Image sensor and method of manufacturing the same, electronic device

Abstract

The application relates to an image sensor and a preparation method thereof and an electronic device, and comprises the following steps: providing a pixel array; forming a first photoresist layer covering the pixel array based on a gray-tone mask; the gray-tone mask comprises a center area and a plurality of peripheral areas which are distributed along the radial direction of the center area and surround the center area; the light transmittance of the center area and the plurality of peripheral areas is different; forming a second photoresist layer and an anti-reflection layer which are stacked in sequence in the direction away from the pixel array on the top surface of the first photoresist layer; wherein the second photoresist layer comprises a center part and a plurality of peripheral parts which are arranged in sequence in the direction away from the center part, the incident light generates first transmitted light through the center part and generates second transmitted light through the peripheral parts; and the light intensity difference value of the first transmitted light and the second transmitted light is within a preset range. Through process structure modification, the problems of uneven light intensity distribution and color shading of the CMOS image sensor can be improved, and the quality of the image sensor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of integrated circuits, and in particular to an image sensor, a preparation method thereof, and an electronic device. BACKGROUND

[0002] A CMOS image sensor (CIS) is a chip that converts optical signals into electrical signals and is widely used in markets such as cameras, smartphones, security monitoring, automotive electronics, and machine vision. Its working principle is mainly based on the photoelectric effect. Photons enter the sensor through the lens and are absorbed by the photodiode in the sensor, generating electrons. The electrons are collected and converted into electrical signals, amplified and processed, and finally form a digital image.

[0003] Uniformity and color shading are important indicators for evaluating the imaging quality of an image sensor. Due to the radial nature of the lens collecting more light in the center, the light intensity received by the sensor is high in the center and low at the periphery, resulting in poor uniformity and color shading.

[0004] Currently, existing technologies mainly rely on software algorithms and image post-processing techniques to correct the above uniformity. How to break through the limitations of light collection efficiency and angle response at the sensor manufacturing level has become one of the technical problems that researchers in the field need to solve. SUMMARY

[0005] Therefore, it is necessary to provide an image sensor, a preparation method thereof, and an electronic device to at least distinguish from existing software methods and image processing methods, and to improve the image quality of the image sensor through internal process structure.

[0006] In a first aspect, the present application provides a preparation method of an image sensor, comprising:

[0007] providing a pixel array;

[0008] forming a first photoresist layer covering the pixel array based on a gray-tone mask; the gray-tone mask comprises a center region and a plurality of peripheral regions surrounding the center region and distributed along the radial direction of the center region; the transmittance of the center region is different from that of the plurality of peripheral regions;

[0009] forming a second photoresist layer and an anti-reflection layer stacked in sequence in a direction away from the pixel array on the top surface of the first photoresist layer;

[0010] The second photoresist layer comprises a center portion and a plurality of peripheral portions arranged in sequence in a direction away from the center portion, the incident light generates first transmitted light via the center portion and generates second transmitted light via the peripheral portions; the light intensity difference between the first transmitted light and the second transmitted light is within a preset range.

[0011] In the preparation method of the above embodiment, a new image sensor structure is prepared by a multi-gray mask, wherein the use of the gray mask allows the light transmittance of different areas to be different, and by adjusting the exposure amount during lithography, the curved surface structure (center part and peripheral part) of different heights or shapes between the first photoresist layer and the second photoresist layer is modified, the propagation path of incident light is controlled, the light intensity difference between the first transmitted light and the second transmitted light is limited within a preset range, the difference between the center and the edge is reduced, and the purpose of homogenizing the light intensity distribution of the incident light is achieved, and the Color Shading problem is solved.

[0012] Compared with the existing software method and image processing method, the process structure inside the sensor is modified (without introducing additional equipment or special materials), and process compatibility and cost efficiency are considered.

[0013] In some embodiments, the light transmittance of the gray mask gradually decreases in a direction away from the center area.

[0014] In some embodiments, the light transmittance of the gray mask is associated with the size of the first photoresist layer away from the pixel array.

[0015] In some embodiments, the first photoresist layer comprises a positive photoresist material.

[0016] In some embodiments, the refractive index of the second photoresist layer is greater than the refractive index of the first photoresist layer.

[0017] In some embodiments, the gray mask comprises at least one peripheral area;

[0018] The number of peripheral parts is the same as the number of peripheral areas.

[0019] In some embodiments, the orthographic projection of the center area on the center part is located within the center part;

[0020] The orthographic projection of the peripheral area on the peripheral part is located within the peripheral part.

[0021] In some embodiments, before forming the first photoresist layer, the method comprises:

[0022] Forming a filter and a lens stacked away from the pixel array on the first surface of the pixel array; the filter is one-to-one arranged with the lens directly above, and arranged in sequence along a first direction parallel to the first surface.

[0023] In a second aspect, the application also provides an image sensor prepared by the preparation method of any of the above embodiments.

[0024] In the image sensor of the above-mentioned embodiments, the new structure prepared by the preparation method provided in the present application can optimize the refraction angle of the light path, significantly improve the uneven distribution of light intensity at the center and edge of the CMOS sensor, reduce the color deviation caused by the difference in incident light angle, improve the consistency of image color, and effectively reduce the computational burden of subsequent image processing.

[0025] In a third aspect, the present application also provides an electronic device, such as the image sensor prepared by the preparation method described in any of the above-mentioned embodiments; or the image sensor described in the above-mentioned embodiments.

[0026] Since the electronic device of the above-mentioned embodiments and the image sensor and its preparation method provided in the present application belong to the same inventive concept, the electronic device using the above-mentioned image sensor has all the advantages of the image sensor and its preparation method provided in the present application, which will not be described one by one here.

[0027] In the above-mentioned embodiments, the image sensor and its preparation method, and the electronic device provided in the present application have the following unexpected technical effects:

[0028] Compared with the passive forming mode of traditional thermal reflow or nano-imprint process relying on material fluidity or fixed template, the present technology controls the exposure amount of photolithography through the difference in light transmittance of gray-scale mask, forms a specific curved surface structure between the first photoresist layer and the second photoresist layer, thereby breaking through the limitation of the radial property of traditional microlens, ensuring the refraction of incident light at the interface between the first photoresist layer and the second photoresist layer at a desired angle, increasing the light intensity in the edge region of the sensor, and then weakening the distribution difference of high center and low periphery of light intensity and reducing the problem of Color Shading, realizing self-balancing of light intensity distribution from the hardware level. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0030] Figure 1 A flowchart of the preparation method provided in an embodiment;

[0031] Figure 2a A schematic diagram of the pixel array structure provided in step S102 of the preparation method provided in an embodiment;

[0032] Figure 2b A schematic diagram of the pixel array structure provided in step S102 of the preparation method provided in an embodiment;

[0033] Figure 3a A structure diagram of a gray-tone mask prepared by the method provided in an embodiment;

[0034] Figure 3b A mapping relationship diagram of the gray-tone mask and the first photoresist layer prepared by the method provided in an embodiment;

[0035] Figure 4 A structure diagram of an image sensor obtained after forming a filter and a lens on the pixel array shown in FIG. 2;

[0036] Figure 5a A first photoresist layer formed in step S502 of the method provided in an embodiment;

[0037] Figure 5b A structure diagram of the first photoresist layer after development in step S504 of the method provided in an embodiment;

[0038] Figure 5c A structure diagram of the first photoresist layer after development in step S504 of the method provided in an embodiment;

[0039] Figure 6a A light path diagram of the image sensor prepared by the method of the present application;

[0040] Figure 6b A light path diagram of a prior art image sensor.

[0041] Explanation of reference signs:

[0042] 10, pixel array; 101, photodiode; 102, metal wiring layer; 11, filter; 12, lens; 13, first photoresist layer; 14, second photoresist layer; 15, anti-reflection layer. DETAILED DESCRIPTION

[0043] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present application will be more thorough and complete.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application.

[0045] It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or connected to the other element or layer or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. It will also be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section; for example, a first doped type could be termed a second doped type; and similarly, a second doped type could be termed a first doped type; a first doped type and a second doped type are different doped types, e.g., a first doped type can be p-type and a second doped type can be n-type, or the first doped type can be n-type and the second doped type can be p-type.

[0046] Spatially relative terms, such as "beneath", "below", "lower", "under", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and / or operation in addition to the orientations depicted in the figures. For example, if a device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can also be oriented in the other direction (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0047] The singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. In addition, use of the term "and / or" includes any and all combinations of associated items.

[0048] Embodiments of the application will be described with reference to cross-sectional illustrations that are schematic representations of ideal embodiments (and intermediate structures) of the application, as would be expected by one of ordinary skill in the art. Thus, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are to be expected. Therefore, embodiments of the application should not be construed as limited to the particular shapes of regions illustrated herein, but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and / or a gradient of implant concentration at its edges rather than a binary change between implanted and non-implanted regions. Similarly, a buried region formed by implantation can result in some implantation in a region between the buried region and a surface through which the implant was performed. Thus, the regions illustrated in the figures are schematic representations for purposes of example only and their shapes are not intended to illustrate the actual shape of a region of a device and are merely intended to more conceptually illustrate the regions.

[0049] Based on this, referring to Figures 1-6b , the application provides a preparation method of an image sensor, comprising steps S102-S106.

[0050] Step S102: providing a pixel array 10.

[0051] CIS mainly divides pixel structures into frontside-illuminated (FSI) and backside-illuminated (BSI) pixel structures according to light transmission processes.

[0052] Specifically, the pixel array 10 can be a frontside-illuminated pixel structure in which the metal wiring layer 102 is located on the top surface of the photodiode 101, as specifically shown in FIG. 1A, or a backside-illuminated pixel structure in which the photodiode 101 is located on the top surface of the metal wiring layer 102, as specifically shown in FIG. 1B. Figure 2a Figure 2b It should be understood that the pixel array 10 can also include a shallow trench isolation structure, and therefore the pixel array 10 should not limit the protection scope of the present disclosure. Since the pixel structure does not affect the subsequent process preparation flow of the application, and is a technology well known to researchers in the field, it will not be described here.

[0053] Step S104: forming a first photoresist layer 13 covering the pixel array 10 based on a gray-tone mask; the gray-tone mask includes a central region and a plurality of peripheral regions surrounding the central region and distributed along the radial direction of the central region; the central region and the plurality of peripheral regions have different light transmittances.

[0054] For example, the surface of the gray-tone mask can achieve different light transmittances of different regions by setting different thicknesses or densities of light shielding layers. The main materials include but are not limited to quartz, chromium or chromium oxide, wherein the quartz is partially a light transmittance region, and a chromium film with different thicknesses is plated on the quartz as a light shielding layer to achieve different light transmittance effects. ​

[0055] Further, in an optional embodiment, the light transmittance of the gray-tone mask gradually decreases in a direction away from the center region.

[0056] For example, by plating three different thicknesses of chromium film on quartz, a light intensity decreasing from the center region to the outer peripheral region can be achieved, and a specific gray-tone mask structure is shown in Figure 3a When the thickness of the chromium film ranges from 80nm to 100nm (for example, the thickness of the chromium film can be 80nm, 90nm or 100nm, etc.), complete blocking of light can be achieved, and the light transmittance is 0%; when the thickness of the chromium film is thinned to 10nm-50nm (for example, the thickness of the chromium film can be 10nm, 20nm, 30nm, 40nm or 50nm, etc.), the light transmittance increases significantly as the film thickness decreases. For example, the light transmittance of the chromium film with a thickness of 20nm can reach about 30%.

[0057] Step S106: Forming a second photoresist layer 14 and an anti-reflection layer 15 on the top surface of the first photoresist layer 13 in a direction away from the pixel array 10; wherein the second photoresist layer 14 includes a center part and a plurality of peripheral parts arranged in a direction away from the center part, the incident light generates first transmitted light via the center part, and generates second transmitted light via the peripheral parts; the light intensity difference between the first transmitted light and the second transmitted light is within a preset range.

[0058] Specifically, due to the thickness variation of the first photoresist layer 13, the second photoresist layer 14 is divided into a center part and a plurality of peripheral parts corresponding to the contact surface (interface) when covering the first photoresist layer 13, when the incident light propagates to the corresponding interface via the center part, it is refracted to generate the first transmitted light, and when the incident light propagates to the corresponding interface via the peripheral parts, it is refracted to generate the second transmitted light.

[0059] The second transmitted light can include a plurality of sub-rays, and the number of sub-rays is the same as the number of peripheral parts.

[0060] In an optional embodiment, the gray-tone mask includes at least one peripheral region;

[0061] The number of peripheral parts is the same as the number of peripheral regions.

[0062] Further, in an optional embodiment, the center region is located within the center part in the orthographic projection on the center part;

[0063] The peripheral region is located within the peripheral part in the orthographic projection on the peripheral part.

[0064] For example, the number of the peripheral part of the second photoresist layer 14 and the peripheral area of the gray-tone mask is the same, the gray-tone mask area is projected and aligned with the structure of the second photoresist layer 14, which ensures the formation of a "one area-one part" mapping relationship. This means that the light dose of each area on the gray-tone mask can accurately control the corresponding first photoresist layer 13 structure during exposure and development. By independently adjusting the light transmittance of each peripheral area, the contact surface (interface) shape between the first photoresist layer 13 and the second photoresist layer 14 can be customized for the incident angle difference of different pixel positions (such as the center, secondary edge, and edge), thereby adjusting the propagation path of the incident light and making the light intensity of different areas consistent. The specific mapping relationship is shown in Figure 3b

[0065] It should be understood that Figure 1 at least one of the steps in the above steps can include multiple steps or multiple stages, which do not necessarily be executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily sequential, but can be alternately or alternately executed with at least one part of other steps or steps in other steps.

[0066] The above steps will be described in detail below with reference to the accompanying drawings.

[0067] Please refer to Figure 4 In some embodiments, before step S104 (i.e., forming the first photoresist layer 13), it includes: forming a filter 11 and a lens 12 stacked in a direction away from the pixel array 10 on the first surface of the pixel array 10; the filter 11 is one-to-one arranged with the lens 12 directly above, and arranged in sequence along a first direction parallel to the first surface.

[0068] For example, the filter 11 includes but is not limited to a red filter, a yellow filter, a blue filter, etc., and the three kinds of filters are arranged adjacent to each other as a pixel group. Among them, the red filter transmits red light waves, the yellow filter transmits yellow light waves, and the blue filter transmits blue light waves. Among them, the filter can be a polymer material, such as a negative photoresist with acrylic polymer as the base material.

[0069] For example, the top of the lens 12 is in a rounded arc shape, which is beneficial for light collection to meet the light collection requirement.

[0070] Please refer to Figure 5a , Figure 5b and Figure 5c , step S104 further includes:

[0071] Step S502: forming a first photoresist layer 13 covering the outer surface of the lens 12.

[0072] For example, please refer to Figure 5a ​The structure can be formed by one or more of a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, a high density plasma (HDP) process, a plasma enhanced deposition process, a spin-on dielectric (SOD) process, etc.

[0073] In an optional embodiment, the first photoresist layer 13 is associated with the light transmittance of the gray-tone mask in terms of the dimension (i.e., thickness) away from the pixel array.

[0074] In an optional embodiment, the first photoresist layer 13 comprises a positive photoresist material.

[0075] The positive photoresist material gradually dissolves when developed under a strong light intensity and gradually remains when developed under a weak light intensity.

[0076] In the above embodiment, the control of the outer surface topography of the first photoresist layer 13 is achieved by establishing the association between the thickness of the first photoresist layer and the light transmittance of the gray-tone mask, and the specific shape can be designed according to the actual Color Shading condition.

[0077] Referring to Figures 5b-5c , step S504: performing exposure and baking on the first photoresist layer 13 based on the gray-tone mask.

[0078] For example, the difference in light transmittance of different regions of the gray-tone mask (high light transmittance in the central region → low light transmittance in the peripheral region) directly affects the exposure dose distribution of photolithography. The exposure dose in the region with high light transmittance (such as the central region) is large, and the thickness of the first photoresist layer 13 is reduced after development; the exposure dose in the region with low light transmittance (such as the peripheral region) is small, and the thickness is retained more after development, so that a shape with high periphery and concave center can be formed.

[0079] When the gray-tone mask comprises at least one peripheral region, the specific structure is shown in Figure 5b . If a smooth interface shape is considered, the gray-scale region of the mask can be further subdivided, and finally the first photoresist layer 13 with an approximately arc-shaped upper surface can be obtained, as shown in Figure 5c .

[0080] In the extended step of step S106, it further comprises:

[0081] The second photoresist layer 14 covering the top surface of the first photoresist layer 13 is formed by any deposition method, and then the anti-reflective layer covering the top surface of the second photoresist layer 14 is formed.

[0082] In an optional embodiment, the second photoresist layer 14 has a refractive index greater than that of the first photoresist layer 13.

[0083] For example, in this structure, the incident light can be refracted when passing through the interface between the first photoresist layer 13 and the second photoresist layer 14, thereby increasing the light intensity in the edge region of the sensor and weakening the difference in the distribution of the light intensity, i.e., the high light intensity in the center and the low light intensity around the center. Figure 6a

[0084] The material of the anti-reflection layer 15 includes, but is not limited to, titanium dioxide (TiO2), calcium fluoride (CaF2), and magnesium fluoride (MgF2).

[0085] In some embodiments, the present application also provides an image sensor, which can be obtained after the steps S102-S106. Figure 6a For the purpose of facilitating the understanding of the present application, Figure 6b is an example of an image sensor prepared without using the preparation method of the present application, Figure 6a is a different example of an image sensor prepared using the preparation method of the present application. The image sensor prepared using the present application can also have other suitable examples, which are not limited herein.

[0086] According to the light path diagram of Figure 6b , the traditional image sensor has the phenomenon of the light intensity in the center being higher than that in the edge due to the radial property of the lens, i.e., the lens collects more light in the center. Meanwhile, the phenomenon is also caused by the angle of the main light incident to the sensor. As the angle increases, the amount of light entering the edge decreases, thereby affecting the brightness uniformity and color uniformity of the BSI-CIS.

[0087] According to the light path diagram of Figure 6a , compared with the traditional image sensor, the image sensor prepared using the preparation method of the present application can optimize the light intensity distribution of the incident light, thereby improving the brightness uniformity and color uniformity.

[0088] In some embodiments, the present application provides an electronic device. As shown above, the electronic device of the above embodiments and the image sensor and the preparation method thereof belong to the same inventive concept, and therefore, the electronic device using the above image sensor has all the advantages of the image sensor and the preparation method thereof.

[0089] In the above embodiments, the image sensor and the preparation method thereof, and the electronic device provided by the present application have the following unexpected technical effects:

[0090] ​The application provides a preparation method for improving the quality of an image sensor through process modification. The method fills a high-transparency first photoresist layer and a second photoresist layer with different refractive indexes above a lens, forms a refractive index transition interface with a curved surface or an inverted trapezoidal shape, and enables the edge area to receive more light intensity, thereby reducing the problems of uneven light intensity distribution and Color Shading without software compensation.

[0091] In addition, compared with a thermal reflow curing method of flowing a photoresist material to form a curved surface structure through heating and a nanoimprint technology of imprinting a microstructure by using a template, the gray-scale mask can reduce process steps as much as possible, avoid template loss and special equipment restrictions, and realize low-cost mass production of high-performance optical structures.

[0092] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features of the above-described embodiments are not described, but as long as the combinations of the technical features do not contradict each other, they should be considered as falling within the scope of the present disclosure.

[0093] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A method of fabricating an image sensor, comprising: The method comprises: providing a pixel array; forming a first photoresist layer covering the pixel array based on a gray-tone mask; the gray-tone mask comprises a center region and a plurality of peripheral regions surrounding the center region and distributed along a radial direction of the center region; the center region and the plurality of peripheral regions have different light transmittances; forming a second photoresist layer and an anti-reflection layer stacked in sequence in a direction away from the pixel array on a top surface of the first photoresist layer; wherein the second photoresist layer comprises a center portion and a plurality of peripheral portions arranged in sequence in a direction away from the center portion, the incident light generates first transmitted light via the center portion and generates second transmitted light via the peripheral portions; the light intensity difference between the first transmitted light and the second transmitted light is within a preset range.

2. The production method according to claim 1, characterized by, The light transmittance of the gray-tone mask gradually decreases in a direction away from the center region.

3. The preparation method according to claim 2, characterized in that, The size of the first photoresist layer in a direction away from the pixel array is related to the light transmittance of the gray-tone mask.

4. The production method according to claim 3, characterized by, The first photoresist layer comprises a positive photoresist material.

5. The preparation method according to claim 4, characterized in that, The refractive index of the second photoresist layer is greater than the refractive index of the first photoresist layer.

6. The method of any one of claims 1-5, wherein, The gray-tone mask comprises at least one peripheral region. The number of the peripheral portions is the same as the number of the peripheral regions.

7. The method of any one of claims 1-5, wherein, The orthographic projection of the center region on the center portion is located within the center portion; The orthographic projection of the peripheral region on the peripheral portion is located within the peripheral portion.

8. The method of any one of claims 1-5, wherein, Before forming the first photoresist layer, the method comprises: forming a filter and a lens stacked in sequence in a direction away from the pixel array on a first surface of the pixel array; the filter is one-to-one arranged with the lens directly above and arranged in sequence along a first direction parallel to the first surface.

9. An image sensor, comprising: The image sensor comprises: prepared by the preparation method of any one of claims 1-8.

10. An electronic device, comprising: The image sensor comprises: prepared by the preparation method of any one of claims 1-8. or the image sensor of claim 9.

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