Novel composite inorganic oxidant-containing polishing solution for fine polishing of silicon carbide substrate

Abstract

The invention discloses a novel composite inorganic oxidant-containing polishing solution for fine polishing of a silicon carbide substrate. The polishing solution comprises the following components in percentage by weight: 1-40% of an abrasive, 0.1-10% of an oxidant and 0.1-5% of a pH regulator, the grinding material adopts silica sol and a composite inorganic oxidizing agent, and the composite inorganic oxidizing agent comprises tetravalent cerium ions Ce < 4 + >, ferric ions Fe < 3 + >, hydrogen peroxide and a cationic surface active agent. According to the polishing solution, small-particle-size silicon dioxide serves as abrasive particles, Ce < 4 + > / Fe < 3 + > / hydrogen peroxide and the like are combined into a composite oxidizing agent for polishing, the adopted composite oxidizing agent can enhance the oxidation effect on the surface of silicon carbide, meanwhile, contact between particles and the surface of a silicon carbide substrate is increased, and the purposes of improving the surface removal rate and reducing roughness are more effectively achieved; and the material can be removed through simple cleaning subsequently, so that subsequent treatment is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor material polishing, in particular to a polishing liquid containing a novel composite inorganic oxidant and used for fine polishing of a silicon carbide substrate. Background Art

[0002] Silicon carbide has many crystal forms, such as 3C, 4H, 6H, etc., but the most stable and common crystal forms are 4H and 6H. One of the characteristics of silicon carbide wafers is that the two sides of the wafer can be divided into silicon side and carbon side, but they are not of the same quality, which makes the polishing methods of the two sides completely different. The epitaxy of silicon carbide devices mainly occurs on the silicon side, and its surface roughness requirement is generally less than 0.2 nanometers. After cutting, the surface of the silicon carbide ingot is extremely uneven, and it needs to be rough ground and fine ground first. In these two processes, grinding is mainly done mechanically, and the resulting substrate surface is very uneven.

[0003] Therefore, silicon carbide needs to be further polished, and this process is divided into rough polishing and fine polishing. Since the hardness of silicon carbide is 8-9, it is the material with the hardness second only to diamond. In the rough polishing process, many hard abrasives are used, such as diamond powder, silicon carbide powder and aluminum oxide particles. These hard abrasives do improve the removal rate of the silicon carbide surface, but the surface roughness of the substrate is still very high, accompanied by scratches. Fine polishing is required. In the fine polishing process, finer nanoparticles are often used as abrasives. Currently, nano-aluminum oxide and nano-silicon oxide are mostly used. However, the hardness of aluminum oxide is high and it is easy to cause defects such as scratches. Although the hardness of silicon oxide is low and it is not easy to cause scratches, the removal efficiency is also low.

[0004] At present, a large amount of research work on the formula of silicon carbide chemical mechanical polishing liquid for silicon dioxide particles at home and abroad shows that oxidants are generally added for improvement, such as potassium permanganate, perhalic acid and hydrogen peroxide. These oxidants react with silicon carbide to soften the surface of the substrate, thereby increasing the polishing rate of silicon dioxide. However, in the fine polishing process, the use of these oxidants also has some difficult-to-overcome shortcomings, such as the removal rate is still low, especially the permanganate ions will cause pollution to the environment and increase the corrosion of the equipment. Therefore, it is still a challenge to develop a fine polishing process that can effectively achieve excellent removal rate and roughness.

[0005] This case was created to solve the above problems. Summary of the invention

[0006] 1. Technical issues to be solved

[0007] In view of the deficiencies in the prior art, the present invention provides a polishing liquid for fine polishing of silicon carbide substrates containing a novel composite inorganic oxidant, which solves the problems raised in the above-mentioned background technology.

[0008] (II) Technical solution

[0009] To achieve the above purpose, the present invention is implemented by the following technical scheme: a polishing liquid for fine polishing of silicon carbide substrate containing a novel composite inorganic oxidant, which comprises the following by weight percentage: 1%-40% abrasive, 0.1%-10% oxidant, 0.1%-5% pH regulator;

[0010] The abrasive material is silica sol and a composite inorganic oxidant, wherein the composite inorganic oxidant includes tetravalent cerium ion Ce. 4+ 、Fe 3+ , hydrogen peroxide, cationic surfactant;

[0011] The pH value of the polishing liquid is controlled at 1-5.

[0012] As a preferred solution, further, the silica sol uses SiO2, and its particle size is 10 to 140 nm.

[0013] As a preferred embodiment, further, the weight percentages of the components in the composite inorganic oxidant are as follows: tetravalent cerium ion Ce 4+ 0.01%-5%, using any one of ammonium cerium sulfate, ammonium cerium nitrate, cerium sulfate, diphenyl cerium glycolate, cerium iodate, cerium oxychloride, trivalent iron ion Fe 3+ The concentration of hydrogen peroxide is 0.01%-0.5%, and any one of ferric nitrate, ferric sulfate and ferric chloride is used, and the concentration of hydrogen peroxide is 0.01%-5%.

[0014] As a preferred embodiment, further, the pH regulator is any one of sulfuric acid, nitric acid, hydrochloric acid, acetic acid, ammonium hydroxide, potassium hydroxide, sodium hydroxide, monoethanolamine, diethanolamine, triethanolamine, citric acid / malic acid / oxalic acid / tartaric acid or a mixture of several thereof.

[0015] As a preferred embodiment, further, the cationic surfactant is any one or more of hexadecyldimethylammonium chloride, octadecyltrimethylammonium chloride, and dodecyldimethylamine oxide.

[0016] (III) Beneficial effects

[0017] After adopting the above technical solution, the present invention provides a kind of polishing liquid for fine polishing of silicon carbide substrate containing a novel composite inorganic oxidant, which has the following beneficial effects compared with the prior art:

[0018] 1. The polishing liquid uses small-sized silica as abrasive, Ce 4+ / Fe 3+The composite oxidant is composed of 2-nitrogen peroxide and the like for polishing. The composite oxidant can enhance the oxidation effect on the silicon carbide surface and increase the contact between the particles and the surface of the silicon carbide substrate, which can more effectively achieve the purpose of increasing the surface removal rate and reducing the roughness. The composite oxidant can be removed by simple cleaning later, which is beneficial to the subsequent processing.

[0019] 2. Zeta potential test can clearly prove that the surface charge of the particles is reversed from negative to positive, thus proving the effectiveness of adding composite oxidants to modify the surface of the particles. Since the surface of the SiC substrate is negatively charged, when the surface of the silica particles is reversed to positive charge, it is more effective to contact the substrate surface.

[0020] 3. In addition, the test data also shows that the particles after this surface modification are highly stable, which helps to improve the dispersion level of the particles. The better the particle dispersion, the higher the effective area in contact with the substrate surface, and the better the improvement in polishing performance. Moreover, under the action of metal ions on the surface of the particles, hydrogen peroxide decomposes to form free radicals, forming micro-oxidation sites on the surface of the particles, making the silicon oxide particles different from other formulas that only play a mechanical role, and at the same time giving the silicon oxide particles a chemical-mechanical synergistic effect during the polishing process. According to experimental results, this effect cannot be achieved by simply adding one or two oxidants in combination. The above hypothetical mechanism can be found in the attached. Figure 1 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The process diagram of the assumed mechanism of chemical-mechanical synergistic effect in the polishing process of the present invention;

[0022] Figure 2 The following is a table showing the change in particle size of the abrasive in Reference Examples 1-6 of the present invention;

[0023] Figure 3 The following is a table showing the particle size variation of the abrasives in all reference examples and embodiments of the present invention. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0025] A polishing liquid for fine polishing of silicon carbide substrate containing a novel composite inorganic oxidant comprises an abrasive, an oxidant and a pH regulator, wherein the abrasive is silica sol (SiO2), the weight percentage of the abrasive is 1%-40%, and the novel composite inorganic oxidant (containing tetravalent cerium ion Ce) is used as a polishing liquid. 4+ 、Fe 3+ and hydrogen peroxide) by weight is 0.1%-10%; the pH value of the polishing liquid is 1-5.

[0026] The specific test is as follows: taking SiO2 abrasive with a particle size of 30nm and a content of 2wt% as an example, the pH is controlled within 2-4, and the content and type of the oxidant are used as variables for the test.

[0027] Particle size test:

[0028] After the sample is prepared, take an appropriate amount of sample with a dropper and add it to a beaker filled with deionized water and stir evenly to prepare a diluted sample. Take 1-1.5 ml of the diluted sample and drop it into the PS sample pool, put it into the nanoparticle size analyzer, set the instrument parameters for particle size test, and measure it in parallel 3 times.

[0029] Zeta potential test:

[0030] After the sample is prepared, take an appropriate amount of sample with a dropper and add it to a beaker filled with deionized water and stir evenly to prepare a diluted sample. Take an appropriate amount of diluted sample and add it to the capillary electrode sample pool, make sure that the sample to be tested completely immerses the two electrodes, and there are no bubbles in the sample pool, and cover the sealing plug. Put the capillary electrode sample pool into the Zeta potential analyzer, adjust the instrument parameters, and perform potential testing, and measure three times in parallel.

[0031] Polishing product quality test:

[0032] Under the same conditions of polishing machine, setting parameters, polishing time and other factors, the above-mentioned polishing liquids were used for polishing, and the effect of the polished products was tested.

[0033] Specific conditions: 6-inch conductive silicon carbide substrate; polishing machine: TSP910A polishing machine; polishing pad: IC1000; set polishing pressure to 0.1-8 psi; polishing machine lower plate speed to 10-90 rpm, polishing head speed to 10-90 rpm; polishing liquid flow rate: 5.0 L / min; polishing time: 4 hours

[0034] For specific results, please refer to the following test Table 1 and Table 2 (including Reference Examples 1-7 and Examples 1-8).

[0035] Table 1: Component data of the embodiments

[0036]

[0037]

[0038] Example results data list (Table 2)

[0039]

[0040]

[0041] Summarize:

[0042] 1. Through the Zeta potential test, it can be clearly proved that the surface charge of the particles is reversed from negative to positive, thus proving the effectiveness of adding composite oxidants to modify the surface of the particles. Since the surface of the SiC substrate is negatively charged, when the surface of the silica particles is reversed to positive charge, it is more effective to contact the substrate surface.

[0043] Zeta potential test shows that the surface of the raw material particles is negatively charged, and the value obtained by the zeta test is negative. After adding the composite oxidant, the surface of the raw material is gradually modified by positive charge, and the value obtained by the zeta test gradually changes from negative to positive, indicating that charge reversal occurs (Reference Example 1-Reference Example 2-Reference Example 5-Example 1-Example 4).

[0044] 2. The test data also show that the particles after this surface modification have high stability and good particle dispersion.

[0045] By comparing the results of the examples, it can be seen that the zeta potential of the composite oxidant is higher than that of a single or two oxidants, indicating that the system is more stable than that of a single or two oxidants. By adjusting the proportion of the composite oxidant, the zeta potential can be stabilized at 30 mV and above, indicating that the particles after surface modification have high stability and good particle dispersion.

[0046] 3. Under the action of metal ions on the surface of the particles, hydrogen peroxide decomposes to form free radicals, forming micro-oxidation sites on the surface of the particles.

[0047] The reactions involved are as follows:

[0048] ①2Ce 4+ +H2O2====2Ce 3+ +2H + +O2

[0049] ②Fe 3+ +H2O2→Fe 2+ +O2+2H +

[0050] ③Fe 2+ +H2O2→Fe 3+ +OH - + OH

[0051] Trivalent iron ions can react with hydrogen peroxide to produce a Fenton-like reaction (②③), whereby trivalent iron ions act as a catalyst to decompose hydrogen peroxide and produce free radicals.

[0052] 4. When only raw material particles are added to the liquid, water molecules are adsorbed on the surface of the raw material, and the particle size is about 130nm. When hydrogen peroxide is added, the particle size is 128nm, indicating that hydrogen peroxide has little effect on the change of particle size and has no surface modification effect on the particles. After the addition of tetravalent cerium ions and trivalent iron ions, the particle size becomes 30-45nm, indicating that metal ions have a surface modification effect on the raw material particles, and the particle size does not change much with the addition of different metal ions.

[0053] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A polishing liquid for fine polishing of silicon carbide substrates containing a novel composite inorganic oxidant, characterized in that: The composition comprises the following by weight percentage: 1%-40% of abrasive, 0.1%-10% of oxidant, and 0.1%-5% of pH regulator; The abrasive material is silica sol and a composite inorganic oxidant, wherein the composite inorganic oxidant includes tetravalent cerium ion Ce. 4+ 、Fe 3+ , hydrogen peroxide, cationic surfactant; The pH value of the polishing liquid is controlled at 1-5.

2. According to claim 1, a polishing liquid for fine polishing of silicon carbide substrate containing a novel composite inorganic oxidant, characterized in that: Silica sol uses SiO2, and its particle size is 10 to 140 nm.

3. According to claim 1, a polishing liquid for fine polishing of silicon carbide substrate containing a novel composite inorganic oxidant, characterized in that: The weight percentages of the components in the composite inorganic oxidant are as follows: tetravalent cerium ion Ce 4+ 0.01%-5%, using any one of ammonium cerium sulfate, ammonium cerium nitrate, cerium sulfate, diphenyl cerium glycolate, cerium iodate, cerium oxychloride, trivalent iron ion Fe 3+ The concentration of hydrogen peroxide is 0.01%-0.5%, and any one of ferric nitrate, ferric sulfate and ferric chloride is used, and the concentration of hydrogen peroxide is 0.01%-5%.

4. According to claim 1, a polishing liquid for fine polishing of silicon carbide substrate containing a novel composite inorganic oxidant, characterized in that: The pH regulator is any one of sulfuric acid, nitric acid, hydrochloric acid, acetic acid, ammonium hydroxide, potassium hydroxide, sodium hydroxide, monoethanolamine, diethanolamine, triethanolamine, citric acid / malic acid / oxalic acid / tartaric acid or a mixture of several thereof.

5. According to claim 1, a polishing liquid for fine polishing of silicon carbide substrate containing a novel composite inorganic oxidant, characterized in that: The cationic surfactant is any one or more of hexadecyl dimethyl ammonium chloride, octadecyl trimethyl ammonium chloride and dodecyl dimethyl amine oxide.

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