Abrading – Machine – Rotary tool
Reexamination Certificate
2000-05-30
2002-08-06
Rose, Robert A. (Department: 3723)
Abrading
Machine
Rotary tool
C451S443000, C451S072000
Reexamination Certificate
active
06428403
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 material removed from a peripheral portion of the workpiece by a polishing action.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography.
Though the photolithographic process can form interconnections that are at most 0.5 &mgr;m wide, it requires that surfaces 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.
Conventionally, a polishing apparatus has a turntable and a top ring which rotate at respective individual speeds. A polishing cloth is attached to the upper surface of the turntable.
A semiconductor wafer to be polished is placed on the polishing cloth and clamped between the top ring and the turntable. An abrasive liquid containing abrasive grains is supplied onto the polishing cloth and retained on the polishing cloth. During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the polishing cloth is therefore polished by a combination of chemical polishing and mechanical polishing to a flat mirror finish while the top ring and the turntable are rotated. This process is called Chemical Mechanical Polishing. operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the polishing cloth is therefore polished by a combination of chemical polishing and mechanical polishing to a flat mirror finish while the top ring and the turntable are rotated. This process is called Chemical Mechanical polishing.
If the semiconductor wafer is not pressed against the polishing cloth under forces which are uniform over the entire surface of the semiconductor wafer, then the semiconductor wafer tends to be polished insufficiently or excessively in local areas depending on the applied forces. The following arrangements have been proposed in the art to prevent the semiconductor wafer from being pressed against the polishing cloth under irregular forces.
1) One conventional solution has been to apply an elastic pad of polyurethane or the like to a workpiece holding surface of the top ring for uniformizing a pressing force applied from the top ring to the semiconductor wafer.
2) According to another solution, the top ring, i.e., a workpiece carrier for holding a semiconductor wafer, is tiltable with respect to the surface of the polishing cloth.
3) Still another attempt has been to press a region of the polishing cloth surrounding the semiconductor wafer, independently of the semiconductor wafer, for thereby eliminating an appreciable step between a region of the polishing cloth pressed by the semiconductor wafer and the surrounding region thereof.
FIG. 8
of the accompanying drawings shows a conventional polishing apparatus. As shown in
FIG. 8
, 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 press the semiconductor wafer
43
against the polishing cloth
42
, 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 presser 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 presser 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
against removal from 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 independently of each other to move the polishing cloth
42
and the semiconductor wafer
43
relatively to each other, thereby polishing the semiconductor wafer
43
. The abrasive liquid Q comprises an alkaline solution containing abrasive grains 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 grains.
FIG. 9
of the accompanying drawings shows in a fragmental cross-section the semiconductor wafer
43
, the polishing cloth
42
, and the elastic pad
47
. As shown in
FIG. 9
, 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 semiconductor wafer
43
, the polishing pressure applied to the semiconductor wafer
43
by the polishing cloth
42
and the elastic pad
47
is not uniform, thus the peripheral portion of the semiconductor wafer
43
is liable to be polished to an excessive degree. As a result, the peripheral edge of the semiconductor wafer
43
is often polished, in a so called “edge-rounding” manner.
In order to prevent the peripheral portion of the semiconductor wafer from being excessively polished, there has been proposed in Japanese patent application No. 8-54055 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. 10
of the accompanying drawings shows the polishing apparatus disclosed in Japanese patent application No. 8-54055.
As shown in
FIG. 10
, a semiconductor wafer
43
is held by a top ring
45
and pressed against a polishing cloth
42
on a turntable
41
. The semiconductor wafer
43
is retained on the top ring
45
by a cylindrical retaining portion extending downwardly from the top ring
45
. A presser ring
46
is disposed around and connected to the top ring
45
by keys
58
. The keys
58
allow the presser
5
ring
46
to move vertically with respect to the top ring
45
and to rotate together with the top ring
45
. The presser ring
46
is rotatably supported by a radial bearing
59
which is held by a bearing holder
60
operatively coupled by a plurality of (e. g. three) circumferentially spaced shafts
61
to a plurality of (e.g. 10 three) circumferentially spaced presser ring air cylinders
62
. The presser ring air cylinders
62
are fixedly mounted on a top ring head
69
. The top ring
45
has an upper surface held in sliding contact with a spherical bearing
65
that is slidably supported on the lower end of a top ring shaft
66
. movable by a top ring air cylinder
67
mounted on the top ring head
69
and operatively connected to the top ring shaft
66
.
The top ring air cylinder
67
and the presser ring air cylinders
62
are connected to a compressed air source
64
respectively through regulators R
1
and R
2
. The regulator R
1
regulates the air pressure supplied from the compressed air source
64
to the top ring air cylinder
67
to adjust the pressing force for pressing the semiconductor wafer
43
Kimura Norio
Yasuda Hozumi
Ebara Corporation
Rose Robert A.
Wenderoth , Lind & Ponack, L.L.P.
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