Tilt adjusting mechanism for chuck table

A tilt adjusting mechanism provided in a processing apparatus including a chuck table having a holding surface for holding a workpiece thereon and a processing unit having a processing surface for processing the workpiece held on the chuck table, for adjusting parallelism between the holding surface and the processing surface. The tilt adjusting mechanism includes at least three support posts supporting the chuck table, the support posts including at least one expansible and contractible support post that is provided with a piezoelectric actuator including layered piezoelectric elements, a direct current power supply electrically connected to the piezoelectric actuator, and a voltage controller for controlling a direct current voltage value of direct current electric power supplied to the piezoelectric actuator.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a tilt adjusting mechanism including a piezoelectric actuator for adjusting the tilt of a chuck table.

Description of the Related Art

A grinding apparatus for grinding a workpiece using grinding stones includes a chuck table having a holding surface for holding a workpiece thereon. Some grinding apparatuses each include a position adjusting unit for tilting the chuck table to keep the holding surface parallel to the processing surfaces of grinding stones, as disclosed in Japanese Patent Laid-open No. H08(1996)-090376.

The position adjusting unit disclosed in JP-H08(1996)-090376 A includes an externally threaded shaft for adjusting the vertical position of a chuck table that is rotatable about its own axis by an electric motor. The externally threaded shaft has threaded portions that are threaded in respective nuts disposed in a base and a flange of a table support base that supports a chuck table. Actually, there are three position adjusting units disposed in angularly equally spaced positions on the flange of the table support base. The externally threaded shafts can be turned manually directly or by a tool to change their vertical positions, thereby adjusting the vertical position of the chuck table and hence the tilt of the chuck table with respect to the base.

SUMMARY OF THE INVENTION

In recent years, as workpieces to be ground have become larger in size, chuck tables for holding the workpieces also have become larger in size and hence weight. Heavier chuck tables pose a problem on the position adjusting unit in that, when the externally threaded shaft is rotated through a given angle, the externally threaded shaft undergoes increased thread friction, possibly failing to change the tilt of the chuck table by a given degree depending on the angle. Therefore, there are demands for a capability to change the tilt of a chuck table by a desired degree even though the chuck table is heavy.

Another problem is that, even when the externally threaded shaft is rotated through a small angle, the externally threaded shaft tends to be twisted due to thread friction and fails to change the tilt of the chuck table. Furthermore, since the externally threaded shaft and the nuts threaded thereover suffer backlash, it is necessary to eliminate the backlash for correctly changing the tilt of the chuck table, resulting in a time-consuming tilt adjusting process. There are also demands for a capability to make fine tilt adjustments.

It is therefore an object of the present invention to provide a tilt adjusting mechanism that is capable of easily adjusting the tilt of a chuck table.

In accordance with an aspect of the present invention, there is provided a tilt adjusting mechanism provided in a processing apparatus including a chuck table having a holding surface for holding a workpiece thereon and a processing unit having a processing surface for processing the workpiece held on the chuck table, for adjusting parallelism between the holding surface and the processing surface, and the tilt adjusting mechanism includes: at least three support posts supporting the chuck table, the support posts including at least one expansible and contractible support post that is provided with a piezoelectric actuator comprising layered piezoelectric elements; a direct current power supply electrically connected to the piezoelectric actuator; and a voltage controller for controlling a direct current voltage value of direct current electric power supplied to the piezoelectric actuator, in which the DC electric power whose direct current voltage value has been controlled by the voltage controller is supplied to the piezoelectric actuator to control the length of the expansible and contractible support post for thereby adjusting the parallelism between the holding surface and the processing surface.

Since the tilt adjusting mechanism adjusts the tilt of the chuck table by changing the DC voltage value of the DC electric power supplied to the piezoelectric actuator, the tilt of the chuck table can be changed reliably by a desired degree. Furthermore, it is not necessary to eliminate backlash for changing the tilt of the chuck table, and hence, the amount of work required for tilt adjustment is reduced. Furthermore, the tilt of the chuck table can be adjusted by a slight degree by slightly changing the DC voltage value of the DC electric power supplied to the piezoelectric actuator with the voltage controller.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claim with reference to the attached drawings showing a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A grinding apparatus1illustrated inFIG. 1is a grinding apparatus for grinding an upper surface Wa of a workpiece W such as a semiconductor wafer or the like in the shape of a circular plate held on a holding surface20aof a chuck table2by abrasively keeping processing surfaces340aof a plurality of grinding stones340against the upper surface Wa of the workpiece W. The grinding apparatus1includes therein a tilt adjusting mechanism5according to a preferred embodiment of the present invention for adjusting the parallelism between the holding surface20aand the processing surfaces340a. The grinding apparatus1and the tilt adjusting mechanism5will be described in detail below.

As illustrated inFIG. 1, the grinding apparatus1includes a control unit9for controlling various mechanisms of the grinding apparatus1. The grinding apparatus1also includes a base10extending in Y-axis directions and a column11erected on an end portion of the base10in a +Y direction that is one of the Y-axis directions.

As illustrated inFIGS. 1 and 2, the chuck table2that is shaped as a circular plate is disposed on the base10of the grinding apparatus1. The chuck table2includes a suction member20and a frame21supporting the suction member20. The suction member20, which is typically made of a porous material, has an upper surface functioning as the holding surface20afor holding the workpiece W under suction thereon. Suction means27is connected through a suction channel28to the holding surface20aof the chuck table2. While the workpiece W is placed on the holding surface20a, the suction means27is actuated to produce suction force. The suction force is transmitted through the suction channel28to the holding surface20awhere the suction force acts therethrough on the workpiece W, holding the workpiece W under suction on the holding surface20aof the chuck table2.

As illustrated inFIG. 2, the chuck table2overlies table rotating means22having a table base23that supports the chuck table2thereon and a support24that supports the table base23for rotation therewith. The table rotating means22also includes an electric motor220disposed in a position adjacent to the support24. The support24is operatively coupled to the electric motor220by a transmission belt221. When the electric motor220is energized, the rotational force of the electric motor220is transmitted by the transmission belt221to the support24, rotating the support24about its own axis. The chuck table2that is coupled to the support24through the table base23is now rotated about a rotational axis25extending in Z-axis directions.

As illustrated inFIG. 1, a cover12is disposed around the chuck table2and coupled on both sides thereof with a bellows13that is stretchable and contractible in the Y-axis directions. When the chuck table2is moved in the Y-axis directions by horizontal moving means, not shown, for example, the cover12is also moved in the Y-axis directions in unison with the chuck table2, stretching and contracting the bellows13.

As illustrated inFIGS. 1 and 2, there is disposed above the base10non-contact thickness measuring means7for applying a laser beam to the upper surface Wa of the workpiece W, for example, to measure the thickness of the workpiece W while the workpiece W is being ground. The non-contact thickness measuring means7is horizontally movable to measure thicknesses of the workpiece W at different locations thereon.

As illustrated inFIG. 1, a grinding feed mechanism4that supports a grinding unit3, for example, is disposed on a side surface of the column11that faces in a-Y direction that is the other of the Y-axis directions. As illustrated inFIG. 1, the grinding unit3includes a spindle30having a rotational axis35extending in the Z-axis directions, a housing31by which the spindle30is rotatably supported, an electric motor32coupled to the spindle30for rotating the spindle30about the rotational axis35, an annular mount33connected to a lower end of the spindle30, and a grinding wheel34detachably mounted on a lower surface of the mount33. The grinding wheel34includes a wheel base341, and the plurality of grinding stones340that are disposed in an annular array on a lower surface of the wheel base341. Each of the grinding stones340is substantially shaped as a rectangular parallelepiped. The grinding stones340have respective lower surfaces functioning as the respective processing surfaces340afor grinding the workpiece W.

As illustrated inFIG. 1, the grinding feed mechanism4includes a ball screw40having a rotational axis45extending in the Z-axis directions, a pair of guide rails41disposed one on each side of the ball screw40and extending parallel to the ball screw40, an electric motor42coupled to an upper end of the ball screw40for rotating the ball screw40about the rotational axis45, a vertically movable plate43having an inner nut threaded over the ball screw40and opposite side portions held in sliding contact with the guide rails41, and a holder44coupled to the vertically movable plate43and holding the spindle30. When the electric motor42is energized, it rotates the ball screw40about the rotational axis45, causing the vertically movable plate43to move vertically in the Z-axis directions while being guided by the guide rails41thereby to move the grinding unit3held by the holder44vertically in the Z-axis directions.

As illustrated inFIGS. 1 and 2, the grinding apparatus1incorporates the tilt adjusting mechanism5that adjusts the parallelism between the holding surface20aand the processing surfaces340a, as described above. The tilt adjusting mechanism5includes an expansible and contractible support post51and a voltage controller60. As illustrated inFIG. 2, an inner base53is disposed below the chuck table2, and at least three support posts50are disposed on the inner base53. At least one of the three support posts50acts as the expansible and contractible support post51that includes a piezoelectric actuator510in the form of layered piezoelectric elements and that is expansible and contractible in the Z-axis directions. The other support posts50act as fixed support posts52that are not expansible and contractible.

InFIG. 2, one expansible and contractible support post51and two fixed support posts52are disposed on the inner base53. However, all of the three support posts50may be expansible and contractible support posts51, or two of the three support posts50may be expansible and contractible support posts51whereas the remaining one may be a fixed support post52. As illustrated inFIG. 2, an annular joint member54surrounding the table base23is disposed on upper ends of the three support posts50, for example, and have respective sides54ajoined to the table base23. The chuck table2is thus supported on the support posts50through the joint member54and the table base23.

As illustrated inFIG. 2, the expansible and contractible support post51is electrically connected to the voltage controller60that is electrically connected to a DC power supply6. The voltage controller60has a function to control the DC voltage value of DC electric power supplied from the DC power supply6to the piezoelectric actuator510of the expansible and contractible support post51.

When DC electric power whose DC voltage value has been controlled by the voltage controller60is supplied to the piezoelectric actuator510, the piezoelectric actuator510is expanded and contracted in the Z-axis directions to adjust the expansible and contractible support post51to a predetermined length. In this manner, the joint member54is angularly moved about the fixed support posts52to adjust the parallelism between the holding surface20aand the processing surfaces340a.

For grinding the workpiece W on the grinding apparatus1described above, a tilt adjusting process is performed in advance to keep the holding surface20aof the chuck table2and the processing surfaces340aof the grinding stones340parallel to each other. Specifically, the DC power supply6is energized to supply DC electric power to the voltage controller60, which controls the DC voltage value of the supplied DC electric power. The voltage controller60supplies DC electric power with the controlled DC voltage value to the piezoelectric actuator510, which is expanded and contracted in the Z-axis directions to adjust the expansible and contractible support post51to a predetermined length. The joint member54is angularly moved about the fixed support posts52to adjust the parallelism between the holding surface20aand the processing surfaces340a.

After the parallelism between the holding surface20aand the processing surfaces340ahas been adjusted, the workpiece W with the upper surface Wa facing upwardly is placed on the holding surface20aof the chuck table2illustrated inFIGS. 1 and 2. With the workpiece W placed on the holding surface20a, the suction means27is actuated to produce suction force, which is transmitted through the suction channel28to the holding surface20awhere the suction force acts therethrough on the workpiece W, holding the workpiece W under suction on the holding surface20aof the chuck table20.

With the workpiece W thus held under suction on the holding surface20a, the horizontal moving means, not shown, is operated to move the chuck table2in the Y-axis directions to a position where the chuck table2is positioned below the grinding unit3as illustrated inFIG. 1. Then, the electric motor220of the table rotating means22is energized to produce rotational power that is transmitted by the transmission belt221to the support24, which is rotated about the rotational axis25. The chuck table2and the workpiece W held under suction on the holding surface20aof the chuck table2are thus rotated also about the rotational axis25.

Furthermore, the electric motor32of the grinding unit3is energized to rotate the spindle30about the rotational axis35, rotating the grinding stones340of the grinding wheel34that is coupled to the spindle30through the mount33, also about the rotational axis35.

While the workpiece W is rotating about the rotational axis25and the grinding stones340are rotating about the rotational axis35, the grinding unit3is lowered by the grinding feed mechanism4illustrated inFIGS. 1 and 2to grind the workpiece W. Specifically, the electric motor42is energized to rotate the ball screw40about its rotational axis45. As the ball screw40is rotated about the rotational axis45, the vertically movable plate43is lowered in a −Z direction that is one of the Z-axis directions while being guided by the guide rails41. When the vertically movable plate43is lowered in the −Z direction, the holder44supported on the vertically movable plate43and the grinding unit3supported by the holder44are also moved in the −Z direction until the processing surfaces340aof the grinding stones340abut against the upper surface Wa of the workpiece W held on the holding surface20aof the chuck table2, starting to grind the workpiece W.

While the workpiece W is being ground, before the workpiece W is thinned to a finished thickness, for example, the non-contact thickness measuring means7measures the thicknesses of the workpiece W at respective three locations, i.e., an outer circumferential edge We of the workpiece W, the center Wo of the workpiece W, and an intermediate position Wh between the outer circumferential edge We and the center Wo of the workpiece W, i.e., a position on the circumference of a circle whose radius is one-half of the radius of the circle representing the workpiece W, as illustrated inFIG. 2. If the measured thicknesses at the three locations are not equal to each other, the tilt of the chuck table2is adjusted by the tilt adjusting mechanism5to make the measured thicknesses at the three locations equal to each other. Specifically, in a manner similar to the tilt adjusting process described above, the DC power supply6is energized to supply DC electric power to the voltage controller60, which controls the DC voltage value of the supplied DC electric power on the basis of the measured thicknesses at the three locations. The voltage controller60supplies DC electric power with the controlled DC voltage value to the piezoelectric actuator510, which is appropriately expanded and contracted in the Z-axis directions to adjust the expansible and contractible support post51to a predetermined length. The joint member54is angularly moved about the fixed support posts52to adjust the parallelism between the holding surface20aand the processing surfaces340a.

By changing the voltage supplied to the piezoelectric actuator510using the voltage controller60, as described above, the length of the expansible and contractible support post51is changed to adjust the tilt of the holding surface20a. The tilt of the holding surface20ais thus reliably changed by a desired degree. With the processing surfaces340aand the holding surface20abeing kept parallel to each other, the workpiece W is ground to a finished thickness by the grinding unit3. The workpiece W can thus be finished to a uniform thickness in its entirety.

Inasmuch as the tilt of the holding surface20aof the chuck table2can be changed by expanding and contracting the piezoelectric actuator510, rather than a conventional externally threaded shaft, using the tilt adjusting mechanism5, it is not necessary to eliminate backlash for changing the tilt of the chuck table2, and hence, the amount of work required for tilt adjustment is reduced. Furthermore, the tilt of the chuck table2can be adjusted by a slight degree by slightly changing the DC voltage value of the DC electric power supplied to the piezoelectric actuator510with the voltage controller60. Therefore, it is possible for the tilt adjusting mechanism5to perform finer tilt adjustment.

Moreover, if a grinding apparatus has a turntable as a table base, then, at least two chuck tables are disposed on the turntable. Providing each of the chuck tables is supported by at least three support posts including respective piezoelectric actuators, the heights of the upper surfaces of the two chuck tables can be equalized by controlling DC voltages applied to the respective piezoelectric actuators. Since workpieces on the chuck tables can then be processed in such a manner that processing surfaces are kept at the same height, a processing fluid is uniformly supplied to the workpieces on the chuck tables, developing no difference between processed results on the two chuck tables.

The embodiment described above illustrates the tilt adjusting mechanism for the chuck table according to the present invention as applied to the grinding apparatus. However, the present invention is not limited to the illustrated embodiment, but is also applicable to tilt adjusting mechanisms for chuck tables of other processing apparatus such as a cutting apparatus, a polishing apparatus, or the like.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claim are therefore to be embraced by the invention.