Abrading – Machine – Rotary tool
Reexamination Certificate
2001-03-06
2003-02-11
Nguyen, George (Department: 3723)
Abrading
Machine
Rotary tool
C451S398000
Reexamination Certificate
active
06517422
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing apparatus for polishing semi-conductor wafers evenly and in mirror-surface, and in particular to a polishing apparatus enabling to control polishing amount around peripheral parts of the semi-conductor wafer.
2. Description of the Related Art
In general, a semi-conductor wafer is subjected to a so-called mirror-face polishing process for providing a mirror face with flatness of high precision and without strain. For performing the mirror-face polishing process, generally plural sheets of the semi-conductor wafer are polished simultaneously, so-called batch type polishing apparatus is served. With respect to the batch type polishing apparatus, explanation will be made in reference to
FIGS. 10 and 11
of the attached drawings.
As shown, this polishing apparatus is equipped with a rotary shaft
1
a
, a polishing level block
1
provided on the upper end of the rotary shaft
1
a
, a polishing cloth pasted on the upper surface of the polishing level block
1
, a polishing head
3
disposed rotatably and movably vertically at a position eccentric from the rotary shaft
1
a
, a plurality of plate holders
6
provided on the outer periphery of the polishing head
3
, and a polishing plate
4
attached to the lower surface of the polishing head
3
and to be positioned by the plate holder
6
.
The semi-conductor wafer
5
are, as shown in
FIG. 11
, arranged in the circumferential direction of the polishing plate
4
, and the plural sheets are pasted to the surface of the polishing plate
4
.
For polishing the semi-conductor wafer
5
by means of this polishing apparatus, the polishing level block
1
is rotated in an arrow direction around the rotary shaft
3
a
, and at the same time the polishing head
3
at the eccentric position with respect to the polishing level block
1
is rotated in the arrow direction. Subsequently, as dropping a polishing liquid A from a center of the polishing cloth
2
(an upper part of the rotary shaft
1
a
), the polishing head
3
is moved down to cause the semi-conductor wafer
5
to press to the polishing cloth
2
.
In this conventional polishing apparatus, for polishing, the polishing liquid A is, as seen in
FIG. 10
, poured to the center of the polishing cloth
2
and flows in the outer circumference of the polishing cloth
2
. As a result, the polishing liquid is much supplied to the circumference of the polishing
5
, so that the polishing is progressed more in the circumference of the semiconductor wafer
5
than the central part (inside part), so-called excessive polishing (sags) takes place.
With respect to sags caused at the circumferential part of the semiconductor wafer, JP-A-11-114806 proposes that there is furnished a polishing face adjusting ring encircling the outer circumference of one sheet of wafer, so that the pressing force of the polishing face adjusting ring is controlled by fluid pressure so as to exert uniform polishing force to the semi-conductor wafer for uniformly polishing the semi-conductor wafer.
PROBLEMS THAT THE INVENTION IS TO SOLVE
In the conventional polishing apparatus using the polishing face adjusting ring, the polishing face adjusting ring is pressed to the polishing cloth by fluid pressure and at the same time the pressure is controlled. As to the control of pressure by the fluid pressure, if the structure of the polishing apparatus is complicated, it is difficult to adjust pressure by the fluid pressure, and the pressure of the polishing face adjusting ring is varied as a time passes or depending on positions, and it is difficult to always effect pressure all over the ranges. In particular, in the batch type polishing apparatus where plural sheets of semi-conductor wafers are pasted on one sheet of plate for performing the polishings concurrently, the polishing face adjusting ring encircling the semi-conductor wafer is of large-diameter, and it is difficult to adjust all over pressing face of the polishing face adjusting ring and maintain the uniform force.
Even if the pressure is controlled by the polishing face adjusting ring to exert the uniform polishing force on the semi-conductor wafers, occurrences of sags could not be prevented and a substantial solution has not yet been realized.
Further, a semi-conductor wafer is made by producing a semi-conductor ingot of single crystal through, for example, a Czochralski method from polycrystal, slicing the ingot into predetermine thickness by means of such as a multi-wire sawyer, grinding the sliced semi-conductor wafer by a grinding apparatus, and further mirror-polishing it by a polishing apparatus.
But recently, accompanied with high integration of semi-conductor device, a demand has been arisen in the semi- conductor wafer as to the degree of flatness, and in the mirror-polishing process, a problem occurs about excessive polishing (outer circumferential sags) in the outer peripheral part of the semi-conductor wafer. It is assumed that one cause is owing to influences by sinking or depressing the abrasive cloth, and measures therefor have been practiced for moderating depression of the polishing cloth into the semi-conductor wafer by hardening the polishing cloth itself or previously pushing the polishing cloth.
For providing the polishing effect by the retainer ring, one of important factors is a distance (clearance) between the semi-conductor wafer and the retainer ring.
Namely, showing in
FIGS. 21 and 22
as the results of simulating pressure dispersions of the retainer ring, the semi-conductor wafer and the polishing cloth by a static analysis, when the clearance C is large as shown in
FIG. 21
, since the polishing cloth
211
once crushed by the retainer ring
212
recovers until contacting the semi-conductor wafer
213
by compression elastic modulus of the polishing cloth
211
, large change does not occur in pressure of the peripheral part
213
c
of the semi-conductor wafer
213
, and reaction force of the peripheral part
213
c
receiving from the polishing cloth
211
becomes large, and an effect for furnishing the retainer ring
212
is not available. When the clearance C is small as shown in
FIG. 22
, the reaction force of the peripheral part
213
c
receiving from the polishing cloth
211
by the retainer ring
212
becomes small, and the effect for furnishing the retainer ring
212
can be sufficiently obtained.
Accordingly, if bringing the clearance to 0 unlimitedly, it is possible to obtain the retainer effect at the maximum, but actually it is difficult to process an inner diameter of the retainer ring equal to the diameter of the semiconductor wafer, taking dispersion of the diameter of the semi-conductor wafer and dispersion of the inner diameter of the retainer ring into consideration.
A method of checking face-sags in the wafer using the retainer ring is disclosed in JP-A-5-326468, and the disclosed polishing method carries out the polishing under a condition where the circumference of the wafer is attached with a ring of thickness smaller than a finished thickness of the wafer and checking the face sags.
But this disclosed method cannot bring the clearance to 0 unlimitedly, because the clearance is fixed during polish processing, and the retainer effect cannot be exhibited at the maximum.
Therefore, such a wafer polishing method has been demanded which can display the effect of the retainer ring to the most and prevent sags in the peripheral part of the wafer.
SUMMARY OF THE INVENTION
The invention has been realized to solve such problems, and it is an object of the invention to provide a polishing apparatus which polishes the semi-conductor wafers under a condition before recovering the polishing cloth (a deformed state), thereby to mirror-finish the semi-conductor wafers of flatness of high precision. It is another object of the invention to provide a polishing apparatus which prevents any invasion of excessive polishing liquid, easily controls a pressing force, has no probability of varying the pressing force, and is ready for being a
Hoshi Yoshihiko
Kawamoto Shinya
Kojima Katsuyoshi
Kotari Katsuaki
Saitou Masayoshi
Nguyen Dung Van
Nguyen George
Toshiba Ceramics Co. Ltd.
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