Workpiece machining method

Abstract

The present invention provides a workpiece machining method for machining a workpiece by interposing electric discharge machining oil between a wire and the workpiece to perform electric discharge, wherein the kinematic viscosity of the electric discharge machining oil at 40°C is 0.70-5.0 mm2 / s, the diameter of the wire is 30-250 μm, the linear velocity of the wire during the machining is 11 m / minute or more, and the tension of the wire during the machining is 1-24 N.

Description

Processing method of workpiece

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

[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 EDM will use EDM used for general metal materials as an example. EDM is a technology that processes workpieces 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 heat of 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 by the flow of the EDM fluid.

[0003] Water is often used as the electrical discharge machining fluid in such electrical discharge machining. For example, Patent Document 1 discloses an electrical discharge machining fluid composition containing an imide compound and water, while Patent Document 2, which concerns a wire electrical discharge machining apparatus used for electrical discharge machining, mentions that water is mainly used as the machining fluid in the apparatus, but that an electrical discharge machining oil with oil as the main component may also be used.

[0004] Japanese Patent Publication No. 2010-179381 Japanese Patent Publication No. 2014-659

[0005] While wire electrical discharge machining (EDM) has seen the development of equipment and methods using water as the machining fluid, there is room for improvement in terms of machining speed and surface smoothness. Under these circumstances, there is a need for a machining method that can increase the machining speed in EDM while simultaneously producing a smooth surface.

[0006] In one aspect of the present invention, a method for machining a workpiece is provided, using an electrical discharge machining fluid having a specific kinematic viscosity and a wire of a specific diameter, and adjusting the wire speed and tension during machining the workpiece to a predetermined range. Specifically, as one aspect of the present invention, for example, the following embodiments [1] to

[12] are provided. [1] A method for machining a workpiece, wherein an electrical discharge machining fluid is interposed between the 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 mm ２[1] A machining method wherein the wire diameter is 30 to 250 μm, the wire speed during machining is 11 m / min or more, and the wire tension during machining is 1 to 24 N. [2] The machining method according to [1] above, wherein the open-circuit voltage during machining is 5 to 800 V. [3] The machining method according to [1] or [2] above, wherein the discharge current during machining is 0.5 to 100 A. [4] The machining method according to any one of [1] to [3] above, wherein the workpiece is an ingot with a maximum machining width of 0.5 inches or more. [5] The machining method according to any one of [1] to [4] above, wherein the workpiece is a semiconductor material containing at least one selected from silicon-based materials and gallium-based materials. [6] The machining method according to any one of [1] to [5] above, wherein the base oil content is 30% by mass or more on a total basis 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 processing method according to any one of [1] to [7] above, wherein the electrical discharge machining oil substantially contains no water. [9] The processing method according to any one of [1] to [8] above, wherein the characteristic temperature of the electrical discharge machining oil, as measured in accordance with JIS K2242, is 300°C or higher.

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

[11] The processing method according to any one of [1] to

[10] above, 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 according to any one of [1] to

[11] above.

[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.

[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, for example, if the numerical range described herein is described as "60 to 100," then it means the range is "60 or more (60 or greater than 60), and 100 or less (100 or less than 100)."

[0009] [Method for processing a 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 performed to process the workpiece, and the following requirements (I) to (IV) are met. Requirement (I): The kinematic viscosity of the electrical discharge fluid at 40°C is 0.70 to 5.0 mm². ２ / s. Requirement (II): The diameter of the wire is 30 to 250 μm. Requirement (III): The wire speed during processing is 11 m / min or more. Requirement (IV): The tension of the wire during processing is 1 to 24 N.

[0010] Furthermore, the 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). • Requirement (V): The open-circuit voltage during the processing is 5 to 800 V. • Requirement (VI): The discharge current during the processing is 0.5 to 100 A.

[0011] As described 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 oils, which are mainly composed of oil, are sometimes used as electrical discharge machining fluids. While these are superior to water-based 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 machining 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 machining speed while forming a smooth machined surface.

[0012] <Workpieces> Examples of workpieces to be processed by the processing method in one aspect of the present invention include materials that are sliced ​​into multiple thin plates, such as semiconductor materials comprising at least one selected from silicon-based materials and gallium-based materials; solar cell materials comprising at least one selected from silicon-based materials and gallium-based materials; various structural members comprising at least one selected from silicon-based materials and gallium-based materials; metallic materials made of 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; and so on. Examples of silicon-based materials include single crystal or polycrystalline silicon and single crystal or polycrystalline silicon carbide (SiC). Examples of gallium-based materials include single crystal or polycrystalline gallium and single crystal or polycrystalline gallium nitride (GaN).

[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 processing 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 to the maximum processing width, and it is usually set by the processing equipment used, but for example, it is 12 inches or less. Note that the "maximum processing width" above refers to the diameter of the circle at the bottom when processing (cutting) a cylindrical ingot from an arbitrary position on the side so as to be approximately parallel to the bottom surface. Furthermore, when processing (cutting) a rectangular ingot with dimensions A (width) x B (length) x C (height) from an arbitrary position on the side with dimensions B (length) x C (height) so as to be approximately parallel to the bottom surface, the maximum processing width is A (width). Also, when processing (cutting) a rectangular ingot with dimensions A (width) x C (height) from an arbitrary position on the side so as to be approximately parallel to the bottom surface, the maximum processing width is B (length).

[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 the electrical discharge machining oil and requirement (I)> In a machining method according to one aspect of the present invention, electrical discharge machining oil is used as the electrical discharge machining fluid. The electrical discharge machining oil 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" means the component that is present in the largest quantity among all components contained in the electrical discharge machining oil. In the electrical discharge machining oil used in one aspect of the present invention, the base oil content should be the largest content among all components contained in the electrical discharge machining oil based on the total amount (100% by mass) of the electrical 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 the electric discharge machining oil used in one aspect of the present invention, the water content is 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. 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. The water content in the "substantially water-free" mode is 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, it is possible to suppress wire breakage and increase the machining speed even when using the electric discharge machining oil, and a smooth machining surface can be formed. From the above viewpoints, the kinematic viscosity at 40 °C of the electric discharge machining oil used in one aspect of the present invention 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 2.3 mm ２ / s or more is preferable, and further, 2.4 mm ２ / s or more, 2.6 mm ２ / s or more, 2.8 mm 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 4.2 mm ２ It may also be set to / s or higher, and also 5.0 mm 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 less than or equal to / s, 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 It may be less than or equal to / s. In this specification, kinematic viscosity means a 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 the wire 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. Also, by setting the wire diameter to 250 μm or less, the processing speed can be increased, and a smooth processed surface can be formed. Furthermore, 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 furthermore, 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, but with a zinc content of 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 the processing method of one aspect of the present invention, as defined in Requirement (III) above, the wire linear velocity during the processing of the workpiece is 11 m / min or more. By setting the wire linear velocity to 11 m / min or more, wire breakage can be suppressed even when using discharge machining oil, the processing speed can be increased, and a smooth processed surface can be formed.In the processing method of one aspect of the present invention, the wire linear velocity during the processing of the workpiece is 11 m / min or more. However, from the perspective of further suppressing wire breakage, further increasing the processing speed, and more easily forming a smooth processed surface even when using discharge machining oil, it is preferably 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. Also, from the perspective of more easily forming a smooth processed surface and suppressing the amount of wire used, it is preferably 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. Furthermore, it may 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 embodiment 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 1 N or more, but from the viewpoint of making it easier to form a smooth processed surface, it is preferable to set it to 1.2 N or more, 1.5 N or more, 2 N or more, 3 N or more, 4 N or more, 5 N or more, 6 N or more, 7 N or more, 8 N or more, 9 N or more, or 10 N or more, and it may also be 12 N or more, 14 N or more, 16 N or more, or 18 N or more, and although it is 24 N 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 23 N or less, 22 N or less, 21 N or less, or 20 N or less, and it may also be 19 N or less, 18 N or less, 17 N or less, 16 N or less, 15 N or less, 14 N or less, 13 N or less, 12 N or less, 11 N or less, 10 N or less, or 9 N 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 800 V, 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 aspect 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 the processing method of one aspect of the present invention, as stipulated in Requirement (VI) above, it is preferable that the discharge current during processing of the workpiece is 0.5 to 100 A. By setting the discharge current within this range, even when using discharge machining oil, wire breakage can be suppressed, the processing speed can be increased, and a smooth processed surface can be formed.In the processing method of one aspect of the present invention, the discharge current during processing of the workpiece is 1 A or more. However, from the perspective of further suppressing wire breakage, increasing the processing speed, and more easily forming a smooth processed surface even when using discharge machining oil, it is preferably 0.5 A or more, 1 A or more, 2 A or more, 3 A or more, 4 A or more, 5 A or more, 6 A or more, 7 A or more, 8 A or more, 9 A or more, or 10 A or more. Further, it may be 12 A or more, 15 A or more, 20 A or more, or 25 A or more. Also, it is 100 A or less. From the same perspective as above, it is preferably 95 A or less, 90 A or less, 85 A or less, 80 A or less, 75 A or less, 70 A or less, 65 A or less, 60 A or less, 55 A or less, 50 A or less, 45 A or less, 40 A or less, 35 A or less, or 30 A or less. Further, it may be 25 A or less, 20 A or less, 18 A or less, 16 A or less, 14 A or less, or 12 A or less.

[0025] <Other Requirements> In the processing method of one aspect of the present invention, it is preferable that the servo voltage during processing of the workpiece is 3 V to 150 V. From the perspective of further suppressing wire breakage, increasing the processing speed, and more easily forming a smooth processed surface even when using discharge machining oil, it may also be 5 V or more, 10 V or more, 15 V or more, 20 V or more, 25 V or more, 30 V or more, 35 V or more, 40 V or more, 45 V or more, 50 V or more, 55 V or more, 60 V or more, 65 V or more, or 70 V or more. Also, it may be 150 V or less, 100 V or less, 90 V or less, 80 V or less, or 70 V or less, 65 V or less, 60 V or less, or 55 V or less.

[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 aspect 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 Fluid> 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 TΩ·m or greater. In this specification, volume resistivity refers to the value obtained from the current value after 1 minute has elapsed since the application of 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 aspect 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 base 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 treatments such as solvent delamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining. However, the mineral oil used in one aspect of the present invention does not necessarily have to contain one or more specific mineral oils selected from the above.

[0032] Examples of synthetic oils include 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); poly-α-olefins; 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 or the like (GTL wax (Gas To Liquids Wax)). In one embodiment of the present invention, the mineral oil used does not necessarily have to contain one or more specific synthetic oils selected from the above.

[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, or it may not contain any additives. Examples of various 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. Furthermore, it is not necessary to include one or more of these additives.

[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 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. Metal sulfonates, metal salicylates, and metal phenates may be overbasic metal salts with a concentration of 100 mg KOH / g or more, or neutral metal salts with a concentration of less than 100 mg KOH / g.

[0036] The content of the organic acid metal salt, 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 by mass or more, 300 ppm by mass or more, or 500 ppm by mass or more. Furthermore, it may be 1000 ppm by mass or less, or 800% by mass. In addition, the content may be limited 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 thickeners 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 versions thereof; cyclopentadiene-dicyclopentadiene copolymer petroleum resins or hydrogenated versions thereof; rosin esters; coumarone resins; coumarone-indene resins, etc. 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, or may 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 content of the rust inhibitor 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, 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.

[0041] Examples of antioxidants used in one aspect of the present invention include amine-based antioxidants such as alkylated diphenylamine, phenylnaphthylamine, and alkylated phenylnaphthylamine; 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; and the like. 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 the processing method according to one embodiment of the present invention, even when using electrical discharge machining oil, wire breakage can be suppressed, the processing speed can be increased, and a smooth processed surface can be formed. In the processing method according to one embodiment of the present invention, the processing speed measured by the method described in the embodiments below 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 a processed surface obtained by a 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. The surface roughness Ra of the processed surface refers to the value measured in accordance with JIS B0633:2001.

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

[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 methods for measuring the following physical properties are as follows: (1) Kinematic viscosity at 40°C: Measured in accordance with JIS K2283:2000. (2) Characteristic temperature: Measured in accordance with JIS K2242. (3) Flash point: Measured in accordance with JIS K2265-4. (4) Volume resistivity: Calculated in accordance with JIS C2101, by applying a voltage of 250 V / mm at an oil temperature of 50°C and taking the current value after 1 minute.

[0047] The machining fluid, wire, and electrical discharge machining equipment used in the following examples and comparative examples are shown below. <Machining Fluid> ・Machining oil (1): Electrical discharge machining oil consisting of mineral oil, kinematic viscosity at 40°C = 2.3 mm ２ / s, characteristic temperature = 546°C, flash point = 96°C, volume resistivity = 29 TΩ·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°C, flash point = 138°C, volume resistivity = 590 TΩ·m. Water: ion-exchanged water, kinematic viscosity at 40°C = 0.658 mm ２ / s. <Wires> ・Wire (1): 200 μm diameter wire, manufactured by OKI Electric Wire 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". <Electrical Discharge Machining Machines> ・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 in the reference example using "water" 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 (wherein L is the processing distance of the workpiece (unit: 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 processing time (unit: minutes).) In addition, the surface roughness Ra of the processed 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]

[0052] As shown in Table 1, the machining methods of Examples 1 to 3, which used machining oil to satisfy predetermined conditions, resulted in machining speeds equivalent to or greater than those of 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 greater 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, 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.

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-based materials and gallium-based materials.

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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