A finishing method for reducing surface defects

Abstract

The application discloses a kind of finishing after finishing surface defect reduction finishing method, specifically relates to semiconductor silicon wafer manufacturing technology field, including the following steps: S1: finishing pretreatment, S2: no pressure ultra-pure water polishing, S3: instant no pressure protective agent polishing, S4: stratified post-processing, S5: quality detection.The application discloses a kind of finishing after finishing surface defect reduction finishing method, the application is by using the clean compressed air of purity ≥99.999%, accurately control blowdown pressure ≤0.1MPa, distance 15-20cm and time 4-6S, remove large particle rate to ≥98%, both thoroughly remove the abrasive particles and silicon scraps of finishing residue, also avoid the indentation of silicon wafer caused by air pressure impact, guarantee the physical integrity of silicon wafer, simultaneously, by selecting the resistivity ≥18.2MΩ·cm of ultra-pure water, with 0MPa no pressure operation, ≥2L / min flow and 30-45 ° inclination spray angle, cooperate with the slight friction of polishing cloth, can flush SiO2 Polishing liquid colloidal particles, silicon oxide byproducts and other micron-sized impurities.

Description

Technical Field

[0001] This invention relates to the field of semiconductor silicon wafer manufacturing technology, and in particular to a finishing process method after fine polishing to reduce surface defects. Background Technology

[0002] In the semiconductor silicon wafer manufacturing industry, the finishing process after polishing directly connects to downstream key processes such as photolithography and coating. Its effect is crucial to the electrical performance and production yield of semiconductor devices. Especially as integrated circuits develop towards higher integration, high-end silicon wafers need to meet stringent requirements such as ≥0.1μm particles ≤5 / wafer, surface roughness Ra ≤0.1nm and no micro-scratches or oxide layer defects. However, the current mainstream process has obvious shortcomings:

[0003] Pre-treatment using compressed air with a purity of <99.99% or improper pressure purging results in a removal rate of <95% for large particles ≥1μm or damage to the silicon wafer surface. Ultrapure water polishing often fails to completely remove residual polishing liquid and byproducts due to resistivity <18.2MΩ·cm, pressurized operation, or vertical spraying. Delay in protective agent spraying exceeding 2 seconds, deviation of the mixing ratio from 1:900-1:1100, or failure to simultaneously rinse the polishing cloth can easily lead to silicon wafer oxidation or stripe defects. Post-treatment lacks layered cleaning, resulting in residual protective agent and metallic impurities, insufficient detection accuracy, and difficulty in identifying hidden defects.

[0004] Therefore, a finishing process method for fine polishing is needed to reduce surface defects. Summary of the Invention

[0005] The main objective of this invention is to provide a finishing process method after fine polishing to reduce surface defects, which can effectively solve the problems mentioned above.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A finishing process for reducing surface defects after polishing includes the following steps:

[0008] S1: Pre-treatment after fine polishing: Clean compressed air is used to blow away large particles ≥1μm on the surface of the silicon wafer after fine polishing to avoid scratching the silicon wafer by particles in subsequent processes.

[0009] S2: Pressureless ultrapure water polishing: After pretreatment, pressureless ultrapure water is used to polish the silicon wafer and polishing cloth to remove residual polishing liquid, reaction by-products and micron-sized impurities from the surface.

[0010] S3: Immediate pressureless protective agent polishing: Within ≤2 seconds after ultrapure water polishing, the silicon wafer is polished with a pressureless protective agent to form a temporary protective film on the silicon wafer surface, blocking the erosion of the silicon wafer surface by air and impurities;

[0011] S4: Post-layer treatment: After polishing with protective agent, the surface is rinsed with ultrapure water, cleaned with SC1 solution and rinsed with ultrapure water in sequence to remove residual protective agent, metal impurities and organic matter.

[0012] S5: Quality Inspection: After the layering process, the surface defects, particle count and cleanliness of the silicon wafers are inspected, and silicon wafers that meet the standards are selected.

[0013] Preferably, in step S1, the purity of the clean compressed air is ≥99.999%, the purging pressure is ≤0.1MPa, the purging distance is 15-20cm, and the purging time is 4-6S, ensuring that the removal rate of large particles is ≥98% without damaging the silicon wafer surface.

[0014] Preferably, in step S2, the resistivity of the ultrapure water is ≥18.2 MΩ·cm, the polishing time is 8-12 s, the polishing pressure is 0 MPa, the ultrapure water flow rate is ≥2 L / min, and the ultrapure water spray direction forms an angle of 30-45° with the silicon wafer surface, thus taking into account both the residue removal effect and the edge protection of the silicon wafer.

[0015] Preferably, in step S3, the protective agent is an aqueous solution of polyoxyethylene alkylphenol ether diluted at a volume ratio of 1:900-1:1100, the polishing time is 5-8 seconds, the polishing pressure is 0 MPa, the protective agent flow rate is 1.5-2 L / min, and the protective film thickness is controlled at 10-20 nm.

[0016] Preferably, in step S3, ultrapure water is sprayed onto the surface of the polishing cloth simultaneously during the polishing process, with an ultrapure water flow rate of 0.5-0.8 L / min, so that the protective agent forms a uniform film on the surface of the polishing cloth, avoiding excessively high local concentration of the protective agent that could cause stripe defects on the silicon wafer surface.

[0017] Preferably, the specific parameters for the post-layering processing of S4 are as follows:

[0018] Ultrapure water rinsing: Ultrapure water resistivity ≥18.2MΩ·cm, flow rate 1.8-2.2L / min, rinsing time 15-20S;

[0019] SC1 solution cleaning: The volume ratio of NH4OH:H2O2:H2O in SC1 solution is 1:2:50, the solution temperature is 60-65℃, and the soaking time is 100-120 seconds.

[0020] Ultrapure water rinsing: Rinse until the pH of the silicon wafer surface is 6.8-7.2, rinsing time 8-12 seconds.

[0021] Preferably, in step S5, a laser particle detector (with a detection accuracy of 0.1 μm) is used to detect the number of surface particles, and an atomic force microscope is used to detect the surface roughness. The detection standards are: ≥0.1 μm particles ≤5 / piece, surface roughness Ra ≤0.1 nm, and no micro-scratches or oxide layer defects.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention utilizes clean compressed air with a purity ≥99.999%, precisely controlling the purging pressure ≤0.1MPa, distance 15-20cm, and time 4-6S to increase the large particle removal rate to ≥98%. This thoroughly removes abrasive particles and silicon chips remaining from fine polishing, while avoiding silicon wafer dents caused by air pressure impact, thus ensuring the physical integrity of the silicon wafer. Simultaneously, by using ultrapure water with a resistivity ≥18.2MΩ·cm, operating at 0MPa pressureless, with a flow rate ≥2L / min and a 30-45° tilted spray angle, combined with slight friction from the polishing cloth, it can comprehensively flush away micron-sized impurities such as colloidal particles and silicon oxide byproducts from the SiO2 polishing slurry.

[0024] 2. Within ≤2 seconds after ultrapure water polishing, this invention immediately sprays a 1:900-1:1100 polyoxyethylene alkylphenol ether aqueous solution to quickly form a 10-20nm temporary protective film to block air erosion. Simultaneously, ultrapure water is sprayed onto the polishing cloth at a flow rate of 0.5-0.8L / min to ensure uniform distribution of the protective agent and completely avoid streak defects. In addition, through a layered process of "ultrapure water rinsing → SC1 solution cleaning → ultrapure water rinsing to neutrality", residual impurities are deeply removed. Combined with high-precision detection such as laser particle detector and atomic force microscope, it is ensured that the silicon wafer meets the high-end standard of ≥0.1μm particles ≤5 / wafer, Ra≤0.1nm and no micro-scratches. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the overall method of the present invention. Detailed Implementation

[0026] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0027] like Figure 1 As shown, a finishing process after fine polishing to reduce surface defects includes the following steps:

[0028] S1: Pre-treatment after fine polishing: Clean compressed air is used to blow away large particles ≥1μm on the surface of the silicon wafer after fine polishing to avoid scratching the silicon wafer by particles in subsequent processes.

[0029] Furthermore, in S1, the purity of the clean compressed air is ≥99.999%, the purging pressure is ≤0.1MPa, the purging distance is 15-20cm, and the purging time is 4-6S, ensuring that the removal rate of large particles is ≥98% without damaging the silicon wafer surface.

[0030] S2: Pressureless ultrapure water polishing: After pretreatment, pressureless ultrapure water is used to polish the silicon wafer and polishing cloth to remove residual polishing liquid, reaction by-products and micron-sized impurities from the surface.

[0031] Furthermore, in S2, the resistivity of ultrapure water is ≥18.2MΩ·cm, the polishing time is 8-12S, the polishing pressure is 0MPa, the ultrapure water flow rate is ≥2L / min, and the ultrapure water spray direction is at a 30-45° angle to the silicon wafer surface, taking into account both the residue removal effect and the edge protection of the silicon wafer.

[0032] S3: Immediate pressureless protective agent polishing: Within ≤2 seconds after ultrapure water polishing, the silicon wafer is polished with a pressureless protective agent to form a temporary protective film on the silicon wafer surface, blocking the erosion of the silicon wafer surface by air and impurities;

[0033] Furthermore, in S3, the protective agent is an aqueous solution of polyoxyethylene alkylphenol ether diluted at a volume ratio of 1:900-1:1100, the polishing time is 5-8 seconds, the polishing pressure is 0 MPa, the protective agent flow rate is 1.5-2 L / min, and the protective film thickness is controlled at 10-20 nm.

[0034] Furthermore, in S3, ultrapure water is simultaneously sprayed onto the surface of the polishing cloth during the polishing process, with an ultrapure water flow rate of 0.5-0.8 L / min. This allows the protective agent to form a uniform film on the surface of the polishing cloth, preventing excessively high local concentrations of the protective agent from causing stripe defects on the silicon wafer surface.

[0035] S4: Post-layer treatment: After polishing with protective agent, the surface is rinsed with ultrapure water, cleaned with SC1 solution and rinsed with ultrapure water in sequence to remove residual protective agent, metal impurities and organic matter.

[0036] Furthermore, the specific parameters for S4's layered post-processing are as follows:

[0037] Ultrapure water rinsing: Ultrapure water resistivity ≥18.2MΩ·cm, flow rate 1.8-2.2L / min, rinsing time 15-20S;

[0038] SC1 solution cleaning: The volume ratio of NH4OH:H2O2:H2O in SC1 solution is 1:2:50, the solution temperature is 60-65℃, and the soaking time is 100-120 seconds.

[0039] Ultrapure water rinsing: Rinse until the pH of the silicon wafer surface is 6.8-7.2, rinsing time 8-12 seconds.

[0040] S5: Quality Inspection: After the delamination process, the surface defects, particle count and cleanliness of the silicon wafers are inspected, and silicon wafers that meet the standards are selected.

[0041] Furthermore, in S5, a laser particle detector (with a detection accuracy of 0.1μm) is used to detect the number of surface particles, and an atomic force microscope is used to detect the surface roughness. The detection standards are: ≥0.1μm particles ≤5 / piece, surface roughness Ra≤0.1nm, and no micro-scratches or oxide layer defects.

[0042] The specific process of this method is as follows:

[0043] In the Class 1 cleanroom after the fine polishing of semiconductor silicon wafers, operators fix the polished silicon wafers on an anti-static carrier, ensuring that the silicon wafer surface is facing upwards and unobstructed. Then, they start the clean compressed air blowing equipment, adjust the nozzle angle to be perpendicular to or slightly tilted to the silicon wafer surface, and slowly move the nozzle along a spiral path from the center of the silicon wafer to the edge. During the process, the blowing pressure, distance, and time are strictly controlled. At the same time, the visual detection device is used to observe in real time to ensure that large particles such as abrasive particles and silicon chips remaining from the fine polishing are completely blown away. For example, in the production of 12-inch semiconductor silicon wafers, if such particles are not removed, they are easy to embed in the polishing cloth during subsequent polishing, resulting in long strip-shaped scratches on the silicon wafer surface, which affects the electrical performance.

[0044] In the Class 1 cleanroom for semiconductor silicon wafer manufacturing, the purity of the clean compressed air is first tested to confirm that the purity is ≥99.999% and remove moisture, oil and impurities. Then, the pressure regulating valve of the purging equipment is adjusted to 0.08-0.1MPa, and the nozzle is fixed on a robotic arm with precise distance control, maintaining a distance of 15-20cm from the silicon wafer. The robotic arm drives the nozzle to reciprocate along the silicon wafer at a speed of 5cm / s for 4-6 seconds. For example, when processing 8-inch photovoltaic silicon wafers, the removal rate of large particles ≥1μm is ensured to be ≥98% through real-time monitoring by an online particle counter. Furthermore, due to proper pressure control, no air pressure impact dents are generated on the surface of the silicon wafer, ensuring flatness.

[0045] After completing the S1 pretreatment, the silicon wafer is immediately transferred to the working chamber of the pressureless ultrapure water polishing equipment. The rotating polishing platform inside the equipment is equipped with a clean polishing cloth. After starting the equipment, the ultrapure water supply system delivers ultrapure water with a resistivity ≥18.2MΩ·cm to the nozzle at a flow rate ≥2L / min. The nozzle is adjusted to be at an angle of 30-45° to the surface of the silicon wafer, and the polishing platform rotates slowly at 30r / min. The ultrapure water is evenly sprayed onto the silicon wafer and the polishing cloth. Pressureless polishing is performed for 8-12 seconds through the flow rinsing and slight friction of the polishing cloth. For example, in the processing of silicon wafers for semiconductor chips, this step can flush out micron-sized impurities such as colloidal particles of SiO2 polishing liquid and silicon oxide reaction by-products remaining after fine polishing, so as to avoid affecting the subsequent formation of protective agent film.

[0046] Before polishing with pressureless ultrapure water, a resistivity meter is used to confirm that the resistivity of ultrapure water is ≥18.2MΩ·cm to prevent ionic impurities from contaminating the silicon wafer. The pressure module of the polishing equipment is adjusted to 0MPa, and the flow rate of the ultrapure water nozzle is adjusted to 2-2.5L / min. The nozzle is fixed at a 30-45° angle with the silicon wafer through the angle adjustment mechanism. For example, when processing 6-inch power device silicon wafers, the polishing platform rotates at 25r / min. The ultrapure water is sprayed at an angle to fully cover the silicon wafer to remove residues, while avoiding water flow impact on the edge of the silicon wafer, which may cause chipping or chamfer wear, thus ensuring edge quality.

[0047] After ultrapure water polishing stops, the equipment's robotic arm switches to the protective agent spraying system within ≤2 seconds. In the system, a polyoxyethylene alkylphenol ether aqueous solution diluted at a volume ratio of 1:900-1:1100 is sprayed onto the silicon wafer through a dedicated nozzle at a flow rate of 1.5-2L / min. The polishing platform continues to rotate at 20r / min to ensure even distribution of the protective agent. Pressureless polishing for 5-8 seconds allows the protective agent to fully physically adsorb onto the silicon wafer surface. For example, in the production of silicon wafers for integrated circuits, the silicon wafer surface is highly active after ultrapure water polishing and is easily oxidized when exposed to air for more than 2 seconds. Immediate polishing can quickly form a 10-20nm temporary protective film, blocking contact between air oxygen and workshop impurities.

[0048] Next, before using the protective agent, polyoxyethylene alkylphenol ether is mixed with ≥18.2MΩ·cm ultrapure water at a volume ratio of 1:900-1:1100 in a clean mixing tank. The mixture is stirred at 100r / min for 5min to ensure uniform concentration and no precipitation. Then, it is transferred to the protective agent spraying system. The system pressure is adjusted to 0MPa and the flow rate to 1.5-2L / min. The polishing platform is started to rotate at 20r / min and the protective agent is sprayed for polishing for 5-8s. During this period, the film thickness is monitored in real time with a film thickness monitor to control the film thickness at 10-20nm. For example, for 12-inch high-end silicon wafers, if the film is too thick (over 20nm), it will be difficult to clean the residue and affect the photolithography. If it is too thin (below 10nm), it will not be able to prevent air erosion. Precise parameter control can avoid such problems.

[0049] When starting the protective agent polishing process, simultaneously activate the dedicated ultrapure water jet branch for the polishing cloth. The ultrapure water in this branch has a resistivity ≥18.2 MΩ·cm, and the flow controller maintains a steady flow of 0.5-0.8 L / min. Position the nozzle at the edge of the polishing cloth to allow the ultrapure water to penetrate the entire cloth surface and mix with the protective agent to form a uniform film. The polishing platform continues to rotate, causing the cloth to rub against the silicon wafer. For example, when polishing an 8-inch silicon wafer, the absence of simultaneous ultrapure water can easily cause the protective agent concentration in the center of the polishing cloth to be too high, forming a striped concentration difference area when in contact with the silicon wafer. This results in bright and dark stripe defects on the silicon wafer surface, affecting the appearance and processing accuracy.

[0050] After polishing with the protective agent, the silicon wafer is transferred by a robotic arm to the first post-layer processing station, where ultrapure water (≥18.2 MΩ·cm) is sprayed in multiple directions at a flow rate of 1.8-2.2 L / min for 15-20 seconds to initially remove most of the residual protective agent. It is then transferred to the second station and immersed in an SC1 solution prepared at 60-65℃ with NH4OH:H2O2:H2O = 1:2:50 for 100-120 seconds, where oxidation and complexation remove metallic impurities (Fe, Cu, Ni, etc.) and organic matter. Finally, it is transferred to the third station and rinsed with ≥18.2 MΩ·cm ultrapure water until pH = 6.8-7.2 (8-12 seconds). For example, in semiconductor silicon wafer manufacturing, residual protective agent affects the adhesion of subsequent metal coatings; the SC1 solution can remove adsorbed metallic impurities during production, preventing impact on electrical performance.

[0051] First, confirm that the resistivity of the ultrapure water is ≥18.2MΩ·cm at the ultrapure water rinsing station, adjust the flow rate to 1.8-2.2L / min, fix the silicon wafer in the cleaning basket rotating at 40r / min, and rinse with ultrapure water in four directions for 15-20 seconds to remove more than 90% of the residual protective agent.

[0052] In the SC1 cleaning station, the solution is prepared in advance in the corrosion-resistant tank according to the ratio and heated to a constant temperature of 60-65℃. After the silicon wafer is immersed, the solution is stirred every 30 seconds and soaked for 100-120 seconds. In the rinsing station, the silicon wafer is transferred to the rinsing tank, and ultrapure water is circulated and ultrasonic waves of 300W are turned on to assist rinsing. The pH probe is monitored in real time, and rinsing is stopped after the standard is met (8-12 seconds). For example, for 6-inch photovoltaic silicon wafers, if the SC1 solution temperature is lower than 60℃, the efficiency of removing metal impurities will decrease. If the rinsing pH deviates from neutral, it will easily cause silicon wafer corrosion or residual liquid, which will affect the packaging process.

[0053] After delamination, the silicon wafers are transferred to a clean testing room. First, a laser particle detector with a detection accuracy of 0.1μm is used to scan the entire effective area at a speed of 10mm / s, and the number of particles ≥0.1μm is recorded. Then, the wafers are moved to an atomic force microscope, and the roughness of the wafers is measured at five points (1μm×1μm scanning area) at the center and around the perimeter in tapping mode, and the average is taken. Finally, a 1000x optical microscope is used to observe micro-scratches and oxide layer defects. Operators wear anti-static gloves to avoid touching the silicon wafers. After inspection, qualified silicon wafers are screened against standards. Unqualified wafers are reworked. For example, if the number of particles in a 12-inch integrated circuit silicon wafer is 8 per wafer, which exceeds the standard, it needs to be delaminated again until it is qualified before proceeding to the photolithography process.

[0054] Before testing, the laser particle detector is calibrated, and the sensitivity is adjusted using a 0.1μm standard particle sample. The silicon wafer is placed on an anti-static stage and the focal length is aligned. The scan is performed according to a 1mm grid path, and the total number of particles ≥0.1μm is automatically counted. Before atomic force microscopy, the probe is cleaned, and after the silicon wafer is fixed, the distance between the probe and the silicon wafer is adjusted to the nanometer level. Five points are scanned and the average Ra value is calculated. Under bright field illumination, a high-magnification optical microscope is used to observe defects by moving the stage radially and circumferentially along the silicon wafer. For example, for an 8-inch power device silicon wafer, if Ra = 0.12nm exceeds the standard, it needs to be repolished to meet the standard to ensure the quality of subsequent thin film deposition.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A finishing process after fine polishing to reduce surface defects, characterized in that, Includes the following steps: S1: Pre-treatment after fine polishing: Clean compressed air is used to blow away large particles ≥1μm on the surface of the silicon wafer after fine polishing to avoid scratching the silicon wafer by particles in subsequent processes. S2: Pressureless ultrapure water polishing: After pretreatment, pressureless ultrapure water is used to polish the silicon wafer and polishing cloth to remove residual polishing liquid, reaction by-products and micron-sized impurities from the surface. S3: Immediate pressureless protective agent polishing: Within ≤2 seconds after ultrapure water polishing, the silicon wafer is polished with a pressureless protective agent to form a temporary protective film on the silicon wafer surface, blocking the erosion of the silicon wafer surface by air and impurities; S4: Post-layer treatment: After polishing with protective agent, the surface is rinsed with ultrapure water, cleaned with SC1 solution and rinsed with ultrapure water in sequence to remove residual protective agent, metal impurities and organic matter. S5: Quality Inspection: After the layering process, the surface defects, particle count and cleanliness of the silicon wafers are inspected, and silicon wafers that meet the standards are selected.

2. The finishing process method for reducing surface defects after fine polishing according to claim 1, characterized in that: In step S1, the purity of the clean compressed air is ≥99.999%, the purging pressure is ≤0.1MPa, the purging distance is 15-20cm, and the purging time is 4-6S, ensuring that the removal rate of large particles is ≥98% without damaging the silicon wafer surface.

3. The finishing process method for reducing surface defects after fine polishing according to claim 1, characterized in that: In S2, the resistivity of ultrapure water is ≥18.2MΩ·cm, the polishing time is 8-12S, the polishing pressure is 0MPa, the ultrapure water flow rate is ≥2L / min, and the ultrapure water spray direction is at a 30-45° angle to the silicon wafer surface, taking into account both the residue removal effect and the edge protection of the silicon wafer.

4. The finishing process method for reducing surface defects after fine polishing according to claim 1, characterized in that: In step S3, the protective agent is an aqueous solution of polyoxyethylene alkylphenol ether diluted at a volume ratio of 1:900-1:1100, the polishing time is 5-8 seconds, the polishing pressure is 0 MPa, the protective agent flow rate is 1.5-2 L / min, and the protective film thickness is controlled at 10-20 nm.

5. The finishing process method for reducing surface defects after fine polishing according to claim 1, characterized in that: In step S3, ultrapure water is sprayed onto the surface of the polishing cloth simultaneously during the polishing process. The ultrapure water flow rate is 0.5-0.8 L / min, which allows the protective agent to form a uniform film on the surface of the polishing cloth, thus avoiding excessively high local concentrations of the protective agent that could cause stripe defects on the silicon wafer surface.

6. The finishing process method for reducing surface defects after fine polishing according to claim 1, characterized in that: The specific parameters for the post-layering processing of S4 are as follows: Ultrapure water rinsing: Ultrapure water resistivity ≥18.2MΩ·cm, flow rate 1.8-2.2L / min, rinsing time 15-20S; SC1 solution cleaning: The volume ratio of NH4OH:H2O2:H2O in SC1 solution is 1:2:50, the solution temperature is 60-65℃, and the soaking time is 100-120 seconds. Ultrapure water rinsing: Rinse until the pH of the silicon wafer surface is 6.8-7.2, rinsing time is 8-12 seconds.

7. The finishing process method for reducing surface defects after fine polishing according to claim 1, characterized in that: In step S5, a laser particle detector is used to detect the number of surface particles, and an atomic force microscope is used to detect the surface roughness. The detection standards are: ≥0.1μm particles ≤5 / piece, surface roughness Ra≤0.1nm, and no micro-scratches or oxide layer defects.

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