CN116031270A - Image sensor and manufacturing method thereof - Google Patents

Abstract

The application discloses an image sensor and a preparation method thereof, which relate to the field of sensor technology. The image sensor includes: a first lens and a second lens, the second lens is used to receive incident light, and the first lens is arranged in the light output direction of the second lens to receive light from the second lens. light; the refractive index of the first lens is greater than that of the second lens; a filling medium layer is arranged between the first lens and the second lens. By adopting the image sensor, the light can be deflected multiple times, so that the marginal illumination intensity can still be guaranteed even when the inclination angle of the chief light does not match the lens design.

Description

Image sensor and manufacturing method thereof

technical field

The present application relates to the field of sensor technology, in particular to an image sensor and a preparation method thereof.

Background technique

With the widespread dissemination of Internet short videos about photography teaching, more and more users are no longer limited to using cameras to take high-quality photos. Under the friendly competition and/or cooperation of major manufacturers, the current mobile terminal equipment has increased the number of lenses and cooperated with the algorithm on the premise of taking into account the portability, so that users can manually choose to use wide-angle, macro, and telephoto shooting methods, thereby improving the user experience. photography experience. Although it cannot completely replace the camera, it has become a choice for most ordinary photography enthusiasts, and even an option for some professional photographers.

However, due to the structure and optical characteristics of the lens of the mobile terminal device, the light gathering ability of the center of the lens is greater than that of the edge, which affects the photographing effect. The existing technology usually uses the lens on the surface of the mobile image sensor, so that there is a gap between the back metal grid (BMG, Backside Metal Grid) and the deep trench isolation structure (DTI, Time Delayed and Integration), and then realizes the gap between the lens and the image sensor. Different chief ray angles (CRA, Chief Ray Angle), so as to reduce the loss of edge light.

Please refer to FIG. 1 . FIG. 1 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 . As shown in (a) in Figure 1, when the inclination angle of the chief ray is 0 degrees, it is called an on-axis pixel. After the incident light passes through the image sensor lens 10, it will be partially blocked by the metal circuit layer 11, and the unblocked incident light It will be focused to the photosensitive area 12, and the light intensity at the center and edge of the photosensitive area 12 is uniform at this time. From the sensor side of the lens, the maximum angle at which a ray of light can be focused onto a pixel is defined by a parameter called the chief ray tilt angle. The general definition of the tilt angle of the chief ray is: the response of the pixel at this angle is reduced to 80% of the response of the pixel at the zero angle angle (at this time, the pixel is perpendicular to the light).

As shown in (b) in Figure 1, when the chief ray inclination angle is 13°, it is called the middle field pixel. Since the incident light enters the image sensor with a certain inclination angle, and part of the incident light will be blocked by the metal circuit layer 11, the existing technology ensures that the side edge of the photosensitive area 12 receives the incident light by moving the lens 10 on the surface of the image sensor. There is only a small amount of loss, so that although the light intensity at the center of the photosensitive area 12 is greater than the light intensity at the edge of one side, it does not affect the user experience.

As shown in (c) in Fig. 1, when the chief ray inclination angle is 25°, it is called a corner pixel. Due to the large inclination angle of the incident light incident on the image sensor, and part of the incident light will be 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 well received due to the insufficient refractive index of the surface lens 10. The light is deflected to the photosensitive area 12, resulting in a large loss of marginal light, which affects the user experience.

Please continue to refer to FIG. 2 . FIG. 2 is a structural view from a light-incoming side of an image sensor disclosed in the prior art and a corresponding cross-sectional view. The image sensor includes a back metal grid 20 and a deep trench isolation structure 21 . The existing image sensor realizes different principal ray inclination angles between the lens and the image sensor by arranging the lens and the back metal grid 20 and the deep trench isolation structure 21 in a staggered manner during the chip preparation process. .

Although the existing technology can reduce the loss of edge rays, as the pixel position changes, the angle at which the light enters the pixel becomes larger and larger, which will cause the inclination angle of the chief ray to no longer match the lens design, thus causing the center of the lens to become larger. The light gathering ability is greater than its edge, which affects the photo effect.

Contents of the invention

The technical problem to be solved in this application is that the inclination angle of the chief ray is too large, and the deflection ability of the lens cannot ensure the uniform distribution of light intensity in the center and edge of the photosensitive area. Therefore, an image sensor and its preparation method are provided, which can ensure the light intensity at the edge of the photosensitive area .

In order to solve the above problems, the present application provides an image sensor, including: a first lens and a second lens, the second lens is used to receive incident light, the first lens is arranged in the light emitting direction of the second lens, Used to receive light from the second lens; the refractive index of the first lens is greater than that of the second lens; a filling medium layer is arranged between the first lens and the second lens.

In a possible specific implementation manner, the image sensor further includes a filter, which is arranged in a light emitting direction of the second lens, and is used for spectrally filtering incident light.

In a possible implementation manner, the optical filter of the image sensor is further configured as a third lens, and a refractive index of the third lens is smaller than a refractive index of the second lens.

In a possible specific implementation manner, 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, The second back metal grid is disposed between adjacent lens groups, and the lens groups include the second lens and the third lens.

In a possible specific implementation manner, the lens group and the first lens are arranged in a dislocation manner.

In a possible specific implementation manner, the first back metal grid and the second back metal grid are arranged in a dislocation manner.

In a possible specific implementation manner, the image sensor further includes a deep trench isolation structure arranged in the light emitting direction of the first lens, and the first back metal grid is aligned with the deep trench isolation structure. cloth.

In order to solve the above problems, the present application also provides a method for preparing an image sensor, which is used to prepare the above 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 initial lens after development to obtain the first lens; forming a filling medium layer; continuing to form the second lens on the surface of the filling medium layer using the above method.

In a possible specific implementation manner, the step of forming a photoresist layer further includes: forming a first back metal grid on the surface of the substrate; forming a patterned grid in the first back metal grid. layer of photoresist.

The above-mentioned image sensor achieves multiple deflection of light by adding lenses and limiting the refractive index of lenses at different positions, and then realizes that the edge illumination intensity can still be guaranteed even when the inclination angle of the chief ray does not match the lens design.

In the above image sensor preparation method, a photoresist is coated on the substrate to form a patterned photoresist layer, and then the photoresist layer is exposed and developed to obtain a first lens, and then a filling medium layer is formed around the first lens, Finally, the second lens is continued to be formed on the surface of the filling medium layer by the above-mentioned method. The image sensor prepared by the method has simple and controllable preparation operation and low process cost.

Description of drawings

In order to more clearly illustrate the technical solutions in the specific embodiments of the present application, the following will briefly introduce the drawings that are required for the description of the specific embodiments. Apparently, the drawings in the following description are only some specific embodiments of the present application, and those skilled in the art can also obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a schematic diagram of the structure and optical path of an image sensor disclosed in the prior art.

FIG. 2 is a structural view from a light-incoming side of an image sensor disclosed in the prior art and a corresponding cross-sectional view.

FIG. 3 is a schematic diagram of a specific embodiment of an image sensor provided by the present application.

FIG. 4 is a schematic diagram of a specific embodiment of an image sensor provided by the present application.

FIG. 5 is a schematic diagram of a specific embodiment of an image sensor provided by the present application.

FIG. 6 is a schematic diagram of a specific embodiment of the image sensor provided by the present application.

FIG. 7 is a schematic diagram of a specific embodiment of an image sensor provided by the present application.

FIG. 8 is a flow chart of a specific embodiment of the image sensor manufacturing method provided by the present application.

in:

10: lens; 11: metal circuit layer; 12: photosensitive area;

20: back metal grid; 21: deep trench isolation structure;

311: first lens; 312: second lens; 32: photosensitive area; 33: filling medium layer;

40: optical filter;

521: the first back metal grid; 522: the second back metal grid;

61: deep trench isolation structure; 613: third lens

71: Substrate.

Detailed ways

The technical solutions in the specific embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described implementations are only a part of the implementations of the present application, rather than all specific implementations. Based on the specific implementation manners in this application, all other specific implementation manners obtained by those skilled in the art without creative efforts shall fall within the protection scope of this application.

Please refer to FIG. 3 . FIG. 3 is a schematic diagram of a specific implementation manner of the image sensor provided in the present application. As shown in FIG. 3 , the image sensor includes a first lens 311 , a second lens 312 and a filling medium layer 33 . Wherein the second lens 312 is used to receive incident light, and the first lens 311 is arranged in the light emitting direction of the second lens 312, and is used to receive light from the second lens 312, and the first lens 311 and A filling medium layer 33 is disposed between the second lenses 312 . The light emitted from the second lens 312 is recognized by the photosensitive area 32 . The refractive index of the first lens 311 is greater than the refractive index of the second lens 312 .

The direction of the optical path of the image sensor will be further described below in conjunction with FIG. 3 . The incident light is deflected for the first time by the second lens 312, and then part of the light is directly incident on the first lens 311, and the other part of the light first passes through the filling medium layer 33, and then enters the first lens 311 for the second light deflection. Deflection, the incident angle of light at this time should meet the preset angle. The preset angle is the incident angle of the incident light corrected by the lens when the light intensity at the center and edge of the photosensitive area 32 is uniform. It should be understood that the reduction of the transmission angle can improve the converging efficiency of light, so the refractive index of the first lens 311 should be greater than the refractive index of the second lens 312 .

In the above specific implementation, by limiting the refractive index of the lens at different positions, it is possible to use lenses with different refractive indices to deflect the light multiple times, and then realize that the edge light intensity.

FIG. 4 is a schematic diagram of a specific embodiment of an image sensor provided by the present application. In a possible specific implementation manner, the image sensor further includes a filter 40, which is arranged in the light emitting direction of the second lens 312, and is used for spectrum filtering the incident light.

The direction of the optical path of the image sensor will be further described below with reference to FIG. 4 . After the incident light is deflected by the second lens 312 , it directly enters the filter 40 for spectrum filtering. Optionally, the filter 40 can also be arranged in the light emitting direction of the first lens 311 , at this time, the incident light will first pass through the first lens 311 and then undergo spectrum filtering. According to the selection of the filter 40 mentioned above, the color of the outgoing light will also change accordingly. The material of the filter 40 is selected from one of plastic and glass. It should be understood that when the light enters the filter 40, the deflection angle of the light will also be affected due to the change of the medium. Since the filter 40 only allows the incident light of a specific color to pass through, the image sensor in the specific embodiment of the present application can also distinguish different colors under the premise of ensuring the intensity of the edge light.

FIG. 5 is a schematic diagram of a specific embodiment of an image sensor provided by the present application. As shown in FIG. 5 , the image sensor further includes a first back metal grid 521 and a second back metal grid 522 . The first back metal grid 521 is arranged between adjacent lenses of the first lens 311, and the second back metal grid 522 is arranged between adjacent lenses of the second lens 312. At this time, the first back metal grid 521 and the second back metal grid 522 are arranged in alignment.

The above specific implementation method solves the problem of light and current crosstalk between pixels and improves the noise control ability and the purity of photos under the premise of ensuring the edge light intensity by adding the metal grid on the back.

FIG. 6 is a schematic diagram of a specific embodiment of the image sensor provided by the present application. As shown in FIG. 6 , the optical filter 40 in FIG. 4 is further configured as a third lens 613 , and the refractive index of the third lens 613 is smaller than that of the second lens 312 .

In the following, the direction of the optical path of the image sensor will be further described. The incident light undergoes spectrum filtering and angle deflection at the same time at the third lens 613, and then undergoes a second light deflection at the second lens 312, and then enters the first lens 311 for the third time. secondary light deflection. The incident angle of the light at this time should satisfy the preset angle and be the preset color.

The preset angle is the incident angle of the incident light corrected by the lens when the light intensity at the center and edge of the photosensitive area 32 is uniform. The corresponding filter 40 can be selected according to the preset color.

In the above specific embodiment, the optical filter 40 is further configured as a lens, which not only ensures the spectral filtering effect, but also further strengthens the deflection ability of the image sensor to light, and further ensures the light intensity of the center and edge areas of the photosensitive area 32 uniform.

In the specific implementation shown in FIG. 6, the first back metal grid 521 is arranged between adjacent first lenses 311, and the second back metal grid 522 is further arranged between adjacent lenses. Between the groups, the lens group includes the second lens 312 and the third lens 613, and the second lens 312 and the third lens 613 in the lens group share the second back metal grid 522, which saves the A metal grid is arranged on the back of the third lens 613 .

Continuing to refer to accompanying drawing 6, the light entrance surface of the second lens 312 in the lens group coincides with the light exit surface of the third lens 613, saving the space between the second lens 312 and the third lens 613, and This prevents the incident light from entering other media before entering the second lens 312 after exiting through the third lens 613 , causing loss of light.

Continuing to refer to FIG. 6 , the lens group and the first lens 311 are staggered, and the first back metal grid 521 and the second back metal grid 522 are staggered. The image sensor in the above-mentioned specific embodiment further increases the matching degree between the inclination angle of the chief ray and the lens design by arranging the dislocation, ensures the light intensity at the edge of the photosensitive area 32, and realizes the distance between the center of the photosensitive area 32 and the edge. Uniform light intensity across the area.

Continuing to refer to FIG. 6 , the 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 . The above-mentioned image sensor further solves the crosstalk problem of optical signals and electrical signals by adding a deep trench isolation structure 61 , and improves the noise control capability and the purity of photos.

FIG. 7 is a schematic diagram of a specific embodiment of an image sensor provided by the present application. As shown in FIG. 7 , 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 .

As shown in FIG. 8 , the present application also provides a specific embodiment of an image sensor preparation method, which is used to prepare the above-mentioned image sensor. The method includes: step S101, providing a substrate 71; step S102, A patterned photoresist layer is formed on the surface; step S103, exposing the photoresist layer to obtain an initial lens; step S104, performing a development process on the initial lens; step S105, exposing the initial lens after the development process The lens is baked to obtain the first lens 311; step S106, forming a filling medium layer 33 around the first lens 311; and step S107, continuing to form the second filling medium layer 33 surface using the above method Two lenses 312.

The above steps will be described in detail below in conjunction with the accompanying drawings 3-7 and the descriptions in the corresponding specific implementation manners.

Step S101 : providing a substrate 71 . In order to enable the image sensor to have the ability to deflect light for incident light, the substrate 71 that meets the preset specifications should be selected first, and then a lens capable of deflecting light should be installed on the substrate 71 . Optionally, the substrate 71 may be a substrate fabricated on a silicon wafer, or may be a substrate fabricated on a germanium, silicon germanium, gallium arsenide substrate or a silicon-on-insulator substrate. Those skilled in the art can select the substrate type according to needs.

Step S102 : forming a patterned photoresist layer on the surface of the substrate 71 . After the selected substrate 71 is determined, 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. In the spin coating process, the problem of 45-degree spin pattern is easy to appear. In order to avoid the above problems, the rotation speed of 500-2000rad/s can be used when coating, and the temperature of the entire coating process should be kept constant, usually constant The temperature is 25°C. Optionally, a lens can also be directly selected for the installation operation. It should be understood that as long as the selected lens can meet the deflection of the light by the image sensor, and finally achieve uniform light intensity at the center and edge of the photosensitive area 32, the described lens can be selected. lens. In a possible implementation manner, this step further includes: forming a first back metal grid 521 on the surface of the substrate 71; forming a patterned photoresist layer in the first back metal grid 521 .

Step S103: exposing the photoresist layer to obtain an initial lens. After the photoresist is coated and fixed, the photoresist layer is exposed by ultraviolet exposure, and an initial lens of a certain size is finally obtained. Optionally, the initial lens is rectangular or semicircular.

Step S104: developing the initial lens. After the exposure is completed to obtain the initial lens, a special developing solution can be put in for development, and the purpose of the step is to wash off excess photoresist through the developing solution. The time for the initial lens to be placed in the developing solution needs to be strictly controlled, and the length of the developing time will directly affect the uniformity of the subsequent lens.

Step S105: Baking the initial lens after the development treatment to obtain the first lens 311 . Put the developed initial lens into an oven for baking, and finally obtain the first lens 311. The purpose of this step is to reduce the influence of the standing wave effect, and at the same time make the photoresist fully react, and the photoresist is completely reacted during the baking process. The active components produced by the resist will diffuse, thereby chemically enhancing the shallow image produced by the light intensity distribution, and more precisely controlling the graphic morphology of the first lens 311 .

Step S106 : forming a filling medium layer 33 around the first lens 311 . After the first lens 311 is obtained, a filling medium layer 33 can be formed around it. It can be understood that a medium with good conductivity and light transmittance, and a material with poor absorption and reflection performance should be selected as the filling medium layer 33. .

Step S107 : continue to form the second lens 312 on the surface of the filling medium layer 33 using the above method. After filling the filling medium layer 33 , continue to form the second lens 312 on the surface of the filling medium layer 33 using the above method.

In the above specific implementation manner, a patterned photoresist layer is formed by coating photoresist on the substrate 71, and then the photoresist layer is exposed and developed to obtain the first lens 311, and then a filling is formed around the first lens 311. The dielectric layer 33, and finally the second lens 312 is continuously formed on the surface of the filling dielectric layer 33 by the above method, so that the method has the advantages of simple and controllable preparation operation and low process cost.

It should be noted that the terms "including" and "having" and their variants involved in the documents of 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 clearly dictates, and it should be understood that the data so used are interchangeable under appropriate circumstances . The term "one or more" depends at least in part on the context and may be used to describe a feature, structure or characteristic in the singular sense or may be used to describe a feature, structure or combination of features in the plural sense. The term "based on" may be understood as not necessarily intended to express an exclusive set of factors, but may instead, again depending at least in part on the context, allow for the presence of other factors not necessarily explicitly described.

In addition, in the case of no conflict, specific implementations in the present application and features in the specific implementations may be combined with each other. Also, in the above description, descriptions of well-known components and techniques are omitted to avoid unnecessarily obscuring the concepts of the present application. In the above-mentioned specific implementation manners, each specific implementation manner focuses on the difference from other specific implementation manners, and the same/similar parts between various specific implementation manners can be referred to each other.

The above description is only the preferred specific implementation mode of the present application. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the application, some improvements and modifications can also be made, and these improvements and modifications should also be It is regarded as the scope of protection of this application.

Claims (9)

1. An image sensor, characterized in that, comprising: A first lens and a second lens, the second lens is used to receive incident light, the first lens is arranged in the light output direction of the second lens, and is used to receive light from the second lens, the first lens the refractive index of the lens is greater than the refractive index of the second lens; A filling medium layer is arranged between the first lens and the second lens. 2 . The image sensor according to claim 1 , further comprising a filter disposed in the light emitting direction of the second lens and configured to perform spectrum filtering on the incident light. 3 . 3. The image sensor according to claim 2, wherein the filter is further configured as a third lens, and the refractive index of the third lens is smaller than the refractive index of the second lens. 4. The image sensor according to claim 3, further comprising a first back metal grid and a second back metal grid; The first back metal grid is arranged between adjacent first lenses, the second back metal grid is arranged between adjacent lens groups, and the lens group includes the second lens and the Describe the third lens. 5. The image sensor according to claim 4, wherein the lens group and the first lens are arranged in a dislocation manner. 6 . The image sensor according to claim 4 , wherein the first back metal grid and the second back metal grid are arranged in a dislocation manner. 7 . 7. The image sensor according to claim 4, further comprising a deep trench isolation structure arranged in the light emitting direction of the first lens, the first back metal grid is isolated from the deep trench The structures are aligned. 8. A method for preparing an image sensor, for preparing the image sensor according to claim 1, comprising the steps of: provide the substrate; forming a patterned photoresist layer on the surface of the substrate; exposing the photoresist layer to obtain an initial lens; subjecting the initial lens to a development process; Baking the initial lens after the development treatment to obtain the first lens; forming a filling medium layer around the first lens; Continue to form the second lens on the surface of the filling medium layer using the above method. 9. The method according to claim 8, wherein the step of forming a photoresist layer further comprises: forming a first back metal grid on the surface of the substrate; A patterned photoresist layer is formed in the first back metal grid.

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