WORKPIECE HOLDER AND METHOD FOR SLICING WORKPIECE

Abstract

A workpiece holder for slicing the workpiece by a wire saw including a workpiece plate which is bonded and fixed to the workpiece through a pad plate, and a holder main body which supports the workpiece plate. The workpieces at an x axis direction and a direction vertical to the same is a y axis direction, the workpiece plate is bonded and fixed to the workpiece to correct a deviation of a crystal orientation axis of the workpiece in the x axis direction. The workpiece holder can adjust a tilt in the y axis direction of the workpiece by tilting the workpiece plate in the y axis direction. The workpiece holder can realize slicing an ingot conforming to specifications with rigorous orientation standards in an external setup manner without using a wire saw including an orientation adjustment mechanism for a single crystal ingot, and a method for slicing a workpiece.

Claims

3. The workpiece holder according to claim 2, wherein a tilt of a tapered surface of each of the two movable pieces, which comes into contact with the curved tip portion of the protruding portion, is 30 to 60.

4. The workpiece holder according to claim 2 or 3claim 2, wherein the workpiece plate has the two protruding portions at both ends thereof in the longitudinal direction, the holder main body has the two receiving portions, and the receiving portions sandwich the curved tip portions of the two protruding portions from the upper and lower sides, respectively.

5. The workpiece holder according to claim 3, wherein the workpiece plate has the two protruding portions at both ends thereof in the longitudinal direction, the holder main body has the two receiving portions, and the receiving portions sandwich the curved tip portions of the two protruding portions from the upper and lower sides, respectively.

6. A method for slicing a workpiece, comprising pressing a workpiece made of a columnar single crystal held by a workpiece holder against a wire row of a wire saw to slice the workpiece with the use of the wire saw comprising the wire row formed by winding a wire which reciprocatively travels in an axial direction around a plurality of grooved rollers, wherein the workpiece holder comprises: a workpiece plate which is bonded and fixed to the workpiece through a pad plate; and a holder main body which supports the workpiece plate from a surface of the workpiece plate on an opposite side of another surface of the same to which the workpiece is bonded and fixed, assuming that, of radial directions of the workpieces, a direction parallel to the surface of the workpiece plate to which the workpiece is bonded and fixed is an x axis direction and a direction vertical to the same is a y axis direction, the workpiece plate is bonded and fixed to the workpiece so as to correct a deviation of a crystal orientation axis of the workpiece in the x axis direction , the workpiece holder having a function to adjust a tilt in the y axis direction of the workpiece held by the workpiece plate by tilting the workpiece plate in the y axis direction and to enable fixing the workpiece plate and the workpiece to the holder main body at the adjusted tilt is used, the workpiece plate is bonded and fixed to the workpiece so as to correct a deviation of the crystal orientation axis of the workpiece in the x axis direction at the time of holding the workpiece by the workpiece holder, a tilt in the y axis direction of the workpiece held by the workpiece plate is adjusted by tilting the workpiece plate bonded and fixed to the workpiece in the y axis direction, and the workpiece is held by the workpiece holder by fixing the workpiece plate and the workpiece to the holder main body at the adjusted tilt, and the workpiece fixed by adjusting the tilt is disposed to the wire saw through the workpiece holder, and the workpiece is pressed against the wire row to slice the workpiece.

7. The method for slicing a workpiece according to claim 6, wherein, as the workpiece holder, the workpiece plate has a protruding portion, which protrudes toward an outer side of the workpiece plate in a longitudinal direction and has a curved tip portion, on the surface thereof on the opposite side of another surface thereof on which the workpiece is held, the holder main body has a receiving portion which sandwiches the curved tip portion of the protruding portion from upper and lower sides, the receiving portion sandwiches the curved tip portion of the protruding portion from the upper and lower sides by two forward-and-backward movable pieces, and each of the two movable pieces is formed into a tapered shape having a tilt on a surface thereof which comes into contact with the curved tip portion of the protruding portion, and as the workpiece holder, adopted is one which is configured to tilt the workpiece plate in the y axis direction by adjusting a positional relationship of the two movable pieces, which sandwich the curved tip portion of the protruding portion, by each forward or backward movement, to adjust a tilt of the workpiece in the y axis direction, and to fix the workpiece at this position.

8. The method for slicing a workpiece according to claim 7, wherein the two movable pieces each of which has a tapered surface, which comes into contact with the curved tip portion of the protruding portion, tilting at 30 to 60 are used.

9. The method for slicing a workpiece according to claim 7, wherein, as the workpiece holder, adopted is one in which the workpiece plate has the two protruding portions at both ends thereof in the longitudinal direction, the holder main body has the two receiving portions, and the receiving portions sandwiching the curved tip portions of the two protruding portions from the upper and lower sides, respectively.

10. The method for slicing a workpiece according to claim 8, wherein, as the workpiece holder, adopted is one in which the workpiece plate has the two protruding portions at both ends thereof in the longitudinal direction, the holder main body has the two receiving portions, and the receiving portions sandwiching the curved tip portions of the two protruding portions from the upper and lower sides, respectively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 is a longitudinal cross-sectional view showing an outline of a workpiece holder according to the present invention;

[0046] FIG. 2 is a view for explaining definitions of an x axis direction and a y axis direction (a lateral cross-sectional view);

[0047] FIG. 3 is an explanatory drawing of a workpiece plate which is bonded and fixed to the workpiece so as to correct a deviation of a crystal orientation axis of a workpiece in the x axis direction;

[0048] FIG. 4 is a schematic drawing of a mode in which the workpiece plate and the workpiece of the workpiece holder according to the present invention are fixed at a tilt;

[0049] FIG. 5 is a schematic view showing an example of a wire saw which can be used in a method for slicing a workpiece according to the present invention;

[0050] FIG. 6 is a flowchart showing an example of the method for slicing a workpiece according to the present invention;

[0051] FIG. 7 is a schematic view of a conventional workpiece holder;

[0052] FIG. 8 is a side view and a top view for explaining a slicing direction of the wire saw;

[0053] FIG. 9 is an explanatory drawing of deviations of a crystal orientation axis of a single crystal ingot;

[0054] FIG. 10 is a view for explaining a change in slicing quality due to directions to slice an ingot by the wire saw; and

[0055] FIG. 11 is a graph showing average values of WARPs of wafers sliced off in Comparative Examples 1 to 3.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0056] An embodiment according to the present invention will now be described hereinafter, but the present invention is not restricted thereto.

[0057] As described above, according to the external setup manner, in conventional examples, before bonding and fixing a workpiece to a workpiece plate, an ingot is rotated around a central axis thereof on a pad plate of a workpiece holder to correct a deviation of a crystal orientation in a y axis direction. However, in an orientation <111>axis product of a semiconductor silicon single crystal ingot or the like, there is a case where WARPs, TTVs, and waviness are greatly degraded depending on a cutting direction of a wire, and hence the cutting direction of the wire becomes a direction in which slicing quality is largely degraded as a result of rotating the ingot in some situations. In this case, to shift the cutting direction of the wire, the ingot must be rotated to change a targeted orientation but, when an orientation standard is rigorous, adjustment to change this targeted orientation cannot be performed, and hence there arises a problem that a non-defective product cannot be sliced by a normal wire saw. Furthermore, in an internal setup manner, the wire saw is expensive, and efficiency in slicing is lowered, which results in a problem of degradation of productivity.

[0058] On the other hand, the present inventors have repeatedly conducted keen examinations to solve such a problem, and discovered that the problem can be solved by adjusting a deviation of the crystal orientation in the y axis direction irrespective of rotation of a workpiece with the use of a workpiece holder which can tilt the workpiece in the y axis direction, thereby bringing the present invention to completion.

[0059] As shown in FIG. 1, a workpiece holder 1 according to the present invention includes a workpiece plate 2 which is bonded and fixed to a workpiece W through a pad plate 3, and a holder main body 4 which supports the workpiece plate 2 from a surface of the workpiece plate 2 on the opposite side of another surface of the same to which the workpiece W is bonded and fixed.

[0060] Moreover, as described above, in this specification, as shown in FIG. 2, of radial directions of the columnar workpiece W, a direction parallel to the surface of the workpiece plate 2 to which the workpiece W is bonded and fixed is defined as an x axis direction, and a direction vertical to the same is defined as a y axis direction. In this case, as shown in FIG. 3, the workpiece plate 2 in the workpiece holder 1 according to the present invention is bonded and fixed to the workpiece W so as to correct a deviation of a crystal orientation axis of the workpiece W in the x axis direction. In the example shown in FIG. 3, the workpiece plate 2 is bonded and fixed to the workpiece W so as to correct a deviation Ax of the crystal orientation axis in the x axis direction.

[0061] Additionally, the workpiece holder 1 according to the present invention has a function to adjust a tilt of the workpiece plate 2 in the y axis direction by tilting the workpiece plate 2 bonded and fixed to the workpiece W in the y axis direction and to enable fixing the workpiece plate 2 and the workpiece W to the holder main body 4 at the adjusted tilt. It is to be noted that the workpiece holder 1 can tilt and fix the workpiece plate 2 in both a state where the workpiece plate 2 is bonded and fixed to the workpiece W and a state where the same is not bonded and fixed to the workpiece W.

[0062] Such a function can be provided by, e.g., such a structure of the workpiece holder as described below. As shown in FIG. 1, the workpiece plate 2 has a protruding portion 5 with a curved tip portion on its surface on the opposite side of its another surface on which the workpiece W is held. This protruding portion 5 can protrude toward the outer side of the workpiece plate 2 in the longitudinal direction as shown in FIG. 1. It is to be noted that the curved shaped mentioned here means, e.g., a semicolumnar shape or a semispherical shape. For example, FIG. 1 shows an example where the tip of the protruding portion 5 is formed into a semicolumnar shape, but the present invention is not restricted thereto.

[0063] Additionally, the holder main body 4 has a receiving portion 6 which sandwiches the curved tip portion of the protruding portion 5 from upper and lower sides. This receiving portion 6 sandwiches the curved tip portion of the protruding portion 5 by using two movable pieces 6a and 6b or two movable pieces 6c and 6d which can move forward and backward.

[0064] Further, each of the two movable pieces 6a and 6b (6c and 6d) is formed into a tapered shape having a tilt on its surface which comes into contact with the curved tip portion of the protruding portion 5. It is to be noted that the movable pieces 6a and 6b (6c and 6d) can be moved forward and backward by using adjustment screws 7a and 7b (7c and 7d) connected to the respective movable pieces 6a and 6b (6c and 6d).

[0065] Furthermore, it is preferable for the tilt of the tapered surface of each of the two movable pieces 6a and 6b, which comes into contact with the curved tip portion of the protruding portion 5, to be 30 to 60. The movable pieces each of which has the tapered surface tilting in this range realize an appropriate tilt, facilitate adjusting the tilt of the workpiece plate 2 in the y axis direction, provide sufficient strength, and assuredly enable fixing and holding the workpiece which is a heavy load. Moreover, when the tilt of the tapered surface is set to 30 or more, an angle adjustment amount of the tilt of the workpiece plate to a movement amount of the movable pieces becomes sufficiently large, and a time required for the adjustment can be reduced. Additionally, when the tilt of the tapered surface is set to 60 or less, the angle adjustment amount of the tilt of the workpiece plate to the movement amount of the movable pieces does not become too large, and hence delicate angle adjustment can be facilitated.

[0066] Additionally, as shown in FIG. 1, it is preferable that the workpiece plate 2 has two protruding portions 5 at both ends in the longitudinal direction, the holder main body 4 has receiving portions 6, and each receiving portion 6 sandwiches the curved tip portion of each of the two protruding portions 5 from the upper and lower sides. As described above, when the tilt of the workpiece plate 2 can be adjusted from both the end portions of the workpiece plate 2 in the longitudinal direction, the tilt of the workpiece bonded to the workpiece plate 2 in the y axis direction can be easily adjusted, and the workpiece can be fixed.

[0067] With such a structure as shown in FIG. 1, the workpiece holder 1 can tilt the workpiece plate 2 in the y axis direction by adjusting a positional relationship of the two movable pieces sandwiching the curved tip portion of the protruding portion 5 therebetween based on the forward and backward movements of each piece, adjust the tilt in the y axis direction of the workpiece W to which the workpiece plate 2 is bonded and fixed, and effect the fixation at this position.

[0068] Here, as a specific example, a description will be given as to a case where, to correct the deviation Ay of the crystal orientation axis in the y axis direction of the workpiece bonded and fixed to the workpiece plate 2, the workpiece plate 2 is tilted by the workpiece holder 1 according to the present invention in such a manner that a left end of the workpiece plate 2 in FIG. 1 is placed on an upper side and a right end of the same is placed on a lower side. As shown in FIG. 4, in the receiving portion 6 on the left end side, the movable piece 6a is retracted toward an outer side of the longitudinal direction of the workpiece plate 2, and the movable piece 6b is advanced toward an inner side of the workpiece plate 2 in the longitudinal direction. Further, in the receiving portion 6 on the right end side, the movable piece 6c is advanced toward the inner side of the workpiece plate 2 in the longitudinal direction, and the movable piece 6d is retracted toward the outer side of the workpiece plate 2 in the longitudinal direction. When the positional relationships between the respective movable pieces 6a, 6b, 6c, and 6d are adjusted in this manner, tilting the workpiece plate 2 and fixing the workpiece plate 2 and the workpiece W on the holder main body 4 at this position enable correcting the deviation Ay in the y axis direction.

[0069] As described above, the workpiece holder according to the present invention can correct the deviation of the crystal orientation axis in the x axis direction at the time of bonding and fixing the workpiece plate to the workpiece. Furthermore, tilting the workpiece plate in the y axis direction enables performing the orientation adjustment in the y axis direction without rotating the workpiece.

[0070] Thus, as different from a case where the workpiece is rotated on the pad plate in conventional examples, there is no fear that a cutting direction of a wire to a circumference of the workpiece becomes a direction to considerably degrade the slicing quality due to the rotation of the workpiece. That is, when a single crystal ingot is sliced by using the workpiece holder according to the present invention, wafers having less WARPs or waviness can be sliced off by the external setup manner even if crystal orientation standards are rigorous. Moreover, when the workpiece holder according to the present invention is used, since the crystal orientation of the workpiece can be adjusted by the external setup manner, the productivity in slicing can be improved. Additionally, since an expensive wire saw including an orientation adjustment mechanism is not required, the wafers can be sliced off at low costs.

[0071] It is to be noted that, in FIG. 1 and FIG. 4, the mode where the workpiece plate is tilted in a state where the workpiece plate 2 is bonded and fixed to the workpiece W has been described as an example, but a work order is not restricted to this order. For example, the workpiece plate 2 may be tilted and fixed in advance in correspondence with a deviation in the y axis direction of the crystal orientation axis of the workpiece W to be held, and then the workpiece plate 2 may be bonded and fixed to the workpiece W while correcting the deviation of the crystal orientation axis of the workpiece W in the x axis direction.

[0072] A method for slicing a workpiece according to the present invention will now be described. Here, a description will be given as to a case where the workpiece holder 1 according to the present invention is used.

[0073] The method for slicing a workpiece according to the present invention uses a wire saw, and a workpiece made of a columnar single crystal held by the workpiece holder is pressed against a wire row, thereby slicing the workpiece. More specifically, such a wire saw as shown in FIG. 5 can be used.

[0074] As shown in FIG. 5, a wire saw 10 includes a wire row 13 formed by winding a wire 12, which reciprocatively travels in an axial direction, around a plurality of grooved rollers 11. Such a wire saw 10 presses the workpiece W made of a columnar single crystal held by the workpiece holder 1 against the wire row 13 of the wire saw 10, thereby slicing the workpiece W into a wafer shape.

[0075] The method for slicing a workpiece according to the present invention is a slicing method adopting an external setup manner to perform orientation adjustment of the workpiece before the workpiece W is attached to the wire saw 10 through the workpiece holder 1. More specifically, first, as shown in FIG. 3, at the time of holding the workpiece W by the workpiece holder 1, the workpiece plate 2 is bonded and fixed to the workpiece W so as to correct a deviation of the crystal orientation axis of the workpiece W in the x axis direction (S 1 in FIG. 6).

[0076] Subsequently, as shown in FIG. 4, the workpiece plate 2 bonded and fixed to the workpiece W is tilted in the y axis direction to adjust the tilt in the y axis direction of the workpiece held by the workpiece plate 2 (S2 in FIG. 6). Further, the workpiece plate 2 and the workpiece W are fixed to the holder main body 4 at this adjusted tilt to hold the workpiece W by using the workpiece holder 1 (S3 in FIG. 6). Consequently, the orientation adjustment of the workpiece W is completed.

[0077] Then, as shown in FIG. 5, the workpiece W having the fixed tilt is disposed to the wire saw 10 through the workpiece holder 1 (S4 in FIG. 6). Subsequently, the workpiece W is pressed against the wire row 13 in FIG. 5 to slice the workpiece W (S5 in FIG. 6).

[0078] According to such a method for slicing a workpiece of the present invention, at the time of bonding and fixing the workpiece plate to the workpiece, the deviation of the crystal orientation axis in the x axis direction is corrected, and then the workpiece is tilted in a state where the workpiece is fixed to the workpiece plate to thereby perform the orientation adjustment in the y axis direction irrespective of rotation of the workpiece. Thus, as different from the example using the method for rotating the workpiece on the pad plate, there is no fear that a cutting direction of the wire to the circumference of the workpiece becomes a direction to considerably degrade the slicing quality. Thus, when a single crystal ingot is sliced by the method for slicing a workpiece according to the present invention, wafers having less WARPs or waviness can be sliced off even though crystal orientation standards are rigorous. Furthermore, since the method for slicing a workpiece according to the present invention enables adjusting the crystal orientation of the workpiece in the external setup manner, the productivity can be improved. Moreover, since an expensive wire saw including an orientation adjustment mechanism is not required, wafers can be sliced off at low costs.

[0079] Additionally, in the method for slicing a workpiece of the present invention, as the workpiece holder, it is possible to use such a workpiece holder 1 as shown in FIG. 1 in which the workpiece plate 2 has the protruding portions 5 and the holder main body 4 has the receiving portions 6 each of which is formed of the two movable pieces which sandwich the curved tip portion of each protruding portion 5 from the upper and lower sides. Using such a workpiece holder 1 enables accurately performing the orientation adjustment in the y axis direction.

[0080] Further, it is preferable to use the two movable pieces 6a and 6b (the movable pieces 6c and 6d) each of which has the tapered surface, which comes into contact with the curved tip portion of the protruding portion 5, being tilted at 30 to 60. The movable pieces whose tapered surfaces have such a tilt can facilitate adjusting the tilt of the workpiece plate 2 in the y axis direction. Further, when the tilt of each tapered surface is set to 30 or more, an angle adjustment amount of the tilt of the workpiece plate to a movement amount of each movable piece becomes sufficiently large, and a time required for the adjustment can be reduced. Furthermore, when the tilt of each tapered surface is set to 60 or less, the angle adjustment amount of the tilt of the workpiece plate to the movement amount of each movable piece does not become too large, and hence delicate angle adjustment can be facilitated.

[0081] Moreover, as shown in FIG. 1, in the slicing method according to the present invention, it is preferable that the workpiece plate 2 has the two protruding portions 5 at both ends thereof in the longitudinal direction, the holder main body 4 has the two receiving portions 6, and the receiving portions 6 sandwich the curved tip portions of the two protruding portions 5 from the upper and lower sides, respectively. As described above, when the tilt of the workpiece plate can be adjusted from both the ends of the workpiece plate in the longitudinal direction, the tilt of the workpiece in the y axis direction can be accurately adjusted, and the workpiece can be fixed.

EXAMPLES

[0082] Although the present invention will now be more specifically described hereinafter with reference to examples and comparative examples of the present invention, the present invention is not restricted to these examples.

Example 1

[0083] Such a workpiece holder 1 of the present invention as shown in FIG. 1 was used, and a workpiece was sliced by using a silicon single crystal ingot having a diameter of 200 mm and a crystal axis <100>in conformity to a flow of the method for slicing a workpiece of the present invention shown in FIG. 6.

[0084] In Example 1, the workpiece plate 2 was bonded and fixed to the ingot in such a manner that a deviation of the ingot having the crystal axis <100>in the x axis direction becomes 0 minute, an angle of the workpiece plate 2 was adjusted in such a manner that a deviation of the ingot in the y axis direction becomes 20 minutes, and the ingot was fixed to the holder main body 4. As described above, the ingot held by the workpiece holder 1 of the present invention was disposed to such a wire saw 10 as shown in FIG. 5, and sliced.

Example 2

[0085] An ingot was sliced under the same conditions as those in Example 1 except that the ingot to be sliced was changed to one having a crystal axis <111>.

[0086] Table 1 shows plane orientations, TTVs, and WARPs of sliced wafers in Examples 1 and 2.

TABLE-US-00001 TABLE 1 Shape(m) Crystal orientation Ingot Wafer position Crystal Actual Operation TTV WARP axis Direction Target measurement Difference level 10 15 Example <100> x 0 minute 2 minutes 2 minutes One end 8.7 14.6 1 Center 6.9 9.7 y 20 minutes 20 minutes 0 minute Other end 9.7 12.0 Average 8.4 12.1 Example <111> x 0 minute 2 minutes 2 minutes One end 8.0 11.7 2 Center 6.5 13.2 y 20 minutes 20 minutes 0 minute Other end 9.8 15.6 Average 8.1 13.5

[0087] As can be understood from Table 1, in Examples 1 and 2, each of differences between targeted orientations and actual measured values was two minutes or less in the x axis direction, and it was one minute or less in the y axis direction. Usually, this difference is approximately 10 minutes, and hence it can be said that wafers each having the targeted plane orientation was able to be accurately sliced off.

[0088] Further, as to the TTVs and WARPs of the wafers, when a crystal axis <100>product or a single crystal ingot having the crystal axis <111>fixed at an appropriate ingot slicing position was sliced by the slicing method adopting the external setup manner which includes the conventional procedure of rotating the ingot on the pad plate, the TTVs are approximately 10 m, and the WARPs are approximately 15 m. As can be understood from Table 1, the TTVs and WARPs of the wafers sliced off in Examples 1 and 2 are suppressed to the same level as those in conventional examples. Since the slicing method according to the present invention does not include the procedure to rotate the ingot on the pad plate, degradation of the WARPs and TTVs can be likewise suppressed in slicing of an orientation <111>axis product of a silicon single crystal ingot.

Comparative Example 1

[0089] A silicon single crystal ingot was rotated on the pad plate of the workpiece holder, a crystal orientation in the y axis direction was adjusted, and an attaching angle of the ingot to the workpiece holder (a tilt in the x axis direction to the workpiece plate) was changed to adjust a crystal orientation in the x axis direction, thereby performing orientation adjustment. Then, the workpiece holder was attached to the wire saw, and the ingot was sliced. The silicon single crystal ingot used in this example is a product having a diameter of 200 mm and an orientation <111>axis. Further, a slicing direction was a (110) direction in FIG. 10.

Comparative Example 2

[0090] An ingot was sliced like Comparative Example 1 except that the silicon single crystal ingot was rotated more by 15 on the pad plate of the workpiece holder than in Comparative Example 1 to adjust a crystal orientation in the y axis direction.

Comparative Example 3

[0091] An ingot was sliced like Comparative Example 1except that the silicon single crystal ingot was rotated more by 30 on the pad plate of the workpiece holder than in Comparative Example 1 to adjust a crystal orientation in the y axis direction. A slicing direction in this example was a (121) direction in FIG. 10.

[0092] FIG. 11 show WARP values of wafers sliced off in Comparative Examples 1 to 3. The WARP of the wafer changed in correspondence with a rotation amount, and in Comparative Example 3 where the slicing direction became (121) in particular, the WARP value was extremely increased. As described above, according to the conventional method, it was confirmed that, when the orientation <111>axis product was sliced, flatness of the wafer might be impaired.

[0093] It is to be noted that the present invention is not restricted to the embodiment. The embodiment is an illustrative example, and any example which has substantially the same structure and exerts the same functions and effects as the technical concept described in claims of the present invention is included in the technical scope of the present invention. [0094] wherein the workpiece plate has a protruding portion, which protrudes toward an outer side of the workpiece plate in a longitudinal direction and has a curved tip portion, on the surface thereof on the opposite side of another surface thereof on which the workpiece is held, [0095] the holder main body has a receiving portion which sandwiches the curved tip portion of the protruding portion from upper and lower sides, the receiving portion sandwiches the curved tip portion of the protruding portion from the upper and lower sides by two forward-and-backward movable pieces, and each of the two movable pieces is formed into a tapered shape having a tilt on a surface thereof which comes into contact with the curved tip portion of the protruding portion, and [0096] the workpiece holder is configured to tilt the workpiece plate in the y axis direction by adjusting a positional relationship of the two movable pieces, which sandwich the curved tip portion of the protruding portion, by each forward or backward movement, to adjust a tilt of the workpiece in the y axis direction, and to fix the workpiece at this position.