Abrading – Machine – Rotary tool
Reexamination Certificate
1999-12-06
2001-09-25
Banks, Derris H. (Department: 3723)
Abrading
Machine
Rotary tool
C451S398000, C451S446000
Reexamination Certificate
active
06293858
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to a flat mirror finish, and more particularly to a polishing apparatus having a mechanism which can control the amount of a material removed from a peripheral portion of the workpiece.
BACKGROUND ART
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections. In case of photolithography which can form interconnections that are at most 0.5 &mgr;m wide, it requires that surfaces of semiconductor wafers on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small. As a means for planarizing the semiconductor wafer, it is polished by a polishing apparatus.
Conventionally, this kind of polishing apparatus has a turntable and a top ring, and the top ring applies a certain pressure to the turntable. The workpiece to be polished is placed between the top ring and the turntable, and while supplying an abrasive liquid, the workpiece is polished to a flat mirror finish.
In the polishing apparatus described above, if the workpiece is not pressed against the polishing cloth under forces which are uniform over the entire surface of the workpiece, then the workpiece tends to be polished insufficiently or excessively in local areas depending on the applied forces. Therefore, in the conventional polishing apparatus, as a means for preventing nonuniform pressing forces, the following arrangements have been proposed.
{circle around (1)} An elastic pad of polyurethane or the like is applied to a wafer holding surface of the top ring for uniformizing a pressing force applied from the top ring to the semiconductor wafer.
{circle around (2)} A workpiece carrier for holding the workpiece, i.e. the top ring, is tiltable with respect to the surface of the polishing cloth.
{circle around (3)} A region of the polishing cloth surrounding the workpiece is pressed independently of the top ring and the workpiece, for thereby eliminating an appreciable step between a region of the polishing cloth pressed by the workpiece and the surrounding region thereof.
FIG. 12
of the accompanying drawings shows a main part of a conventional polishing apparatus. The conventional polishing apparatus comprises a turntable
41
with a polishing cloth
42
attached to an upper surface thereof, a top ring
45
for holding a semiconductor wafer
43
to allow the semiconductor wafer
43
to be rotated and to be pressed, and an abrasive liquid supply nozzle
48
for supplying an abrasive liquid Q to the polishing cloth
42
. The top ring
45
is connected to a top ring shaft
49
, and is provided with an elastic pad
47
of polyurethane or the like on its lower surface. The semiconductor wafer
43
is held by the top ring
45
in contact with the elastic pad
47
. The top ring
45
also has a cylindrical guide ring
46
A on an outer circumferential edge thereof for retaining the semiconductor wafer
43
on the lower surface of the top ring
45
. Specifically, the guide ring
46
A is fixed to the top ring
45
, and has a lower end projecting downwardly from the lower surface of the top ring
45
for holding the semiconductor wafer
43
on the elastic pad
47
to prevent removal of the top ring
45
under frictional engagement with the polishing cloth
42
during a polishing process.
In operation, the semiconductor wafer
43
is held against the lower surface of the elastic pad
47
which is attached to the lower surface of the top ring
45
. The semiconductor wafer
43
is then pressed against the polishing cloth
42
on the turntable
41
by the top ring
45
, and the turntable
41
and the top ring
45
are rotated to move the polishing cloth
42
and the semiconductor wafer
43
relatively to each other, thereby polishing the semiconductor wafer
43
. At this time, the abrasive liquid Q is supplied onto the polishing cloth
42
from the abrasive liquid supply nozzle
48
. The abrasive liquid Q comprises an alkaline solution containing an abrasive grain of fine particles suspended therein, for example. The semiconductor wafer
43
is polished by a composite action comprising a chemical polishing action of the alkaline solution and a mechanical polishing action of the abrasive grain.
FIG. 13
of the accompanying drawings shows in an enlarged fragmentary cross-section the semiconductor wafer, the polishing cloth and the elastic pad during polishing by the polishing apparatus shown in FIG.
12
. As shown in
FIG. 13
, in case of such structure in which only the workpiece presses the polishing cloth, the workpiece, i.e. the semiconductor wafer
43
, has a peripheral portion which is a boundary between contact and noncontact with the polishing cloth
42
and also is a boundary between contact and noncontact with the elastic pad
47
. At the peripheral portion of the workpiece, the polishing pressure applied to the workpiece by the polishing cloth and the elastic pad is not uniform, and thus the peripheral portion of the workpiece is liable to be polished to an excessive degree. As a result, the peripheral edge of the workpiece is often polished into a so-called edge-rounding.
In order to prevent the peripheral portion of the semiconductor wafer from being excessively polished, there has been proposed in Japanese patent application No. 9-105252 a polishing apparatus having a structure for pressing an area of the polishing cloth which is located around the peripheral portion of the semiconductor wafer.
FIG. 14
of the accompanying drawings shows the polishing apparatus disclosed in Japanese patent application No. 9-105252. In
FIG. 14
, the reference numeral
51
represents a top ring which comprises a top ring body
51
A and a retainer ring
51
B removably fixed to the peripheral portion of the top ring body
51
A by bolts
181
. A recess
51
a
for accommodating a semiconductor wafer
54
is formed by a lower surface of the top ring body
51
A and the retainer ring
51
B. The semiconductor wafer
54
has an upper surface held by the lower surface of the top ring body
51
A, and an outer peripheral edge held by the retainer ring
51
B. A presser ring
53
is vertically movably disposed around the top ring body
51
A and the retainer ring
51
B. A leaf spring
67
having a U-shaped cross-section is provided between the presser ring
53
and the top ring
51
to prevent a direct contact of the presser ring
53
and the top ring
51
and to suppress excessive tilting of the top ring
51
.
An elastic pad
52
is attached to a lower surface of the top ring
51
. A turntable
55
having a polishing cloth
56
attached thereto is disposed below the top ring
51
. An attachment flange
182
having a spherical concave surface
182
a
is fixed to the top ring body
51
A. A top ring shaft
58
is disposed above the top ring
51
. A drive shaft flange
184
having a spherical concave surface
184
a
is fixed to the lower end of the top ring shaft
58
. A spherical bearing
57
is disposed between the spherical concave surfaces
182
a
and
184
a
. A space
183
is formed between the top ring body
51
A and the attachment flange
182
, and vacuum, pressurized air, and liquid such as water can be supplied to the space
183
.
The top ring shaft
58
is coupled to a top ring air cylinder (not shown) fixed to a top ring head
59
. The top ring shaft
58
is vertically movable by the top ring air cylinder, and the semiconductor wafer
54
held by the lower end surface of the top ring
51
is pressed against the polishing cloth
56
on the turntable
55
. Further, the top ring shaft
58
is coupled to a top ring motor (not shown), and the top ring
51
is rotated by the top ring motor. The presser ring
53
provided around the top ring
51
is coupled at its upper end to presser ring air cylinders
72
. The presser ring air cylinders
72
are fixed to the top ring head
59
. A plurality of (e.g. three) the presser ring air cylinder
Katsuoka Seiji
Kimura Norio
Kojima Shunichiro
Maruyama Toru
Ohwada Shin
Banks Derris H.
Ebara Corporation
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Polishing device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polishing device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polishing device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2503717