Method of manufacturing an image sensor

Abstract

The application provides a manufacturing method of an image sensor, before a silicon wafer is processed and manufactured, one or more P / N type high-energy ion implantations are preferentially performed to reduce the pressure of a thick photoresist process and high-energy ion implantation in subsequent processes; on the other hand, through the advance of the corresponding high-energy ion implantation, a deeper P-Well isolation can be implanted, the surface damage of a photodiode caused by back thinning is improved, and the performance of the image sensor is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for manufacturing an image sensor. Background Technology

[0002] In the field of semiconductor technology, ultra-thin stacked CMOS image sensors (UTSCIS) are formed by bonding separately manufactured logic wafers and pixel wafers together. Because the logic wafer and pixel wafer are manufactured separately, the manufacturing process is flexible and low-cost. Another advantage of this process is that the logic devices and pixel devices do not interfere with each other, allowing for greater performance maximization. A stacked CIS typically consists of two silicon wafers: a logic wafer, whose main function is to provide the CIS's logic circuitry, timing circuitry, and memory cells; and a pixel wafer, whose main function is to provide the CIS's pixel cells and photodiodes.

[0003] Typically, ion implantation is used to isolate adjacent pixel units in image sensors, separating the photodiodes of adjacent pixel units and reducing crosstalk between pixel units. With advancements in image sensor fabrication processes, pixel sizes are continuously decreasing. As image sensor pixel sizes shrink to the sub-micron range, the area of ​​a single pixel unit decreases significantly. To ensure that each pixel unit continues to provide performance similar to that of previously larger pixel units (especially full-well capacity), the depth of the photodiode (PD) region in the image sensor is increased to maintain an appropriate photosensitive volume. This increased PD depth places higher demands on the depth of the isolation implantation between pixel units.

[0004] On the other hand, high-energy deep isolation implantation requires the use of thick photoresist. The increase in PD volume leads to an increase in isolation implantation depth, and the thickness of the photoresist used to block non-implanted areas also increases. Combined with the reduction in pixel size, this results in the remaining photoresist after development becoming thinner and taller. Such a photoresist block has an excessively high center of gravity and a small contact area between the bottom and the substrate, making it difficult for the adhesion force to fix the entire photoresist. Therefore, the flow of solution during the development process may cause the photoresist block to collapse, resulting in subsequent ion implantation failure. Summary of the Invention

[0005] The purpose of this invention is to provide a method for manufacturing an image sensor, which reduces the pressure of thick photoresist processes and high-energy ion implantation, improves the surface damage caused by back-side thinning of photodiodes, and thus improves the performance of the image sensor.

[0006] To achieve the above objectives, the present invention provides a method for manufacturing an image sensor, comprising:

[0007] A method for manufacturing an image sensor, comprising:

[0008] Provide semiconductor substrates;

[0009] A well region is formed by deep implantation of first-type ions into the semiconductor substrate;

[0010] An active region is formed by performing an isolation trench process on the semiconductor substrate;

[0011] A photodiode region is formed by performing multiple deep implantations of type I ions in the active region.

[0012] An isolation region is formed by performing multiple rounds of second-type ion deep implantation in the photodiode region.

[0013] Specifically, the deep implantation of at least one first-type ions to form the photodiode region is moved forward before the formation of the active region, or the implantation of at least one second-type ions to form the isolation region is moved forward before the formation of the active region.

[0014] Optionally, the method for fabricating the image sensor includes moving at least one first-type ion deep implantation to form the photodiode region before forming the active region and after forming the trap region.

[0015] Optionally, the method for fabricating the image sensor includes: implanting at least one second-type ion to form an isolation region before moving it forward to form a trap region.

[0016] Optionally, moving at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before forming the active region further includes forming an oxide layer on the semiconductor substrate.

[0017] Optionally, at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region, which is moved forward before the formation of the active region, are both patternless high-energy ion implantations.

[0018] Optionally, the first type of ion implantation is N-type ion implantation and the second type of ion implantation is P-type ion implantation; or, the first type of ion implantation is P-type ion implantation and the second type of ion implantation is N-type ion implantation.

[0019] Optionally, the first type of ion implantation is As ion implantation, and the second type of ion implantation is B ion implantation.

[0020] Optionally, the isolation trench process is the STI process.

[0021] Optionally, moving at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before forming the active region includes: moving at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before photoresist formation in the STI process.

[0022] Optionally, after forming the isolation zone, the method further includes:

[0023] A back-side thinning process is performed on the semiconductor substrate;

[0024] Deep trench isolation is performed in the photodiode region.

[0025] In summary, the image sensor fabrication method provided by this invention, during the fabrication of the photodiode region, moves at least one N-type ion deep implantation to form the photodiode region or at least one P-type ion deep implantation to form the isolation region before forming the active region, thereby reducing the pressure of thick photoresist processing and high-energy ion implantation in subsequent processes. On the other hand, by moving the corresponding high-energy ion implantation forward, a deeper P-Well isolation layer can be implanted, improving the surface damage caused by back-side thinning of the photodiode, and thus improving the performance of the image sensor. Attached Figure Description

[0026] Figure 1 A flowchart illustrating a method for manufacturing an image sensor;

[0027] Figure 2 A flowchart illustrating a method for manufacturing an image sensor according to an embodiment of the present invention;

[0028] Figure 3 A flowchart illustrating the forward implantation of DNPPD ions in a method for fabricating an image sensor according to an embodiment of the present invention;

[0029] Figure 4 This is a flowchart illustrating the forward implantation of DDPW ions in a method for fabricating an image sensor according to an embodiment of the present invention. Detailed Implementation

[0030] With the increasing demand for ultra-high resolution image sensors, the pixel size of image sensors is becoming smaller and smaller. To meet certain application requirements, photodiodes need to be designed to be narrow and deep, and the corresponding surrounding p-wells also need to be very deep to prevent blooming. Therefore, high-performance, high-energy, deep ion implantation has become the method currently used. However, multi-pass high-energy ion implantation has a certain impact on production capacity. Similarly, high-energy, deep ion implantation requires thicker photoresist to protect other areas, thus placing high demands on the photolithography process.

[0031] The front-end processes of CIS image sensors are not significantly different from traditional CMOS processes, which is a key reason why CIS image sensors can outperform CCD image sensors in achieving much lower costs. In the front-end processes of CIS image sensors, multi-pass high-energy ion implantation mainly involves various well implantations and pixel-related implantations before and after the AA / STI process. A typical process flow is as follows: Figure 1 As shown, deep N-well implantation (ADNW) is first performed on the substrate to form the well region. Next, an AA / STI process (AA loop) is performed to form the active region. Then, N-type ion implantation (DNPPD loop) is performed on the photodiode region, followed by deep P-type ion implantation (DDPW loop) to form the isolation region. On the other hand, the current main manufacturing process for small-pixel image sensors is a stacked process. Therefore, after two wafers (logica wafer and pixel wafer) are joined together, the silicon wafer surface (the back side of the pixel wafer) needs to be thinned to bring the photodiode closer to the surface to receive light, thereby reducing light loss from the sensor to the photodiode. However, since the current photodiode is connected to the well region (ADNW), which is currently the deepest ion implantation region, thinning the back side easily exposes the ADNW to the surface, thus affecting performance.

[0032] The inventors discovered that achieving the desired ion implantation depth and concentration using thick photoresist and high-energy multi-stage ion implantation presents a significant challenge for both lithosomes and implanters. A thick oxide layer can effectively protect the silicon substrate while allowing for high-energy, deep ion implantation. Addressing this issue, the inventors have developed a method for fabricating an image sensor. Before the silicon wafer undergoes further manufacturing processes, one or more stages of P / N-type high-energy ion implantation are performed first, reducing the pressure on subsequent thick photoresist processes and high-energy ion implantation. Furthermore, by advancing the high-energy ion implantation, a deeper P-well isolation layer can be implanted, mitigating surface damage to the photodiode caused by back-side thinning, thereby improving the image sensor's performance.

[0033] To make the content of this invention clearer and easier to understand, the following description, in conjunction with the accompanying drawings, further illustrates the invention. Of course, this invention is not limited to this specific embodiment, and common substitutions well-known to those skilled in the art are also covered within the scope of protection of this invention.

[0034] Secondly, the present invention is described in detail using schematic diagrams. When describing the examples of the present invention in detail, for ease of explanation, the schematic diagrams are not enlarged to a certain extent according to the general proportions, and this should not be regarded as a limitation of the present invention.

[0035] This invention provides a method for manufacturing an image sensor, the method comprising:

[0036] Provide semiconductor substrates;

[0037] A well region is formed by deep implantation of first-type ions into the semiconductor substrate;

[0038] An active region is formed by performing an isolation trench process on the semiconductor substrate;

[0039] A photodiode region is formed by performing multiple deep implantations of type I ions in the active region.

[0040] An isolation region is formed by performing multiple rounds of second-type ion deep implantation in the photodiode region.

[0041] Specifically, the deep implantation of at least one first-type ions to form the photodiode region is moved forward before the formation of the active region, or the implantation of at least one second-type ions to form the isolation region is moved forward before the formation of the active region.

[0042] Furthermore, in some embodiments of the present invention, the deep implantation of at least one first-type ions to form the photodiode region is moved forward to before the formation of the active region and after the formation of the trap region.

[0043] Furthermore, in some embodiments of the present invention, the process includes: implanting at least one second-type ion to form the isolation region before the formation of the trap region.

[0044] The process of advancing at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before forming the active region further includes forming an oxide layer of a certain thickness on the semiconductor substrate to prevent high-energy implantation from damaging the surface of the semiconductor substrate. Furthermore, the at least one first-type ion deep implantation to form the photodiode region or the at least one second-type ion implantation to form the isolation region before forming the active region are both patternless high-energy ion implantations.

[0045] Furthermore, the isolation trench process is a shallow trench isolation (STI) process.

[0046] Accordingly, moving at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before forming the active region includes: moving at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before photoresist formation (AA-PH) in the STI process.

[0047] Furthermore, in the image sensor fabrication method provided by the present invention, after forming the isolation region, the method further includes: performing a back-side thinning process on the semiconductor substrate and performing a deep trench isolation (DTI) process on the photodiode region. By forming a deep trench isolation (DTI) structure to enclose each photodiode in the photodiode region, in some embodiments of the present invention, combined with a specifically designed DTI process, the ion implantation of the entire isolation region can be effectively reduced or even eliminated, and effective isolation can be formed, thereby improving performance more effectively.

[0048] In the image sensor fabrication method provided by this invention, a thick oxide layer is deposited, and a certain amount of ions are implanted using high-energy ion implantation. This involves advancing the high-energy ion implantation steps to reduce the need for high-energy ion implantation in certain subsequent processes (photodiode region and isolation region). This reduces both the amount of high-energy ion implantation and the pressure on the photolithography thick resist process. Furthermore, by moving the ion implantation of certain steps forming the photodiode region and isolation region before the formation of the active region (e.g., the formation of the trap region), some deep ion implantation isolation is performed beforehand, improving the surface damage to the photodiode caused by back-side thinning, thereby improving the performance of the image sensor.

[0049] It should be noted that the first type of ion implantation is N-type ion implantation, and the second type of ion implantation is P-type ion implantation; or, the first type of ion implantation is P-type ion implantation, and the second type of ion implantation is N-type ion implantation. For example, the first type of ion implantation is arsenic (As) ion implantation, and the second type of ion implantation is boron (B) ion implantation.

[0050] The following section uses N-type ion implantation as the first type and P-type ion implantation as the second type to illustrate the fabrication method of the image sensor provided by this invention.

[0051] Figure 2 A flowchart illustrating a method for manufacturing an image sensor according to an embodiment of the present invention is shown below. Figure 2 As shown, the method for manufacturing the image sensor includes:

[0052] Provide semiconductor substrates;

[0053] An N-well is formed by deep N-type ion implantation into the semiconductor.

[0054] An active region is formed by performing an isolation trench process on the semiconductor substrate;

[0055] A photodiode region is formed by performing multiple deep N-type ion implantations in the active region.

[0056] Multiple deep P-type ion implantations are performed in the photodiode region to form an isolation region DDPW.

[0057] Specifically, at least one deep N-type ion implantation to form the photodiode region is moved forward before the formation of the active region, or at least one deep P-type ion implantation to form the isolation region is moved forward before the formation of the active region.

[0058] Specifically, firstly, a semiconductor substrate is provided, which can be a single-crystal silicon (Si) substrate, a single-crystal germanium (Ge) substrate, a silicon-on-insulator (SOI) substrate, or a germanium-on-insulator (GOI) substrate, etc. The material of the substrate 100 can also be a compound semiconductor. For example, the substrate can be a gallium arsenide (GaAs) substrate, an indium phosphide (InP) substrate, or a silicon carbide (SiC) substrate, etc. It is worth noting that the substrate described in this embodiment can also be prepared using at least one of other semiconductor materials known in the art.

[0059] Next, deep N-type ion implantation is performed on the semiconductor substrate to form a well region (ADNW).

[0060] Next, an active region AA is formed by performing an isolation trench process on the semiconductor substrate, wherein the isolation trench process adopts the STI process.

[0061] Next, multiple deep N-type ion implantations are performed in the active region AA to form a photodiode region;

[0062] Next, multiple deep P-type ion implantations are performed in the photodiode region to form an isolation region;

[0063] For example, such as Figure 3 As shown, the first ion implantation (IMP) of the photodiode region (DNPPD) is moved forward to the N-type well region (ADNW) fabrication. That is, after completing three deep N-type ion implantations in the well region, an additional deep high-energy N-type ion implantation is added. In the subsequent seven N-type ion implantations of the photodiode region (DNPPD), by adjusting the ion implantation conditions of the corresponding channels, one ion implantation can be reduced (e.g., IMP1). The full well capacitance (FWC) of the sensor fabricated in this way is close to that obtained by conventional processes, and the number of white pixels (WP) is reduced, resulting in better image sensor performance.

[0064] As another example, such as Figure 4 As shown, the four ion implantation passes (IMP4-7) forming the isolation region (DDPW) in the photodiode region are moved forward to the N-type well region (ADNW) fabrication. That is, before completing the three deep N-type ion implantations in the well region, an additional deep high-energy P-type ion implantation is added to form a P-well region (ADPW). The ion implantation of the N-type well region (ADNW) can be adjusted accordingly, for example, it can be refined and split. In the subsequent seven N-type ion implantations of the isolation region DDPW, by adjusting the ion implantation conditions of the corresponding passes, the number of three ion implantations in DDPW can be reduced, for example, performing IMP1-3 and skipping IMP4-7. The sensor fabricated in this way has an 18% higher FWC and a 22% lower WP, resulting in better overall performance. Furthermore, the ion implantation of the corresponding channel in the isolation region (DDPW) is moved forward to the N-type well region (ADNW), which is equivalent to first implanting a deep P-Well isolation layer, improving the surface damage caused by the back thinning of the photodiode, thereby improving the performance of the image sensor.

[0065] It should be noted that the above-mentioned N-type ion implantation is arsenic (As) ion implantation, and P-type ion implantation is boron (B) ion implantation. In other embodiments of the present invention, other N-type and P-type ions can also be used for ion implantation processes. In addition, the N-type ion implantation for moving the photodiode region DNPPD to the well region ADNW can be the same as the N-type ion implantation for the well region ADNW, for example, both can be As ions, or different N-type ion implantations can be performed according to the process.

[0066] Furthermore, both the aforementioned deep high-energy N-type ion implantation in the ADNW well region and the deep high-energy P-type ion implantation in the ADNW well region are patternless high-energy ion implantations. Before performing the aforementioned high-energy ion implantation, an oxide layer of a certain thickness is formed on the semiconductor substrate to prevent damage to the semiconductor substrate surface caused by the high-energy implantation.

[0067] Furthermore, the image sensor fabrication method also includes subsequent gate processes, metal interconnect processes, flip bonding processes with logic silicon wafers, back-side thinning processes on the semiconductor substrate after bonding, deep trench isolation (DTI) processes for the photodiode region, metal grid processes, and subsequent fabrication of optical modules (color filters and microlenses). In some embodiments of this invention, by forming a deep trench isolation (DTI) structure to enclose each photodiode in the photodiode region, combined with a specifically designed DTI process, it is possible to effectively reduce or even eliminate ion implantation for the entire isolation zone, achieving effective isolation and significantly improving performance.

[0068] In summary, this embodiment provides a method for fabricating an image sensor. During the fabrication of the photodiode region, at least one N-type ion deep implantation to form the photodiode region or at least one P-type ion deep implantation to form the isolation region is moved forward before the formation of the active region. This reduces the pressure of subsequent thick photoresist processes and high-energy ion implantation. On the other hand, by moving the corresponding high-energy ion implantation forward, a deeper P-Well isolation layer can be implanted, improving the surface damage caused by back-side thinning of the photodiode, thereby improving the performance of the image sensor.

[0069] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for manufacturing an image sensor, characterized in that, include: Provide semiconductor substrates; A well region is formed by deep implantation of first-type ions into the semiconductor substrate; An active region is formed by performing an isolation trench process on the semiconductor substrate; A photodiode region is formed by performing multiple deep implantations of type I ions in the active region. An isolation region is formed by performing multiple rounds of second-type ion deep implantation in the photodiode region. Specifically, the deep implantation of at least one first-type ions to form the photodiode region is moved forward before the formation of the active region, or the implantation of at least one second-type ions to form the isolation region is moved forward before the formation of the active region.

2. The method for manufacturing an image sensor according to claim 1, characterized in that, This includes moving at least one first-type ion deep implantation for forming the photodiode region before forming the active region and after forming the trap region.

3. The method for manufacturing an image sensor according to claim 1, characterized in that, include: At least one second-type ion implantation to form the isolation zone is moved forward before the formation of the trap region.

4. The method for manufacturing an image sensor according to claim 2 or 3, characterized in that, Moving at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before forming the active region also includes forming an oxide layer on the semiconductor substrate.

5. The method for manufacturing an image sensor according to claim 4, characterized in that, Both the deep implantation of first-type ions to form the photodiode region or the deep implantation of second-type ions to form the isolation region, which are moved forward to the point before the formation of the active region, are patternless high-energy ion implantations.

6. The method for manufacturing an image sensor according to claim 1, characterized in that, The first type of deep ion implantation is N-type ion implantation, and the second type of ion implantation is P-type ion implantation; or, the first type of deep ion implantation is P-type ion implantation, and the second type of ion implantation is N-type ion implantation.

7. The method for manufacturing an image sensor according to claim 6, characterized in that, The first type of deep ion implantation is As ion implantation, and the second type of ion implantation is B ion implantation.

8. The method for manufacturing an image sensor according to claim 1, characterized in that, The isolation trench process is the STI process.

9. The method for manufacturing an image sensor according to claim 8, characterized in that, Moving at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before the formation of the active region includes: moving at least one first-type ion deep implantation to form the photodiode region or at least one second-type ion implantation to form the isolation region before the formation of the photoresist in the STI process.

10. The method for manufacturing an image sensor according to claim 1, characterized in that, After the isolation zone is formed, it also includes: A back-side thinning process is performed on the semiconductor substrate; Deep trench isolation is performed in the photodiode region.

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