Processing method of workpiece

Abstract

There is a need for a machining method that can improve the machining speed in electrical discharge machining and produce a smooth machined surface. [Solution] A method for machining a workpiece, wherein an electrical discharge machining fluid is interposed between a wire and the workpiece, and the workpiece is machined by electrical discharge, wherein the kinematic viscosity of the electrical discharge machining fluid at 40°C is 0.70 to 5.0 mm². 2 A processing method wherein the speed of the wire during processing is 11 m / min or more, the diameter of the wire is 30 to 250 μm, the wire speed during processing is 11 m / min or more, and the tension of the wire during processing is 1 to 24 N.

Description

[Technical Field]

[0001] The present invention relates to a method for processing a workpiece and a method for manufacturing a wafer. [Background technology]

[0002] In recent years, electrical discharge machining (EDM) technology has been developed that allows for the simultaneous cutting of multiple workpieces, such as silicon carbide (SiC) ingots, in a short amount of time. This explanation of electrical discharge machining (EDM) uses general metal material processing as an example. Electrical discharge machining is a technique that processes a workpiece using the heat generated by an electrical discharge phenomenon. Specifically, when a workpiece is immersed in an insulating EDM fluid and a pulse voltage is applied between the workpiece and the electrode, an arc discharge occurs between the workpiece and the electrode, causing the workpiece to become hot, evaporate, and melt, thereby processing the workpiece. The molten portion of the workpiece, heated by the arc column, is blown away by a superheating phenomenon and enters the EDM fluid, where surface tension causes it to become fine spherical metal powder. This metal powder is then discharged outside the electrode due to the flow of the EDM fluid.

[0003] Water is often used as the electrical discharge machining fluid in such electrical discharge machining processes. For example, Patent Document 1 discloses an electrical discharge machining fluid composition containing an imide compound and water. On the other hand, Patent Document 2 is a document relating to a wire electrical discharge machining apparatus used for electrical discharge machining, and it is stated in a single line that while water is mainly used as the machining fluid in the apparatus, an electrical discharge machining oil with oil as the main component may also be used. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-179381 [Patent Document 2] Japanese Patent Publication No. 2014-659 [Overview of the project] [Problems that the invention aims to solve]

[0005] As wire electrical discharge machining, apparatuses and machining methods using water as a machining fluid have been developed, but there is room for improvement in terms of machining speed and surface smoothing of the machined surface. Under such circumstances, a machining method for a workpiece that can form a smooth machined surface while increasing the machining speed in electrical discharge machining is required.

Means for Solving the Problem

[0006] In one aspect of the present invention, there is provided a machining method for a workpiece in which when machining the workpiece using a wire of a specific diameter, the linear speed and tension of the wire are adjusted within a predetermined range using a wire electrical discharge machining oil having a specific kinematic viscosity. Specifically, as one aspect of the present invention, for example, the following aspects [1] to

[12] are provided. [1] A machining method for a workpiece in which electrical discharge is performed with a wire electrical discharge machining oil interposed between the wire and the workpiece to machine the workpiece, wherein the kinematic viscosity of the wire electrical discharge machining oil at 40 °C is 0.70 to 5.0 mm 2 / s, the diameter of the wire is 30 to 250 μm, the linear speed of the wire during the machining is 11 m / min or more, the tension of the wire during the machining is 1 to 24 N, machining method. [2] The open discharge voltage during the machining is 5 to 800 V, and the machining method according to [1] above. [3] The discharge current during the machining is 0.5 to 100 A, and the machining method according to [1] or [2] above. [4] The workpiece is an ingot having a maximum machining width of 0.5 inches or more, and the machining method according to any one of [1] to [3] above. [5] The processing method according to any one of the above [1] to [4], wherein the workpiece is made of a semiconductor material containing at least one selected from silicon compounds and gallium compounds. [6] The machining method according to any one of the above [1] to [5], wherein the base oil content is 30% by mass or more based on the total amount of the electrical discharge machining oil. [7] The processing method according to [6] above, wherein the base oil comprises one or more selected from paraffinic synthetic oil, olefinic synthetic oil, esteric synthetic oil, and mineral oil. [8] The machining method according to any one of the above [1] to [7], wherein the electrical discharge machining oil substantially does not contain water. [9] The machining method according to any one of the above [1] to [8], wherein the characteristic temperature of the electrical discharge machining oil, as measured in accordance with JIS K2242, is 300°C or higher.

[10] The machining method according to any one of the above [1] to [9], wherein the volume resistivity of the electrical discharge machining oil at 50°C is 800 TΩ·m or less.

[11] The machining method according to any one of the above [1] to

[10] , wherein the flash point of the electrical discharge machining oil is 70°C or higher.

[12] A method for manufacturing a wafer, comprising a step of processing a workpiece by any one of the processing methods described in item [1] to

[11] above. [Effects of the Invention]

[0007] According to a preferred embodiment of the present invention, a workpiece processing method can suppress wire breakage even when using electrical discharge machining oil, increase processing speed, and form a smooth processed surface. Therefore, by using this processing method, wafers can be manufactured with improved productivity. [Modes for carrying out the invention]

[0008] The numerical ranges described herein can be any combination of upper and lower limits. For example, if the numerical range is described as "preferably 30 to 100, more preferably 40 to 80," then the ranges of "30 to 80" and "40 to 100" are also included in the numerical range described herein. Similarly, if the numerical range is described as "preferably 30 or more, more preferably 40 or more, and also preferably 100 or less, more preferably 80 or less," then the ranges of "30 to 80" and "40 to 100" are also included in the numerical range described herein. In addition, as a numerical range described in this specification, for example, "60 to 100" means a range of "60 or more (60 or greater than 60) and 100 or less (100 or less than 100)."

[0009] [Processing method of workpiece] A method for processing a workpiece according to one aspect of the present invention (hereinafter also simply referred to as the "processing method") is a method for processing a workpiece in which an electrical discharge fluid is interposed between a wire and the workpiece and an electrical discharge is made to process the workpiece, and the following requirements (I) to (IV) are satisfied. • Requirement (I): The kinematic viscosity of the electrical discharge machining fluid at 40°C is 0.70 to 5.0 mm². 2 It is / s. Requirement (II): The diameter of the wire is 30 to 250 μm. Requirement (III): The wire speed during the processing described above is 11 m / min or more. Requirement (IV): The tension of the wire during the processing described above is 1 to 24 N.

[0010] Furthermore, a method for processing a workpiece according to one aspect of the present invention preferably satisfies one or more of the following requirements (V) and (VI), and more preferably satisfies both requirements (V) and (VI). • Requirements (V): The open-circuit voltage during the processing described above is 5 to 800V. Requirement (VI): The discharge current during the machining process is 0.5 to 100 A.

[0011] As mentioned above, the main type of electrical discharge machining fluid used in electrical discharge machining is a water-based fluid, as described in Patent Documents 1 and 2. However, in electrical discharge machining methods using water-based fluids, the machining speed is slow, and there is room for improvement in smoothing the machined surface. On the other hand, as described in Patent Document 2, oil-based machining fluids, which are mainly composed of oil, are sometimes used as electrical discharge machining fluids. While these are superior to water-based machining fluids in terms of increasing machining speed and smoothing the machined surface, they have the problem of wire breakage being more likely during machining. In particular, wire breakage is more likely to occur when machining workpieces with a maximum machining width of 2 inches or more. In view of these problems, in a processing method according to one aspect of the present invention, by adjusting to satisfy the above requirements (I) to (IV), it is possible to suppress wire breakage and increase the processing speed while forming a smooth processed surface.

[0012] <Workpiece> One embodiment of the present invention describes a workpiece to be processed by a processing method that involves slicing a material into multiple thin plates. Examples include semiconductor materials containing at least one selected from silicon compounds and gallium compounds; solar cell materials containing at least one selected from silicon compounds and gallium compounds; various structural members containing at least one selected from silicon compounds and gallium compounds; and metallic materials made from metals selected from the group consisting of tool steel, cemented carbide, iron, titanium, aluminum, titanium alloys, alloy steels, nickel-based alloys, niobium alloys, tantalum alloys, molybdenum alloys, tungsten alloys, stainless steel, aluminum alloys, and high-manganese steel. Examples of the aforementioned silicon compound include single-crystal or polycrystalline silicon, and single-crystal or polycrystalline silicon carbide (SiC). Examples of the gallium compound include single crystal or polycrystalline gallium, single crystal or polycrystalline gallium nitride (GaN), and the like.

[0013] In a processing method according to one aspect of the present invention, the workpiece to be processed is preferably an ingot with a maximum processing width of 0.5 inches or more (12.7 mm or more). With the processing method according to one aspect of the present invention, even for workpieces with such a large maximum processing width, wire breakage can be suppressed, and a smooth processed surface can be formed while increasing the processing speed. The maximum machining width may be 1.0 inch or more (25.4 mm or more), 1.5 inches or more (38.1 mm or more), 2.0 inches or more (50.8 mm or more), 3.0 inches or more (76.2 mm or more), or 4.0 inches or more (101.6 mm or more). There is no particular upper limit on the maximum machining width, and it is usually set by the machining equipment used, but for example, it is 12 inches or less. The "maximum processing width" mentioned above refers to the diameter of the base circle when processing (cutting) a cylindrical ingot from any point on its side so that it is approximately parallel to the base. Furthermore, when processing (cutting) a rectangular ingot with width A x length B x height C from an arbitrary position on the side with length B x height C so that it is approximately parallel to the bottom surface, width A becomes the maximum processing width. When processing (cutting) from an arbitrary position on the side with width A x height C so that it is approximately parallel to the bottom surface, length B becomes the maximum processing width.

[0014] Examples of materials used to form the ingot include the aforementioned semiconductor materials, solar cell materials, various structural components, and metallic materials.

[0015] <Regarding electrical discharge machining fluid, requirement (I)> In one embodiment of the present invention, a machining oil is used as the electrical discharge machining fluid. The electrical discharge machining fluid used in one aspect of the present invention is a machining fluid mainly composed of a base oil selected from synthetic oil or mineral oil. In this specification, "main component" refers to the component present in the highest concentration. In the electric discharge machining oil used in one aspect of the present invention, the content of the base oil may be the highest content based on the total amount (100% by mass) of the electric discharge machining oil, and may be 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass.

[0016] The electric discharge machining oil used in one aspect of the present invention may contain water, or may not substantially contain water. In this specification, "substantially free of water" excludes the mode of adding water with a specific intention, and does not exclude the mode in which water is unavoidably contained. In the electric discharge machining oil used in one aspect of the present invention, the water content may be less than 30% by mass, less than 20% by mass, less than 10% by mass, less than 5.0% by mass, less than 3.0% by mass, 2.0% by mass or more, less than 1.0% by mass, less than 0.50% by mass, less than 0.10% by mass, less than 0.01% by mass, less than 0.001% by mass, less than 0.0001% by mass, or less than 0.00001% by mass based on the total amount (100% by mass) of the electric discharge machining oil.

[0017] The electric discharge machining oil used in one aspect of the present invention has a kinematic viscosity at 40°C of 0.70 to 5.0 mm 2 / s as defined in the above requirement (I). By setting the kinematic viscosity of the electric discharge machining oil at 40°C within this range, wire breakage can be suppressed even when using the electric discharge machining oil, the machining speed can be increased, and a smooth machining surface can be formed. From the above viewpoints, the kinematic viscosity of the electric discharge machining oil used in one aspect of the present invention at 40°C is 0.80 mm 2 / s or more, 0.90 mm 2 / s or more, 1.0 mm 2 / s or more, 1.2 mm 2 / s or more, 1.4 mm 2 / s or more, 1.6 mm 2 / s or more, 1.8 mm 2 / s or more, 2.0 mm 2 / s or more, 2.2 mm 2 / s or more, or 2.3mm 2 It is preferable to have a value of / s or higher, and furthermore, 2.4 mm 2 / s or more, 2.6mm 2 / s or more, 2.8mm 2 / s or more, 3.0mm 2 / s or more, 3.2mm 2 / s or more, 3.4mm 2 / s or more, 3.6mm 2 / s or more, 3.8mm 2 / s or more, 4.0mm 2 / s or more, or 4.2mm 2 It is also acceptable to set it to / s or higher, and also 5.0mm 2 / s or less, 4.9mm 2 / s or less, 4.8mm 2 / s or less, 4.7mm 2 / s or less, 4.6mm 2 / s or less, 4.5mm 2 / s or less, 4.4mm 2 / s or less or 4.3mm 2 It is preferable to set it to / s or less, and furthermore, 4.2 mm 2 / s or less, 4.0mm 2 / s or less, 3.8mm 2 / s or less, 3.6mm 2 / s or less, 3.4mm 2 / s or less, 3.2mm 2 / s or less, 3.0mm 2 / s or less, 2.8mm 2 / s or less, 2.6mm 2 / s or less or 2.4mm 2 You may also use a value less than / s. In this specification, kinematic viscosity refers to the value measured in accordance with JIS K2283:2000.

[0018] Details regarding the physical properties of the electrical discharge machining fluid used in one aspect of the present invention, other than its kinematic viscosity, and the components contained in the electrical discharge machining fluid, are described below.

[0019] <Regarding wires and requirement (II)> As specified in requirement (II) above, the diameter of the wire used in the processing method of one embodiment of the present invention is 30 to 250 μm. By setting the wire diameter to 30 μm or more, wire breakage is suppressed even when using electrical discharge machining oil, the processing speed can be increased, and a smooth processed surface can be formed. Furthermore, by setting the wire diameter to 250 μm or less, the processing speed can be increased, and a smooth processed surface can be formed. In addition, the area to be cut from the workpiece can be kept from becoming too wide, and the amount of processing chips generated from the workpiece can be reduced. The diameter of the wire used in the processing method according to one embodiment of the invention is 30 μm or more, but from the viewpoint of suppressing wire breakage even when using electrical discharge machining oil, increasing the processing speed, and making it easier to form a smoother processed surface, it is preferable to have a diameter of 40 μm or more, 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 90 μm or more, or 100 μm or more, and further, 110 μm or more, 120 μm or more, 130 μm or more, 140 μm or more, 150 μm or more, 160 μm or more, 170 μm or more, 180 μm or more, 190 μm or more, or It may be 200 μm or more, and from the viewpoint of maintaining the processing speed and making it easier to form a smooth processed surface, as well as from the viewpoint of reducing the amount of processing scrap generated from the workpiece, it is preferable to set it to 250 μm or less, 240 μm or less, 230 μm or less, 220 μm or less, 210 μm or less, or 200 μm or less, and furthermore, it may be 190 μm or less, 180 μm or less, 170 μm or less, 160 μm or less, 150 μm or less, 140 μm or less, 130 μm or less, 120 μm or less, 110 μm or less, or 100 μm or less.

[0020] The wire used in the processing method according to one embodiment of the present invention may be made of any conductive material, such as brass (an alloy of copper and zinc, provided that the amount of zinc is 20% by mass or less), oxygen-free copper, tungsten, molybdenum, or steel. Alternatively, piano wire coated with brass or zinc may be used.

[0021] <Regarding Requirement (III)> In a processing method according to one aspect of the present invention, the wire speed when processing the workpiece is 11 m / min or more, as specified in requirement (III) above. By setting the wire speed to 11 m / min or more, wire breakage is suppressed even when electrical discharge machining oil is used, the processing speed can be increased, and a smooth processed surface can be formed. In a machining method according to one embodiment of the present invention, the wire speed when machining the workpiece is 11 m / min or more. However, from the viewpoint of further suppressing wire breakage even when using electrical discharge machining oil, increasing the machining speed, and making it easier to form a smooth machined surface, the wire speed may be set to 13 m / min or more, 15 m / min or more, 17 m / min or more, 20 m / min or more, 30 m / min or more, 40 m / min or more, 50 m / min or more, 60 m / min or more, 70 m / min or more, 80 m / min or more, 90 m / min or more, or 100 m / min or more. It is preferable that the rate of application be 300 m / min or less, 280 m / min or less, 260 m / min or less, 240 m / min or less, 220 m / min or less, 200 m / min or less, 180 m / min or less, 160 m / min or less, 150 m / min or less, 140 m / min or less, 130 m / min or less, or 120 m / min or less, and it may also be 110 m / min or less, 100 m / min or less, or 90 m / min or less.

[0022] <Regarding Requirement (IV)> In a machining method according to one aspect of the present invention, the wire tension when machining the workpiece is 1 to 24 N, as specified in requirement (IV) above. By setting the wire tension within this range, wire breakage is suppressed even when using electrical discharge machining fluid, the machining speed can be increased, and a smooth machined surface can be formed. In a processing method according to one embodiment of the present invention, the tension of the wire when processing the workpiece is 1N or more, but from the viewpoint of making it easier to form a smooth processed surface, it is preferable to set it to 1.2N or more, 1.5N or more, 2N or more, 3N or more, 4N or more, 5N or more, 6N or more, 7N or more, 8N or more, 9N or more, or 10N or more, and it may also be 12N or more, 14N or more, 16N or more, or 18N or more, and although it is 24N or less, from the viewpoint of further suppressing wire breakage even when using electrical discharge machining oil and further increasing the processing speed, it is preferable to set it to 23N or less, 22N or less, 21N or less, or 20N or less, and it may also be 19N or less, 18N or less, 17N or less, 16N or less, 15N or less, 14N or less, 13N or less, 12N or less, 11N or less, 10N or less, or 9N or less.

[0023] <Regarding requirement (V)> In a machining method according to one aspect of the present invention, it is preferable that the open-circuit voltage when machining the workpiece is 5 to 800V, as specified in requirement (V) above. By setting the open-circuit voltage within this range, wire breakage can be suppressed even when using electrical discharge machining fluid, the machining speed can be increased, and a smooth machined surface can be formed. In a machining method according to one embodiment of the present invention, the open-circuit voltage when machining a workpiece is preferably 10V or more, 20V or more, 30V or more, 40V or more, 50V or more, 60V or more, 70V or more, or 80V or more, from the viewpoint of further suppressing wire breakage even when using electrical discharge machining oil, further increasing the machining speed, and making it easier to form a smooth machined surface. Furthermore, it may be 90V or more, 100V or more, 120V or more, 140V or more, 160V or more, or 180V or more. Also, from the same viewpoint as above, it is preferably 700V or less, 600V or less, 500V or less, 400V or less, 300V or less, 280V or less, 260V or less, 240V or less, 220V or less, or 200V or less. Furthermore, it may be 180V or less, 160V or less, 140V or less, 120V or less, 100V or less, or 90V or less.

[0024] <Regarding Requirement (VI)> In a machining method according to one aspect of the present invention, it is preferable that the discharge current used when machining the workpiece is 0.5 to 100 A, as specified in requirement (VI) above. By setting the discharge current within this range, wire breakage can be suppressed even when using electrical discharge machining fluid, the machining speed can be increased, and a smooth machined surface can be formed. In a machining method according to one aspect of the present invention, the discharge current when machining the workpiece is 1A or more, but from the viewpoint of further suppressing wire breakage even when using electrical discharge machining oil, further increasing the machining speed, and making it easier to form a smooth machined surface, it is preferable to set it to 0.5A or more, 1A or more, 2A or more, 3A or more, 4A or more, 5A or more, 6A or more, 7A or more, 8A or more, 9A or more, or 10A or more, and furthermore, 12A or more, 15A or more, 2 It may be 0A or more, or 25A or more, and although it is 100A or less, from the same viewpoint as above, it is preferable to set it to 95A or less, 90A or less, 85A or less, 80A or less, 75A or less, 70A or less, 65A or less, 60A or less, 55A or less, 50A or less, 45A or less, 40A or less, 35A or less, or 30A or less, and furthermore, it may be 25A or less, 20A or less, 18A or less, 16A or less, 14A or less, or 12A or less.

[0025] <Other requirements> In a machining method according to one embodiment of the present invention, the servo voltage used when machining the workpiece is preferably 3V to 150V. From the viewpoint of further suppressing wire breakage even when using electrical discharge machining oil, further increasing the machining speed, and making it easier to form a smooth machined surface, the servo voltage may be 5V or higher, 10V or higher, 15V or higher, 20V or higher, 25V or higher, 30V or higher, 35V or higher, 40V or higher, 45V or higher, 50V or higher, 55V or higher, 60V or higher, 65V or higher, or 70V or higher. Alternatively, it may be 150V or lower, 100V or lower, 90V or lower, 80V or lower, or 70V or lower, 65V or lower, 60V or lower, or 55V or lower.

[0026] In a processing method according to one aspect of the present invention, the pulse width when processing the workpiece is preferably 50 ns to 1000 ns, and may be 100 ns or more, 150 ns or more, 200 ns or more, or 250 ns or more, or 950 ns or less, 900 ns or less, 850 ns or less, 800 ns or less, 750 ns or less, 700 ns or less, 650 ns or less, 600 ns or less, 550 ns or less, 500 ns or less, 450 ns or less, 400 ns or less, or 350 ns or less.

[0027] In a processing method according to one embodiment of the present invention, the pause time when processing the workpiece is preferably 1.0 μs to 5.0 μs, and may be 1.5 μs or more, 2.0 μs or more, 2.5 μs or more, 3.0 μs or more, or 3.2 μs or more, or 4.5 μs or less, 4.0 μs or less, or 3.7 μs or less.

[0028] <Various physical properties of electrical discharge machining oils> The characteristic temperature of the electrical discharge machining fluid used in the machining method according to one embodiment of the present invention, as measured in accordance with JIS K2242, is preferably 300 to 650°C, and from the viewpoint of cooling performance during machining of the workpiece, it is preferably 310°C or higher, 320°C or higher, 340°C or higher, 360°C or higher, 380°C or higher, or 400°C or higher. There is no particular upper limit to the characteristic temperature of the electrical discharge machining fluid, but for example, it is 650°C or lower.

[0029] The volume resistivity at 50°C of the electrical discharge machining oil used in a machining method according to one embodiment of the present invention is 1 × 10⁻⁶ -8 It is preferable that the resistivity is ~800 TΩ·m, and from the viewpoint of increasing the machining speed and making it easier to form a smooth machined surface, it is preferable that it is 800 TΩ·m or less, 600 TΩ·m or less, 400 TΩ·m or less, 200 TΩ·m or less, 180 TΩ·m or less, 160 TΩ·m or less, 140 TΩ·m or less, 120 TΩ·m or less, or 100 TΩ·m or less. There is no particular lower limit for the volume resistivity of the electrical discharge machining oil at 50°C, but for example, 1 × 10 -8 It is greater than or equal to TΩ·m. In this specification, volume resistivity refers to the value obtained from the current value after 1 minute has elapsed since applying a voltage of 250 V / mm at an oil temperature of 50°C, in accordance with JIS C2101.

[0030] The flash point of the electrical discharge machining oil used in the machining method according to one embodiment of the present invention is preferably 70 to 300°C, and from the viewpoint of handling, it is 74°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, 110°C or higher, or 120°C or higher. There is no particular upper limit on the flash point of the electrical discharge machining oil, but for example, it is 300°C or lower. In this specification, the flash point refers to the value measured in accordance with JIS K2265-4.

[0031] <Components of electrical discharge machining oil> The electrical discharge machining oil used in the machining method according to one embodiment of the present invention preferably contains one or more base oils selected from mineral oils and synthetic oils. Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; and refined oils obtained by subjecting the distillates to one or more refining processes such as solvent delamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining.

[0032] Examples of synthetic oils include poly-α-olefins such as normal paraffins, isoparaffins, α-olefins, α-olefin homopolymers, or α-olefin copolymers (e.g., 8-14 carbon olefin copolymers such as ethylene-α-olefin copolymers); isoparaffins; polyalkylene glycols; ester oils such as polyol esters and dibasic acid esters; ether oils such as polyphenyl ethers; alkylbenzenes; alkylnaphthalenes; and synthetic oils (GTL) obtained by isomerizing waxes produced from natural gas by the Fischer-Tropsch process, etc. (GTL waxes (Gas To Liquids Wax)).

[0033] Among these, from the viewpoint of being easy to adjust to the above requirement (I), and from the viewpoint of further suppressing wire breakage even when using electrical discharge machining oil, further increasing the machining speed, and making it easier to form a smooth machined surface, the base oil used in the machining method of one embodiment of the present invention preferably contains one or more selected from paraffinic synthetic oil, olefinic synthetic oil, esteric synthetic oil, and mineral oil.

[0034] The electrical discharge machining oil used in the machining method according to one embodiment of the present invention may contain various additives along with the base oil. Examples of additives include organic acid metal salts, thickeners, oil-soluble resins, rust inhibitors, defoamers, antioxidants, and metal deactivators. These additives may be used individually or in combination of two or more.

[0035] Examples of organic acid metal salts used in one aspect of the present invention include metal sulfonates, metal salicylates, metal phenates, and organic acid zinc salts. Examples of metal atoms found in metal sulfonates, metal salicylates, and metal phenates include alkali metals such as sodium atoms, and alkaline earth metals such as calcium atoms and magnesium atoms. The metal sulfonates, metal salicylates, and metal phenates may be overbasic metal salts with a KOH content of 100 mg or more, or neutral metal salts with a KOH content of less than 100 mg.

[0036] The content of organic acid metal salts, in terms of metal atoms, is preferably 0 to 1500 ppm by mass, based on the total amount (100% by mass) of the electrical discharge machining oil. It may also be 100 ppm or more by mass, 300 ppm or more by mass, or 500 ppm or more by mass, or 1000 ppm or less by mass, or 800% by mass, and the content may be further restricted to less than 100 ppm by mass, less than 50 ppm by mass, less than 10 ppm by mass, less than 1.0 ppm by mass, or less than 0.1 ppm by mass.

[0037] Examples of thickening agents used in one aspect of the present invention include polybutene, polyisobutylene, polyvinyl acetate, polyalkyl acrylate, ethylene-propylene copolymer, and polyalkylene glycol. The content of the thickener is preferably 0 to 15% by mass based on the total amount (100% by mass) of the electrical discharge machining oil, and may be 0.1% by mass or more, 0.5% by mass or more, or 1.0% by mass or more, or 5.0% by mass or less, or 2.0% by mass or less, and may be further limited to 1.0% by mass or less, 0.1% by mass or less, 0.01% by mass or less, 0.001% by mass or less, or 0.0001% by mass or less.

[0038] Examples of oil-soluble resins used in one aspect of the present invention include polymers of dipentene, tetraterpenes, and polyterpenes, or hydrogenated products thereof; cyclopentadiene-dicyclopentadiene copolymer petroleum resins or hydrogenated products thereof; rosin esters; coumarone resins; coumarone-indene resins, and the like. The number-average molecular weight of the oil-soluble resin used in one aspect of the present invention is preferably 200 to 5000, and may be 300 or more, 400 or more, or 500 or more, and may also be 4000 or less, 3000 or less, or 2000 or less. The oil-soluble resin content is preferably 0 to 15% by mass based on the total amount (100% by mass) of the electrical discharge machining oil, and may be 0.1% by mass or more, 0.5% by mass or more, or 1.0% by mass or more, or 5.0% by mass or less, or 2.0% by mass or less, and may be further limited to 1.0% by mass or less, 0.1% by mass or less, 0.01% by mass or less, 0.001% by mass or less, or 0.0001% by mass or less.

[0039] Examples of rust inhibitors used in one aspect of the present invention include alkylbenzene sulfonates, dinonyl naphthalene sulfonates, alkenyl succinate esters, and polyhydric alcohol esters. The rust inhibitor content is preferably 0 to 5.0% by mass based on the total amount (100% by mass) of the electrical discharge machining oil, and may be 0.01% by mass or more, 0.05% by mass or more, or 0.10% by mass or more, or 3.0% by mass or less, or 2.0% by mass or less, and may be further limited to 1.0% by mass or less, 0.1% by mass or less, 0.01% by mass or less, 0.001% by mass or less, or 0.0001% by mass or less.

[0040] Examples of defoaming agents used in one aspect of the present invention include silicone-based defoaming agents, fluorosilicone-based defoaming agents, fluoroalkyl ether-based defoaming agents, and polyacrylate-based defoaming agents. The content of the defoaming agent is preferably 0 to 3.0% by mass based on the total amount (100% by mass) of the electrical discharge machining oil, and may be 0.001% by mass or more, 0.005% by mass or more, or 0.01% by mass or more, or 1.0% by mass or less, or 0.50% by mass or less, or the content may be further restricted to 1.0% by mass or less, 0.1% by mass or less, 0.01% by mass or less, 0.001% by mass or less, or 0.0001% by mass or less.

[0041] Examples of antioxidants used in one aspect of the present invention include amine-based antioxidants such as alkylated diphenylamine, phenylnaphthylamine, and alkylated phenylnaphthylamine; and phenol-based antioxidants such as 2,6-di-t-butylphenol, 4,4'-methylenebis(2,6-di-t-butylphenol), isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate. The antioxidant content is preferably 0 to 7.0% by mass based on the total amount (100% by mass) of the electrical discharge machining oil, and may be 0.01% by mass or more, 0.05% by mass or more, or 0.10% by mass or more, or 5.0% by mass or less, or 3.0% by mass or less, and may be further limited to 2.0% by mass or less, 1.0% by mass or less, 0.1% by mass or less, 0.01% by mass or less, 0.001% by mass or less, or 0.0001% by mass or less.

[0042] Examples of metal deactivators used in one aspect of the present invention include benzotriazole, imidazoline, pyrimidine derivatives, thiadiazole, and the like. The content of the metal deactivator is preferably 0 to 2.0% by mass based on the total amount (100% by mass) of the electrical discharge machining oil, and may be 0.01% by mass or more, 0.05% by mass or more, or 0.10% by mass or more, or 1.0% by mass or less, or 0.50% by mass or less, and may be further limited to 0.10% by mass or less, 0.01% by mass or less, 0.001% by mass or less, 0.0001% by mass or less, or 0.00001% by mass or less.

[0043] <Characteristics of the processing method according to one embodiment of the present invention> According to one embodiment of the present invention, wire breakage can be suppressed even when using electrical discharge machining oil, the machining speed can be increased, and a smooth machined surface can be formed. In a processing method according to one aspect of the present invention, the processing speed measured by the method described in the following examples can be 0.15 mm / min or more, 0.20 mm / min or more, 0.25 mm / min or more, 0.30 mm / min or more, 0.35 mm / min or more, 0.40 mm / min or more, 0.45 mm / min or more, or 0.48 mm / min or more.

[0044] The surface roughness Ra of the processed surface obtained by the processing method according to one embodiment of the present invention can be 1.5 μm or less, 1.3 μm or less, 1.2 μm or less, 1.1 μm or less, 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, 0.7 μm or less, 0.6 μm or less, 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, or 0.2 μm or less. Note that the surface roughness Ra of the machined surface refers to the value measured in accordance with JIS B0633:2001.

[0045] [Wafer manufacturing method] A processing method according to one aspect of the present invention is suitable for wafer manufacturing because it has the above-described characteristics. In one aspect of the present invention, the following [1] and [2] may also be provided. [1] A method for manufacturing a wafer, comprising the step of processing a workpiece by a processing method according to one aspect of the present invention described above. [2] A wafer obtained by the manufacturing method described in [1] above. [Examples]

[0046] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples. In the following examples, the method for measuring the physical properties is as follows. (1)Kinematic viscosity at 40℃ Measurements were taken in accordance with JIS K2283:2000. (2)Characteristic temperature Measurements were taken in accordance with JIS K2242. (3) Flash point Measurements were taken in accordance with JIS K2265-4. (4) Volume resistivity In accordance with JIS C2101, a voltage of 250 V / mm was applied at an oil temperature of 50°C, and the current value was calculated from the value after 1 minute had elapsed since the application of the voltage.

[0047] The machining fluid, wire, and electrical discharge machining equipment used in the following examples and comparative examples are shown below. <Processing fluid> • Machining oil (1): Electrical discharge machining oil made from mineral oil, kinematic viscosity at 40°C = 2.3 mm 2 / s, characteristic temperature = 546°C, flash point = 96°C, volume resistivity = 29TΩ·m. • Machining oil (2): Electrical discharge machining oil made from mineral oil, kinematic viscosity at 40°C = 4.3 mm 2 / s, characteristic temperature = 336℃, flash point = 138℃, volume resistivity = 590 TΩ·m. • Water: Ion-exchanged water, kinematic viscosity at 40°C = 0.658 mm 2 / s. <wire> • Wire (1): 200 μm diameter wire, manufactured by OKI Electric Cable Co., Ltd., product name "MOS WIRE 4000". • Wire (2): 200 μm diameter wire, manufactured by Proterial Co., Ltd., product name "PROTERIAL HBZ-B 20". • Wire (3): 100 μm diameter wire, manufactured by Sumitomo Electric Industries, Ltd., product name "SUMI SPARK G-100". • Wire (4): 20 μm diameter wire, manufactured by Technos Co., Ltd., product name "SP Neo". <Electric discharge machine> • AP250L (oil) (product name, manufactured by Sodick Co., Ltd.): Used in the examples and comparative examples using "Processing Fluid (1), (2)" as the processing fluid. • AQ360L (product name, manufactured by Sodick Co., Ltd.): Used as a reference example where "water" is used as the processing fluid.

[0048] Examples 1-2, Comparative Examples 1-3, Reference Example 1 The workpiece was a cylindrical workpiece with a diameter of 4 inches (101.6 mm) (TankeBlue, SiC ingot dummy grade), and the side of the cylindrical workpiece was placed on the sample stage. Then, using the processing fluid described in Table 1, and under the wire and discharge conditions described in Table 1, the cylindrical workpiece was cut from an arbitrary position on the side of the workpiece in a direction approximately parallel to both bottom surfaces of the workpiece (approximately perpendicular to the sample stage).

[0049] Examples 3-4, Reference Example 2 The workpiece was a rectangular parallelepiped (TankeBlue, SiC block) with a width of 13.3 mm, and it was placed on the sample stage so that the wire was approximately parallel to the width during processing. Then, using the processing fluid described in Table 1, and under the wire and discharge conditions described in Table 1, the rectangular parallelepiped workpiece was cut from an arbitrary position on the top bottom surface where the wire was approximately parallel to the width, to a depth of 5 mm in a direction approximately perpendicular to the sample stage.

[0050] The cutting speed was calculated from the processing distance L and processing time t in the examples, comparative examples, and reference examples using the following formula. ·Processing speed (mm / min)=L / t (In the formula, L is the machining distance of the workpiece (in mm), which is 101.6 mm in Examples 1-2, Comparative Examples 1-3, and Reference Example 1, and 5 mm in Examples 3-4 and Reference Example 2. t is the machining time (in minutes).) Furthermore, the surface roughness Ra of the machined surface (cut surface) of each workpiece was measured in accordance with JIS B0633:2001 using a contact-type surface roughness measuring instrument SV-3100 (product name, manufactured by Mitutoyo Corporation). These results are shown in Table 1.

[0051] [Table 1]

[0052] As shown in Table 1, the machining methods of Examples 1 to 3, which used machining oil to meet predetermined conditions, resulted in machining speeds equivalent to or better than Reference Examples 1 to 2, which used machining fluid, and also showed superior machining performance with a smaller surface roughness Ra of the machined surface. In Example 4, although the surface roughness Ra of the workpiece was not measured, it was confirmed that the machining speed was equivalent to or better than that of Reference Example 2. On the other hand, in Comparative Examples 1 to 3, the wire broke during the machining of the workpiece. Therefore, machining evaluation was not performed in Comparative Examples 1 to 3.

Claims

1. A method for machining a workpiece, comprising interposing electrical discharge machining oil between a wire and the workpiece and machining the workpiece by applying an electrical discharge, The kinematic viscosity of the aforementioned electrical discharge machining oil at 40°C is 0.70 to 5.0 mm. ２ / s, The diameter of the aforementioned wire is 30 to 250 μm. The wire speed during the aforementioned processing is 11 m / min or more. The tension of the wire during the aforementioned processing is 1 to 24 N. Processing method.

2. The processing method according to claim 1, wherein the open-circuit voltage during the processing is 5 to 800V.

3. The machining method according to claim 1 or 2, wherein the discharge current during the machining is 0.5 to 100 A.

4. The processing method according to any one of claims 1 to 3, wherein the workpiece is an ingot with a maximum processing width of 0.5 inches or more.

5. The processing method according to any one of claims 1 to 4, wherein the workpiece is made of a semiconductor material comprising at least one selected from silicon compounds and gallium compounds.

6. The machining method according to any one of claims 1 to 5, wherein the base oil content is 30% by mass or more based on the total amount of the electrical discharge machining oil.

7. The processing method according to claim 6, wherein the base oil comprises one or more selected from paraffinic synthetic oil, olefinic synthetic oil, esteric synthetic oil, and mineral oil.

8. The machining method according to any one of claims 1 to 7, wherein the electrical discharge machining oil substantially does not contain water.

9. The machining method according to any one of claims 1 to 8, wherein the characteristic temperature of the electrical discharge machining oil, as measured in accordance with JIS K2242, is 300°C or higher.

10. The machining method according to any one of claims 1 to 9, wherein the volume resistivity of the electrical discharge machining oil at 50°C is 800 TΩ·m or less.

11. The machining method according to any one of claims 1 to 10, wherein the flash point of the electrical discharge machining oil is 70°C or higher.

12. A method for manufacturing a wafer, comprising the step of processing a workpiece by the processing method described in any one of claims 1 to 11.

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