Abrading – Abrading process – Utilizing nonrigid tool
Reexamination Certificate
2000-08-31
2002-08-20
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
Utilizing nonrigid tool
C451S288000, C451S290000, C451S398000
Reexamination Certificate
active
06435949
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for polishing workpiece, and more particularly to an apparatus and method for polishing a workpiece such as a semiconductor wafer to a flat mirror finish.
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. The photolithographic process 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. It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus.
Conventionally, a polishing apparatus has a turntable having a polishing cloth attached thereon, and a top ring for applying a constant pressure on the turntable. A semiconductor wafer to be polished is placed on the polishing cloth and clamped between the top ring and the turntable, and the surface of the semiconductor wafer on which circuits are formed is chemically and mechanically polished, while supplying a polishing liquid onto the polishing cloth. This process is called chemical mechanical polishing (CMP).
The polishing apparatus is required to have such performance that the surfaces of semiconductor wafers have a highly accurate flatness. Therefore, it is considered that the holding surface, i.e. the lower end surface of the top ring which holds a semiconductor wafer, and the upper surface of the polishing cloth which is held in contact with the semiconductor wafer, and hence the surface of the turntable to which the polishing cloth is attached, preferably have a highly accurate flatness, and the holding surface and the surface of the turntable which are highly accurately flat have been used. It is also considered that the lower surface of the top ring and the upper surface of the turntable are preferably parallel to each other, and such parallel surfaces have been used.
It is known that the polishing action of the polishing apparatus is affected not only by the configurations of the holding surface of the top ring and the contact surface of the polishing cloth, but also by the relative velocity between the polishing cloth and the semiconductor wafer, the distribution of pressure applied to the surface of the semiconductor wafer which is being polished, the amount of the polishing liquid on the polishing cloth, and the period of time when the polishing cloth has been used. It is considered that the surface of the semiconductor wafer can be highly accurately flat if the above factors which affect the polishing action of the polishing apparatus are equalized over the entire surface of the semiconductor wafer to be polished.
However, some of the above factors can easily be equalized over the entire surface of the semiconductor wafer, but the other factors cannot be equalized. For example, the relative velocity between the polishing cloth and the semiconductor wafer can easily be equalized by rotating the turntable and the top ring at the same rotational speed and in the same direction. However, it is difficult to equalize the amount of the polishing liquid on the polishing cloth because of a centrifugal forces imposed on the polishing liquid.
The above approach which tries to equalize all the factors affecting the polishing action, including the flatnesses of the lower end surface, i.e. the holding surface of the top ring and the upper surface of the polishing cloth on the turntable, over the entire surface of the semiconductor wafer to be polished poses limitations on efforts to make the polished surface of the semiconductor wafer flat, often resulting in a failure to accomplish a desired degree of flatness of the polishing surface. According to the study of the inventors, it is found that the lower surface (holding surface) of the top ring and the polishing surface of the turntable are preferably not parallel and flat.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an apparatus and method for polishing a workpiece which can easily correct irregularities of a polishing action on a workpiece such as a semiconductor wafer, and polish a workpiece with an intensive polishing action or a weak polishing action on a desired localized area thereof.
In order to achieve the above object, according to a first aspect of the present invention, there is provided an apparatus for polishing a workpiece, the apparatus comprising: a turntable having a polishing surface; a top ring for holding a workpiece and pressing the workpiece against the polishing surface; a holding surface of the top ring for holding the workpiece, the holding surface being deformable by fluid having variable pressure; and a retainer ring for retaining the workpiece within the holding surface of the top ring, the retainer ring pressing the polishing surface under a variable pressing force.
According to another aspect of the present invention, there is provided a method for polishing a workpiece, the method comprising: holding a workpiece between a polishing surface of a turntable and a holding surface of a top ring; pressing the workpiece against the polishing surface in such a state that the holding surface for holding the workpiece is deformed to a desired shape by fluid having variable pressure; and pressing a retainer ring for retaining the workpiece within the holding surface of the top ring against the polishing surface under a variable pressing force.
FIG. 1
shows the basic principles of the first aspect of present invention. As shown in
FIG. 1
, the top ring
1
comprises a top ring body
2
, and a holding plate
3
for holding a workpiece, to be polished, such as a semiconductor wafer
4
. A chamber C is defined between the top ring body
2
and the holding plate
3
, and is connected to a fluid source
5
through a regulator R
1
. An elastic pad
6
of polyurethane or the like is attached to the lower surface of the holding plate
3
. A retainer ring (guide ring)
7
for holding the semiconductor wafer
4
on the lower surface, i.e. the wafer holding surface
3
a
of the holding plate
3
is disposed around the outer peripheral portion of the top ring
1
. A fluid pressure bag
8
comprising an annular tube is provided between the retainer ring
7
and the top ring
1
. The fluid pressure bag
8
is connected to the fluid source
5
through a regulator R
2
. A turntable
22
having a polishing cloth
21
attached thereon is disposed below the top ring
1
. The polishing cloth
21
constitutes a polishing surface which is brought in sliding contact with the semiconductor wafer
4
for thereby polishing the semiconductor wafer
4
.
The top ring
1
is connected to a top ring shaft
12
through a ball
11
. The top ring shaft
12
is connected to a fluid pressure cylinder
14
fixedly mounted on a top ring head
13
. The fluid pressure cylinder
14
serves as an actuator for moving the top ring
1
vertically, and is connected to the fluid source
5
through a regulator R
3
.
In the above structure, by supplying a pressurized fluid such as a compressed air to the fluid pressure cylinder
14
from the fluid source
5
, the top ring
1
presses the semiconductor wafer
4
to be polished against the polishing cloth
21
on the turntable
22
under a certain pressing force F
1
for thereby polishing the semiconductor wafer
4
. The pressing force F
1
is variable by regulating the regulator R
3
.
FIG. 2
is a schematic view showing the configuration of the wafer holding surface
3
a
of the holding plate
3
. In
FIG. 2
, the horizontal axis represents a distance (mm) from the center (O) of the holding plate
3
, and the vertical axis represents a height of the wafer holding surface. In
FIG
Katsuoka Seiji
Kojima Shunichiro
Sone Tadakazu
Tsujimura Manabu
Yasuda Hozumi
Ebara Corporation
Eley Timothy V.
Wenderoth , Lind & Ponack, L.L.P.
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