POLISHING METHOD AND HOLDER

BACKGROUND OF THE INVENTION

The present invention relates to a polishing method including a polishing process of polishing a surface to be polished of an object by relatively rotating a holding fixture and a polishing pad with the surface to be polished of the object held on the holding fixture being pressed against and placed in contact with the polishing pad, while supplying a polishing composition onto the polishing pad, and to the holding fixture used in the polishing method.

Conventionally, there has been known a method for polishing a surface to be polished of an object by relatively rotating a holding fixture and a polishing pad with the surface to be polished of the object held on the holding fixture being pressed against and placed in contact with the polishing pad, while supplying a polishing composition onto the polishing pad. This type of polishing method is practiced using a single-sided polishing apparatus or a double-sided polishing apparatus. For example, Japanese Laid-Open Patent Publication No. 2011-253896 discloses a method for polishing one surface of a semiconductor wafer using a single-sided polishing apparatus. Japanese Laid-Open Patent Publication No. 7-156061 discloses a method for simultaneously polishing both surfaces of a computer disk substrate including magnetic films on both sides using a double-sided polishing apparatus.

Hereinafter, the configuration of a single-sided polishing apparatus and a conventional polishing method using the single-sided polishing apparatus will be described with reference to FIGS. 12A and 12B. As illustrated in FIG. 12A, a single-sided polishing apparatus 10 is provided with a surface plate 11 that rotates around a rotational axis extending in the vertical direction. A polishing pad 12 is attached to the upper surface of the surface plate 11. A plurality of holding fixtures 13, each being provided with a polishing head 14 that rotates around a rotational axis P1 extending in the vertical direction, are disposed on the polishing pad 12. As illustrated in FIG. 12B, a plurality of (three) objects W are held on the lower surface of the polishing head 14 of each holding fixture 13 with the surface to be polished of each object W facing down. The objects W held on each holding fixture 13 are arranged around the rotational axis P1 of the corresponding polishing head 14 in the circumferential direction thereof.

As illustrated in FIG. 12A, the surface plate 11 and the polishing head 14 of each holding fixture 13 are rotated at predetermined rotational speeds with an object W held on the lower surface of the polishing head 14 of the holding fixture 13 being pressed against and placed in contact with a polishing pad 12, while supplying a polishing composition 15 onto the polishing pad 12. Consequently, the surface of the object W held on the holding fixture 13 is polished by the polishing pad 12 and the polishing composition 15.

SUMMARY OF THE INVENTION

Incidentally, polishing unevenness is caused in some cases on a polished surface of the object when the above-described conventional polishing method is used. Specifically, as illustrated in FIG. 12B, the polished amount of a location A (location positioned on the inner side of the object), which is close to the rotational axis P1 of the polishing head 14 is smaller in some cases than the polished amount of a location B (location positioned on the outer side of the object), which is far away from the rotational axis P1 of the polishing head 14.

This problem is considered to be attributable to the polishing composition 15 supplied to the surface to be polished of the object W. That is, since the polishing head 14 rotates around the rotational axis P1 during polishing, the polishing composition 15 supplied onto the polishing pad 12 gets into between the object W and the polishing pad 12 from the periphery of the polishing head 14 and flows inward in the radial direction of the polishing head 14. Accordingly, the location B of the object W, which is positioned radially outward of the polishing head 14, is polished using a fresh polishing composition 15. On the other hand, the location A, which is positioned radially inward of the polishing head 14, is polished using the polishing composition 15 that has already been used to polish the location B and is, therefore, not fresh since abrasive grains or the like of the composition are worn-out. As described above, a difference in the degree of wear of the polishing composition 15 (i.e., whether or not the polishing composition 15 is fresh) used to polish the respective locations of the object W is considered to be contributory to a location-by-location variation in the amount of polishing. The above-described problem of polishing unevenness occurs not only in polishing methods using a single-sided polishing apparatus but also in polishing methods using a double-sided polishing apparatus.

An objective of the present invention, which has been accomplished in view of such circumstances as described above, is to provide a polishing method and a holding fixture capable of preventing the occurrence of polishing unevenness.

In order to achieve the objective described above and in accordance with one aspect of the present invention, there is provided a polishing method including a polishing process of polishing a surface to be polished of an object by relatively rotating a holding fixture and a polishing pad with the surface to be polished of the object held on the holding fixture being pressed against and placed in contact with the polishing pad, while supplying a polishing composition onto the polishing pad. During the polishing process, the object held on the holding fixture turns around with the surface to be polished of the object facing the polishing pad to change the orientation of the object.

The polishing process preferably includes temporarily stopping an operation to polish the surface to be polished of the object to restart the operation to polish the surface to be polished of the object after changing the orientation of the object.

The object is preferably one of a plurality of objects to be polished held on the holding fixture.

The surface to be polished of the object may be a curvilinear surface. In that case, the surface to be polished of the object is preferably polished while pressing the object against the polishing pad and deforming the polishing pad into a shape conforming to the surface to be polished, which is the curvilinear surface.

The surface to be polished of the object may be composed of a plurality of surfaces. In that case, the surface to be polished of the object is preferably polished while pressing the object against the polishing pad and deforming the polishing pad into a shape conforming to the surface to be polished, which is composed of the plurality of surfaces.

The polishing process is preferably carried out by disposing a spacer between the holding fixture and the object and placing the surface to be polished of the object in a state of projecting toward the polishing pad.

In order to achieve the objective described above and in accordance with another aspect of the present invention, there is provided a holding fixture used in a polishing method of polishing a surface to be polished of an object by relatively rotating the holding fixture and a polishing pad with the surface to be polished of the object held on the holding fixture being pressed against and placed in contact with the polishing pad, while supplying a polishing composition onto the polishing pad. The holding fixture is provided with a polishing head for holding the object; and a rotating mechanism for turning around the object held on the polishing head with the surface to be polished of the object facing the polishing pad to change the orientation of the object.

The rotating mechanism is preferably provided with a rotating table onto which the object is fixed.

The holding fixture is preferably further provided with a spacer disposed between the rotating table and the object to project the surface to be polished of the object toward the polishing pad.

The rotating table is preferably arranged so as to project from the polishing head toward the polishing pad.

The polishing head is preferably configured to be able to hold a plurality of objects to be polished.

Other aspects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings illustrating examples of the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are illustrations of surfaces to be polished of objects;

FIG. 2 is a side view and a partial cross-sectional view of a holding fixture;

FIG. 3 is a cross-sectional view illustrating a state of an object to be polished being pressed against and placed in contact with a polishing pad;

FIGS. 4A, 4B, 4C, and 4D are schematic views used to describe the orientations of objects to be polished in a polishing process;

FIG. 5 is an illustration of a holding fixture provided with a rotating mechanism;

FIG. 6 is another illustration of a holding fixture provided with a rotating mechanism;

FIG. 7 is an illustration of a holding fixture and a spacer;

FIG. 8 is an illustration of a holding fixture provided with a rotating mechanism and a spacer;

FIG. 9 is an illustration of a holding fixture provided with a rotating mechanism;

FIGS. 10A, 10B, and 10C are illustrations of surfaces to be polished of objects;

FIGS. 11A and 11B are illustrations of examples;

FIG. 12A is an illustration of a polishing method and a single-sided polishing apparatus; and

FIG. 12B is a bottom view of a holding fixture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, one embodiment of the present invention will be described.

First, a description will be made of an object W to be polished using a polishing method of the present embodiment.

As the object W to be polished, it is possible to use an object composed of metal, synthetic resin, ceramics, or a composite thereof. Examples of the metal include magnesium, aluminum, titanium, iron, nickel, cobalt, copper, zinc, manganese, and alloys consisting primarily of at least one of these metals. Examples of the synthetic resin include thermosetting resins, such as phenol resin, epoxy resin, urethane resin, and polyimide, and thermoplastic resins, such as polyethylene, polypropylene, and acrylic resin. Examples of the ceramics include oxides, carbides, nitrides, and borides of silicon, aluminum, zirconium, calcium, and barium, in addition to pottery, glass, and fine ceramics.

The outer shape of the object W is not limited in particular but may be polygonal, such as triangular and quadrangular, circular, elliptical, or annular.

The object W includes, as one surface thereof, a surface to be polished. The shape of the surface to be polished is not limited in particular. Specifically, as illustrated in FIG. 1A, the object W may include a flat surface W1 to be polished. Alternatively, as illustrated in FIG. 1B, the object W may include a surface W2 to be polished part or the entirety of which is a curvilinear surface. The surface W2 may be curved so as to be convexed toward the outer side thereof or so as to be convexed toward the inner side thereof, or may have a shape combining these shapes. Yet alternatively, as illustrated in FIG. 1C, the object W may include a surface W3 to be polished composed of a plurality of surfaces W3a, W3b, and W3c. The surface W3 may be polyhedrally shaped so as to be convexed toward the outer side thereof or so as to be convexed toward the inner side thereof, or may have a shape combining these shapes. One or more of the surfaces constituting the surface W3 may be a curvilinear surface. The surface W3 has only to be composed of two or more surfaces.

Next, a description will be made of a polishing apparatus used in the polishing method of the present embodiment.

Such a conventional single-sided polishing apparatus 10 as illustrated in FIGS. 12A and 12B can be used in the polishing method of the present embodiment. The single-sided polishing apparatus 10 is provided with a surface plate 11 that rotates around a rotational axis extending in the vertical direction. The surface plate 11 is coupled with an unillustrated motor and rotates in response to driving of the motor.

A polishing pad 12 is attached to the upper surface of the surface plate 11. The polishing pad 12 can be of any type of polishing pad suited to polish the surface to be polished of the object W according to, for example, the material of the object W and the shape of the surface to be polished of the object W. The polishing pad 12 preferably has a surface shape capable of uniformly coming into contact with the entire surface to be polished of the object W. From a similar point of view, the thickness and hardness of the polishing pad 12 are set as appropriate.

Specific examples of the material of the polishing pad 12 include fabric, nonwoven, resinated nonwoven, synthetic leather, synthetic resin foams, and composites of these materials. The polishing pad 12 may be composed of only one of the specific examples described above or may be composed of a combination of some of the specific examples described above.

The hardness of the polishing pad 12 is not limited in particular. The polishing pad 12 has a Shore A hardness of preferably 5 or higher, however, if the surface to be polished of the object W has a non-planar shape, for example, a curvilinear surface or a polyhedral shape composed of a plurality of surfaces. The Shore A hardness of the polishing pad 12 can be measured using a rubber hardness meter (A-type) compliant with the Japanese Industrial Standard JIS K6253 after the polishing pad 12 is left to stand for 60 minutes or longer in a dry condition with a humidity of 20 to 60% and at room temperature.

In the single-sided polishing apparatus 10 illustrated in FIG. 12A, a plurality of holding fixtures 13, each being provided with a polishing head 14 that rotates around a rotational axis P1 extending in the vertical direction, are disposed above the polishing pad 12. The polishing head 14 is coupled with an unillustrated motor and rotates in response to driving of the motor.

As illustrated in FIG. 12B, a plurality of objects W are held on the lower surface of each polishing head 14 with the surface to be polished of each object facing down (outward). A holding section that, though excluded from the drawings, includes recesses into which the respective objects W are fitted and a mechanism onto which the objects W are vacuum-adsorbed is provided on the lower surface of each polishing head 14. The objects W are thus held by the holding sections. The objects W held on the lower surface of each polishing head 14 are arranged around the rotational axis P1 of the polishing head 14 in the circumferential direction thereof.

Next, the polishing method of the present embodiment will be described. Here, a description will be made of a case where such an object W as illustrated in FIG. 1B, specifically, an object W having a square outer shape and including a curvilinear surface W2 to be polished is polished.

As illustrated in FIGS. 2 and 12B, three objects W are held on the lower surface of a polishing head 14a of a holding fixture 13, so that the surface W2 to be polished of each object W faces down. Then, the holding fixture 13 is moved down toward a polishing pad 12 to press the surface W2 of the object W held on the lower surface of the polishing head 14 against the polishing pad 12 and place the surface W2 in contact therewith.

At this time, the polishing pad 12 deforms into a shape conforming to the surface W2, as illustrated in FIG. 3, as the result of the curvilinear surface W2 being pressed against the polishing pad. Consequently, the entire surface W2 comes into contact with the polishing pad 12. In other words, the holding fixture 13 is moved down to apply a load (polishing load) until the polishing pad 12 deforms into the shape conforming to the surface W2 and comes into contact with the entire surface W2. In FIGS. 2 and 3, the surface plate 11 is excluded from the drawings.

Subsequently, as illustrated in FIG. 12A, the surface plate 11 and the polishing head 14 of each holding fixture 13 are rotated at the respective predetermined rotational speeds, while supplying a polishing composition 15 onto the polishing pad 12. In this way, the polishing pad 12 attached onto the surface plate 11 and objects W held on the polishing head 14 of each holding fixture 13 relatively rotate in close contact with each other. Thus, the surface W2 of each object W is polished by the polishing pad 12 and the polishing composition 15 (polishing process).

As the polishing composition 15, it is possible to use a known polishing composition, specifically, a processing liquid, such as a polishing liquid, a lapping liquid, and a grinding fluid, primarily containing abrasive grains and water. Examples of the abrasive grains include alumina, silica, ceria, diamond, and silicon carbide. The polishing composition 15 may contain only one type or more than one type of the abrasive grains described above. The polishing composition 15 may contain other components, such as a surfactant, a polymer material, a pH adjuster, an antiscattering agent, a thickening agent, and a redox agent.

Various conditions used in the polishing process described above are not limited in particular but may be set as appropriate according to, for example, the material and shape of the object W. For example, the flow rate of the polishing composition 15 supplied onto the polishing pad 12 is preferably 10 ml/min or higher. The rotational speed of the surface plate 11 and the rotational speed of the polishing head 14 of the holding fixture 13 are preferably such that a linear velocity is within the range from 10 m/min to 300 m/min on the surface to be polished of each object W. The polishing load is preferably 0.05 kg/cm²to 10 kg/cm²per a unit area of the surface to be polished of each object W.

Also in the polishing method of the present embodiment, both temporarily stopping a polishing operation, i.e., an operation to relatively rotate the objects W and the polishing head 14 while supplying the polishing composition 15 onto the polishing pad 12, and changing the orientations of the objects W held on the polishing head 14 of each holding fixture 13 are performed during a polishing process when a predetermined period of time elapses.

Specifically, as illustrated in FIGS. 4A and 4B, each object W is rotated 90° clockwise around an axial line P2 parallel to the rotational axis P1 of each holding fixture 13, while maintaining the state of the surface W2 facing the polishing pad 12. That is, each object W is changed from the holding condition illustrated in FIG. 4A to the holding condition illustrated in FIG. 4B to change the orientation of the object W. For ease of understanding, a star is put as a mark of a location of the surface to be polished of each object W initially positioned close to the rotational axis P1 of the holding fixture 13 in FIGS. 4A to 4D. The changing of the orientation of each object W is performed by temporarily detaching the objects W from the polishing head 14 of each holding fixture 13, and then once again holding the objects W on the polishing head 14 with the orientations of the objects W changed.

After the objects W are changed in orientation, a polishing operation is performed under the holding condition illustrated in FIG. 4B. Thereafter, each object W is changed from the holding condition illustrated in FIG. 4B to the holding condition illustrated in FIG. 4C to change the orientation of the object W in the same way as described above, when another period of the above-mentioned predetermined time elapses. Then, a polishing operation is performed under the holding condition illustrated in FIG. 4C. Thereafter, each object W is changed from the holding condition illustrated in FIG. 4C to the holding condition illustrated in FIG. 4D to change the orientation of the object W when yet another period of the above-mentioned predetermined time elapses. Then, a polishing operation is performed for the above-mentioned predetermined period of time under the holding condition illustrated in FIG. 4D. Accordingly, in the present embodiment, the objects W are polished under each of the four holding conditions in which the orientation of each object W differs in increments of 90°.

Next, the action of the present embodiment will be described.

As illustrated in FIGS. 4A to 4D and in accordance with the polishing method of the present embodiment, the orientations of objects W held on the polishing head 14 of each holding fixture 13 are changed during a polishing process. Thus, polishing operations are performed under respective holding conditions in which the orientations of the objects W differ. Accordingly, during a polishing process, a specific location of the surface to be polished of each object W neither continues to be placed in a position (position radially outward of the polishing head 14) to which a fresh polishing composition 15 is supplied and in which the amount of polishing is relatively large nor continues to be placed in a position (position radially inward of the polishing head 14) to which a non-fresh polishing composition 15 is supplied and in which the amount of polishing is relatively small. This therefore prevents the occurrence of polishing unevenness in which a specific location of the surface to be polished of each object W is larger or smaller in the amount of polishing than other locations.

Next, the advantageous effects of the present embodiment will be described.

(1) The polishing method includes a polishing process of polishing a surface to be polished of an object W by rotating a holding fixture 13 and a polishing pad 12 with the surface to be polished of the object W held on the holding fixture 13 being pressed against and placed in contact with the polishing pad 12, while supplying a polishing composition 15 onto the polishing pad 12. During the polishing process, the object W held on the holding fixture 13 turns around with the surface W2 to be polished of the object W facing the polishing pad 12 to change the orientation of the object W. Accordingly, the polishing method prevents the occurrence of polishing unevenness in which a specific location of the surface to be polished of each object W is larger or smaller in the amount of polishing than other locations.

(2) The orientation of each object W is changed so that each location of the surface to be polished of the object W switches in rotation among a position (position radially outward of the polishing head 14) where the amount of polishing is relatively large, a position (position radially inward of the polishing head 14) where the amount of polishing is relatively small, and a position intermediate between those positions. If the location of each object W marked with a star in FIGS. 4A to 4D is taken for example, the location is placed in a position where the location is relatively less likely to be polished under the condition illustrated in FIG. 4A, the location is placed in a position where the location is relatively more likely to be polished under the condition illustrated in FIG. 4C, and the location is placed in a position intermediate between those positions under the conditions illustrated in FIGS. 4B and 4D.

Accordingly, the entire surface to be polished of each object W is likely to be polished more uniformly, compared with a case where each object W is rotated in increments of 180°, rather than 90°, to change the orientation of the object W, so that the object W switches between a position where the amount of polishing is relatively small and a position where the amount of polishing is relatively large. As a result, the occurrence of polishing unevenness is prevented more effectively.

(3) The polishing process includes temporarily stopping the operation to polish the surface to be polished of the object W, changing the orientation of the object W, and then restarting the operation to polish the surface to be polished of the object W. Accordingly, it is possible to use an existing single-sided polishing apparatus 10 as is.

(4) The object W includes a curvilinear surface W2 to be polished, and the surface W2 is polished while pressing the object W against the polishing pad 12 to deform the polishing pad 12 into a shape conforming to the surface W2 to be polished. In this case, the area of contact of the polishing pad 12 with the surface W2 increases, and the polishing pad 12 comes into very close contact with the surface W2. For this reason, a polishing composition 15 having got into between the object W and the polishing pad 12 has difficulty in flowing therebetween and is less likely to be supplied inward in the radial direction of the polishing head 14 during the polishing process. As a result, the problem in which the amount of polishing of a location A (positioned radially inward of the polishing head 14), which is close to the rotational axis P1 of the polishing head 14 is smaller than the amount of polishing of a location B (positioned radially outward of the polishing head 14), which is far away from the rotational axis P1 of the polishing head 14 develops remarkably (see FIG. 12B).

Accordingly, the effect of suppressing polishing unevenness by the polishing method of the present embodiment is especially significant when the surface W2 is polished while deforming the polishing pad 12 into a shape conforming to the surface W2. The same effect is available in a case where the object W includes a plurality of surfaces W3 to be polished, and the surfaces W3 are polished while pressing the object W against the polishing pad 12 to deform the polishing pad 12 into a shape conforming to the surfaces W3 to be polished.

The present embodiment can be modified as described below and put into effect.

- The number of objects W held on each holding fixture 13 is not limited in particular, but may be two or less or four or more. In addition, the number of objects W may differ for each holding fixture 13.
- In the embodiment described above, each holding fixture 13 is rotated by means of motor drive. Methods for rotating the holding fixture 13 are not limited to this method, however. For example, holding fixtures 13 may be disposed on the polishing pad 12 with the polishing head 14 being rotatable, and then the polishing pad 12 may be rotated. In this case, the polishing head 14 of each holding fixture 13 rotates correspondingly with the rotation of the polishing pad 12.
- In the embodiment described above, both the holding fixtures 13 and the polishing pad 12 are rotated in the polishing process. Alternatively, the embodiment may be configured to relatively rotate the holding fixtures 13 and the polishing pad 12. That is, only the holding fixtures 13 may be rotated without rotating the polishing pad 12, or only the polishing pad 12 may be rotated without rotating the holding fixtures 13.

The problem of polishing unevenness in objects W due to the difference in the degree of wear of the polishing composition 15 (i.e., whether or not the polishing composition 15 is fresh) arises also when only the polishing pad 12 is rotated without rotating the holding fixtures 13. That is, if only the polishing pad 12 is rotated, the polishing composition 15 supplied onto the polishing pad 12 flows arcuately along the rotational direction of the polishing pad 12 and between each object W held on the holding fixture 13 and the polishing pad 12.

Here, assume that in the example illustrated in FIG. 12B, the polishing composition 15 flows arcuately from the upper side of the drawing toward the lower side thereof. At this time, the location B of each object W positioned on the upper side is polished using a fresh polishing composition 15, whereas the location A is polished using a non-fresh polishing composition 15 that has been used to polish the location B, and therefore, the abrasive grains and the like of which are worn-out.

Conversely, assume that the polishing composition 15 flows arcuately from the lower side of the drawing toward the upper side thereof. At this time, the location A of each object W positioned on the upper side is polished using a fresh polishing composition 15, whereas the location B is polished using a non-fresh polishing composition 15 that has been used to polish the location A, and therefore, the abrasive grains and the like of which are worn-out.

In this way, the degree of wear of the polishing composition 15 used to polish the respective locations of each object W differs also when only the polishing pad 12 is rotated without rotating the holding fixtures 13. Thus, polishing unevenness occurs in the object W due to this difference. Such polishing unevenness caused when only the polishing pad 12 is rotated can also be prevented from occurring by changing the orientation of the object W during the polishing process.

- In the embodiment described above, the orientation of each object W is changed three times in increments of 90° in the polishing process. The orientation angle of each object W changed at a time is not limited to 90°, however. The number of times with which the orientation of the object W is changed is not limited to three times, either. For example, the orientation of the object W may be changed twice in increments of 120°, or may be changed by 180° only once.

An angle S by which the orientation of each object W is changed at a time and the number of times T with which the orientation of each object W is changed are preferably in the relationship satisfying “S(T+1)=360”. In this case, it is possible to more effectively prevent the occurrence of polishing unevenness. The angle by which the orientation of each object W is changed may be varied for each operation to change the orientation of the object W.

- In the embodiment described above, the surface to be polished is polished while pressing each object W against the polishing pad 12 to deform the polishing pad 12 into a shape conforming to the surface to be polished. Alternatively, however, the surface to be polished may be polished by pressing each object W against the polishing pad 12 to the extent of not deforming the polishing pad 12 and bringing the object W into contact therewith. This polishing method is suited, for example, for such an object W including a flat surface W1 to be polished as illustrated in FIG. 1A.
- In the embodiment described above, the orientation of each object W is changed by temporarily detaching the objects W from the polishing head 14 of each holding fixture 13, and then once again holding the objects W on the polishing head 14 with the orientations of the objects W changed. The orientation of the object W may be changed by other methods, however. For example, a holding fixture 13 provided with a rotating mechanism for changing the orientation of each object W may be used and the orientation of the object W may be changed by operating the rotating mechanism, as illustrated in FIGS. 5 and 6.

In the example illustrated in FIG. 5, an insertion hole 21 vertically penetrating through the polishing head 14 of each holding fixture 13 is formed in the polishing head 14, and a circular housing recess 22 centered around the opening of the insertion hole 21 is formed on the lower surface of the polishing head 14. A rotational axis 23 is inserted through the insertion hole 21. A circular plate-like rotating table 24 received in the housing recess 22 is fixed on the lower end of the rotational axis 23 projecting into the housing recess 22. An operating member 25 is fixed on the upper end of the rotational axis 23 projecting from the upper surface of the polishing head 14. In this case, the rotating mechanism is configured with the rotational axis 23, the rotating table 24, and the operating member 25.

In the configuration of FIG. 5, an object W is held on the lower surface of the rotating table 24. An operator turns around the operating member 25 when changing the orientation of the object W. Consequently, the rotating table 24 and the object W held thereon turn around in conjunction with each other by way of the rotational axis 23, thereby changing the orientation of the object W. According to the configuration described above, the object W need not be detached from the polishing head 14 of the holding fixture 13 when changing the orientation of the object W. Thus, it is possible to easily change the orientation of the object W.

In the example illustrated in FIG. 6, the circular housing recess 22 is formed in the lower surface of the polishing head 14 and the circular plate-like rotating table 24 is received in the housing recess 22. The rotational axis of a motor 26 fitted in the polishing head 14 is fixed on the rotating table 24. The holding fixture 13 is provided with a control unit (not illustrated) for controlling the revolution of the motor 26. In this case, the rotating mechanism is configured with the rotating table 24, the motor 26, and the control unit.

In the configuration of FIG. 6, an object W is held on the lower surface of the rotating table 24. The control unit rotates the motor 26 when the orientation of the object W is changed. Consequently, the rotating table 24 and the object W held thereon turn around, thereby changing the orientation of the object W.

According to the configuration of FIG. 6, it is possible to change the orientation of the object W while performing a polishing operation when changing the orientation of the object W. Accordingly, the polishing operation need not be stopped temporarily, and therefore, it is possible to shorten the time required for a polishing process.

- As illustrated in FIG. 7, a polishing operation may be performed with a spacer 30 disposed between the polishing head 14 of the holding fixture 13 and the object W. That is, the polishing operation may be performed with the object W held on the polishing head 14 through the spacer 30. In this case, the object W largely projects toward the polishing pad 12 due to the presence of the spacer 30. Accordingly, it is easy to press the object W against the polishing pad 12 when polishing a plurality of surfaces W3 or a curvilinear surface W2 (see FIG. 1B), even if the object W is small in thickness. It is therefore easy to deform the polishing pad 12 into a shape conforming to the surface to be polished.

The same holds true when a holding fixture 13 including a rotating mechanism is used. As illustrated in FIG. 8, a polishing operation may be performed with the spacer 30 disposed between the rotating table 24 and the object W. The same effect is available by using a holding fixture 13 on which the rotating table 24 is mounted to project from the lower surface of the polishing head 14, as illustrated in FIG. 9, instead of using the spacer 30.

- In a double-sided polishing method for polishing both sides of an object W using a double-sided polishing apparatus, an operation to change the orientations of the objects W may be performed during a polishing process in the same way as in the embodiment described above.

In this case, such an object including surfaces to be polished on both sides as illustrated in FIG. 10A, 10B, or 10C is used as the object W. FIG. 10A illustrates an object W including flat surfaces W1 to be polished on upper and lower sides. FIG. 10B illustrates an object W including surfaces W2 to be polished, part or the entirety of each of which is a curvilinear surface, on upper and lower sides. FIG. 10C illustrates an object W including surfaces W3 to be polished, each of which is composed of a plurality of surfaces W3a, W3b, and W3c, on upper and lower sides. Although both the upper and lower sides of each object W have the same shape in the examples illustrated in FIG. 10A to FIG. 10C, the upper and lower sides of each object W may differ in shape from each other.

As the double-sided polishing apparatus, it is possible to use such a known double-sided polishing apparatus as disclosed in Japanese Laid-Open Patent Publication No. 7-156061. The double-sided polishing apparatus is provided with a pair of polishing pads oppositely disposed on the upper and lower sides of the apparatus; and a holding fixture for holding an object W to be polished between these polishing pads. The holding fixture is, for example, a plate-like member including a holding hole corresponding in shape to the outer shape of the object W. The object W is inserted in the holding hole and held by means of interaction, such as engagement, between the inner circumferential surface of the holding hole and a side surface Ws of the object W (see FIGS. 10A to 10C), with both surfaces to be polished of the object W projecting to the upper and lower sides of the holding fixture.

In the double-sided polishing method, a polishing process of polishing two surfaces of the object W is carried out by relatively rotating the holding fixture and the polishing pads with both surfaces of the object W held on the holding fixture being pressed against and placed in contact with the upper and lower polishing pads, while supplying a polishing composition onto the polishing pads. The object W is temporarily detached from the holding hole of the holding fixture in the course of this polishing process. Thereafter, the object W is inserted in the holding hole with the orientation of the object W changed, and is once again held on the holding fixture, as illustrated in, for example, FIGS. 4A to 4D. Then, the polishing operation is restarted. If an operation to change the orientation of the object W is performed during the polishing process, as described above, in the double-sided polishing method, it is possible to prevent polishing unevenness from occurring in both surfaces to be polished of the object W in the same way as in the embodiment described above.

Next, the present invention will be described more specifically by referring to Examples and Comparative Examples.

Examples

Using the single-sided polishing apparatus illustrated in FIG. 12A, a surface to be polished of each object was polished by rotating a holding fixture and a polishing pad (surface plate) with the surface to be polished of the object held on the holding fixture being pressed against and placed in contact with the polishing pad, while supplying a polishing composition onto the polishing pad. Specific polishing conditions are as shown in Table 1 below.

TABLE 1

Polishing machine
Type of polishing machine: Single-sided polishing

(polishing
machine

apparatus)
Surface plate diameter: φ914 mm

Holding fixture (polishing head) diameter: 360 mm

Polishing pad
Suede-based polishing pad to the underlying layer of

which a resin sponge is attached

Polishing load
530 g/cm²

Rotating speed
30 rpm

of surface plate

Linear velocity
67 m/min

Polishing
Abrasive grains: CeO₂(particle diameter 2.1 μm)

composition
Abrasive grain content: 100 g/L

pH: 7.0

Polishing
80 ml/min

composition

supply rate

Such a flat glass plate (56 mm in depth×60 mm in width×0.86 mm in thickness) including a curvilinear surface to be polished as illustrated in FIG. 1B was used as the object to be polished. The holding conditions of the object with respect to the holding fixture are as illustrated in FIG. 11A. The object was pressed against the polishing pad under a polishing load with which the polishing pad deformed into a shape conforming to the surface to be polished.

The rotation of the surface plate and the holding fixture was stopped in six minutes after the start of polishing operation. Then, the object held on a holding fixture was turned around 180° and changed from the holding condition illustrated in FIG. 11A to the holding condition illustrated in FIG. 11B, thereby changing the orientation of the object. Then, polishing was restarted, and finished after a lapse of another six minutes.

Thereafter, a surface roughness measurement was made for the respective locations WA, WB, and WC of the polished surface of each object illustrated in FIGS. 11A and 11B. The location WA is an edge of the curvilinear surface of the object W and is a location positioned radially inward of the holding fixture at the time of a first polishing operation and positioned radially outward of the holding fixture at the time of a second polishing operation. The location WB is an edge of the curvilinear surface of the object W and is a location positioned radially outward of the holding fixture at the time of the first polishing operation and positioned radially inward of the holding fixture at the time of the second polishing operation. The location WC is a middle portion of the curvilinear surface of the object W and is a location positioned radially at the center of the holding fixture at the time of both the first and second polishing operations.

Table 2 shows the results of surface roughness measurement of the respective locations described above. For reference, Table 2 also shows the surface roughness of each location before polishing. Surface roughness measurements were conducted using the SURFCOM 1500DX surface roughness measuring instrument made by Tokyo Seimitsu Co., Ltd under the conditions of “standard: JIS'94, filter cut off: 250 μm, measurement length: 1 mm”.

Comparative Examples

Polishing operation was performed under the same polishing conditions of Examples using the same object as in Examples. In Comparative Examples, however, polishing was finished after the object was polished for 10 minutes under the holding condition illustrated in FIG. 11A, without performing the operation to change the orientation of the object. Thereafter, the surface roughness of the respective locations WA, WB, and WC of the polished surface of the object was measured in the same way as in Examples. Table 2 shows the results of the measurement.

TABLE 2

Measured
Surface roughness [nm]

location
Before polishing
Examples
Comparative Examples

WA
579
25
575

WB
606
28
13

WC
130
1.4
1.5

As shown in Table 2, in accordance with Comparative Examples, in which the operation to change the orientation of the object was not performed, polishing of the location WA (location positioned radially inward of the holding fixture) progressed less compared with the location WB (location positioned radially outward of the holding fixture). Thus, polishing unevenness occurred between the location WA and the location WB. In contrast, in accordance with Examples, in which the operation to change the orientation of the object was performed, the location WA and the location WB were substantially the same in surface roughness. Thus, no polishing unevenness occurred between the location WA and the location WB.

The foregoing description is intended to be illustrative and not restrictive. For example, the above-described examples (or one or a plurality of aspects thereof) may be used in combination with each other. By examining the foregoing description, other embodiments may be used by, for example, a person skilled in the art. In the detailed description presented above, various characteristic features may be grouped together in order to simplify the disclosure. This should not be construed as unclaimed characteristic features of the disclosure being intended to be essential for any claims for patent. Rather, the subject matter of the present invention may lie in less than all characteristic features of the specific embodiments disclosed. Accordingly, the appended claims are incorporated into the detailed description, with each claim claiming itself as a separate embodiment. The scope of the present invention should be defined by reference to the appended claims for patent and along with the full range of equivalents to which the appended claims are entitled.

POLISHING METHOD AND HOLDER

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