JP2015211047A - Method for polishing silicon carbide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for polishing a silicon carbide substrate, which enables the polishing of a silicon carbide substrate at a high polishing speed, and enables the reduction in strain of a silicon carbide substrate surface after polishing.SOLUTION: A method for polishing a silicon carbide substrate 14 comprises the steps of: setting the silicon carbide substrate 14 with a polished surface facing a conductive platen 12 so as to be opposed to the conductive platen through an electrolytic solution 16 including gap-forming materials 17, polishing grains 18 and an electrolyte; and performing an electrolytic polishing on the silicon carbide substrate while using the surface of the silicon carbide substrate as an anode and the conductive platen as a cathode with at least a part of the polished surface of the silicon carbide substrate remaining in contact with the electrolytic solution.

Description

  The present invention relates to a method for polishing a silicon carbide substrate.

  In the field of power semiconductors, utilization of silicon carbide (SiC) power devices, which are superior in high-temperature operability compared to silicon (Si), are small and have high energy-saving effects, is expected. In addition, the substrate diameter has become larger and mass-produced, and the importance of substrate processing technology has increased accordingly. However, silicon carbide is extremely difficult to process because it has extremely high hardness and is chemically and thermally stable.

  The processing process of the SiC substrate is basically configured by cutting an ingot, grinding or lapping for aligning the thickness and shape of the cut wafer, and finishing polishing for removing the damaged layer, as with the Si substrate. However, since SiC is much harder and more chemically and thermally stable than Si, green silicon carbide (GC) abrasive grains and FO abrasive grains (a mixture of brown alumina and zircon used for lapping of Si substrates) General abrasive grains such as) cannot be used, and the SiC substrate in which the wet etching used for removing the damaged layer in the Si substrate is chemically stable cannot be applied. Therefore, high-hardness diamond or cubic boron nitride (cBN) abrasive grains must be used for processing of the SiC substrate by mechanical action, resulting in high costs. In addition, since wet etching cannot be used, the damage layer removal must be relied only on chemical mechanical polishing (CMP), and is performed over a long period of time. This also contributes to the deterioration of the substrate shape accuracy.

  The surface of the semiconductor material is required to have flatness at the atomic level without damage, but processing with diamond causes damage no matter how small particles are used. Therefore, various polishing methods for a SiC substrate using a slurry based on silica or alumina abrasive grains have been proposed. For example, Patent Document 1 discloses a method of polishing an SiC substrate using an abrasive having a pH of 4 to 9 containing colloidal silica and a dispersion medium in which the colloidal silica is dispersed.

  Also proposed is a method of oxidizing the SiC surface using various energies and removing the oxide film by etching or polishing. Patent Document 2 discloses a method for polishing a modified layer by irradiating the surface of a difficult-to-process material such as a SiC substrate with high-density radicals generated by atmospheric pressure plasma to form the modified layer. Yes.

  In Patent Document 3, the surface to be polished of the SiC wafer is disposed opposite to the polishing surface plate, and at least part of the surface to be polished of the SiC wafer is electrolyzed having a hydrogen fluoride (HF) concentration of 0.001 to 10 wt%. In a SiC wafer manufacturing method in which a SiC wafer is electropolished using a SiC wafer as an anode and a counter electrode sandwiching an electrolyte as a cathode, the current density and applied voltage during electropolishing are in a specific range. A method for manufacturing a SiC wafer to which a voltage is applied is disclosed.

Japanese Patent Laid-Open No. 2005-117027 JP 2011-176243 A JP 2013-40373 A

  However, the polishing methods described in Patent Documents 1 and 2 have a problem that a long polishing time is required. In addition, in the polishing method described in Patent Document 3, although the polishing time is shortened, strain remains on the polished surface or the lower surface of the SiC wafer, and the surface is “epi-ready” (that is, ready to receive an element for epitaxial growth). There was a problem of not being.

  Therefore, an object of the present invention is to provide a method for polishing a silicon carbide substrate that can polish a silicon carbide substrate at a high polishing rate and can reduce distortion of the surface of the silicon carbide substrate after polishing.

  In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, it has been found that the above problem can be solved by a polishing method in which an SiC substrate is electropolished using an anodizing phenomenon using an electrolytic solution containing a gap forming material, abrasive grains, and an electrolyte. And based on the said knowledge, it came to complete this invention.

  That is, in the present invention, the surface to be polished of the silicon carbide substrate is disposed so as to face the conductive surface plate with an electrolyte solution containing a gap forming material, abrasive grains, and an electrolyte interposed therebetween, and the surface of the silicon carbide substrate is used as an anode, A method for polishing a silicon carbide substrate, comprising using a conductive surface plate as a cathode and electrolytic polishing while contacting at least part of a surface to be polished of the silicon carbide substrate in contact with the electrolytic solution.

  ADVANTAGE OF THE INVENTION According to this invention, the grinding | polishing method of a SiC substrate which can grind | polish a SiC substrate with a high grinding | polishing speed and can reduce the distortion of the SiC substrate surface after grinding | polishing is provided.

It is the schematic which shows an example of the grinding | polishing apparatus used in order to implement the grinding | polishing method of this invention.

  In the present invention, a surface to be polished of a silicon carbide substrate is disposed opposite to a conductive surface plate with an electrolyte containing a gap forming material and abrasive grains interposed therebetween, the surface of the silicon carbide substrate is used as an anode, and the conductive surface plate is This is a method for polishing a silicon carbide substrate, in which at least a part of the surface to be polished of the silicon carbide substrate is electrolytically polished as a cathode while being in contact with the electrolytic solution. Such a polishing method of the present invention can polish a silicon carbide (SiC) substrate at a high polishing rate, and can reduce distortion of the surface of the SiC substrate after polishing.

  Hereinafter, the present invention will be described in detail.

  FIG. 1 is a schematic view showing an example of a polishing apparatus used for carrying out the polishing method of the present invention.

  A polishing apparatus 10 shown in FIG. 1 is disposed on an upper surface of an acrylic plate 11 and an upper surface of the conductive platen 12 and is fixed to a metal holding plate 13. 14 has a resin coating 15 capable of holding 14 and a nozzle (not shown) for supplying an electrolyte solution 16. The conductive surface plate 12 is electrically connected to the DC power source 20 and serves as a cathode. Further, the SiC substrate 14 is electrically connected to the DC power source 20 to be an anode (anode). At the time of electrolytic polishing of the SiC substrate 14, a positive voltage is applied from the DC power source 20 to the surface to be polished of the SiC substrate 14 (hereinafter also referred to as a surface to be polished), and a negative voltage is applied from the DC power source 20 to the conductive surface plate 12. And is energized.

  The conductive surface plate 12 and the resin coating 15 can be rotated by a motor (not shown). The nozzle for supplying the electrolytic solution 16 is disposed above the resin coating 15, and the electrolytic solution 16 is supplied from the nozzle between the SiC substrate 14 and the conductive surface plate 12, and at least one of the SiC substrate 14 is provided. The part comes into contact with the electrolytic solution 16.

  The resin coating 15 may be relatively moved in a direction parallel to the surface to be polished of the SiC substrate 14. By moving the resin coating 15 relative to the polished surface of the SiC substrate 14, electrolytic polishing can be performed on the entire polished surface of the SiC substrate 14. For example, by rotating the conductive surface plate 12 and rotating the resin coating 15, the SiC substrate 14 fixed to the resin coating 15 is rotated, whereby the conductive surface plate 12 and the SiC substrate 14 are polished. Between the surfaces, the electrolyte solution 16 can more easily permeate more uniformly, and better current can be obtained. The method for moving the conductive surface plate 12 relative to the surface to be polished of the SiC substrate 14 is not limited to this, and various methods can be used. As another form, for example, a belt-like conductive surface plate that performs rectilinear or reciprocating motion can be used.

  The polishing apparatus 10 can adjust the polishing pressure within a predetermined range by moving the resin coating 15 in the vertical and horizontal directions to adjust the position of the resin coating 15 with respect to the conductive surface plate 12.

  At the time of polishing the surface to be polished of the SiC substrate 14, the SiC substrate 14 is mounted and held on the resin coating 15, and the surface to be polished of the SiC substrate 14 is separated by a predetermined distance by the conductive surface plate 12 and the gap forming material 17. And is polished by the abrasive grains 18 held on the surface of the gap forming material 17 (see enlarged view 1b in FIG. 1). The resin coating 15 holds the SiC substrate 14 via a conductive adhesive 19 such as a silver paste. In the polishing apparatus shown in FIG. 1, six SiC substrates 14 are held on the resin coating 15 as shown in the enlarged view 1a, but the number of SiC substrates 14 held is not limited to this.

  Electropolishing is a polishing method that utilizes the dissolution of an anode conductive material, such as metal, during electrolysis. In the present invention, the conductive material is a SiC substrate that is an object to be polished, but utilizes a phenomenon in which the SiC substrate is anodized as follows.

In the SiC substrate 14 serving as the anode, the surface SiC is electrochemically oxidized to form SiO ₂ on the surface layer. As shown in FIG. 1B, since the electrolytic solution according to the present invention contains abrasive grains and a gap forming material, a gap G is formed between the SiC substrate 14 and the conductive surface plate 12 and The gap G is kept substantially constant, and the oxidation rate of Si becomes substantially constant. Therefore, in the present invention, an SiO ₂ layer with little void and less void is formed by anodic oxidation. The SiO ₂ layer thus formed is polished and etched by the abrasive grains 18 and the gap forming material 17 contained in the electrolytic solution 16, and the SiO ₂ layer existing on the surface layer is removed. The carbon contained in the SiC substrate is electrochemically oxidized to form highly volatile CO ₂ and volatilizes and is quickly removed from the surface layer.

  According to such a polishing method of the present invention, the SiC substrate can be polished at a high polishing rate, and the distortion of the surface of the SiC substrate after polishing can be reduced.

  In addition, it is lower than the method using atmospheric pressure plasma as described in the above-mentioned Patent Document 2, and the method of oxidizing and polishing or etching a SiC substrate by ultraviolet irradiation, catalyst-based etching (CARE), electrolytic etching, or the like. The SiC substrate can be polished at a cost.

  In addition, in the method of electrolytic polishing by bringing a SiC wafer such as the above-mentioned Patent Document 3 into contact with a surface plate or a polishing pad, the polishing time is shortened, but the surface or lower surface of the SiC wafer after polishing is distorted. Another problem is that the polishing pad has poor durability. Such a problem can also be solved by the polishing method of the present invention.

Furthermore, in the electropolishing of the present invention, SiO ₂ generated on the surface of the SiC substrate is removed from the surface of the SiC substrate using abrasive grains and a gap forming material, thereby ensuring contact between the surface of the SiC substrate and the electrolyte. In addition, a decrease in the anodic oxidation rate can be prevented, and the SiC substrate can be polished at a high polishing rate.

[Silicon carbide (SiC) substrate]
The silicon carbide (SiC) substrate that is an object to be polished may be an n-type doped with a Group 15 element of a long-period periodic table, or may be doped with a Group 13 element of a long-period periodic table. It may be p-type. Further, SiC is a material exhibiting crystal polymorphism (polytype) having the same composition and various laminated structures, and there are several hundred or more polytypes. Examples of the crystal structure of the SiC substrate used in the present invention include 2H, 3C, 4H, 6H, 8H, 10H, and 15R, and are not particularly limited.

  The electrical resistivity of the SiC substrate is not particularly limited, but is preferably 1 Ωcm or less. If it is this range, it can be made to conduct easily and electropolishing can be performed efficiently.

[Conductive surface plate]
Examples of the material for the conductive surface plate include metals such as aluminum, copper, brass, cast iron, stainless steel, and nickel.

  The flatness of the conductive surface plate is preferably 10 μm or less. Within this range, contact between the SiC substrate and the conductive surface plate can be prevented. In addition, the flatness of a conductive surface plate shall employ | adopt the value measured by the method of JISB7513: 1992.

  Further, the lower limit value of the surface roughness (Ra) of the conductive surface plate is preferably 1 μm or more. When the surface roughness is 1 μm or more, the retention of the abrasive grains and the gap forming material is improved, and the polishing rate is improved. On the other hand, the upper limit of Ra is preferably less than r, where r is the average particle diameter of the gap forming material. If the surface roughness is less than r, direct contact between the SiC substrate and the surface plate can be prevented, and scratches and distortion on the SiC substrate surface can be prevented.

[Electrolyte]
[Abrasive]
Specific examples of abrasive grains contained in the electrolytic solution used in the polishing method of the present invention include, for example, aluminum oxide (alumina), silicon oxide (silica), colloidal silica, cerium oxide (ceria), and zirconium oxide (zirconia). ), Ferric oxide (bengala) and the like. These abrasive grains can be used alone or in combination of two or more. The abrasive grains may be commercially available products or synthetic products.

  Among these, aluminum oxide (alumina), silicon oxide (silica), and cerium oxide (ceria) are preferable, and aluminum oxide (alumina) is more preferable from the viewpoint of oxide film removal efficiency, finished surface roughness, quality, and the like. .

  The lower limit value of the average particle diameter of the abrasive grains is preferably 5 nm or more, and more preferably 30 nm or more. The upper limit of the average particle diameter of the abrasive grains is preferably 30 μm or less, and more preferably 10 μm or less. If it is this range, a high-quality finished surface can be obtained efficiently. In addition, the average particle diameter of an abrasive grain is computed from the specific surface area of the abrasive grain measured by BET method, for example. The specific surface area of the abrasive grains can be measured using, for example, “Flow Sorb II 2300” manufactured by Micromeritex Corporation.

  The lower limit of the content of abrasive grains in the electrolytic solution is preferably 1% by mass or more, and more preferably 10% by mass or more. As the abrasive grain content increases, the oxide film can be efficiently removed.

  Moreover, it is preferable that it is 50 mass% or less, and, as for the upper limit of content of the abrasive grain in electrolyte solution, it is more preferable that it is 30 mass% or less. As the abrasive content decreases, a stable electrolyte solution having a low viscosity can be obtained.

[Gap forming material (spacer)]
The gap forming material according to the present invention functions as a spacer for preventing scratches and distortion of the substrate surface due to direct contact between the SiC substrate and the conductive surface plate, and as a carrier that holds abrasive grains and transports them to the polishing region. work.

  The gap between the SiC substrate formed of the gap forming material and the conductive surface plate is preferably 5 to 100 μm. If it is this range, a uniform oxide film can be produced | generated efficiently.

  The gap forming material according to the present invention is supplied between a SiC substrate as an object to be polished and a conductive surface plate, and if the SiC substrate is polished by adhering abrasive grains to the surface thereof, its shape and There is no size limit. Therefore, the gap forming material may be an organic polymer compound or an inorganic compound. The gap forming material can be used alone or in combination of two or more. The gap forming material may be a commercially available product or a synthetic product.

  Examples of organic polymer compounds include, for example, polyurethane, polyamide, polyimide, polyester, polyethylene, polystyrene, crosslinked polystyrene, polypropylene, polyvinyl chloride, polyvinylidene chloride, ABS resin, polystyrene / AS resin, acrylic resin, methacrylic resin, Phenol resin, urea / melamine resin, silicone resin, epoxy resin, polyacetal resin, benzoguanamine resin, polycarbonate, polyphenylene ether, polyphenylene sulfide, polysulfone, polyarylate, polyetherimide, polyethersulfone, polyetherketone, or their co-polymer Examples include coalescence.

  Examples of inorganic compounds include alumina, zirconia, silica, silicon carbide, boron carbide, silicon nitride, aluminum nitride, zircon sand, and the like. In particular, it is preferable to use particles having a new Mohs hardness of 12 or less, such as alumina, zirconia, silica, and silicon nitride, from the viewpoint of roughness and quality of the finished surface.

  Furthermore, the gap forming material may be a composite of an organic polymer compound and an inorganic compound. For example, the above organic polymer compound is used as a nucleus, and the inorganic compound is chemically or physically supported, adsorbed or chemically bonded to the surface of the organic polymer compound, and the organic polymer compound is synthesized in the presence of the inorganic compound. The organic polymer compound includes an inorganic compound, the inorganic compound is used as a core, the surface of the organic polymer compound is coated, or a graft chain is formed by chemical bonding. The surface may be modified. In addition, the organic polymer compound itself having a hollow part, or a substance in which a gas or liquid other than air is sealed in the hollow part may be used. As a complex of such an organic polymer compound and an inorganic compound, for example, the organic polymer compound or other inorganic compound is added at the time of polymerization of the organic polymer compound or other polymer, and the organic polymer that is a polymer is then added. Examples thereof include a gap forming material in which an inorganic compound is contained on the surface or inside of the compound.

  Among these gap forming materials, it is at least one selected from the group consisting of polyurethane, acrylic resin, polyethylene, polystyrene, polyamide, phenol resin, melamine resin, and alumina from the viewpoint of roughness of the finished surface, quality, and the like. It is preferable.

  The lower limit value of the average particle diameter of the gap forming material is preferably 1 μm or more, and more preferably 5 μm or more. As the average particle diameter of the gap forming material increases, contact between the SiC substrate and the surface plate can be prevented.

  Moreover, the upper limit of the average particle diameter of the gap forming material is preferably 100 μm or less, and more preferably 50 μm or less. As the average particle diameter of the gap forming material decreases, a sufficient current flows through the SiC substrate, and a desired anodic oxidation rate can be obtained.

  The average particle diameter of the gap forming material is a value measured by an image analysis type particle diameter distribution measuring apparatus using a CCD camera.

  The shape of the gap forming material is not limited to a spherical shape, but is a football shape, a polygonal column shape such as a triangular column or a quadrangular column, a columnar shape, a bowl shape in which the center portion of the cylinder is recessed from the end portion, and the center portion of the cylinder is more than the end portion. Various shapes that can form a swollen bowl shape, a donut shape through which the central portion of the disk penetrates, a plate shape, a complex tow shape having a number of protrusions on the surface, and other solid shapes can be selected. In addition, pores may be formed on the surface or inside of the particles having these shapes, or when the particles are organic polymer compounds, microprojections made of organic polymer compound chains or the like are formed on the surface. You may have. In the present invention, the average particle diameter in the case of an irregular shape other than a true spherical shape of the gap forming material is the average of the shortest lengths.

  The lower limit of the content of the gap forming material in the electrolytic solution is preferably 1% by mass or more, and more preferably 3% by mass or more. As the content of the gap forming material increases, contact between the SiC substrate and the surface plate can be prevented.

  Further, the upper limit value of the content of the gap forming material in the electrolytic solution is preferably 30% by mass or less, and more preferably 20% by mass or less. Polishing can be performed efficiently as the content of the gap forming material decreases.

  In the electrolytic solution according to the present invention, it is preferable that abrasive grains are supported on, or contacted with, the surface of the gap forming material in the polishing step. In the case of being held on the surface of the gap forming material, the holding form is not limited. The gap forming material preferably has an average particle size larger than that of the abrasive grains. Thereby, an abrasive grain can be hold | maintained on the surface of a gap formation material. On the other hand, when the abrasive grains are not held on the surface of the gap forming material, the SiC substrate cannot be polished because the average particle diameter of the gap forming material is larger than that of the abrasive grains. The gap forming material and the abrasive grains in the electrolytic solution exist as composite particles in which the abrasive grains are held on at least the surface of the gap forming material, and the binding force at this time is also electrostatic force, ionic bond, van der Waals force, or This may be due to physical or mechanical forces. In the electrolytic solution according to the present invention, the gap forming material and the abrasive grains may form composite particles in advance when the electrolytic solution is prepared. However, it is not always necessary to form composite particles, and it is sufficient that the gap forming material substantially functions as a spacer and functions as a medium for conveying abrasive grains in the electropolishing process. Therefore, the gap forming material and the abrasive grains are separated during storage of the electrolytic solution. However, when supplying the electrolytic polishing process, the gap forming material and the abrasive grains are brought into contact with each other by stirring or the like. In the electrolytic polishing step, the gap forming material and the abrasive grains come into contact with each other by the rotational force of the SiC substrate and the abrasive grains are held on the surface of the gap forming material, so that the surface of the SiC substrate can be substantially polished. It may be the case.

〔Electrolytes〕
Examples of the electrolyte (supporting electrolyte) contained in the electrolytic solution include, for example, lithium hydroxide (LiOH), sodium chloride (NaCl), sodium hydroxide (NaOH), sodium sulfate (Na ₂ SO ₄ ), sodium hydrogen sulfate ( NaHSO ₄ ), sodium nitrate (NaNO ₃ ), trisodium phosphate (Na ₃ PO ₄ ), potassium chloride (KCl), potassium hydroxide (KOH), potassium sulfate (K ₂ SO ₄ ), potassium hydrogen sulfate (KHSO ₄₎ ), Tripotassium phosphate (K ₃ PO ₄ ), magnesium hydroxide (Mg (OH) ₂ ), calcium hydroxide (Ca (OH) ₂ ), ammonium fluoride (NH ₄ F), ammonium chloride (NH ₄ Cl ), ammonium nitrate _(NH 4 _NO 3), ammonium hydrogen sulfate _{((NH 4) HSO 4)} , phosphorus Ammonium _{((NH 4) 2 HPO 4} ), hydrochloric acid (HCl), nitric acid _(HNO 3), sulfuric acid _(H 2 _SO 4), phosphoric acid _(H 3 _PO 4), acetic acid, oxalic acid, various organic such as citric acid Examples thereof include acids and salts thereof, and hydrogen peroxide (H ₂ O ₂ ). These electrolytes can be used alone or in combination of two or more.

  Furthermore, these electrolyte solutions include nonionic, anionic or cationic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, alkyl ammonium chloride, glycerin, ethylene glycol, propylene glycol, polyethylene Polyhydric alcohols such as glycol may be added appropriately as an auxiliary additive, alone or in admixture of two or more.

  The lower limit of the content of the electrolyte in the electrolytic solution is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and further preferably 5.0% by mass or more. Moreover, it is preferable that the upper limit of content of the electrolyte in electrolyte solution is 30 mass% or less, and it is more preferable that it is 20 mass% or less. If it is this range, the electrical conductivity of electrolyte solution can be preferably controlled in the range of 50-300 mS / cm, and electropolishing can be performed efficiently.

[Other ingredients]
The electrolyte solution according to the present invention may further contain other components such as a dispersant, a processing accelerator, a surface accuracy improver, a rust inhibitor, an antiseptic, an antifungal agent, and a viscosity modifier as necessary. .

[Method for producing electrolyte solution]
The method for producing an electrolytic solution according to the present invention is not particularly limited, and for example, by stirring and mixing abrasive grains, a gap forming material, an electrolyte, and other components as necessary in a solvent such as water and ethanol. Can be obtained.

  When water is used, water containing as little impurities as possible is preferable from the viewpoint of suppressing the inhibition of the action of other components. Specifically, after removing impurity ions with an ion exchange resin, the water is passed through a filter. Pure water, ultrapure water or distilled water from which foreign substances have been removed is preferred.

  Although the temperature at the time of mixing each component is not specifically limited, 10-40 degreeC is preferable and you may heat in order to raise a dissolution rate. Further, the mixing time is not particularly limited.

[Polishing method]
Although it does not restrict | limit especially as a grinding | polishing apparatus used when grind | polishing the SiC substrate of this invention, For example, the single-sided grinding | polishing apparatus as shown in FIG. 1 is mentioned.

[Polishing pressure]
An example of polishing conditions in the polishing method according to the present invention is polishing pressure. In general, the higher the pressure, the higher the frictional force between the abrasive grains and the SiC substrate, and the higher the mechanical working force, the higher the polishing rate. The polishing pressure in the polishing method according to the present invention is not particularly limited, but the lower limit is preferably 5 kPa or more, more preferably 10 kPa or more. The upper limit of the polishing pressure is preferably 100 kPa or less, and more preferably 50 kPa or less. If it is this range, sufficient polishing rate will be exhibited and it can suppress that defects, such as a damage | wound and a distortion | strain, generate | occur | produce on the substrate surface.

[Applied voltage]
The lower limit value of the applied voltage when performing electropolishing is preferably 1 V or more, and more preferably 5 V or more. When the applied voltage is 1 V or more, the contact resistance (Schottky barrier) between the electrode material and the SiC substrate, the resistance of the SiC substrate itself, or the resistance of the electrolyte solution between the SiC substrate and the counter electrode is lowered, and the desired oxidation is achieved. Sufficient current flows to form the film.

Further, the upper limit value of the applied voltage is preferably 50 V or less, and more preferably 30 V or less. When the applied voltage is 50 V or less, the SiO ₂ layer is formed at an appropriate speed, and generation of voids and film thickness in the SiO ₂ layer can be suppressed, and a flat polished surface is obtained. be able to. In addition, bubbles generated at the cathode can be reduced, liquid drainage can be prevented, and generation of electric discharge and defects on the surface of the SiC substrate can be prevented.

[Current]
The initial current value varies depending on the type of the electrolyte, the electrode material, the gap (gap distance) between the SiC substrate and the conductive surface plate, the electrical resistivity of the SiC substrate, and the like, and is proportional to the substrate area. During polishing, the current value varies depending on the thickness of the oxide film at that time, that is, the balance between the oxide film formation rate and the polishing rate. In the present invention, from the viewpoint of improving the polishing rate, electrolytic conditions and polishing conditions in which the anodic oxidation rate is high and the formed oxide film is immediately removed are preferable.

  As described above, the polishing method of the present invention is suitably used for polishing a SiC substrate. Therefore, this invention provides the manufacturing method of a SiC substrate including the process of grind | polishing a SiC substrate with the said grinding | polishing method.

  The present invention will be described in further detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

(Examples 1-5)
An abrasive solution, a gap forming material, an electrolyte, and water shown in Table 1 below were mixed as shown in Table 1 to prepare an electrolytic solution. After the electrolyte was dissolved in water, the abrasive grains and the gap forming material were mixed, and each component was dispersed using a stirrer and an ultrasonic bath. The amount of each component added is as shown in Table 1 below. Moreover, about an abrasive grain and a gap formation material, the average particle diameter is also shown.

  Using these electrolytic solutions, a silicon carbide substrate was polished under the following polishing conditions by a single-side polishing apparatus remodeled for electrolytic polishing, and polishing efficiency (polishing rate) and finished surface roughness were evaluated. The results are shown in Table 1. In Comparative Examples 1 and 2, polishing was performed without applying a voltage.

<Processing conditions>
Polishing device: Single-side polishing device (MA-200 Musashino Electronics Co., Ltd.) Modified for electrolytic polishing Cathode (negative electrode): Conductive surface plate is in contact with a carbon brush and energized Anode (positive electrode): Metal holding plate A carbon brush was brought into contact with the upper end surface of the battery and energized. The substrate was affixed to a metal holding plate with a conductive adhesive. Substrate: 12 × 18 × 10 mm n-type 4H—SiC pieces, 6 affixed. Pre-processed surface is diamond wrap surface Ra = about 4nm
Conductive surface plate: Aluminum surface plate φ200 mm Flatness: 10 μm Surface roughness (Ra): 5.5 μm
Conductive surface plate rotation speed: 70rpm
Polishing pressure: 42 kPa
Polishing time: 30 minutes <Polishing efficiency>
After six SiC pieces were evenly attached to the metal holding plate with a conductive adhesive, the thickness of the SiC was measured at three locations per sheet using a height meter. After polishing for 30 minutes, the sample was washed and dried, and measured at three locations in the same manner, and the difference between the average values was taken as the polishing amount. Furthermore, the average value of 6 sheets was taken out, and the polishing amount per hour was calculated as the polishing efficiency. The polishing efficiency is excellent when the polishing efficiency is 5 μm / hour or more (◎), good when the polishing efficiency is 1 μm / hour or more but less than 5 μm / hour (◯), less than 0.1 μm / hour is less than 1 μm / hour (Δ), less than 0.1 μm / hour Was evaluated in four grades of bad (x).

<Roughness of finished surface>
The average roughness Ra of the polished SiC substrate surface was measured using a scanning white interferometer New View 7300 (manufactured by Zygo). Then, Ra is less than 0.2 nm (excellent), 0.2 nm or more and less than 0.5 nm is good (◯), 0.5 nm or more and less than 1 nm is acceptable (Δ), and 1 nm or more is defective (×). It was evaluated with.

  The evaluation results are shown in Table 1.

  As apparent from Table 1 above, according to the polishing methods of the present invention in Examples 1 to 5, the SiC substrate can be polished at a high polishing rate, and the distortion of the polished SiC substrate surface can be reduced. Can do.

10 Polishing device,
11 Acrylic board,
12 Conductive surface plate,
13 metal holding plate,
14 SiC substrate,
15 resin coating,
16 electrolyte,
17 Gap forming material,
18 abrasive grains,
19 conductive adhesive,
20 DC power supply.
A ammeter,
G gap,
V voltmeter,
1a View of the SiC substrate and the resin coating from below,
1b Details of processing area.

Claims (5)

  The surface to be polished of the silicon carbide substrate is disposed opposite to a conductive surface plate with an electrolyte containing a gap forming material, abrasive grains, and an electrolyte interposed therebetween, and the surface to be polished of the silicon carbide substrate is used as an anode, and the conductive surface plate A method for polishing a silicon carbide substrate, wherein the electrode is used as a cathode and electrolytic polishing is performed while at least part of the surface to be polished of the silicon carbide substrate is in contact with the electrolyte.   The polishing method according to claim 1, wherein an average particle diameter of the gap forming material is 5 μm or more and 50 μm or less.   The gap forming material is polyurethane, polyamide, polyimide, polyester, polyethylene, polystyrene, crosslinked polystyrene, polypropylene, polyvinyl chloride, polyvinylidene chloride, ABS resin, polystyrene / AS resin, acrylic resin, methacrylic resin, phenol resin, urea Melamine resin, silicone resin, epoxy resin, polyacetal resin, benzoguanamine resin, polycarbonate, polyphenylene ether, polyphenylene sulfide, polysulfone, polyarylate, polyetherimide, polyethersulfone, polyetherketone, and copolymers thereof, alumina, zirconia And at least one selected from the group consisting of silica, silicon nitride, aluminum nitride, and zircon sand. Or polishing method according to.   The polishing method according to claim 1, wherein an applied voltage in the electrolytic polishing is 1 V or more and 50 V or less.   The manufacturing method of a silicon carbide board | substrate including the process of grind | polishing the silicon carbide board | substrate with the grinding | polishing method of any one of Claims 1-4.