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

Abstract

The invention discloses a silicon wafer chemical polishing solution with high etching rate and high flatness and application thereof. The silicon wafer chemical polishing solution is prepared from the following raw materials in percentage by mass: 20-60% of nitric acid, 3-15% of hydrofluoric acid, 1-20% of sulfuric acid, 5-30% of phosphoric acid, 0.01-5% of an additive and the balance of water, wherein the additive consists of a rate stabilizer and a flow regulator. The silicon wafer chemical polishing solution prepared by the invention can be used for chemically polishing a silicon wafer at the temperature of 35 DEG C or below, residual stress and a damaged layer generated after grinding are eliminated, the risk of fragment is reduced, and the silicon wafer subjected to chemical polishing treatment has a mirror surface, the roughness (Ra) is less than 1nm and the TTV is less than 0.2 mu m.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic chemicals, and in particular relates to a silicon wafer chemical polishing liquid with high etching rate and high flatness and an application thereof. Background Art

[0002] Integrated circuit chip packaging tends to develop in the direction of smaller size, higher density, higher performance and more functions. To meet this development direction, wafer thinning has become a very important process in semiconductor manufacturing. Wafer back thinning is a key process in the integrated circuit manufacturing process. On the one hand, it can be thinned by mechanical grinding; on the other hand, it can be thinned by chemical thinning, using chemical liquid to corrode the body material on the back of the silicon wafer to achieve the purpose of reducing the wafer thickness, thereby reducing the chip thickness, improving the heat dissipation effect of the chip, and facilitating the subsequent packaging process.

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

[0004] Chinese patent CN103077889A discloses a method for thinning the back side of a wafer, which uses two-step wet etching 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, and 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 completely exposed. Finally, the preparation of an ultra-thin and uniform wafer with a thickness of 2μm and a thickness difference of less than 0.1μm can be completed. It has the advantages of low cost, no need for an oxide layer, and high speed, and the etching rate is maintained at 8-12μm / min.

[0005] Chinese patent CN109321253A discloses an etching solution for silicon wafers, the main components of which include electronic grade nitric acid, electronic grade hydrofluoric acid, electronic grade sulfuric acid, electronic grade phosphoric acid, electronic grade acetic acid, surfactants, and ultrapure water; wherein nitric acid is used as an oxidant to oxidize silicon into silicon oxides; hydrofluoric acid is used as a dissolving agent to dissolve and remove silicon oxides to achieve etching of silicon wafers; sulfuric acid can increase the viscosity of the solution, stabilize the reaction rate, do not change the etching morphology, and increase the etching uniformity; phosphoric acid can also increase the viscosity of the solution, increase the mass transfer resistance, reduce the etching rate, and do not change the etching morphology; acetic acid is used as a diluent to reduce the ionization degree of nitric acid, inhibit the oxidizing ability of nitric acid, reduce the reaction rate, and affect the surface morphology after etching; the surfactant reduces the surface tension of the solution and improves the surface morphology of the silicon wafer after etching; the final etching rate is below 15μm / min.

[0006] Chinese patent CN109913222A discloses a silicon wafer polishing liquid composed of hydrofluoric acid, nitric acid, sulfuric acid, ammonium salt and ultrapure water, which can chemically corrode the silicon wafer and 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, and the final etching rate is below 10μm / min.

[0007] In the prior art, the etching rate of silicon wafers is almost always less than 20μm / min, and no attention is paid to the TTV (Total Thickness Variation) of the wafer after etching. TTV is the difference between the maximum and minimum thickness of the silicon wafer, and is an important indicator for measuring the thickness uniformity and quality of the silicon wafer. The existence of thin and thick wafers will affect the qualified rate of silicon wafers and the production process of solar cells. Therefore, it is necessary to develop a treatment solution with a high etching rate and can improve the problem of excessively high TTV of the wafer after etching, so as to improve the performance of silicon wafers. Summary of the invention

[0008] In view of the above technical problems, the present invention provides a silicon wafer chemical polishing solution with high etching rate and high flatness and its application. The silicon wafer chemical polishing solution can improve the problem of TTV of the wafer after etching, and has the advantages of high etching rate and high flatness after etching.

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

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

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

[0012] Further preferably, the rate stabilizer is used in an amount of 0.01-5% in the silicon wafer chemical polishing solution; and the flow regulator is used in an amount of 0.01-1% in the silicon wafer chemical polishing solution.

[0013] More preferably, the rate stabilizer is any one of polyacrylic acid, sodium polyacrylate, sodium polymethacrylate, ammonium polyacrylate, polyacrylamide, polyvinyl cyclohexane, polyethylene polyamine, polyethylene oxide, poly(vinyl phosphonic acid), poly(4-vinyl pyridine), 3-buteneamine hydrochloride, 3-cyclobutene sulfone, polysulfone, cyclobutane sulfone, trifluorobutylene acid, 1-buteneboric acid, benzocyclobutenone, and 3-butene-1-amine.

[0014] More preferably, 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, polyvinyl pyrrolidone, 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 of ≥15.0 MΩ*cm at 25°C.

[0017] The present invention also provides a method for preparing a chemical polishing solution for silicon wafers with a high etching rate and high flatness, which specifically comprises placing ultrapure water in a container, slowly adding nitric acid, phosphoric acid, sulfuric acid and hydrofluoric acid in sequence while stirring, and finally adding additives, and mixing evenly to obtain a chemical polishing solution for silicon wafers with a high etching rate and high flatness.

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

[0019] Preferably, during the rotary spraying, the temperature of the silicon wafer chemical polishing liquid is less than 35° C., and the flow rate is 400-1000 mL / min.

[0020] Preferably, the rotary spray adopts a single-chip 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.

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

[0022] The beneficial effects of the present invention are: 1. Chemical polishing liquid is prepared by using sulfuric acid, nitric acid, hydrofluoric acid and phosphoric acid as the main raw materials, which effectively removes the surface damage layer and surface defects of silicon wafers after mechanical grinding, and the etching rate is maintained at more than 20μm / min, which can effectively shorten the process time and increase production efficiency. The surface of the etched silicon wafer is crystal-faceted, with a roughness of Ra<1nm; the surface after etching is uniform, and the TTV is less than 0.2μm, which improves the qualified rate of silicon wafers, so that the polished silicon wafers can meet the production process requirements of solar cells and have higher economic value.

[0023] 2. Nitric acid usually produces a variety of corrosion products in the etching solution. Some corrosion products such as nitrogen dioxide, nitric oxide, and nitrous acid greatly promote the reaction, so the corrosion rate of Si will become faster and faster. The addition of a rate stabilizer can reduce the solubility of corrosion products in the etching solution and make the corrosion products evaporate or decompose quickly, thereby stabilizing the rate and improving the roughness. Flow regulators are generally substances that can change the viscosity of the solution. A small amount of addition can reduce the use of high-viscosity inorganic acids (sulfuric acid and phosphoric acid) to reduce costs, and also make the solution flow more evenly on the wafer surface during the spraying process, and the mass transfer is more stable, thereby improving TTV. Based on this mechanism, the combination of the two substances can enable the solution to maintain good roughness and TTV under conditions of high nitric acid and high hydrofluoric acid, that is, high etching rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the morphology of the silicon wafer after mechanical grinding and before etching with chemical polishing liquid.

[0025] Figure 2 This is a morphology image of a silicon wafer after being etched by the chemical polishing solution prepared in Example 2. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further explained below in conjunction with 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 understood as limiting the present invention. The protection scope of the present invention shall be based on the contents recorded in the claims. Any modification or replacement made by those skilled in the art to the technical solution of the present invention without creative work shall fall within the protection scope of the present invention.

[0027] 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%.

[0028] Examples 1-4, Comparative Examples 1-7 A chemical polishing solution for silicon wafers with high etching rate and high flatness, the formula of which is shown in Table 1; Preparation method: (1) Mixing a rate stabilizer and a flow regulator to obtain an additive; (2) Place ultrapure water in a container, slowly add nitric acid, phosphoric acid, sulfuric acid, hydrofluoric acid and additives in sequence while stirring, and mix well to obtain a silicon wafer chemical polishing solution.

[0029] Table 1 Silicon wafer chemical polishing liquid formula

[0030] Result detection: Take the silicon wafer chemical polishing liquid prepared in the above embodiment and comparative example, place it in a single-wafer etching machine, heat it to 25°C, and set the swing arm range to ±50%, the swing arm speed to 15rad / s, and the rotation speed to 500r / min at a flow rate of 700mL / min to rotate and spray the silicon wafer (Shanghai Integrated Circuit Materials Research Institute, heavily doped boron silicon wafer). After 30s, the spraying is completed and the polishing is completed. The etching rate, Ra and TTV are statistically analyzed. The results are shown in Table 1: Table 2 Effect of nitric acid and hydrofluoric acid dosage on polishing effect

[0031] The results can be seen from Table 1-2: It can be seen from Examples 1-3 and Comparative Example 6 that when other conditions remain unchanged, with the increase in the amount of nitric acid and the decrease in the amount of hydrofluoric acid, the etching rate of the chemical polishing solution gradually decreases, the roughness (Ra) also gradually decreases, and the TTV remains below 0.19μm; the influence of hydrofluoric acid is greater than that of nitric acid.

[0032] It can be seen from Comparative Example 1 that when acetic acid is used as a rate stabilizer and the surfactant - fatty alcohol polyoxyethylene ether is used as a flow regulator, 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 the rate stabilizer (Comparative Example 2) or only the flow regulator (Comparative Example 3) is used, although the etching rate is maintained above 33μm / min, the roughness and TTV are both high.

[0033] Examples 5-8, Comparative Examples 8-9 The preparation method and etching method are the same as in Example 1, except that the formula of the chemical polishing solution is adjusted, see Table 3: Table 3 Silicon wafer chemical polishing liquid formula

[0034] From Figures 5-8, it can be seen that when other conditions remain unchanged, as the amount of phosphoric acid increases and the amount of sulfuric acid decreases, 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.

[0035] Examples 9-15, Comparative Examples 10-13 The preparation method and etching method are the same as in Example 1, except that the formula of the chemical polishing solution is adjusted, see Table 4: Table 4 Silicon wafer chemical polishing solution formula

[0036] Table 5 Effect of additives on polishing effect

[0037] It can be seen from Tables 4-5 that when other conditions remain unchanged, as the amount of rate stabilizer increases, the overall etching rate tends to decrease. The rate stabilizer has a greater impact on Ra, and increasing the stabilizer is beneficial to reducing Ra. Increasing the amount of flow regulator is beneficial to reducing TTV. Comparative Examples 11-13 show that excessive additives will not improve the etching effect, and may even deteriorate the experimental effect.

[0038] Examples 16-19, Comparative Example 14 Without changing the formula of the chemical polishing solution, only changing the etching temperature, the effect of the etching temperature on the etching effect of the chemical polishing solution was observed. The conditions are shown in Table 6, and the etching results are shown in Table 7.

[0039] Table 6 Recipe and etching temperature

[0040] Table 7 Effect of etching temperature on polishing effect

[0041] The results can be seen from Table 6-7: When the formula of the chemical polishing solution remains unchanged, the etching rate, roughness (Ra) and TTV all gradually increase with the increase of etching temperature. When the etching temperature exceeds 35°C, the etching rate, roughness (Ra) and TTV all increase significantly, which is not suitable for polishing silicon wafers.

Claims

1. A chemical polishing solution for silicon wafers with high etching rate and high flatness, characterized in that: The invention is composed of the following raw materials in percentage by mass: 20-60% nitric acid, 3-15% hydrofluoric acid, 1-20% sulfuric acid, 5-30% phosphoric acid, 0.01-5% additives, and the balance is water.

2. The chemical polishing solution for silicon wafers with high etching rate and high flatness according to claim 1, characterized in that: The additives consist of a rate stabilizer and a flow regulator.

3. The chemical polishing solution for silicon wafers with high etching rate and high flatness according to claim 2, characterized in that: The usage amount of the rate stabilizer in the silicon wafer chemical polishing solution is 0.01-5%; the usage amount of the flow regulator in the silicon wafer chemical polishing solution is 0.01-1%.

4. The chemical polishing solution for silicon wafers with high etching rate and high flatness according to claim 3, characterized in that: 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-buteneamine hydrochloride, 3-cyclobutene sulfone, polysulfone, cyclobutane sulfone, trifluorobutenoic acid, 1-buteneboric acid, benzocyclobutenone, and 3-butene-1-amine.

5. The chemical polishing solution for silicon wafers with high etching rate and high flatness according to claim 3, characterized in that: 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, polyvinyl pyrrolidone, polyacrylamide and polyvinyl methyl ether.

6. The chemical polishing solution for silicon wafers with high etching rate and high flatness 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%.

7. A chemical polishing solution for silicon wafers with high etching rate and high flatness according to claim 1, characterized in that: The water is ultrapure water having a resistivity of ≥15.0 MΩ*cm at 25°C.

8. An application of a chemical polishing solution for silicon wafers with high etching rate and high flatness as claimed in any one of claims 1 to 7, characterized in that: The application is the use of rotary spraying to chemically polish silicon wafers.

9. The use according to claim 8, characterized in that: During the rotary spraying, the temperature of the silicon wafer chemical polishing liquid is less than 35° C., and the flow rate is 400-1000 mL / min.

10. The use according to claim 8, characterized in that: The rotary spray adopts a single-chip etching machine, with a swing arm range of ±50%, a swing arm speed of 15-40rad / s, and a rotation speed of 300-800r / min.

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