Wafer surface treatment method and method for manufacturing CMOS image sensor

Abstract

The application provides a wafer surface treatment method and a preparation method of a CMOS image sensor, and the method comprises the following steps: adopting a plasma treatment process to treat a wafer surface, and eliminating the electric charge accumulated on the wafer surface due to electrostatic discharge. According to the application, the electric charge accumulated on the wafer surface due to electrostatic discharge is eliminated through the plasma treatment process, and the white pixel performance of the image sensor can be improved.

Description

Technical Field

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

[0002] Compared to CCD image sensors, CMOS image sensors are compatible with mature CMOS technology and have advantages such as high integration, low cost, and low power consumption. After commercialization, CMOS image sensors have become more popular and are developing rapidly with broad application prospects. They are gradually replacing CCD image sensors in automotive, mobile phone, camera, security, medical imaging, aerospace and military fields, as well as industrial production.

[0003] A key performance indicator for CMOS image sensors is the white pixel (WP). WP refers to the difference between the output value of a measured pixel and the average output value of its surrounding pixels under no-light conditions exceeding a certain threshold. This performance directly reflects the imaging quality of the CMOS image sensor and is closely related to its design, surface charge, damage caused by ion implantation, and metal contamination. Reducing WP is a crucial method for improving the imaging quality of CMOS image sensors, especially for small-sized, high-pixel image sensors.

[0004] As the pixel size of CMOS image sensors continues to shrink, the energy of deep N-type (DDN) ion implantation is typically increased to improve full-well capacity, and the energy of deep P-type (PB) ion implantation is correspondingly increased for better isolation. To block high-energy ion implantation, both DDN and PB photolithography employ thick photoresist processes. This process results in a significant amount of charge remaining on the silicon wafer surface after photoresist development and exposure. The large amount of charge formed on the silicon wafer alters the charge balance in the ion beam during subsequent ion implantation, causing beam enlargement and uneven dose distribution, thus affecting the distribution of the full-well capacity (WP). Excessive charge also degrades WP performance. Summary of the Invention

[0005] The purpose of this invention is to provide a wafer surface treatment method and a CMOS image sensor fabrication method, which are used to eliminate the charge accumulated on the wafer surface due to electrostatic discharge and improve the white pixel performance of the image sensor.

[0006] Based on the above considerations, the present invention provides a wafer surface treatment method, comprising: The wafer surface is treated with plasma processing technology to eliminate the charge accumulated on the wafer surface due to electrostatic discharge.

[0007] Optionally, the process gas for the plasma processing is a gas that can react with the photoresist.

[0008] Optionally, the process gas is any one or a combination of two or more of O2, O3, NO, and NO2.

[0009] Optionally, the plasma treatment process further includes a gas extraction process.

[0010] Optionally, the power of the plasma processing technology is 50~1000W.

[0011] Optionally, the plasma treatment process takes 10 to 100 seconds.

[0012] Optionally, the gas flow rate of the plasma treatment process is 10~1000 sccm.

[0013] Optionally, the pressure of the plasma treatment process is 100~1000 mTorr.

[0014] Optionally, it also includes a layout design step, in which the layout design size is compensated for the amount of photoresist consumed by the plasma gas.

[0015] Optionally, the plasma gas consumption on the photoresist side is 1~50nm.

[0016] This invention also provides a method for fabricating a CMOS image sensor, comprising: A patterned photoresist layer is formed on the surface of a wafer using photolithography. The wafer surface is treated using any of the methods described above to eliminate the charge accumulated on the wafer surface due to electrostatic discharge.

[0017] Optionally, it also includes an ion implantation process; after the plasma processing is completed, ion implantation is performed using a patterned photoresist layer as a mask layer to form a photogenerated carrier collection region and an isolation region in the wafer.

[0018] The wafer surface treatment method and the CMOS image sensor fabrication method provided by this invention have the following beneficial effects: By using plasma processing technology, surface charge on the wafer can be eliminated without adding new photomasks or increasing costs, thereby reducing white pixels in the image sensor. Using a gas that can react with photoresist as the process gas can solve the problem of photoresist residue (PR residue) and make the photolithography window larger; Using any one or a combination of two or more of O2, O3, NO, and NO2 as process gases can eliminate the charge accumulated on the wafer surface due to electrostatic discharge without damaging the wafer surface. The plasma processing also includes a pumping process to remove byproducts from the reaction with the photoresist from the plasma chamber, which can better eliminate the charge on the wafer surface. Attached Figure Description

[0019] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments, taken in conjunction with the accompanying drawings.

[0020] Figure 1 The diagram shows the photoresist structure before and after processing by the wafer surface treatment method provided by the present invention. Figure 2 The diagram shown is a schematic diagram of the layout design provided by this invention.

[0021] Throughout the figures, the same or similar reference numerals denote the same or similar devices (modules) or steps. Detailed Implementation

[0022] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the present invention is described in detail using schematic diagrams. When describing the embodiments of the present invention in detail, the schematic diagrams are merely examples for ease of explanation and should not limit the scope of protection of the present invention.

[0024] The applicant found that reducing the spin speed during photoresist spin coating can slightly reduce the surface charge on the wafer, but cannot completely eliminate it. In addition, reducing the spin speed not only affects production capacity, but also causes insufficient photolithography windows due to reasons such as incomplete development.

[0025] In addition, the surface charge problem of wafers can be improved by etching and wet cleaning. This method can completely remove the charge brought by the photolithography process, but it will completely remove the photoresist, making subsequent ion implantation impossible.

[0026] To address the aforementioned problems, this invention provides a wafer surface treatment method and a CMOS image sensor fabrication method, which eliminates the charge accumulated on the wafer surface due to electrostatic discharge, thereby improving the white pixel performance of the image sensor.

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the method of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] This invention provides a wafer surface treatment method, comprising: The wafer surface is treated with plasma processing technology to eliminate the charge accumulated on the wafer surface due to electrostatic discharge.

[0029] After photolithography or cleaning, a plasma treatment process is performed on the wafer surface to eliminate the charge accumulation caused by electrostatic discharge resulting from friction between the photoresist or cleaning solution and the wafer surface during the photolithography or cleaning process. Of course, this invention is also applicable to eliminating charges accumulated due to electrostatic discharge in other processes.

[0030] In this embodiment, the process gas for the plasma processing is a gas that can react with photoresist. As an example, the process gas can be any one or a combination of two or more of O2, O3, NO, and NO2. By using a gas that can react with photoresist as the process gas during plasma processing, the surface charge on the wafer can be eliminated, and the problem of photoresist residue (PR residue) can also be solved, thus increasing the size of the photolithography window. Furthermore, gases such as O2, O3, NO, and NO2 will not damage the wafer surface, avoiding the occurrence of wafer surface defects.

[0031] Furthermore, the plasma processing also includes a gas extraction process. Extracting the gases after plasma treatment, especially the byproducts of the reaction with the photoresist, from the plasma cavity can better eliminate the charge on the wafer surface.

[0032] Furthermore, it also includes the layout design step, during which the layout design dimensions are compensated for based on the amount of photoresist consumed by the plasma gas. Please refer to... Figures 1 to 2 Because the plasma gas reacts with the photoresist 11, the plasma gas is consumed at both the top and sides of the photoresist. Figure 1 The dashed line represents the photoresist after plasma processing. The single-sided consumption of the photoresist 11 after plasma processing is set as x. Figure 1 As can be seen, after plasma treatment, the opening of the photoresist increases by x on one side. Therefore, during layout design, the size of the ion implantation region 12 in the layout needs to be correspondingly reduced by x on one side to ensure that the opening of the photoresist meets the requirements of the ion implantation region after plasma treatment. The consumption can be set by controlling the process conditions of the plasma treatment. In this embodiment, the consumption range of x is 1~50nm.

[0033] In this embodiment, the power of the plasma treatment process is selected to be 50~1000W, the treatment time is selected to be 10~100s, the gas flow rate is selected to be 10~1000sccm, and the pressure is selected to be 100~1000mTorr. Of course, other parameters can be selected according to actual needs, and there are no restrictions here.

[0034] This invention also provides a method for fabricating a CMOS image sensor, comprising: A patterned photoresist layer is formed on the surface of a wafer using photolithography. The wafer surface is treated using the above-mentioned wafer surface treatment method to eliminate the charge accumulated on the wafer surface due to electrostatic discharge.

[0035] The fabrication method of a CMOS image sensor also includes: after the plasma processing is completed, ion implantation is performed using a patterned photoresist layer as a mask layer to form a photogenerated carrier collection region and an isolation region within the wafer. Of course, the fabrication method of a CMOS image sensor also includes steps such as forming transport transistors, reset transistors, floating diffusion regions, filters, and microlenses. If charge accumulates on the wafer surface during the fabrication process, the wafer surface treatment method provided above can be used to treat the wafer surface.

[0036] In summary, this invention provides a wafer surface treatment method and a method for fabricating a CMOS image sensor. The method includes: treating the wafer surface using a plasma treatment process to eliminate the charge accumulated on the wafer surface due to electrostatic discharge. This invention, through plasma treatment, eliminates the charge accumulated on the wafer surface due to electrostatic discharge, thereby improving the white pixel performance of the image sensor.

[0037] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and not restrictive in any way. Furthermore, it is clear that the word "comprising" does not exclude other elements and steps, and the word "a" does not exclude a plurality. Multiple elements recited in the apparatus claims may also be implemented by a single element. The terms "first," "second," etc., are used to denote names and do not indicate any particular order.

Claims

1. A method for fabricating a CMOS image sensor, characterized in that, include: A patterned photoresist layer is formed on the surface of a wafer using photolithography. The wafer surface is treated with plasma processing technology to eliminate the charge accumulated on the wafer surface due to electrostatic discharge; The process gas in the plasma treatment process is a gas that can react with photoresist to remove residual photoresist from the thick photoresist process. It also includes an ion implantation process; after the plasma processing is completed, ion implantation is performed using a patterned photoresist layer as a mask layer to form a photogenerated carrier collection region and an isolation region in the wafer respectively. It also includes the layout design step, in which the layout design size is compensated for the amount of photoresist consumed by the plasma gas.

2. The method for fabricating a CMOS image sensor according to claim 1, characterized in that, The process gas is any one or a combination of two or more of O2, O3, NO, and NO2.

3. The method for fabricating a CMOS image sensor according to claim 1, characterized in that, The plasma treatment process also includes an air extraction process.

4. The method for fabricating a CMOS image sensor according to claim 1, characterized in that, The power of the plasma processing technology is 50~1000W.

5. The method for fabricating a CMOS image sensor according to claim 1, characterized in that, The processing time for plasma treatment is 10~100s.

6. The method for fabricating a CMOS image sensor according to claim 1, characterized in that, The gas flow rate for plasma processing is 10~1000 sccm.

7. The method for fabricating a CMOS image sensor according to claim 1, characterized in that, The pressure of the plasma treatment process is 100~1000 mTorr.

8. The method for fabricating a CMOS image sensor according to claim 1, characterized in that, The plasma gas consumption on the photoresist side is 1~50nm.

Images