CN116657231A - Silicon carbide substrate polishing method - Google Patents
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- CN116657231A CN116657231A CN202310608067.2A CN202310608067A CN116657231A CN 116657231 A CN116657231 A CN 116657231A CN 202310608067 A CN202310608067 A CN 202310608067A CN 116657231 A CN116657231 A CN 116657231A
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- 238000005498 polishing Methods 0.000 title claims abstract description 102
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- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 99
- 239000000758 substrate Substances 0.000 title claims abstract description 26
- 238000000034 method Methods 0.000 title claims abstract description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 20
- 239000001301 oxygen Substances 0.000 claims abstract description 20
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 20
- DNIAPMSPPWPWGF-UHFFFAOYSA-N Propylene glycol Chemical compound CC(O)CO DNIAPMSPPWPWGF-UHFFFAOYSA-N 0.000 claims description 24
- 238000000227 grinding Methods 0.000 claims description 15
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 14
- 239000007770 graphite material Substances 0.000 claims description 14
- 238000007517 polishing process Methods 0.000 claims description 12
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 10
- -1 polyoxypropylene glycerol Polymers 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 10
- 238000006243 chemical reaction Methods 0.000 claims description 8
- 239000008367 deionised water Substances 0.000 claims description 8
- 229910021641 deionized water Inorganic materials 0.000 claims description 8
- RBNPOMFGQQGHHO-UHFFFAOYSA-N glyceric acid Chemical compound OCC(O)C(O)=O RBNPOMFGQQGHHO-UHFFFAOYSA-N 0.000 claims description 8
- 229910052708 sodium Inorganic materials 0.000 claims description 8
- 238000001035 drying Methods 0.000 claims description 7
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- 238000005273 aeration Methods 0.000 claims 1
- 238000007254 oxidation reaction Methods 0.000 abstract description 15
- 230000003647 oxidation Effects 0.000 abstract description 14
- 239000000126 substance Substances 0.000 abstract description 8
- 230000000694 effects Effects 0.000 abstract description 7
- 238000006056 electrooxidation reaction Methods 0.000 abstract description 4
- 239000000243 solution Substances 0.000 description 32
- 235000012431 wafers Nutrition 0.000 description 20
- 239000013078 crystal Substances 0.000 description 13
- 239000000463 material Substances 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 8
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- 239000007788 liquid Substances 0.000 description 7
- 238000012545 processing Methods 0.000 description 7
- 239000004065 semiconductor Substances 0.000 description 7
- 230000003746 surface roughness Effects 0.000 description 7
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- 238000009423 ventilation Methods 0.000 description 6
- 239000003792 electrolyte Substances 0.000 description 5
- 239000007800 oxidant agent Substances 0.000 description 5
- 229910052814 silicon oxide Inorganic materials 0.000 description 5
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 4
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- 238000005516 engineering process Methods 0.000 description 4
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910052581 Si3N4 Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 239000005708 Sodium hypochlorite Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 238000013473 artificial intelligence Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
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- RTZKZFJDLAIYFH-UHFFFAOYSA-N ether Substances CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 239000006260 foam Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- QWPPOHNGKGFGJK-UHFFFAOYSA-N hypochlorous acid Chemical compound ClO QWPPOHNGKGFGJK-UHFFFAOYSA-N 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 231100000956 nontoxicity Toxicity 0.000 description 1
- 150000002926 oxygen Chemical class 0.000 description 1
- 230000002572 peristaltic effect Effects 0.000 description 1
- 229920002635 polyurethane Polymers 0.000 description 1
- 239000004814 polyurethane Substances 0.000 description 1
- 239000012286 potassium permanganate Substances 0.000 description 1
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- 229920005989 resin Polymers 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
- C25F3/00—Electrolytic etching or polishing
- C25F3/16—Polishing
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Carbon And Carbon Compounds (AREA)
Abstract
The invention provides a silicon carbide substrate polishing method, which adopts electrochemical and chemical mechanical polishing to treat the surface of silicon carbide, and effectively improves the oxide layer degree of the surface of the silicon carbide by anodic electrochemical oxidation and cathodic active oxygen oxidation to improve the polishing effect of the silicon carbide.
Description
Technical Field
The invention belongs to the technical field of polishing processing, and relates to an electrochemical mechanical polishing method for a silicon carbide wafer.
Background
With the development of high and new technology enterprises such as semiconductors, new energy sources, high-end intelligent manufacturing, 5G information technology, AI artificial intelligence and the like, the semiconductor industry becomes a novel popular industry more and more. The preparation of the semiconductor material and the progress of the process research are also closely related to important national strategic fields such as national military, national defense, aerospace and aviation. With the explosion in the semiconductor market, the demand for the quantity of semiconductor materials is increasing, and the demand for quality is also increasing. Among various semiconductor materials, a silicon carbide (SiC) Single crystal is one of the most representative third generation semiconductor materials, and SiC Single crystal is widely used in many important fields such as IT, consumption, automobile, industry, aerospace, smart grid, rail transportation, power electronics, and ships.
The silicon carbide has the characteristics of small thermal expansion coefficient, high hardness, good strength, stable performance at high temperature and high pressure, high breakdown electric field strength, high maximum current density, high corrosion resistance, high elastic modulus, long service life and the like, can be used for environments with various complex working conditions such as radioactivity, corrosiveness, high temperature and high pressure, and is also an ideal substrate material. In addition, the SiC single crystal component material has the characteristics of higher dimensional stability, stronger thermal shock resistance, stable chemical property, no toxicity, no harm, moderate density and the like, so the SiC single crystal component material is also used as a reflector material in optical systems such as foundations, spaces and the like, and is widely used for developing light-weight and large-scale optical parts.
At present, the processing process flow of the SiC single crystal wafer is approximately as follows: cutting, rough grinding, finish grinding, rough polishing (mechanical polishing), finish polishing (chemical mechanical polishing), and the like. Because the hardness of SiC is high, the processing difficulty is high, when the diameter of the crystal is large (the diameter is 50mm or more), the traditional technology cannot meet the requirements, and the linear cutting technology is generally adopted by people to lead the workpiece to be a method with the required size and shape precision, and the surface roughness of the SiC crystal after final processing can reach the nano-scale.
For single crystal SiC device applications, a smooth surface free of scratches and subsurface damage is critical. However, single crystal SiC is difficult to polish due to its hard and brittle material properties and strong chemical inertness. However, the polishing effect can be improved by improving the reaction rate through electrochemical anodic oxidation of SiC, and excessive corrosion of a SiC test piece is avoided in the electrochemical process of SiC. In the electrochemical mechanical polishing process, the surface of SiC is changed to a loose oxide layer by anodic oxidation, and then by an abrasive having a hardness smaller than that of SiC, such as CeO 2 /SiO 2 And the surface is easily removed, and no scratch and subsurface damage are finally realized.
Specifically:
CN110197789a university of western-style worker discloses an ultrasonic-assisted electrochemical mechanical polishing device and method for a SiC single crystal wafer, wherein the SiC single crystal wafer and a stainless steel electrode are respectively connected with the positive electrode and the negative electrode of a pulse power supply, a closed loop is formed in a polishing solution, the wafer is used as the anode to generate an oxide film through anodic oxidation, and the polishing material removal efficiency is high by mechanically removing the oxide layer through a polishing pad and abrasive particles, so that the loss of the SiC single crystal substrate can not be caused by mechanical polishing; in addition, the processing device is simple, the processing method is easy to realize, and the processing device is suitable for being popularized and used in a large range.
An electrochemical mechanical polishing method for CN114654380A silicon carbide wafers belongs to the technical field of polishing processing. First, a silicon carbide wafer is bonded to a power supply through a conductive adhesiveAnd a copper polishing head connected with the positive electrode, wherein the polyurethane polishing pad with the through hole is fixed on a graphite disc connected with the negative electrode of the power supply by using a resin screw. The polishing power supply is a direct current stabilized power supply. The polishing pad and the wafer are driven by a motor to move relatively, the polishing pad and the wafer are immersed in electrolyte during polishing, the liquid level of the electrolyte is higher than the surface of the polishing pad, and the polishing liquid is dripped on the surface of the polishing pad through a peristaltic pump. The invention uses silicon carbide crystal in NaNO 3 The anodic oxidation reaction in the electrolyte realizes the high-efficiency polishing of the silicon carbide wafer, and the small-particle diamond abrasive is used in the polishing solution, so that the effect of providing a stress source for the oxidation process can be achieved, the anodic oxidation is accelerated, and the polishing efficiency is improved. In addition, the polishing rate of the silicon carbide wafer can be obviously improved, and good surface quality can be ensured in the fine polishing stage.
Although the above patents disclose means for electro-oxidizing silicon carbide wafers or using a pulsed power source to treat silicon carbide, the above patents do not disclose specific reagents or compositions for electrochemical polishing.
Disclosure of Invention
Based on the problems, the invention provides a neutral oxidant-free electrochemical polishing solution and a polishing method thereof, oxidation and reduction of a silicon carbide wafer are realized through pulse switching of a power supply, OH-ions are effectively obtained when the silicon carbide is used as an anode, hydrogen peroxide with strong oxidation property is obtained when the silicon carbide is used as a cathode, silicon carbide is effectively oxidized to obtain a silicon carbide-silicon oxide surface, then chemical mechanical polishing is carried out through silicon oxide in the polishing solution, and finally a silicon carbide wafer product with nanoscale roughness is obtained, the electrochemical polishing solution is green and pollution-free, a neutral solution is convenient to store and use, the composition is simple, the cost performance is extremely high, and the method comprises the following steps:
a method of polishing a silicon carbide substrate, comprising the steps of:
(1) Pretreating the surface of a silicon carbide substrate;
(2) Silicon carbide is used as a working electrode, a graphite material is used as a counter electrode, and the counter electrode is placed in electrolytic polishing solution to carry out electrolytic polishing reaction;
(3) Nitrogen purging and drying treatment;
wherein the electrolytic polishing solution comprises the following components:
20-30wt% of 20-40nm alumina grinding media;
5-7wt.%Na 2 SO 4 ；
0.2 to 0.3wt.% polyoxypropylene glycerol ether;
0.1 to 0.2wt.% of an alpha-alkenyl sulfonate;
2-3wt% propylene glycol;
deionized water;
oxygen inlet amount is 0.2-0.3m 3 /h。
The oxygen ventilation device is a bubble stone;
the distance between the silicon carbide and the graphite material is 3-5cm.
The power supply is a pulse power supply.
The pulse power parameters are as follows: forward pulse voltage: 10-12V, forward pulse width: 400-500 mus, forward duty cycle: 30-40%, negative pulse voltage: 20-30V, negative pulse width: 2-3s, negative duty cycle: 50-65%, pulse time is 5-30min, temperature: 10-15 ℃.
The pretreatment of the surface of the silicon carbide substrate comprises directional cutting, grinding and mechanical polishing.
The polishing solution is used for ultra-precise polishing of silicon carbide.
The surface roughness of the polished silicon carbide wafer is 0.05-0.1nm.
The removal rate of the silicon carbide wafer in the polishing solution is 200-400nm/h.
The theoretical basis for the electrochemical treatment of polished silicon carbide according to the invention is as follows:
in the electrochemical polishing process, the principle that the dissolution speed of metal at the micro-rough peak bulge on the surface of an anode workpiece in proper electrolyte is high is utilized, the peak value is gradually reduced, the surface roughness is reduced, and the ion-level polishing precision can be achieved theoretically.
The invention uses a bi-directional pulse power supply, i.e. silicon carbide is switched between anode and cathode at any time.
When used as an anode, the rough tip part of the silicon carbide is subjected to electrochemical oxidation to modify the SiC surface of the invention to be looseThe main occurrence of the SiO2 oxide layer in the process, namely electrochemical oxidation, is that the main equation may be: sic+4h 2 O-8e - →SiO 2 +CO 2 +8H + ；
When the cathode is used, oxygen is continuously introduced into the polishing solution, the polishing solution is in a saturated oxygen state, and high-activity oxide, HO, is formed near the electrode 2- And OH (OH) - Newly prepared HO 2- And OH (OH) - Losing electrons to form OH, O2 gives electrons to O 2- The oxidizing property is far higher than hydrogen peroxide, potassium permanganate or hypochlorous acid, and then silicon nitride is chemically oxidized, and a possible equation is as follows:
O 2 +H 2 O+2e - →HO 2- +OH - ;
O 2 +H 2 O+4e - →4OH - ;
2H 2 O+2 e - →2OH - +H 2 ;
SiC+8 OH - →SiO 2 +CO 2 +4H 2 o; namely, electrochemical anodic oxidation is adopted as an anode, chemical active group oxidation is adopted as a cathode, the rough silicon carbide surface can be effectively oxidized into a low-hardness silicon oxide layer, and then the polishing pad and 20-30nm polishing particle silicon oxide medium particles in chemical mechanical polishing are used for mechanical polishing, so that the requirements of no scratch and subsurface damage are met, and the low-roughness silicon carbide wafer surface is obtained.
About the electrochemical polishing solution, comprising 20-30wt% of 20-40nm alumina grinding media;
5-7wt.%Na 2 SO 4 ；
0.2 to 0.3wt.% polyoxypropylene glycerol ether;
0.1 to 0.2wt.% of an alpha-alkenyl sulfonate;
2-3wt% propylene glycol;
deionized water;
oxygen inlet amount is 0.2-0.3m 3 /h。
Firstly, the grinding medium is alumina, the hardness of the grinding medium is higher than that of silicon oxide oxidized on the surface of silicon carbide, the surface of a wafer is closely contacted with a polishing pad, and the alumina medium in polishing solution enters between the SiC surface and the polishing pad, so that the oxide on the surface of the silicon carbide is effectively removed by friction, and the surface of the wafer with low roughness is obtained in the continuous oxidation-polishing process.
Wherein the electrolyte solution is Na 2 SO 4 In the prior art, sodium chloride is used as an electrolyte solution, but chlorine ions in the electrolyte solution are electrolyzed to form chlorine gas, which is unfavorable for polishing, so that the electrolyte solution disclosed by the invention strictly prohibits the use of sodium chloride as the electrolyte, and the grasp of deionized water is also noted.
Regarding the oxidant, the polishing solution of the invention does not contain any oxidant raw materials, hydrogen peroxide and sodium hypochlorite are usually used as the oxidants in the prior art, but the oxidants are easy to decompose after being prepared into the polishing solution, so the polishing solution is generally prepared and used at present and is not easy to preserve.
The alpha-alkenyl sulfonate is a surfactant, is beneficial to improving the contact area between the polishing solution and the hydrophobic silicon carbide surface, so that the polishing effect is effectively improved, but bubbles are easy, so that the defoaming agent is required to have a very small foam degree, polyoxypropylene glycerol ether is required to be added, the water solubility of the surfactant and the defoaming agent is general, and especially the water solubility of the oxypropylene glycerol ether is poor, so that propylene glycol is required to be added into the polishing solution, and the defoaming agent and the surfactant are effectively dispersed.
In addition, the oxygen is the main oxidation component of the invention, and needs to be introduced in advance before polishing, and the oxygen is generally introduced in an amount of 0.2-0.3m 3 And/h, introducing for 3-5min in advance to reach the saturation state of the dissolving liquid.
The electrolytic polishing of the silicon carbide belongs to the ultra-fine polishing solution for ultra-precise polishing of the silicon carbide. The surface roughness of the polished silicon carbide wafer is 0.05-0.1nm, the removal rate of the silicon carbide wafer in the polishing solution is 200-400nm/h, namely, the surface pretreatment of the silicon carbide is needed before polishing, the pretreatment comprises directional cutting, grinding and mechanical polishing, and as shown in figure 1, the roughness of the surface of the silicon carbide subjected to the surface pretreatment is Ra=2.73 nm.
The beneficial technical effects are as follows:
(1) The invention adopts electrochemistry and chemical mechanical polishing to treat the silicon carbide surface, and effectively improves the oxide layer degree of the silicon carbide surface by anodic electrochemical oxidation and cathodic active oxygen oxidation, thereby improving the polishing effect of the silicon carbide.
(2) The polishing solution adopted by the invention is a neutral reagent, has high storage stability, does not contain any oxidant, is green and pollution-free, and has high cost performance.
Drawings
FIG. 1 is a graph of AMF of silicon carbide after mechanical polishing (without polishing according to the invention).
FIG. 2 is a chart of AMF of silicon carbide treated in example 2.
FIG. 3 is a graph of AMF of silicon carbide treated in comparative example 1.
FIG. 4 is a chart of AMF of silicon carbide treated in comparative example 2.
Detailed Description
Example 1
A method of polishing a silicon carbide substrate, comprising the steps of:
(1) Pretreating the surface of a silicon carbide substrate;
(2) Silicon carbide is used as a working electrode, a graphite material is used as a counter electrode, and the counter electrode is placed in electrolytic polishing solution to carry out electrolytic polishing reaction;
(3) Nitrogen purging and drying treatment;
wherein the electrolytic polishing solution comprises the following components:
20wt% of an alumina grinding media of 20-40 nm;
5wt.%Na 2 SO 4 ；
0.2wt.% polyoxypropylene glycerol ether;
0.1wt.% of an alpha-alkenyl sulfonate;
2wt% propylene glycol;
deionized water;
oxygen inlet amount 0.2m 3 /h。
The oxygen ventilation device is a bubble stone;
the distance between the silicon carbide and the graphite material was 3cm.
The power supply is a pulse power supply.
The pulse power parameters are as follows: forward pulse voltage: 10V, forward pulse width: 400 mus, forward duty cycle: 30%, negative pulse voltage: 20V, negative pulse width: 2s, negative duty cycle: 50%, pulse time 5min, temperature: 10 ℃.
Example 2
A method of polishing a silicon carbide substrate, comprising the steps of:
(1) Pretreating the surface of a silicon carbide substrate;
(2) Silicon carbide is used as a working electrode, a graphite material is used as a counter electrode, and the counter electrode is placed in electrolytic polishing solution to carry out electrolytic polishing reaction;
(3) Nitrogen purging and drying treatment;
wherein the electrolytic polishing solution comprises the following components:
25wt% of 20-40nm alumina grinding media;
6wt.%Na 2 SO 4 ；
0.25wt.% polyoxypropylene glycerol ether;
0.15wt.% of an alpha-alkenyl sulfonate;
2.5wt% propylene glycol;
deionized water;
oxygen inlet amount of 0.25m 3 /h。
The oxygen ventilation device is a bubble stone;
the distance between silicon carbide and graphite material was 4cm.
The power supply is a pulse power supply.
The pulse power parameters are as follows: forward pulse voltage: 11V, forward pulse width: 450 mus, forward duty cycle: 35%, negative pulse voltage: 25V, negative pulse width: 2.5s, negative duty cycle: 558%, pulse time 25min, temperature: 12.5 ℃.
Example 3
A method of polishing a silicon carbide substrate, comprising the steps of:
(1) Pretreating the surface of a silicon carbide substrate;
(2) Silicon carbide is used as a working electrode, a graphite material is used as a counter electrode, and the counter electrode is placed in electrolytic polishing solution to carry out electrolytic polishing reaction;
(3) Nitrogen purging and drying treatment;
wherein the electrolytic polishing solution comprises the following components:
30wt% of 20-40nm alumina grinding media;
7wt.%Na 2 SO 4 ；
0.3wt.% polyoxypropylene glycerol ether;
0.2wt.% of an alpha-alkenyl sulfonate;
3wt% propylene glycol;
deionized water;
oxygen inlet amount of 0.3m 3 /h。
The oxygen ventilation device is a bubble stone;
the distance between the silicon carbide and the graphite material was 5cm.
The power supply is a pulse power supply.
The pulse power parameters are as follows: forward pulse voltage: 12V, forward pulse width: 500 mus, forward duty cycle: 40%, negative pulse voltage: 30V, negative pulse width: 3s, negative duty cycle: 65%, pulse time 30min, temperature: 15 ℃.
Comparative example 1
A method of polishing a silicon carbide substrate, comprising the steps of:
(1) Pretreating the surface of a silicon carbide substrate;
(2) Silicon carbide is used as a working electrode, a graphite material is used as a counter electrode, and the counter electrode is placed in electrolytic polishing solution to carry out electrolytic polishing reaction;
(3) Nitrogen purging and drying treatment;
wherein the electrolytic polishing solution comprises the following components:
25wt% of 20-40nm alumina grinding media;
6wt.%Na 2 SO 4 ；
0.25wt.% polyoxypropylene glycerol ether;
0.15wt.% of an alpha-alkenyl sulfonate;
2.5wt% propylene glycol;
deionized water;
oxygen inlet amount of 0.25m 3 /h。
The oxygen ventilation device is a bubble stone;
the distance between silicon carbide and graphite material was 4cm.
The power supply is a direct current power supply, wherein silicon carbide is an anode.
Comparative example 2
A method of polishing a silicon carbide substrate, comprising the steps of:
(1) Pretreating the surface of a silicon carbide substrate;
(2) Silicon carbide is used as a working electrode, a graphite material is used as a counter electrode, and the counter electrode is placed in electrolytic polishing solution to carry out electrolytic polishing reaction;
(3) Nitrogen purging and drying treatment;
wherein the electrolytic polishing solution comprises the following components:
25wt% of 20-40nm alumina grinding media;
6wt.%Na 2 SO 4 ；
oxygen inlet amount of 0.25m 3 /h。
The oxygen ventilation device is a bubble stone;
the distance between silicon carbide and graphite material was 4cm.
The power supply is a pulse power supply.
The pulse power parameters are as follows: forward pulse voltage: 11V, forward pulse width: 450 mus, forward duty cycle: 35%, negative pulse voltage: 20-30V, negative pulse width: 2-3s, negative duty cycle: 50-65%, pulse time is 5-30min, temperature: 10-15 ℃.
As shown in fig. 2, fig. 3 and fig. 4, wherein the surface roughness ra=0.05 nm obtained in example 2, the removal rate in the polishing liquid was 253nm/h; the surface roughness ra=1.13 nm of comparative example 1, the removal rate in the polishing liquid was 198nm/h; the surface roughness ra=0.89 nm of comparative example 2, the removal rate in the polishing liquid was 249nm/h, in which the comparative example was low in oxidation degree, resulting in lower removal rate in the polishing liquid and high roughness was obtained, whereas the comparative example 2 lacks necessary additives, and the degree of oxidation or removal rate was not significantly different, but the roughness was significantly higher than that of example 2.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (6)
1. A silicon carbide substrate polishing method is characterized by comprising the following steps:
(1) Pretreating the surface of a silicon carbide substrate;
(2) Silicon carbide is used as a working electrode, a graphite material is used as a counter electrode, and the counter electrode is placed in electrolytic polishing solution to carry out electrolytic polishing reaction;
(3) Nitrogen purging and drying treatment;
wherein the electrolytic polishing solution comprises the following components:
20-30wt% of 20-40nm alumina grinding media;
5-7wt.%Na 2 SO 4 ；
0.2 to 0.3wt.% polyoxypropylene glycerol ether;
0.1 to 0.2wt.% of an alpha-alkenyl sulfonate;
2-3wt% propylene glycol;
deionized water;
oxygen inlet amount is 0.2-0.3m 3 /h。
2. A method of polishing a silicon carbide substrate according to claim 1 wherein the oxygen aeration device is a bubble stone.
3. A method of polishing a silicon carbide substrate according to claim 1 wherein the silicon carbide is spaced from the graphite material by a distance of 3cm to 5cm.
4. A silicon carbide substrate polishing method according to claim 1 wherein the electropolishing power source is a pulsed power source.
5. A silicon carbide substrate polishing method according to claim 4 wherein the pulse power supply parameters are as follows: forward pulse voltage: 10-12V, forward pulse width: 400-500 mus, forward duty cycle: 30-40%, negative pulse voltage: 20-30V, negative pulse width: 2-3s, negative duty cycle: 50-65%, pulse time is 5-30min, temperature: 10-15 ℃.
6. A method of polishing a silicon carbide substrate according to claim 1 wherein said surface of said silicon carbide substrate is pretreated by a process comprising directional cutting, grinding and mechanical polishing.
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