Green silicon wafer chemical mechanical polishing solution and preparation method thereof

Abstract

The invention discloses a green silicon wafer chemical mechanical polishing solution and a preparation method thereof, and relates to the technical field of polishing solutions. According to the technical scheme, the grinding fluid is prepared from the following components in percentage by mass: 1 to 10 percent of grinding material, 0.1 to 2 percent of rate accelerant, 0.01 to 0.2 percent of oxidation catalyst, 0.1 to 2 percent of pH buffering agent, 0.002 to 0.05 percent of surfactant and the balance of deionized water, wherein the rate accelerator is an organic super base, and the oxidation catalyst is a free radical oxidant. The green chemical mechanical polishing solution for the silicon wafer can greatly reduce the cost and improve the removal rate and the surface quality of the silicon wafer.

Description

Technical Field

[0001] The present invention relates to the technical field of polishing fluids, and particularly to a green chemical mechanical polishing fluid for silicon wafers and a preparation method thereof. Background Art

[0002] Silicon wafers are the basic materials in the IC (Integrated Circuit) industry and play a crucial role in all aspects of chip manufacturing. Especially as the substrate material for chip manufacturing, it is required not only to have high purity, perfect crystal structure, high-precision dimensions, but also to have ultra-clean surface quality and high flatness. If the wafer thickness is uneven or the surface is not flat, it will cause uneven exposure during the lithography process, affecting the resolution and accuracy of the pattern. Chemical mechanical polishing (CMP) technology is considered the most effective method to achieve global planarization in the current semiconductor industry. The CMP process basically consists of three parts, including polishing material, polishing fluid, and polishing pad. Among them, the polishing fluid is the key factor affecting the polishing quality of materials in CMP and also occupies most of the market for CMP materials.

[0003] Chinese Patent CN101857774A discloses a polishing composition for improving the chemical mechanical polishing rate of silicon substrates and its application, which includes abrasives, pH regulators, fluorine-containing compounds, etc. However, the content of the fluorine-containing compound reaches 2 - 3.5%, which will increase the cost of waste liquid treatment.

[0004] Chinese Patent CN118460117A discloses a polysilicon polishing fluid, which includes silicon dioxide abrasives, pH regulators, surfactants, fungicides, etc. The surface quality can be controlled to a roughness of about 0.3 nm, but the removal rate is low and the composition is complex.

[0005] In summary, in view of the problems existing in the current silicon wafer polishing fluids, it is necessary to develop a new silicon wafer polishing fluid. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a green chemical mechanical polishing fluid for silicon wafers and a preparation method thereof, which can greatly reduce costs, improve the removal rate and surface quality of silicon wafers.

[0007] The technical solution of the present invention is as follows:

[0008] On the one hand, the present invention provides a green chemical mechanical polishing fluid for silicon wafers, which is composed of the following components in mass percentage: abrasives 1 - 10%, rate promoter 0.1 - 2%, oxidation catalyst 0.01 - 0.2%, pH buffer 0.1 - 2%, surfactant 0.002 - 0.05%, and the rest is deionized water; wherein, the rate promoter is an organic superbase, and the oxidation catalyst is a free radical type oxidant.

[0009] Preferably, the abrasive content is 2-5%.

[0010] Preferably, the abrasive is spherical silica with a particle size of 200-300 nm.

[0011] Preferably, the spherical silica is monodisperse silica, and PDI < 0.05.

[0012] Preferably, the content of the organic superbase is 0.2-1%.

[0013] Preferably, the content of the oxidation catalyst is 0.02-0.1%.

[0014] Preferably, the content of the pH buffer is 0.2-1%.

[0015] Preferably, the content of the surfactant is 0.005-0.02%.

[0016] Preferably, the organic superbase is an amidine superbase, a guanidine superbase, a N-heterocyclic carbene superbase, a pyrrolidine superbase, or a phosphazene superbase.

[0017] Preferably, the organic superbase is one or more of 1,3-disubstituted imidazol-2-ylidene N-heterocyclic carbene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, tris(dimethylamino)methylpyrrolidine, tris(tert-butyl)phosphine, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicycloundecene, 1,5-diazabicyclo[4.3.0]non-5-ene, tetramethylguanidine, pentamethylguanidine, tert-butylphosphazene, and tris(dimethylamino)methane.

[0018] Preferably, the radical oxidant is pyrrolidine nitroxide, pyridine nitroxide, or oxazolidine nitroxide.

[0019] Preferably, the radical oxidant is one or more of 2,2,6,6-tetramethylpiperidine oxide, 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide, 2,2,5,5-tetramethylpyrrolidine oxidant, 3-carboxy-2,2,5,5-tetramethylpyrrolidine oxidant, and diethylamine nitroxide.

[0020] Preferably, the pH buffer is an amino acid, an organic ammonium salt, or an inorganic ammonium salt; preferably, the pH buffer is one or more of proline, 1,2,4-triazole, 3-(cyclohexylamino)-1-propanesulfonic acid, ammonium citrate, and ammonium chloride.

[0021] Preferably, the surfactant is a non-ionic surfactant; preferably, the surfactant is one or more of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, polysorbate, sorbitol, alkyl alkanolamide, polyoxyethylene alkyl alkanolamide, polyethylene glycol, sucrose fatty acid ester, and methyl glucoside polyoxyethylene ether.

[0022] Preferably, the pH of the green silicon wafer chemical mechanical polishing liquid is 9 - 12.

[0023] Preferably, the pH of the green silicon wafer chemical mechanical polishing liquid is 10 - 11.

[0024] On the other hand, the present invention provides a preparation method of the above-mentioned green silicon wafer chemical mechanical polishing liquid. Add a pH buffer, a surfactant, a rate promoter, and an oxidation catalyst to deionized water in sequence, and stir to obtain solution A; add the abrasive to solution A under the condition of uniform stirring, and then perform ultrasonic treatment or continuous stirring to obtain the green silicon wafer chemical mechanical polishing liquid.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The polishing liquid of the present invention is suitable for polishing silicon wafers. Without adding a surfactant, the removal rate far exceeds that of commercial polishing liquids. After adding a surfactant, the removal rate is still much higher than that of commercial polishing liquids. In addition, on the premise of maintaining a high removal rate, the polishing liquid of the present invention can greatly reduce the roughness of the silicon wafer, so that the surface roughness of the polished silicon wafer is controlled below 0.37 nm. Generally speaking, compared with commercial polishing liquids, the polishing liquid of the present invention has certain advantages.

[0027] 2. The polishing liquid of the present invention uses silica with a uniform particle size distribution as the abrasive. The effective abrasive percentage is high, and the percentage content in the polishing liquid is low, reducing the production cost. Since the nano-sized silica abrasive is spherical and uniformly distributed, it is beneficial to reduce the damage on the surface of the silicon wafer and obtain higher flatness. At the same time, the polishing liquid of the present invention uses an organic superbase as the rate promoter, with a low usage content and low toxicity, and is almost harmless to the environment; in addition, the organic superbase used has a very high ionization degree and is almost completely ionized in the solution to generate hydroxide ions, so a relatively low amount can be added to reach the required pH range. The pH buffer used in the polishing liquid of the present invention ensures that the pH will not be too high, ensuring that the abrasive will not be damaged and maintaining stability. The combined action of the pH buffer and the organic superbase keeps the pH of the polishing liquid at 9 - 12, enabling a relatively high removal rate without the need to add other pH regulators. The oxidation catalyst used in the polishing liquid of the present invention is a free radical type oxidant, which is a very effective type of oxidation catalyst and can continuously and stably oxidize the surface layer of the silicon wafer into a soft-textured silicon oxide layer uniformly, improving the oxidation rate and the removal rate. In addition, the free radical type oxidant has good stability and recyclability.

[0028] 3. The surfactant used in the polishing liquid of the present invention is a non-ionic surfactant. By forming hydrogen bonds with the hydroxyl groups on the surface of the silica abrasive, it increases the steric hindrance of the abrasive, ensuring excellent suspension stability of the abrasive. In addition, the surfactant can be adsorbed into the concave parts of the silicon wafer to protect the concave parts from being over-corroded. While improving the flatness of the surface of the silicon wafer, it is beneficial for the cleaning work after CMP. However, it should be noted that the surfactant also plays a lubricating role, which will reduce the mechanical force when the silica contacts the silicon wafer, resulting in a decrease in the removal rate.

[0029] 4. The abrasive and additives used in the polishing liquid of the present invention do not contain metal ions and will not affect the subsequent processing of the silicon wafer. Description of the Drawings

[0030] Figure 1 It is the SEM image of the silica with a particle size of 220 nm in Example 1 of the present invention.

[0031] Figure 2 It is the particle size distribution diagram of the silica with a particle size of 220 nm in Example 1 of the present invention, PDI = 0.01.

[0032] Figure 3 It is the SEM image of the silica with a particle size of 250 nm in Comparative Example 3 of the present invention.

[0033] Figure 4 It is the particle size distribution diagram of the silica with a particle size of 250 nm in Comparative Example 3 of the present invention, PDI = 0.007.

[0034] Figure 5 It is the SEM image of the silica with a particle size of 280 nm in Comparative Example 4 of the present invention.

[0035] Figure 6 It is the particle size distribution diagram of the silica with a particle size of 280 nm in Comparative Example 4 of the present invention, PDI = 0.008.

[0036] Figure 7 It is the surface morphology of the polished silicon wafer in Comparative Example 1 measured by atomic force microscopy, Ra = 0.401 nm.

[0037] Figure 8 It is the surface morphology of the polished silicon wafer in Comparative Example 2 measured by atomic force microscopy, Ra = 0.356 nm.

[0038] Figure 9 It is the surface morphology of the polished silicon wafer in Comparative Example 9 measured by atomic force microscopy, Ra = 0.953 nm. Detailed implementation manners

[0039] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention.

[0040] Examples 1 - 3 and Comparative Examples 1 - 9

[0041] The formulations of the silicon wafer polishing liquids in Examples 1 - 3 and Comparative Examples 1 - 9 are shown in Table 1. All the raw materials used in the polishing liquids are purchased from InnoChem Technology Co., Ltd. The commercial polishing liquid in Comparative Example 9 is a commonly used silica-based alkaline polishing liquid in the market. Among them, the SEM image and particle size distribution diagram of the silica with a particle size of 220 nm in Example 1 are as shown in Figure 1-2 shown; the SEM image and particle size distribution diagram of the silica with a particle size of 250 nm in Comparative Example 3 are as shown in Figure 3-4 shown; the SEM image and particle size distribution diagram of the silica with a particle size of 280 nm in Comparative Example 4 are as shown in Figure 5-6 shown.

[0042] Table 1 Formulations of the silicon wafer polishing liquids in Examples 1 - 3 and Comparative Examples 1 - 9

[0043]

[0044]

[0045]

[0046] The preparation methods of the silicon wafer polishing liquids of Examples 1-3 and Comparative Examples 1-8 are as follows: Add a pH buffer, a surfactant, a rate promoter, and an oxidation catalyst to deionized water successively, and stir for 10 min to obtain Solution A; Add the abrasive to Solution A under the condition of uniform stirring, and then perform ultrasonic treatment for 20 min to obtain a green silicon wafer chemical mechanical polishing liquid.

[0047] The polished workpieces in Examples 1-3 and Comparative Examples 1-9 are 4-inch single crystal silicon wafers. The polishing of the above silicon wafers is all carried out on a UNIPOL-1203 type chemical mechanical polishing machine. The pressure is controlled by a GPC-100A precise polishing controller, and the flow rate of the polishing liquid is controlled by an SKZD-4 type automatic dropper. The operating parameters of the polishing machine during the test are as follows: The polishing pressure is 25.46 g / cm 2 , the rotation speed of the polishing head is 15 r / min, the rotation speed of the polyurethane polishing pad is 90 r / min, the flow rate of the polishing liquid is 8 mL / min, and the polishing time is 15 min.

[0048] Table 2 shows the polishing results of the polished workpieces using the polishing liquids of Examples 1-3 and Comparative Examples 1-9. The removal rate is the average value of the removal rates of the silicon wafer after three times of polishing; the accurate value of the surface roughness Ra is obtained by an atomic force microscope.

[0049] Among them, the removal rate is obtained by calculating the change in the mass of the silicon wafer before and after polishing, and is calculated according to the following formula:

[0050] MRR = (ΔM) / (ρ×S×t)×10 7

[0051] In the formula, MRR - removal rate, nm / min; ΔM - change in the mass of the silicon wafer before and after polishing, g; ρ - density of the silicon wafer, g / cm 3 , S - area of the silicon wafer, cm 2 ; t - single polishing time, min.

[0052] The polishing results of the polished workpieces using the polishing liquids of Examples 1-3 and Comparative Examples 1-9 are shown in Table 2:

[0053] Table 2 Polishing Results of the Polished Workpieces Using the Polishing Liquids of Examples 1-3 and Comparative Examples 1-9

[0054] Polishing liquid Removal rate (nm / min) Surface scratch condition Surface roughness Ra (nm) Example 1 172.57 No obvious scratches 0.356 Example 2 162.71 No obvious scratches 0.302 Example 3 168.52 No obvious scratches 0.367 Comparative example 1 118.27 No obvious scratches 0.580 Comparative example 2 155.11 No obvious scratches 0.401 Comparative example 3 146.45 No obvious scratches 0.522 Comparative example 4 143.33 No obvious scratches 0.556 Comparative example 5 135.43 There are a small number of scratches 0.895 Comparative example 6 45.29 No obvious scratches 0.680 Comparative example 7 90.30 There are a small number of scratches 1.067 Comparative example 8 81.31 No obvious scratches 0.734 Comparative example 9 135.73 There are a small number of scratches 0.953

[0055] As can be seen from Table 2, compared with Example 1, surfactant and oxidation catalyst were not added in Comparative Example 1, resulting in a decrease in removal rate and surface quality. This is because the surfactant plays a lubricating role in the polishing liquid to avoid scratches caused by excessive local pressure. The oxidation catalyst can oxidize the surface of the silicon wafer to generate a softer layer that is more easily removed, thus helping to improve the removal rate.

[0056] Compared with Example 1, the oxidation catalyst was not added in the polishing liquids of Comparative Examples 2-4, and the removal rates all decreased to some extent. This is because the weakening of the chemical oxidation effect failed to achieve smoothness with mechanical removal, also leading to an increase in the roughness of the silicon wafer.

[0057] Compared with Example 1, too much abrasive was added in Comparative Example 5, but both the removal rate and surface quality decreased significantly. This is because the high-concentration abrasive will reduce the fluidity of the polishing liquid, making the polished polishing liquid unable to flow out of the polishing pad in time. At the same time, it will also cause uneven distribution of the abrasive, resulting in excessive local friction, generating scratches, and increasing the surface roughness.

[0058] Compared with Example 1, the organic superbase was not added in Comparative Example 6, resulting in a significant decrease in the removal rate. This is because the organic superbase acts as a rate promoter and can react with the silicon wafer to produce silicate dissolved in water, thus greatly increasing the removal rate.

[0059] Compared with Example 1, too much organic superbase was added in Comparative Example 7, resulting in too high a pH of the polishing liquid, thus destroying the structure of the abrasive and significantly reducing both the removal rate and surface quality.

[0060] Compared with Example 1, too much oxidation catalyst was added in Comparative Example 8, resulting in too intense oxidation and the mechanical action could not remove it in time, thus greatly reducing both the removal rate and surface quality.

[0061] In Comparative Example 9, a commercially available polishing liquid was used. It can be seen that its removal rate is lower than that of Example 1 and the roughness is higher.

[0062] Figure 7-9 These are the 10×10μm regions of the silicon wafers polished by Example 1, Comparative Example 2, and Comparative Example 9, respectively, photographed by an atomic force microscope. It can be seen that the surface of the silicon wafer polished by Example 1 is relatively flat without obvious scratches. Although there are no obvious scratches in Comparative Example 2, the surface roughness has increased. There are obvious scratches on the surface of the silicon wafer polished by the commercial polishing liquid of Example 9, so the surface roughness is higher.

[0063] In summary, the green chemical mechanical polishing fluid for silicon wafers of the present invention has low contents of each component, does not contain toxic substances, and has the advantages of low cost, environmental friendliness. In addition, the green chemical mechanical polishing fluid for silicon wafers of the present invention has a high removal rate, can also greatly improve the surface quality of silicon wafers, and can significantly improve the flatness of silicon wafers.

Claims

1. Green silicon wafer chemical mechanical polishing liquid, characterized in that, It consists of components in the following mass percentages: abrasive 1 - 10%, rate promoter 0.1 - 2%, oxidation catalyst 0.01 - 0.2%, pH buffer 0.1 - 2%, surfactant 0.002 - 0.05%, and the balance is deionized water; wherein, the rate promoter is an organic superbase, and the oxidation catalyst is a free - radical type oxidant.

2. The green silicon wafer chemical mechanical polishing liquid according to claim 1, wherein The abrasive is spherical silica with a particle size of 200 - 300 nm.

3. The green silicon wafer chemical mechanical polishing liquid according to claim 1, wherein, The organic superbase is an amidine - type superbase, a guanidine - type superbase, an N - heterocyclic carbene - type superbase, a pyrrolidine - type superbase, or a phosphazene - type superbase.

4. The green silicon wafer chemical mechanical polishing liquid according to claim 3, characterized in that, The organic superbase is one or more of 1,3 - disubstituted imidazole - 2 - ylidenes, 1,5,7 - triazabicyclo[4.4.0]dec - 5 - ene, tris(dimethylamino)methylpyrrolidine, tris(tert - butyl)phosphine, 7 - methyl - 1,5,7 - triazabicyclo[4.4.0]dec - 5 - ene, 1,8 - diazabicycloundecene, 1,5 - diazabicyclo[4.3.0]non - 5 - ene, tetramethylguanidine, pentamethylguanidine, tert - butylphosphazene, and tris(dimethylamino)methane.

5. The green silicon wafer chemical mechanical polishing liquid according to claim 1, characterized in that The free - radical type oxidant is a pyrrolidine nitroxide, a pyridine nitroxide, or an oxazolidine nitroxide.

6. The green silicon wafer chemical mechanical polishing liquid according to claim 5, wherein The free - radical type oxidant is one or more of 2,2,6,6 - tetramethylpiperidine N - oxide, 4 - hydroxy - 2,2,6,6 - tetramethylpiperidine N - oxide, 2,2,5,5 - tetramethylpyrrolidine N - oxide, 3 - carboxy - 2,2,5,5 - tetramethylpyrrolidine N - oxide, and diethylamine nitroxide.

7. The green silicon wafer chemical mechanical polishing liquid according to claim 1, wherein, The pH buffer is an amino acid, an organic ammonium salt, or an inorganic ammonium salt.

8. The green silicon wafer chemical mechanical polishing liquid according to claim 1, characterized in that, The surfactant is a non - ionic surfactant.

9. The green silicon wafer chemical mechanical polishing liquid according to claim 1, wherein The pH of the green silicon wafer chemical mechanical polishing liquid is 9 - 12.

10. The preparation method of the green silicon wafer chemical mechanical polishing liquid according to any one of claims 1-9, characterized in that, Add the pH buffer, surfactant, rate promoter, and oxidation catalyst to deionized water successively, and stir to obtain solution A; add the abrasive to solution A under uniform stirring conditions, and then perform ultrasonic treatment or continuous stirring to obtain the green silicon wafer chemical mechanical polishing liquid.

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