Method for forming an isolation region of a photodiode
By employing two photolithography and ion implantation processes to form a mesh isolation region in the CMOS image sensor, the problem of easy peeling of photoresist is solved, thereby improving the reliability of the photolithography process and the yield and reliability of the image sensor.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUA HONG SEMICON WUXI LTD
- Filing Date
- 2026-03-20
- Publication Date
- 2026-07-10
AI Technical Summary
In high-pixel CMOS image sensors, as pixel size is miniaturized, photoresist in existing photolithography processes is prone to peeling off, leading to failure of the ion implantation process in the isolation region, causing signal crosstalk and increased dark current, which affects product yield and reliability.
The first and second photoresist patterns are formed on the substrate by two photolithography and ion implantation processes. The first and second ion implantations are performed to form a mesh-structured isolation region, which increases the contact area between the photoresist pattern and the substrate, reduces the aspect ratio, and disperses stress.
It effectively reduces the risk of photoresist pattern peeling, improves the reliability and production efficiency of photolithography processes, and enhances the yield and reliability of image sensors.
Smart Images
Figure CN122373493A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor devices and integrated circuit technology, and in particular to a method for forming the isolation region of a photodiode. Background Technology
[0002] In the field of image sensors (CMOS Image Sensor, CIS), the physical size of a pixel is directly determined by the structure and size of the photodiode (PD). A photodiode typically includes an electron collecting region and an isolation region that isolates the electron collecting region (the conductivity type of the impurities doped in the isolation region differs from that of the impurities doped in the electron collecting region). For example... Figure 1 As shown, in the CIS provided in the related technology, taking the non-stacked CIS as an example, the isolation region of the photodiode is formed by photolithography to form a grid pattern gap and then by ion implantation. This grid-shaped isolation region can completely electrically isolate the electron collection area surrounding it, ensuring the signal independence between pixels.
[0003] With the development of high-pixel CIS technology, pixel size continues to shrink, posing challenges to the photolithography process for small-sized photodiode structures. Specifically, the smaller the pixel pitch, the narrower the photoresist linewidth and pattern gap need to be achieved in the photolithography process. When the pixel pitch shrinks to below 0.8 micrometers (μm), the photoresist thickness usually needs to be maintained at 2μm-3μm or even higher, resulting in a photoresist aspect ratio of 10:1 or even higher. Under these process conditions, in the method of forming the isolation region by single-pattern design and single-step photolithography implantation provided in related technologies, an independent photoresist pillar structure is formed in one photolithography step. Because the contact area between these photoresist pillars and the wafer surface is extremely small, the mechanical stress and chemical forces on the photoresist pillars increase significantly during exposure and development processes, making them prone to photoresist peeling. Photoresist peeling directly leads to the failure of the ion implantation process in the isolation region, resulting in a decrease in the isolation effect between photodiodes, causing problems such as signal crosstalk between pixels and increased dark current, leading to performance degradation of CIS and restricting product yield and reliability. Summary of the Invention
[0004] This application provides a method for forming an isolation region in a photodiode, which helps to reduce the risk of photoresist peeling off easily.
[0005] In view of this, this application provides a method for forming an isolation region of a photodiode, comprising:
[0006] Photolithography is performed using a first patterned mask to form a first photoresist pattern on a substrate, exposing the surface area of the first substrate.
[0007] The first photoresist pattern is used as a mask to perform the first ion implantation on the substrate, forming a first isolating sub-region in the substrate. After the first ion implantation, the first photoresist pattern is removed.
[0008] Photolithography is performed using a second patterned mask to form a second photoresist pattern on the substrate, exposing the surface area of the second substrate;
[0009] Using the second photoresist pattern as a mask, a second ion implantation is performed on the substrate to form a second isolating sub-region in the substrate. The first isolating sub-region and the second isolating sub-region constitute the isolation region. Viewed from a top angle, the isolation region has a mesh structure.
[0010] Optionally, viewed from a top view, the first substrate surface region includes a plurality of first spaced regions spaced apart along the X direction, and the first spaced regions include a plurality of first spaced sub-regions spaced apart along the Y direction, with the X and Y directions perpendicular to each other.
[0011] Optionally, viewed from a top view, the second substrate surface region includes a plurality of second spaced regions spaced apart along the Y direction, and the second spaced regions include a plurality of second spaced sub-regions spaced apart along the X direction.
[0012] Optionally, from a top-down view, the first interval sub-regions in adjacent first interval regions are staggered.
[0013] Optionally, from a top-down view, the second interval sub-regions in adjacent second interval regions are staggered.
[0014] Alternatively, when viewed from a top-down angle, the spacing between the first spaced sub-regions along the X direction is the same as the spacing between the second spaced sub-regions along the Y direction.
[0015] Alternatively, when viewed from a top-down angle, the spacing between the second spaced sub-regions along the X direction is the same as the spacing between the first spaced sub-regions 1111 along the Y direction.
[0016] Optionally, the thickness of the first photoresist pattern is the same as the thickness of the second photoresist pattern.
[0017] Optionally, the method is applied to the manufacturing process of an image sensor, wherein the pixel pitch of the image sensor does not exceed 0.8 μm.
[0018] Optionally, the thickness of the first photoresist pattern and the second photoresist pattern is greater than 2 μm.
[0019] Optionally, the second photoresist pattern on the substrate is removed after the second ion implantation.
[0020] The technical solution of this application has at least the following advantages:
[0021] Compared to a single photolithography injection process, this solution uses a two-stage photolithography injection process to form the isolation region. This allows the photoresist patterns formed by each photolithography step to be interconnected without changing the structure of the isolation region. This increases the contact area between the photoresist patterns formed by each photolithography step and the substrate, and reduces the aspect ratio of the overall structure. This helps to disperse stress in the photoresist patterns, making the photoresist patterns less likely to fall off, thereby reducing rework and reliability risks caused by photoresist pattern detachment. Attached Figure Description
[0022] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0023] Figure 1 This is a top view schematic diagram of the isolation region of a photodiode provided by related technologies;
[0024] Figure 2 This is a cross-sectional schematic diagram of the photodiode isolation region formation method provided in an exemplary embodiment of this application after forming a first photoresist pattern on a substrate;
[0025] Figure 3 This is a top view schematic diagram of the first substrate surface region exposed on the substrate in the method for forming the isolation region of a photodiode provided in an exemplary embodiment of this application;
[0026] Figure 4 This is a cross-sectional schematic diagram of the photodiode isolation region formation method provided in an exemplary embodiment of this application after forming a second photoresist pattern on a substrate;
[0027] Figure 5 This is a top view schematic diagram of the second substrate surface region exposed on the substrate in the isolation region formation method of a photodiode provided in an exemplary embodiment of this application;
[0028] Figure 6 This is a top view schematic diagram of the isolation region formed in the substrate in the isolation region formation method of the photodiode provided in an exemplary embodiment of this application;
[0029] Figure 7 This is a schematic diagram of the process flow of a method for forming an isolation region of a photodiode provided in an exemplary embodiment of this application;
[0030] The markings in the diagram represent:
[0031] 001, Isolation Zone
[0032] 100, Substrate; 110, First substrate surface region; 111, First spacer region; 120, Second substrate surface region; 121, Second spacer region; 130, First isolation region; 140, Second isolation region;
[0033] 200. First photoresist pattern;
[0034] 300. Second photoresist pattern. Detailed Implementation
[0035] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0036] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0037] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.
[0038] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.
[0039] The following is combined with Figures 1 to 7 This describes an embodiment of the present application.
[0040] refer to Figure 7 The illustration shows an embodiment of this application, providing a method for forming an isolation region of a photodiode, comprising:
[0041] S1, a first pattern mask is used for photolithography to form a first photoresist pattern on the substrate, exposing the surface area of the first substrate.
[0042] For example, the substrate 100 can be a silicon substrate, a germanium (Ge) substrate, a gallium arsenide (GaAs) substrate, or other materials suitable for photodiode manufacturing. Forming a photoresist pattern on the substrate 100 is typically achieved through a photolithography process. For instance, for a silicon substrate, a positive photoresist (i.e., photoresist or photopolymer resist) can be uniformly coated onto the surface of the silicon substrate. Then, a patterned mask is used to expose the substrate using a photolithography machine. Finally, the photoresist in the exposed areas is removed by a developing solution, thereby forming the photoresist pattern.
[0043] In one embodiment, such as Figure 3 As shown, viewed from a top view, the first substrate surface region 110 includes a plurality of first spaced regions spaced apart along the X direction, and the first spaced regions include a plurality of first spaced sub-regions 111 spaced apart along the Y direction, with the X and Y directions perpendicular to each other.
[0044] Specifically, the first spacer sub-region 111 can be elongated, such as a right rectangle, a rounded rectangle, or an ellipse. The length of the elongated shape is parallel to the Y-direction, and the X-direction is perpendicular to the Y-direction.
[0045] By forming a first photoresist pattern 200 on the substrate 100 that exposes the first substrate surface region 110, the contact area between the first photoresist pattern 200 and the substrate 100 can be increased, which is beneficial to improving the stress dispersion ability of the first photoresist pattern 200, reducing the risk of stress concentration points in the first photoresist pattern 200, and thus reducing the risk of the first photoresist pattern 200 peeling off.
[0046] In one embodiment, viewed from a top-down perspective, the first interval sub-regions 111 in adjacent first interval regions are staggered.
[0047] Understandably, the first interval sub-regions 111 in adjacent first interval regions are staggered, meaning that any two first interval sub-regions 111 located in adjacent first interval regions have a displacement difference Δy in the Y direction, where Δy > 0. This staggered arrangement helps to disperse stress in different directions, avoids continuous stress paths, and further reduces the risk of peeling off the first photoresist pattern 200.
[0048] It should be noted that Δy can also be 0. In this case, the first photoresist pattern 200 interconnected with each other can also be formed on the substrate 100.
[0049] In one embodiment, viewed from a top-down angle, the spacing between the first spacer sub-regions 1111 along the X-direction is the same as the spacing between the second spacer sub-regions 140 along the Y-direction. Setting equal spacing helps to further uniformly distribute stress and further reduce the risk of peeling off the first photoresist pattern 200.
[0050] S2, using the first photoresist pattern as a mask, the substrate is subjected to the first ion implantation to form a first isolator region in the substrate. After the first ion implantation, the first photoresist pattern is removed.
[0051] For example, when ion implantation is performed on substrate 100, different types of implanted impurity ions result in different types of isolation regions formed in substrate 100. For instance, implanting P-type impurities will form P (Positive) type isolation regions in substrate 100, while implanting N-type impurities will form N (Negative) type isolation regions. After ion implantation, the photoresist pattern is typically removed using an etching process.
[0052] S3, photolithography is performed using a second patterned mask to form a second photoresist pattern on the substrate, exposing the surface area of the second substrate;
[0053] In one embodiment, such as Figure 5 As shown, viewed from a top view, the second substrate surface region 120 includes a plurality of second spaced regions spaced apart along the Y direction, and the second spaced regions include a plurality of second spaced sub-regions 121 spaced apart along the X direction.
[0054] Specifically, the second spacer sub-region 121 can be elongated, such as a right rectangle, a rounded rectangle, or an ellipse, with the length direction of the elongated shape parallel to the X-direction and the X-direction perpendicular to the Y-direction.
[0055] By forming a second photoresist pattern 300 on the substrate 100 that exposes the surface region 120 of the second substrate, the contact area between the second photoresist pattern 300 and the substrate 100 can be increased, which is beneficial to improving the stress dispersion ability of the second photoresist pattern 300, reducing the risk of stress concentration points in the second photoresist pattern 300, and thus reducing the risk of peeling off the second photoresist pattern 300.
[0056] In one embodiment, viewed from a top-down perspective, the second spacer sub-regions 121 in adjacent second spacer regions are staggered. This staggered arrangement helps to distribute stress in different directions, avoids continuous stress paths, and further reduces the risk of peeling off the second photoresist pattern 300.
[0057] Understandably, the second interval sub-regions 121 in adjacent second interval regions are staggered, that is, any two first interval sub-regions 1111 located in adjacent first interval regions have a displacement difference Δx in the X direction, where Δx > 0.
[0058] It should be noted that Δx can also be 0. In this case, a second photoresist pattern 300 interconnected with each other can also be formed on the substrate 100.
[0059] In one embodiment, viewed from a top-down angle, the spacing between the second spacer sub-regions 121 along the X-direction is the same as the spacing between the first spacer sub-regions 1111 along the Y-direction. Setting equal spacing helps to further uniformly distribute stress and further reduce the risk of peeling off the second photoresist pattern 300.
[0060] In one embodiment, the thickness of the first photoresist pattern 200 is the same as the thickness of the second photoresist pattern 300.
[0061] S4. Using the second photoresist pattern as a mask, a second ion implantation is performed on the substrate to form a second isolator region in the substrate. The first isolator region and the second isolator region constitute the isolation region. When viewed from a top angle, the isolation region has a mesh structure.
[0062] It should be noted that the parameters for the second ion implantation (impurity ion type, implantation energy, dose, angle, etc.) are consistent with those for the first ion implantation.
[0063] In the CIS provided by related technologies, taking non-stacked CIS as an example, such as Figure 1 As shown, the isolation region of a photodiode is formed by ion implantation after photolithography creates a grid-like pattern gap. This grid-like isolation region completely electrically isolates the electron collection area surrounding it, ensuring signal independence between pixels. With the development of high-pixel CIS technology, pixel size continues to miniaturize. The smaller the pixel pitch, the narrower the photoresist linewidth and pattern gap need to be achieved in the photolithography process. When the pixel pitch shrinks to below 0.8 micrometers (μm), the photoresist thickness usually needs to be maintained at 2μm-3μm or even higher, resulting in a photoresist aspect ratio of 10:1 or even higher. Under these process conditions, in the method of forming the isolation region by single-pattern design and single photolithography implantation provided in related technologies, a single photolithography will form an independent photoresist pillar structure. Because the contact area between these photoresist pillars and the wafer surface is extremely small, the mechanical stress and chemical forces on the photoresist pillars are significantly increased during exposure and development processes, making them prone to photoresist peeling.
[0064] The photodiode isolation region formation method provided in this application embodiment forms a first isolation sub-region 130 and a second isolation sub-region 140 in a substrate 100 through two photolithography and implantation processes. The first isolation sub-region 130 and the second isolation sub-region 140 constitute a mesh structure isolation region 001. This means that, without changing the isolation region structure, the photoresist patterns formed by each photolithography can be interconnected, increasing the contact area between the photoresist patterns formed by each photolithography and the substrate, and reducing the aspect ratio of its overall structure. This is beneficial for the dispersion of stress in the photoresist patterns, making the photoresist patterns less prone to falling off.
[0065] When the isolation region formation method of a photodiode provided in an exemplary embodiment of this application is applied to the fabrication process of an image sensor, the pixel pitch of the image sensor does not exceed 0.8 μm. Specifically, the pixel pitch of the image sensor can be 0.8 μm, 0.7 μm, 0.6 μm, 0.5 μm, 0.4 μm, etc.
[0066] When forming the isolation region using a single photolithography injection process, the smaller the pixel pitch of the CIS, the more prone the independent photoresist pillar structure formed in a single photolithography step is to peeling off. Applying the photodiode isolation region formation method provided in an exemplary embodiment of this application to the fabrication process of an image sensor allows for the interconnection of photoresist patterns formed in each photolithography step without altering the isolation region structure. This increases the contact area between the photoresist patterns formed in each photolithography step and the substrate, reduces the aspect ratio of the overall structure, and facilitates stress dispersion within the photoresist patterns, making them less prone to peeling off. This, in turn, improves production efficiency and the yield and reliability of CIS products. The method of this application is not limited by the CIS pixel pitch and is particularly suitable for the fabrication of image sensors with pixel pitches of 0.8 μm and below.
[0067] In one embodiment, the thickness of the first photoresist pattern 200 and the second photoresist pattern 300 is greater than 2 μm. The method of this application is particularly suitable for fabricating image sensors with a photoresist thickness greater than 2 μm.
[0068] In one embodiment, the second photoresist pattern 300 on the substrate 100 is removed after the second ion implantation. After the second photoresist pattern 300 is removed, the substrate 100 can be further processed according to conventional subsequent process flows to fabricate a CIS product.
[0069] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.
Claims
1. A method for forming an isolation region in a photodiode, characterized in that, include: Photolithography is performed using a first pattern mask to form a first photoresist pattern (200) on a substrate (100), exposing the surface region (110) of the first substrate. The first photoresist pattern (200) is used as a mask to perform a first ion implantation on the substrate (100) to form a first isolation sub-region (130) in the substrate (100). After the first ion implantation, the first photoresist pattern (200) is removed. Photolithography is performed using a second pattern mask to form a second photoresist pattern (300) on the substrate (100), exposing the surface region (120) of the second substrate; Using the second photoresist pattern (300) as a mask, a second ion implantation is performed on the substrate (100) to form a second isolation sub-region (140) in the substrate. The first isolation sub-region (130) and the second isolation sub-region (140) constitute the isolation region (001). From a top view, the isolation region (001) has a mesh structure.
2. The method according to claim 1, characterized in that, Viewed from a top angle, the first substrate surface region (110) includes a plurality of first spaced regions spaced apart along the X direction, and the first spaced regions include a plurality of first spaced sub-regions (111) spaced apart along the Y direction, with the X and Y directions perpendicular to each other.
3. The method according to claim 2, characterized in that, Viewed from a top angle, the second substrate surface region (120) includes a plurality of second spaced regions spaced apart along the Y direction, and the second spaced regions include a plurality of second spaced sub-regions (121) spaced apart along the X direction.
4. The method according to claim 2, characterized in that, Viewed from above, the first interval sub-regions of adjacent first interval regions are staggered.
5. The method according to claim 3, characterized in that, Viewed from above, the second interval sub-regions in adjacent second interval regions are staggered.
6. The method according to claim 4 or 5, characterized in that, Viewed from above, the spacing between the first spaced sub-regions (111) along the X direction is the same as the spacing between the second spaced sub-regions (121) along the Y direction.
7. The method according to claim 6, characterized in that, Viewed from above, the spacing between the second interval sub-regions (121) along the X direction is the same as the spacing between the first interval sub-regions (111) along the Y direction.
8. The method according to any one of claims 1 to 7, characterized in that, The thickness of the first photoresist pattern (200) is the same as the thickness of the second photoresist pattern (300).
9. The method according to claim 8, characterized in that, The method is applied in the manufacturing process of an image sensor, wherein the pixel pitch of the image sensor does not exceed 0.8 μm.
10. The method according to claim 9, characterized in that, The thickness of the first photoresist pattern (200) and the second photoresist pattern (300) is greater than 2 μm.
11. The method of preparation according to claim 10, characterized in that, Also includes: The second photoresist pattern (300) on the substrate is removed after the second ion implantation.