JP5658443B2 - Abrasive composition for silicon carbide substrate - Google Patents

Description

  The present invention relates to an abrasive composition for polishing a silicon carbide substrate or the like. More specifically, the present invention relates to an abrasive composition useful for effectively polishing a base substrate on which a gallium nitride thin film is formed in the fields of silicon carbide power semiconductors and optical devices.

  The silicon carbide power semiconductor has the following excellent characteristics compared to the silicon power semiconductor. (1) The forbidden band width of silicon carbide is about three times that of silicon and can be used under high temperature conditions. (2) The breakdown voltage of silicon carbide is about 10 times that of silicon, enabling a high withstand voltage, and reducing the size of the power device. (3) The thermal conductivity of silicon carbide is about three times that of silicon, has excellent heat dissipation, is easily cooled, and can increase the current. Silicon carbide has characteristics superior to those of silicon, and is being developed as a semiconductor substrate for power devices in information devices such as servers and inverters for motors in hybrid vehicles.

  A silicon carbide wafer is generally a silicon carbide powder that is sublimated from silicon carbide powder, and a cylindrical silicon carbide semiconductor single crystal block that has been grown by recrystallization is cut into a predetermined thickness with a diamond saw, chamfered, and double-sided lapping. It is processed through a series of steps of chemical mechanical polishing and cleaning.

  Silicon carbide is a hard material that has a Mohs hardness of 9.6 and is second only to diamond, is insoluble in acid, and is extremely chemically stable. Although various abrasive compositions for silicon carbide have been disclosed, there is a problem that the time required for polishing becomes long.

  Since silicon carbide is a hard material as described above, a method of polishing a silicon carbide substrate with diamond abrasive grains has been conventionally known.

  Patent Document 1, Patent Document 2, and Patent Document 3 disclose a mechanochemical polishing method for a semiconductor wafer using chromium (III) oxide for polishing a silicon carbide substrate.

  Patent Document 4 discloses a method in which a silicon carbide substrate is chemically polished with an oxidizing agent such as orthoperiodic acid or metaperiodic acid, and mechanically polished with colloidal silica abrasive grains.

  Patent Document 5 discloses a method in which a silicon carbide substrate is chemically polished with an oxidizing agent such as vanadate such as ammonium vanadate or sodium vanadate, and mechanically polished with colloidal silica abrasive grains.

JP 7-288243 A Japanese Patent Laid-Open No. 7-80770 Japanese Patent Laid-Open No. 2001-205555 Japanese Patent Laid-Open No. 2007-27663 Japanese Patent Laid-Open No. 2008-179655

  However, the conventional mechanochemical method for polishing a silicon carbide substrate has a problem in productivity because the polishing rate is slow.

  In the conventional polishing of a silicon carbide substrate with diamond abrasive grains, the polishing rate is fast, but scratches and the like are generated on the surface to be polished.

  The polishing methods using chromium oxide (III) for polishing silicon carbide substrates of Patent Document 1, Patent Document 2 and Patent Document 3 have environmental problems such as environmental pollution in the used polishing waste liquid, and have practical limitations. .

  Patent Document 4 is a polishing method in which an iodine compound such as orthoperiodic acid or metaperiodic acid is used as an oxidizing agent for polishing a silicon carbide substrate, and polishing is performed with colloidal silica. Free iodine produced as a by-product from the oxidizing agent. If the worker inhales, there is a risk of harming the health, which is not practical.

  Patent Document 5 is a method in which a vanadate is used for polishing a silicon carbide substrate, and a silicon-carbon bond is oxidatively cleaved. Although it is an effective polishing method, for example, ammonium vanadate, a kind of vanadate, is carcinogenic category: 2 germ cell mutagenic group, according to the International Chemical Safety Card (ICSC number: 1522): 2 (DFG2005). Since it is toxic to aquatic organisms and bronchial damage to the human body by suction, it is not practical from the environmental and health aspects. Vanadate is an expensive oxidizing agent, and high performance and low cost are desired.

  This invention is made | formed in view of such a subject, and makes it a subject to provide the abrasive | polishing agent composition which can produce the board | substrate excellent in surface roughness with a high polishing rate.

  The inventor comprises at least one selected from the group consisting of isopolyacids, heteropolyacids, isopolyacid salts and heteropolyacid salts, which are metal oxo acids and salts thereof, abrasive grains, oxygen donors, pH adjusters, and water. The above-mentioned problem can be solved by using a polishing composition comprising an isopolyacid is tungstic acid and / or molybdic acid, and an isopolyacid salt is tungstate and / or molybdate. I found out. That is, according to this invention, the abrasive | polishing agent composition used when grind | polishing board | substrates, such as a silicon carbide board | substrate, is provided.

[1] is a metal oxo acid and its salts, at least the one selected from the group consisting of F heteropolyacid San及 beauty heteropoly acid salts, abrasives, oxygen donating agent, and also contains pH modifiers, and water, wherein A polishing composition for a silicon carbide substrate , wherein the abrasive grains are colloidal silica and the oxygen donor is hydrogen peroxide .

[2] is said heteropolyacid tungsten-based heteropoly acid and / or molybdenum-based heteropoly acid, silicon carbide according to the heteropolyacid salt is tungsten-based heteropoly acid salt and / or molybdenum-based heteropoly acid salt [1] Abrasive composition for substrates .

[3] The abrasive composition for a silicon carbide substrate according to [2], wherein the tungsten-based heteropolyacid is at least one selected from the group consisting of phosphotungstic acid, silicotungstic acid, and phosphotungstomolybdic acid.

[4] The abrasive composition for a silicon carbide substrate according to [2] or [3], wherein the molybdenum-based heteropolyacid is at least one selected from the group consisting of phosphomolybdic acid, phosphotungstomolybdic acid, and phosphovanadomolybdic acid. object.

[5] The abrasive composition for a silicon carbide substrate according to any one of [2] to [4], wherein the molybdenum-based heteropolyacid salt is sodium phosphomolybdate.

[ 6 ] The abrasive composition for a silicon carbide substrate according to any one of [1] to [ 5 ], wherein the pH is 1.0 or more and less than 11.0.

[ 7 ] Contains at least one compound selected from the group consisting of inorganic acids, organic acids, inorganic basic compounds, and organic basic compounds as the pH adjuster that adjusts the pH to 1.0 or more and less than 11.0. The polishing composition for a silicon carbide substrate according to the above [ 6 ].

[ 8 ] The abrasive composition for a silicon carbide substrate according to any one of [1] to [ 7 ], which is used when polishing a hexagonal silicon carbide single crystal wafer (0001) silicon surface.

[ 9 ] Hexagonal silicon carbide single crystal wafer (0001) The abrasive composition for a silicon carbide substrate according to any one of [1] to [ 7 ], which is used when polishing a surface other than a silicon surface.

  By using the abrasive composition of the present invention, the surface to be polished can be finished without scratches or scratches at a high polishing rate. Further, the abrasive composition of the present invention shortens the production time, and at low cost, semiconductor substrates such as silicon carbide, silicon, germanium, gallium arsenide, gallium phosphide, indium phosphide, sapphire, lithium tantalate, lithium niobate, etc. Single crystal substrates, magnetic disk substrates such as Ni-P plated aluminum and glass, magnetic heads, and the like can be manufactured. In particular, it can be suitably used for polishing a silicon carbide substrate.

Embodiments of the present invention will be described below. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

  The abrasive composition of the present invention is a metal oxo acid and its salt, at least one selected from the group consisting of isopolyacids, heteropolyacids, isopolyacid salts and heteropolyacid salts, abrasive grains, oxygen donors, pH control. It contains an agent and water. The isopolyacid is tungstic acid and / or molybdate, and the isopolyacid salt is tungstate and / or molybdate.

  In addition, examples of the heteropolyacid include a tungsten-based heteropolyacid and / or a molybdenum-based heteropolyacid, and examples of the heteropolyacid salt include a tungsten-based heteropolyacid salt and / or a molybdenum-based heteropolyacid salt.

  Oxo acid refers to a compound in which a hydroxyl group (—OH) and an oxo group (═O) are bonded to a certain atom, and the hydroxyl group gives an acidic proton. Polyoxoacid is produced by dehydration condensation of oxoacid. Among polyoxoacids, transition metal element oxoacids are referred to as metal oxoacids (polyacids). A compound composed of one kind of transition metal ion among metal oxo acids is called isopolyacid, and a condensed polynuclear oxo complex containing two or more elements is called heteropolyacid.

  Here, examples of the tungsten-based heteropolyacid include at least one selected from the group consisting of phosphotungstic acid, silicotungstic acid, and phosphotungstomolybdic acid. Here, the heteropolyacid containing tungsten is referred to as a tungsten-based heteropolyacid.

  Here, examples of the molybdenum-based heteropolyacid include at least one selected from the group consisting of phosphomolybdic acid, phosphotungstomolybdic acid, and phosphovanadomolybdic acid. Here, the heteropolyacid containing molybdenum is referred to as a molybdenum-based heteropolyacid.

  Here, examples of the tungstate include one or more selected from the group consisting of ammonium paratungstate, ammonium metatungstate, potassium tungstate, and calcium tungstate. Examples of the molybdenum-based heteropoly acid salt include sodium phosphomolybdate. The content of tungstic acid, molybdic acid, tungsten-based heteropolyacid, molybdenum-based heteropolyacid, tungstate, molybdate, tungsten-based heteropolyacid salt and molybdenum-based heteropolyacid salt in the polishing composition is 0.1 mass If it is less than%, the polishing rate may be reduced. If it exceeds 10% by mass, insoluble matter is generated from the viewpoint of solubility, which is not economical. The range of 0.1-10 mass% is preferable. More preferably, it is 0.5-5 mass%. More preferably, it is 1-3 mass%.

  Here, as an abrasive grain, 1 type, or 2 or more types chosen from the group which consists of colloidal silica, fumed silica, wet synthetic silica, and alumina is mentioned. Of these, colloidal silica is preferred. When the content of the abrasive grains in the abrasive composition is less than 2% by mass, the polishing rate may decrease. Even if it exceeds 40% by mass, the polishing rate is not improved and is not economically effective. More preferably, it is 5-25 mass%. More preferably, it is 7-15 mass%.

  The average particle diameter of the abrasive grains is preferably in the range of 10 to 200 nm because the polishing rate decreases when it is less than 10 nm, and the surface roughness of the surface to be polished is not necessarily good when it exceeds 200 nm. 30-100 nm is more preferable. More preferably, it is 40-90 nm.

In the present specification, the average particle diameter is a value measured by a known Sears titration method in the case of colloidal silica. The Sears titration method is converted from a specific surface area by titration with sodium hydroxide as described in ANALYTIKAL CHEMISTRY Vol. 28 No. 12 (December 1956), p. 1981. The particle diameter is calculated from the value (Sa) of the BET method specific surface area using the following conversion formula.
Dp = 6000 / ρ · Sa
(However, Dp: average particle diameter (nm), Sa: BET specific surface area (m ² / g), ρ: density (g / cm ³ ))

  The oxygen donor is a kind of oxidizing agent, and is a substance that generates hydroxy ions, hydroxy radicals, oxygen ions, oxygen radicals, and active oxygen (the nascent oxygen), and the abrasive composition of the present invention. Contains one or more selected from the group consisting of hydrogen peroxide, peracetic acid and cumene hydroperoxide as oxygen donors.

  The content of the oxygen donor in the abrasive composition is preferably in the range of 0.2 to 8% by mass. 0.5-5 mass% is more preferable. More preferably, it is the range of 1-3 mass%.

  Although it does not specifically limit as a pH adjuster, In order to adjust pH of an abrasive | polishing agent composition to a desired value, an acidic substance or a basic substance is used suitably. As acids, inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid and phosphoric acid, and organic acids are preferably acetic acid. As the base, ammonia, caustic soda, caustic potash, monoethanolamine, diethanolamine, triethanolamine, piperazine and the like are preferable.

  The abrasive composition of the present invention is a semiconductor substrate such as silicon carbide, silicon, germanium, gallium arsenide, gallium phosphide, indium phosphide, single crystal substrate such as sapphire, lithium tantalate, lithium niobate, Ni-P plated It can be used for polishing magnetic disk substrates such as aluminum and glass, magnetic heads, and the like. In particular, it can be suitably used as a polishing composition for silicon carbide substrates.

  Types of crystal planes of silicon carbide include planes such as (0001), (000-1), (1-100), and (11-20). The abrasive composition of the present invention can be suitably used for polishing any of crystal planes other than the (0001) plane and the (0001) plane, which are difficult to polish, particularly the (0001) plane and (0001) plane. Among the crystal planes other than the above, it is preferable to use for polishing the (000-1) plane.

  When the silicon surface of the (0001) plane of the hexagonal silicon carbide single crystal substrate is polished with the abrasive composition, the pH of the abrasive composition is preferably in the range of 1 to 11, more preferably in the range of 2 to 9. Furthermore, the range of 3-8 is more preferable. More preferably, it is the range of 4-6.

  The polishing of the silicon surface of (0001) with the silicon carbide polishing composition is considered to progress by the following action. Silicon carbide is a silicon-carbon covalent bond, but has Pauling's electronegativity (Xp) of silicon 1.8 and carbon 2.5. Thus, silicon is positively charged and carbon is negatively charged. About 13% of the silicon-carbon covalent bonds are formed by ionic bonds.

  For example, taking tungstic acid as an example, in the acidic region of the polishing composition, tungstic acid releases hydrogen ions and is in the state of tungstate ions (formula-1).

  It is surmised that the hexagonal silicon carbide single crystal wafer (0001) silicon surface and tungstate ion (formula-1) have a coordination structure of (formula-2).

In the coordination structure (Formula-2), O ^{− of the} tungstate ion is coordinated to the positively charged Si ⁺ of the hexagonal silicon carbide single crystal wafer (0001). On the other hand, tungstate ions are coordinated to C ⁻ of a hexagonal silicon carbide single crystal wafer (0001) in which free H ⁺ ions are negatively charged. The hexagonal silicon carbide single crystal wafer (0001) has a coordination structure (formula-2), which weakens the bonding force of Si-C, and further undergoes an oxidative cleavage reaction under the attack of hydrogen peroxide. . On the (0001) Si surface, a thin film of silicon oxide is formed on the outermost surface by the oxidizing action of hydrogen peroxide. The thin film is peeled off and polished by colloidal silica (abrasive grains). On the other hand, it is presumed that C is carbon particles, and part thereof is oxidized and gasified by hydrogen peroxide.

Hexagonal silicon carbide single crystal substrate (0001) When a carbon surface (000-1) other than a silicon surface is polished using an abrasive composition, the pH of the abrasive composition is preferably in the range of 3-8. . Furthermore, the range of 4-7 is more preferable. If the pH of the abrasive composition is 8 or less, polishing can be performed at an economical polishing rate. The reason why the polishing rate of the carbon surface (000-1) is improved as the pH is lowered is considered to be as follows. H ⁺ ions in the abrasive composition are electrostatically attracted to the negatively charged (000-1) carbon surface. Tungstate ions are coordinated through the H ⁺ ions. As a result, the bonding force of Si—C becomes weak, and further, an oxidative cleavage reaction occurs due to the action of hydrogen peroxide, and the carbon surface (000-1) generates carbon, carbon dioxide gas, etc. due to the oxidizing action of hydrogen peroxide. It is thought that polishing is promoted.

  Therefore, when polishing the hexagonal silicon carbide single crystal substrate (0001) silicon surface and the (000-1) carbon surface at the same time, the pH of the abrasive composition is preferably in the range of 1 to 11, more preferably 2 to 9. The range is preferable, and the range of 3 to 8 is more preferable. More preferably, it is the range of 4-7.

  Examples of the water used in the abrasive composition of the present invention include distilled water and ion exchange water. In view of the cleanability of the silicon carbide substrate, ion exchange water is preferred. In addition, although the abrasive | polishing agent composition of this invention may manufacture what was adjusted to the density | concentration suitable for grind | polishing a silicon carbide board | substrate, you may adjust suitably what was manufactured as a concentrated liquid at the time of use.

  The abrasive | polishing agent composition of this invention may contain the component contained in this kind of normal abrasive | polishing agent composition for substrates as needed. Examples of such components include surfactants, detergents, rust inhibitors, surface modifiers, viscosity modifiers, antibacterial agents, and dispersants.

  As described above, by using the abrasive composition of the present invention, it is possible to improve the polishing rate and produce a silicon carbide substrate having a good surface roughness.

  The abrasive | polishing agent composition of this invention may be supplied with the 1 liquid type containing all the compositions, and may be supplied with a 2 liquid type.

  Next, the abrasive | polishing agent composition of this invention is demonstrated using an Example. In addition, this invention is not limited to the following Examples at all, and as long as it belongs to the technical scope of this invention, it cannot be overemphasized that it can implement with a various aspect.

(Examples 1-6, Reference Examples 1-22 , Comparative Examples 1-8)
Mix tungstic acid, phosphotungstic acid, silicotungstic acid, phosphotungstomolybdic acid, tungstate, molybdic acid, phosphomolybdic acid, phosphomolybdate, oxygen donor, abrasive, pH adjuster and pure water. Then, an abrasive composition having the composition shown in Table 1 was obtained by stirring.

  Table 2 shows the substance names of tungstate, phosphomolybdate, oxygen donor, abrasive grains, and pH adjuster.

  Using the obtained abrasive composition, a silicon carbide substrate was polished using a single-side polishing machine under the following polishing conditions.

(Polishing conditions)
Polishing machine: Fujikoshi Machine Co., Ltd. SLM-100 Single-side polishing machine Polishing pressure: 500 g / cm ²
Polishing pad: SUBA-800 (Rodernitta Co., Ltd.)
Surface plate rotation speed: 100 rpm
Abrasive composition supply amount: 100 ml / min
Polishing time: 5 hours

  In the evaluation of the characteristics of the surface to be polished, the polishing rate was determined by the following equation (Equation 1). The state of scratches and scratches was examined using an optical microscope at a magnification of 200 times. The state where there was no scratch or scratch on the surface was indicated as “◯”, the recognized one was indicated as “X”, and the case where the polishing test was not performed or the surface was not observed was indicated as “−”.

Polishing rate (nm / hr) = (mass before polishing of silicon carbide substrate−mass after polishing of silicon carbide substrate) (g) ÷ polishing area of silicon carbide substrate (cm ² ) ÷ density of silicon carbide substrate (g / cm ³ ) ÷ Polishing time (hr) × 10 ⁷ (Equation 1)

Table 3 shows the results of polishing rates and polishing surface states of Examples 1 to 6, Reference Examples 1 to 22 , and Comparative Examples 1 to 8.

As shown in Table 3, the polishing rates of the silicon surfaces of (0001) and (000-1) of Examples 1 to 6 and Reference Examples 1 to 22 are higher than those of Comparative Examples 1 to 8, and Also, the polished surface condition is good with no scratches or scratches. In addition, the polishing rate “0” in Comparative Examples 1 and 5 indicates that the polishing was not performed at all, and the polishing rate “−” on the carbon surface in Examples 2 to 4 and Example 6 was performed only on the silicon surface. It represents that.

  Since the abrasive composition of the present invention passes through a structure in which tungstic acid, molybdic acid, heteropolyacid, tungstate, molybdate and / or heteropolyacid salt are coordinated to silicon and carbon on the surface of the silicon carbide substrate, The (0001) silica surface and the (000-1) carbon surface can be efficiently polished.

  The abrasive composition of the present invention can be used for production of a base substrate of a gallium nitride thin film in the field of silicon carbide power semiconductors and optical devices.

Claims (9)

A salt thereof with a metal oxo acid, and also contains at least the one selected from the group consisting of F heteropolyacid San及 beauty heteropoly acid salts, abrasives, oxygen donating agents, pH adjusting agents, and water,
The abrasive is colloidal silica,
A polishing composition for a silicon carbide substrate, wherein the oxygen donor is hydrogen peroxide .   The polishing agent for a silicon carbide substrate according to claim 1, wherein the heteropolyacid is a tungsten-based heteropolyacid and / or a molybdenum-based heteropolyacid, and the heteropolyacid salt is a tungsten-based heteropolyacid salt and / or a molybdenum-based heteropolyacid salt. Composition.   The abrasive composition for a silicon carbide substrate according to claim 2, wherein the tungsten-based heteropolyacid is at least one selected from the group consisting of phosphotungstic acid, silicotungstic acid, and phosphotungstomolybdic acid.   The abrasive composition for a silicon carbide substrate according to claim 2 or 3, wherein the molybdenum-based heteropolyacid is at least one selected from the group consisting of phosphomolybdic acid, phosphotungstomolybdic acid, and phosphovanadomolybdic acid.   The abrasive composition for a silicon carbide substrate according to any one of claims 2 to 4, wherein the molybdenum-based heteropolyacid salt is sodium phosphomolybdate. The polishing composition for silicon carbide substrates according to any one of claims 1 to 5 , wherein the pH is 1.0 or more and less than 11.0. The said pH adjuster which adjusts pH to 1.0 or more and less than 11.0 contains at least 1 type of compound chosen from the group which consists of an inorganic acid, an organic acid, an inorganic basic compound, and an organic basic compound. 6. The abrasive composition for silicon carbide substrates according to 6. The abrasive composition for a silicon carbide substrate according to any one of claims 1 to 7 , which is used when a hexagonal silicon carbide single crystal wafer (0001) silicon surface is polished. The abrasive composition for a silicon carbide substrate according to any one of claims 1 to 7 , which is used for polishing a surface other than a hexagonal silicon carbide single crystal wafer (0001) silicon surface.