Abrading – Machine – Rotary tool
Reexamination Certificate
2000-02-22
2001-09-18
Banks, Derris H. (Department: 3723)
Abrading
Machine
Rotary tool
C451S398000
Reexamination Certificate
active
06290585
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a polishing machine, more precisely relates to a polishing machine having: a plate holder rotatably provided to a base; a polishing plate, whose upper face is covered with a polishing cloth as a polishing face, mounted on the plate holder; and a press unit for pressing a surface of a work piece onto the polishing face so as to polish the surface of the work piece like a mirror face.
A conventional polishing machine for polishing surfaces of silicon wafers, etc. is shown in FIG.
9
. In the polishing machine, a plurality of silicon wafers, etc. are simultaneously polished like mirror faces. An upper face of a polishing plate, which is rotated in a direction of an arrow A, is covered with a polishing cloth
108
. A plurality of press units
110
, which are provided above the polishing clothe
108
, are respectively rotated in directions of arrows B. Each of the press units
110
presses the silicon wafer onto the polishing cloth
108
so as to polish the silicon wafer.
A partial sectional view of the polishing machine shown in
FIG. 9
is shown in FIG.
10
. As shown in
FIG. 10
, a plate holder
104
is rotatably provided in a base
100
. The plate holder is rotated, together with a rotary shaft in the direction A, by a motor (not shown). A polishing plate
106
is mounted on the plate holder
104
. As described above, the polishing cloth
108
is fixed on an upper face of the polishing plate so as to form the polishing face.
The press unit
110
is provided above the polishing plate
106
and covers an outer edge part thereof. The press unit
110
presses work pieces
105
, e.g., the silicon wafers, onto the polishing face of the polishing plate
106
. The work pieces
105
are adhered on a lower face of the press unit
110
, which faces the polishing face of the polishing plate
106
.
Lower surfaces of the work pieces
105
are polished by the polishing cloth
108
with slurry, which is supplied by a pipe
107
.
Weight of the polishing plate
106
and pressing force of the press unit
110
are applied to an outer edge part of the plate holder
104
, so the outer edge part of the plate holder
104
is downwardly deformed with respect to a center part thereof, which is connected to the rotary shaft
102
. Thus, it is difficult to keep the polishing face of the polishing plate
106
flat. Thus, in the conventional polishing machine, a ball bearing
112
is provided between the outer edge part of the plate holder
104
and the base
100
.
As shown in
FIG. 10
, by providing the ball bearing
112
between the outer edge part of the plate holder
104
and the base
100
, the plate holder
104
is capable of rotating and keeping the polishing face of the polishing plate
106
flat even if the weight of the polishing plate
106
and the pressing force of the press unit
110
are applied to the outer edge part of the plate holder
104
.
However, balls of the ball bearings
112
are not true spheres and have minute errors in size. The errors can be reduced but cannot be zero. Therefore, the plate holder
104
, which is supported by the ball bearing
112
, is moved on the balls of the bearing
112
, which rotate with the movement of the plate holder
104
, so that fine vibrations of the plate holder
104
, which are caused by the minute errors, are occurred. The fine vibrations of the plate holder
104
makes fine projections like ripples on the polished surfaces of the work pieces
105
, so that flatness of the work pieces cannot be improved.
Generally, the polishing step is a final step, so the work pieces, which have been polished by the polishing machine, are forwarded. However, in the case of the silicon wafers for semiconductor devices, the flatness of the polished surfaces must be higher, so the work pieces whose surfaces have fine ripple-shaped projections badly influence to final products.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polishing machine capable of preventing the fine vibrations of a polishing face of a polishing plate, which are caused by rotation of the polishing plate.
The inventor of the present invention studied to achieve the object and found that a fluid bearing could effectively employed instead of the ball bearing.
Namely, the polishing machine of the present invention comprises:
a plate holder being rotatably provided to a base;
a polishing plate being mounted on the plate holder, an upper face of the polishing plate being covered with a polishing cloth as a polishing face; and
a press unit for pressing a surface of a work piece onto the polishing face of the polishing plate so as to polish the surface of the work piece like a mirror face,
characterized by,
a fluid bearing rotatably supporting the plate holder by fluid pressure, at a position between the plate holder and the base, so as to keep the polishing face of the polishing plate flat.
In the polishing machine, the fluid bearing may be a static fluid bearing, which rotatably supports the plate holder by the pressure of the fluid, which is jetted from a plurality of jet nozzles formed in the base. With this structure, the plate holder can be rotatably supported by the fluid pressure while the plate holder is stopped.
In the polishing machine, the fluid bearing may be a dynamic fluid bearing including:
a circular groove being formed in the base, the circular groove holding the fluid, an inner bottom face of the circular groove being formed into a flat face; and
a circular projection being downwardly projected from the plate holder, a lower end section of the circular projection being inserted in the circular groove,
whereby dynamic pressure for rotatably supporting the plate holder is applied to the lower end section of the circular projection when the plate holder is rotated. With this structure, the dynamic fluid bearing has the simple structure and maintenance can be easier.
In the polishing machine of the present invention, the fluid bearing rotatably can support the plate holder by the fluid pressure, at the position between the plate holder and the base, so as to keep the polishing face of the polishing plate flat. Since the weight of the plate holder, etc. can be supported by the fluid pressure, the fine vibrations, which are caused by balls in a ball bearing, are not occurred. Therefore, the work piece can be highly precisely polished like a mirror.
REFERENCES:
patent: 5558568 (1996-09-01), Talieh et al.
patent: 6086456 (2000-07-01), Weldon et al.
patent: 6111634 (2000-08-01), Pecen et al.
patent: 6132295 (2000-10-01), Tietz et al.
patent: 9123058 (1997-05-01), None
patent: 9267258 (1997-10-01), None
Banks Derris H.
Fujikoshi Kikai Kogyo Kabushiki Kaisha
Jordan and Hamburg LLP
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