Cleaning and caustic etching process to reduce post-polish bulk nickel contamination

Abstract

This invention relates to a cleaning and alkaline etching process for reducing nickel contamination after polishing, belonging to the field of silicon wafer processing technology. The process includes the following steps: Step 1: In the cleaning equipment's chemical bath, the silicon wafer is pre-cleaned in the first bath before alkaline etching, followed by rapid drainage rinsing in the second bath. Step 2: In the cleaning equipment's chemical bath, the silicon wafer undergoes alkaline etching in the third bath, followed by rapid drainage rinsing in the fourth bath. Step 3: In the cleaning equipment's chemical bath, the silicon wafer undergoes post-etching cleaning in the fifth bath, followed by rapid drainage rinsing in the sixth bath. Step 4: In the seventh bath, a slow-lifting tank structure is used for cleaning in pure water at 35°C. Step 5: Infrared drying is used to remove moisture from the silicon wafer surface at 60°C. This process solves the problem of controlling Ni diffusion while ensuring production capacity. It effectively removes nickel contamination from the surface caused by the polishing process.

Description

Technical Field

[0001] This invention relates to the field of silicon wafer processing technology, specifically to a cleaning and alkaline etching process for reducing bulk nickel contamination after grinding. Background Technology

[0002] Single-sided grinding uses diamond wheels to grind the surface of silicon wafers, removing the damage layer left by double-sided grinding. Nickel contamination can occur on the silicon wafer surface after single-sided grinding because the diamond wheels used in single-sided grinding are coated with nickel or nickel-phosphorus alloy using chemical plating, electroplating, or CVD methods during manufacturing. This nickel- or nickel-phosphorus alloy-coated diamond particles are then bonded to the metal substrate surface through high-temperature sintering. The cleaning step after single-sided grinding is often overlooked, with alkaline etching typically considered sufficient to remove contamination from the silicon wafer surface. However, in our production practice, we have found that nickel contamination caused during the grinding process can even be detected on the final polished silicon wafer surface.

[0003] Nickel is an element with a high diffusion coefficient in single-crystal silicon substrates. Studies have shown that at an alkaline corrosion temperature of approximately 80°C, the rate of nickel diffusion into the silicon wafer is greater than the corrosion rate of the silicon wafer. Therefore, nickel residue on the surface of the silicon wafer after the polishing process will diffuse into the silicon wafer during the alkaline corrosion process, forming bulk nickel contamination. Detection shows that impurities of nickel contained in the raw material solution will also diffuse into the silicon wafer during the alkaline corrosion process. Nickel that diffuses into the silicon substrate readily combines with Si, forming NiSi2 precipitates with plate-like characteristics on the (111) crystal plane of Si. The crystal orientation of the crystal rod is (100), and the Notch orientation is... <110> Because NiSi2 forms plate-like precipitates on the Si(111) plane, the intersection line of the precipitates and the (100) crystal plane is along... <110> Crystal orientation. Due to the difference in physicochemical properties between NiSi2 precipitates and the Si matrix, electrochemical reactions occur during CMP and cleaning processes, forming corrosion pits at defects.

[0004] From a device application perspective, NiSi2 precipitates form a continuous distribution of energy levels with band-like characteristics within the band gap of the silicon substrate. This facilitates electron-hole recombination, shortens minority carrier lifetime, and generates dark current. Bulk Ni contamination caused by polishing and alkaline etching processes must be effectively removed.

[0005] To ensure production capacity, higher alkaline corrosion temperatures are typically used (usually ≥80℃, such as US7288206B2 (48% NaOH, 85℃), US7332437B2 (50% NaOH, 85℃), and CN201811519492.X (42% KOH, 90±2℃). Higher corrosion temperatures are detrimental to controlling Ni diffusion, while lower temperatures will reduce production capacity. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a cleaning and alkaline etching process to reduce nickel contamination after polishing, controlling Ni diffusion while ensuring production capacity. A mixture of H₂O₂ and HF, along with porphyrin, is used to etch the surface of the single-crystal silicon wafer after polishing, effectively removing nickel contamination caused by the polishing process.

[0007] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions:

[0008] A cleaning and alkaline etching process for reducing bulk nickel contamination after grinding includes the following steps:

[0009] Step 1: In the chemical solution tank of the cleaning equipment, the silicon wafer is pre-cleaned before alkaline etching in the first tank. The cleaning solution consists of 0.3% to 1% HF, 1% to 5% H2O2 and 5 to 50 mg porphyrin. Then, the second tank is used to quickly drain and rinse the silicon wafer to clean the residual chemical solution on the surface of the silicon wafer with pure water.

[0010] Step 2: In the chemical solution tank of the cleaning equipment, the silicon wafer undergoes an alkaline etching reaction in the third tank. The alkaline etching solution is water with 50-200 ml of 50% EDTA-4K added as a metal chelating agent, and the concentration of the alkaline etching solution is 25%-35%.

[0011] The alkaline etching reaction temperature is set at 55℃~65℃, the circulation flow rate is 25±5L / min, and the silicon wafer is rotated by the rolling tray at the bottom of the chemical solution tank at a speed of 10rpm. After the alkaline etching reaction is completed, the fourth tank uses rapid drainage to rinse the silicon wafer, so that the residual chemical solution on the surface of the silicon wafer is cleaned by pure water.

[0012] Step 3: In the chemical solution tank of the cleaning equipment, the silicon wafer is etched and cleaned in the fifth tank. The chemical solution in the fifth tank consists of 1% to 3% HCl and 2% to 5% H2O2. After etching and cleaning, the silicon wafer is rinsed by rapid drainage in the sixth tank, so that pure water can clean the residual chemical solution on the surface of the silicon wafer.

[0013] Step 4: In the seventh tank, a slow-lifting tank structure is used to clean the water in pure water at a temperature of 35℃. The overflow flow rate of pure water is 10±3L / min, and the slow-lifting speed is 1.2mm / s.

[0014] Step 5: Use infrared drying to remove moisture from the surface of the silicon wafer at a temperature of 60°C.

[0015] Preferably, the porphyrin is 5,10,15,20-tetra(4-hydroxyphenyl), CAS RN: 51094-17-8.

[0016] As a preferred method, after a long cleaning process, a high concentration of Ni ions will accumulate in the first tank. During subsequent cleaning processes, the high concentration of Ni ions will deposit on the silicon wafer surface, causing back contamination. A chelating agent is used to chelate the Ni ions in the solution tank to reduce or avoid the redeposition of Ni ions on the silicon wafer surface.

[0017] The chelating effect on metals is poor under acidic conditions (hydrogen ions inhibit the ionization of weak acids). Porphyrin is used as a chelating agent because it is a highly conjugated macrocyclic compound with a strong chelating effect on transition metals.

[0018] The molecule of porphyrin:

[0019] Common chelating agents are mostly weak acids (as shown in the table below):

[0020]

[0021] Preferably, the diffusion coefficient of Ni in single-crystal silicon has the following relationship with temperature:

[0022] Where A and B are constants, D(T) is the diffusion coefficient that varies with temperature, and T is the temperature. The logarithm of the diffusion coefficient has a negative reciprocal relationship with temperature. The lower the temperature, the smaller the diffusion coefficient, and the more obvious the change is in the low temperature range. The diffusion of Ni on the surface of the silicon wafer is reduced by lowering the reaction temperature of alkaline corrosion.

[0023] At the same temperature, the effect of KOH concentration on the corrosion rate does not show a monotonically increasing trend, but rather a parabolic characteristic. At 60℃, the highest corrosion rate corresponds to a KOH concentration of 30%, which is close to the corrosion rate of 50% KOH at 80℃. By optimizing the KOH concentration and temperature, the production capacity can be maximized while reducing Ni diffusion on the Si surface.

[0024] Preferably, the temperature of the cleaning solution is at room temperature and the circulation flow rate is 25±5L / min during the pre-cleaning before and after alkaline corrosion.

[0025] Preferably, the EDTA-4K is CAS: 5964-35-2, C 10 H 12 N2K4O8.

[0026] The mixture of H2O2 and HF is rarely used in the silicon wafer processing industry or IC factories because the oxidation and etching effects of H2O2 and HF severely degrade the surface roughness of the silicon wafer. In the field of silicon wafer (chip) cleaning, the more commonly used metal removal solutions are HF or SC2 (a mixture of H2O2 and HCl). Since double-sided polishing is performed after the alkaline etching process, the roughness of the silicon wafer before polishing has no effect on the roughness after polishing. Therefore, the mixture of H2O2 and HF is chosen as the cleaning solution after the grinding process. The mixture of H2O2 and HF oxidizes and etches the silicon wafer surface, thoroughly removing nickel contamination from the grinding process.

[0027] The present invention can achieve the following effects:

[0028] This invention provides a cleaning and alkaline etching process to reduce bulk nickel contamination after polishing. Compared with existing technologies, it solves the problem of controlling Ni diffusion while ensuring production capacity. A mixed solution of H2O2 and HF and porphyrin is used to etch the surface of the single-crystal silicon wafer after the polishing process, effectively removing nickel contamination caused by the polishing process. Detailed Implementation

[0029] The technical solution of the invention will be further described in detail below through examples.

[0030] Example 1: A cleaning and alkaline etching process for reducing nickel contamination after grinding, comprising the following steps:

[0031] Step 1: In the cleaning equipment's chemical solution tank, the silicon wafers are pre-cleaned in the first tank before alkaline etching. The chemical solution temperature is room temperature, and the circulation flow rate is 25±5 L / min. The cleaning solution consists of 0.5% HF, 2% H2O2, and 20 mg of porphyrin (5,10,15,20-tetra(4-hydroxyphenyl), CASRN: 51094-17-8). Then, in the second tank, rapid drainage and rinsing ensure that pure water thoroughly cleans the residual chemical solution from the silicon wafer surface.

[0032] After a long cleaning process, a high concentration of Ni ions will accumulate in the first tank. During subsequent cleaning processes, the high concentration of Ni ions will deposit on the silicon wafer surface, causing back contamination. A chelating agent is used to chelate the Ni ions in the cleaning solution tank to reduce or avoid the redeposition of Ni ions on the silicon wafer surface.

[0033] The diffusion coefficient of Ni in single-crystal silicon is related to temperature in the following form:

[0034] Where A and B are constants, D(T) is the diffusion coefficient that varies with temperature, and T is the temperature. The logarithm of the diffusion coefficient has a negative reciprocal relationship with temperature. The lower the temperature, the smaller the diffusion coefficient, and the more obvious the change is in the low temperature range. The diffusion of Ni on the surface of the silicon wafer is reduced by lowering the reaction temperature of alkaline corrosion.

[0035] Step 2: In the cleaning equipment's chemical solution tank, the silicon wafer undergoes an alkaline etching reaction in the third tank. The alkaline etching solution is water with 50 ml of 50% EDTA-4K added as a metal chelating agent. EDTA-4K has CAS: 5964-35-2, C 10 H 12 N2K4O8, alkaline corrosion solution concentration is 30%.

[0036] The alkaline etching reaction temperature is set at 65℃, the circulation flow rate is 25±5L / min, and the silicon wafer is rotated by the rolling tray at the bottom of the chemical solution tank at a speed of 10rpm. After the alkaline etching reaction is completed, the fourth tank uses rapid drainage to rinse the silicon wafer, so that the residual chemical solution on the surface of the silicon wafer is cleaned by pure water.

[0037] Step 3: In the cleaning equipment's chemical solution tank, the silicon wafer undergoes etching and cleaning in the fifth tank. The chemical solution temperature is room temperature, and the circulation flow rate is 25±5 L / min. The chemical solution in the fifth tank consists of 1% HCl and 2% H2O2. After etching, the silicon wafer is rinsed by rapid drainage in the sixth tank, ensuring that pure water removes any remaining chemical solution from the surface of the silicon wafer.

[0038] Step 4: In the seventh tank, a slow-lifting tank structure is used to clean the water in pure water at a temperature of 35℃. The overflow flow rate of pure water is 10±3L / min, and the slow-lifting speed is 1.2mm / s.

[0039] Step 5: Use infrared drying to remove moisture from the surface of the silicon wafer at a temperature of 60°C.

[0040] The silicon wafer processed under the above conditions (etch depth 4 μm) was analyzed using VPD-ICPMS, and the bulk nickel content of the silicon wafer was 8.7E9 atoms / cm³. 3 The concentration was significantly lower than that of the sample without FPM pre-cleaning (5.2 F11 atoms / cm). 3 ).

[0041] Example 2: A cleaning and alkaline etching process to reduce nickel contamination after grinding, comprising the following steps:

[0042] Step 1: In the cleaning equipment's chemical solution tank, the silicon wafers are pre-cleaned in the first tank before alkaline etching. The chemical solution temperature is room temperature, and the circulation flow rate is 25±5 L / min. The cleaning solution consists of 1% HF, 3% H2O2, and 50 mg of porphyrin (5,10,15,20-tetra(4-hydroxyphenyl), CASRN: 51094-17-8). Then, in the second tank, rapid drainage and rinsing ensure that pure water thoroughly cleans the silicon wafer surface of any remaining chemical solution.

[0043] After a long cleaning process, a high concentration of Ni ions will accumulate in the first tank. During subsequent cleaning processes, the high concentration of Ni ions will deposit on the silicon wafer surface, causing back contamination. A chelating agent is used to chelate the Ni ions in the cleaning solution tank to reduce or avoid the redeposition of Ni ions on the silicon wafer surface.

[0044] The diffusion coefficient of Ni in single-crystal silicon is related to temperature in the following form:

[0045] Where A and B are constants, D(T) is the diffusion coefficient that varies with temperature, and T is the temperature. The logarithm of the diffusion coefficient has a negative reciprocal relationship with temperature. The lower the temperature, the smaller the diffusion coefficient, and the more obvious the change is in the low temperature range. The diffusion of Ni on the surface of the silicon wafer is reduced by lowering the reaction temperature of alkaline corrosion.

[0046] Step 2: In the cleaning equipment's chemical solution tank, the silicon wafer undergoes an alkaline etching reaction in the third tank. The alkaline etching solution is water with 50 ml of 50% EDTA-4K added as a metal chelating agent. EDTA-4K has CAS: 5964-35-2, C 10 H 12 N2K4O8, alkaline corrosion solution concentration is 30%.

[0047] The alkaline etching reaction temperature is set at 60℃, the circulation flow rate is 25±5L / min, and the silicon wafer is rotated by the rolling tray at the bottom of the chemical solution tank at a speed of 10rpm. After the alkaline etching reaction is completed, the fourth tank uses rapid drainage to rinse the silicon wafer, so that the residual chemical solution on the surface of the silicon wafer is cleaned by pure water.

[0048] Step 3: In the cleaning equipment's chemical solution tank, the silicon wafer undergoes etching and cleaning in the fifth tank. The chemical solution temperature is room temperature, and the circulation flow rate is 25±5 L / min. The chemical solution in the fifth tank consists of 1% HCl and 2% H2O2. After etching, the silicon wafer is rinsed by rapid drainage in the sixth tank, ensuring that pure water removes any remaining chemical solution from the surface of the silicon wafer.

[0049] Step 4: In the seventh tank, a slow-lifting tank structure is used to clean the water in pure water at a temperature of 35℃. The overflow flow rate of pure water is 10±3L / min, and the slow-lifting speed is 1.2mm / s.

[0050] Step 5: Use infrared drying to remove moisture from the surface of the silicon wafer at a temperature of 60°C.

[0051] The silicon wafer processed under the above conditions (etch depth 4 μm) was analyzed using VPD-ICPMS, and the bulk nickel content of the silicon wafer was 2.1E9 atoms / cm³. 3 The concentration was significantly lower than that of the sample without FPM pre-cleaning (5.2 F11 atoms / cm). 3 ).

[0052] In summary, this cleaning and alkaline etching process for reducing bulk nickel contamination after polishing solves the problem of controlling Ni diffusion while ensuring production capacity. A mixture of H2O2 and HF, along with a porphyrin solution, is used to etch the surface of the single-crystal silicon wafer after the polishing process, effectively removing nickel contamination caused by the polishing process.

[0053] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A cleaning and alkaline corrosion process for reducing nickel contamination in the bulk after grinding, characterized in that... The following steps are included: Step 1: In the chemical solution tank of the cleaning equipment, the silicon wafer is pre-cleaned before alkaline etching in the first tank. The cleaning solution consists of 0.3% to 1% HF, 1% to 5% H2O2 and 5 to 50 mg porphyrin. Then, the second tank is used to quickly drain and rinse the silicon wafer to clean the residual chemical solution on the surface of the silicon wafer with pure water. Step 2: In the chemical solution tank of the cleaning equipment, the silicon wafer undergoes an alkaline etching reaction in the third tank. The alkaline etching solution is water with 50-200 ml of 50% EDTA-4K added as a metal chelating agent, and the concentration of the alkaline etching solution is 25%-35%. The alkaline etching reaction temperature is set at 55℃~65℃, the circulation flow rate is 25±5L / min, and the silicon wafer is rotated by a rolling tray at the bottom of the chemical solution tank at a speed of 10rpm. After the alkaline etching reaction is completed, the fourth tank uses rapid drainage to rinse the silicon wafer, so that pure water can clean the residual chemical solution on the surface of the silicon wafer. Step 3: In the chemical solution tank of the cleaning equipment, the silicon wafer is etched and then cleaned in the fifth tank. The chemical solution in the fifth tank consists of 1% to 3% HCl and 2% to 5% H2O2. After etching and cleaning, the silicon wafer is rinsed by rapid drainage in the sixth tank, so that pure water can clean the residual chemical solution on the surface of the silicon wafer. Step 4: In the seventh tank, a slow-lifting tank structure is used to clean the water in pure water at a temperature of 35℃. The overflow flow rate of pure water is 10±3L / min, and the slow-lifting speed is 1.2mm / s. Step 5: Use infrared drying to remove moisture from the surface of the silicon wafer at a temperature of 60℃.

2. The cleaning and alkaline corrosion process for reducing bulk nickel contamination after grinding according to claim 1, characterized in that: The porphyrin is 5,10,15,20-tetra(4-hydroxyphenyl), CAS RN: 51094-17-8.

3. The cleaning and alkaline corrosion process for reducing nickel contamination after grinding according to claim 2, characterized in that: After a long cleaning process, Ni ions will accumulate in the first tank. During subsequent cleaning processes, high concentrations of Ni ions will deposit on the silicon wafer surface, causing back contamination. A chelating agent is used to chelate the Ni ions in the cleaning solution tank to reduce or avoid the redeposition of Ni ions on the silicon wafer surface.

4. The cleaning and alkaline corrosion process for reducing nickel contamination after grinding according to claim 3, characterized in that: The diffusion coefficient of Ni in single-crystal silicon is related to temperature in the following form: Where A and B are constants, D(T) is the diffusion coefficient that varies with temperature, and T is the temperature. The logarithm of the diffusion coefficient has a negative reciprocal relationship with temperature, and the lower the temperature, the smaller the diffusion coefficient.

5. The cleaning and alkaline corrosion process for reducing nickel contamination after grinding according to claim 1, characterized in that: During the pre-cleaning before and after alkaline corrosion, the solution temperature was at room temperature and the circulation flow rate was 25±5L / min.

6. The cleaning and alkaline corrosion process for reducing bulk nickel contamination after grinding according to claim 1, characterized in that: The EDTA-4K mentioned is CAS: 5964-35-2,C 10 H 12 K4N2O8.

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