Polishing apparatus

An upper polishing plate is moved downward until facing a lower polishing plate to polish a work piece. The upper polishing plate is rotated in a horizontal plane together with a first elastic member, a second elastic member, an outer member and a connecting member. A pressure difference between a first pressing force pressing the outer member or an inner member upward and a second pressing force pressing the outer member or the inner member downward, which is produced in a first closed space by supplying a compressed fluid into and discharging the same from the first closed space, is adjusted, so that a third pressing force of the upper polishing plate, which presses a work piece, can be adjusted.

BACKGROUND OF THE INVENTION

The present invention relates to a polishing apparatus for polishing thin work pieces, e.g., wafers.

A conventional polishing apparatus is disclosed in Japanese Patent Gazette No. 11-48126. The polishing apparatus is shown inFIG. 7. In the polishing apparatus10, an upper polishing plate12is vertically moved by a cylinder unit14provided on a base13together with a rod14a, a connecting section14b, a rotary plate15and connecting rods16. The connecting section14includes a suitable mechanism, e.g., universal joint, for rotating the upper polishing plate12along an upper face of a lower polishing plate18. Keys19are engaged with key grooves of a rotor head20. With this structure, the upper polishing plate12is rotated in a horizontal plane by a motor with a shaft20a, gears and a reduction gear unit21. On the other hand, the lower polishing plate18is rotated by the motor22with a hollow shaft18a, gears and the reduction gear unit21. A sun gear23is rotated by the motor22with a shaft23a, gears and the reduction gear unit21. An internal gear24is also rotated by the motor22with a shaft24a, gears and the reduction gear unit21. Carriers25are engaged with the sun gear23and the internal gear24, so that the carriers25perform sun-and-planet motion. A work piece26is fitted in a through-hole of each carrier25and moved together with the carrier25. By rotating the polishing plates12and18, both surfaces of each work piece26can be polished.

In the apparatus10, an upper polishing plate12is suspended by a cylinder unit14while polishing work pieces26. A pressing force of the upper polishing plate12, which is applied to the work pieces26, is adjusted by adjusting pressure of a pressurized fluid, which is supplied to a lower cylinder chamber of the cylinder unit14. By adjusting the pressure, the pressing force from the upper polishing plate12to the work pieces26can be adjusted in a range, which is from a force smaller than weight of the upper polishing plate12to a force equal to the weight of the upper polishing plate12. Note that, the pressing force greater than the weight of the upper polishing plate12can be applied to the work pieces26by supplying the pressurized fluid to an upper cylinder chamber of the cylinder unit14.

However, the conventional polishing apparatus10has following disadvantages.

Firstly, a piston, which is provided to an upper end of a rod14aof the cylinder unit14, slides on an inner face of a cylinder of the cylinder unit14. Therefore, friction is generated between a seal member of the piston and the inner face of the cylinder, so that it is difficult to precisely control the vertical movement of the upper polishing plate12. Especially, when the cylinder unit14is actuated from a stopping state, friction coefficient is changed from a high static frictional coefficient to a low dynamic frictional coefficient, so that knocking easily occurs.

Driving forces for driving the polishing plates12and18, the sun gear23and the internal gear24are transmitted by various gears, and the keys19are engaged with the key grooves of the rotor head20connected to the upper polishing plate12. Therefore, backlashes are occurred between gears and between keys19and the key grooves, so that vibrations easily occur therebetween. If the work pieces26are thin, they will be damaged or broken by the vibrations.

SUMMARY OF THE INVENTION

The present invention has been invented to solve the disadvantages of the conventional polishing apparatus.

An object of the present invention is to provide a polishing apparatus, which is capable of linearly and precisely controlling a pressing force applied from an upper polishing plate to a work piece and which is capable of suitably polishing a thin work piece.

To achieve the object, the present invention has following structures.

Namely, the polishing apparatus of the present invention comprises:

a lower polishing plate;

an upper polishing plate being relatively moved with respect to the lower polishing plate so as to polish a work piece clamped between the lower polishing plate and upper polishing plate; and

a holding mechanism for holding the upper polishing plate,

wherein the holding mechanism includes:an inner member;an outer member having an upper open end and a lower open end, the outer member accommodating the inner member;a first elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the first elastic member connecting an upper part of the inner member and an upper part of the outer member and closing the upper open end of the outer member;a second elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the second elastic member connecting a lower part of the inner member and a lower part of the outer member and closing the lower open end of the outer member;a first closed space being enclosed by an outer face of the inner member, an inner face of the outer member, the first elastic member and the second elastic member; anda fluid supply section supplying a pressurized fluid into the first closed space,

one of the inner member and the outer member is connected to a rotary drive unit, the other is connected to the upper polishing plate, and

the upper polishing plate is rotated in a horizontal plane, by the rotary drive unit, with the inner member and the outer member, and a pressure difference between a first pressing force pressing the outer member or the inner member upward and a second pressing force pressing the outer member or the inner member downward, which is produced in the first closed space by supplying the compressed fluid into and discharging the same from the first closed space, is adjusted so as to adjust a third pressing force of the upper polishing plate, which presses the work piece, while polishing the work piece.

Another polishing apparatus of the present invention comprises:

a lower polishing plate;

an upper polishing plate being relatively moved with respect to the lower polishing plate so as to polish a work piece clamped between the lower polishing plate and upper polishing plate; and

a holding mechanism for holding the upper polishing plate,

wherein the holding mechanism includes:an inner member;an outer member having an upper open end and a lower open end, the outer member accommodating the inner member;a first elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the first elastic member connecting an upper part of the inner member and an upper part of the outer member and closing the upper open end of the outer member;a second elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the second elastic member connecting a lower part of the inner member and a lower part of the outer member and closing the lower open end of the outer member;a first closed space being enclosed by an outer face of the inner member, an inner face of the outer member, the first elastic member and the second elastic member;a fluid supply section supplying a pressurized fluid into the first closed space;a rotary drive unit to which one of the inner member and the outer member is connected;a connecting member connecting the other of the inner member and the outer member to the upper polishing plate; anda vertical drive unit being provided above the upper polishing plate, the vertical drive unit vertically moving the rotary drive unit and the upper polishing plate with respect to the lower polishing plate, and

the upper polishing plate is downwardly moved to face the lower polishing plate by the vertical drive unit, the upper polishing plate is rotated in a horizontal plane, by the rotary drive unit, with the inner member, the outer member and the connecting member, and a pressure difference between a first pressing force pressing the outer member or the inner member upward and a second pressing force pressing the outer member or the inner member downward, which is produced in the first closed space by supplying the compressed fluid into and discharging the same from the first closed space, is adjusted so as to adjust a third pressing force of the upper polishing plate, which presses the work piece, while polishing the work piece.

In the polishing apparatus, the first pressing force may be greater than the second pressing force, and

a range of the third pressing force may be from a force smaller than a weight of the upper polishing plate to a force equal to the weight thereof.

In the polishing apparatus, the first pressing force may be smaller than the second pressing force, and

a range of the third pressing force may be from a force greater than a weight of the upper polishing plate to a force equal to the weight thereof.

In the polishing apparatus, a torque for rotating one of the inner member and the outer member may be transmitted to the other by the first elastic member and the second elastic member.

In another case, the torque for rotating one of the inner member and the outer member may be transmitted to the other by a transmission pin.

Further, the polishing apparatus of the present invention comprises:

a lower polishing plate;

an upper polishing plate being relatively moved with respect to the lower polishing plate so as to polish a work piece clamped between the lower polishing plate and upper polishing plate; and

a holding mechanism for holding the upper polishing plate,

wherein the holding mechanism includes:an inner member;an outer member having an upper open end and a lower open end, the outer member accommodating the inner member;a third elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the third elastic member connecting an upper part of the inner member and an upper part of the outer member and closing the upper open end of the outer member;a fourth elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the fourth elastic member connecting a mid part of the inner member and a mid part of the outer member and closing a gap therebetween;a fifth elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the fifth elastic member connecting a lower part of the inner member and a lower part of the outer member and closing the lower open end of the outer member;a second closed space being enclosed by an outer face of the inner member, an inner face of the outer member, the third elastic member and the fourth elastic member;a third closed space being enclosed by the outer face of the inner member, the inner face of the outer member, the fourth elastic member and the fifth elastic member;a first fluid supply section supplying a pressurized fluid into the second closed space;a second fluid supply section supplying a pressurized fluid into the third closed space,

one of the inner member and the outer member is connected to a rotary drive unit, the other is connected to the upper polishing plate, and

the upper polishing plate is rotated in a horizontal plane, by the rotary drive unit, with the inner member, the outer member and a connecting member, and a pressure difference between a first pressing force pressing the outer member or the inner member upward and a second pressing force pressing the outer member or the inner member downward, which is produced in the second closed space and/or the third closed space by supplying the compressed fluid into and discharging the same from the second closed space and/or the third closed space, is adjusted so as to adjust a third pressing force of the upper polishing plate, which presses the work piece, while polishing the work piece.

Further, the polishing apparatus of the present invention comprises:

a lower polishing plate;

an upper polishing plate being relatively moved with respect to the lower polishing plate so as to polish a work piece clamped between the lower polishing plate and upper polishing plate; and

a holding mechanism for holding the upper polishing plate,

wherein the holding mechanism includes:an inner member;an outer member having an upper open end and a lower open end, the outer member accommodating the inner member;a third elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the third elastic member connecting an upper part of the inner member and an upper part of the outer member and closing the upper open end of the outer member;a fourth elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the fourth elastic member connecting a mid part of the inner member and a mid part of the outer member and closing a gap therebetween;a fifth elastic member being made of an elastic material and formed into a ring-shape with a prescribed width, the fifth elastic member connecting a lower part of the inner member and a lower part of the outer member and closing the lower open end of the outer member;a second closed space being enclosed by an outer face of the inner member, an inner face of the outer member, the third elastic member and the fourth elastic member;a third closed space being enclosed by the outer face of the inner member, the inner face of the outer member, the fourth elastic member and the fifth elastic member;a first fluid supply section supplying a pressurized fluid into the second closed space;a second fluid supply section supplying a pressurized fluid into the third closed space;a rotary drive unit to which one of the inner member and the outer member is connected;a connecting member connecting the other of the inner member and the outer member to the upper polishing plate; anda vertical drive unit being provided above the upper polishing plate, the vertical drive unit vertically moving the rotary drive unit and the upper polishing plate with respect to the lower polishing plate, and

the upper polishing plate is downwardly moved to face the lower polishing plate by the vertical drive unit, the upper polishing plate is rotated in a horizontal plane, by the rotary drive unit, with the inner member, the outer member and the connecting member, and a pressure difference between a first pressing force pressing the outer member or the inner member upward and a second pressing force pressing the outer member or the inner member downward, which is produced in the second closed space and/or the third closed space by supplying the compressed fluid into and discharging the same from the second closed space and/or the third closed space, is adjusted so as to adjust a third pressing force of the upper polishing plate, which presses the work piece, while polishing the work piece.

In the polishing apparatus, the first pressing force generated in the second closed space may be greater than the second pressing force therein, and

the first pressing force generated in the third closed space may be smaller than the second pressing force therein,

whereby a range of the third pressing force is from a force smaller than a weight of the upper polishing plate to a force greater than the weight thereof

In the polishing apparatus, the first pressing force generated in the second closed space may be smaller than the second pressing force therein, and

the first pressing force generated in the third closed space may be greater than the second pressing force therein,

whereby a range of the third pressing force is from a force greater than a weight of the upper polishing plate to a force smaller than the weight thereof

In the polishing apparatus, an engage section, which is capable of restraining relative downward displacement of the inner member and the outer member, may be provided between the inner member and the outer member.

In the polishing apparatus, the rotary drive unit may be a direct drive motor.

By employing the polishing apparatus of the present invention, the pressing force applied from the upper polishing plate to the work piece can be linearly and precisely controlled, so that the work piece, especially the thin work piece, can be suitably polished.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Firstly, a first embodiment will be explained with reference toFIGS. 1–4.

FIG. 1is a schematic view of a polishing apparatus30.FIG. 2is a driving mechanism for driving a lower polishing plate32, a sun gear34and an internal gear36.

Firstly, the driving mechanism for driving the lower polishing plate32, etc. will be explained with reference toFIG. 2.

The lower polishing plate32is mounted and fixed on a holder37. The holder37is rotated by a known direct drive motor (DD motor)38, so that the lower polishing plate32can be rotated in a horizontal plane. The DD motor38directly rotates a driven member without a reduction gear unit. The DD motor38has a donut-shaped or a hollow structure. The DD motor38is provided on a holding table40, and the holder37is fixed to a rotary ring41of the DD motor38by bolts (not shown).

The sun gear34is fixed to a shaft43and rotated by a DD motor42, which is provided in a mid part of the holding table40. The shaft43is pierced through a hollow part of the DD motor38. Since the DD motors38and42are coaxially arranged, the polishing apparatus30can be made compact. The internal gear36is fixed to an upper end of a rotary ring45, which is rotatably supported by the holding table40. The rotary ring45is rotated by a DD motor46via gears47and48, so that the internal gear36can be rotated.

An upper polishing plate50is held and allowed to rotate and vertically move by a holding mechanism51. A carrier25(seeFIG. 7) is provided between the lower polishing plate32and the upper polishing plate50and engaged with the sun gear34and the internal gear36. Work pieces26(seeFIG. 7) are respectively set in through-holes (not shown) of the carrier25.

Next, the holding mechanism51will be explained with reference toFIGS. 1 and 3.

InFIG. 1, a movable plate52has cylindrical guide sections57. The guide sections57are guided by guide poles56, which are vertically provided to a frame54, so that the movable plate52can be moved upward and downward.

A vertical drive unit (ex. cylinder unit)58is located above the upper polishing plate50and fixed to an upper part of the frame54. A rod59of the vertical drive unit58is connected to the movable plate52by a coupler60, so that the vertical drive unit58is capable of vertically moving the movable plate52.

Stoppers55make the movable plate52stop at a prescribed position when the movable plate52is moved downward by the cylinder unit58.

A DD motor62is fixed on a bottom face of the movable plate52. As shown inFIG. 3, the DD motor62rotates the upper polishing plate50in a horizontal plane together with a rotary plate63, an inner member64, a first elastic member70, a second elastic member72, an outer member65, connecting members66, etc..

The rotary plate63is fixed to a rotary ring67of the DD motor62by bolts (not shown).

The inner member64is fixed to a bottom face of the rotary plate63by bolts (not shown) and rotated about a vertical axis together with the rotary plate63.

The inner member64is formed into an inverted cup-shape, and its lower end is opened. A small diameter part64a, a medium diameter part64band a large diameter part64care formed in an outer circumferential face of the inner member64in that order. A step face64dis formed between the small diameter part64aand the medium diameter part64b; another step face64eis formed between the medium diameter part64band the large diameter part64c.

The outer member65is formed into a hollow shape and has an upper open end and a lower open end. The inner member64is accommodated in the hollow outer member65.

An upper flange65ais extended from an inner edge of the upper open end of the outer member65toward the medium diameter part64bof the inner member64; a lower flange65bis outwardly extended from an outer edge of the lower open end of the outer member65.

The first elastic member70is made of an elastic material, e.g., rubber, and formed into a ring-shape with a prescribed width. The first elastic member70connects the upper part (the step face64d) of the inner member64to the upper part (an upper face of the upper flange65a) of the outer member65and closes the upper open end of the outer member65. The first elastic member70is fixed the upper parts by, for example, an adhesive and bolts. A ring-shaped space is formed between an outer circumferential face of the medium diameter part64band an inner circumferential face of the upper flange65a.

The second elastic member72is made of an elastic material, e.g., rubber, and formed into a ring-shape with a prescribed width. The second elastic member72connects the lower part of the inner member64to the lower part of the outer member65and closes the lower open end of the outer member65. The second elastic member72is fixed the lower parts by, for example, an adhesive and bolts. A ring-shaped space is formed between an outer circumferential face of the large diameter part64cand an inner circumferential face of the outer member65.

Note that, in the present embodiment, the diameter of the second elastic member72is greater than that of the first elastic member70.

With this structure, a first closed space73is formed between the outer circumferential face of the inner member64and an inner circumferential face of the outer member65and closed by the first and second elastic members70and72.

By forming the first closed space73, the outer member65is capable of vertically displacing with respect to the inner member64without contact.

A pressurized fluid, e.g., compressed air, can be supplied into and discharged from the first closed space73via a fluid path78of the inner member64, a joint79and a hose80(seeFIG. 3). The hose80is connected to a rotary joint (not shown) provided in the coupler60via a pipe (not shown) provided in a hollow part of the DD motor62. The rotary joint is connected to an external pressure source, e.g., compressor. A fluid supply section81is constituted by the fluid path78, the joint79, the hose80, the rotary joint, etc..

When a lower face of the flange65acontacts the step face64e, a downward movement of the outer member65is restrained. Namely, the lower face of the flange65aand the step face64econstitute an engage section.

When the cylinder unit58, which acts as a vertical drive unit, upwardly moves the movable plate52together with the inner member64, the outer member65and the upper polishing plate50are moved upward due to the engage section. Note that, the engage section is not limited to the lower face of the flange65aand the step face64e, other parts, which can be mutually engaged, may be used as the engage section.

The connecting members66are rods, which connect a lower face of the flange65bwith an upper face of the upper polishing plate50. With this structure, the upper polishing plate50can be vertically moved together with the outer member65.

Next, a method of polishing work pieces26will be explained.

The work pieces26are respectively set in the thorough-holes of the carrier25.

Then, the pressurized fluid is supplied into the first closed space73from the fluid supply section81. The vertical drive unit58is driven so as to downwardly move the upper polishing plate50until facing the lower polishing plate32or reaching a stop position, at which the movement of the movable plate52is stopped by the stoppers55.

As described above, the diameter of the first elastic member70is smaller than that of the second elastic member72. As clearly shown inFIG. 3, in the closed space73, a pressure receiving area, which receives fluid pressure for moving the outer member65upward (a first pressing force), is broader than the other pressure receiving area, which receives the fluid pressure for moving the outer member65downward (a second pressing force). Therefore, the outer member65is biased upward by a third pressing force, which is generated by the difference between the first pressing force and the second pressing force. The third pressing force, which presses the work pieces26, is smaller than weight of the upper polishing plate50(exactly, sum of weight of the upper polishing plate50, the connecting members66and the outer member65).

Since the inner member64is fixed to the rotary plate63, the inner member64is not moved even if the second pressing force works in the closed space73. In the closed space73, the fluid pressure uniformly works in every direction. However, the inner member64is fixed and the outer member65is movable, further the pressure receiving areas for generating the first and second pressing forces are different, so that the third pressing force can be applied to the movable outer member65.

In an early stage of polishing the work pieces26, fine projections and concaves exist in surfaces of the work pieces. Preferably, the work pieces26are polished with relatively small pressing force. Therefore, in the early stage, the high pressure fluid is supplied into the first closed space73so as to increase the first pressing force and reduce the third pressing force applied to the work pieces26. Then, the DD motor62is driven to rotate the upper polishing plate50. Further, slurry is supplied from a slurry supply section (not shown) so as to polish the work pieces26with the slurry.

A torque of the DD motor62is transmitted to the upper polishing plate50via the rotary plate63, the inner member64, the first and second elastic members70and72, the outer member65and the connecting members66.

By supplying the high pressure fluid into the first closed space73in the early stage of the polish, the first and second elastic members70and72are outwardly expanded and made rigid. A relatively great driving force is required to rotate the upper polishing plate50from a resting state, so the rigid elastic members70and72are suitably used.

With advancing the polish, the pressure of the fluid supplied into the first closed space73is reduced and the third pressing force applied to the work pieces26is increased so as to raise polishing rate. The maximum third pressing force applied to the work pieces26is equal to weight of the upper polishing plate50.

In the present embodiment, the outer member65is displaced without contacting the inner member64, so that knocking, which is caused by using the conventional cylinder unit, can be prevented. Therefore, the third pressing force, which is applied from the upper polishing plate50to the work pieces26, can be linearly and precisely controlled. Especially, thin work pieces can be suitably polished.FIG. 4is a graph showing a relationship between the fluid pressure in the first closed space73and a load of the upper polishing plate50. According toFIG. 4, the load of the upper polishing plate50was linearly varied. InFIG. 4, “AIR PRESSURE (KPa)” means air pressure in the closed space73; “REDUCING PRESSURE” means the actual load of the upper polishing plate50which was measured when the air pressure in the closed space73was reduced; and “INCREASING PRESSURE” means the actual load of the upper polishing plate50which was measured when the air pressure in the closed space73was increased.

When the fluid pressure in the first closed space73is reduced to increase the polishing rate, the expansion of the first and second elastic members70and72are loosened and relatively softened. But the softened elastic members70and72do not badly influence the continuous rotation of the upper polishing plate50, and they suitably absorb vibrations of the upper polishing plate50rotating at high speed.

As described above, the DD motors are employed to rotate the upper polishing plate50, etc., so that backlashes of the gears and the keys can be reduced. By restraining vibrations of parts, thin work pieces can be polished without damaging.

In the first embodiment, the first pressing force, which is generated in the first closed space73and biases the outer member65upward, is greater than the second pressing force, which is generated in the first closed space73and biases the outer member65downward. Therefore, a range of the third pressing force, which presses the work pieces26, is from a force smaller than a weight of the upper polishing plate50to a force equal to the weight thereof.

A second embodiment will be explained with reference toFIG. 5. Note that, the structural elements used in the first embodiment are assigned the same symbols and explanation will be omitted.

In the second embodiment, the first pressing force, which biases the outer member65upward, is smaller than the second pressing force, which biases the outer member65downward. A range of the third pressing force, which presses the work pieces26, is from a force greater than a weight of the upper polishing plate50to a force equal to the weight thereof.

A mid part of the inner member64is a large diameter part64f, and a lower part is a medium diameter part64g. A lower flange65cis inwardly extended from a lower part of the outer member65. A bottom face of the lower flange65cand a bottom face of the medium diameter part64gare connected by the second elastic member72. The first closed space73is formed between outer circumferential faces of the large diameter part64fand the medium diameter part64gand the inner circumferential face of the outer member65. A step face64his formed between the large diameter part64fand the medium diameter part64g.

A torque of the DD motor62is transmitted to the upper polishing plate50by the elastic members70and72. By employing the elastic members70and72, the upper polishing plate50is capable of following an upper face of the lower polishing plate32, so that the suitable mechanism, e.g., universal joint, for rotating the upper polishing plate50along the upper face of the lower polishing plate32, which is used in the conventional polishing apparatus, can be omitted. Namely, the polishing apparatus can be simplified.

The torque of the DD motor62may be transmitted to the upper polishing plate50by not only the elastic members70and72but also other suitable means. For example, a transmission pin which is engaged with the outer member65, may be provided to the rotary plate63so as to transmit the torque of the DD motor62to the upper polishing plate50. In this case, the outer member65is capable of vertically displacing. Note that, rigidity of the elastic members70and72need not be considered.

A third embodiment will be explained with reference toFIG. 6. Note that, the structural elements used in the former embodiments are assigned the same symbols and explanation will be omitted.

The polishing apparatus of the third embodiment has the features of the first and second embodiments.

Namely, a third elastic member82, which is made of an elastic material and formed into a ring-shape with a prescribed width, connects the upper part of the inner member64and the upper part of the outer member65and closes the upper open end of the outer member65; a fourth elastic member83, which is made of an elastic material and formed into a ring-shape with a prescribed width, connects a mid part of the inner member64and a mid part of the outer member65and closes a gap therebetween; and a fifth elastic member84, which is made of an elastic material and formed into a ring-shape with a prescribed width, connects the lower part of the inner member64and the lower part of the outer member65and closing the lower open end of the outer member65. A second closed space85is formed between the outer circumferential face of the inner member64, the inner circumferential face of the outer member65and closed by the third and fourth elastic members82and83; a third closed space86is formed between the outer circumferential face of the inner member64, the inner circumferential face of the outer member65and closed by the fourth and fifth elastic members83and84. A first fluid supply section87supplies the pressurized fluid into the second closed space85; a second fluid supply section88supplies the pressurized fluid into the third closed space86. The fluid supply sections87and88may be connected to rotary joints as well as the first embodiment. The fluid supply sections87and88are capable of independently supplying and discharging the pressurized fluids.

To polish the work pieces26, firstly the vertical drive unit58downwardly moves the upper polishing plate50until facing the lower polishing plate32. The DD motor62rotates the upper polishing plate50, in a horizontal plane, with the inner member64, the elastic members82,83and84, the outer member65and the connecting members66. Slurry is supplied onto the upper polishing plate50from a slurry supply section (not shown). By supplying the pressurized fluids into and discharging the same from the second closed space85and/or the third closed space86by the fluid supply sections87and88, the third pressing force pressing the work pieces26can be adjusted while polishing the work pieces26. Note that, as described above, the third pressing force of the upper polishing plate50(exactly, the upper polishing plate50, the connecting members66and the outer member65) is equal to the difference between the first pressing force biasing the outer member65upward and the second pressing force biasing the outer member65downward, which are generated in the second closed space85and/or the third closed space86.

In the present embodiment, pressure receiving areas in the closed spaces85and86are determined so as to make the first pressing force in the second closed space85greater than the second pressing force therein and make the first pressing force in the third closed space86smaller than the second pressing force therein. Therefore, the third pressing force can be adjusted between a force smaller than the weight of the upper polishing plate50and a force greater than the weight thereof while polishing the work pieces26.

In another case, the pressure receiving areas in the closed spaces85and86may be determined so as to make the first pressing force in the second closed space85smaller than the second pressing force therein and make the first pressing force in the third closed space86greater than the second pressing force therein. Therefore, the third pressing force of the upper polishing plate50can be adjusted between the force greater than the weight of the upper polishing plate50and the force smaller than the weight thereof while polishing the work pieces26.

In the both cases, the third pressing force applied to the work pieces26may be precisely controlled by simultaneously controlling pressure of the fluids supplied into the second and third closed spaces85and86.

In the above described embodiments, the inner member64is fixed to the DD motor62and rotated so as to transmit the torque to the outer member65. In another case, the outer member65may be fixed to the DD motor62, the inner member64may be connected to the upper polishing plate50by suitable means (not shown), the torque of the outer member65may be transmitted to the inner member64via elastic members or a transmission pin, and the torque may be further transmitted to the upper polishing plate50via a suitable connecting member.

In the above described embodiments, the vertical drive unit58is the cylinder unit. The vertical drive unit is not limited to the cylinder unit. For example, a mechanism constituted by a motor, a ball screw, etc. may be employed.

In some cases, the lower polishing plate32may be vertically moved instead of the upper polishing plate50.

Further, the polishing apparatus may polish one surface of each work piece26. In another case, the polishing apparatus may polish both surfaces of each work piece26. The polishing apparatus includes the one which have the upper and lower polishing plates with a polishing cloth on the polishing surface thereof.