Surface machining apparatus

Abstract

A surface machining apparatus (1) is provided with a discharge device (30) having: a base unit (31); a plurality of electrode pieces (EP) that are arranged along the circumferential edge of the base unit (31); and a power supply unit (35) that supplies power to the plurality of electrode pieces (EP). The power supply unit (35) can independently supply power to some electrode pieces (EP) and the other electrode pieces (EP) among the plurality of electrode pieces (EP), and the base unit (31) is disposed such that at least two of the electrode pieces (EP), which can discharge power independently while partially overlapping a machining target object, overlap the machining target object in a plan view.

Description

surface processing equipment

[0001] The technology disclosed herein belongs to the technical field of surface processing devices.

[0002] BACKGROUND ART Conventionally, there has been known a surface processing apparatus in which a conductive workpiece and an electrode are placed opposite each other and a current is passed between the workpiece and the electrode to process the surface of the workpiece.

[0003] For example, Patent Document 1 discloses a surface processing device that includes a substrate (object to be processed) on which a metal film is formed, a counter electrode arranged opposite the substrate at a predetermined distance, and a reference electrode that serves as a reference potential for the metal film, all of which are disposed in an electrolyte, and that passes a current through the metal film via the electrolyte based on the potential of the metal film relative to the reference electrode.

[0004] Japanese Patent Application Laid-Open No. 2003-342800

[0005] By the way, machining using electric current includes electrical discharge machining, which uses electrical discharge from an electrode to the workpiece. In order to improve the machining efficiency of electrical discharge machining, it is effective to discharge over a wide area.

[0006] In the surface processing device described in Patent Document 1, the entire portion facing the workpiece is used as a single electrode, so there is only one discharge point per discharge. Also, in the surface processing device described in Patent Document 1, almost the entire workpiece faces the electrode. Because the workpiece and the electrode have unevenness, with a configuration like that described in Patent Document 1, there is a risk that discharge points will concentrate in specific locations. When the discharge points are limited, processing efficiency decreases.

[0007] The technique disclosed herein has been made in view of the above points, and its purpose is to improve the machining efficiency of electrical discharge machining.

[0008] To solve the above problems, a first aspect of the technology disclosed herein is directed to a surface processing apparatus for electrical discharge machining of a surface of a workpiece. The surface processing apparatus includes a table on which the workpiece is placed and held, a first rotation device for rotating the workpiece about its central axis, a base portion having a circular shape in a plan view, a plurality of electrodes arranged along the periphery of the base portion, and a discharge device having a power supply unit for supplying power to the plurality of electrodes and for discharging electricity from the electrodes to the workpiece, the power supply unit being capable of independently supplying power to some of the plurality of electrodes and the other electrodes, and the base portion being arranged so that at least two of the electrodes that are capable of independently discharging electricity overlap the workpiece in a plan view.

[0009] In the first aspect, simultaneous discharge is possible from at least two electrode pieces, allowing discharge at at least two locations. Furthermore, by rotating the workpiece while the workpiece and the base part are partially overlapping, the part of the workpiece facing the electrode piece can be changed. This prevents the discharge location from being limited, allowing discharge to occur over a wide area of ​​the workpiece. Therefore, the surface processing device can improve processing efficiency.

[0010] In the second aspect, in the first aspect, the plurality of electrode pieces are divided into a plurality of electrode groups each including at least two of the electrode pieces, and the electrode pieces belonging to the same electrode group are arranged in the circumferential direction of the base portion, and the electrode pieces belonging to different electrode groups are arranged adjacent to each other in the circumferential direction, the power supply portion supplies power independently to each electrode group, and the base portion is arranged so that it partially overlaps with the workpiece in a planar view and so that the plurality of electrode pieces overlap with the workpiece.

[0011] In the second aspect, the electrode pieces belonging to the same electrode group are arranged so as not to be adjacent to each other in the circumferential direction, and multiple electrode pieces overlap with the workpiece in a plan view. Therefore, even if there are electrode pieces belonging to the same electrode group in the circumferential direction, the multiple electrode pieces overlapping with the workpiece always include electrode pieces belonging to different electrode groups. Since the power supply unit supplies power independently to each electrode group, multiple electrode pieces can discharge electricity to the workpiece simultaneously, improving machining efficiency.

[0012] In the second aspect, only one component group for separating the power supply paths is required for each electrode group, and it is not necessary to provide one for each electrode piece. Therefore, even if the number density of the electrode pieces is increased, the device size can be prevented from increasing.

[0013] Therefore, the surface processing device can improve processing efficiency while suppressing an increase in size of the device.

[0014] In a third aspect, in the second aspect, the base portion is positioned relative to the workpiece so that only one of the electrode pieces belonging to each electrode group has its entire electrode piece overlapping with the workpiece.

[0015] In the third aspect, the electrode pieces that overlap the workpiece belong to different electrode groups, so that the number of electrode pieces that can discharge simultaneously increases, thereby improving the processing efficiency of the surface processing device.

[0016] In a fourth aspect, in the third aspect, the discharge device further includes a second rotation device that rotates the base portion around a central axis.

[0017] In electrical discharge machining, a portion of the electrode piece is removed by the discharge, and repeated discharges with the same electrode piece result in a shape that is significantly different from the other electrode pieces. If the shapes of the electrode pieces are significantly different, there is a possibility that the ease of discharge between the electrodes will be uneven, making simultaneous discharge difficult. In the fourth aspect, the electrode piece that overlaps with the workpiece can be changed, allowing discharge to be evenly distributed from each electrode piece, and preventing significant unevenness in the shape of the electrode pieces. This allows multiple electrode pieces to discharge simultaneously over a long period of time. The surface processing device can improve processing efficiency.

[0018] In the fifth aspect, in the fourth aspect, the plurality of electrode pieces are arranged so that when the base portion rotates and an electrode piece belonging to one of the electrode groups moves away from the workpiece, another electrode piece belonging to the same electrode group newly overlaps with the workpiece.

[0019] In the fifth aspect, the number of electrode groups can be minimized, and all of the electrode pieces that overlap with the workpiece can be made to belong to different electrode groups. This allows the surface processing device to increase the number density of the electrode pieces while preventing the device from becoming too large.

[0020] In a sixth aspect, in any one of the first to fifth aspects, the electrode pieces belonging to the same electrode group among the plurality of electrode pieces are arranged at equal intervals in the circumferential direction of the base portion.

[0021] In the sixth aspect, the number density of the electrode pieces can be made as high as possible, so that the surface processing device can improve processing efficiency.

[0022] As described above, according to the technique disclosed herein, the surface processing device can improve the processing efficiency of electric discharge processing.

[0023] FIG. 1 is a schematic diagram of a surface processing apparatus according to an exemplary embodiment. FIG. 2 is a diagram illustrating the positional relationship between a wafer and a base. FIG. 3 is a plan view showing the arrangement of electrodes. FIG. 4 is a diagram showing an equivalent circuit of a power supply circuit. FIG. 5 is a diagram illustrating the operation of the surface processing apparatus, showing a state in which a wafer is fixed to a mounting table. FIG. 6 is a diagram illustrating the operation of the surface processing apparatus, showing a state in which the base has been moved to a predetermined position from the state of FIG. 5. FIG. 7 is a diagram illustrating the position of the electrode pieces before the base is rotated in the arrangement of FIG. 6. FIG. 8 is a diagram illustrating the position of the electrode pieces when the base has been rotated from the state of FIG. 7. FIG. 9 is a diagram illustrating the position of the electrode pieces when the base has been further rotated from the state of FIG. 8. FIG. 10 shows the position of the base when electrical discharge machining is started. FIG. 11 shows voltage waveforms and current waveforms between a wafer and an electrical discharge device when the surface of a wafer is processed by the surface processing apparatus. FIG. 12 is a plan view showing an electrical discharge device of a surface processing apparatus according to a first modification. FIG. 13 is a plan view showing an electrical discharge device of a surface processing apparatus according to a second modification.

[0024] Exemplary embodiments will be described in detail below with reference to the drawings. In the following description, up, down, left, and right refer to the arrows in FIG. 1. The directions shown here do not limit the positioning of the surface processing device 1 when it is actually used. In this specification, "surface processing" does not only refer to processing that simply processes the shape of a surface, but also includes processing that changes the properties of a surface.

[0025] (1) Overall Structure of the Surface Processing Apparatus FIG. 1 schematically illustrates a surface processing apparatus 1 according to the first embodiment. This surface processing apparatus 1 processes a conductive wafer W, particularly a semiconductor wafer, into a desired shape by electrical discharge machining. The wafer W to be processed can be made of a variety of materials, including Si, Ge, SiC, GaAs, GaP, InP, GaN, and AlN. The wafer W may be a wafer sliced ​​from an ingot using a wire saw, or a wafer grown to a single wafer. The workpiece is not limited to a wafer, and may also be, for example, a rectangular plate-shaped SiC or GaN wafer having a thickness of 1 to 10 mm.

[0026] The surface processing device 1 includes a box-shaped housing 2 disposed on a floor surface F. Inside the housing 2, there are provided a processing tank 10 in which a processing liquid is stored, a table 20 on which a wafer W is placed and held, and a discharge device 30 that generates a discharge between the wafer W and the processing tank 2.

[0027] (1-1) Machining Tank The machining tank 10 has a tank body 11 in which machining fluid is stored, and a plurality of legs 12 that support the tank body 11. The machining fluid stored in the tank body 11 is water or oil. The machining fluid is used to remove debris generated by electrical discharge machining from the wafer W and to cool the wafer W during electrical discharge machining. The machining tank 10 may be provided with a flow generator for creating a flow in the machining fluid.

[0028] (1-2) Table The table 20 has a mounting portion 21 on which the wafer W is placed, a base 22 installed on the underside of the housing 2, and support columns 23 that vertically connect the mounting portion 21 and the base 22. As shown in FIG. 1 , the mounting portion 21 is located within the tank of the tank body 11, and the base 22 is located below the bottom of the tank body 11. The support columns 23 extend through the bottom of the tank body 11. When the wafer W is placed on the mounting portion 21, the wafer W is immersed in the processing liquid. Although not shown, a sealing mechanism is provided between the support columns 23 and the bottom of the tank body 11 to prevent leakage of the processing liquid.

[0029] When placed on the table 20, the wafer W is held so as not to move from the mounting portion 21. In particular, the wafer W is held on the mounting portion 21 so that when the mounting portion 21 rotates as described below, the wafer W rotates together with the mounting portion 21. The wafer W can be held on the mounting portion 21 by various methods, such as by vacuum suction, by bonding with a conductive adhesive, or by fixing with adhesive tape.

[0030] The table 20 is a rotary table on which the mounting portion 21 rotates, and the base 22 houses a first motor 24 for rotating the mounting portion 21. The rotation shaft of the first motor 24 extends inside the support column 23. Therefore, when the first motor 24 is driven, the mounting portion 21 rotates around the rotation shaft of the first motor 24 without rotating the support column 23. Although not shown, the mounting portion 21 is provided with a guide for mounting the wafer W so that the rotation shaft of the first motor 24 and the central axis X1 of the wafer W (see FIG. 2 ; hereinafter, referred to as the first central axis X1) are coaxial. As a result, when the mounting portion 21 rotates, the wafer W rotates around the first central axis X1. Note that the mounting portion 21 may be configured to rotate together with the support column 23 by the first motor 24. The first motor 24 corresponds to a first rotating device that rotates the wafer W around its central axis X1.

[0031] A first power supply unit 25 for supplying an electric charge to the wafer W is provided on the support 23 of the table 20. The first power supply unit 25 is provided on a portion of the support 23 located outside the tank body 11.

[0032] 1 and 2, the discharge device 30 has a base portion 31 that is circular in plan view. The outer radius R of the base portion 31 is larger than the radius r of the wafer W. The base portion 31 is made of, for example, SUS.

[0033] An electrode region ER in which a plurality of electrode pieces EP are arranged is provided on the periphery of the base portion 31. The electrode region ER has a cylindrical shape with a width d. The arrangement of the electrode pieces EP in the electrode region ER will be described later.

[0034] The discharge device 30 is held by a holder 32 attached to the ceiling of the housing 2 via a shaft 33. The shaft 33 is connected to the center of the base 31. A second motor 34 for rotating the base 31 is built into the holder 32. The base 31 is connected to the shaft 33 so that the rotation axis of the second motor 34 and its own central axis X2 (hereinafter referred to as the second central axis X2) are coaxial. When the second motor 34 is driven, the discharge device 30 rotates around the second central axis X2. The second motor 34 corresponds to a second rotation device that rotates the base 31 around its central axis X2.

[0035] The holding portion 32 is configured to be movable in the horizontal direction. Although not shown, a rail that supports the holding portion 32 and extends in the left-right direction is provided on the ceiling of the housing 2, and the holding portion 32 is movable in the left-right direction along the rail. As a method for moving the holding portion 32 in the left-right direction, a known method such as a rack and pinion mechanism or a servo motor can be used.

[0036] The movement direction of the holder 32 is along the radial direction of the wafer W. Therefore, the center of the wafer W is located on a straight line RL along a trajectory drawn by the center of the base portion 31 when the holder 32 moves.

[0037] The holding unit 32 is configured to raise and lower the base unit 31 by extending and contracting the shaft unit 33 in the vertical direction. Specifically, the holding unit 32 is configured so that the base unit 31 descends when the shaft unit 33 is extended, and the base unit 31 ascends when the shaft unit 33 is contracted. As a method for extending and contracting the shaft unit 33, a known method such as a method using a servo motor can be adopted.

[0038] The holding portion 32 is provided with a supply portion 35d of the second power supply portion 35 for supplying electric charge to each electrode piece EP. The lower end of the supply portion 35d is in contact with the base portion 32, and supplies electric charge to the electrode piece EP via this contact portion. The supply portion 35d supplies electric charge without rotating even when the base portion 32 rotates. The supply portion 35d may be configured to contact the shaft portion 33.

[0039] (1-4) Controller 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 a controller based on a well-known microcomputer, and has a central processing unit (CPU), a memory, and an I / F circuit.

[0040] The controller 50 is electrically connected to the first motor 24, the second motor 34, the first power supply unit 25, and the second power supply unit 35. The controller 50 is also electrically connected to a mechanism that moves the holding unit 32 in the left-right direction (hereinafter referred to as the horizontal movement mechanism) and a mechanism that extends and retracts the shaft unit 33 (hereinafter referred to as the extension and retraction mechanism).

[0041] (2) Structure of the Electrode Piece Next, the structure of the electrode piece EP will be described with reference to FIGS. 3 and 4. FIG.

[0042] The discharge device 30 has a plurality of electrode pieces EP for discharging electricity onto the wafer W. The electrode pieces EP are made of, for example, SUS. The electrode pieces EP are lined up along the periphery of the base portion 31. In this embodiment, 18 electrode pieces EP are provided. The electrode pieces EP are arranged at equal intervals in the circumferential direction. In the following description, the 18 electrode pieces may be referred to as the first electrode piece EP1, the second electrode piece EP2, ..., the 18th electrode piece EP18. When it is not necessary to distinguish between the first electrode piece EP1 to the 18th electrode piece EP18, they will simply be referred to as the electrode pieces EP.

[0043] The first electrode piece EP1 to the eighteenth electrode piece EP18 are divided into six electrode groups EG. Each electrode group EG has three electrodes EP. Specifically, the first electrode group EG1 has the first electrode piece EP1, the seventh electrode piece EP7, and the thirteenth electrode piece EP13. The second electrode group EG2 has the second electrode piece EP2, the eighth electrode piece EP8, and the fourteenth electrode piece EP14. The third electrode group EG3 has the third electrode piece EP3, the ninth electrode piece EP9, and the fifteenth electrode piece EP15. The fourth electrode group EG4 has the fourth electrode piece EP4, the tenth electrode piece EP10, and the sixteenth electrode piece EP16. The fifth electrode group EG5 has the fifth electrode piece EP5, the eleventh electrode piece EP11, and the seventeenth electrode piece EP17. The sixth electrode group EG6 has a sixth electrode piece EP6, a twelfth electrode piece EP12, and an eighteenth electrode piece EP18. Since each electrode group EG has the electrode pieces EP as described above, the multiple electrode pieces EP are arranged in a manner such that electrode pieces EP belonging to the same electrode group EG are adjacent to electrode pieces EP belonging to different electrode groups EG in the circumferential direction of the base portion 31. Furthermore, among the multiple electrode pieces EP, the electrode pieces EP belonging to the same electrode group EG are arranged at equal intervals in the circumferential direction of the base portion 31.

[0044] 4 shows an equivalent circuit of the power supply circuit, in which the discharge device 30 serves as a positive electrode and the wafer W serves as a negative electrode.

[0045] The second power supply portion 35 is configured to be able to supply power independently to each electrode group EG. Specifically, six discharge portions 35b are provided in parallel, and each discharge portion 35b is connected to one electrode group EG via a resistor 35c. Furthermore, in each discharge portion 35b, three electrodes EP (the first electrode group EG1 is illustrated in FIG. 4 ) constituting the electrode group EG are connected in parallel. The resistors 35c included in each discharge portion 35b are the same size. The resistors 35c are arranged between the base portion 32 and the electrodes EP in the circuit. In this embodiment, even if there are 18 electrodes EP, only six resistors 35c are required.

[0046] The electric charge is supplied from the power source 35a to the base portion 32 via the supply portion 35d, and then supplied to each discharge portion 35b. Since the resistances 35c have the same value, the electric charge is supplied evenly to each discharge portion 35b.

[0047] The second power supply unit 35 enables the first electrode group EG1 to the sixth electrode group EG6 to independently discharge to the wafer W. On the other hand, among the three electrode pieces EP belonging to each electrode group EG, discharge is performed only from one of the electrode pieces EP. In other words, in this embodiment 1, discharge can be performed simultaneously from a maximum of six electrode pieces EP.

[0048] (3) Electrical Discharge Machining Next, a method for performing surface processing of the wafer W using the surface processing device 1 will be described. In Figures 5 and 6, the upper figure is a side view, and the lower figure is a top view. In the following description, "the wafer W and the base portion 31 overlap" means that the wafer W and the base portion 31 overlap in a plan view.

[0049] 5 shows a state in which the wafer W is held on the table 20. At this time, the base portion 31 is located at the initial position. In this state, the wafer W and the base portion 31 do not overlap, and the distance L between the central axes of the wafer W and the base portion 31 is greater than the sum of the outer radius R of the base portion 31 and the radius r of the wafer W.

[0050] Next, from the state shown in Fig. 5, the controller 50 moves the holder 32 using the horizontal movement mechanism to move the base portion 31 toward the inside in the radial direction of the wafer W (to the left in this case). As shown in Fig. 6, the controller 50 positions the base portion 31 so that the electrode region ER of the base portion 31 is positioned on the first central axis X1 of the wafer W. More specifically, the controller 50 moves the base portion 31 to position the base portion 31 so that the midpoint of the width of the electrode region ER is positioned on the first central axis X1. At this time, the distance L between the central axes is given by: L = R - d / 2 (A). By positioning the base portion 31 in this manner, the wafer W and the base portion 31 partially overlap each other.

[0051] The controller 50 then operates the first motor 24 and the second motor 34 to rotate the wafer W about the first central axis X1 and the base portion 31 about the second central axis X2. The maximum rotation speed of the wafer W is 300 rpm, and the maximum rotation speed of the base portion 31 is 2300 rpm. The rotation speed of the base portion 31 is adjusted so as not to be an integer multiple of the rotation speed of the wafer W. Specifically, the rotation speed of the base portion 31 is adjusted so as to be an irrational multiple, such as √2, of the rotation speed of the wafer W. As shown in FIG. 6 , the rotation direction of the wafer W and the rotation direction of the base portion 31 are the same. As a result, in the overlapping portion between the wafer W and the base portion 31, the movement direction of the base portion 31 and the movement direction of the wafer W are opposite to each other.

[0052] 7 to 9 show the positions of the electrode pieces EP. Fig. 7 shows a state in which the base portion 31 is disposed in a position that satisfies formula (A) above and before the base portion 31 is rotated. At this time, the first electrode piece EP1 to the sixth electrode piece EP6 overlap with the wafer W. In other words, the base portion 31 is disposed so that it partially overlaps with the wafer W in a plan view, and so that multiple electrode pieces EP overlap with the wafer W. Furthermore, the base portion 31 is disposed with respect to the wafer W so that only one electrode piece EP of each electrode group EG entirely overlaps with the wafer W.

[0053] When the base portion 31 rotates from the state shown in Fig. 7 , the first electrode piece EP1 moves away from the wafer W, while the seventh electrode piece EP7 moves closer to the wafer W, as shown in Fig. 8 . In other words, the multiple electrodes EP are arranged such that, when an electrode piece EP belonging to one electrode group EG moves away from the wafer W due to the rotation of the base portion 31, another electrode piece EP belonging to the same electrode group EG newly overlaps with the wafer W. In the state shown in Fig. 8 , the first electrode piece EP1 and the seventh electrode piece EP7 are partially overlapping with the wafer W. In other words, none of the electrode pieces EP belonging to the first electrode group EG1 (the first electrode piece EP1, the seventh electrode piece EP7, and the thirteenth electrode piece EP13) are entirely overlapping with the wafer W.

[0054] 8, as shown in Fig. 9, the first electrode piece EP1 is completely separated from the wafer W, while the seventh electrode piece EP7 is in a state where the entire electrode piece overlaps the wafer W. Thus, in this embodiment, even if the base part 31 is rotated, only one of the electrode pieces EP belonging to each electrode group EG has the entire electrode piece overlapping the wafer W.

[0055] After rotating the wafer W and the base 31, the controller 50 extends the shaft 33 using the telescopic mechanism to bring the electrode region ER closer to the wafer W, as shown in FIG. 10 . When the vertical distance between the wafer W and the electrode region ER becomes equal to or less than a predetermined distance, the controller 50 activates the first power supply 25 and the second power supply 35 to start electric discharge machining. The discharge voltage is approximately 50 V to 300 V. The predetermined distance is a distance at least sufficient to immerse the electrode region ER in the machining fluid. The controller 50 also activates the first power supply 25 and the second power supply 35 to generate a pulsed electric discharge between the wafer W and the electrode region ER. Because the wafer W and the electrode region ER of the base 31 partially overlap, the electric discharge region is limited to the overlapping portion. The electrode region ER overlapping with the wafer W includes each of the electrode pieces EP of the first electrode group EG1 to the sixth electrode group EG6, so that discharge can be applied to the wafer W from a maximum of six electrode pieces EP.

[0056] In the surface processing device 1, the polarity of the electric discharge machining can be selected from either a positive polarity in which the wafer W is the positive polarity and the discharge device 30 is the negative polarity, or a reverse polarity in which the wafer W is the negative polarity and the discharge device 30 is the positive polarity. In particular, it is preferable that the polarity of the electric discharge machining be changed appropriately depending on the purpose of machining the wafer W. For example, when priority is given to machining speed, it is preferable to use a positive polarity for the electric discharge machining, while when priority is given to the surface roughness of the wafer surface, it is preferable to use a reverse polarity for the electric discharge machining. The polarity of the electric discharge machining may be changed appropriately between the start and end of the electric discharge machining. Furthermore, the polarity of the electric discharge machining may be changed appropriately depending on the material of the workpiece to be machined. The polarity of the electric discharge machining may be selected appropriately by the operator each time machining is performed, or may be automatically selected by the controller 50.

[0057] 11 shows the voltage waveform and the current waveform between the wafer W and the discharge device 30. The upper graph in FIG. 11 shows the voltage waveform, and the lower graph in FIG. 11 shows the current waveform. The voltage supplied by the power supply 35a is V ０ If the current flowing between the wafer W and the discharge device 30 is I and the resistance included in the discharge section 35b is R, the following equation (B) is obtained.

[0058] V ０ = I × (R / n) (B), where n is the number of discharged electrode pieces EP. From equation (B), it can be seen that the more discharged electrode pieces EP there are, the larger the current flowing between the wafer W and the discharge device 30. In other words, the number of discharged electrode pieces EP can be determined by looking at the current waveform. In reality, however, due to wiring resistance and leakage current, the current does not increase in strict direct proportion to the number of discharged electrode pieces EP.

[0059] In the current waveform of FIG. 11, the current value I when discharged from only one electrode piece EP is ＭＩＮ As shown in FIG. 11, the current value I ＭＩＮ This indicates that discharge occurs from a plurality of electrode pieces EP. In other words, the surface processing device 1 according to this embodiment can improve processing efficiency.

[0060] (4) Effects of the Embodiment The surface processing apparatus 1 according to this embodiment includes a base portion 31 having a circular shape in a plan view, multiple electrode pieces EP arranged along the periphery of the base portion 31, and a second power supply unit 35 that supplies power to the multiple electrode pieces EP. The discharge device 30 discharges from the electrode pieces EP to the wafer W. The second power supply unit 35 can supply power independently to some of the multiple electrode pieces EP and other electrode pieces EP. The base portion 31 is arranged in a plan view so that at least two electrode pieces EP that partially overlap the wafer W and can independently discharge electricity overlap the wafer W. The surface processing apparatus 1 can simultaneously discharge electricity from at least two electrode pieces EP, enabling discharge at at least two locations. Furthermore, by rotating the wafer W while the wafer W and the base portion 31 partially overlap, the portion of the wafer W facing the electrode piece EP can be changed. This prevents limited discharge locations and allows discharge to be performed on the wafer W over a wide area. Therefore, the surface processing device 1 can improve processing efficiency.

[0061] In this embodiment, the multiple electrode pieces EP are divided into multiple electrode groups EG, each including three electrode pieces EP. The electrode pieces EP belonging to the same electrode group EG are arranged circumferentially around the base portion 31, and the electrode pieces EP belonging to different electrode groups EG are arranged adjacent to each other in the circumferential direction of the base portion 31. The second power supply unit 35 supplies power independently to each electrode group EG. The base portion 31 is arranged so that it partially overlaps the wafer W in a plan view, and multiple electrode pieces EP overlap the wafer W. In this embodiment, the electrode pieces EP belonging to the same electrode group EG are arranged so that they are not adjacent to each other in the circumferential direction, and multiple electrode pieces EP overlap the wafer W in a plan view. Therefore, even if there are electrode pieces EP belonging to the same electrode group EG in the circumferential direction, the multiple electrode pieces EP overlapping the wafer W always include electrode pieces EP belonging to different electrode groups EG. Because the second power supply unit 35 supplies power independently to each electrode group EG, multiple electrode pieces EP can discharge to the wafer W simultaneously. Therefore, the processing efficiency of the surface processing apparatus 1 can be improved. Also, it is sufficient to provide only one component group for each electrode group EG to separate the power supply paths, and it is not necessary to provide one for each electrode piece EP. Therefore, even if the numerical density of the electrode pieces EP is increased, the surface processing apparatus 1 can prevent the device from becoming larger.

[0062] In this embodiment, the base portion 31 is positioned with respect to the wafer W so that only one of the electrode pieces EP belonging to each electrode group EG has an electrode piece that entirely overlaps with the wafer W. The surface processing device can increase the number of electrode pieces EP that can discharge simultaneously, thereby improving processing efficiency.

[0063] In this embodiment, the discharge device 30 includes a second motor 34 that rotates the base portion 31 around the central axis. By rotating the base portion 31, the electrode pieces EP that overlap the wafer W can be changed, allowing discharge to occur evenly from each electrode piece EP. This prevents significant deviation in the shape of the electrode pieces EP. The surface processing device 1 can simultaneously discharge multiple electrode pieces EP over a long period of time, improving processing efficiency.

[0064] In this embodiment, the multiple electrode pieces EP are arranged so that, when an electrode piece EP belonging to one electrode group EG moves away from the wafer W due to rotation of the base portion 31, another electrode piece EP belonging to the same electrode group EG newly overlaps with the wafer W. This makes it possible to minimize the number of electrode groups EG while making all of the electrode pieces EP overlapping with the wafer W electrode pieces EP belonging to different electrode groups EG. The surface processing apparatus 1 can increase the number density of the electrode pieces EP while suppressing an increase in the size of the entire apparatus.

[0065] In this embodiment, the electrode pieces EP belonging to the same electrode group EG among the plurality of electrode pieces EP are arranged at equal intervals in the circumferential direction of the base portion 31. The surface processing device 1 can increase the number density of the electrode pieces EP as much as possible, thereby improving processing efficiency.

[0066] In this embodiment, the rotation speed of the base portion 31 is adjusted so as not to be an integer multiple of the rotation speed of the wafer W. This prevents the same electrode piece EP from overlapping with the same location on the wafer W as much as possible, thereby preventing large deviations in the shape of the electrode piece EP. The surface processing device 1 can simultaneously discharge multiple electrode pieces EP over a long period of time, improving processing efficiency.

[0067] (5) Modification 1 Fig. 12 shows a modification 1 of the surface processing device. In Fig. 12, the numbers written on the electrode pieces EP indicate the electrode group EG to which the electrode pieces EP belong.

[0068] 12 , in Modification 1, the electrode groups EG are divided differently from the above-described embodiment. Specifically, the electrodes EP are divided into a first electrode group EG1 and a second electrode group EG2. The electrode pieces EP belonging to the first electrode group EG1 and the electrode pieces EP belonging to the second electrode group EG2 are arranged alternately in the circumferential direction of the base portion 31. Even in this configuration, the multiple electrodes EP are arranged such that the electrode pieces EP belonging to the same electrode group EG are arranged in the circumferential direction, and the electrode pieces EP belonging to different electrode groups EG are arranged adjacent to each other in the circumferential direction.

[0069] In the first modification, the number of parts required to separate the power supply paths can be minimized, making it possible to make the device compact.

[0070] (6) Modification 2 Fig. 13 shows a modification 2 of the surface processing device. In Fig. 13, the numbers written on the electrode pieces EP indicate the electrode group EG to which the electrode pieces EP belong.

[0071] 13 , in Modification 2, the electrode groups EG are divided in a different way than in the above-described embodiment. Specifically, the electrodes EP are divided into nine electrode groups EG, namely, a first electrode group EG1 to a ninth electrode group EG9. The multiple electrode pieces EP are arranged such that the electrode pieces EP belonging to the same electrode group EG are arranged in the circumferential direction, and the electrode pieces EP belonging to different electrode groups EG are arranged adjacent to each other in the circumferential direction.

[0072] In the second modification, the maximum number of electrode pieces EP that discharge simultaneously is nine, so that even when processing the surface of a wafer W with a large diameter, the processing efficiency can be improved.

[0073] Other Embodiments The technology disclosed herein is not limited to the above-described embodiments, and can be substituted within the scope of the claims.

[0074] For example, in the above-described embodiment, the workpiece is a wafer W, but the workpiece may be an ingot, and the end face of the ingot may be subjected to electrical discharge machining.

[0075] In the above-described embodiment, the base portion 31 is configured to be movable in the horizontal direction. However, the present invention is not limited to this, and the relative positions of the base portion 31 and the workpiece may be fixed. In this case, the base portion 31 is positioned so that the electrode region ER is located on the first central axis X1 of the workpiece. This allows the entire surface of the workpiece to be electric discharge machined by rotating the workpiece about the first central axis X1.

[0076] In the above-described embodiment, the number of electrode pieces EP is 18, but the number of electrode pieces EP is not particularly limited. Also, although the number of electrode pieces EP belonging to each electrode group EG is the same, the number of electrode pieces EP belonging to each electrode group EG does not have to be the same.

[0077] In the above-described embodiment, the second power supply unit 35 is configured to supply power to each electrode group EG, but may be configured to supply power independently to each electrode piece EP. In other words, the electrode pieces EP may not be divided into electrode groups EG, but may be independent of each other.

[0078] The above-described embodiments are merely examples and should not be construed as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims, and all modifications and variations that fall within the scope of the claims equivalents are within the scope of the present disclosure.

[0079] The techniques disclosed herein are useful when electrical discharge machining the surface of a workpiece.

[0080] REFERENCE SIGNS LIST 1 Surface processing device 20 Table 24 First rotation device 30 Discharge device 31 Base portion 34 Second motor (second rotation device) 35 Second power supply portion EP Electrode piece EG Electrode group W Wafer (processing object)

Claims

1. A surface processing device for electrical discharge machining of the surface of a workpiece, comprising: a table on which the workpiece is placed and held; a first rotation device for rotating the workpiece around its central axis; a base portion having a circular shape in a plan view, a plurality of electrode pieces lined up along the periphery of the base portion, and a discharge device having a power supply unit for supplying power to the plurality of electrode pieces, and discharging from the electrode pieces to the workpiece, wherein the power supply unit is capable of independently supplying power to some of the plurality of electrode pieces and to other electrode pieces; and the base portion is arranged so that it partially overlaps the workpiece in a plan view and at least two of the electrode pieces that can independently discharge electricity overlap the workpiece.

2. A surface processing device as described in claim 1, wherein the plurality of electrode pieces are divided into a plurality of electrode groups each including at least two of the electrode pieces, the electrode pieces belonging to the same electrode group are arranged in the circumferential direction of the base part, and the electrode pieces belonging to different electrode groups are arranged so as to be adjacent to each other in the circumferential direction, the power supply part supplies power independently to each of the electrode groups, and the base part is arranged so as to partially overlap the workpiece in a plan view and so that the plurality of electrode pieces overlap the workpiece.

3. A surface processing device according to claim 2, characterized in that the base portion is positioned relative to the object to be processed so that only one of the electrode pieces belonging to each electrode group has its entire electrode piece overlapping with the object to be processed.

4. A surface processing device according to claim 3, wherein said discharge device further includes a second rotation device for rotating said base portion around a central axis.

5. A surface processing device as described in claim 4, characterized in that the plurality of electrode pieces are arranged so that when an electrode piece belonging to one of the electrode groups moves away from the workpiece due to rotation of the base part, another electrode piece belonging to the same electrode group newly overlaps with the workpiece.

6. A surface processing device according to any one of claims 1 to 5, characterized in that, of the plurality of electrode pieces, those belonging to the same electrode group are arranged at equal intervals in the circumferential direction.

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