Special CMP (Chemical Mechanical Polishing) solution for silicon carbide wafer and preparation method of special CMP solution

Abstract

The invention discloses a special CMP (Chemical Mechanical Polishing) solution for a silicon carbide wafer. The special CMP solution consists of the following components: 5-12% of alpha-spherical nano aluminum oxide; 1-5% of a complexing agent, preferably citric acid; 0.1%-1.0% of a composite inhibitor; 0.5-3% of an oxidizing agent which is ammonium persulfate; 0.05%-0.5% of a dispersion stabilizer; the pH regulator is tetramethylammonium hydroxide and is used for regulating the pH of the polishing solution to 8-11; and the balance of deionized water or ultrapure water. The preparation method of the polishing solution comprises the following steps: S1, adding the alpha-spherical nano aluminum oxide into polyether polyol and ultrapure water, and carrying out ultrasonic dispersion; s2, adding a complexing agent, a composite inhibitor and an oxidizing agent, and magnetically stirring; s3, adjusting the pH (Potential of Hydrogen) to 8 to 11 by using a tetramethylammonium hydroxide solution; and S4, after standing at room temperature, filtering through a filter membrane to obtain the CMP polishing solution. The silicon carbide CMP polishing solution provided by the invention combines alpha-spherical nano aluminum oxide and an ammonium persulfate / PEG 6000 / composite inhibitor synergistic system, can ensure high material removal rate and low defect density, and has excellent dispersion stability and metal residue control ability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of chemical mechanical polishing (CMP), and particularly relates to a CMP polishing liquid special for silicon carbide wafers and a preparation method thereof. BACKGROUND

[0002] In the currently published literature and industry known technology, the polishing liquid suitable for chemical mechanical polishing (CMP) of silicon carbide (SiC) wafers generally uses alumina or silica abrasive, and is supplemented with hydrogen peroxide, organic amine inhibitor or fluorine-containing compound as an oxidizing agent. However, the traditional silicon nitride chemical mechanical polishing system generally has the following problems: 1. Low material removal rate (MRR): due to the high hardness (Mohs 9.3) and chemical inertness of SiC, when using conventional alumina or silica polishing liquid, the MRR is often less than 20 nm / min, the polishing efficiency is limited, and it is difficult to meet the high-efficiency processing demand.

[0003] 2. Surface roughness (Ra) is generally above 1.0 nm, which is difficult to meet the final polishing demand of advanced devices.

[0004] 3. High scratch density (more than 10~20 pieces / cm²) after polishing: the traditional alumina abrasive has sharp edges and corners, and the particle size distribution is wide (PDI>0.3), which easily leads to a scratch density of more than 12 pieces / cm², affecting the yield of SiC wafers.

[0005] 4. Surface contamination problem: some polishing liquids contain benzotriazole (BTA) or metal contaminants, which may form residues on the SiC surface, such as metal ion residues or fluorine ion corrosion, which affect subsequent processes such as epitaxial growth or electrical performance.

[0006] 5. Poor slurry dispersibility, poor stability, easy to settle or agglomerate, difficult to store and recycle. SUMMARY

[0007] In view of the problems mentioned in the background art, the present application provides a silicon carbide wafer CMP polishing liquid and a preparation method, and constructs a systematic optimized "oxidizing agent-dispersant-composite inhibitor-highly spheroidized abrasive" synergistic system. The application discloses the synergistic mechanism of ammonium persulfate and PEG 6000 in SiC polishing, controls the ultrasonic time and pH at the same time, realizes the unity of high MRR (80 nm / min), low defects (Ra≤0.8 nm) and long-term stability (TSI<1.0), and can be suitable for ultra-precision polishing of advanced process silicon carbide.

[0008] The technical scheme adopted by the present application to achieve the above-mentioned purposes is as follows: A CMP polishing solution special for silicon carbide wafer, the polishing solution is composed of the following components in mass percentage: alpha-spherical nano-alumina: 5-12%, spheroidization rate is greater than or equal to 95%; composite inhibitor: 0.1-1.0%, composed of poly-aspartic acid and dodecyl benzene sulfonic acid in a mass ratio of (1.5-3):1; oxidizing agent: 0.5-3%, ammonium persulfate; dispersion stabilizer: 0.05-0.5%, polyether polyol; pH regulator: tetramethylammonium hydroxide, the pH of the polishing solution is adjusted to 8-11; the rest is deionized water or ultrapure water.

[0009] Preferably, the average particle size of the alpha-spherical nano-alumina is 50 nm, and the content is 10-12%.

[0010] Preferably, the mass ratio of poly-aspartic acid to dodecyl benzene sulfonic acid in the composite inhibitor is 2:1, and the total content of the composite inhibitor is 0.5-0.6%.

[0011] Preferably, the dispersion stabilizer is PEG 6000, and the content is 0.1%.

[0012] Preferably, the pH regulator adjusts the pH value of the polishing solution to the range of 10.0-10.5.

[0013] Preferably, the polishing solution contains a complexing agent, and the complexing agent is selected from citric acid, and the content is 3%.

[0014] The application also provides a preparation method of the above-mentioned CMP polishing solution, comprising the following steps: step S1 pre-dispersion: adding alpha-spherical nano-alumina into polyether polyol and ultrapure water or deionized water, ultrasonic dispersion, ultrasonic condition is 40 kHz, 300 W, processing 2 hours, control temperature ≤30℃; step S2 mixing and dissolving: adding complexing agent, composite inhibitor, oxidizing agent, magnetic stirring for 30 minutes, speed is 500 rpm, temperature is 25±1℃; step S3 pH adjustment: using 10% tetramethylammonium hydroxide solution to adjust the pH of the mixed solution to 8-11; step S4 aging and filtering: after standing at room temperature for 12 hours, filtering through a filter membrane with a pore size of 0.2 μm, to obtain the CMP polishing solution.

[0015] Preferably, in the step S2 mixing and dissolving, the complexing agent, the composite inhibitor and the oxidizing agent are added in the order of complexing agent→composite inhibitor→oxidizing agent.

[0016] Preferably, in the step S3 pH adjustment, the pH of the mixed solution is adjusted to 10.0-10.5 using the tetramethylammonium hydroxide solution.

[0017] Compared with the prior art, the application has the following beneficial effects: 1. Significant correlation mechanism between particle morphology and polishing defects: Using high-spheroidization rate alpha-alumina abrasives with an average particle size of 50 nm, the scratch density is reduced from the traditional >12 / cm² to <1 / cm² under the same formulation, far exceeding the existing sharp corner alumina system, and proposing a "particle size + spheroidization rate + synergistic additive" three-factor synergistic design path in the field; 2. Synergistic effect between oxidizing agent and dispersant: ammonium persulfate and PEG 6000 are compounded for use in silicon carbide CMP liquid, forming a synergistic oxidation-dispersion structure, and PEG 6000 not only maintains the Zeta potential (-35 mV) as a dispersion stabilizer, but also accelerates the formation of Si-O oxide film after compounding with ammonium persulfate under the condition of pH=10.5 (film thickness is increased and Ra is significantly reduced). This synergistic mechanism has not been reported in the prior art; 3. With PASP / DBSA complex inhibitor, a dense oxidized soft layer is formed under the condition of pH 10.0-10.5, which realizes the formation of a uniform and stable oxidized soft layer on the SiC surface, and the material removal rate is increased to more than 80 nm / min, and the metal residue (Cu, Fe, Al) on the polished wafer surface is less than 5×10 10 atoms / cm²; 4. Parameter robustness under wide process window: The polishing liquid provided by the present application maintains sub-nanometer surface roughness Ra ≤ 0.8 nm and MRR ≥ 75 nm / min under different pH, pressure and speed, showing strong robustness and industrial adaptability, and can be specially used for ultra-precision polishing of wide-bandgap semiconductor material silicon carbide (SiC) substrate, especially for ultra-precision final polishing process of 6-inch and above high-power device wafers; 5. Compared with the traditional alumina system (MRR about 15~20 nm / min), the present application can shorten the polishing time of unit wafer by more than 60%, and the scratch rate is significantly reduced, which is expected to improve the overall wafer yield by 3~5%; The Zeta potential of the system is maintained at -35 mV, the slurry stability is significantly improved, the Turbiscan stability index TSI is less than 1.0, and the storage stability is more than 30 days. BRIEF DESCRIPTION OF DRAWINGS Figure 1 : Schematic diagram of the preparation method of the CMP polishing liquid for silicon carbide wafers. DETAILED DESCRIPTION

[0018] The application provides a CMP polishing solution special for silicon carbide wafers, which mainly comprises the following components: alpha-spherical nano-alumina: 5-12 wt%, spheroidization rate is greater than or equal to 95%; composite inhibitor: 0.1-1.0 wt%, which is composed of polyaspartic acid and dodecyl benzene sulfonic acid in a mass ratio of (1.5-3):1; oxidizing agent: 0.5-3 wt%, which is ammonium persulfate; dispersion stabilizer: 0.05-0.5 wt%, which is polyether polyol; pH regulator: tetramethylammonium hydroxide, the pH of the polishing solution is adjusted to 8-11; and the rest is deionized water or ultrapure water.

[0019] The alpha-spherical nano-alumina has the function of mechanical grinding, so that the specific surface area is greater than or equal to 30.8 m² / g (BET method), and the active site density is improved; the composite inhibitor has the function of dynamic passivation, the polyaspartic acid (PASP) and the dodecyl benzene sulfonic acid (DBSA) are compounded, and the polishing uniformity is improved; the oxidizing agent is mainly chemical oxidation, the ammonium persulfate can accelerate the formation of the SiC surface oxide film, and the removal rate is improved; the dispersion stabilizer can prevent agglomeration, the polyether polyol makes the Zeta potential be less than or equal to -35 mV, and the dispersion stability is ensured; and the pH regulator mainly controls the reaction environment, the tetramethylammonium hydroxide (TMAH) is alkaline adjustment, and the residual metal ions can be prevented.

[0020] In addition, the preparation method provided by the application mainly comprises the following four steps. Step S1: pre-dispersion treatment: alpha-spherical nano-alumina (50 nm, 10 wt%) and polyether polyol (0.1 wt%) are added into ultrapure water (resistivity is greater than or equal to 18 MΩ·cm), and placed in a 40 kHz / 300 W ultrasonic reactor for treatment for 2 hours, and the whole process is circulated and cooled to keep the temperature less than 30 DEG C. The particle size distribution median (D50) of the nano-alumina particles used in the application is about 50 nm, that is, 50% of the particle size is less than or equal to 50 nm, 50% of the particle size is greater than or equal to 50 nm, the polydispersity index (PDI) of the particles is 0.12, which indicates that the particle size distribution is uniform and narrow, and has good monodispersity.

[0021] Step S2: mixing and dissolving: a complexing agent (citric acid 3 wt%), a composite inhibitor (DBSA 0.2 wt%+PASP 0.4 wt%), and an oxidizing agent ammonium persulfate ((NH4)2S2O8) are sequentially added, and stirred in a magnetic stirrer (500 rpm, 25±1 DEG C) for 30 minutes. An important control point is that the oxidizing agent and the inhibitor are added in sequence to avoid early reaction (HPLC monitoring no by-product is generated).

[0022] Step S3 pH adjustment: 10% tetramethylammonium hydroxide (TMAH) solution was added dropwise to pH 10.0-10.5, and the pH meter (Mettler Toledo, accuracy ±0.01) was monitored in real time. Among them, the mechanism of action: alkaline conditions enhance the dissociation of the carboxyl group of PASP, forming a dense passivation film (QCM-D detects film thickness 1.50 nm).

[0023] Step S4 aging and filtration: standing at room temperature for 12 hours, removing trace agglomerates by 0.2 μm nylon filter membrane. Among them, verify stability: no sedimentation within 30 days (Turbiscan Lab index TSI <1.0), viscosity remains 3.2±0.3 cP (Brookfield DV2T).

[0024] Example 1 The polishing solution of the embodiment includes the following components: α-spherical nano-alumina (preferably particle size 50 nm): 12wt%, ammonium persulfate ((NH4)2S2O8): 2wt%, citric acid: 3wt%, polyaspartic acid (PASP): 0.4wt%, DBSA 0.2wt%, polyether polyol (PEG6000): 0.1wt%, ultra-pure water to 100wt%, pH adjusted to 10.0~10.5 by TMAH.

[0025] The preparation process of the polishing solution of the embodiment mainly includes the following steps: Pre-dispersion stage: α-spherical nano-alumina is added to ultra-pure water and PEG6000, and ultrasonic dispersion is carried out at 40 kHz / 300 W for 2 hours, with the temperature controlled at 25±1℃; dynamic light scattering detection result: D50=50 nm, PDI=0.12, Zeta potential-35 mV.

[0026] Mixed dissolution stage: citric acid (3wt%) → composite inhibitor (DBSA 0.2wt%+PASP 0.4wt%) → ammonium persulfate (2wt%) are added in turn, 500 rpm stirring for 30 minutes to avoid the early reaction of the oxidizing agent.

[0027] pH adjustment and aging: 10% TMAH is added dropwise, the pH is adjusted to 10.5±0.2, and it is left to stand for 12 hours and filtered through a 0.2 μm nylon filter membrane.

[0028] To verify the performance advantages of the polishing liquid in the silicon carbide (SiC) CMP process, systematic comparative experiments were conducted on different formula systems, covering removal rate, surface roughness, scratch density, slurry stability, and metal residue control. The polishing experiment conditions are as follows: equipment model: Strasbaugh 6EC, polishing pad: AGC-PAD3 cerium oxide soft pad, slurry flow: 200 mL / min, pressure: 3 psi, rotation speed: 60 rpm, time: 5 min.

[0029] Table 1 Performance data of different formula systems of polishing liquid

[0030] From the above data comparison, it can be seen that: (1) The removal rate of silicon carbide treated by the preferred embodiment 1 of the present application reaches 80 nm / min, which is higher than 20 nm / min of the existing traditional aluminum oxide system comparative example 3, significantly improving the production efficiency; (2) The silicon carbide polished by the silicon carbide treated by the embodiments 1-3 of the present application reaches sub-nanometer roughness (Ra=0.7 nm), which is suitable for advanced processes; (3) The scratch density of the silicon carbide treated by the embodiments 1 and 3 of the present application is <1 / cm², which is significantly reduced compared with the traditional process, meeting the production needs of high-end devices; (4) The particle size stability change of the polishing liquid of the embodiments of the present application is less than 1% in 30 days, and the Turbiscan index is <1.0, fully reflecting the excellent storage stability of the polishing liquid.

[0031] In addition, the metal residues of the silicon carbide treated by the embodiment 1 of the present application are tested by VPD-ICPMS / XPS, which shows that the metal residues are lower than 5×10 10 atoms / cm², which fully meets the stringent cleanliness standards of semiconductor manufacturing.

[0032] And XPS analysis and nanoindentation test further show that the silicon carbide surface treated by the CMP of the present application forms a uniform oxide layer (Si-O bond ratio increases to 62%), which reduces the surface hardness by about 40%, significantly improves the brittleness of the wafer surface, and is more beneficial to subsequent epitaxial growth and other processes, thereby effectively improving the overall wafer yield.

Claims

1. A CMP polishing slurry specifically for silicon carbide wafers, characterized in that, The polishing slurry consists of the following components by mass percentage: α-Spherical nano-alumina: 5~12%, average particle size 50 nm, sphericity ≥95%; Complexing agent: 1~5%; Complex inhibitor: 0.1~1.0%, composed of polyaspartic acid and dodecylbenzenesulfonic acid in a mass ratio of (1.5~3):1; Oxidizing agent: 0.5~3%; Dispersing stabilizer: 0.05~0.5%, wherein the dispersing stabilizer is a polyether polyol; pH adjuster: Tetramethylammonium hydroxide, to adjust the pH of the polishing solution to 8-11; The rest is deionized water or ultrapure water.

2. The polishing slurry according to claim 1, characterized in that, The mass ratio of polyaspartic acid to dodecylbenzenesulfonic acid is 2:1, and the content of the composite inhibitor is 0.5~0.6%.

3. The polishing slurry according to claim 1, characterized in that, The complexing agent is citric acid, with a content of 3%.

4. The polishing slurry according to claim 1, characterized in that, The oxidant is ammonium persulfate, with a content of 1.5-2.5%.

5. The polishing slurry according to claim 1, characterized in that, The dispersant stabilizer is PEG 6000, with a content of 0.1%.

6. The polishing slurry according to claim 1, characterized in that, The pH value adjustment range is 10.0~10.

5.

7. A method for preparing the polishing slurry according to any one of claims 1-6, characterized in that, Includes the following steps: Step S1 Pre-dispersion: Add α-spherical nano-alumina to polyether polyol and ultrapure water or deionized water, and perform ultrasonic dispersion. The ultrasonic conditions are 40 kHz, 300 W, and the treatment is carried out for 2 hours, with the temperature controlled at ≤30℃. Step S2 Mixing and Dissolving: Add complexing agent, complex inhibitor, and oxidant, stir magnetically for 30 minutes at 500 rpm and 25±1℃; Step S3 pH adjustment: Adjust the pH of the mixture to 8-11 using a 10% tetramethylammonium hydroxide solution; Step S4: Aging and Filtration: After standing at room temperature for 12 hours, filter through a filter membrane with a pore size of 0.2 μm to obtain the CMP polishing solution.

8. The preparation method according to claim 7, characterized in that, During the mixing and dissolution process in step S2, the complexing agent, complex inhibitor, and oxidant are added in the following order:

9. The preparation method according to claim 8, characterized in that, In step S3, pH adjustment, tetramethylammonium hydroxide solution is used to adjust the pH of the mixture to 10.0~10.5.

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