Image sensor and manufacturing method thereof
By designing doped base layer and multi-layer doping structure in the image sensor to form an electric field with doped concentration gradient, the problem of low quantum efficiency in the near-infrared band of CMOS image sensor is solved, and efficient photogenerated electron collection and near-infrared are achieved Improvement of band quantum efficiency.
Patent Information
- Application Number
- CN202310723167.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-16
- Publication Date
- 2024-12-27
AI Technical Summary
The quantum efficiency of CMOS image sensors in the near infrared band is low, mainly because the silicon substrate has weak absorption in the 750nm to 1100nm band, resulting in the inability to be collected effectively, and the front illuminated structure is difficult to enhance the near infrared by adding light reflection structure. Absorption of light.
An image sensor is designed, including a doped substrate layer and a plurality of pixel units, each pixel unit consisting of a first and a second doped layer, a second doped layer disposed on the doped substrate layer, and a first doped layer A photodiode is formed on the second doped layer, and the doping concentration gradient generates an electric field deep enough to ensure the collection of photogenerated electrons in the deep.
The strong electric field generated by doping the concentration gradient effectively improves the quantum efficiency of the near-infrared band and improves the performance of the image sensor.
Smart Images
Figure CN119208336A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of image sensing technology, and in particular to an image sensor and a manufacturing method thereof. Background Art
[0002] Image sensors in the near-infrared (NIR) band have broad applications in security monitoring, machine vision, and biometrics. For CMOS image sensors, the silicon substrate has weak absorption in the near-infrared band of 750nm to 1100nm, resulting in low quantum efficiency. Therefore, enhancing the quantum efficiency of pixels in the near-infrared band is critical to improving the performance of image sensors.
[0003] The penetration depth of near-infrared light in silicon substrates can usually reach 10μm or more. For front-illuminated image sensors, due to the limited depth of its photodiode (<5um), photogenerated electrons deeper in the substrate cannot be collected, resulting in low quantum efficiency. At the same time, it is difficult for front-illuminated structures to increase the absorption of near-infrared light by adding light-reflecting structures. Summary of the invention
[0004] In view of this, the present application provides an image sensor that can be effectively collected into a photodiode by a sufficiently strong electric field, so that the collection efficiency of photogenerated electrons is high.
[0005] An image sensor includes a doped base layer and a plurality of pixel units arranged in rows and columns formed on the doped base layer, each pixel unit includes a first doped layer and at least one second doped layer, the second doped layer is arranged on the doped base layer, the first doped layer is arranged on the second doped layer, a photodiode is formed on the first doped layer, the doping concentration of the doped base layer is greater than the doping concentration of the second doping layer, and the doping concentration of the second doping layer is greater than the doping concentration of the first doping layer.
[0006] In an embodiment of the present invention, each of the pixel units includes at least two layers of the second doping layers, and each of the second doping layers is stacked in sequence along a direction perpendicular to the doping base layer, and the doping concentration of the second doping layer close to the doping base layer is greater than the doping concentration of the second doping layer stacked thereon.
[0007] In an embodiment of the present invention, the thicknesses of each of the second doping layers are equal, or the thickness of the second doping layer close to the doped base layer is greater than the thickness of the second doping layer stacked thereon, or the thickness of the second doping layer close to the doped base layer is less than the thickness of the second doping layer stacked thereon.
[0008] In an embodiment of the present invention, the above-mentioned second doping layer includes an upper surface and a lower surface that are relatively arranged, the lower surface is formed on the doping base layer, the first doping layer is formed on the upper surface, and the doping concentration of the second doping layer gradually decreases from the lower surface toward the direction close to the upper surface.
[0009] In an embodiment of the present invention, the P-type doping concentration of the second doping layer is 10 14 ~10 20 cm -3 .
[0010] In an embodiment of the present invention, the thickness of the second doping layer is 1-10 um.
[0011] In an embodiment of the present invention, the first doping layer includes an isolation portion formed by P-type doping and a photodiode formed by N-type doping, and the isolation portion is arranged around the circumference of the photodiode.
[0012] In an embodiment of the present invention, each of the pixel units further includes a transfer transistor, a floating diffusion region, a reset transistor and a source follower transistor, the photodiode is used to convert a light signal containing image information into an electrical signal during an exposure process; the transfer transistor is connected to the photodiode and the floating diffusion region, and is used to transfer the electrical signal of the photodiode to the floating diffusion region; the source follower transistor is used to output the electrical signal of the floating diffusion region; and the reset transistor is used to reset the floating diffusion region.
[0013] In an embodiment of the present invention, each of the pixel units further includes a selection transistor, and the selection transistor is used to select and output the electrical signal output by the source follower transistor to a column line.
[0014] In an embodiment of the present invention, each pixel unit further includes a dual conversion gain transistor connected between the reset transistor and the floating diffusion region, and the dual conversion gain transistor is used to increase the full well capacity of the photodiode during exposure.
[0015] In an embodiment of the present invention, the image sensor further comprises a color filter and a lens array, wherein the color filter is arranged on the light incident side of the first doping layer, and the lens array is arranged on the light incident side of the color filter.
[0016] The present application also provides a method for manufacturing the above-mentioned image sensor, the manufacturing method comprising:
[0017] P-type doping forms a doped base layer;
[0018] Forming a first doped layer and at least one second doped layer by P-type doping on the doped base layer, wherein the second doped layer is formed on the doped base layer, and the first doped layer is formed on the second doped layer;
[0019] The first doping layer is N-type doped to form a photodiode, the doping concentration of the doped base layer is greater than the doping concentration of the second doping layer, and the doping concentration of the second doping layer is greater than the doping concentration of the first doping layer.
[0020] In an embodiment of the present invention, at least two second doping layers are formed on the doped base layer by P-type doping, so that the doping concentration of the second doping layer close to the doped base layer is greater than the doping concentration of the second doping layer stacked thereon.
[0021] In an embodiment of the present invention, the second doping layer comprises an upper surface and a lower surface which are arranged opposite to each other, and the doping concentration of the second doping layer gradually decreases from the lower surface toward the upper surface.
[0022] In the image sensor of the present invention, since the doping concentration of the doped base layer is greater than the doping concentration of the second doping layer, and the doping concentration of the second doping layer is greater than the doping concentration of the first doping layer, the doping base layer, the second doping layer, and the first doping layer form a doping concentration gradient, which can generate a sufficiently deep electric field. Photogenerated electrons in the deep layer can be effectively collected by a sufficiently strong electric field and enter the photodiode, so that the collection efficiency of photogenerated electrons is high, and the quantum efficiency (QE) in the near-infrared (NIR) band can be effectively increased. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 It is a schematic diagram of the partial structure of the image sensor of the first embodiment of the present application.
[0024] Figure 2 Schematic diagram of a pixel circuit structure of an image sensor according to an embodiment of the present application.
[0025] Figure 3 Schematic diagram of a pixel circuit structure of an image sensor according to another embodiment of the present application.
[0026] Figure 4 It is a schematic diagram of the partial structure of the image sensor of the second embodiment of the present application.
[0027] Figure 5 It is a schematic diagram of the partial structure of the image sensor of the third embodiment of the present application. DETAILED DESCRIPTION
[0028] The following is an explanation of the implementation of the present application by means of specific embodiments. People familiar with the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification.
[0029] In the following description, reference is made to the accompanying drawings, which describe several embodiments of the present application. It should be understood that other embodiments may be used and that mechanical, structural, electrical, and operational changes may be made without departing from the spirit and scope of the present application. The following detailed description should not be considered limiting, and the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application.
[0030] Although the terms first, second, etc. are used herein to describe various elements in some instances, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.
[0031] Furthermore, as used in this article, the singular forms "one", "an" and "the" are intended to include plural forms as well, unless there is an indication to the contrary in the context. It should be further understood that the terms "comprise", "include" indicate the presence of features, steps, operations, elements, components, projects, kinds, and / or groups, but do not exclude the presence, occurrence or addition of one or more other features, steps, operations, elements, components, projects, kinds, and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or mean any one or any combination. Therefore, "A, B or C" or "A, B and / or C" means "any of the following: A; B; C; A and B; A and C; B and C; A, B and C". Only when the combination of elements, functions, steps or operations is inherently mutually exclusive in some way, will there be an exception to this definition.
[0032] First embodiment
[0033] Figure 1 is a schematic diagram of a partial structure of an image sensor according to the first embodiment of the present application. Figure 1 As shown, the image sensor includes a doped substrate layer 11 and a plurality of pixel units 12 arranged in rows and columns formed on the doped substrate layer 11, each pixel unit 12 includes a first doped layer 121 and at least one second doped layer 122, the second doped layer 122 is arranged on the doped substrate layer 11, the first doped layer 121 is arranged on the second doped layer 122, a photodiode 123 is formed on the first doped layer 121, the doping concentration of the doped substrate layer 11 is greater than the doping concentration of the second doped layer 122, and the doping concentration of the second doped layer 122 is greater than the doping concentration of the first doped layer 121. The image sensor of the present application is a front-illuminated image sensor.
[0034] In the image sensor of the present application, since the doping concentration of the doped base layer 11 is greater than the doping concentration of the second doping layer 122, and the doping concentration of the second doping layer 122 is greater than the doping concentration of the first doping layer 121, the doped base layer 11, the second doping layer 122, and the first doping layer 121 form a doping concentration gradient, which can generate a sufficiently deep electric field. The photogenerated electrons in the deep layer can be effectively collected by the sufficiently strong electric field and enter the photodiode 123, so that the collection efficiency of the photogenerated electrons is high, which can effectively increase the quantum efficiency (QE) in the near-infrared (NIR) band.
[0035] Optionally, the second doping layer 122 has a thickness of 1 to 10 um, for example, 2 um, 3 um, 4 um, 5 um, 6 um, 7 um, 8 um, or 9 um.
[0036] Optionally, the thickness of the first doping layer 121 is 1-10 um, for example, 2 um, 3 um, 4 um, 5 um, 6 um, 7 um, 8 um, or 9 um.
[0037] Optionally, the first doping layer 121 includes an isolation portion 124 formed by P-type doping (such as boron) and a photodiode 123 formed by N-type doping (such as phosphorus or arsenic), and the isolation portion 124 is arranged around the circumference of the photodiode 123 .
[0038] In other embodiments, the isolation portion 124 may also be a trench etched on the upper surface of the first doped layer 121 and the trench is filled with a dielectric material, such as silicon oxide, silicon nitride, silicon oxynitride, fluorine-doped silicate glass (FSG), a low-k dielectric material (e.g., a material with a k value less than 3.9) and / or a suitable insulating material. The isolation portion 124 may include a corresponding front shallow trench isolation structure (STI).
[0039] Optionally, Figure 2 is a schematic diagram of a pixel circuit structure of an image sensor according to an embodiment of the present application. Figure 1 and Figure 2As shown, each pixel unit 12 further includes a transfer transistor TX, a floating diffusion region FD, a reset transistor RST, and a source follower transistor SF. The photodiode 123PD is used to convert an optical signal containing image information into an electrical signal during the exposure process. The transfer transistor TX is connected to the photodiode 123PD and the floating diffusion region FD, and is used to transfer the electrical signal of the photodiode 123PD to the floating diffusion region FD. The source follower transistor SF is used to output the electrical signal of the floating diffusion region FD. The reset transistor RST is used to reset the floating diffusion region FD. The first doping layer 121 is doped, such as plasma implantation, so that the photodiode 123PD, the floating diffusion region FD, and the source and drain of the transfer transistor TX, the source follower transistor SF, the reset transistor RST, and the selection transistor RS are formed in the first doping layer 121.
[0040] Alternatively, if Figure 2 As shown, each pixel unit 12 further includes a selection transistor RS, and the selection transistor RS is used to select and output the electrical signal output by the source follower transistor SF to a column line (Pixel out).
[0041] Optionally, Figure 3 is a schematic diagram of a pixel circuit structure of an image sensor according to another embodiment of the present application. Figure 3 As shown, each pixel unit also includes a dual conversion gain transistor DCG, which is connected between the reset transistor RST and the floating diffusion area FD, and is used to increase the full well capacity of the photodiode 123PD during exposure. When the image sensor works in a normal exposure environment, the dual conversion gain transistor DCG is disconnected, the reset transistor RST is turned on, and the photodiode 123PD is normally exposed; when the image sensor works in a high exposure environment, the dual conversion gain transistor DCG is turned on, the reset transistor RST is disconnected, and the drain of the dual conversion gain transistor DCG is connected to the capacitor C, thereby increasing the full well capacity, which is beneficial to improving the dynamic range of the image sensor (the number of electrons received by the floating diffusion area FD increases, and the signal-to-noise ratio is higher), thereby improving image quality.
[0042] Alternatively, if Figure 1As shown, the image sensor further includes a color filter and a lens array, the color filter is arranged on the light incident side of the first doping layer 121, and the lens array is arranged on the light incident side of the color filter. In this embodiment, the color filter includes a plurality of color filter units 131 arranged corresponding to each pixel unit 12, and each color filter unit 131 can be an R color filter unit 131 for filtering red light, a G color filter unit 131 for filtering green light, a B color filter unit 131 for filtering blue light, or a color filter unit 131 for filtering white light; the lens array includes a plurality of lens units 141 arranged corresponding to each pixel unit 12, and each lens unit 141 is arranged one-to-one with each color filter unit 131.
[0043] Optionally, the doping concentration of the first doping layer 121 is 1e15 cm -3 ; The doping concentration of the second doping layer 122 is 1e16-1e17 cm -3 ; The doping concentration of the doped base layer 11 is 1e18 cm -3 ; but it is not limited to this.
[0044] Second embodiment
[0045] Figure 4 is a schematic diagram of a partial structure of an image sensor according to a second embodiment of the present application. Figure 4 As shown, the structure of the image sensor of this embodiment is substantially the same as that of the image sensor of the first embodiment, except that the number of the second doping layers 122 is different.
[0046] Alternatively, if Figure 4 As shown, each pixel unit 12 includes at least two second doping layers 122, and each second doping layer 122 is stacked in sequence along a direction perpendicular to the doped base layer 11, and the doping concentration of the second doping layer 122 close to the doped base layer 11 is greater than the doping concentration of the second doping layer 122 stacked thereon.
[0047] Alternatively, if Figure 4 As shown, the thickness of each second doping layer 122 is equal, or the thickness of the second doping layer 122 close to the doped base layer 11 is greater than the thickness of the second doping layer 122 stacked thereon, or the thickness of the second doping layer 122 close to the doped base layer 11 is less than the thickness of the second doping layer 122 stacked thereon.
[0048] Optionally, the thickness of the first doping layer 121 is 4 um; the thickness of each second doping layer 122 is 2 um.
[0049] Please refer to the first embodiment for other structures of the image sensor, which will not be described again here.
[0050] Third embodiment
[0051] Figure 5is a schematic diagram of a partial structure of an image sensor according to a third embodiment of the present application. Figure 5 As shown, the structure of the image sensor of this embodiment is substantially the same as that of the image sensor of the above embodiment, except that the doping concentration of the second doping layer 122 varies differently.
[0052] Alternatively, if Figure 5 As shown, the second doping layer 122 includes an upper surface and a lower surface that are relatively arranged. The lower surface is formed on the doping base layer 11, and the first doping layer 121 is formed on the upper surface. The doping concentration of the second doping layer 122 gradually decreases from the lower surface to the direction close to the upper surface, and the doping concentration changes linearly or nonlinearly.
[0053] Optionally, the P-type doping concentration of the second doping layer 122 is 10 14 ~10 20 cm -3 .
[0054] Please refer to the first embodiment for other structures of the image sensor, which will not be described again here.
[0055] Fourth embodiment
[0056] The present application also relates to a method for manufacturing the above-mentioned image sensor, the method comprising:
[0057] P-type doping forms a doped base layer 11;
[0058] P-type doping is performed on the doped base layer 11 to form a first doped layer 121 and at least one second doped layer 122, wherein the second doped layer 122 is formed on the doped base layer 11, and the first doped layer 121 is formed on the second doped layer 122;
[0059] The first doping layer 121 is N-type doped to form a photodiode 123 . The doping concentration of the doped base layer 11 is greater than the doping concentration of the second doping layer 122 . The doping concentration of the second doping layer 122 is greater than the doping concentration of the first doping layer 121 .
[0060] Optionally, at least two second doping layers 122 are formed by P-type doping on the doped base layer 11 , so that the doping concentration of the second doping layer 122 close to the doped base layer 11 is greater than the doping concentration of the second doping layer 122 stacked thereon.
[0061] Optionally, the second doping layer 122 includes an upper surface and a lower surface that are arranged opposite to each other, and the doping concentration of the second doping layer 122 gradually decreases from the lower surface toward the upper surface.
[0062] The above embodiments are merely illustrative of the principles and effects of the present application and are not intended to limit the present application. Anyone familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed in the present application shall still be covered by the claims of the present application.
Claims
1. An image sensor, characterized in that: It includes a doped base layer and a plurality of pixel units arranged in rows and columns formed on the doped base layer, each of the pixel units includes a first doped layer and at least one second doped layer, the second doped layer is arranged on the doped base layer, the first doped layer is arranged on the second doped layer, a photodiode is formed in the first doped layer, the doping concentration of the doped base layer is greater than the doping concentration of the second doping layer, and the doping concentration of the second doping layer is greater than the doping concentration of the first doping layer.
2. The image sensor according to claim 1, wherein: Each of the pixel units includes at least two layers of the second doping layers, each of the second doping layers is stacked in sequence along a direction perpendicular to the doping base layer, and the doping concentration of the second doping layer close to the doping base layer is greater than the doping concentration of the second doping layer stacked thereon.
3. The image sensor according to claim 2, wherein: The thickness of each second doping layer is equal, or the thickness of the second doping layer close to the doped base layer is greater than the thickness of the second doping layer stacked thereon, or the thickness of the second doping layer close to the doped base layer is less than the thickness of the second doping layer stacked thereon.
4. The image sensor according to any one of claims 1 to 3, characterized in that: The second doping layer includes an upper surface and a lower surface that are arranged opposite to each other, the lower surface is formed on the doping base layer, the first doping layer is formed on the upper surface, and the doping concentration of the second doping layer gradually decreases from the lower surface toward the upper surface.
5. The image sensor according to claim 4, wherein: The P-type doping concentration of the second doping layer is 10 14 ~10 20 cm -3 .
6. The image sensor according to claim 1, wherein: The thickness of the second doping layer is 1-10 um.
7. The image sensor according to claim 1, wherein: The first doping layer includes an isolation portion formed by P-type doping and a photodiode formed by N-type doping, and the isolation portion is arranged around the circumference of the photodiode.
8. The image sensor according to claim 1, wherein: Each of the pixel units also includes a transfer transistor, a floating diffusion area, a reset transistor and a source follower transistor. The photodiode is used to convert the light signal containing image information into an electrical signal during the exposure process; the transfer transistor connects the photodiode and the floating diffusion area, and is used to transfer the electrical signal of the photodiode to the floating diffusion area; the source follower transistor is used to output the electrical signal of the floating diffusion area; and the reset transistor is used to reset the floating diffusion area.
9. The image sensor according to claim 8, wherein: Each of the pixel units further includes a selection transistor, and the selection transistor is used to select and output the electrical signal output by the source follower transistor to a column line.
10. The image sensor according to claim 8, wherein: Each of the pixel units further includes a dual conversion gain transistor, which is connected between the reset transistor and the floating diffusion region, and is used to increase the full well capacity of the photodiode during exposure.
11. The image sensor according to claim 1, wherein: The image sensor further includes a color filter and a lens array. The color filter is arranged on the light incident side of the first doping layer, and the lens array is arranged on the light incident side of the color filter.
12. A method for manufacturing the image sensor according to any one of claims 1 to 11, characterized in that: The production method comprises: P-type doping forms a doped base layer; Forming a first doped layer and at least one second doped layer by P-type doping on the doped base layer, wherein the second doped layer is formed on the doped base layer, and the first doped layer is formed on the second doped layer; The first doping layer is N-type doped to form a photodiode, the doping concentration of the doped base layer is greater than the doping concentration of the second doping layer, and the doping concentration of the second doping layer is greater than the doping concentration of the first doping layer.
13. The method for manufacturing an image sensor according to claim 12, wherein: At least two second doping layers are formed on the doped base layer by P-type doping, so that the doping concentration of the second doping layer close to the doped base layer is greater than the doping concentration of the second doping layer stacked thereon.
14. The method for manufacturing an image sensor according to claim 12 or 13, characterized in that: The second doping layer includes an upper surface and a lower surface that are opposite to each other, and the doping concentration of the second doping layer gradually decreases from the lower surface toward the upper surface.