Abrading – Machine – Rotary tool
Reexamination Certificate
2000-10-06
2002-08-27
Ostrager, Allen (Department: 3725)
Abrading
Machine
Rotary tool
C451S041000, C451S288000, C451S398000
Reexamination Certificate
active
06439980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a workpiece carrier for holding a workpiece such as a semiconductor wafer while the workpiece is being polished to make a surface of the workpiece to a flat mirror finish, and-a polishing apparatus having such a workpiece carrier.
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.
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, and such a process is called Chemical Mechanical polishing.
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 (or material) 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.
If the relative pressure between the semiconductor wafer being polished and the polishing cloth is not uniform over the entire surface of the semiconductor wafer, then the semiconductor wafer tends to be locally polished excessively or insufficiently depending on the applied pressure.
FIG. 6
of the accompanying drawings shows a conventional polishing apparatus. As shown in
FIG. 6
, a top ring drive shaft
51
has on its lower end a spherical portion
52
which is received in a spherical seat recess
55
defined in an upper surface of a top ring
54
which holds a semiconductor wafer
53
to be polished. The top ring
54
is thus tiltable with respect to the top ring drive shaft
51
so that the top ring
54
follows automatically any possible inclinations of a turntable
56
beneath the top ring
54
. The tiltable top ring
54
allows its wafer holding surface
54
a
to be kept parallel to the upper surface of the turntable
56
for uniformizing the relative pressure between the semiconductor wafer
53
and a polishing cloth
57
attached to the upper surface of the turntable
56
over the entire surface of the semiconductor wafer
53
.
According to another proposed polishing apparatus, the top ring drive shaft and the spherical portion are separate from each other and include a top ring drive shaft and a spherical bearing comprising a ball, and the spherical bearing is interposed between the top ring drive shaft and the top ring (see Japanese laid-open patent publication No. 6-198561).
In the polishing apparatus shown in
FIG. 6
, while the semiconductor wafer
53
is being polished, the top ring drive shaft
51
applies a pressing force F through the top ring
54
to the semiconductor wafer
53
, thus developing a frictional force &mgr;F (&mgr;: coefficient of friction) on the surface of the semiconductor wafer
53
slidingly held against the polishing cloth
57
. The frictional force &mgr;F produces a rotating moment M=&mgr;FH which tends to tilt the top ring
54
depending on the height H of the center O of the spherical portion
52
from the lower surface of the semiconductor wafer
53
slidingly held against the polishing cloth
57
. Because of the rotating moment M, the entire lower surface of the semiconductor wafer
53
cannot uniformly be pressed against the polishing cloth
57
. In order to make the moment M zero, it is necessary to make the height H of the center of the spherical portion
52
zero. To meet this requirement, there has been proposed a polishing apparatus having a spherical bearing whose tilting center is positioned on the surface of the semiconductor wafer that is slidingly held against the polishing cloth.
The spherical bearing of the above mentioned proposed polishing apparatus has a convex spherical surface of relatively large area disposed on the upper surface side of the top ring and a concave spherical surface disposed on the lower end side of the top ring drive shaft and held in sliding contact with the convex spherical surface. The top ring is tiltable with respect to the top ring drive shaft due to sliding contact between the convex spherical surface and the concave spherical surface. Because of the sliding contact between the convex and concave spherical surfaces, the top ring cannot follow quickly and smoothly the inclinations of the turntable. Consequently, the wafer holding surface of the top ring and the surface of the turntable may be brought out of parallelism with each other, thus tending to cause the semiconductor wafer to be polished while the semiconductor wafer is being tilted with respect to the polishing cloth.
Another problem is that the convex and concave spherical surfaces of the spherical bearing need to be machined to accurate radii of curvature in order to make the spherical bearing function properly.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a workpiece carrier which is capable of allowing a top ring to quickly and smoothly follow possible movements (inclinations) of the upper surface of a turntable, thereby keeping a workpiece holding surface of the top ring in parellelism with the upper surface of the turntable.
Another object of the present invention is to provide a polishing apparatus having such a workpiece carrier.
According to the present invention, there is provided a workpiece carrier for holding a workpiece to be polished and pressing the workpiece against a polishing surface on a turntable, comprising a top ring body for holding the workpiece, a drive shaft for rotating the top ring body and moving the top ring body toward the turntable to press the workpiece against the polishing surface, and a universal joint for transmitting a pressing force from the drive shaft to the top ring body while allowing the drive shaft and top ring body to be tilted respective to each other, the universal joint comprising two members having curved surfaces formed along arcs having a predetermined radius of curvature from a center positioned on a surface of the workpiece which is held in contact with the polishing surface on the turntable, and at least four rolling elements held in rolling contact with the curved surfaces, wherein at least two of the rolling elements are held in rolling contact with the respective curved surfaces to allow the top ring body to be tilted relative to the drive shaft about a point positioned on the surface of the workpiece which is held in contact with the polishing surface on the turntable.
According to the present invention, there is also provided a polishing apparatus for a workpiece, comprising a turntable having a polishing surface thereon, a top ring body for holding the workpiece, a drive shaft for rotating the top ring body and moving the top ring body toward the turntable to press the workpiece against the polishing surface, and a universal joint for transmitting a pressing force from the drive shaft to the top ring body while allowing the draft shaft and the top ring body to be tilted relative to each other, the universal joint comprising two members having curved surfaces formed along arcs having a predetermined radius of curvature from a cen
Ebara Corporation
Hong William
Ostrager Allen
Wenderoth , Lind & Ponack, L.L.P.
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