Surface processing method and surface processing device

Abstract

A machining electrode (30), which is circular in plan view and has an outer diameter equal to or greater than the outer diameter of an object to be machined, is disposed on the upper side of the object to be machined so as to partially overlap the object to be machined in plan view, and the object to be machined is rotated about a first central axis (X1) and the machining electrode (30) is rotated about a second central axis (X2). The discharge is performed between the machining electrode (30) and the object to be machined in a state in which both the object to be machined and the machining electrode (30) are rotated.

Description

Technical Field

[0001] The technology disclosed herein belongs to the technical field related to surface processing methods and surface processing apparatuses. Background Art

[0002] So far, for a disk-shaped workpiece having conductivity, technologies for processing its surface into a required shape or changing the properties of the surface state have been well-known. For example, in the case where the workpiece is a semiconductor wafer, the surface of the wafer is flattened or made drum-shaped according to the manufacturing conditions of semiconductor chips. In the case where the workpiece is a seed crystal of SiC, in order to improve the close contact between the seed crystal and the base, the properties of its bonding surface with the base are sometimes changed.

[0003] Patent Document 1 discloses the following method: physically polishing the surface of a semiconductor wafer using polishing slurry.

[0004] Patent Document 2 discloses the following method: flattening the surface of a wafer blank by discharging on the surface of the wafer blank in a state where a processing electrode is arranged so as to cover the entire wafer blank.

[0005] Patent Document 3 discloses the following method: forming a processed modified layer by electrical discharge machining on the surface of a disk-shaped SiC seed crystal, and bonding the processed modified layer to a base using an adhesive.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Laid-Open Publication No. 2009-81186

[0009] Patent Document 2: Japanese Patent Laid-Open Publication No. 2012-236241

[0010] Patent Document 3: Japanese Patent Laid-Open Publication No. 2015-30659 Summary of the Invention

[0011] -Technical Problem to be Solved by the Invention-

[0012] However, as described in Patent Document 1, in the case of processing the surface using polishing slurry, it is necessary to frequently confirm whether the polishing slurry is unevenly distributed on the surface of the workpiece, and the processing efficiency is not necessarily high. In a method of processing while contacting the workpiece like polishing slurry, when the workpiece is made of a high-hardness material such as SiC, in order to improve the rigidity of the apparatus, it is necessary to increase the size of the apparatus.

[0013] In contrast, if the surface of the object to be machined is machined by electrical discharge machining as in Patent Document 2, machining can be performed in a state where the object to be machined and the electrode are not in contact. Therefore, the management burden during machining can be reduced, and the enlargement of the device can be suppressed. However, as described in Patent Document 2, when the entire object to be machined is covered with the machining electrode, concentrated discharge occurs at portions where charges are likely to concentrate, such as at the edge shape portions of the entire surface of the object to be machined, and it is difficult to machine the surface of the object to be machined into the required shape. In addition, if the machining electrode is worn due to the concentration of the discharge portion and the offset of the machining electrode, an offset will occur at the discharge portion due to the surface shape of the machining electrode, and it may be even more difficult to obtain the required shape.

[0014] In Patent Document 3, although the roughness of the bonding surface is described, the machining device for achieving the required roughness is not disclosed in detail.

[0015] The technology disclosed herein is completed to solve the above technical problems. Its purpose is to suppress an unexpected offset at the machining portion when the surface of a disk-shaped object to be machined is machined by electrical discharge machining.

[0016] - Technical solution for solving technical problems -

[0017] To solve the above problems, the technology disclosed herein is directed to a surface machining method of electrically discharging the surface of a disk-shaped object to be machined using a machining electrode. The machining electrode is circular in plan view and has an outer diameter greater than or equal to the outer diameter of the object to be machined. The surface machining method includes an arrangement step, an object rotation step, an electrode rotation step, and a discharge step. In the arrangement step, the machining electrode is arranged above the object to be machined in such a manner that the object to be machined and the machining electrode partially overlap in plan view; in the object rotation step, the object to be machined is rotated about the central axis of the object to be machined; in the electrode rotation step, the machining electrode is rotated about the central axis of the machining electrode; and in the discharge step, discharge is performed between the machining electrode and the object to be machined in a state where both the object to be machined and the machining electrode have rotated.

[0018] According to this configuration, since the object to be machined and the machining electrode partially overlap, the discharge region is limited. On the other hand, since the object to be machined rotates about the central axis, at least once the surface of the object to be machined is located directly below the machining electrode. As a result, the discharge region can be limited and the entire surface of the object to be machined can be electrically discharged. As a result, it is possible to suppress local concentration of the machining portion due to the surface state of the object to be machined.

[0019] Since the machining electrode itself also rotates around the cylinder axis, the portions in the machining electrode that generate discharges with the object to be machined also change sequentially. Thereby, it is possible to suppress the local deterioration of the wear of the machining electrode, and thus it is possible to suppress the occurrence of deviation at the machining part due to the wear state of the machining electrode.

[0020] In the surface machining method, the following configuration may also be adopted, wherein the machining electrode has a cylindrical shape with an open end on the side facing the object to be machined.

[0021] According to this configuration, the discharge region can be further limited, and electrical discharge machining can be performed on the surface of the object to be machined. Since the object to be machined rotates, even if the machining electrode has a cylindrical shape, the entire surface of the object to be machined can be machined. Thereby, it is possible to more effectively suppress the influence of the surface state of the object to be machined. As a result, it is possible to more effectively suppress the occurrence of unexpected deviation at the machining part.

[0022] In one embodiment of the surface machining method, the discharging process further includes a horizontal movement process, in which at least one of the object to be machined and the machining electrode is moved in the horizontal direction.

[0023] That is, when it is desired to flatten the surface of the object to be machined, it is preferable to perform uniform electrical discharge machining on the entire object to be machined. If the relative positions of the object to be machined and the machining electrode are kept fixed, the machining times at the central part and the peripheral part may be uneven. If at least one of the object to be machined and the machining electrode is moved in the horizontal direction, the machining electrode can be moved away from the central part of the object to be machined, and a state can be achieved in which only the peripheral part of the object to be machined is subjected to electrical discharge machining. Thereby, it is possible to minimize the unevenness of the machining times at the central part and the peripheral part of the object to be machined as much as possible. As a result, a flat surface can be easily obtained.

[0024] On the other hand, when it is desired to make the surface of the object to be machined into a so-called drum shape in which the thickness of the periphery is thinner than that of the center, it is necessary to extend the discharging time of the peripheral part as much as possible. At this time, the state is maintained in which only the peripheral part of the object to be machined overlaps with the machining electrode, and only the peripheral part of the object to be machined is subjected to electrical discharge machining. Thereby, a drum-shaped surface can be obtained.

[0025] In this way, it is possible to suppress the occurrence of unexpected deviation at the machining part. On the other hand, it is possible to deliberately cause deviation at the machining part according to the required surface shape.

[0026] Since the surface of the machining electrode facing the object to be machined can be made to face all parts of the surface of the object to be machined, the machining electrode can be worn more evenly.

[0027] In the above-described embodiment, the machining electrode is in the shape of a cylinder with an open end on one side of the object to be machined. The following configuration may also be adopted. In the horizontal movement step, when the radius of the surface of the object to be machined is r, the outer radius of the machining electrode is R, the width of the cylindrical portion of the machining electrode is d, and d < r, at least one of the object to be machined and the machining electrode is horizontally moved within the range of R - d < L < r + R, where L is the distance between the central axes of the object to be machined and the machining electrode.

[0028] That is to say, if the relative positions of the object to be machined and the machining electrode are changed within the above range, the entire object to be machined can be machined. That is, the area where the object to be machined and the machining electrode overlap can be further limited, and the entire object to be machined can be appropriately machined. As a result, the influence of the surface state of the object to be machined can be more effectively suppressed, and the local concentration of the worn parts of the machining electrode can be suppressed. As a result, the occurrence of unexpected offsets at the machining site can be more effectively suppressed.

[0029] In the above-described embodiment where the range of horizontal movement is limited, the following configuration may also be adopted. The rotation direction of the object to be machined in the object rotation step is the same as the rotation direction of the machining electrode in the electrode rotation step.

[0030] According to this configuration, in the area where the object to be machined and the machining electrode overlap, the moving direction of the object to be machined can be made different from the moving direction of the machining electrode. As a result, the unevenness of the machining time can be more effectively suppressed, and the occurrence of unexpected offsets at the machining site can be more effectively suppressed.

[0031] In the above-described embodiment where the rotation direction of the object to be machined and the rotation direction of the machining electrode are the same, the following configuration may also be adopted. The rotational speed of the machining electrode in the electrode rotation step is not an integer multiple of the rotational speed of the object to be machined in the object rotation step.

[0032] Even when the rotational speed of the machining electrode is an integer multiple of the rotational speed of the object to be machined, the relative positions of the machining electrode and the object to be machined can have regularity, which may cause deviations at the machining site. If the rotational speed of the machining electrode is adjusted so as not to be an integer multiple of the rotational speed of the object to be machined, the relative positions of the machining electrode and the object to be machined will be random, and thus the occurrence of unexpected offsets at the machining site can be more effectively suppressed.

[0033] The technology disclosed herein is also directed to a surface machining apparatus for performing electrical discharge machining on the surface of a disk-shaped workpiece. Specifically, the surface machining apparatus includes a worktable, a machining electrode, a first rotating device, a second rotating device, and a controller. The worktable is used to carry and hold the workpiece. The machining electrode is circular in a top view and has an outer diameter greater than or equal to the outer diameter of the workpiece. The first rotating device rotates the workpiece about the central axis of the workpiece. The second rotating device rotates the machining electrode about the central axis of the machining electrode. The controller is electrically connected to the machining electrode, the first rotating device, and the second rotating device. In a state where the workpiece and the machining electrode partially overlap in a top view, the controller performs electrical discharge machining by rotating the workpiece using the first rotating device and rotating the machining electrode using the second rotating device.

[0034] In this configuration, the discharge area can be defined and electrical discharge machining can be performed on the entire surface of the workpiece. Therefore, it is possible to suppress local concentration of the machining part due to the surface state of the workpiece. Since the machining electrode itself also rotates about the cylindrical axis, it is possible to suppress local deterioration of the wear of the machining electrode. Therefore, it is possible to suppress unexpected deviation in the machining part.

[0035] In the surface machining apparatus, the following configuration may also be adopted. The machining electrode is in the shape of a cylinder with an open end on the side of the workpiece.

[0036] According to this configuration, the discharge area can be further defined and electrical discharge machining can be performed on the surface of the workpiece. Since the workpiece rotates, even if the machining electrode is in the shape of a cylinder, it is possible to machine the entire surface of the workpiece. As a result, it is possible to more effectively suppress the influence of the surface state of the workpiece, and therefore it is possible to more effectively suppress unexpected deviation in the machining part.

[0037] The surface machining apparatus may adopt the following configuration. At least one of the worktable or the machining electrode is configured to be movable in the horizontal direction. The controller may be configured to perform electrical discharge machining while moving at least one of the worktable and the machining electrode in the horizontal direction.

[0038] In this configuration, it is also possible to adjust the machining time of the central part and the outer peripheral part of the workpiece according to the required surface shape to be machined. Moreover, it is possible to make the surface of the machining electrode facing the workpiece face all parts of the surface of the workpiece. In this way, it is possible to suppress unexpected deviation in the machining part. On the other hand, it is possible to deliberately deviate the machining part according to the required surface shape.

[0039] In the surface processing apparatus, the following configuration may also be adopted, where the controller controls the first rotating device and the second rotating device so that the rotation speed of the processing electrode is not an integer multiple of the rotation speed of the object to be processed.

[0040] If the rotation speed of the processing electrode is adjusted so as not to be an integer multiple of the rotation speed of the object to be processed, the position where the processing electrode faces the object to be processed is random. Therefore, it is possible to more effectively suppress the occurrence of unexpected deviation at the processing site.

[0041] - Effects of the Invention -

[0042] As described above, according to the technology disclosed herein, when processing an object to be processed by electrical discharge machining, it is possible to more effectively suppress the occurrence of unexpected deviation at the processing site. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a schematic diagram of the surface processing apparatus according to the first embodiment;

[0044] Figure 2 is a diagram for explaining the positional relationship between the wafer and the processing electrode;

[0045] Figure 3 is a working diagram of the surface processing apparatus, showing the state where the wafer is fixed on the carrier stage;

[0046] Figure 4 is a working diagram of the surface processing apparatus, showing the state where the processing electrode moves from Figure 3 to a specified position;

[0047] Figure 5 is a working diagram of the surface processing apparatus, showing the state where the processing electrode descends from Figure 4 to start surface treatment;

[0048] Figure 6 is a working diagram of the surface processing apparatus, showing the state where the processing electrode moves horizontally in the radial direction of the wafer from Figure 5 ;

[0049] Figure 7 is a working diagram of the surface processing apparatus, showing the state after the surface treatment is completed;

[0050] Figure 8 is a schematic diagram showing the arrangement state of the processing electrodes when only a specific position of the wafer is processed using the surface processing apparatus;

[0051] Figure 9 is a cross-sectional view of the SiC seed crystal after electrical discharge machining using the surface processing apparatus;

[0052] Figure 10 Schematic diagram of the surface processing apparatus according to the second embodiment;

[0053] Figure 11 Working drawing of the surface processing apparatus according to the second embodiment. Detailed implementation mode

[0054] The following describes exemplary embodiments in detail with reference to the accompanying drawings. It should be noted that in the following description, up, down, left, and right are as shown by the arrow lines of Figure 1 . The directions shown here do not limit the arrangement status when actually using the surface processing apparatus 1. In this specification, "surface processing" includes not only processing the shape of the processing surface, but also processing to change the properties of the surface.

[0055] 〈First Embodiment〉

[0056] Figure 1 Briefly shows the surface processing apparatus 1 according to the first embodiment. The surface processing apparatus 1 is an apparatus that uses a conductive wafer W as a processing object, particularly a semiconductor wafer, and processes the surface of the wafer W into a required shape by electrical discharge machining. The wafer W as a processing object includes various wafers such as Si, Ge, SiC, GaAs, GaP, InP, GaN, and AlN. The wafer W can be a wafer obtained by slicing an ingot with a wire saw, or a wafer fabricated by growing a single wafer. The processing object is not limited to wafers, and any object with a circular surface is acceptable. For example, it can also be a disk-shaped SiC or GaN with a thickness of 1 to 10 mm.

[0057] The surface processing apparatus 1 includes a box-shaped housing 2 arranged on the ground F. Inside the housing 2, there are provided: a processing tank 10 storing a processing liquid; a workbench 20 for carrying and holding the wafer W; and a processing electrode 30 that generates electrical discharge between it and the wafer W.

[0058] The processing tank 10 has a tank main body 11 for storing the processing liquid and a plurality of legs 12 for supporting the tank main body 11. The processing liquid stored in the tank main body 11 is water or oil. The processing liquid is used to remove debris generated by electrical discharge machining from the wafer W, or to cool the wafer W during electrical discharge machining. The processing tank 10 may also be provided with a flow generator for making the processing liquid flow.

[0059] The workbench 20 has a carrying portion 21 for carrying the wafer W, a base portion 22 provided on the lower surface of the housing 2, and a pillar 23 connecting the carrying portion 21 and the base portion 22 in the vertical direction. As Figure 1As shown, the carrying part 21 is located in the groove of the groove main body 11, and the base part 22 is located on the lower side of the bottom of the groove main body 11. The support column 23 penetrates through the bottom of the groove main body 11 and extends. When the wafer W is carried on the carrying part 21, the wafer W is immersed in the processing liquid. Although not shown in the figure, a sealing mechanism for preventing the leakage of the processing liquid is provided between the support column 23 and the bottom of the groove main body 11.

[0060] The wafer W is held so that the wafer W does not move from the carrying part 21 when carried by the workbench 20. In particular, the wafer W is held on the carrying part 21, and when the carrying part 21 rotates, the wafer W rotates together with the carrying part 21, which will be described in detail later. The method of holding the wafer W on the carrying part 21 can adopt various methods such as holding by vacuum adsorption, bonding by a conductive adhesive, fixing by a tape, etc.

[0061] The workbench 20 is a rotary workbench on which the carrying part 21 rotates, and a first motor 24 for rotating the carrying part 21 is built in the base part 22. The rotation axis of the first motor 24 extends into the support column 23. Therefore, when the first motor 24 is operating, the support column 23 does not rotate, and the carrying part 21 rotates around the rotation axis of the first motor 24. Although not shown in the figure, in order to make the rotation axis of the first motor 24 coaxial with the central axis X1 of the wafer W (refer to Figure 2 , hereinafter referred to as the first central axis X1), a guide for carrying the wafer W is provided on the carrying part 21. In this way, when the carrying part 21 rotates, the wafer W rotates around the first central axis X1. Therefore, the first motor 24 is equivalent to a first rotating device for rotating the wafer W around its central axis X1. It should be noted that it may also be a configuration in which the first motor 24 is used to rotate the carrying part 21 and the support column 23 together.

[0062] A first power supply part 25 for supplying electric charge to the wafer W is provided on the support column 23 of the workbench 20. The first power supply part 25 is provided on the part of the support column 23 located outside the groove main body 11.

[0063] As Figure 1 and Figure 2 shown, the processing electrode 30 is circular when viewed from above. Specifically, the processing electrode 30 is a bottomed cylindrical shape with an open mouth on the side of the processing electrode 30 facing the wafer W (here, the lower side). The outer radius R of the processing electrode 30 is larger than the radius r of the wafer W. The cylindrical part 31 of the processing electrode 30 is a cylinder with a width d, and it is the part where discharge occurs between it and the wafer W.

[0064] The processing electrode 30 is held on the holding part 40 via the shaft part 41. The shaft part 41 is connected to the central part of the bottom 32 of the processing electrode 30. A second motor 42 for rotating the processing electrode 30 is built in the holding part 40. The processing electrode 30 is connected to the shaft part 41 in such a way that the rotation axis of the second motor 42 is coaxial with its own central axis X2 (equivalent to the cylinder axis, hereinafter referred to as the second central axis X2). Therefore, when the second motor 42 is operating, the processing electrode 30 rotates around the second central axis X2. Therefore, the second motor 42 is equivalent to a second rotating device that rotates the processing electrode 30 around its central axis X2.

[0065] The holding part 40 is configured to be movable in the horizontal direction. Although not shown in the figure, a guide rail that supports the holding part 40 and extends in the left - right direction is provided at the top of the housing 2, and the holding part 40 can move in the left - right direction along this guide rail. As a method of moving the holding part 40 in the left - right direction, known methods such as using a rack - and - pinion mechanism and using a servo motor can be adopted.

[0066] As Figure 2 shown, the moving direction of the holding part 40 is along the radial direction of the wafer W. Therefore, the center of the wafer W is located on the straight line RL along the trajectory described by the center of the processing electrode 30 when the holding part 40 moves.

[0067] The holding part 40 is configured to raise and lower the processing electrode 30 by making the shaft part 41 expand and contract in the up - down direction. Specifically, the holding part 40 is configured such that when the shaft part 41 extends, the processing electrode 30 descends; when the shaft part 41 contracts, the processing electrode 30 ascends. Regarding the method of making the shaft part 41 expand and contract, known methods such as using a servo motor can also be adopted.

[0068] The holding part 40 has a mechanism for tilting the shaft part 41 relative to the vertical direction. When the shaft part 41 is tilted, the processing electrode 30 is also tilted relative to the horizontal direction (refer to Figure 8 ). Known methods can also be adopted for the method of tilting the shaft part 41. It should be noted that after the shaft part 41 is tilted, the second motor 42 is tilted together. That is, after the shaft part 41 is tilted, the rotation axis of the second motor 42 is tilted to the same extent as the shaft part 41.

[0069] A second power supply part 43 for supplying charge to the processing electrode 30 is provided on the holding part 40. The lower end of the second power supply part 43 is in contact with the bottom 32 of the processing electrode 30, and charge is supplied to the processing electrode 30 via this contact part. Therefore, even when the processing electrode 30 rotates, the second power supply part 43 can supply charge without rotating. It should be noted that the second power supply part 43 can also be structured to be in contact with the shaft part 41.

[0070] The surface processing apparatus 1 has a controller 50 that operates each device to perform surface processing on the wafer W. The controller 50 is electrically connected to the first motor 24, the first power supply unit 25, the second motor 42, and the second power supply unit 43. The controller 50 is also electrically connected to a mechanism that moves the holding unit 40 in the left-right direction (hereinafter referred to as the horizontal movement mechanism), a mechanism that expands and contracts the shaft portion 41 (hereinafter referred to as the expansion and contraction mechanism), and a mechanism that tilts the shaft portion 41 (hereinafter referred to as the tilting mechanism).

[0071] (Electrical discharge machining)

[0072] Next, with reference to Figures 3 to 7 A method for surface processing of the wafer W using the surface processing apparatus 1 will be described in detail. Figures 3 to 7 The upper figure in[] is a view observed from the side, and the lower figure is a view observed from the upper side (when looking down). It should be noted that in the following description, "the wafer W overlaps with the processing electrode 30" means that the wafer W overlaps with the processing electrode 30 when looking down.

[0073] Figure 3 It shows a state where the wafer W is held on the workbench 20. At this time, the processing electrode 30 is located at the initial position. In this state, the wafer W and the processing electrode 30 do not overlap in the up-down direction, and the distance L between the central axes of the wafer W and the processing electrode 30 is greater than the sum of the outer radius R of the processing electrode 30 and the radius r of the wafer W.

[0074] Next, the controller 50 uses the horizontal movement mechanism to move the holding unit 40 from Figure 3 this state, and moves the processing electrode 30 radially inward (here, to the left) of the wafer W. As Figure 4 shown, the controller 50 arranges the processing electrode 30 such that the cylindrical portion 31 of the processing electrode 30 is located on the first central axis X1 of the wafer W. More specifically, the controller 50 arranges the processing electrode 30 so as to move the processing electrode 30 so that the midpoint of the width of the cylindrical portion 31 is located on the first central axis X1. At this time, the distance L between the central axes is L = R - d / 2. By arranging the processing electrode 30 as described above, the wafer W and the processing electrode 30 partially overlap.

[0075] Then, the controller 50 operates the first motor 24 and the second motor 42 to rotate the wafer W around the first central axis X1 and rotate the processing electrode 30 around the second central axis X2. The maximum rotation speed of the wafer W is 300 rpm, and the maximum rotation speed of the processing electrode 30 is 2300 rpm. The rotation speed of the processing electrode 30 is adjusted so as not to be an integer multiple of the rotation speed of the wafer W. Specifically, the rotation speed of the processing electrode 30 is adjusted to an irrational multiple such as times that of the rotation speed of the wafer W. As Figure 4As shown, the rotation direction of the wafer W is the same as that of the processing electrode 30. In this way, in the overlapping portion between the wafer W and the processing electrode 30, the moving direction of the processing electrode 30 and the moving direction of the wafer W become opposite directions.

[0076] Next, the controller 50 uses the telescopic mechanism to extend the shaft portion 41 from Figure 4 the state where it is in, causing the processing electrode 30 to descend and approach the wafer W. When the vertical distance between the wafer W and the processing electrode 30 reaches below a specified distance, the controller 50 activates the first power supply unit 25 and the second power supply unit 43 to start electrical discharge machining. The discharge voltage is around 50V to 300V. It should be noted that the specified distance refers to the distance at which at least the cylindrical portion 31 of the processing electrode 30 is immersed in the machining fluid. The controller 50 activates the first power supply unit 25 and the second power supply unit 43 to generate pulsed discharges between the wafer W and the processing electrode 30. Since the wafer W and the processing electrode 30 partially overlap, the discharge area is limited to the overlapping portion.

[0077] In the surface machining apparatus 1, as the polarity of the electrical discharge machining, it is possible to select either the positive polarity with the wafer W as the anode and the processing electrode 30 as the cathode, or the reverse polarity with the wafer W as the cathode and the processing electrode 30 as the anode. In particular, the polarity of the electrical discharge machining is preferably appropriately changed according to the machining purpose of the wafer W. For example, when giving priority to the machining speed, it is preferable to set the polarity of the electrical discharge machining to the positive polarity. On the other hand, when giving priority to the surface roughness of the wafer surface, it is preferable to set the polarity of the electrical discharge machining to the reverse polarity. The polarity of the electrical discharge machining can be appropriately changed during the period from the start to the end of the electrical discharge machining. The polarity of the electrical discharge machining can also be appropriately changed according to the material of the workpiece to be machined. The polarity of the electrical discharge machining can be appropriately selected by the operator each time machining is performed, or can be automatically selected by the controller 50.

[0078] Next, the controller 50, in a state where the first power supply unit 25 and the second power supply unit 43 are already activated, that is, in a state where discharges are occurring between the wafer W and the processing electrode 30, uses the horizontal movement mechanism to move the processing electrode 30 back and forth along the radial direction of the wafer W. The range of the back-and-forth movement of the processing electrode 30 is in the range where the center-to-center distance L satisfies R - d < L < r + R.

[0079] More specifically, as Figure 6 shown, the controller 50 moves the processing electrode 30 back and forth between the machining start position and the position where the midpoint of the width of the cylindrical portion 31 is located above the outer periphery of the wafer W, that is, the position where the center-to-center distance L is L = r + R - d / 2. In detail, the movement range of the processing electrode 30 is in the range where the center-to-center distance L satisfies R - d / 2 ≤ L ≤ r + R - d / 2.

[0080] Within the range where the wafer W does not contact the processing electrode 30, the controller 50 gradually reduces the vertical distance between the wafer W and the processing electrode 30. The controller 50 adjusts the horizontal movement speed of the processing electrode 30 according to the required surface shape, or stops the horizontal movement of the processing electrode 30. For example, when the required surface shape is drum-shaped, in order to process the outer peripheral portion of the wafer W more than the central portion of the wafer W, when only the cylindrical portion 31 of the processing electrode 30 overlaps with the outer peripheral portion of the wafer W, the horizontal movement speed of the processing electrode 30 is reduced, or the horizontal movement of the processing electrode 30 is stopped.

[0081] After the surface shape of the wafer W has become the required shape, the controller 50 stops the first power supply unit 25 and the second power supply unit 43. After that, as Figure 7 shown, the controller 50 uses the above-mentioned telescopic mechanism to contract the shaft portion 41, raising the processing electrode 30 away from the wafer W. After the controller 50 stops the rotation of the wafer W and the processing electrode 30 respectively, it then moves the processing electrode 30 to Figure 3 the initial position shown.

[0082] By doing the above, the surface treatment of the wafer W is completed by electrical discharge machining. After the holding of the wafer W by the holding portion 21 is released, the wafer W is recovered by an operator.

[0083] Therefore, in the present first embodiment, the processing electrode 30 is circular in plan view and has an outer diameter greater than or equal to the outer diameter of the wafer W. The processing electrode 30 is arranged above the wafer W in such a way that the wafer W and the processing electrode 30 partially overlap in plan view. The wafer W is rotated around the first central axis X1, and the processing electrode 30 is rotated around the second central axis X2. Electrical discharge is carried out between the processing electrode 30 and the wafer W in a state where both the wafer W and the processing electrode 30 have rotated. In this way, since the electrical discharge is carried out in a state where the wafer W and the processing electrode 30 partially overlap, the discharge area is limited. On the other hand, since the wafer W is rotated around the first central axis X1, at least once the surface of the wafer W is located directly below the processing electrode 30. In this way, since the discharge area can be limited and electrical discharge machining can be carried out on the entire surface of the wafer W, it is possible to suppress the local concentration of the machining part due to the surface state of the wafer W. Since the processing electrode 30 itself also rotates around the second central axis X2, it is possible to suppress the local deterioration of wear, and thus it is possible to suppress the occurrence of deviation in the machining part due to the wear state of the processing electrode 30. As a result, it is possible to suppress the accidental occurrence of deviation in the machining part, and it is easy to machine the surface shape of the wafer W into the required shape.

[0084] In this first embodiment, the machining electrode 30 has a cylindrical shape with an open end on one side of the wafer W. The discharge area can be further defined to perform electrical discharge machining on the surface of the wafer W. Since the wafer W rotates, even if the machining electrode 30 has a cylindrical shape, the entire surface of the wafer W can be machined. As a result, the influence of the surface state of the wafer W can be more effectively suppressed, and consequently, the occurrence of unexpected offsets at the machining sites can be more effectively suppressed.

[0085] In the first embodiment, during electrical discharge machining, the machining electrode 30 is moved in the horizontal direction. As a result, the machining time for the central portion and the outer peripheral portion of the wafer W can be adjusted according to the desired surface shape to be machined. The cylindrical portion 31 of the machining electrode 30 can be opposed to all parts of the surface of the wafer W. In this way, the occurrence of unexpected offsets at the machining sites can be suppressed. On the other hand, the machining sites can be intentionally offset according to the desired surface shape.

[0086] Particularly in this first embodiment, the movement range of the machining electrode 30 is in the range where the center-to-center distance L satisfies R - d / 2 ≤ L ≤ r + R - d / 2. As a result, the overlapping area between the wafer W and the machining electrode 30 can be further defined, and the entire wafer W can be appropriately machined. Consequently, the influence of the surface state of the wafer W can be more effectively suppressed, and the local concentration of the worn parts of the machining electrode 30 can be more effectively suppressed.

[0087] In this first embodiment, the rotation direction of the wafer W is the same as the rotation direction of the machining electrode 30. In this way, in the area where the wafer W and the machining electrode 30 overlap, the movement direction of the wafer W can be made as different as possible from the movement direction of the machining electrode 30. As a result, the non-uniformity of the machining time can be more effectively suppressed. Consequently, the occurrence of unexpected offsets at the machining sites can be more effectively suppressed.

[0088] In this first embodiment, the rotational speed of the machining electrode 30 is adjusted so as not to be an integer multiple of the rotational speed of the wafer W. Even when the rotational speed of the machining electrode 30 is an integer multiple of the rotational speed of the wafer W, the portions of the cylindrical portion 31 of the machining electrode 30 opposed to the surface of the wafer W can have regularity, and offsets may occur at the machining sites. If the rotational speed of the machining electrode 30 is adjusted so as not to be an integer multiple of the rotational speed of the wafer W, the portions of the cylindrical portion 31 of the machining electrode 30 opposed to the surface of the wafer W will be random, and thus the occurrence of unexpected offsets at the machining sites can be more effectively suppressed.

[0089] Figure 8 Shows another usage method of the surface machining apparatus 1 according to this first embodiment. As Figure 8As shown, in the surface processing apparatus 1, the shaft portion 41 is tilted by the tilting mechanism to tilt the processing electrode 30, whereby the discharge region can be further defined. As a result, the surface shape of the wafer W can be finely adjusted, and it is easy to process the surface shape of the wafer W into a desired shape.

[0090] (Processing of SiC seed)

[0091] Figure 9 This shows the result of performing electrical discharge machining on the surface of a seed crystal of SiC (hereinafter simply referred to as seed crystal 100) as an object to be processed using the surface processing apparatus 1 according to the first embodiment. The seed crystal 100 has a disk shape with a thickness of 0.1 mm to 10 mm. For example, the seed crystal 100 can be manufactured by slicing a single crystal of SiC using a wire saw.

[0092] As Figure 9 shown, it can be seen that after performing electrical discharge machining, a layer with changed properties (hereinafter referred to as modified layer 101) is formed on the surface portion of the seed crystal 100. This modified layer 101 is a layer containing carbon, SiO2, etc. in addition to SiC. In the electrical discharge machining using the surface processing apparatus 1, the thickness of the modified layer 101 is about 0.1 μm to 10 μm.

[0093] By performing surface processing using the surface processing apparatus 1 according to this embodiment in this way, it is possible to suppress the occurrence of deviation at the processing site and form a modified layer 101 with an appropriate surface roughness. By forming the above-mentioned modified layer 101, the adhesion between the seed crystal 100 and the base can be improved when the seed crystal 100 is bonded to the base, and subsequent crystal growth can proceed appropriately.

[0094] 〈Second Embodiment〉

[0095] Hereinafter, the second embodiment will be described in detail with reference to the drawings. It should be noted that in the following description, the same parts as those in the above first embodiment are denoted by the same reference numerals and detailed descriptions thereof are omitted.

[0096] The surface processing apparatus 201 of this second embodiment is different from the above first embodiment in that no motor is provided on the base portion 22. In this second embodiment, it is configured that instead of the motor, the nozzle 260 that supplies the processing liquid into the processing tank 10 is used to rotate the carrier portion 21 to rotate the wafer W. On the other hand, the processing electrode 30 is rotated by the second motor 42 as in the above first embodiment.

[0097] Specifically, as Figure 10 and Figure 11As shown, a nozzle 260 for supplying machining fluid to the machining tank 10 is provided on the side opposite to the machining electrode 30 with the workbench 20 therebetween. The nozzle 260 is connected to a pump P through a hose 261, and the machining fluid is pumped by the pump P. A discharge pipe (not shown) is provided in the machining tank 10, and the discharge pipe discharges the surplus machining fluid (that is, the part of the machining fluid that cannot be contained in the tank) generated by supplying the machining fluid through the nozzle 260. The machining fluid discharged from the discharge pipe is conveyed to the pump P and supplied again from the nozzle 260 into the machining tank 10. The pump P is electrically connected to the controller 50 and can adjust the flow rate, i.e., the supply pressure, of the pumped machining fluid.

[0098] As Figure 11 shown, the nozzle 260 is located on the extension of the tangent line of the wafer W. In this way, the force generated by the flow of the discharged machining fluid is input to the wafer W in the tangential direction, causing the wafer W to rotate. The rotational speed is adjusted by adjusting the supply pressure of the machining fluid from the pump P to the nozzle 260 by the controller 50 and adjusting the flow pattern of the machining fluid supplied from the nozzle 260 into the tank.

[0099] In this second embodiment, except for the rotating device used to rotate the wafer W being changed, other aspects are the same as those of the above first embodiment. That is, the machining electrode 30 discharges electricity to the wafer W in a state of partially overlapping with the wafer W. More specifically, the machining electrode 30 discharges electricity to the wafer W while reciprocating between a position where the center-axis distance L is L = R - d / 2 and a position where L = r + R - d / 2.

[0100] Even with the above-described configuration, it is possible to define the discharge area and rotate the wafer W around the first central axis X1 to perform electrical discharge machining on the entire surface of the wafer W, so that it is possible to suppress the local concentration of the machining part due to the surface state of the wafer W. Since the machining electrode 30 itself also rotates around the second central axis X2, it is possible to suppress the local deterioration of wear, and thus it is possible to suppress the occurrence of deviation at the machining part due to the wear state of the machining electrode 30. As a result, it is possible to suppress the accidental occurrence of deviation at the machining part, and it is easy to machine the surface shape of the wafer W into the required shape.

[0101] 〈Other Embodiments〉

[0102] The technology disclosed herein is not limited to the above embodiments and can be modified within the scope not exceeding the gist of the claims.

[0103] For example, in the above-described first and second embodiments, the machining electrode 30 is configured to be movable in the horizontal direction. However, this is not limitative, and the relative position between the machining electrode 30 and the object to be machined may also be fixed. At this time, the machining electrode 30 is arranged such that the cylindrical portion 31 is located on the first central axis X1 of the object to be machined. In this way, if the object to be machined is rotated about the first central axis X1, it is possible to perform electrical discharge machining on the entire surface of the object to be machined.

[0104] In the above-described first and second embodiments, the relative position between the object to be machined and the machining electrode 30 is changed by moving the machining electrode 30 in the horizontal direction. However, this is not limitative, and the relative position between the object to be machined and the machining electrode 30 may also be changed by moving the worktable 20 together with the object to be machined in the horizontal direction. At this time, it is preferable to provide a mechanism for moving the base portion 22 in the horizontal direction with the entire worktable 20 located inside the machining tank 10. The first power supply unit 25 is preferably configured to be built into the base portion 22.

[0105] In the above-described first and second embodiments, the machining electrode 30 reciprocates between a position where the distance L between the central axes is L = R - d / 2 and a position where L = r + R - d / 2. However, this is not limitative, and as long as the distance L between the central axes satisfies the range of R - d < L < r + R and the cylindrical portion 31 of the machining electrode 30 is located on the first central axis X1 once in one reciprocation, the machining electrode 30 can reciprocate within an arbitrary range in accordance with the required surface shape.

[0106] In the above-described first and second embodiments, the machining electrode 30 has a bottomed cylindrical shape. However, this is not limitative, and the machining electrode 30 may have a circular plate shape or may have a cylindrical shape with both the side facing the object to be machined and the side facing the holding portion open.

[0107] The above-described embodiments are merely examples, and the scope of the present disclosure is not limited thereto. The scope of the present disclosure is defined by the scope of the claims, and all modifications or changes within the equivalent scope of the claims are included in the scope of the present disclosure.

[0108] -Industrial Applicability-

[0109] The technology disclosed herein is useful when performing electrical discharge machining on the surface of a circular plate-shaped object to be machined using a machining electrode.

[0110] -Symbolic Explanation-

[0111] 1 Surface machining device

[0112] 20 Worktable

[0113] 24 First motor (first rotating device)

[0114] 30 Machining electrode

[0115] 31 Cylindrical part

[0116] 42 Second motor (second rotating device)

[0117] 50 Controller

[0118] 100 Seed crystal (object to be machined)

[0119] W Wafer (object to be machined)

[0120] X1 First central axis (central axis of object to be machined)

[0121] X2 Second central axis (central axis of machining electrode).

Claims

1. A surface machining method for performing electrical discharge machining on the surface of a circular plate-shaped workpiece using a machining electrode, characterized in that: the machining electrode is circular in a top view and has an outer diameter greater than or equal to the outer diameter of the workpiece; the surface machining method includes an arrangement process, a workpiece rotation process, an electrode rotation process, and a discharge process; in the arrangement process, the machining electrode is arranged above the workpiece in such a manner that the workpiece and the machining electrode partially overlap in a top view; in the workpiece rotation process, the workpiece is rotated about the central axis of the workpiece; in the electrode rotation process, the machining electrode is rotated about the central axis of the machining electrode; in the discharge process, electrical discharge is performed between the machining electrode and the workpiece in a state where both the machining electrode and the workpiece have rotated.

2. The surface machining method according to claim 1, characterized in that: the machining electrode is in the shape of a cylinder with an open end on the side of the workpiece.

3. The surface machining method according to claim 1 or 2, characterized in that: the discharge process further includes a horizontal movement process, in which at least one of the workpiece and the machining electrode is moved in a horizontal direction.

4. The surface machining method according to claim 3, characterized in that: the machining electrode is in the shape of a cylinder with an open end on the side of the workpiece; the horizontal movement process is a process in which at least one of the workpiece and the machining electrode is horizontally moved within a range where the distance L between the central axes of the workpiece and the machining electrode satisfies R - d < L < r + R, where r is the radius of the surface of the workpiece, R is the outer radius of the machining electrode, and d is the width of the cylindrical portion of the machining electrode, and d < r.

5. The surface machining method according to claim 4, characterized in that: the rotation direction of the workpiece in the workpiece rotation process is the same as the rotation direction of the machining electrode in the electrode rotation process.

6. A surface machining device that performs electrical discharge machining on the surface of a disk-shaped workpiece to be machined, characterized in that: The surface machining apparatus includes a worktable, a machining electrode, a first rotation device, a second rotation device, and a controller; the worktable is used to carry and hold the workpiece; the machining electrode is circular in a top view and has an outer diameter greater than or equal to the outer diameter of the workpiece; the first rotation device rotates the workpiece about the central axis of the workpiece; the second rotation device rotates the machining electrode about the central axis of the machining electrode; the controller is electrically connected to the machining electrode, the first rotation device, and the second rotation device; in a state where the workpiece and the machining electrode partially overlap in a top view, the controller performs electrical discharge machining by rotating the workpiece using the first rotation device and rotating the machining electrode using the second rotation device.

7. The surface machining apparatus according to claim 6, characterized in that: The processing electrode is in a cylindrical shape with an open end on one side of the processing object.

8. The surface processing device according to claim 6 or 7, characterized in that: At least one of the worktable or the processing electrode is configured to be movable in the horizontal direction, The controller is configured to perform electrical discharge machining while moving at least one of the worktable and the processing electrode in the horizontal direction.

9. The surface processing method according to claim 5, characterized in that: The rotational speed of the processing electrode in the electrode rotation step is not an integer multiple of the rotational speed of the processing object in the object rotation step.

10. The surface processing device according to claim 6, characterized in that: The controller controls the first rotating device and the second rotating device so that the rotational speed of the processing electrode does not become an integer multiple of the rotational speed of the processing object.

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