JPH11170167A - Polishing method and polishing device of optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a highly precise surface form free from twisted surface form in a short time by alternately repeating normal rotation and reverse rotation of a polisher in polishing work. SOLUTION: A workpiece 3 is rotated C following the rotation of a polisher 2 together with an abrasive ring 6 supported by a roller 8. At this time, since a slight clearance is provided between the outer diameter of an abrasive frame 4 and the inner diameter of the abrasive ring 6, the workpiece 3 and the abrasive frame 4 can be following rotated C by properly regulating the rotating period of the abrasive ring 6. The oscillation B of the workpiece 3 is performed so that the workpiece 3 is never protruded from the polisher 2. After a prescribed time, the rotating direction of the polisher 2 is reversed from A to A' Accordingly, the following rotating direction of the workpiece 3 is also reversed from C to C'. The reversion of rotating direction of the polisher is repeated to provide a highly precise polished surface of a prescribed surface form free from twisting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a large rod-shaped optical element which requires a highly accurate surface shape.

[0002]

2. Description of the Related Art As a rod-shaped optical element, a mirror for a laser length measuring interferometer required for controlling the position of a reticle / wafer stage of a semiconductor exposure apparatus, a reference element of an interferometer for measuring the surface shape of an optical element and a wavefront aberration. Or a mirror used in a soft X-ray optical system. Optical glass, ceramics, and the like are known as mirror members. As a typical polishing method for these rod-shaped optical elements, a workpiece disposed on a polisher (an elastic member pressed against a surface to be processed) is held by a jig such as a polishing frame, and a polishing liquid is processed with the polisher. A surface transfer processing method is generally used in which the polisher and the workpiece are interposed between the workpieces and the shape of the polisher surface is transferred to the workpiece surface while giving relative movement between the polisher and the workpiece. As a processing device, a polishing machine using a polisher made of a pitch, a lapping machine using a polisher made of a polishing cloth, a synthetic resin or the like is usually used. Hereinafter, a conventional polishing method will be described with reference to FIG. FIG. 4 is a side view showing a state in which the workpiece 3 is polished by the polisher 2 and a polishing liquid (abrasive grains are dispersed in pure water and supplied from a polishing liquid nozzle 9). The main components of the apparatus include a disk-shaped rotary table 1 having a polisher 2 on its upper surface, a polishing frame 4 for holding the workpiece 3, a polishing ring 6 for holding the workpiece 3 and the polishing frame 4. ,
A station 7 for supporting the polishing ring 6, a roller 8, a polishing liquid nozzle 9 for spraying a polishing liquid, a crank 10 for rocking a workpiece, and a rocking arm 11. As a polishing procedure of the workpiece 3, the polishing ring 6, the polishing frame 4, the workpiece 3, and the load 5 are arranged in the station 7 and placed on a polisher. Then, a polishing liquid is sprayed from the polishing liquid nozzle 9 between the workpiece 3, the polishing frame 4, the polishing ring 6 and the polisher 2, and the polisher 2 is rotated A to give a swing B to the workpiece. is there. In this process, the workpiece 3 rotates C with the rotation of the polisher 2 while being supported by the rollers 8 together with the polishing ring 6, and the processing proceeds.

[0003]

In the case where the workpiece is a large bar-shaped optical element (having an elongated rectangular polishing surface), in such a polishing method, when the workpiece rotates along with the rotation of the rotary table, the rotation of the rotary table causes the workpiece to rotate. However, there is a problem that the moment of the force resulting from friction with the polisher acts on the workpiece, which adversely affects the processed shape. That is, a moment of force always acts in the rotational direction on the co-rotating workpiece due to friction with the polisher, and the side face of the workpiece comes into strong contact with the end of the diagonal side face of the polishing frame, and makes contact. The workpiece rises there. For this reason, the surface of the workpiece cannot obtain a uniform pressing force distribution on the polisher surface during polishing, and the processing proceeds in a form in which the wear in the diagonal direction is constantly increased, so that the processed surface has a twisted surface shape. More cases. The degree of the torsion surface shape of the work surface is also affected by the rigidity of the work object, and the degree of occurrence varies depending on the type and shape of the work material (cross-sectional area with respect to length). As a measure for preventing the twisted surface shape in such polishing, when the workpiece is placed in the polishing frame, the distance between the workpiece and the polishing frame is reduced to reduce the movable range in the frame of the workpiece, so-called play. Attempts have been made to reduce the size of the workpiece or to lower the contact portion between the side surface of the workpiece and the inner surface of the polishing frame as much as possible toward the workpiece surface, thereby stabilizing the posture of the workpiece during polishing. In order to absorb the external force during polishing, a cushioning material is adhered to the contact portion to reduce the influence during polishing. Further, polishing with a polisher rotation speed of 1 rpm and a swinging speed of a workpiece set at a low speed of 1500 mm / min or less has been conventionally performed. That is, in order to finish the target surface accuracy without causing a twisted surface on the workpiece, processing has been performed in which the relative movement speed of the polisher and the workpiece is set to a low speed. Therefore, at present, it takes a long time for setting before the start of processing and a long time for polishing itself. In addition, even if the above measures are taken, the degree of twisting is reduced, but there is a problem that it is difficult to reduce the value to a predetermined value or less. The present invention has been made in view of the problems of the prior art, and in a processing apparatus and a processing method for a large rod-shaped optical component, a processing apparatus and a processing method for finishing a highly accurate surface without twisting in a short time. The purpose is to provide.

[0004]

According to the present invention, there is provided the following:
A rotating table for rotating a polisher, a holding member for rotatably pressing and holding a workpiece on the polisher, a swinging member for giving a swinging motion to the holding member, and a polishing apparatus having a polishing liquid supply member. An apparatus in which the rotation of the polisher alternately repeats normal rotation and reverse rotation during polishing is used. As a second means, in the first apparatus, in particular, the rotation speed of the polisher is 3 to 5 rpm, and the oscillation speed of the workpiece is 2
500 mm / min to 3500 mm / min, and 2
An apparatus in which the rotating table repeatedly rotates forward and backward every 8 hours. As a third means, a polisher is arranged on a rotary table, the object to be polished is rotatably pressed to the polisher via a polishing liquid, the rotary polisher is rotated, and the object to be polished is oscillated. In the polishing method for polishing an object to be polished, the direction of rotation of the polisher is alternately repeated between normal rotation and reverse rotation during polishing. As a fourth means, to work particularly effectively in the third means,
The number of rotations of the polisher is 3 to 5 rpm, and the number of swings of the workpiece is 2500 mm / min to 3500 mm / min,
The rotation table is repeatedly rotated forward and backward every 2 to 8 hours.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention basically does not provide uniformity of pressure contact between a workpiece and a polisher simply by improving the method of holding the workpiece, and therefore, the twisted surface is inevitably formed. It is based on the fact that twisting is completely corrected by reversing the rotation of the polisher, and that highly accurate surfaces can be machined efficiently.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the polishing method according to the present invention will be described below. 1 and 2 are a plan view and a side view showing a processing state. A workpiece 3 made of silicon nitride ceramic is polished by an Oscar type polishing apparatus using a hard polisher 2 and a polishing liquid in which abrasive grains are dispersed in pure water. The Oscar-type polishing apparatus includes a disk-shaped rotary table 1 on which a polisher 2 is provided on an upper surface, a polishing frame 4 for holding a workpiece 3, a polishing ring 6 for holding the workpiece 3 and the polishing frame 4, and a polishing ring. The apparatus has a station 7 supporting the roller 6, a roller 8, a polishing liquid nozzle 9 for jetting a polishing liquid, a crank 10 for rocking a workpiece, and a rocking arm 11. A load 5 is placed on the workpiece 3 to increase the processing speed. Polishing frame 4 and polishing ring 6
Are in direct contact with the work surface of the polisher 2 in the same manner as the work piece 3. The polishing liquid is obtained by dispersing iron oxide (Fe ₂ O ₃ ) having a particle diameter of 0.3 μm in pure water, and has a concentration of 5 wt%. Fig. 2
As shown in FIG. 5, a V-shaped circumferential groove having a groove depth H of 2 mm and a groove pitch P of 2.5 mm is formed on the surface. Hard epoxy resin is used as the polisher material. The polishing procedure of the workpiece 3 will be described below. First, before processing, the surface shape of the surface of the hard resin polisher 2 that acts on the upper surface of the hard resin polisher 2 is processed by another tool so as to have a desired surface shape. Next, the polishing ring 6, the polishing frame 4, the workpiece 3, and the load 5 are arranged in the station 7. Then, a polishing liquid is sprayed from the polishing liquid nozzle 9 between the workpiece 3, the polishing frame 4, the polishing ring 6 and the polisher 2, and the polisher 2 is rotated A. At the same time, the crank 10 and the crank arm 11 move the station 7 into the station 7. Swing B is applied to the workpiece placed at the center. In this process, the workpiece 3 together with the polishing ring 6 supported by the roller 8 rotates C with the rotation of the polisher 2. On this occasion,
Since a small gap is provided between the outer diameter of the polishing frame 4 and the inner diameter of the polishing ring 6, the workpiece 3 and the polishing frame 4 can rotate and rotate C with the rotation cycle of the polishing ring 6 adjusted appropriately. . The swing B of the workpiece 3 is such that the workpiece 3 is
Do so that it does not protrude. After a predetermined time, the direction of rotation of the polisher is reversed to change from A to A 'in the figure. As a result, the rotational direction of the co-rotation of the workpiece is also reversed, and C to C ′
Becomes By repeating the reversal of the rotation direction of the polisher, a highly accurate polished surface having a predetermined surface shape and having no twist is obtained.

In the embodiment of the invention, the direction of rotation of the polisher 2, the number of rotations, and the number of swings of the workpiece 3 are set, and polishing is performed for a predetermined time under the set processing conditions.
The data of the torsion surface shape that occurs in advance is grasped in advance.
FIGS. 3A and 3B show the torsion surface shape generated on the workpiece 3 when the workpiece 3 is polished by the polisher normal rotation A and the reverse rotation A ′. In the polishing with the polisher forward rotation A, the workpiece 3 is C
3a, the surface to be processed is-
In the polishing with the polisher reverse rotation A ', the workpiece 3 rotates in the direction C', so that the surface to be processed has a diagonal of-as shown in FIG. Wear increases, and a wear difference h occurs. The data of the difference in wear obtained as a result of the polishing is added to a control device (not shown) of the Oscar polishing apparatus, and programmed, and the rotation table A and the reverse rotation A ′ are added to the rotation table at predetermined polishing times.
Polishing while repeatedly giving the drive of. In addition, it is also possible to measure the surface shape of the object to be polished in the course of the polishing process and control the polishing conditions based on the measured values. Furthermore, if the surface to be machined is already twisted in the pre-processing prior to this polishing step, it is possible to select the table rotation direction that matches the twisting direction, correct twisting, and then finish polishing by the above method It is. As described above, by this method, a high-precision surface having no twist on the surface to be processed can be finished in a short time. In this embodiment, the Oscar type polishing apparatus is used, but another apparatus may be used as long as the workpiece 3 and the polisher 2 can be relatively moved. In this embodiment, the workpiece 3 is a silicon nitride ceramic. However, the above polishing method can be applied to a workpiece formed of another ceramic or glass by changing the abrasive grain or polisher material. Can be adopted.

When processing a rod-shaped workpiece having a length of 540 mm, a width of 30 mm, and a height of 30 mm using this Oscar-type polishing apparatus, the rotation conditions of the rotary table 1 include the forward rotation A and the reverse rotation. The rotation speed of A 'is 3 to 5 rpm
m, the swing speed B of the workpiece is 2500 mm / mim to 3
500 mm / min, the pressing force P of the workpiece against the hard polisher 2 was set to 20 gf / cm ^2, and the workpiece was polished by repeatedly applying forward rotation A and reverse rotation A ′ to the polishing table every 2 to 8 hours. With a processing time of 16 hours, a high-precision surface with a surface accuracy of 0.15 μm or less and no twist was able to be finished. On the other hand, in the conventional method, satisfactory surface accuracy could not be obtained even if polishing was performed for about 30 hours while repeating the adjustment.

[0009]

In summary, the method for polishing a rod-shaped large-sized optical element according to the present invention is such that the polisher is processed by using a polishing apparatus having a function capable of driving in normal rotation and reverse rotation, thereby obtaining a twisted surface shape. It is possible to produce a high-precision surface shape without any material in a short time.

[Brief description of the drawings]

FIG. 1 is a plan view of a polishing apparatus as an embodiment according to the present invention.

FIG. 2 is a side view showing an arrangement of a workpiece and a holder.

3A is a diagram showing a torsion shape generated on the workpiece surface in the normal rotation of the polisher; FIG. 3B is a diagram showing a torsion shape generated on the workpiece surface in the reverse rotation of the polisher;

FIG. 4 is a diagram illustrating a conventional polishing method.

[Explanation of symbols]

 1: Rotary table 2: Resin hard polisher 3: Workpiece 4: Polishing frame 5: Load 6: Polishing ring 7: Station 8: Roller 9: Polishing liquid nozzle 10: Crank 11: Swing arm

Claims (4)

[Claims] 1. A polishing apparatus having a rotary table for rotating a polisher, a holding member for rotatably pressing and holding a workpiece on the polisher, a swinging member for giving a swinging motion to the holding member, and a polishing liquid supply member. A polishing apparatus characterized in that the rotation of the polisher alternately repeats normal rotation and reverse rotation during polishing. 2. The polishing apparatus according to claim 1, wherein the rotation speed of the polisher is 3 to 5 rpm, and the oscillation speed of the workpiece is 250.
0 mm / min to 3500 mm / min, 2 to 8
A polishing apparatus characterized in that a rotating table repeatedly rotates forward and backward at intervals of time. 3. A polisher is arranged on a rotary table, and an object to be polished is rotatably pressed against the polisher via a polishing liquid, and the rotary polisher is rotated to oscillate the object to be polished so that the object is polished. A polishing method for polishing an object to be polished, characterized in that the direction of rotation of the polisher is alternately repeated in forward and reverse rotation during polishing. 4. The polishing method according to claim 3, wherein the number of rotations of the polisher is 3 to 5 rpm, and the number of swings of the workpiece is 250.
0 mm / min to 3500 mm / min, 2 to 8
A polishing method characterized in that a rotating table repeatedly rotates forward and backward at intervals of time.