light transmittance of the microlens 47 under normal light or weak light. The normal light or weak light in this embodiment refers to light whose light intensity is within the dynamic response range of the image sensor, and strong light refers to light whose light intensity is higher than the maximum value of the dynamic response range of the image sensor.

[0056] It should be noted that this embodiment is described by taking the lens material doped with photosensitive powder to form the color-changing layer of the microlens as an example, but it is not limited to this. The color-changing layer of the microlens can also be formed by using a resin material doped with pyrochlore or a silver halide (such as silver chloride, silver bromide, etc.) photosensitive material. Among them, the content of the photosensitive color-changing material in the color-changing layer can be determined according to the relationship between the dynamic response range of the image sensor and the light intensity. Generally, the stronger the light intensity of the incident light, the more the doping amount of the photosensitive color-changing material should be in order to reduce the overexposure phenomenon.

[0057] In this embodiment, a color-changing layer mixed with a photochromic material is covered on the existing microlens. The color-changing layer can be formed by a conventional microlens forming process. The forming process is simple and easy to implement, and will not affect the manufacturing process of the image sensor.

[0058] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. An image sensor, characterized in that: include: A semiconductor substrate having discretely arranged photodiodes formed therein; a color filter, located on the semiconductor substrate and corresponding to the photodiode; A microlens is located on the color filter, wherein the microlens is doped with a photochromic material; the content of the photochromic material is determined according to the relationship between the dynamic response range of the image sensor and the light intensity; the microlens is formed by a lens material doped with photosensitive powder, a resin material doped with pyrrolidone, or a silver halide photosensitive material; the microlens comprises a lens layer and a color-changing layer covering the lens layer, wherein the color-changing layer is formed by a lens material doped with photosensitive powder, a resin material doped with pyrrolidone, or a silver halide photosensitive material.

2. The image sensor according to claim 1, wherein: The content of the photosensitive powder in the lens material is 0.8% to 3%.

3. The image sensor according to claim 2, wherein: The lens material is also doped with a light stabilizer and an antioxidant.

4. The image sensor according to claim 3, wherein: The content of the light stabilizer and the antioxidant in the lens material is 0.5 to 5 times the content of the photosensitive powder.

5. The image sensor according to claim 1, wherein: The thickness of the color-changing layer ranges from 40 nm to 80 nm.

6. The image sensor according to any one of claims 1 to 5, characterized in that: When the microlens changes color, the light transmittance decreases by 5% to 10%.

7. A method for manufacturing an image sensor, characterized in that: include: Providing a semiconductor substrate having discretely arranged photodiodes formed therein; forming a color filter on the semiconductor substrate, the color filter corresponding to the photodiode; forming a microlens on the color filter, wherein the microlens is doped with a photochromic material; The formation of the microlens includes: using a lens material doped with photosensitive powder, a resin material doped with pyrrolidone or a silver halide photosensitive material to form the microlens; forming the microlens includes: forming a lens layer and a color-changing layer covering the lens layer on the color filter, the color-changing layer is formed of a lens material doped with photosensitive powder, a resin material doped with pyrrolidone or a silver halide photosensitive material; and the lens material is further doped with a light stabilizer and an antioxidant.

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