Surface machining method for single crystal SiC substrate, manufacturing method thereof, and grinding plate for surface machining single crystal SiC substrate

Abstract

A surface machining method for a single crystal SiC substrate, including: a step of mounting a grinding plate which includes a soft pad and a hard pad sequentially attached onto a base metal having a flat surface, a step of generating an oxidation product by using the grinding plate, and a step of grinding the surface while removing the oxidation product, wherein abrasive grains made of at least one metallic oxide that is softer than single crystal SiC and has a bandgap are fixed to the surface of the hard pad.

Claims

1. A surface machining method for a single crystal SiC substrate, comprising: a step of mounting a grinding plate which includes a first pad and a second pad harder than the first pad sequentially attached onto a base metal having a mounting surface in a grinder, a step of generating an oxidation product by using the grinding plate, and a step of grinding the surface while removing the oxidation product, wherein abrasive grains made of at least one metallic oxide that is softer than single crystal SiC and has a bandgap are fixed to the surface of the second pad; the grinder has a table for a substance to be machined for fixing a driving unit for rotatably mounting the grinding plate and a single crystal SiC substrate; and the step of grinding the surface is carried out by rotating the grinding plate at a rotational speed of 500 rpm to 3000 rpm.

2. The surface machining method for a single crystal SiC substrate according to claim 1, wherein pure water is used as a coolant.

3. The surface machining method for a single crystal SiC substrate according to claim 1, wherein a coolant is not used or the supply rate of pure water used as the coolant is greater than 0 ml/min and less than or equal to 100 ml/min.

4. The surface machining method for a single crystal SiC substrate according to claim 1, wherein the metal oxide is one or more selected from cerium oxide, titanium oxide, silicon oxide, aluminum oxide, iron oxide, zirconium oxide, zinc oxide, and tin oxide.

5. The surface machining method for a single crystal SiC substrate according to claim 1, wherein the metal oxide includes at least cerium oxide.

6. The surface machining method for a single crystal SiC substrate according to claim 1, wherein the abrasive grains are fixed by using a binding agent and/or an adhesive.

7. The surface machining method for a single crystal SiC substrate according to claim 1, wherein the abrasive grains are fixed by attaching an abrasive grain-fixed film to the second pad.

8. A method for producing a single crystal SiC substrate, comprising: a step of mounting a grinding plate which includes first pad and second pad harder than the first pad sequentially attached onto a base metal having mounting surface in a grinder, a step of generating an oxidation product by using the grinding plate, and a step of grinding the surface while removing the oxidation product, wherein abrasive grains made of at least one metallic oxide that is softer than single crystal SiC and has a bandgap are fixed to the surface of the second pad, the grinder has a table for a substance to be machined for fixing a driving unit for rotatably mounting the grinding plate and a single crystal SiC substrate; and the step of grinding the surface is carried out by rotating the grinding plate at a rotational speed of 500 rpm to 3000 rpm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B are a schematic view illustrating the structure of a grinding plate of the present invention.

(2) FIG. 2 is a schematic view illustrating a part of the structure of an example of a surface grinder in which the grinding plate of the present invention is used.

(3) FIG. 3 is an optical photomicrograph of a surface of a single crystal SiC ingot before machining in a first example of the present invention.

(4) FIG. 4 is an optical photomicrograph of the surface of the single crystal SiC ingot after the machining in the first example of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) Hereinafter, for a surface machining method for a single crystal SiC substrate, a manufacturing method thereof, and a grinding plate for surface machining a single crystal SiC substrate to which the present invention is applied, the configurations thereof will be described using drawings. In the drawings, there are cases in which the characteristic portions are enlarged for the better understanding of the characteristics and the dimensional ratios and the like of the respective constituent components are not always identical to the actual dimensional ratios and the like thereof. In addition, materials, dimensions, and the like exemplified in the following description are simple examples and the present invention is not limited thereto and can be carried out in an appropriately modified manner within the scope of the gist of the present invention.

Grinding Plate for Surface Machining a Single Crystal SiC Substrate

(6) FIGS. 1A and 1B contain schematic views illustrating an example of a grinding plate for surface machining a single crystal SiC substrate according to an embodiment of the present invention. FIG. 1A is a sectional view and FIG. 1B is a plan view.

(7) A grinding plate 10 illustrated in FIGS. 1A and 1B includes a base metal 1 having a flat surface and a soft pad 2 and a hard pad 3 sequentially attached onto the base metal 1. Abrasive grains (not illustrated) made of at least one metallic oxide that is softer than single crystal SiC and has a bandgap are fixed to the surface of the hard pad 3.

(8) In this example, the soft pad 2 and the hard pad 3 are attached to each other through an adhesive sheet 4 and the hard pad 3 is made up of eight sheets (3a) that are segmented in a right-angled triangular shape. In addition, the base metal 1 includes a screw hole 1a for fixing the grinding plate to a grinder. In this case, the adhesive sheet 4 is used to prevent water absorption of the soft pad when a coolant such as pure water or the like is used and to stabilize the attachment of the hard pad. However, the hard pad 3 and the soft pad 2 may be directly attached to each other without using the adhesive sheet.

(9) In addition, as illustrated in this example, the soft pad 2 and the adhesive sheet 4 need not have a hole at a portion corresponding to the screw hole 1a for the purpose of covering the screw hole 1a with a lid to prevent the intrusion of chips or the coolant.

(10) When mechanically rubbed with a substance to be machined during surface grinding of the single crystal SiC substrate, the abrasive grains having a bandgap supply energy, thus, electrons on the surfaces of the abrasive grains are excited, and then electron-hole pairs are generated, active species having an extremely strong oxidation power such as a superoxide anion, a hydroxyl radical, or atomic oxygen and the surface of the specimen is oxidized. In addition, SiO.sub.2.nH.sub.2O generated due to the oxidization of the surface of the specimen is removed using abrasive grains, whereby the surfaces of the single crystal SiC substrate can be machined. That is, a tribo-catalytic action is exhibited.

(11) As a material having a bandgap which exhibits a tribo-catalytic action, particularly, metallic oxides are all materials softer than the single crystal SiC. In addition, since almost all metallic oxides are materials having a bandgap, and powder having tribo-catalytic action can be industrially produced and used in abrasive grains, pigments, photocatalysts, and the like, metallic oxides can be preferably used.

(12) The powder of at least one metallic oxide selected from cerium oxide, titanium oxide, silicon oxide, aluminum oxide, iron oxide, zirconium oxide, zinc oxide, and tin oxide is preferable since the metallic oxide can be easily produced industrially and is a material having a bandgap and thus has a tribo-catalytic action.

(13) Cerium oxide is the metallic oxide, the powder of which can be most preferably used, in consideration of the fact that cerium oxide can be, industrially, easily procured and is a semiconductor material having a bandgap and thus exhibits the tribo-catalytic action.

(14) Since the abrasive grains need to have the capability to remove SiO.sub.2.nH.sub.2O, they need to have a specific particle diameter. However, when the primary particle diameter is large, the specific surface area becomes small and, similar to a photocatalytic action, the tribo-catalytic action cannot be efficiently exhibited, and thus there is an appropriate range therefor. That is, in terms of the mechanical removal capability of the abrasive grains, a large grain diameter, that is, a small specific surface area is advantageous. Meanwhile, similar to an ordinary catalytic action, the tribo-catalytic action is affected by the surface and thus a large specific surface area leads to a strong effect. Therefore, a range in which both the grain diameter and the specific surface area are well-balanced becomes the above-described appropriate range.

(15) The specific surface area of the abrasive grains is preferably in a range of 0.1 m.sup.2/g to 300 m.sup.2/g. This is because, when the specific surface area is smaller than 0.1 m.sup.2/g, there is a concern that the tribo-catalytic action cannot be efficiently exhibited and, when the specific surface area is larger than 300 m.sup.2/g, there is a concern that SiO.sub.2.nH.sub.2O cannot be efficiently removed.

(16) The specific surface area of the abrasive grains is more preferably in a range of 0.5 m.sup.2/g to 200 m.sup.2/g. This is because, when the specific surface area is set to 0.5 m.sup.2/g or more, the tribo-catalytic action can be more efficiently exhibited and, when the specific surface area is set to 200 m.sup.2/g or less, SiO.sub.2.nH.sub.2O can be more efficiently removed.

(17) The specific surface area of the abrasive grains is still more preferably in a range of 1 m.sup.2/g to 100 m.sup.2/g. This is because, when the specific surface area is set to 1 m.sup.2/g or more, the tribo-catalytic action can be still more efficiently exhibited and, when the specific surface area is set to 100 m.sup.2/g or less, SiO.sub.2.nH.sub.2O can be still more efficiently removed.

(18) Since the grinding plate includes the base metal, the grinding plate can be mounted in a grinder in order to be used in the grinder.

(19) As the base metal, a well-known base metal can be used and examples thereof include base metals the material of which is an aluminum alloy such as silumin.

(20) The base metal has a flat surface facing a substance to be machined and the grinding plate has a structure in which the soft pad and the hard pad are sequentially attached onto the flat surface thereof. When the above-described structure is provided, the machining of the surface standard, that is, the machining uniformly flattening the surface of a substance to be machined on the basis of the surface to be machined of the substance to be machined as the standard surface, is possible and it is possible to suppress scratches generated on the surface of the single crystal SiC substrate, which is the substance to be machined, to the minimum extent.

(21) As the soft pad, it is possible to use a non-woven fabric or suede-based pad.

(22) As the hard pad, it is possible to use a foamed polyurethane-based pad.

(23) On the outermost surface of the grinding plate which is subjected to machining, the abrasive grains made of at least one metallic oxide that is softer than single crystal SiC and has a bandgap is fixed to the surface of the hard pad. These abrasive grains can be fixed to the surface of the hard pad using a binding agent or an adhesive.

(24) In addition, the abrasive grains can be fixed by attaching a commercially available abrasive grain-fixed film to the hard pad.

The Surface Machining Method for the Single Crystal SiC Substrate

(25) In a surface machining method for a single crystal SiC substrate according to an embodiment of the present invention, a grinding plate including a soft pad and a hard pad sequentially attached onto a base metal having a flat surface, in which abrasive grains made of at least one metallic oxide that is softer than single crystal SiC and has a bandgap is fixed to the surface of the hard pad, is mounted in a grinder, an oxidation product is generated by using the grinding plate, and the surface is ground while removing the oxidation product.

(26) As the grinder in which the grinding plate is mounted, a well-known grinder can be used.

(27) FIG. 2 is a schematic view illustrating the structure of a part that grinds the single crystal substrate of an example of the grinder in which the grinding plate of the present invention is mounted. The grinding plate 10 illustrated in FIGS. 1A and 1B is mounted in a driving unit 11 and the driving unit is rotated using a motor belt. A single crystal SiC substrate 12 is fixed to a table for a substance to be machined 13 through vacuum adsorption using a vacuum chucking device (not illustrated). A substrate-holding section 14 is sent in a grinding plate direction while being rotated together with the table for a substance to be machined 13, whereby the substrate is ground.

(28) When the grinding conditions are appropriately selected, the tribo-catalytic action of the grinding plate with respect to single crystal SiC is significantly exhibited and thus an oxidation product can be generated.

(29) The rotation speed of the grinding plate is preferably in a range of 300 rpm to 3000 rpm. This is because, when the rotation speed is lower than 300 rpm, the mechanical energy supplied to the abrasive grains is too small and there is a concern that the tribo-catalytic action may not be exhibited and, when the rotation speed is higher than 3000 rpm, there is a concern that a problem of heat generation or the vibration of the device may become unignorable. Since there has been no experience of applying a grinding plate having the tribo-catalytic action to a grinder, it has not been clear whether or not the tribo-catalytic action is exhibited in the existing specification of the grinder. As a result of intensive studies, it has been clarified that an ordinary rotation speed of the grinding plate can be applied.

(30) The rotation speed of the grinding plate is more preferably in a range of 500 rpm to 2000 rpm. This is because, when the rotation speed is set to 500 rpm or higher, it becomes possible to generate more sufficient mechanical energy for the tribo-catalytic action and, when the rotation speed is set to 2000 rpm or lower, it becomes possible to more reliably avoid the problem of heat generation or the vibration of the device.

(31) The rotation direction of the table for a substance to be machined can be set in the forward direction (the same direction) of the rotation direction of the grinding plate. In this case, the rotation speed of the table for a substance to be machined is preferably in a range of 80% to 120% of the rotation speed of the grinding plate. This is because, when the rotation speed of the table for a substance to be machined is set to lower than 80% or higher than 120% of the rotation speed of the grinding plate, the amount of the machined surface removed becomes uneven.

(32) The rotation direction of the table for a substance to be machined can be set in the inverse direction of the rotation direction of the grinding plate. In this case, in order to uniform the amount of the machined surface removed, the rotation speed of the table for a substance to be machined is preferably in a range of 30 rpm to 300 rpm under the condition that the hard pad is segmented into an appropriate shape.

(33) The reasons therefore are as described below.

(34) When the hard pad is segmented, that is, the hard pad is divided and attached in an appropriate size, it is possible to control the contact frequency between the abrasive grains on the grinding plate, which rotates in the inverse direction to the substance to be machined, and the surface to be machined of the substance to be machined and, for example, it is possible to prevent uneven machining in which only the central portion of the substance to be machined is ground to a great extent. In an ordinary grinder, the table for a substance to be machined is disposed so that the rotation center of the table for a substance to be machined lies on an outer circumferential portion of the grinding plate and the rotation direction of the table for a substance to be machined is the inverse direction of the rotation direction of the grinding plate. Therefore, when the abrasive grains are present throughout the entire surface of the grinding plate, the contact frequency of the abrasive grains to the central portion of the substance to be machined increases and only the central portion is ground. Appropriate segmentation for preventing the above-described phenomenon is effective.

(35) In addition, when the rotation speed of the table for a substance to be machined is set to lower than 30 rpm or higher than 300 rpm, the grinder operates outside the ordinary specification and there is a concern that the amount of the machined surface removed becomes uneven.

(36) In a case in which a coolant is used, pure water is preferably used. This is because, when there is an impurity component, there is a concern that the tribo-catalytic action may not be exhibited. For the tribo-catalytic action, it is important to make the mechanical energy efficiently contribute to the generation of electron-hole pairs. However, there is a concern that the interposition of impurities itself may hinder the efficient contribution of the mechanical energy, in addition, the enhancement of the lubrication action of water decreases the friction resistance and, consequently, there is a concern that the mechanical energy supplied to the abrasive grains may decrease. In addition, there is another concern that the interposition of impurities may hinder a process in which the abrasive grains efficiently remove the oxidation product.

(37) The coolant may not be used and, when pure water is used as the coolant, the supply rate of pure water is preferably 100 ml/min or lower. This is because, when the supply rate thereof is higher than 100 ml/min, the energy supplied to the abrasive grains due to mechanical rubbing becomes too small and there is a concern that the tribo-catalytic action may not be sufficiently exhibited. In addition, this is because, when the supply rate of pure water is too high, the action of pure water as a lubricant becomes strong and the friction resistance decreases. As a result, the energy supplied to the abrasive grains becomes small and there is another concern that only an insufficient number of electron-hole pairs may be generated.

The Method for Manufacturing the Single Crystal SiC Substrate

(38) A method for manufacturing a single crystal SiC substrate according to an embodiment of the present invention includes a step of mounting a grinding plate which includes a soft pad and a hard pad sequentially attached onto a base metal having a flat surface, a step of generating an oxidation product by using the grinding plate, and a step of grinding the surface while removing the oxidation product, wherein abrasive grains made of at least one metallic oxide, that is softer than single crystal SiC and has a bandgap, are fixed to the surface of the hard pad. In the method for the present invention, since the oxidation on the surface of SiC is used, the method has a relationship with the height of the oxidation barrier and can be preferably applied to a C plane of a (0001) plane of the SiC substrate.

EXAMPLES

(39) Hereinafter, the present invention will be more specifically described by using examples, but the present invention is not limited to the following examples.

First Example

(40) The surface of an aluminum alloy base metal having a M12 screw hole and an outer diameter of 150 mm, which was prepared so as to be capable of being mounted on a grinder MHG-2000 manufactured by Shuwa Industry Co., Ltd., which faced a substance to be machined, was machined to be flat and a pad for CMP SUBA600 (soft pad) manufactured by Nitta Haas Incorporated was attached onto the above-described surface. Next, eight pads for CMP IC1000 (hard pads) manufactured by Nitta Haas Incorporated, which were segmented into a 30 mm40 mm50 mm right-angled triangular shape, were attached onto the SUBA600 through an FEP adhesive sheet film manufactured by AS ONE Corporation, thereby producing a grinding plate base body. Truing was carried out on the grinding plate base body using a conditioner CMP-M100A manufactured by Asahi Diamond Industrial Co., Ltd. Finally, TRIZACT film (cerium oxide) manufactured by 3M, which was segmented into a 30 mm40 mm50 mm right-angled triangular shape, was attached onto the surface of the trued IC1000 segment, thereby producing a grinding plate for surface machining single crystal SiC substrates having the tribo-catalytic action.

(41) Next, the produced grinding plate was mounted in a grinder MHG-2000. An n-type (000-1) 4HSiC (4 off) single crystal ingot (C plane) (single crystal SiC substrate) having a diameter of three inches manufactured by Tankeblue Semiconductor Co., Ltd., which was previously ground to be flat using a vitrified bond diamond wheel (#4000) manufactured by Asahi Diamond Industrial Co., Ltd., was fixed to a table for a substance to be machined using a vacuum chucking device, and the surface on the C plane side was machined.

(42) The rotation direction of the table for a substance to be machined was set in the inverse direction of the rotation direction of the grinding plate, the rotation speed of the table for a substance to be machined was set, and the surface was machined at a supply rate of pure water of 0 ml/min, that is, in a dry mode. The table for a substance to be machined was manually sent slowly and the current value of a motor for the rotation of the grindstone was set in a range of 2.4 A to 2.8 A. The machining time was three minutes.

(43) Regarding the amount of the single crystal ingot removed, as a result of measuring the heights of the ingot before and after the machining at nine points in the surface using a height meter manufactured by Mitutoyo Corporation and computing the amounts, the average value was 3.8 m. The machining speed had a high value of 1.3 m/min. The difference between the maximum value and the minimum value of the height of the ingot after the machining was 1.4 m and the surface was uniformly machined.

(44) The results of the dark-field observation of the surface of the ingot before and after machining carried out by using an optical microscope manufactured by Olympus Corporation are illustrated in FIGS. 3 and 4.

(45) Numerous scratches due to grinding generated by the #4000 diamond abrasive grains observed in the ingot before machining completely disappeared. Only bright points caused by crystal defects or fine foreign substances were observed, and a mirror finish with no machining strain was achieved.

Second Example

(46) The grinding plate for surface machining single crystal SiC produced in the first example was used and the machining was carried out under the same grinding conditions as in the first example except for the fact that the amounts of pure water supplied were set to 10 ml/min, 50 ml/min, and 100 ml/min.

(47) The machining rates were 1.0 m/min, 0.6 m/min, and 0.2 m/min respectively and, similar to the case of the first example, it was confirmed that grinding scratches completely disappeared in the dark-field observation by using an optical microscope.

Comparative Example 1

(48) The grinding plate for surface machining single crystal SiC produced in the first example was used and the machining was carried out under the same grinding conditions as in the first example except for the fact that the amount of pure water supplied was set to 150 ml/min. As a result, it was confirmed that the machining rate was almost zero and grinding scratches rarely disappeared in the dark-field observation using an optical microscope. It is considered that, at the amount of pure water supplied of 150 ml/min, the energy supplied to the abrasive grains by the mechanical rubbing was too small and the tribo-catalytic action was not exhibited.

Comparative Example 2

(49) As a result of using a resin-bonded cerium oxide grindstone manufactured by Nihon Grinding Wheel Co., Ltd. as a grinding plate and carrying out the same machining as in the first example, the average value of the machining rates was 0.7 m/min. However, the grinding was not uniformly carried out so that the central portion of the ingot was ground to a great extent and small scratches were observed in the dark-field observation using an optical microscope. It is considered that, unlike the present invention, the grinding plate did not have a configuration of the combination of the soft pad and the hard pad and thus machining on the basis of the surface standard was not possible and, furthermore, it was not possible to suppress the generation of small scratches.

Industrial Applicability

(50) The surface machining method for a single crystal SiC substrate, the manufacturing method thereof, and the grinding plate for surface machining a single crystal SiC substrate of the present invention can be used for the production of single crystal SiC substrates and can be used in a step of machining a substrate to be thin by grinding the back surface of the substrate after device fabrication.

REFERENCE SIGNS LIST

(51) 1 BASE METAL

(52) 2 SOFT PAD

(53) 3 HARD PAD

(54) 10 GRINDING PLATE FOR SURFACE MACHINING SINGLE CRYSTAL SiC SUBSTRATE