Device for machining a workpiece

Abstract

The present invention is a device for machining a workpiece, comprising: a central drum rotatable about an axis of rotation and having at least one first groove formed in the axial direction on the circumferential surface, a support having a holding hole into which a workpiece to be machined is inserted and held there, an upper rotary table and a lower rotary table rotatable about the axis of rotation in a state in which the support holding the workpiece is located between them, at least one hook fitted into the inner circumference of the upper rotary table, the tip being inserted into the first groove and being movable along the first groove;wherein the central drum has at least a second groove formed axially on its circumferential surface, and the second groove has a length different from that of the first groove and a bearing surface to support the hook from below in a position above a position in which the upper rotary table is machining the workpiece. This allows the upper rotary table to be held horizontally under the influence of a force perpendicular to the polishing surface of the upper rotary table when the upper rotary table is stopped in a position above a position in which the workpiece is being machined.

Description

TECHNICAL AREA

[0001] The present invention relates to a device for machining a workpiece, in which a plate workpiece such as a silicon wafer is inserted and held in the retaining hole of the carrier, and in which both surfaces of the workpiece are machined simultaneously, comprising a double-sided polishing device and a double-sided lapping device. STATE OF THE ART

[0002] Double-sided polishing devices and double-sided lapping devices were previously used to flatten a sheet workpiece such as a silicon wafer.

[0003] In the double-sided polishing device, for example, a disc-shaped carrier with a planetary gear on its periphery is positioned between upper and lower rotary tables, each of which is covered with a polishing wheel made of urethane foam or non-woven fabric. This carrier is set in motion by rotating the sun gear and the ring gear, which mesh with the planetary gear, in both directions, while the carrier holds a workpiece in its retaining hole. The rotation and revolution of the carrier, along with the rotations of the upper and lower rotary tables, cause the workpiece to rub against these tables, polishing both its upper and lower surfaces simultaneously. During polishing, a polishing slurry is supplied from several holes in the upper rotary table to ensure effective polishing.

[0004] The upper rotary table is equipped with an up-and-down movement mechanism that allows it to move up and down (e.g., patent specification 1). While the upper rotary table is in the raised position to which it has been moved upwards, the support is positioned on the lower rotary table, and a workpiece is held by the support. The upper rotary table can also be moved downwards from the raised position to an intermediate height position. The downward movement of the upper rotary table is stopped to create a suitable gap between the upper and lower rotary tables, and a cleaning nozzle is inserted between them to clean the polishing surfaces of the polishing wheels.In the intermediate height position, the polishing surfaces of the polishing wheels can be dressed by inserting a dressing head between the upper rotary table and the lower rotary table to regulate the surface condition of the polishing wheels.

[0005] In such a cleaning and dressing process of the polishing wheel's surface, the cleaning nozzles and the dressing head often have an area that is apparently smaller than the polishing surface of the wheel glued to the rotary table. Such a head is attached to an arm, and this arm can move the head from the outermost periphery of the rotary table to its innermost circumference by means of linear or rotary motion. This movement, together with the simultaneous rotation of the upper and lower rotary tables, allows these heads to clean or dress the entire polishing surface.

[0006] With the high integration of semiconductor devices in recent years, the requirements for the flatness and surface quality of silicon wafers have become more stringent. To meet these quality requirements, it is essential to maintain the polishing surface of a double-sided polishing device and a double-sided lapping device in a suitable condition at all times.

[0007] However, during actual processing, residual substances, such as those left on the polishing surface after lapping, can impede the flow of the slurry; for example, clogging of the polishing wheel surface during double-sided polishing; as well as deterioration and deformation of the surface resin of the polishing wheel itself. These changes in processing conditions result in a deterioration and fluctuations in wafer quality.

[0008] To prevent such deterioration and fluctuations in wafer quality, it is important to maintain the polishing surface in a uniform and good condition. Accordingly, regular cleaning of the polishing surface and dressing of the polishing wheel are usually performed, as described in the prior art.

[0009] However, the devices have become larger due to increasing wafer diameters, making it more difficult to maintain a uniform polishing surface over a large area.

[0010] In many cases, the upper rotary table of a double-sided polishing or lapping device is connected to a cylindrical shaft located at the top of the device via a universal joint or spherical bearing to allow for angle adjustment. This is intended to enable polishing of a workpiece while maintaining a uniform load continuously applied to the upper rotary table, even when the workpiece or the support holding it has variations in thickness. LIST OF REFERENCES PATENT LITERATURE

[0011] Patent specification 1: Unexamined Japanese patent application (Kokai) No. H10-230452 BRIEF DESCRIPTION OF THE INVENTIONAL PROBLEM STATEMENT

[0012] However, the upper turntable with this mechanism is unstable in its tilt due to this movable universal joint or articulated bearing when the upper turntable is stopped at the intermediate height position. The upper turntable is susceptible to changing its tilt even with slight external forces. This change in tilt means that the gap between the upper and lower turntables varies depending on the time and location.

[0013] Accordingly, the gap between the upper rotary table and the lower rotary table fluctuates when a cleaning or dressing head is inserted into the aforementioned gap to clean or dress the polishing surface of the polishing wheel, and the effects of cleaning or dressing the polishing surface vary from place to place, making it impossible to achieve a uniform condition of the polishing surface.

[0014] The present invention was made in consideration of the problem described above. The object of the present invention is to provide a device for machining a workpiece which can hold the upper rotary table horizontally under the influence of force in a direction perpendicular to the polishing surface of the upper rotary table when the upper polishing table is stopped in a position that lies above a position in which the workpiece is being machined. PROBLEM SOLVING

[0015] To solve the problem described above, the present invention provides a device for machining a workpiece, comprising: a central drum which is rotatable about an axis of rotation and has at least one first groove on the circumferential surface, wherein each first groove is formed in the axial direction; a carrier which has a holding hole into which a workpiece to be machined is inserted and held there; an upper rotary table and a lower rotary table, which can be rotated about the axis of rotation in a state in which the support holding the workpiece is located between them; at least one hook, wherein each hook is fitted into the inner circumference of the upper turntable, wherein the tip of each hook is inserted into the first groove and is movable along the first groove; wherein the central drum has at least one second groove on its circumferential surface, with each second groove being formed in the axial direction; and the second groove has a length that differs from that of the first groove and has a load-bearing surface to support the hook from below in a position above a position in which the upper rotary table is machining the workpiece.

[0016] In such a device, the load-bearing surface(s) of the second groove(s) support the hook(s), making it possible to hold the upper rotary table horizontally under force in a direction perpendicular to the polishing surface of the upper rotary table when the upper rotary table is stopped in a position above a position where the workpiece is being machined. This makes it possible to clean and dress the polishing wheels bonded to the upper and lower rotary tables uniformly while the upper rotary table is held horizontally.

[0017] Preferably, the load-bearing surface of the second groove has a surface area that supports at least the entire load of the upper rotary table via the hook.

[0018] In such a device, the entire load of the upper rotary table can be supported by the supporting surface via the hook, thus enabling the upper rotary table to be held horizontally under the influence of force in a direction perpendicular to the polishing surface of the upper rotary table.

[0019] Preferably, the at least one hook, the at least one first groove and the at least one second groove each form a pair, arranged in the corresponding pair at angular intervals of 180°.

[0020] In such a device, the upper rotary table can be stably supported by the hook from the supporting surface.

[0021] Preferably, the pair consisting of the at least one first groove and the pair consisting of the at least one second groove on the central drum are arranged at angular intervals of 90°.

[0022] In such a device, the first groove and the second groove can be swapped as needed.

[0023] The device for processing a workpiece can be a double-sided polishing device or a double-sided lapping device.

[0024] Such a device can be advantageously applied to a manufacturing process for a workpiece such as a silicon wafer, which is required to have a particularly high flatness. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0025] In the inventive device for machining a workpiece, the upper rotary table can be held horizontally while stationary in a position above the workpiece being machined, even when the upper rotary table is rotating or a force is acting on it perpendicular to its polishing surface. Accordingly, operations such as dressing the polishing wheel of the upper rotary table can be performed uniformly, enabling high-quality machining of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] They show:

[0027] Fig. 1 a schematic view showing a double-sided polishing device as an example of the inventive device for machining a workpiece;

[0028] Fig. 2 a schematic view showing a state in which the upper rotary table has been moved downwards into a position in which a workpiece is being machined in the inventive double-sided polishing device;

[0029] Fig. 3 a schematic view showing an example of the central drum in the inventive double-sided polishing device;

[0030] Fig. 4 a schematic view in which the in Fig. 3 the central drum shown in the inventive double-sided polishing device is rotated by 90° in the axial direction;

[0031] Fig. 5 a schematic view showing a method for applying force in a vertical direction to the polishing surface of the upper rotary table using an air cushion in Example 1;

[0032] Fig. 6 a diagram showing the change in the height position of the upper rotary table when force is applied in a perpendicular direction to the polishing surface of the upper rotary table, using an air cushion in Example 1 and Comparative Example 1;

[0033] Fig. 7 a schematic view showing a method for applying force in a vertical direction to the polishing surface of the upper rotary table using an air cushion in Comparative Example 1;

[0034] Fig. Figure 8 shows a schematic view illustrating one method of dressing polishing wheels glued to the upper and lower rotary tables in Example 2.

[0035] Fig. 9 a flowchart showing a process for performing double-sided polishing as well as cleaning and dressing the polishing surface in Example 2;

[0036] Fig. 10 a graphical representation showing the relationships between the polishing rate and batches in Example 2 and Comparative Example 2.

[0037] Fig. 11 a schematic view showing a type of dressing of polishing wheels glued to the upper and lower rotary table in comparative example 2. DESCRIPTION OF THE EXECUTION FORMS

[0038] The embodiments of the present invention are described below, but the present invention is not limited to these.

[0039] As described above, the upper rotary table cannot be held horizontally under the influence of force in a perpendicular direction to the polishing surface of the upper rotary table if the upper rotary table is stopped in a position above a position in which a workpiece is being machined.

[0040] The inventors in question have carefully investigated in order to solve the aforementioned problem. As a result, the inventors found a central drum comprising at least one first groove arranged axially on the circumferential surface, and further comprising at least one second groove arranged axially on the circumferential surface, the second groove having a length different from that of the first groove, and having a supporting surface to support a hook fitted from below into the inner circumference of the upper rotary table at a position above the position in which the upper rotary table is machining the workpiece.

[0041] The inventors discovered that the second groove for carrying the hook allows the upper rotary table to be held horizontally under force in a direction perpendicular to the polishing surface of the upper rotary table when the upper rotary table is stopped in a position above the position where the workpiece is being machined. The inventors investigated the best way to accomplish this, thereby completing the present invention.

[0042] The inventive device for machining a workpiece is described in detail. Illustrative examples of the inventive device for machining a workpiece include a double-sided polishing device or a double-sided lapping device.

[0043] Such a device can be advantageously applied to a manufacturing process for a workpiece such as a silicon wafer, which is required to have a particularly high flatness.

[0044] The inventive device for machining a workpiece by representing a double-sided polishing device is described below.

[0045] As in Fig. Figure 1 shows the inventive double-sided polishing device 1 with the upper turntable 2 and the lower turntable 3 provided, which are arranged opposite each other, one above and one below. Both the upper rotary table 2 as well as the lower turntable 3 are with the polishing wheel 4 covered. Between the upper turntable 2 and the lower turntable 3 A sun gear (not shown in the figure) is provided on the central part, and a ring gear (not shown in the figure) is provided on the peripheral part.

[0046] As in Fig. 2 shown, is the carrier 5 with the retaining hole 6designed to hold the workpiece W securely. During double-sided polishing, the support 5 between the upper turntable 2 and the lower turntable 3 arranged, with the workpiece W in the holding hole 6 is recorded.

[0047] The upper turntable 2 is connected to a cylindrical shaft (not shown in the figure), which is provided at the upper part of the device, via the universal joint 7 or a spherical bearing is connected to allow for optional angle adjustment. This enables uniform loading from the upper rotary table. 2 continuously during polishing, even if the thickness of the workpiece W or the carrier 5 The shape that holds the workpiece W varies. In this embodiment, the universal joint 7 used.

[0048] The middle drum 8 is rotatably arranged around the axis of rotation. The central drum 8 has at least one first groove9 on, which is formed in the axial direction on the circumferential surface.

[0049] The upper turntable 2 has at least one hook 11 on, which is fitted into its inner circumference. Each hook 11 , whose tip fits into the first groove 9 is introduced along the first groove 9 movable.

[0050] If the upper turntable 2 When moved downwards into a position where the workpiece W is machined, the workpiece W is moved into the upper rotary table. 2 fitted hooks 11 into the first groove 9 introduced, which is on the middle drum 8 is provided for, and fitted into this. This situation allows the drive torque of the center drum to be 8 to the upper turntable 2 is transferred to the upper turntable 2 to turn.

[0051] Both sides of the workpiece W can be polished simultaneously by using the carrier 5 , which holds the workpiece W, is rotated and set in motion, with the upper and lower polishing wheels 4 against both the front and back of the workpiece W, while both the upper rotary table 2 as well as the lower turntable 3 rotated around the axis of rotation.

[0052] The middle drum 8 is furthermore equipped with at least one second groove 10 provided, which is formed in the axial direction on the circumferential surface. The second groove 10 has a length that differs from that of the first groove 9 differs, and has a load-bearing surface 10a up to the hook 11 to carry from below in a position that is above a position in which the upper turntable 2 the workpiece W is being processed.

[0053] As in Fig. 3 and Fig. As shown in 4, the length of the second groove is 10 shorter than the first groove 9 On the other hand, the first groove 9 a sufficient length to accommodate the upper turntable 2 in contact with the workpiece W, the carrier 5 or the lower turntable 3 bring to.

[0054] If the upper turntable 2 is moved downwards, with the hook 11 into the second groove 10 Once it is inserted and fitted into it, the catch comes... 11 with the load-bearing surface 10a at the lower end of the second groove 10 in contact, which makes the upper rotary table 2 prevents it from moving downwards. Accordingly, the upper turntable holds it in place. 2 at the intermediate height position where the hook 11 in contact with the load-bearing surface 10ahas come into contact. In this intermediate height position, cleaning and dressing of the polishing surfaces of the upper and lower rotary tables is possible. 2 and 3 be performed.

[0055] The length of the second groove 10 is preferably set up so that the upper rotary table 2 which can prevent it from moving downwards to the desired position at the intermediate height.

[0056] As in Fig. As shown in section 3, the load-bearing surface has 10a the second groove 10 preferably a surface area that extends over the hook 11 at least the entire load of the upper rotary table 2 can wear.

[0057] In such a device, the hook can be used 11 the entire load of the upper rotary table 2 supported by the load-bearing surface, thus enabling the upper rotary table 2under the influence of force in a direction perpendicular to the polishing surface of the upper rotary table 2 is held horizontally.

[0058] The second groove 10 can, for example, but are not limited to, take the form of a recess, whereby the load-bearing surface 10a can have a flat shape.

[0059] Each of the hooks 11 , the first grooves 9 and the second grooves 10 preferably form a pair and are arranged in the respective pair at angular intervals of 180°.

[0060] In such a device, the upper rotary table can 2 about the hooks 11 from the load-bearing surfaces 10a the two second grooves 10 They are supported by objects positioned at 180° to each other. The load of the upper turntable 2The workpiece, which has been stopped at the intermediate height position, is fully or partially supported by the two points as described above. Accordingly, the upper turntable can 2 to be supported stably, and the height position in which the upper turntable 2 is stopped, and its inclination can be maintained with remarkably improved stability.

[0061] In this case, a pair of the first grooves 9 and a pair of the second grooves 10 on the middle drum 8 preferably arranged at angular intervals of 90°, as shown in Fig. 3 and Fig. 4 shown.

[0062] In such a device, the first groove can be 9 and the second groove 10 They can be exchanged as needed.

[0063] When swapping, for example, the first slots 9 to the second grooves 10 will the upper turntable 2moved to the top position and the hooks 11 are completely removed from the first grooves 9 pulled. At this point, the hooks remain. 11 in unchanged positions, since the upper turntable 2 does not rotate. The middle drum 8 In this situation, it is rotated 90°, and then the upper turntable is 2 moved downwards to engage the hooks 11 into the second grooves 10 to introduce. In this way, the swapping of the first grooves can be avoided. 9 to the second grooves 10 be carried out.

[0064] In the aforementioned embodiment, there are two sets of the first groove 9 and the second groove 10 , which together form four grooves of two different lengths, on the center drum 8 arranged at 90° intervals. However, a total of six slots can also be arranged, each containing three of the first slots. 9and the second grooves 10 at angular intervals of 60°. This makes it possible to maintain stability while keeping the height and tilt of the turntable constant. 2 to improve further when the upper turntable 2 is stopped at the intermediate height position. If there are two types of second grooves 10 are provided for, the turntable 2 be stopped in two positions at the intermediate height.

[0065] In such a double-sided polishing device according to the present invention, the upper rotary table can be held horizontally while stationary in a position above the workpiece being machined, even when the upper rotary table is rotating or a force is acting on it perpendicular to its polishing surface. This makes it possible to perform uniform cleaning and dressing of the polishing wheels bonded to the upper and lower rotary tables while the upper rotary table is held horizontally. Accordingly, high-quality polishing of a workpiece can be achieved by using a double-sided polishing device in which the dressing and cleaning are performed uniformly as described above.

[0066] The inventive device for machining a workpiece has been described using a double-sided polishing device, but the inventive device can be applied to a double-sided lapping device to achieve the same effects described above. EXAMPLE

[0067] The present invention is described in more detail below by providing examples and comparative examples; however, the present invention is not limited to these. (Example 1)

[0068] The in Fig. 1 Inventive double-sided polishing device shown 1 was used to improve the stability of the upper turntable 2 to investigate the force in the perpendicular direction to the polishing surface of the upper rotary table 2 was subjected to when the upper turntable 2 was stopped at the intermediate height position.

[0069] The upper turntable 2 was stopped at the intermediate altitude position and the air cushion 12 was between the upper turntable 2 and the lower turntable 3 introduced as in Fig. 5 described. Then the pressure of the air cushion was 12 increased to increase the force required to push up the upper rotary table 2 to increase.

[0070] At this point, the changes to the height position of the upper turntable were made. 2 with the dial gauge 13 on the side of the upper turntable 2 observed, which is opposite the point where the air cushion 12 was introduced. In other words, the height position of the upper rotary table should be adjusted. 2 be lowered on the opposite side when the upper turntable 2 due to the pressure of the air cushion 12 is tilted. The one with the dial gauge 13 measured results are in Fig. 6 shown. Fig. Figure 6 also shows the results of comparison example 1, which will be described later.

[0071] As in Fig. As shown in Figure 6, Example 1, in which the load of the upper rotary table was supported by the undersides of the shorter grooves, could consequently reduce the height changes of the upper rotary table on the side opposite the air cushion by approximately 1 / 10 compared to Comparative Example 1.

[0072] Since the hooks 11 contact with the load-bearing surfaces 10a the second grooves 10 had to, as in Fig. 5 shown, the upper turntable 2 through the load-bearing surfaces 10a To carry, the upper turntable tilts 2 not, even if an attempt is made to move the upper turntable 2 using the air cushion 12 to push upwards. As a result, the height of the upper rotary table changed. 2, which was measured on the opposite side, hardly. (Comparative example 1)

[0073] As in Fig. As shown in 7, the double-sided polishing device was used. 101 with the upper turntable 102 and the lower turntable 103 equipped with features that are positioned opposite each other, one above and one below, and the turntable 102 and 103 were each used with the polishing wheel 104 covered with stickers. The upper turntable 102 was connected to the universal joint 107 connected to change the angle as desired.

[0074] The one on the upper turntable 102 provided hook 111 were inserted into the first grooves 109 introduced, which is on the middle drum 108 are provided. The upper turntable 102 was moved downwards and stopped at the intermediate height position. Then the air cushion 12 between the upper turntable 102and the lower turntable 103 introduced. The pressure of the air cushion 12 was increased to achieve the same measured value as in Example 1. The results are presented in Fig. 6 as described above.

[0075] As a result, comparative example 1 showed how in Fig. 6 shown, on the air cushion 12 On the opposite side, the fluctuation in the height position of the upper rotary table is approximately 10 times greater compared to Example 1. 102 .

[0076] When dressing was performed while the upper turntable 2 When the machine, which had been lowered to the intermediate height position, was stopped, the dressing head was pressed against the polishing surface. In other words, part of the upper rotary table was pushed upwards by the dressing head and moved upwards when dressing in the intermediate height position using the first groove. 9This was done, as can be seen from the results of comparative example 1. This resulted in a reduction of the pressing pressure, which meant that a sufficient dressing effect could not be achieved.

[0077] On the other hand, the inclination of the upper turntable changed. 2 hardly, if the dressing is done in the intermediate height position using the second groove(s) 10 as can be seen from the results of Example 1, which indicates that the dressing could be carried out at a desired pressure. (Example 2)

[0078] The workpiece W was subjected to double-sided polishing, whereby the hooks 11 , as in Fig. 2 shown, in the first grooves 9 were introduced. Then the workpiece W was picked up and the cleaning and dressing was carried out on the polishing surface of the upper and lower rotary tables. 2 and 3glued-on polishing discs 4 carried out. The training was done as in Fig. 8 shown, with the hooks in the second grooves 10 were introduced, and the dressing head 14 between the upper turntable 2 and the lower turntable 3 was introduced.

[0079] In particular, according to the in Fig. The following sequence was performed according to the flowchart shown in Figure 9: Inserting a workpiece (SP1), moving the upper rotary table downwards (using longer slots) (SP2), polishing (SP3), moving the upper rotary table upwards (SP4), removing the workpiece (SP5), rotating the center drum by 90° (SP6), moving the upper rotary table downwards (using shorter slots to stop at the intermediate position) (SP7), cleaning and dressing the polishing surfaces (SP8), moving the upper rotary table upwards (SP9), and rotating the center drum by 90° (SP10). This was carried out for 30 batches, reversing the sequence back to SP1 through SP10.

[0080] In SP4 and SP9, the hooks were used to move the upper turntable upwards. 11 completely from the first grooves 9 or the second groove 10 pulled. At that point, the hooks remained. 11 in unchanged positions, since the upper turntable 2did not rotate. In this situation, the middle drum 8 Both SP6 and SP10 were rotated 90°. Then the upper rotary table was 2 moved downwards in step SP7 or SP2 to swap the grooves into which the hooks are inserted. 11 were introduced.

[0081] The relationship between the batch number and the polishing rate is in Fig. 10 shown. Fig. Figure 10 also shows the results of comparison example 2, which is described later. The flatness of the double-sided polished workpiece W was measured using the GBIR (Global Backsurface-referenced Ideal plane / Range) and the SFQRmax (Site Frontsurface referenced least sQuares / Range).

[0082] As in Fig. As shown in Figure 10, the polishing rate after 30 batches in Example 2 was reduced by only approximately 2% from the polishing rate immediately after specifying continuous polishing, which is defined as 100. In Example 2, the GBIR and SFQRmax values, which indicate the flatness of the workpiece after double-sided polishing, were improved by 4.2% and 6.0%, respectively, compared to those in Comparison Example 2. (Comparative example 2)

[0083] Double-sided polishing of the workpiece W was carried out together with cleaning and dressing of the polishing surface of the polishing wheel. 104 as in Example 2, however, the one in Fig. 11 Double-sided polishing device shown 101 used and the dressing was carried out in the intermediate height position using the first grooves 109 carried out. This means that SP6 and SP10 are in Fig. 9 were not executed.

[0084] The relationship between the batch number and the polishing rate was measured as in Example 2 and in Fig. 10 as described above. The GBIR and SFQRmax were measured as the flatness of the double-sided polished workpiece W.

[0085] As a result, the polishing rate in comparative example 2 showed a decrease of approximately 5% after 30 batches, as shown in Fig. Figure 10 shows that in comparative example 2, the GBIR and SFQRmax of the workpiece deteriorated by 4.2% and 6.0% respectively after double-sided polishing compared to those in example 2.

[0086] As described above, it was found that cleaning and dressing could be carried out while stabilizing the height and tilt of the upper rotary table by modifying the center drum to have the first and second grooves with different groove types, and only the operations of steps SP6 and SP10 were added.

[0087] It should be noted that the present invention is not limited to the embodiment described above. The embodiment is merely an illustration, and all examples that exhibit essentially the same features and demonstrate the same functions and effects as the technical concepts described in the claims of the present invention are included within the technical scope of the present invention.

Claims

[1] Device for machining a workpiece, comprising: a central drum which is rotatable about an axis of rotation and has at least one first groove on the circumferential surface, wherein each first groove is formed in the axial direction; a carrier which has a holding hole into which a workpiece to be machined is inserted and held there; an upper rotary table and a lower rotary table, which can be rotated about the axis of rotation in a state in which the support holding the workpiece is located between them; at least one hook, wherein each hook is fitted into the inner circumference of the upper turntable, wherein the tip of each hook is inserted into the first groove and is movable along the first groove; wherein the central drum has at least one second groove on its circumferential surface, with each second groove being formed in the axial direction; and the second groove has a length that differs from that of the first groove and has a load-bearing surface to support the hook from below in a position above a position in which the upper rotary table is machining the workpiece. [2] Device for machining a workpiece according to claim 1, wherein the load-bearing surface of the second groove has a surface area which carries at least the entire load of the upper rotary table via the hook. [3] Device for machining a workpiece according to claim 1 or 2, wherein the at least one hook, the at least one first groove and the at least one second groove each form a pair, arranged at angular intervals of 180° in the respective pair. [4] Device for machining a workpiece according to claim 3, wherein the pair of at least one first groove and the pair of at least one second groove are arranged on the central drum at angular intervals of 90°. [5] The device for machining a workpiece according to any one of claims 1 to 4, wherein the device for machining a workpiece is a double-sided polishing device or a double-sided lapping device.