A silicon wafer chemical polishing solution with high etching rate and high flatness and application thereof

Abstract

The application discloses a kind of high etching rate and high flatness silicon wafer chemical polishing liquid and application, the silicon wafer chemical polishing liquid is by following mass percentage raw materials: 20-60% nitric acid, 3-15% hydrofluoric acid, 1-20% sulfuric acid, 5-30% phosphoric acid, 0.01-5% additive, the rest is water;Wherein additive is by rate stabilizer and flow regulator composition.The silicon wafer chemical polishing liquid prepared by the application can be chemically polished to silicon wafer below 35 DEG C, eliminate the residual stress and damage layer generated after polishing, reduce the risk of broken piece, and after chemical polishing treatment, the surface of silicon wafer is mirror surface, roughness (Ra) is less than 1nm, TTV is less than 0.2 μm.

Description

Technical Field

[0001] This invention belongs to the field of electronic chemicals technology, specifically relating to a high etching rate and high flatness chemical polishing slurry for silicon wafers and its application. Background Technology

[0002] Integrated circuit chip packaging is trending towards miniaturization, higher density, higher performance, and more functions. To meet this trend, wafer thinning has become a crucial process in semiconductor manufacturing. Wafer backside thinning is a key process in integrated circuit manufacturing. It can be achieved through mechanical grinding or chemical thinning, which uses chemical solutions to etch the substrate material on the back of the silicon wafer, thereby reducing wafer thickness, improving chip thickness, and facilitating subsequent packaging processes.

[0003] During the wafer thinning process, the wafer surface quality requirements are very high. Key indicators include etching rate, surface roughness after etching, and TTV (total thickness deviation within the wafer). In particular, TTV directly affects the final quality of the chip.

[0004] Chinese patent CN103077889A discloses a method for thinning the back side of a wafer. The method employs a two-step wet etching process to thin the back side of the wafer. First, a mixture of hydrofluoric acid, nitric acid, phosphoric acid, and sulfuric acid is used to wet etch the silicon substrate. Then, a mixture of hydrofluoric acid, nitric acid, and acetic acid is used to continue wet etching the silicon substrate and the exposed epitaxial layer on the back side of the wafer until the epitaxial layer is fully exposed. This method can ultimately produce an ultra-thin and uniform wafer with a thickness of 2 μm and a thickness difference of less than 0.1 μm. It has the advantages of low cost, no need for an oxide layer, and high speed, with the etching rate maintained at 8-12 μm / min.

[0005] Chinese patent CN109321253A discloses an etching solution for silicon wafers, whose main components include electronic-grade nitric acid, electronic-grade hydrofluoric acid, electronic-grade sulfuric acid, electronic-grade phosphoric acid, electronic-grade acetic acid, surfactant, and ultrapure water. Nitric acid acts as an oxidant, oxidizing silicon into silicon oxide. Hydrofluoric acid acts as a solvent, dissolving and removing the silicon oxide to etch the silicon wafer. Sulfuric acid increases the solution viscosity, stabilizes the reaction rate, does not change the etching morphology, and increases etching uniformity. Phosphoric acid also increases the solution viscosity, increases mass transfer resistance, reduces the etching rate, and does not change the etching morphology. Acetic acid acts as a diluent, reducing the ionization degree of nitric acid, inhibiting its oxidizing ability, reducing the reaction rate, and affecting the surface morphology after etching. The surfactant reduces the surface tension of the solution, improving the surface morphology of the etched silicon wafer. The final etching rate is below 15 μm / min.

[0006] Chinese patent CN109913222A discloses a silicon wafer polishing slurry composed of hydrofluoric acid, nitric acid, sulfuric acid, ammonium salt and ultrapure water. It can chemically etch silicon wafers to remove the surface damage layer and microcrack area caused by mechanical grinding at the front end, thereby obtaining a surface with low roughness and few defects. The final etching rate is below 10 μm / min.

[0007] In existing technologies, the etching rate for silicon wafers is almost always less than 20 μm / min, and no attention is paid to the total thickness variation (TTV) of the etched wafer. TTV, the difference between the maximum and minimum thickness of a silicon wafer, is a crucial indicator of wafer thickness uniformity and quality. The presence of thin or thick wafers affects wafer yield and the manufacturing process of solar cells. Therefore, it is necessary to develop a processing solution with a high etching rate that can mitigate the problem of excessively high TTV after etching, thereby improving the performance of silicon wafers. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a silicon wafer chemical polishing slurry with high etching rate and high flatness, and its application. The silicon wafer chemical polishing slurry can improve the TTV problem of the wafer after etching and has the advantages of high etching rate and high flatness after etching.

[0009] To achieve the above objectives, the present invention provides a silicon wafer chemical polishing slurry with high etching rate and high flatness, which is composed of the following raw materials by mass percentage: 20-60% nitric acid, 3-15% hydrofluoric acid, 1-20% sulfuric acid, 5-30% phosphoric acid, 0.01-5% additives, and the balance being water.

[0010] Preferably, the silicon wafer chemical polishing slurry is composed of the following raw materials by mass percentage: 35%-55% nitric acid, 5-10% hydrofluoric acid, 5-10% sulfuric acid, 15-20% phosphoric acid, 0.01-5% additives, and the balance being ultrapure water.

[0011] Preferably, the additive consists of a rate stabilizer and a flow modifier.

[0012] More preferably, the rate stabilizer is used in the silicon wafer chemical polishing slurry at an amount of 0.01-5%; and the flow modifier is used in the silicon wafer chemical polishing slurry at an amount of 0.01-1%.

[0013] More preferably, the rate stabilizer is any one of polyacrylic acid, sodium polyacrylate, sodium polymethacrylate, ammonium polyacrylate, polyacrylamide, polyvinylcyclohexane, polyethylene polyamine, polyethylene oxide, poly(vinylphosphonic acid), poly(4-vinylpyridine), 3-butenamine hydrochloride, 3-cyclobuten sulfone, polysulfone, cyclobutene sulfone, trifluorobutenoic acid, 1-butenboronic acid, benzocyclobutenone, and 3-buten-1-amine.

[0014] More preferably, the flow conditioner is any one of stearic acid, calcium stearate, ammonium stearate, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxybutyl methyl cellulose, ethyl hydroxyethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, polyacrylamide, and polyvinyl methyl ether.

[0015] Preferably, the mass concentration of the nitric acid is 68-72%; the mass concentration of the hydrofluoric acid is 48-51%; the mass concentration of the sulfuric acid is 95-97%; and the mass concentration of the phosphoric acid is 85-90%.

[0016] Preferably, the water is ultrapure water with a resistivity ≥15.0 MΩ*cm at 25°C.

[0017] The present invention also provides a method for preparing a silicon wafer chemical polishing slurry with high etching rate and high flatness. Specifically, ultrapure water is placed in a container, and nitric acid, phosphoric acid, sulfuric acid and hydrofluoric acid are added slowly while stirring in sequence. Finally, additives are added, and after mixing evenly, a silicon wafer chemical polishing slurry with high etching rate and high flatness is obtained.

[0018] The present invention also provides an application of a high etching rate and high flatness silicon wafer chemical polishing slurry, wherein the application is in the chemical polishing of silicon wafers by rotary spraying.

[0019] Preferably, during the rotary spraying process, the temperature of the silicon wafer chemical polishing solution is <35℃, and the flow rate is 400-1000mL / min.

[0020] Preferably, the rotary spraying uses a single-piece etching machine with a swing arm range of ±50%, a swing arm speed of 15-40 rad / s, and a rotational speed of 300-800 r / min.

[0021] Preferably, the etching rate of the silicon wafer chemical polishing slurry is >20μm / min, and the roughness Ra of the silicon wafer after etching is <1nm, and the TTV is <0.2μm.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. A chemical polishing solution is prepared using sulfuric acid, nitric acid, hydrofluoric acid, and phosphoric acid as main raw materials. This solution effectively removes the surface damage layer and defects of silicon wafers after mechanical grinding, while maintaining an etching rate above 20 μm / min. This significantly shortens process time and increases production efficiency. The etched silicon wafer surface exhibits crystalline characteristics with a roughness Ra < 1 nm. The etched surface is uniform, with a TTV < 0.2 μm, improving the silicon wafer yield and ensuring that the polished silicon wafers meet the production process requirements of solar cells, thus possessing higher economic value.

[0024] 2. Nitric acid in etching solutions typically produces various corrosion products. Some of these products, such as nitrogen dioxide, nitric oxide, and nitrous acid, significantly accelerate the reaction, leading to an increasingly rapid etching rate for Si. Adding a rate stabilizer reduces the solubility of these corrosion products in the etching solution, causing them to evaporate or decompose quickly, thus stabilizing the etching rate and improving surface roughness. Flow modifiers, generally substances that alter the viscosity of the solution, can be added in small amounts to reduce the use of high-viscosity inorganic acids (sulfuric acid and phosphoric acid), lowering costs. They also ensure more uniform flow and stable mass transfer of the etching solution on the wafer surface during spraying, thereby improving TTV (Total TV). Based on this mechanism, a combination of these two substances can maintain good surface roughness and TTV even under conditions of high nitric acid and high hydrofluoric acid, i.e., high etching rates. Attached Figure Description

[0025] Figure 1 This is a topographic image of a silicon wafer after mechanical grinding and before etching with a chemical polishing solution.

[0026] Figure 2 The image shows the morphology of a silicon wafer after etching with the chemical polishing solution prepared in Example 2. Detailed Implementation

[0027] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0028] In the following examples, the mass concentration of nitric acid is 70%, the mass concentration of phosphoric acid is 90%, the mass concentration of hydrofluoric acid is 50%, the mass concentration of sulfuric acid is 97%, and the mass concentration of acetic acid is 99.5%.

[0029] Examples 1-4, Comparative Examples 1-7

[0030] A chemical polishing slurry for silicon wafers with high etching rate and high flatness, the formulation of which is shown in Table 1;

[0031] Preparation method:

[0032] (1) Mix the rate stabilizer and flow conditioner to obtain the additive;

[0033] (2) Place ultrapure water in a container and slowly add nitric acid, phosphoric acid, sulfuric acid, hydrofluoric acid and additives in sequence while stirring. After mixing evenly, a chemical polishing solution for silicon wafers is obtained.

[0034] Table 1. Formulation of Chemical Polishing Fluid for Silicon Wafers

[0035]

[0036] Results: The silicon wafer chemical polishing slurries prepared in the above examples and comparative examples were placed in a single-wafer etching machine. After heating to 25°C, the silicon wafer (heavily boron-doped silicon wafer) was subjected to rotary spraying at a flow rate of 700 mL / min, with the swing arm range set to ±50%, the swing arm speed to 15 rad / s, and the rotation speed to 500 r / min. The spraying was stopped after 30 s to complete the polishing. The etching rate, Ra, and TTV were statistically analyzed. The results are shown in Table 1.

[0037] Table 2. Effect of Nitric Acid and Hydrofluoric Acid Doses on Polishing Results

[0038]

[0039] The results, as shown in Tables 1-2, indicate that, as seen in Examples 1-3 and Comparative Example 6, when other conditions remain unchanged, the etching rate of the chemical polishing solution gradually decreases and the roughness (Ra) gradually decreases with the increase of nitric acid and the decrease of hydrofluoric acid, while the TTV remains below 0.19 μm; the influence of hydrofluoric acid is greater than that of nitric acid.

[0040] As shown in Comparative Example 1, when acetic acid is used as a rate stabilizer and the surfactant fatty alcohol polyoxyethylene ether is used as a flow conditioner, the etching rate of the chemical polishing solution is only 9.9, and the TTV is as high as 0.561, which seriously affects the performance of the silicon wafer. When only a rate stabilizer is used (Comparative Example 2) or only a flow conditioner is used (Comparative Example 3), although the etching rate is maintained above 33 μm / min, the roughness and TTV are both high.

[0041] Examples 5-8, Comparative Examples 8-9

[0042] The preparation and etching methods are the same as in Example 1, except that the formulation of the chemical polishing solution is adjusted, as shown in Table 3:

[0043] Table 3. Formulation of Chemical Polishing Fluid for Silicon Wafers

[0044]

[0045] As shown in 5-8, when other conditions remain unchanged, with the increase of phosphoric acid and the decrease of sulfuric acid, the etching rate and TTV of the chemical polishing solution do not change much, and the roughness gradually decreases. When the content of sulfuric acid and phosphoric acid is too small, the roughness increases.

[0046] Examples 9-15, Comparative Examples 10-13

[0047] The preparation and etching methods are the same as in Example 1, except that the formulation of the chemical polishing solution is adjusted, as shown in Table 4:

[0048] Table 4. Formulation of Chemical Polishing Slurry for Silicon Wafers

[0049]

[0050] Table 5. Effect of additives on polishing effect

[0051]

[0052] Table 4-5 shows that, under constant conditions, the etching rate tends to decrease as the amount of rate stabilizer increases. The rate stabilizer has a significant impact on Ra, and increasing the amount of stabilizer is beneficial for reducing Ra. Increasing the amount of flow conditioner is beneficial for reducing TTV. Comparative Examples 11-13 show that excessive additives do not improve the etching effect and may even degrade the experimental results.

[0053] Examples 16-19, Comparative Example 14

[0054] Without changing the chemical polishing solution formula, only the etching temperature was changed to observe the effect of etching temperature on the etching effect of the chemical polishing solution. The conditions are shown in Table 6, and the etching results are shown in Table 7.

[0055] Table 6 Formulation and Etching Temperature

[0056]

[0057] Table 7. Effect of Etching Temperature on Polishing Results

[0058]

[0059] The results in Table 6-7 show that when the chemical polishing solution formula remains unchanged, the etching rate, roughness (Ra), and TTV gradually increase with the increase of etching temperature. When the etching temperature exceeds 35℃, the etching rate, roughness (Ra), and TTV all increase significantly, making it unsuitable for polishing silicon wafers.

Claims

1. A chemical polishing slurry for silicon wafers with high etching rate and high flatness, characterized in that: It is composed of the following raw materials by mass percentage: 20-60% nitric acid, 3-15% hydrofluoric acid, 1-20% sulfuric acid, 5-30% phosphoric acid, 0.01-5% rate stabilizer, 0.01-1% flow conditioner, and the balance is water; The rate stabilizer is any one of polyacrylic acid, sodium polyacrylate, sodium polymethacrylate, ammonium polyacrylate, polyacrylamide, polyvinylcyclohexane, polyethylene polyamine, polyethylene oxide, poly(vinylphosphonic acid), poly(4-vinylpyridine), 3-butenamine hydrochloride, 3-cyclobutenyl sulfone, polysulfone, cyclobutene sulfone, trifluorobutenoic acid, 1-butenboronic acid, benzocyclobutenone, and 3-buten-1-amine. The flow regulator is any one of stearic acid, calcium stearate, ammonium stearate, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxybutyl methyl cellulose, ethyl hydroxyethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, polyacrylamide, and polyvinyl methyl ether.

2. The high etching rate and high flatness chemical polishing slurry for silicon wafers according to claim 1, characterized in that: The mass concentration of the nitric acid is 68-72%; the mass concentration of the hydrofluoric acid is 48-51%; the mass concentration of the sulfuric acid is 95-97%; and the mass concentration of the phosphoric acid is 85-90%.

3. The high etching rate and high flatness chemical polishing slurry for silicon wafers according to claim 1, characterized in that: The water has a resistivity ≥15.0 MΩ at 25℃. cm of ultrapure water.

4. The application of a high etching rate and high flatness chemical polishing slurry for silicon wafers as described in any one of claims 1-3, characterized in that: The application is in the chemical polishing of silicon wafers using rotary spraying.

5. The application according to claim 4, characterized in that: During the rotary spraying process, the temperature of the silicon wafer chemical polishing solution is <35℃, and the flow rate is 400-1000mL / min.

6. The application according to claim 4, characterized in that: The rotary spraying system uses a single-piece etching machine with a swing arm range of ±50%, a swing arm speed of 15-40 rad / s, and a rotation speed of 300-800 r / min.

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