A processing method for improving process defects of an image sensor
By oxidizing the trench sidewalls with SiN layer before the photolithography process of the image sensor to form SiOxNy layer, the problem of photoresist residue is solved, ensuring the accuracy and uniformity of P-type ion implantation and improving the performance of the image sensor chip.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GEKKO SEMICON (SHANGHAI) CO LTD
- Filing Date
- 2024-12-20
- Publication Date
- 2026-06-23
AI Technical Summary
During the manufacturing process of image sensors, photoresist residues are easily generated inside high aspect ratio trenches, which can lead to P-type ion implantation failure and affect the performance of image sensor chips.
Before the photolithography process, the SiN layer on the trench sidewall is oxidized. By introducing oxygen-containing gas to react with SiN, a SiOxNy layer is formed, which improves the hydrophilicity of the trench sidewall. Combined with hydrophilic surfactants and cleaning agents, tiny particles are removed to ensure the effectiveness of the photoresist development process.
It effectively removes photoresist residue, improves the accuracy and uniformity of P-type ion implantation, reduces white pixel defects, and enhances the performance of image sensor chips.
Smart Images
Figure CN122269836A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of image sensor technology, and more specifically to a method for improving the processing defects of image sensors. Background Technology
[0002] In advanced image sensor manufacturing, P-type ion implantation plays a crucial role on the surface of the photodetector (PD) after the gate sidewall process. Introducing holes into the PD surface through P-type ion implantation lowers its surface potential, effectively preventing electrons from migrating from the PD's interior to the surface. Furthermore, the implanted P-type ions can capture defect electrons generated by surface damage during manufacturing, such as lattice defects, significantly reducing the potential adverse effects of electrons from various sources on the semiconductor device (e.g., short circuits), thereby improving the performance of the white pixel (WP). Therefore, performing an effective P-type ion implantation process on the PD surface is one of the core elements for ensuring the imaging quality of image sensors.
[0003] However, with the continuous development of image sensor technology, P-type ion implantation technology faces challenges due to the gradual miniaturization of the PD area. To improve image resolution, more pixels are integrated onto image sensors of the same size. This leads to a continuous decrease in the pixel pitch on the image sensor, while the dimensions of key components such as transmission gates, selection gates, selection lines, and reset transistors remain relatively unchanged. This directly results in a continuous reduction in the size of the trenches formed between these key components. Before P-type ion implantation, a photolithography process is typically required. This involves exposing and developing the photoresist (PR) coated in these trenches to expose the PD surface at the bottom of the trench, allowing for P-type ion implantation. However, in practical applications, it has been found that after the photoresist development process, a large amount of photoresist residue appears inside the narrower trenches. This residue can cause P-type ion implantation failure, ultimately leading to a reduction in the performance of the image sensor chip. Summary of the Invention
[0004] To overcome the shortcomings of the prior art, the purpose of this invention is to solve the problem of photoresist residues easily generated inside high aspect ratio trenches in image sensor chips, and to improve the ion implantation effect of subsequent P-type ion implantation processes by reducing the formation of photoresist residues.
[0005] To achieve the above objectives, the present invention provides a method for improving manufacturing defects in image sensors, comprising:
[0006] Step 1, provide a substrate, which includes a substrate, a polysilicon layer is disposed on the substrate, the polysilicon layer is provided with a plurality of trenches, and sidewalls are formed on the sidewalls of the trenches, the sidewalls being SiN layers;
[0007] Step 2: Introduce oxygen-containing gas, which reacts with the surface of the SiN layer to form SiO. x N y ;
[0008] Step 3: Clean the substrate with a cleaning agent;
[0009] Step 4: Form a photoresist pattern over the substrate to expose the trenches;
[0010] The SiO x N y In this context, x represents the atomic proportion of O, and y represents the atomic proportion of N.
[0011] Furthermore, in step 2, the oxygen-containing gas includes any one or more of N2O, NO, NO2, or O2.
[0012] Furthermore, the oxygen-containing gas is N2O.
[0013] Furthermore, the process parameters for introducing N2O are as follows: the gas flow rate of N2O is 1100 sccm to 1300 sccm, the introduction time is 10 s to 15 s, the chamber pressure is 4 torr to 6 torr, and the chamber temperature is 300℃ to 500℃.
[0014] Furthermore, between step 1 and step 2, an immersion step is also included: immersing the substrate in a hydrophilic surfactant to activate the surface of the SiN layer.
[0015] Furthermore, the hydrophilic surfactant is SC1.
[0016] Furthermore, the hydrophilic surfactant includes ammonia, hydrogen peroxide, and water.
[0017] Furthermore, the volume ratio of the ammonia, hydrogen peroxide, and water is 1:2:(40-100).
[0018] Furthermore, between the impregnation step and step 2, the substrate is cleaned with deionized water or distilled water.
[0019] Furthermore, in step 3, the cleaning reagent includes at least one or more of SC1, SC2, deionized water, and distilled water.
[0020] Furthermore, the cleaning agent is SC1.
[0021] Furthermore, the depth-to-width ratio of the trench is greater than or equal to 2:1.
[0022] Furthermore, after step 4, step 5 is also included: P-type ion implantation is performed on the bottom of the trench.
[0023] Furthermore, in step 5, the ion beam of the P-type ion implantation contains at least one of boron difluoride and boron.
[0024] Compared with the prior art, the beneficial effects of the present invention include at least the following:
[0025] (1) Before coating a substrate with high aspect ratio trenches with photoresist, the present invention introduces oxygen-containing gas into the reaction chamber, so that the SiN layer surface on the trench sidewall reacts with O-containing active particles to form silicon oxynitride (SiO2). x N y (where x represents the atomic proportion of O and y represents the atomic proportion of N), and then the substrate is cleaned to effectively remove tiny particles (micro-defects) generated by the previous process on the trench sidewalls, avoiding negative impacts of these tiny particles on subsequent photoresist exposure and development. On the one hand, SiO x N y It is an amorphous structure, and amorphous structures have high solid surface tension (r). SG According to Young's equation, the height r SG The material has high hydrophilicity, therefore SiO x N y It can improve the hydrophilicity of the trench sidewall surface; on the other hand, SiO x N y In the amorphous structure, the structural ends are O and / or N. Both O and N can form hydrogen bonds with water molecules. The hydrogen bond formed by O and H is stronger than the hydrogen bond formed by N and H. Therefore, SiO x N y Compared to SiN, it can improve the hydrophilicity of the trench sidewall surface. Therefore, SiO x N y The formation of this layer allows the trench sidewall surface to fully contact the aqueous cleaning agent during subsequent cleaning steps, effectively removing tiny particles from the trench sidewall surface. This improves the photoresist development capability in subsequent photolithography processes and prevents the formation of photoresist residues. Due to the reduction in photoresist residues, the P-type ion implantation area becomes more precise, and the uniformity of P-type ion implantation in the target area is higher, which helps reduce white pixels and improve the performance of the image sensor chip.
[0026] (2) Further, the present invention includes an impregnation step before introducing oxygen-containing gas. The substrate is impregnated in a hydrophilic surfactant, which activates the SiN layer surface of the trench sidewalls, facilitating a rapid and complete reaction between the subsequently introduced oxygen-containing gas and the SiN layer surface to form SiO₂. x N y Layer. Simultaneously, the strong oxidizing component (e.g., H₂O₂) in the hydrophilic surfactant can also undergo an oxidation reaction with SiN to form SiO₂. x N y This helps to improve the hydrophilicity of the trench sidewall surface. Attached Figure Description
[0027] Figure 1 This is a partially enlarged schematic diagram of a substrate; where a represents the substrate surface with trenches of high aspect ratio, in region A, the white area represents the trenches, and the black area represents the gate electrode (polysilicon layer); b represents a partially enlarged schematic diagram of region A in a; c represents the substrate after photolithography, and region B represents the photoresist residue that appears.
[0028] Figure 2 Scanning images of defects released on the substrate surface after a P-type ion implantation process is performed on a substrate that has not utilized the processing method of the present invention for improving process defects in image sensors.
[0029] Figure 3 This is a process flow diagram of a method for improving manufacturing defects in an image sensor according to the present invention.
[0030] Figure 4 This is a partial (including one trench) cross-sectional schematic diagram of a substrate with a high aspect ratio trench according to the present invention.
[0031] Figure 5 SiO2 is formed on the sidewall surface of the substrate in step 2. x N y A schematic diagram of the cross-section behind the layer.
[0032] Figure 6 A cross-sectional schematic diagram of a substrate forming a photoresist pattern; where a represents a cross-sectional schematic diagram of the substrate after being coated with photoresist and covered with a mask; b represents a cross-sectional schematic diagram of the substrate after being developed with photoresist to form a photoresist pattern.
[0033] Figure 7 This is a scanned image of the defects released on the substrate surface after a P-type ion implantation process is performed on a substrate using the processing method for improving process defects in an image sensor according to the present invention.
[0034] Explanation of reference numerals in the attached diagram:
[0035] Substrate 10,
[0036] Gate oxide layer 20,
[0037] Polycrystalline silicon layer 30,
[0038] Trench 40,
[0039] SiN layer 41,
[0040] SiO x N y Floor 411,
[0041] Photoresist 50,
[0042] Mask 60. Detailed Implementation
[0043] The technical solution of the present invention 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 the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0044] In the description of this invention, it should be noted that the terms "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 invention and for 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 invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0045] In the description of this invention, it should be noted that, unless otherwise explicitly 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; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0046] The terms "photoresist" and "photoresist" used in this article are interchangeable.
[0047] As described in the background section, in order to improve the performance of white pixels (WP) in image sensors, a technique of P-type ion implantation is attempted on the surface of photodetectors (PDs) exposed between key components on the chip. This aims to prevent electrons inside the PD from migrating to the surface and to capture electrons from defects on the PD surface, thereby avoiding electrical interference to the image sensor from electrons of different sources. Typically, before performing the P-type ion implantation process, in order to achieve precise control of the P-type ion implantation area, a photolithography process must be performed on the substrate used to form the image sensor chip. This involves coating photoresist, exposing and developing the photoresist, and etching it to form the required photoresist pattern, thereby exposing the PD surface to be implanted with P-type ions. At the same time, the top surface of each key component is covered with photoresist to prevent the key components from being bombarded by unwanted ion beams.
[0048] Specifically, the process steps prior to P-type ion implantation include:
[0049] Step S1: A substrate is provided, which includes a substrate, a polysilicon layer is disposed on the substrate, the polysilicon layer has a plurality of trenches, and sidewalls are formed on the sidewalls of the trenches, the sidewalls being SiN layers.
[0050] Step S2: Clean the substrate with deionized water or distilled water to remove impurities from the surface of the substrate.
[0051] Step S3: After coating the substrate with photoresist, a mask is placed over the polysilicon layer and the sidewalls to expose and develop the photoresist, thereby exposing the trenches.
[0052] The exposure and development process includes exposing a substrate coated with photoresist, then dissolving and removing the exposed photoresist areas with a developer to expose the trenches, the bottom of which exposes the substrate surface to be implanted with P-type ions. Figure 1 The white area in a shows the substrate surface on which P-type ion implantation is required.
[0053] However, with the current development trend of image sensor technology, the spacing between key components on the chip is gradually narrowing, meaning that the trenches on the substrate are gradually shrinking. The aspect ratio (AR) of these trenches is gradually increasing, evolving from less than 1:1 to greater than or equal to 2:1. For example... Figure 1As shown in b, for example, for a 50M pixel image sensor, the width of the trench on the substrate has been reduced from the traditional 0.612μm to 55nm. When the AR of the trench is less than 1:1, the substrate achieves improved WP performance after P-type ion implantation. However, the inventors found that when the AR of the trench is greater than or equal to 2:1, the WP performance of the substrate does not achieve the expected improvement after P-type ion implantation, and more defects appear. See [reference needed]. Figure 2 , Figure 2 The black dots in the image indicate defects on the substrate (trench AR ≥ 2:1) obtained by scanning. This invention reveals that the main reasons for the different effects achieved by P-type ion implantation due to different trench AR are as follows:
[0054] In the front-end process, for example, during step S1 described above, when sidewalls (SiN layers) are formed by etching, microparticles (microdefects) are inevitably introduced onto the surface of the SiN layer. Due to the weak hydrophilicity of SiN, the contact area between the SiN layer surface and the aqueous cleaning agent is small. Therefore, during cleaning, the SiN layer surface cannot fully contact the aqueous cleaning agent, making it difficult to effectively remove the microparticles. Consequently, these microparticles remain in the subsequently coated photoresist. When the AR ratio of the trench is less than 1:1, the wider trench allows light to easily enter and fully contact the photoresist inside, making the exposure of the photoresist inside the trench negligible due to the influence of microparticles. However, when the AR ratio of the trench is greater than or equal to 2:1, the narrower trench results in very weak light intensity deep within the trench, significantly increasing the interference of microparticles on photoresist exposure. In low-light conditions, tiny particles directly block the path of light, altering its direction and causing uneven light exposure to the photoresist. Unexposed photoresist cannot be dissolved by the developer, leading to photoresist residue during development. (See also...) Figure 1 Region B of image c shows photoresist residue inside the trenches after photoresist development of the substrate. This photoresist residue affects the precise execution of subsequent P-type ion implantation processes, preventing P-type ions from being implanted onto the substrate surface obscured by the photoresist residue, causing defects, and resulting in reduced chip manufacturing yield and WP performance.
[0055] Therefore, there is an urgent need for a process that can effectively remove tiny particles from the sidewall surface to reduce photoresist residue, thereby reducing defects on the substrate surface and ensuring the effective implementation of subsequent P-type ion implantation processes.
[0056] To address the aforementioned problems, this invention proposes a method for improving process defects in image sensors. Before photolithography on the substrate, the SiN layer on the trench sidewalls undergoes surface oxidation. Oxygen-containing gas is then introduced, allowing O-containing active particles in the gas to react with SiN to form SiO2. x N y (x represents the atomic proportion of O, y represents the atomic proportion of N), the SiO x N y Its hydrophilicity is stronger than that of SiN, which is beneficial for thoroughly cleaning and removing tiny particles from the sidewall surface during the cleaning process, thereby avoiding the generation of photoresist residues after development and improving the implantation effect of P-type ion implantation process for image sensors with high aspect ratio.
[0057] The following is a detailed description in conjunction with the accompanying drawings.
[0058] like Figure 3 As shown, the present invention provides a method for improving manufacturing defects in image sensors, comprising:
[0059] Step 1: Provide a substrate comprising a substrate, wherein a polysilicon layer is disposed on the substrate, the polysilicon layer having a plurality of trenches, and sidewalls formed on the sidewalls of the trenches, the sidewalls being SiN layers.
[0060] like Figure 4 The diagram shows a partial cross-sectional view of a substrate (including a trench). In some embodiments, the substrate includes a substrate 10, a gate oxide layer 20, a polysilicon layer 30, and a trench 40. Sidewalls, which are SiN layers 41, are formed on the sidewalls of the polysilicon layer 30. The trench 40 penetrates the polysilicon layer 30, exposing a portion of the gate oxide layer 20 beneath the polysilicon layer 30.
[0061] In the manufacturing process of an image sensor, the polysilicon layer 30 is typically formed using a chemical vapor deposition process. The polysilicon layer 30 serves as a gate electrode, used to control the current flow between the source and drain electrodes.
[0062] In some embodiments, prior to forming the polysilicon layer 30, a step of depositing a gate oxide layer 20 is included. The gate oxide layer 20, typically a silicon oxide layer, provides isolation and insulation between the gate and the semiconductor, and helps reduce stress caused by thermal expansion mismatch, thereby reducing device deformation. After sequentially depositing the polysilicon layer 30 and etching to form a plurality of sidewalls composed of the polysilicon layer 30 and a bottom-defined opening structure composed of the gate oxide layer 20, a silicon oxide layer is then self-aligned and deposited on the sidewalls and top surface of the polysilicon layer 30 for further isolation and deformation reduction.
[0063] To prevent the polysilicon layer 30 from being eroded by moisture and air, and to reduce unintended carrier leakage between the source and drain, a spacer process is typically required. In some embodiments, the spacer formation step includes: after forming a sidewall consisting of a silicon oxide layer on the sidewalls of the polysilicon layer 30 and a bottom-defined opening structure consisting of a gate oxide layer 20 on the substrate surface, a SiN layer is conformally deposited on the sidewalls of the opening structure, the bottom surface of the opening structure, and the top surface of the silicon oxide layer above the polysilicon layer 30 by introducing silicon and nitrogen source precursors; then, the SiN above the polysilicon layer 30 and at the bottom of the opening structure is removed by vertical etching, leaving only the SiN on the sidewalls of the opening structure, thereby forming the spacer. At this time, a trench 40 is formed by the sidewall consisting of the SiN layer 41 and the bottom-defined trench consisting of the gate oxide layer 20.
[0064] Step 2: Introduce oxygen-containing gas, which reacts with the surface of the SiN layer to form SiO. x N y The SiO x N y In this context, x represents the atomic proportion of O, and y represents the atomic proportion of N.
[0065] The oxygen-containing gas includes any one or more of N2O, NO, NO2, or O2. The oxygen-containing gas contains oxygen-containing active particles that can react with SiN to form SiO. x N y The reaction equation is: O· + SiN → SiO x N y O· refers to the active particles containing O.
[0066] In some embodiments, the oxygen-containing gas introduced into the reaction chamber is N2O, which has strong oxidizing properties and can oxidize SiN to SiO. x N y The N2O gas flow rate is 1100 sccm to 1300 sccm, the N2O introduction time is 10 s to 15 s, the pressure in the reaction chamber is 4 torr to 6 torr, and the temperature in the reaction chamber is 300℃ to 500℃.
[0067] like Figure 5 As shown, after step 2, the surface of the SiN layer 41 on the sidewall of the trench 40 is oxidized to SiO. x N y Layer 411. An unexpected discovery in this invention is that SiO... x N y The formation of layer 411 facilitates the removal of minute particles from the sidewall surface of the trench 40 through subsequent cleaning steps. (SiO)x N y It has an amorphous structure, which has a higher specific surface area and more active sites, thus exhibiting higher r. SG (Solid surface tension) value, according to Young's equation: r SG -r SL =r GL cosθ(r SL Represents the surface tension of solids and liquids, r GL (where θ represents the surface tension of the liquid, and θ represents the contact angle between the water molecule and the contact surface). A higher r SG A value that favors a decrease in θ allows water molecules to interact with SiO₂. x N y The contact surface of layer 411 is increased, therefore SiO x N y It has strong hydrophilicity. Furthermore, SiO₂ x N y In the amorphous structure, the structural ends are O and / or N. Both O and N can form hydrogen bonds with water molecules. The hydrogen bond formed by O and H is stronger than the hydrogen bond formed by N and H. Therefore, SiO x N y Compared to SiN, it can improve the hydrophilicity of the sidewall surface of trench 40, so that the sidewall surface of trench 40 can fully contact the cleaning agent in the subsequent cleaning steps, thereby effectively cleaning and removing the tiny particles on the sidewall surface of trench 40 and avoiding their impact on the exposure and development of photoresist.
[0068] In some embodiments, an immersion step is included between step 1 and step 2: the substrate is immersed in a hydrophilic surfactant to activate the surface of the SiN layer.
[0069] In some embodiments, the hydrophilic surfactant is SC1, comprising ammonia (NH4OH), hydrogen peroxide (H2O2), and water; wherein the volume ratio of the ammonia, hydrogen peroxide, and water is 1:2:(40-100).
[0070] This invention unexpectedly discovered that when the substrate is immersed in a liquid tank containing SC1 for a period of time, the SC1 can activate the surface of the SiN layer 41. Because ammonia is corrosive, it can slightly corrode the surface of the SiN layer 41, weakening the Si-N bonds and increasing the number of surface active sites. This provides more opportunities for the subsequent surface reaction in step 2, where oxygen-containing gas is introduced, to form SiO2. x N y Layer 411. Simultaneously, due to the strong oxidizing properties of hydrogen peroxide, it can also react with the SiN layer 41 to form the target amorphous SiO2 structure on the surface of the SiN layer 41. x Ny The reaction equation is: H₂O₂ + SiN → SiO₂ x N y +H2O. Therefore, through the synergistic effect of its components, SC1 can not only perform a conventional cleaning function, but also activate the surface of the SiN layer 41, ensuring that the surface of the SiN layer 41 can be fully oxidized to form SiO. x N y Layer 411.
[0071] Step 3: Clean the substrate with a cleaning agent.
[0072] The cleaning agent comprises any one or more of SC1, SC2, deionized water, and distilled water. In some embodiments, the cleaning agent is SC1, which comprises ammonia (NH4OH), hydrogen peroxide (H2O2), and water.
[0073] The cleaning principle of SC1 is based on a combination of chemical reaction and physical dissolution. In SC1, ammonia water can form soluble complexes with metal ions in the microparticles, causing the metal particles to dissolve; simultaneously, hydrogen peroxide has strong oxidizing properties, which can oxidize and decompose organic matter in the microparticles, thereby achieving the purpose of removing impurities. In this invention, SiO2 is formed... x N y Layer 411 improves the hydrophilicity of the sidewall surface of trench 40, increasing the contact area between microparticles and SC1, making the microparticles easier to clean and remove under the action of SC1. Furthermore, as mentioned earlier, since hydrogen peroxide in SC1 has strong oxidizing properties, it is understandable that using SC1 to clean the substrate in this step further ensures that the surface of the SiN layer 41 is sufficiently oxidized to form SiO. x N y Layer 411 enhances surface hydrophilicity, facilitating the complete removal of fine particles.
[0074] Step 4: Form a photoresist pattern over the substrate to expose the trenches;
[0075] The step of forming the photoresist pattern includes: coating a photoresist 50 over the substrate, the photoresist 50 filling the trench 40 and covering the top of the polysilicon layer 30 and the sidewalls, so that the top surface of the substrate is flat. (See also...) Figure 6 a. After covering the polysilicon layer 30 and the sidewalls with a mask 60 having a characteristic structure (e.g., an opening or a via), the substrate is exposed so that the photoresist 50 exposed by the characteristic structure of the mask 60 is irradiated by light.
[0076] In this invention, due to SiO x Ny The formation of layer 411 allows for thorough cleaning and removal of minute particles by SC1 in step 3, effectively improving the presence of minute particles in the photoresist 50. This avoids risks such as light blocking and light scattering caused by the presence of minute particles, thereby enhancing the uniformity of light reception in the photoresist 50 inside the trench 40, especially for trenches 40 with an aspect ratio greater than or equal to 2:1.
[0077] Due to uniform light exposure, the exposed photoresist 50 is fully dissolved and removed in the developing tank containing the developer, exposing the trench 40. The bottom of the trench 40 exposes the surface to be implanted with P-type ions. The unexposed photoresist 50 is retained, forming the photoresist pattern. See [link to documentation]. Figure 6 b. The unexposed photoresist 50 acts as a mask, protecting the underlying polysilicon layer 30 and sidewalls from bombardment by the P-type ion beam, thereby ensuring that P-type ions are implanted only into specific target areas (implanted from the bottom surface of the trench 40), avoiding unnecessary ion implantation damage to the polysilicon layer 30 and sidewalls.
[0078] Step 5: Perform P-type ion implantation at the bottom of the trench.
[0079] The ion beam of the P-type ion implantation includes at least one of boron difluoride and boron. By introducing holes into the surface of the substrate 10 through the P-type ion implantation process, its surface potential is reduced, thereby effectively preventing electrons from migrating from inside the substrate 10 to the surface. Furthermore, the implanted P-type ions can capture defect electrons generated by surface damage during manufacturing, such as lattice defects, thus significantly reducing the potential adverse effects of electrons on the device (e.g., short circuits).
[0080] Figure 7 These are scanned images obtained by scanning the substrate processed in steps 1 to 5 using a scanning machine to count the number of defects. Figure 1 The comparison clearly shows that, prior to photolithography, the N2O oxidation treatment of the sidewall surface and the SC1 cleaning technique described in this invention effectively reduce defects on the substrate surface with high aspect ratio trenches. This demonstrates that N2O can oxidize the SiN layer surface on the trench sidewalls to SiO. x N y The layer enhances the hydrophilicity of the sidewall surface, allowing tiny particles to fully contact SC1 and be cleaned and removed. This reduces the possibility of photoresist residue in subsequent processes, thereby reducing defects on the substrate surface and improving the performance of white pixels in the image sensor chip.
[0081] In summary, the method for improving process defects in image sensors provided by this invention involves introducing oxygen-containing gas, causing the surface of the SiN layer on the trench sidewalls of the substrate to react with oxygen-containing active particles, forming silicon oxynitride (SiO2). x N y Oxide layer. SiO x N y Its amorphous structure enhances hydrophilicity, facilitating thorough contact with aqueous cleaning agents during the cleaning process and effectively removing fine particulate matter. Before introducing oxygen-containing gas, the invention also includes an impregnation step, treating the SiN layer surface with a hydrophilic surfactant to promote a rapid and complete reaction between the subsequent oxygen-containing gas and the SiN layer surface. The strong oxidant in the surfactant then reacts with the SiN to form amorphous SiO₂. x N y This improves hydrophilicity, ensuring that subsequent cleaning steps can effectively remove tiny particles from the surface. Thorough removal of these particles enhances the exposure and development capabilities of the photoresist in subsequent photolithography processes, preventing the formation of photoresist residues. This, in turn, ensures the effective implementation of the P-type ion implantation process, thereby reducing white pixels and improving the performance of the image sensor chip.
[0082] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.
Claims
1. A method for improving manufacturing defects in image sensors, characterized in that, Include: Step 1, provide a substrate, which includes a substrate, a polysilicon layer is disposed on the substrate, the polysilicon layer is provided with a plurality of trenches, and sidewalls are formed on the sidewalls of the trenches, the sidewalls being SiN layers; Step 2: Introduce oxygen-containing gas, which reacts with the surface of the SiN layer to form SiO. x N y ; Step 3: Clean the substrate with a cleaning agent; Step 4: Form a photoresist pattern over the substrate to expose the trenches; The SiO x N y In this context, x represents the atomic proportion of O, and y represents the atomic proportion of N.
2. The method for improving manufacturing defects in image sensors as described in claim 1, characterized in that, In step 2, the oxygen-containing gas includes any one or more of N2O, NO, NO2, or O2.
3. The method for improving manufacturing defects in image sensors as described in claim 2, characterized in that, The oxygen-containing gas is N2O.
4. The method for improving manufacturing defects in image sensors as described in claim 3, characterized in that, The process parameters for introducing N2O are as follows: the gas flow rate of N2O is 1100 sccm to 1300 sccm, the introduction time is 10 s to 15 s, the chamber pressure is 4 torr to 6 torr, and the chamber temperature is 300℃ to 500℃.
5. The method for improving manufacturing defects in an image sensor as described in claim 1, characterized in that, Between step 1 and step 2, there is also an immersion step: immersing the substrate in a hydrophilic surfactant to activate the surface of the SiN layer.
6. The method for improving manufacturing defects in an image sensor as described in claim 5, characterized in that, The hydrophilic surfactant is SC1.
7. The method for improving manufacturing defects in an image sensor as described in claim 5, characterized in that, The hydrophilic surfactant includes ammonia, hydrogen peroxide, and water.
8. The method for improving manufacturing defects in an image sensor as described in claim 7, characterized in that, The volume ratio of ammonia, hydrogen peroxide and water is 1:2:(40-100).
9. The method for improving manufacturing defects in an image sensor as described in claim 5, characterized in that, Between the impregnation step and step 2, the substrate is further cleaned with deionized water or distilled water.
10. The method for improving manufacturing defects in an image sensor as described in claim 1, characterized in that, In step 3, the cleaning reagent includes at least one or more of SC1, SC2, deionized water, and distilled water.
11. The method for improving manufacturing defects in an image sensor as described in claim 10, characterized in that, The cleaning agent is SC1.
12. The method for improving manufacturing defects in an image sensor as described in claim 1, characterized in that, The depth-to-width ratio of the trench is greater than or equal to 2:
1.
13. The method for improving manufacturing defects in an image sensor as described in claim 1, characterized in that, After step 4, step 5 is also included: P-type ion implantation is performed on the bottom of the trench.
14. The method for improving manufacturing defects in an image sensor as described in claim 13, characterized in that, In step 5, the ion beam of the P-type ion implantation contains at least one of boron difluoride and boron.