Image sensor and method of manufacturing the same

Abstract

The application discloses an image sensor and a preparation method thereof, and relates to the technical field of sensing. The image sensor comprises a first lens and a second lens, the second lens is used for receiving incident light, the first lens is arranged in the light-out direction of the second lens and is used for receiving light from the second lens, the refractive index of the first lens is greater than the refractive index of the second lens, and a filling medium layer is arranged between the first lens and the second lens. By adopting the image sensor, light can be deflected multiple times, and thus the edge light intensity can be ensured in the case that the main light inclination angle no longer matches the lens design.

Description

Technical Field

[0001] This application relates to the field of sensor technology, and in particular to an image sensor and its fabrication method. Background Technology

[0002] With the widespread dissemination of short online videos teaching photography, more and more users are moving beyond simply using cameras to take high-quality photos. Through friendly competition and / or cooperation among major manufacturers, mobile devices are now offering more lenses and algorithms while maintaining portability, allowing users to manually select shooting modes such as wide-angle, macro, and telephoto, thus enhancing the user's photography experience. While they cannot completely replace cameras, they have become a viable option for most ordinary photography enthusiasts and even a viable option for some professional photographers.

[0003] However, due to the structure and optical characteristics of mobile terminal device lenses, the light-gathering ability at the center of the lens is greater than that at the edges, affecting the image quality. Existing technologies typically use lenses on the surface of the image sensor to create gaps between the backside metal grid (BMG) and the deep trench isolation structure (DTI), thereby achieving different chief ray angles (CRA) between the lens and the image sensor, thus reducing edge light loss.

[0004] Please see Figure 1 , Figure 1 This is a schematic diagram of an image sensor structure and optical path disclosed in the prior art. The image sensor includes a lens 10, a metal circuit layer 11, and a photosensitive area 12. Figure 1 As shown in (a), when the principal ray tilt angle is 0 degrees, it is called an on-axis pixel. After the incident light passes through the image sensor lens 10, part of it is blocked by the metal circuit layer 11. The unblocked incident light will be focused onto the photosensitive area 12. At this time, the light intensity at the center and edge of the photosensitive area 12 is uniform. The maximum angle of light that can be focused onto a pixel from the sensor side of the lens is defined as a parameter called the principal ray tilt angle. The general definition of the principal ray tilt angle is: the pixel response at this angle is reduced to 80% of the zero-degree angle pixel response (at which point the pixel is perpendicular to the light).

[0005] like Figure 1As shown in (b), when the tilt angle of the main ray is 13°, it is called the intermediate field pixel. Since the incident light is incident on the image sensor at a certain tilt angle, and some of the incident light is blocked by the metal circuit layer 11, the prior art ensures that only a small amount of light is lost when the edge of the photosensitive area 12 receives the incident light by moving the lens 10 on the surface of the image sensor. As a result, although the light intensity at the center of the photosensitive area 12 is greater than the light intensity at one edge, it does not affect the user experience.

[0006] like Figure 1 As shown in (c), when the tilt angle of the main ray is 25°, it is called a corner pixel. Since the incident light is incident on the image sensor at a large tilt angle, and some of the incident light is blocked by the metal circuit layer 11, if the lens 10 on the surface of the image sensor is moved, the incident light cannot be deflected to the photosensitive area 12 well due to the insufficient refractive index of the surface lens 10, resulting in a large loss of edge light and affecting the user experience.

[0007] Please continue reading. Figure 2 , Figure 2 This is a structural view and corresponding cross-sectional view of an image sensor disclosed in the prior art from the light-intake side. The image sensor includes a back metal grid 20 and a deep trench isolation structure 21. Existing image sensors achieve different principal ray tilt angles between the lens and the image sensor by staggering the lens and the back metal grid 20 and the deep trench isolation structure 21 during chip fabrication.

[0008] While existing technologies can reduce edge light loss, as pixel positions change, the angle at which light enters the pixel becomes larger, causing the tilt angle of the main ray to no longer match the lens design. This results in the lens's center focusing ability being greater than its edge, affecting the image quality. Summary of the Invention

[0009] The technical problem to be solved by this application is that the tilt angle of the main ray is too large, and the lens deflection capability cannot guarantee the uniform distribution of light intensity at the center and edge of the photosensitive area. To this end, an image sensor and its preparation method are provided, which can guarantee the light intensity at the edge of the photosensitive area.

[0010] To address the aforementioned issues, this application provides an image sensor, comprising: a first lens and a second lens, wherein the second lens is used to receive incident light, and the first lens is disposed in the light-emitting direction of the second lens and is used to receive light from the second lens; the refractive index of the first lens is greater than the refractive index of the second lens; and a filling medium layer is disposed between the first lens and the second lens.

[0011] In one possible specific embodiment, the image sensor further includes a filter disposed in the light-emitting direction of the second lens for spectral filtering of the incident light.

[0012] In one possible implementation, the filter of the image sensor is further configured as a third lens, and the refractive index of the third lens is less than that of the second lens.

[0013] In one possible embodiment, the image sensor further includes a first back metal grid and a second back metal grid; the first back metal grid is disposed between adjacent first lenses, and the second back metal grid is disposed between adjacent lens groups, the lens group including the second lens and the third lens.

[0014] In one possible specific implementation, the lens group is arranged in a staggered manner from the first lens.

[0015] In one possible specific implementation, the first back metal grid and the second back metal grid are arranged in a staggered manner.

[0016] In one possible specific implementation, the image sensor further includes a deep trench isolation structure disposed in the light-emitting direction of the first lens, and the first back metal grid is aligned with the deep trench isolation structure.

[0017] To address the aforementioned problems, this application also provides a method for fabricating an image sensor. The method includes the following steps: providing a substrate; forming a patterned photoresist layer on the surface of the substrate; exposing the photoresist layer to obtain an initial lens; developing the initial lens; baking the developed initial lens to obtain a first lens; forming a filling dielectric layer around the first lens; and further forming a second lens on the surface of the filling dielectric layer using the method described above.

[0018] In one possible specific embodiment, the step of forming the photoresist layer further includes: forming a first back metal grid on the surface of the substrate; and forming a patterned photoresist layer within the first back metal grid.

[0019] The image sensor described above achieves multiple refractions of light by adding lenses and limiting the refractive index of lenses at different positions, thereby ensuring edge illumination intensity even when the tilt angle of the main ray no longer matches the lens design.

[0020] The above-described image sensor fabrication method involves coating a substrate with photoresist to form a patterned photoresist layer, then exposing and developing the photoresist layer to obtain a first lens. A filling dielectric layer is then formed around the first lens, and finally, a second lens is formed on the surface of the filling dielectric layer using the same method. The image sensor fabricated using this method is simple, controllable, and inexpensive. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of this application, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are only some specific embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of an image sensor structure and optical path disclosed in the prior art.

[0023] Figure 2 The present invention discloses a structural view and corresponding cross-sectional view of an image sensor from the light-inlet side.

[0024] Figure 3 This is a schematic diagram of a specific embodiment of the image sensor provided in this application.

[0025] Figure 4 This is a schematic diagram of a specific embodiment of the image sensor provided in this application.

[0026] Figure 5 This is a schematic diagram of a specific embodiment of the image sensor provided in this application.

[0027] Figure 6 This is a schematic diagram of a specific embodiment of the image sensor provided in this application.

[0028] Figure 7 This is a schematic diagram of a specific embodiment of the image sensor provided in this application.

[0029] Figure 8 This is a flowchart illustrating a specific implementation of the image sensor fabrication method provided in this application.

[0030] in:

[0031] 10: Lens; 11: Metal circuit layer; 12: Photosensitive area;

[0032] 20: Metal grid on the back; 21: Deep trench isolation structure;

[0033] 311: First lens; 312: Second lens; 32: Photosensitive area; 33: Filling dielectric layer;

[0034] 40: Filter;

[0035] 521: First rear metal grid; 522: Second rear metal grid;

[0036] 61: Deep trench isolation structure; 613: Third lens

[0037] 71: Substrate. Detailed Implementation

[0038] The technical solutions in the specific embodiments of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the specific embodiments. Based on the specific embodiments in this application, all other specific embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0039] Please see Figure 3 , Figure 3 This is a schematic diagram illustrating a specific embodiment of the image sensor provided in this application. (See attached diagram.) Figure 3 As shown, the image sensor includes a first lens 311, a second lens 312, and a filling medium layer 33. The second lens 312 receives incident light, and the first lens 311 is positioned in the light-emitting direction of the second lens 312 to receive light from it. A filling medium layer 33 is disposed between the first lens 311 and the second lens 312. Light emitted from the second lens 312 is detected by a photosensitive area 32. The refractive index of the first lens 311 is greater than that of the second lens 312.

[0040] The following combination Figure 3 The optical path of the image sensor is further explained. The incident light is first deflected by the second lens 312. Then, a portion of the light directly enters the first lens 311, while the other portion first passes through the filling dielectric layer 33 and then enters the first lens 311 for a second deflection. The incident angle at this point should meet a preset angle. This preset angle is the incident angle of the incident light after lens correction, when the light intensity at the center and edge of the photosensitive area 32 is uniform. It should be understood that a reduced transmission angle improves the light converging efficiency; therefore, the refractive index of the first lens 311 should be greater than that of the second lens 312.

[0041] The above specific implementation method, by limiting the refractive index of the lens at different positions, enables the light to be deflected multiple times using lenses with different refractive indices, thereby ensuring the edge illumination intensity even when the tilt angle of the principal ray no longer matches the lens design.

[0042] Figure 4 This is a schematic diagram of a specific embodiment of the image sensor provided in this application. In one possible embodiment, the image sensor further includes a filter 40 disposed in the light-emitting direction of the second lens 312 for spectral filtering of the incident light.

[0043] The following combination Figure 4 To further explain the optical path of the image sensor, the incident light, after being deflected by the second lens 312, directly enters the filter 40 for spectral filtering. Optionally, the filter 40 can also be positioned in the light-emitting direction of the first lens 311, in which case the incident light will first pass through the first lens 311 before undergoing spectral filtering. Depending on the choice of filter 40, the color of the emitted light will also change accordingly. The material of the filter 40 is selected from either plastic or glass. It should be understood that when light enters the filter 40, the change in medium will also affect the deflection angle of the light. Since the filter 40 only allows incident light of a specific color to pass through, the image sensor in this embodiment of the application ensures both edge illumination intensity and the ability to distinguish different colors.

[0044] Figure 5 This is a schematic diagram illustrating a specific embodiment of the image sensor provided in this application. (See attached diagram.) Figure 5 As shown, the image sensor also includes a first back metal grid 521 and a second back metal grid 522. The first back metal grid 521 is disposed between the lenses of adjacent first lenses 311, and the second back metal grid 522 is disposed between the lenses of adjacent second lenses 312, in which case the first back metal grid 521 and the second back metal grid 522 are aligned.

[0045] The above-described specific implementation method, by adding a metal grid on the back, not only ensures the edge illumination intensity but also solves the problem of light and current crosstalk between pixels, thereby improving noise control and image purity.

[0046] Figure 6 This is a schematic diagram illustrating a specific embodiment of the image sensor provided in this application. (See attached diagram.) Figure 6 As shown, attached Figure 4 The filter 40 is further configured as a third lens 613, and the refractive index of the third lens 613 is less than the refractive index of the second lens 312.

[0047] The following further explains the optical path of the image sensor. The incident light undergoes both spectral filtering and angular deflection at the third lens 613, a second deflection at the second lens 312, and then a third deflection at the first lens 311. At this point, the incident angle of the light should meet a preset angle and be of a preset color.

[0048] The preset angle is the incident angle of the incident light after lens correction when the light intensity at the center and edge positions of the photosensitive area 32 is uniform. A corresponding filter 40 can be selected according to the preset color.

[0049] The above-described specific implementation further sets the filter 40 as a lens, which not only ensures the spectral filtering effect, but also further enhances the image sensor's ability to deflect light, and further ensures the uniformity of light intensity in the center and edge areas of the photosensitive area 32.

[0050] In the appendix Figure 6 In the specific embodiment shown, the first back metal grid 521 is disposed between adjacent first lenses 311, and the second back metal grid 522 is further disposed between adjacent lens groups. The lens group includes the second lens 312 and the third lens 613. By sharing the second back metal grid 522 between the second lens 312 and the third lens 613 in the lens group, the back metal grid that should have been disposed in the third lens 613 is saved.

[0051] Continue to refer to the appendix Figure 6 The light-inlet surface of the second lens 312 in the lens group coincides with the light-outlet surface of the third lens 613, which saves space between the second lens 312 and the third lens 613, and avoids the incident light from entering other media before entering the second lens 312 after exiting the third lens 613, thus preventing light loss.

[0052] Continue to refer to the appendix Figure 6 The lens group is staggered with the first lens 311, and the first back metal grid 521 is staggered with the second back metal grid 522. In the above specific embodiment, the image sensor, by using a staggered arrangement, further increases the matching degree between the main ray tilt angle and the lens design, ensuring the light intensity at the edge of the photosensitive area 32 and achieving uniform illumination intensity between the center and edge areas of the photosensitive area 32.

[0053] Continue to refer to the appendix Figure 6The image sensor further includes a deep trench isolation structure 61 disposed in the light-emitting direction of the first lens 311, and the first back metal grid 521 is aligned with the deep trench isolation structure 61. By adding the deep trench isolation structure 61, the image sensor further solves the problem of crosstalk between optical and electrical signals, improving noise control and image clarity.

[0054] Figure 7 This is a schematic diagram illustrating a specific embodiment of the image sensor provided in this application. (See attached diagram.) Figure 7 As shown, the image sensor is disposed on the surface of the substrate 71, and a filling medium layer 33 is disposed between the first lens 311 and the second lens 312.

[0055] like Figure 8 As shown, this application also provides a specific embodiment of an image sensor fabrication method for fabricating the above-mentioned image sensor. The method includes: step S101, providing a substrate 71; step S102, forming a patterned photoresist layer on the surface of the substrate 71; step S103, exposing the photoresist layer to obtain an initial lens; step S104, developing the initial lens; step S105, baking the developed initial lens to obtain a first lens 311; step S106, forming a filling dielectric layer 33 around the first lens 311; and step S107, continuing to form a second lens 312 on the surface of the filling dielectric layer 33 using the above method.

[0056] The following is in conjunction with the appendix Figure 3-7 The steps described above are explained in detail, along with the corresponding specific implementation methods.

[0057] Step S101: Provide substrate 71. To enable the image sensor to deflect incident light, a substrate 71 conforming to preset specifications is first selected, and then a lens capable of deflecting light is mounted on the substrate 71. Optionally, the substrate 71 can be a substrate fabricated on a silicon wafer, or a substrate fabricated on a germanium, germanium-silicon, gallium arsenide, or silicon-on-insulator substrate. Those skilled in the art can select the substrate type as needed.

[0058] Step S102: A patterned photoresist layer is formed on the surface of the substrate 71. After determining the selected substrate 71, a coater is used to uniformly coat a fixed thickness of photoresist on the substrate 71 by spin coating to form a patterned photoresist layer. During spin coating, 45-degree swirl marks are prone to occur. To avoid this problem, a rotation speed of 500-2000 rad / s can be used during coating, and the temperature should be kept constant throughout the coating process, typically 25°C. Optionally, a lens can be directly selected for the mounting operation. It should be understood that as long as the selected lens can meet the image sensor's requirements for light deflection and ultimately achieve uniform light intensity at the center and edge of the photosensitive area 32, the lens can be selected. In one possible embodiment, this step further includes: forming a first back metal grid 521 on the surface of the substrate 71; and forming a patterned photoresist layer within the first back metal grid 521.

[0059] Step S103: Expose the photoresist layer to obtain an initial lens. After coating and fixing the photoresist, ultraviolet exposure is then used to expose the photoresist layer, ultimately obtaining an initial lens of a certain size. Optionally, the initial lens is rectangular or semi-circular.

[0060] Step S104: Develop the initial lens. After exposure to obtain the initial lens, it can be placed in a dedicated developing solution for development. The purpose of this step is to clean away excess photoresist using the developing solution. The immersion time of the initial lens in the developing solution needs to be strictly controlled, as the development time directly affects the uniformity of subsequent lenses.

[0061] Step S105: Bake the developed initial lens to obtain the first lens 311. The developed initial lens is placed in an oven for baking to finally obtain the first lens 311. The purpose of this step is to reduce the influence of the standing wave effect, while ensuring complete reaction of the photoresist. During baking, the active components generated by the photoresist will diffuse, thereby enhancing the shallow image generated by the light intensity distribution through chemical methods and more precisely controlling the pattern morphology of the first lens 311.

[0062] Step S106: A filling medium layer 33 is formed around the first lens 311. After obtaining the first lens 311, a filling medium layer 33 can be formed around it. It is understood that a conductive medium with good light transmittance and a material with poor absorption and reflection properties should be selected as the filling medium layer 33.

[0063] Step S107: The second lens 312 is further formed on the surface of the filling medium layer 33 using the method described above. After filling the filling medium layer 33, the second lens 312 is further formed on the surface of the filling medium layer 33 using the method described above.

[0064] The above-described specific embodiment forms a patterned photoresist layer by coating photoresist on the substrate 71, then exposes and develops the photoresist layer to obtain a first lens 311, then forms a filling dielectric layer 33 around the first lens 311, and finally forms a second lens 312 on the surface of the filling dielectric layer 33 using the above method. This method has the advantages of simple and controllable fabrication operation and low process cost.

[0065] It should be noted that the terms "comprising" and "having," and their variations, used in this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence; unless the context explicitly indicates otherwise, it should be understood that such use of terms can be interchanged where appropriate. The term "one or more," at least in part depending on the context, can be used to describe features, structures, or characteristics in a singular sense, or in a plural sense, to describe combinations of features, structures, or characteristics. The term "based on" can be understood as not necessarily intended to express an exclusive set of factors, but rather, alternatively, also at least in part depending on the context, allowing for the presence of other factors that are not necessarily explicitly described.

[0066] Furthermore, where there is no conflict, the specific embodiments and features described in this application can be combined with each other. In addition, descriptions of well-known components and technologies have been omitted in the above description to avoid unnecessarily obscuring the concepts of this application. In each of the above specific embodiments, the focus is on describing the differences from other specific embodiments; similar or identical parts between the various specific embodiments can be referred to interchangeably.

[0067] The above description is only a preferred embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. An image sensor, characterized in that, include: A first lens and a second lens, wherein the second lens is used to receive incident light, and the first lens is disposed in the light-emitting direction of the second lens to receive light from the second lens. The refractive index of the first lens is greater than that of the second lens. The light emitted from the first lens is recognized by the photosensitive area. A filling medium layer is disposed between the first lens and the second lens. The incident light is first deflected by the second lens, and then part of the light directly enters the first lens, while the other part of the light passes through the filling medium layer and then enters the first lens. The incident angle of the light at this time meets a preset angle. The preset angle is the incident angle of the incident light after lens correction when the light intensity at the center position and the edge position of the photosensitive area is uniform.

2. The image sensor according to claim 1, characterized in that, It also includes a filter, which is disposed in the light-emitting direction of the second lens, for spectral filtering of the incident light.

3. The image sensor according to claim 2, characterized in that, The filter is further configured as a third lens, and the refractive index of the third lens is less than that of the second lens.

4. The image sensor according to claim 3, characterized in that, It also includes a first back metal grid and a second back metal grid; the first back metal grid is disposed between adjacent first lenses, and the second back metal grid is disposed between adjacent lens groups, the lens group including the second lens and the third lens.

5. The image sensor according to claim 4, characterized in that, The lens group is arranged in a staggered manner compared to the first lens.

6. The image sensor according to claim 4, characterized in that, The first back metal grid and the second back metal grid are arranged in a staggered manner.

7. The image sensor according to claim 4, characterized in that, It also includes a deep trench isolation structure disposed in the light-emitting direction of the first lens, wherein the first back metal grid is aligned with the deep trench isolation structure.

8. A method for fabricating an image sensor, used to fabricate the image sensor of claim 1, characterized in that, The process includes the following steps: providing a substrate; forming a patterned photoresist layer on the surface of the substrate; exposing the photoresist layer to obtain an initial lens; and developing the initial lens. The initial lens after development is baked to obtain the first lens; a filling medium layer is formed around the first lens; and the second lens is formed on the surface of the filling medium layer using the method described above.

9. The method according to claim 8, characterized in that, The step of forming the photoresist layer further includes: forming a first back metal grid on the surface of the substrate; and forming a patterned photoresist layer within the first back metal grid.

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