Plasma liquid nano-polishing solution applied to conductive SiC material and polishing process thereof

Abstract

The application provides a kind of plasma liquid nano polishing liquid applied to conductive SiC material, containing main conductive salt, oxidizing agent, electrolyte stabilizer, strong chelating agent, dispersing agent, multifunctional activator, pH buffer, intelligent corrosion inhibitor and rheological modifier, the main conductive salt includes lithium perchlorate, the oxidizing agent includes sodium nitrate, the electrolyte stabilizer includes sodium sulfate and / or potassium sulfate, the strong chelating agent includes diethylene triamine pentamethylene phosphonic acid, the dispersing agent includes at least one of sodium hexametaphosphate, sodium tripolyphosphate or sodium lignosulfonate, the multifunctional activator includes lithium bisfluorosulfonylimide, the pH buffer includes at least one of boric acid, acetic acid, succinic acid, the intelligent corrosion inhibitor includes cerium nitrate, and the rheological modifier includes hydroxyethyl cellulose. Through the plasma liquid nano polishing liquid and its polishing process of the application, the preparation of high-efficiency, low-damage and super-smooth SiC surface is realized.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material surface treatment technology, specifically relating to a PLNP (Plasma Electrolytic Nano Polishing) polishing slurry formulation and matching polishing process suitable for conductive silicon carbide (Type 4 silicon carbide: 4H-SiC, conductivity 10S / m), single crystal substrates or epitaxial wafers. Background Technology

[0002] Conductive SiC (type 4 silicon carbide: 4H-SiC, with an electrical conductivity of 10 S / m) is an ideal substrate material for manufacturing high-voltage, high-temperature, and high-frequency power devices due to its wide bandgap, high thermal conductivity, and high breakdown field strength. However, its extremely high hardness (Mohs hardness 9.2-9.5) and chemical inertness make it extremely difficult to obtain an ultra-smooth, damage-free surface.

[0003] Traditional chemical mechanical polishing (CMP), while achieving good surface quality, suffers from drawbacks such as low efficiency, high cost, and susceptibility to subsurface damage. Plasma liquid nanopolishing technology utilizes a stable vapor plasma layer (VGE) formed on the workpiece surface for global planarization, offering advantages such as high efficiency and the absence of mechanical stress. However, when applied to SiC polishing, existing plasma liquid nanopolishing technologies generally suffer from problems such as poorly targeted polishing slurry formulations, coarse process control leading to uneven surface quality, and susceptibility to microscopic defects, making it difficult to meet the stringent substrate surface requirements of high-performance SiC devices. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of uneven surface quality and difficulty in balancing efficiency and damage control in existing conductive SiC materials, and to achieve efficient, low-damage, and ultra-smooth SiC surface preparation.

[0005] To achieve the above objectives, this invention provides a plasma liquid nanopolishing slurry formulation and matching polishing process specifically for conductive SiC materials.

[0006] This invention provides a plasma liquid nanopolishing slurry for use with conductive SiC materials (preferably, the conductive SiC material is type 4 silicon carbide: 4H-SiC, with a conductivity of 10 S / m). The slurry contains a main conductive salt, an oxidant, an electrolyte stabilizer, a potent chelating agent, a dispersant, a multifunctional activator, a pH buffer, a smart corrosion inhibitor, and a rheology modifier. The main conductive salt includes lithium perchlorate; the oxidant includes sodium nitrate; the electrolyte stabilizer includes sodium sulfate and / or potassium sulfate; the potent chelating agent includes diethylenetriaminepentamethylphosphonic acid; the dispersant includes at least one of sodium hexametaphosphate, sodium tripolyphosphate, or sodium lignosulfonate; the multifunctional activator includes lithium difluorosulfonylimide; the pH buffer includes at least one of boric acid, acetic acid, and succinic acid; the smart corrosion inhibitor includes cerium nitrate; and the rheology modifier includes hydroxyethyl cellulose.

[0007] Preferably, the plasma liquid nanopolishing solution comprises, by mass percentage, 1.5% to 2.0% of a main conductive salt, 0.6% of an oxidant, 0.5% of an electrolyte stabilizer, 0.7% of a potent chelating agent, 0.4% of a dispersant, 0.5% to 0.6% of a multifunctional activator, 0.3% of a pH buffer, 0.05% to 0.1% of a smart corrosion inhibitor, and 0.45% to 0.5% of a rheology modifier, with the balance being water.

[0008] Preferably, the main conductive salt in the plasma liquid nanopolishing solution has a mass percentage concentration of 1.5% to 2.0%, and more preferably 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% and the range thereof.

[0009] Preferably, the oxidant in the plasma liquid nanopolishing solution has a mass percentage concentration of 0.6%.

[0010] Preferably, the electrolyte stabilizer in the plasma liquid nanopolishing solution has a mass percentage concentration of 0.5%.

[0011] Preferably, the mass percentage concentration of the potent chelating agent in the plasma liquid nanopolishing solution is 0.7%.

[0012] Preferably, the mass percentage concentration of the dispersant in the plasma liquid nanopolishing slurry is 0.4%.

[0013] Preferably, the mass percentage concentration of the multifunctional activator in the plasma liquid nanopolishing slurry is 0.5% to 0.6%, and more preferably 0.5%, 0.55%, 0.6% or a range thereof.

[0014] Preferably, the mass percentage concentration of the pH buffer in the plasma liquid nanopolishing solution is 0.3%.

[0015] Preferably, the mass percentage concentration of the intelligent corrosion inhibitor in the plasma liquid nanopolishing slurry is 0.05% to 0.1%, and more preferably 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1% and the range thereof.

[0016] Preferably, the mass percentage concentration of the rheology modifier in the plasma liquid nanopolishing slurry is 0.45% to 0.5%, more preferably 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, 0.50% and the range thereof.

[0017] In a preferred embodiment of the present invention, the plasma liquid nanopolishing solution comprises, by mass percentage, 1.5% to 2.0% lithium perchlorate, 0.6% sodium nitrate, 0.5% electrolyte stabilizer (preferably 0.5% sodium sulfate; or, preferably 0.5% potassium sulfate; or, preferably a combination of sodium sulfate and potassium sulfate with a total concentration of 0.5%), 0.7% diethylenetriaminepentamethylphosphonic acid (DTPMP), 0.4% dispersant (preferably 0.4% sodium hexametaphosphate; or, preferably 0.4% sodium tripolyphosphate; or, preferably 0.4% sodium lignosulfonate; or, preferably a combination of two or three of sodium hexametaphosphate, sodium tripolyphosphate, and sodium lignosulfonate, with a total concentration of 0.4%), and 0.5% to 2.0% sodium perchlorate. 0.6% lithium bis(fluorosulfonyl)imide (LiFSI), 0.3% pH buffer (preferably 0.3% boric acid; or, more preferably 0.3% acetic acid; or, more preferably 0.3% succinic acid; or, more preferably a combination of two or three of boric acid, acetic acid, and succinic acid, with a total concentration of 0.3%), 0.05% to 0.1% cerium nitrate, and 0.45% to 0.5% hydroxyethyl cellulose, with the balance being water.

[0018] The present invention also provides a polishing process for a plasma liquid nanopolishing slurry according to any one of the above claims, wherein the plasma liquid nanopolishing slurry is used to polish conductive SiC materials.

[0019] Preferably, the conductive SiC material includes silicon carbide (SiC) single crystal substrates or epitaxial wafers, etc.

[0020] A polishing process for polishing conductive SiC materials using the aforementioned plasma liquid nano-polishing slurry involves adding the plasma liquid nano-polishing slurry and the conductive SiC material to a polishing apparatus for polishing, and includes the following steps:

[0021] Step 1: Main polishing stage: Set the initial power supply voltage to 80 V, and linearly increase the voltage from 80 V to the target DC working voltage of 360 V at a constant rate; maintain the voltage of 360 V for polishing, and control the polishing fluid temperature to be kept at 80±2℃;

[0022] Step 2: Asymmetric AC pulse co-polishing: A high-frequency asymmetric square wave pulse signal is superimposed on the 360 ​​V DC voltage during the main polishing stage in Step 1;

[0023] Step 3: Adaptive control: Acquire the broadband acoustic signal generated by plasma discharge, and calculate the root mean square value (RMS) of the acoustic signal in the 200-500 kHz frequency band in real time; if the RMS value meets the requirements, it is determined that the surface of the conductive SiC material is initially flat; at this time, adjust the DC working voltage and pulse signal to perform final trimming on the conductive SiC material.

[0024] Step 4: In-situ thermo-electric synergistic annealing post-treatment: After the final finishing in Step 3, without disconnecting the power and without removing the workpiece, rapidly heat the plasma liquid nano-polishing liquid to the preset temperature within a preset time; at the preset temperature, reduce the DC voltage and perform constant voltage treatment; after constant voltage treatment, turn off the power, remove the workpiece, and clean and dry it.

[0025] Preferably, in any of the above embodiments, the pH of the system for polishing conductive SiC materials using the plasma liquid nanopolishing slurry is stable in a weakly acidic range of 6.0-7.5. The pH of the plasma liquid nanopolishing slurry is 6.0-7.5.

[0026] In any of the above-mentioned embodiments, in step 1, the voltage is linearly increased from 80 V to the target DC operating voltage of 360 V at a constant rate of 8 to 10 V / s. A further preferred constant rate is 8, 9, or 10 V / s or a range thereof.

[0027] Preferably, in step 2, the pulse parameters of the high-frequency asymmetric square wave pulse signal are: positive pulse amplitude +40~50 V, pulse width 45 μs; negative pulse amplitude -15 V, pulse width 5 μs; frequency 10 kHz. Preferably, in step 1, the high-frequency asymmetric square wave pulse signal is superimposed simultaneously with the start of polishing when the target DC operating voltage reaches 360 V.

[0028] In any of the above-mentioned preferred embodiments, in step 3, a high-frequency acoustic emission sensor is provided on the side wall of the polishing tank to collect broadband acoustic signals generated by plasma discharge, wherein the center frequency of the high-frequency acoustic emission sensor is 1 MHz.

[0029] In any of the above-mentioned preferred embodiments, in step 3, the RMS value of the acoustic signal in the 200-500kHz frequency band is calculated in real time by a signal processing system.

[0030] In any of the above preferred embodiments, in step 3, if the RMS value meets the requirements, the specific method for determining that the surface of the conductive SiC material is initially smooth is as follows: when the standard deviation of the RMS value drops to within 30% of the initial stage (the initial stage being the first 5 seconds of polishing in the main polishing stage of step 1) within 10 consecutive seconds, and the real-time average RMS value drops to 45-60% of the set threshold within 10 consecutive seconds, it is determined that the surface of the conductive SiC material has been initially smoothed and the plasma gas layer has become stable. The set threshold is the peak value of the RMS monitored at the start of polishing in the main polishing stage of step 1. The maximum RMS value monitored in the first few seconds of entering the main polishing stage, generally around 5 seconds, is the peak value of the RMS.

[0031] The polishing device of this invention is equipped with a high-frequency acoustic emission sensor and a signal processing system. Both the high-frequency acoustic emission sensor and the signal processing system are conventional components in the prior art. When installed in the polishing device according to conventional methods, they can acquire broadband acoustic signals generated by plasma discharge and calculate the RMS value of the acoustic signal in the 200-500 kHz frequency band in real time using the signal processing system. Preferred high-frequency acoustic emission sensors and signal processing systems of this invention include, but are not limited to, Xiangyang Lianle, model: AE104S, paired with a PXDAQ series data acquisition card. After the high-frequency acoustic emission sensor acquires the signal, the signal processing system calculates the root mean square value (RMS value) of the acoustic signal in the 200-500 kHz frequency band in real time.

[0032] In any of the above-mentioned preferred embodiments, the specific method for final finishing in step 3 is as follows: Based on the RMS value, when it is determined that the surface of the conductive SiC material has been initially smoothed and the plasma gas layer has stabilized, the DC operating voltage is reduced from 360 V to 300 V, and simultaneously the negative amplitude of the pulse signal is adjusted from -15 V to -8 V. This mode is maintained for 2-3 minutes to achieve the final finishing of the nanoscale contour of the conductive SiC material surface. This method avoids over-polishing.

[0033] In any of the above-mentioned preferred embodiments, in step 4, the plasma liquid nanopolishing liquid is rapidly heated to a preset temperature within a preset time; preferably, the preset time is 30s; preferably, the preset temperature is 98℃.

[0034] In any of the above-mentioned preferred embodiments, in step 4, the DC voltage is lowered and constant voltage treatment is performed at a preset temperature; preferably, the preset temperature is 98°C, and the preferred constant voltage treatment condition is a DC voltage of 100~120 V; preferably, the constant voltage treatment time is 30~40 seconds, and more preferably 30s, 35s, 40s and the range therebetween.

[0035] In any of the above-mentioned preferred embodiments, in step 4, after the 300 V stable polishing is completed (i.e. after the final finishing), the power is not interrupted and the workpiece is not removed; within 30 seconds, the temperature of the plasma liquid nanopolishing liquid is rapidly increased from 80°C to 98°C; at the high temperature of 98°C, the DC voltage is reduced to 100~120 V and processed for 30~40 seconds; after the processing is completed, the power is turned off, the workpiece is removed, and it is cleaned and dried with deionized water and / or organic solvent.

[0036] The present invention also provides the application of the plasma liquid nanopolishing slurry or the polishing process according to any one of the preceding claims in the preparation of conductive silicon carbide materials.

[0037] The present invention relates to a plasma liquid nanopolishing slurry and polishing process, which achieves uniform and stable plasma discharge and nanoscale precision leveling and polishing by rationally compounding components such as main conductive salt, oxidant, stabilizer, and chelating agent.

[0038] Lithium perchlorate provides high mobility Ions significantly improve the conductivity of the plasma liquid nanopolishing fluid, reduce the arc initiation and maintenance voltage of the plasma gas layer (VGE), and promote the formation of a uniform and stable plasma discharge layer.

[0039] Sodium nitrate decomposes at the anodic potential to produce reactive oxygen species, which promote the electrochemical oxidation of Si atoms on the SiC surface, generating easily removable silicon oxides. ), to control the basic oxidation rate.

[0040] Electrolyte stabilizers provide stable Ions enhance the ionic strength of the solution, buffer local pH fluctuations, and ensure polishing uniformity.

[0041] Diethylenetriamine pentamethylphosphonic acid effectively chelates polishing products and metal ions, preventing the precipitation of silicic acid or metal hydroxides, keeping the polishing solution clean for a long time, and avoiding secondary damage to particles.

[0042] The dispersant is adsorbed on the surface of fine particles, preventing particle agglomeration through steric hindrance and electrostatic repulsion, and also helps to disperse and remove the detached oxide particles in the solution.

[0043] Lithium difluorosulfonylimide increases reactive sites, and its decomposition products help form an extremely thin oxide layer on the surface of the conductive SiC material, thereby changing the surface chemical state of the conductive SiC material and improving the material removal rate and leveling efficiency.

[0044] The pH buffer stabilizes the working pH in a weakly acidic range of 6.0-7.5, which is beneficial for the controllable formation and dissolution of the oxide layer on the SiC surface.

[0045] Cerium nitrate forms a cerium-containing deposition film at the anodic potential. This film preferentially covers the micro-protrusion regions with excessive oxidation rates, inhibiting local over-corrosion and achieving "self-regulating" intelligent protection. This significantly reduces the surface roughness (Ra) and defect density of the conductive SiC material.

[0046] Hydroxyethyl cellulose improves the viscosity and stability of the polishing slurry, thereby improving the surface spreadability and heat dissipation performance of the conductive SiC material.

[0047] In this invention, lithium bis(fluorosulfonyl)imide (LiFSI) and cerium nitrate (Ce(NO3)3) work synergistically when used in combination.

[0048] The working principle of cerium nitrate Ce(NO3)3:

[0049] In plasma-liquid nanopolishing systems, cerium nitrate acts as a smart corrosion inhibitor. At anodic potential, Ce... 3+ Ions migrate to the SiC surface and are oxidized to Ce. 4+ Ce 4+ Exhibiting high oxidizing properties, it preferentially undergoes reduction reactions in micro-protrusion regions on the conductive SiC material surface where activity is high and oxidation rates are too fast, and hydrolyzes to form a Ce(OH)3 / CeO2 deposition film. This dense cerium-containing passivation film can effectively suppress local over-corrosion, achieving a self-regulating protective function, thereby significantly reducing Ra and micro-defect density.

[0050] LiFSI and Synergistic mechanism:

[0051] Lithium bisfluorosulfonylimide (LiFSI), as a strong electrolyte, provides high ionic conductivity due to its high degree of dissociation, promoting uniform discharge at the polished interface. Simultaneously, the fluorine-containing components generated from the decomposition of LiFSI contribute to the activation of the SiC surface.

[0052] When LiFSI is combined with cerium nitrate, the uniform electric field created by the former promotes the orderly adsorption and uniform film formation of Ce³⁺ on the conductive SiC substrate surface, while the latter precisely controls the oxidation rate. The synergistic effect of these two components ensures both a high material removal rate (MRR) and ultra-low surface roughness of the conductive SiC material.

[0053] This invention experimentally verified the synergistic effect of LiFSI and cerium nitrate composite. Lithium bis(fluorosulfonyl)imide (LiFSI) promoted the uniform distribution and rapid film formation of cerium nitrate (Ce(NO3)3) at the interface, while the self-regulating protective function of cerium nitrate (Ce(NO3)3) compensated for the tendency of LiFSI to over-polish. Ultimately, the surface roughness of the conductive SiC material was reduced by up to approximately 66.32% and the defect density by up to approximately 48.78% compared to the single component. This significant "1 + 1 > 2" effect is due to the synergistic effect of lithium bis(fluorosulfonyl)imide (LiFSI) and cerium nitrate (Ce(NO3)3)). The result of synergistic effect.

[0054] The plasma liquid nanopolishing slurry and polishing process provided by this invention are specifically suitable for conductive SiC materials. The conductive SiC material exhibits low surface roughness after polishing, with a surface roughness (Ra) of 0.030 μm to 0.047 μm and a surface defect density (EPD) of 4000 / cm² to 5800 / cm², meeting the process requirements for semiconductor material surfaces. The polishing process provided by this invention is simple and easy to implement, suitable for the needs of industrial mass production. Attached Figure Description

[0055] Figure 1 The figures show the performance test results of preferred embodiments 1-5 and comparative examples 1-5 of the present invention. Detailed Implementation

[0056] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] Table 1 below shows the preferred polishing liquid formula of the present invention, as well as the working principle and core function of its main components.

[0058] Table 1:

[0059]

[0060]

[0061] The preferred polishing process steps of this invention are as follows:

[0062] Step 1: Main polishing stage:

[0063] The initial power supply voltage is set to 80 V, and the voltage is linearly increased from 80 V to the target DC operating voltage of 360 V at a constant rate of 8~10 V / s. Polishing begins while maintaining the 360 ​​V voltage, and the polishing solution temperature is kept at 80±2℃. Preferably, the polishing device is equipped with an external circulation temperature control system to maintain the polishing solution temperature at 80±2℃. The external circulation temperature control system is a conventional component of existing ionic liquid nanopolishing solution devices.

[0064] Step 2: Asymmetric AC pulse (ACP) co-polishing:

[0065] During the main polishing stage (on a DC voltage of 360 V), a high-frequency asymmetric square wave pulse signal is superimposed. The pulse parameters are: positive pulse amplitude +40~50 V, pulse width 45 μs; negative pulse amplitude -15 V, pulse width 5 μs; frequency 10 kHz.

[0066] Step 3: Adaptive Control

[0067] A high-frequency acoustic emission sensor (center frequency 1 MHz) is installed on the sidewall of the polishing tank to collect broadband acoustic signals generated by plasma discharge in real time. The signal processing system calculates the root mean square (RMS) value of the acoustic signal in the 200-500 kHz frequency band in real time. When the standard deviation of the RMS value drops to within 30% of the initial stage (the initial stage being the first 5 seconds of polishing in step 1), and the real-time average RMS value drops to 45-60% of the set threshold in 10 seconds, it is determined that the discharge intensity has been halved, the gas layer is stabilizing, and the surface of the conductive SiC material has been initially smoothed, and the plasma gas layer is stabilizing. At this time, the DC operating voltage is reduced from 360 V to 300 V, and the negative amplitude of the pulse signal is adjusted from -15 V to -8 V. This mode is maintained for 2-3 minutes to achieve the final trimming of the nanoscale contour of the conductive SiC material surface and avoid over-polishing. The set threshold is the peak value of the RMS monitored at the beginning of polishing in step 1.

[0068] Step 4: Post-annealing treatment after in-situ thermo-electric synergistic annealing:

[0069] After stable polishing at 300 V, the power is not interrupted and the workpiece is not removed. Within 30 seconds, the temperature of the plasma liquid nanopolishing solution is rapidly increased from 80°C to 98°C (near boiling point). At this high temperature, the DC voltage is reduced to 100-120 V, and the treatment lasts for 30-40 seconds. After the treatment, the power is turned off, the workpiece is removed, and it is cleaned and dried with deionized water and an organic solvent. Preferably, the polishing tank of the polishing device is equipped with a high-efficiency heater to rapidly increase the temperature of the plasma liquid nanopolishing solution from 80°C to 98°C (near boiling point). The high-efficiency heater is a conventional component of existing plasma liquid nanopolishing devices.

[0070] Preferred test method of the present invention:

[0071] Surface roughness (Ra) measurement:

[0072] A JIMTEC TR200 handheld surface roughness tester was used. Before testing, the samples were ultrasonically cleaned for 5 minutes each with anhydrous ethanol and deionized water, and then dried with high-purity nitrogen. The evaluation length was set to 0.8 mm, the sampling length to 0.25 mm, and the testing speed to 0.5 mm / s. Five different test areas were randomly selected on the sample surface for testing, and the arithmetic mean was taken as the final Ra value (unit: μm).

[0073] Surface defect density (EPD) measurement:

[0074] The SGO-HD830M650X ultra-high resolution industrial microscope (650×) from Shenzhen Optics Valley Optical Instrument Co., Ltd. was used. Samples were sequentially ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 5 min each, and then dried with high-purity nitrogen. The magnification was adjusted to 650×, and five fields of view were randomly selected for photographing. The number of defects such as scratches, pits, and residual particles was counted using the accompanying software. The EPD was calculated using the formula: EPD = Σ (number of defects in each field of view) / (5 × area of ​​a single field of view), with units of defects per cm².

[0075] The polishing device described in this invention is a conventional plasma liquid nanopolishing device in the prior art.

[0076] The polishing device is equipped with a high-frequency asymmetric square wave pulse signal device, preferably from Xi'an Synchronous Electronics Technology Co., Ltd., model: SYN5610.

[0077] The polishing device is equipped with a high-frequency acoustic emission sensor and signal processing system, preferably from Xiangyang Lianle, model: AE104S, and is paired with a PXDAQ series data acquisition card. The high-frequency acoustic emission sensor is mounted on the side wall of the polishing tank.

[0078] Example 1

[0079] The plasma liquid nanopolishing slurry was composed of: lithium perchlorate 1.8 wt%, sodium nitrate 0.6 wt%, sodium sulfate 0.5 wt%, DTPMP 0.7 wt%, sodium hexametaphosphate 0.4 wt%, LiFSI 0.55 wt%, boric acid 0.3 wt%, cerium nitrate 0.075 wt%, and hydroxyethyl cellulose 0.475 wt%. The process was performed as follows: stepped voltage ramp rate 9 V / s; ACP parameters were +45 V / 45 μs and -15 V / 5 μs; adaptive voltage reduction to 300 V / -8 V for 2.5 min for fine polishing; in-situ annealing involved heating to 98℃ within 30 s and treating at 110 V for 35 s. The surface roughness (Ra) after polishing was measured to be 0.032 μm, and the surface defect density (EPD) was 4200 / cm².

[0080] Example 2

[0081] In the plasma liquid nanopolishing slurry, the proportions of lithium perchlorate (2.0 wt%), LiFSI (0.60 wt%), and cerium nitrate (0.10 wt%) were increased, and potassium sulfate was used instead of sodium sulfate. Sodium tripolyphosphate was selected as the dispersant. The process parameters were adjusted as follows: step voltage ramp rate to 10 V / s, ACP positive pulse amplitude to +50 V, annealing voltage to 120 V, and processing time to 40 seconds. The surface roughness (Ra) after polishing was measured to be 0.041 μm, and the surface defect density (EPD) was 5800 / cm².

[0082] Example 3

[0083] The concentrations of lithium perchlorate, LiFSI, and cerium nitrate in the polishing slurry were reduced to 1.5 wt%, 0.50 wt%, and 0.05 wt%, respectively. Sodium lignosulfonate was used as the dispersant, and succinic acid was used as the pH buffer. The process parameters were exactly the same as in Example 1. The surface roughness (Ra) after polishing was measured to be 0.047 μm, and the surface defect density (EPD) was 5200 / cm².

[0084] Example 4

[0085] This embodiment uses the exact same formulation as Example 1, except that the dispersant is replaced with sodium tripolyphosphate and the sodium sulfate is replaced with potassium sulfate. The process parameters are exactly the same as in Example 1. Testing showed that the surface roughness (Ra) after polishing was 0.034 μm and the surface defect density (EPD) was 4600 / cm².

[0086] Example 5

[0087] This embodiment uses the exact same formula as Example 1, only adjusting the in-situ annealing process parameters, setting the annealing voltage to 120 V and shortening the processing time to 30 seconds. Testing showed that the surface roughness (Ra) after polishing was 0.030 μm and the surface defect density (EPD) was 4000 / cm².

[0088] Comparative Example 1

[0089] Comparative Example 1, based on Example 1, removed lithium bis(fluorosulfonyl)imide (LiFSI) and used an equal mass of sodium chloride to make up the mass fraction of the system. The process parameters were the same as in Example 1. Testing revealed that due to the lack of strong ion conduction and activation provided by LiFSI, the plasma gas layer was extremely unstable, leading to a sharp deterioration in the surface roughness (Ra) after polishing to 0.120 μm, and a surface defect density (EPD) as high as 9500 / cm².

[0090] Comparative Example 2

[0091] Comparative Example 2, based on Example 1, removed cerium nitrate and used deionized water to replenish the system mass fraction. The process parameters were the same as in Example 1. Testing revealed that due to the lack of a dynamic protective film formed by cerium nitrate, the surface micro-protrusions underwent uncontrolled etching under plasma impact, resulting in a surface roughness (Ra) of 0.095 μm and a surface defect density (EPD) of 8200 / cm² after polishing.

[0092] Comparative Example 3

[0093] Comparative Example 3 used the same formulation as Example 1, but changed the asymmetric pulse to a symmetric pulse during the main polishing stage, i.e., a positive amplitude of +30 V / 25 μs and a negative amplitude of -30 V / 25 μs. The rest of the process was the same as in Example 1. Testing revealed that due to the lack of the asymmetric synergistic mechanism of "positive activation and negative leveling" in the symmetric pulse, the surface underwent periodic over-etching, exhibiting regular micro-ripples. After polishing, the surface roughness (Ra) was 0.068 μm, and the surface defect density (EPD) was 7500 / cm².

[0094] Comparative Example 4

[0095] This comparative example uses the formulation of Example 1, but omits the acoustic emission (AE) adaptive control step. Specifically, after a fixed 15-minute run at 360 V during the main polishing stage, annealing is performed directly without voltage-reduced fine polishing. Testing revealed that due to the lack of leveling effect from adaptive fine polishing, the surface energy distribution was uneven, resulting in a surface roughness (Ra) of 0.061 μm and a surface defect density (EPD) of 8000 / cm² after polishing.

[0096] Comparative Example 5

[0097] This comparative example uses the formulation and polishing process of Example 1, but after completing the fine polishing mode, the power is directly turned off and the workpiece is removed without subsequent in-situ thermo-electric synergistic annealing treatment. Testing revealed that due to the lack of surface repair and stress relief from the annealing step, the surface roughness (Ra) after polishing was 0.055 μm, and the surface defect density (EPD) was 7200 / cm².

[0098] Table 2 shows the formulations and process parameters of Examples 1-5 and Comparative Examples 1-5; Table 3 shows the performance test results of Examples 1-5 and Comparative Examples 1-5. Figure 1 The figures shown are performance test results of Examples 1-5 and Comparative Examples 1-5.

[0099] Table 2:

[0100]

[0101] Table 3:

[0102]

[0103] Example 6

[0104] Example 6 included control group 1, control group 2, control group 3, and the present invention group, to experimentally verify the synergistic effect of LiFSI and Ce(NO3)3. The polishing solution formulations and test results for each experimental group are shown in Table 4.

[0105] Table 4:

[0106]

[0107] In Table 4, the composition of the base solution is 1.8 wt% lithium perchlorate, 0.6 wt% sodium nitrate, 0.5 wt% sodium sulfate, 0.7 wt% DTPMP, 0.4 wt% sodium hexametaphosphate, 0.3 wt% boric acid, and 0.475 wt% hydroxyethyl cellulose.

[0108] Control group 1, control group 2, control group 3 and the present invention group were processed according to the process steps described in Example 1.

[0109] Based on the data in Table 4, it can be inferred that although adding lithium bis(fluorosulfonyl)imide (LiFSI) or cerium nitrate (Ce(NO3)3) alone can reduce surface roughness to a certain extent, it is difficult to achieve the expected goal and the suppression effect on surface micro-defects is limited.

[0110] When used in combination, lithium bis(fluorosulfonyl)imide (LiFSI) promotes the uniform distribution and rapid film formation of cerium nitrate (Ce(NO3)3) at the interface, while the self-regulating protective function of cerium nitrate (Ce(NO3)3) compensates for the tendency of lithium bis(fluorosulfonyl)imide (LiFSI) to cause over-polishing. Ultimately, the surface roughness is reduced by up to approximately 66.32% and the defect density is reduced by up to approximately 48.78% compared to the single component. This significant "1 + 1 > 2" effect is the result of the synergistic effect of lithium bis(fluorosulfonyl)imide (LiFSI) and cerium nitrate (Ce(NO3)3).

[0111] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A plasma liquid nanopolishing slurry for conductive SiC materials, comprising a main conductive salt, an oxidant, an electrolyte stabilizer, a potent chelating agent, a dispersant, a multifunctional activator, a pH buffer, a smart corrosion inhibitor, and a rheology modifier, characterized in that, The primary conductive salt includes lithium perchlorate, the oxidant includes sodium nitrate, the electrolyte stabilizer includes sodium sulfate and / or potassium sulfate, the potent chelating agent includes diethylenetriaminepentamethylphosphonic acid, the dispersant includes at least one of sodium hexametaphosphate, sodium tripolyphosphate, or sodium lignosulfonate, the multifunctional activator includes lithium difluorosulfonylimide, the pH buffer includes at least one of boric acid, acetic acid, and succinic acid, the intelligent corrosion inhibitor includes cerium nitrate, and the rheology modifier includes hydroxyethyl cellulose.

2. The plasma liquid nanopolishing slurry as described in claim 1, characterized in that, It includes a main conductive salt with a mass percentage concentration of 1.5% to 2.0%, an oxidant of 0.6%, an electrolyte stabilizer of 0.5%, a strong chelating agent of 0.7%, a dispersant of 0.4%, a multifunctional activator of 0.5% to 0.6%, a pH buffer of 0.3%, a smart corrosion inhibitor of 0.05% to 0.1%, and a rheology modifier of 0.45% to 0.5%, with the balance being water.

3. The polishing process of the plasma liquid nanopolishing slurry according to claim 1 or 2, wherein the conductive SiC material is polished using the plasma liquid nanopolishing slurry, includes the following steps: Step 1: Main polishing stage: Set the initial power supply voltage to 80 V, and linearly increase the voltage from 80 V to the target DC working voltage of 360 V at a constant rate; maintain the voltage of 360 V for polishing, and control the polishing fluid temperature to be kept at 80±2℃; Step 2: Asymmetric AC pulse co-polishing: A high-frequency asymmetric square wave pulse signal is superimposed on the 360 ​​V DC voltage during the main polishing stage; Step 3: Adaptive control: Acquire the broadband acoustic signal generated by plasma discharge, and calculate the root mean square value (RMS) of the acoustic signal in the 200-500kHz frequency band in real time; if the RMS value meets the requirements, it is determined that the surface of the conductive SiC material is initially flat; at this time, adjust the DC working voltage and pulse signal to perform final trimming on the conductive SiC material. Step 4: In-situ thermo-electric synergistic annealing post-treatment: After the final finishing in Step 3, without disconnecting the power and without removing the workpiece, rapidly heat the plasma liquid nano-polishing liquid to the preset temperature within a preset time; at the preset temperature, reduce the DC voltage and perform constant voltage treatment; after constant voltage treatment, turn off the power, remove the workpiece, and clean and dry it.

4. The polishing process as described in claim 3, characterized in that, In step 1, the voltage is linearly increased from 80 V to the target DC operating voltage of 360 V at a constant rate of 8~10 V / s.

5. The polishing process as described in claim 3, characterized in that, In step 2, the pulse parameters of the high-frequency asymmetric square wave pulse signal are: positive pulse amplitude +40~50 V, pulse width 45 μs; negative pulse amplitude -15 V, pulse width 5 μs; frequency 10 kHz.

6. The polishing process as described in claim 3, characterized in that, In step 3, a high-frequency acoustic emission sensor is installed on the side wall of the polishing tank to collect broadband acoustic signals generated by plasma discharge. The center frequency of the high-frequency acoustic emission sensor is 1MHz.

7. The polishing process as described in claim 3, characterized in that, In step 3, if the RMS value meets the requirements, the specific method for determining that the surface of the conductive SiC material is initially smooth is as follows: if the standard deviation of the RMS value drops to less than 30% of the initial stage within 10 consecutive seconds, and the real-time average RMS value drops to 45-60% of the set threshold within 10 consecutive seconds, it is determined that the surface of the conductive SiC material has been initially smoothed and the plasma gas layer tends to be stable; the set threshold is the peak value of the RMS monitored when the main polishing stage starts in step 1, and the initial stage is the first 5 seconds of the main polishing stage in step 1.

8. The polishing process as described in claim 7, characterized in that, In step 3, the specific method for adjusting the DC working voltage and pulse signal to perform the final trimming of the conductive SiC material is as follows: when the RMS value determines that the surface of the conductive SiC material has been initially smoothed and the plasma gas layer tends to be stable, the DC working voltage is reduced from 360 V to 300 V, and the negative amplitude of the pulse signal is adjusted from -15 V to -8 V. This mode is maintained for 2 to 3 minutes to achieve the final trimming of the nanoscale contour of the conductive SiC material surface.

9. The polishing process as described in claim 3, characterized in that, In step 4, the rapid heating means heating to a preset temperature within a preset time of 30 seconds; the preset temperature is 98℃; the constant voltage treatment condition is a DC voltage of 100~120 V; the constant voltage treatment time is 30~40 seconds.

10. The application of the plasma liquid nanopolishing slurry according to claim 1 or 2 or the polishing process according to any one of claims 3-9 in the preparation of conductive silicon carbide materials.

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