EP0931624A2

EP0931624A2 - Surface polishing apparatus with upper surface plate elevating mechanism

Info

Publication number: EP0931624A2
Application number: EP99300410A
Authority: EP
Inventors: Shiro Furusawa; Yoshihiro Nakajo
Original assignee: SpeedFam Co Ltd
Current assignee: SpeedFam Co Ltd
Priority date: 1998-01-22
Filing date: 1999-01-20
Publication date: 1999-07-28
Also published as: JPH11207608A; EP0931624A3

Abstract

A surface polishing apparatus is provided with an upper surface plate elevating mechanism that can use a small elevating mechanism to simply and accurately raise and lower an upper surface plate 3 and stop it at a specified position even if the total weight of the upper surface plate, including associated equipment, is large. A plurality of air cylinders 15 constantly support part of the load of the upper surface plate assembly 3A, which includes the upper surface plate 3 and a surface plate supporting frame 5. A servo motor 16 is used to raise and lower the upper surface plate assembly 3A and to stop it at a specified position.

Description

The present invention relates to a surface polishing apparatus which polishes both surfaces of a workpiece held by a carrier using an upper and a lower surface plate, and in particular, to an elevating mechanism for raising and lowering the upper and lower surface plates while the workpiece is being loaded, unloaded, or polished.
A known surface polishing apparatus for uses such as lapping or polishing comprises rotatable sun and internal gears that are coaxially located and upper and lower surface plates. A workpiece, such as a semiconductor wafer, held by a carrier that engages the sun and internal gears to follow an epicyclic path is sandwiched by the upper and lower surface plates for polishing.
In such a surface polishing apparatus, when the workpiece is loaded or unloaded or the upper surface is raised or lowered for polishing, an air cylinder or a servo motor is used for elevation or lowering.
Use of an air cylinder or servo motor alone creates no problem if the upper surface plate is relatively light, for example, several tens of kilograms to several hundred kilograms. However, in a modern polishing apparatus that has a complicated structure to provide improved polishing accuracy and in which the total weight of an upper surface plate assembly--including an upper surface plate, a support frame for the plate, and a drive and other associated mechanisms--is several to 10 tons, it is very difficult to raise and lower this upper surface plate assembly using only an air cylinder or servo motor. In the former case a large air cylinder is required which, because of air compression, cannot stop the upper surface plate assembly accurately at a specified position. The latter requires a large, expensive servo motor resulting in the need for a large-scale elevating mechanism, including a control apparatus for the elevating mechanism.
It is a technical object of this invention to provide an upper surface plate elevating mechanism that can use a small elevating mechanism to simply and accurately raise and lower an upper surface plate and stop the plate at a specified position even if the total weight of the upper surface plate including its associated equipment is large.
The present invention provides an elevating mechanism which uses a load receiving air cylinder to constantly urges upward a frame that supports the upper surface plate. This arrangement allows the air cylinder to support part of the load of the upper surface plate assembly, including the upper surface plate and the surface plate supporting frame. The upper surface plate assembly is then raised and lowered by a servo motor.
This configuration makes it possible to use a small air cylinder and servo mechanism, thus reducing the size of the elevating mechanism. Furthermore the small servo motor used to raise and lower the upper surface plate assembly can stop it at a specified position simply and accurately.
According to one preferred embodiment, a plurality of load-receiving air cylinders are provided arranged in a regular pattern, and a drive shaft for the servo motor is disposed at the center of the arrangement of the air cylinders.
According to a specific embodiment, the surface plate supporting frame is cantilevered on a base member provided on a body of the surface polishing apparatus. The load-receiving air cylinders are installed between the base member and the surface plate supporting frame.
The base member can be rotated relative to the body so that the surface plate supporting frame can be swiveled, via the base member, between a workpiece polishing position and an unloading position.
The invention will now be further described by way of example with reference to the accompanying drawings in which:
FIG. 1 is a side view showing one embodiment of a polishing apparatus using an elevating mechanism according to this invention.
FIG. 2 is an enlarged sectional view of the integral part of FIG. 1.
FIG. 3 is a top view of the integral part of FIG. 1.
FIG. 1 shows an example of a surface polishing apparatus to which an upper surface plate elevating mechanism according to this invention has been added. Reference numeral 1 designates a body, 2 is a lower surface plate disposed so as to be rotatable on the body 1 and coupled to a drive source (not shown), and 3 is an upper surface plate coaxially located over the lower surface plate 2. The upper surface plate 3 is attached so as to be rotatable to the tip of a surface plate supporting frame 5, the proximal end of which is supported by the body 1 so as to be operated like a cantilever and which extends in the horizontal direction. The upper surface plate 3 is driven by an upper-surface-plate driving servo motor 6 via a transmission mechanism provided 1 inside the surface plate supporting frame 5.
In addition a sun gear 7 and an internal gear 8 are coaxially disposed at the center of the lower surface plate 2 and on the outer circumference of the plate 2, respectively. A plurality of carriers 9 are disposed on the lower surface plate to engage the sun and internal gears 7 and 8 to make an epicyclic motion around the sun gear 7. A workpiece 4 such as a semiconductor wafer or a magnetic disc substrate held by each carrier 9 is sandwiched on both sides between the upper and lower surface plates for polishing.
As is seen in FIG. 2, the upper surface plate supporting frame 5 is supported by an elevating mechanism 10 so as to be arbitrarily raised or lowered on a base member 12 mounted at one end of the body 1 via a bearing 11 so as to be arbitrarily rotated.
The elevating mechanism 10 includes a guide mechanism 14 for guiding the elevation and lowering of the surface plate supporting frame 5; a plurality of air cylinders 15 that constantly urge upward the surface plate supporting frame 5 to receive part of the load on the upper surface plate assembly 3A, including the surface plate supporting frame 5 and the upper surface plate 3; and an elevating servo motor 16 that elevates and lowers the surface plate supporting frame 5 for which part of the load is supported by the air cylinders 15 and that stops the frame 5 at a specified position.
The guide mechanism 14 is composed of a linear guide 19 formed axially on the outer circumference of a first shaft 18 standing on the base member 12; and a slide member 21 formed on the inner surface of a second shaft 20 fixed to the bottom surface of the surface plate supporting frame 5 so as to fit on the first shaft 18, the slide member fitting on the linear guide 19. The guide mechanism 14, however, is not limited to this configuration, and other configurations may be used as long as they can guide the surface plate supporting frame 5 linearly in the vertical direction.
Three air cylinders 15 are provided so as to correspond to the respective vertices of an equilateral triangle on the internal bottom of the first shaft 18, and a rod 15a of the air cylinder 15 is coupled to a frame member 20a integrated with the second shaft 20. The elevating servo motor 16 is mounted in the body 1 so as to be located at the center of the arrangement of the three air cylinders 15. The elevating servo motor 16 has an output shaft 16a coupled to the frame member 20a.
The three air cylinders 15 are controlled to constantly support about half to two-thirds of the load (about 6 to 10 tons) on, for example, the upper surface plate assembly 3A, with the remaining load supported by the servo motor 16. This configuration does not only enable the use of smaller air cylinders 15 and servo motors 16 than in the unitary use of an air cylinder or a servo motor to reduce the size of the elevating mechanism 10 but can also use the small servo motor 16 and its control mechanism to raise and lower the upper surface plate assembly 3A and stop it at a specified position simply and accurately.
In addition, the surface plate supporting frame 5 can be swiveled between a polishing position A and a workpiece 4 unloading position B as shown in FIG. 3, via a swiveling mechanism 22 consisting of the base member 12, a swiveling servo motor 23 attached to the body 1, a gear 24 attached to the output shaft of the servo motor 23, and a gear section 12a partly formed on part of the outer circumference of the base member 12.
The upper surface plate 3 has suction holes at positions corresponding to the workpieces 4 on the work surface so as to vacuum-chuck and lift the workpieces that have been polished. After the upper surface plate 3 is swiveled to the unloading position B while still vacuum-chucking the workpieces 4, an unloading means 26 sequentially unloads the workpieces 4. In addition, the polishing apparatus has a loading means 27 for loading unprocessed workpieces 4. While processed workpieces are being unloaded after the upper surface plate 3 has been swiveled to the unloading position B, the loading means can supply an unprocessed workpiece to each carrier 9 on the lower surface plate 2.
The vacuum chuck means and the loading or unloading means 27 or 26 may be well-known ones, so their configurations are nor referred to herein.
In the surface polishing apparatus of the above configuration, the workpiece 4 supplied to each carrier 9 on the lower surface plate 2 after the upper surface plate 3 has been elevated is sandwiched on both sides between the upper and lower surface plates 2 and 3 when the upper surface plate 3 lowers, so that both surfaces of the workpiece are polished by the rotating surface plates 2 and 3. Then, each carrier 9 is driven by the sun and internal gears 7 and 8 to make an epicyclic motion around the sun gear 7. In addition, the action of lowering the upper surface plate 3 down to a processing position is carried out by the elevating servo motor 16 in the elevating mechanism 10 via the surface plate supporting frame 5. During processing, processing pressure is added by another pressurizing cylinder (not shown) provided in the surface plate supporting frame 5.
Once the workpiece 4 has been polished and the upper and lower surface plates 2 and 3 have stopped at predetermined rotational positions, the upper surface plate 3 is guided and lifted by a guide mechanism 14 driven by the elevating servo motor 16 up to a predetermined height while still vacuum-chucking the processed workpieces 4. The upper surface plate 3 is then swiveled to the unloading position B, where the processed workpieces 4 are unloaded by the unloading means 26. Then, the loading means 27 supplies an unprocessed workpiece to each carrier 9 on the lower surface plate 2.
Once the processed workpieces have been unloaded and the unprocessed workpieces have been supplied, the upper surface plate 3 is swiveled to a position immediately above the lower surface plate 2 and is then lowered by the elevating servo motor 16. Then, the polishing of the workpieces 4 is started again.
Since the upper surface plate 3 is raised and lowered by the servo motor 16 while the load receiving air cylinder 15 in the elevating mechanism 10 is supporting part of the load on the upper surface plate assembly 3A to reduce the load, the small servo motor 16 and its control mechanism can be used to simply raise and lower the upper surface plate 3 and to reliably and accurately stop it at a specified position even if the upper surface plate assembly 3A is extremely heavy, such as several to 10 tons.
As described above, the elevating mechanism according to this invention can use the small elevating mechanism to simply and accurately effect the elevation and lowering of the upper surface plate and stop it at a specified position even if the total weight of the upper surface plate is large.

Claims

A surface polishing apparatus for polishing both surfaces of a workpiece having a carrier for holding the workpiece, upper and lower surface plates, a frame for supporting the upper surface plate and an upper surface plate elevating mechanism for raising and lowering the upper surface plate and stopping it at a specified position comprising at least one air cylinder for constantly urging the surface plate support frame upwardly and a servo motor that raises and lowers the surface plate supporting frame.
A surface polishing apparatus as claimed in Claim 1 wherein three air cylinders are provided arranged at the respective vertices of a triangle, and wherein an output shaft of the servo motor is disposed at the center of the triangular cylinder arrangement.
A surface polishing apparatus as claimed in either Claim 1 or Claim 2 further comprising a guide mechanism for guiding the surface plate supporting frame.
A surface polishing apparatus as claimed in Claim 3 wherein the surface plate supporting frame is cantilevered from a base member provided on a body, wherein the upper surface plate is attached to the free end of the surface plate supporting frame, and wherein the guide mechanism and the load-receiving air cylinder(s) are provided between the surface plate supporting frame and the base member.
A surface polishing apparatus as claimed in Claim 4 wherein the base member is rotatable relative to the body, and wherein a drive means is provided that rotates the base member so that the surface plate supporting frame can be moved between a workpiece processing position and an unloading position.