Abrading – Machine – Rotary tool
Reexamination Certificate
1999-02-24
2004-08-31
Hail, III, Joseph J. (Department: 3723)
Abrading
Machine
Rotary tool
C451S041000, C451S261000, C451S283000
Reexamination Certificate
active
06783446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for polishing a substrate for planarization by chemical mechanical polishing. The invention relates further to a method of chemical mechanical polishing.
2. Description of the Related Art
FIGS. 1A
to
1
E illustrate respective steps in a method of forming a buried metal layer in a semiconductor device.
First, as illustrated in
FIG. 1A
, a semiconductor substrate
101
including active devices fabricated thereon is covered entirely with an insulating film
102
.
Then, a resist film
105
having a certain pattern is formed on the insulating film
102
, and subsequently, the insulating film
102
is etched with the patterned resist film
105
being used as a mask, to thereby form a contact hole
106
through the insulating film
102
, as illustrated in FIG.
1
B.
After removal of the resist film
105
, as illustrated in
FIG. 1C
, a barrier film
103
composed of metal such as Ti or Ta is deposited over the insulating film
102
so that the contact hole
106
is covered at a sidewall and a bottom thereof with the barrier film
103
.
Then, as illustrated in
FIG. 1D
, an electrically conductive layer
104
is deposited over the product to thereby fill the contact hole
106
with the electrically conductive layer
104
.
Then, the electrically conductive film
104
is planarized by means of a chemical mechanical polishing apparatus
107
, as illustrated in FIG.
1
E. Thus, a buried metal layer
108
is formed.
The chemical mechanical polishing apparatus
107
includes a carrier on which a wafer to be polished is fixed, and a rotatable level block on which a polishing pad is mounted. A wafer is compressed onto a rotating polishing pad to thereby be polished. While a wafer is being polished by the polishing pad, polishing powder such as alumina or silica, and polishing slurry containing etchant such as H
2
O
2
are supplied between the polishing pad and the wafer.
FIG. 2
illustrates a conventional apparatus for polishing a wafer by chemical mechanical polishing. The illustrated apparatus is comprised of a level block
23
connected to a rotatable shaft
24
, a polishing pad
29
fixed onto the level block
23
, a wafer holder
26
connected to a rotatable shaft
27
and holding a wafer
25
on a bottom thereof, and a slurry source
30
supplying polishing slurry onto the polishing pad
29
through a slurry supply port
21
.
The wafer
25
is sandwiched between the polishing pad
29
and the wafer holder
26
. While the wafer
25
is being polished by the polishing pad
29
, polishing slurry
22
is supplied between the polishing pad
29
and the wafer
25
around a periphery of the wafer
25
.
Though the illustrated apparatus is designed to have one wafer holder
26
, the apparatus may be designed to have a plurality of wafer holders
26
. For instance, the apparatus may be designed to have four wafer holders
26
equally spaced from one another above the level block
23
in order to concurrently polish four wafers at a time.
A conventional apparatus for polishing a wafer, such as the apparatus illustrated in
FIG. 2
, is accompanied with a problem of non-uniformity in polishing speed in a wafer, which results in that a wafer is polished around a center thereof to a greater degree than a periphery thereof.
In order to overcome this problem, there has been suggested a first polishing apparatus in which a polishing pad mounted on a level block is formed with a plurality of small through-holes through which polishing slurry is supplied onto a surface of the polishing pad from a polishing slurry source. The small through-holes are positioned in concentration with an axis of the polishing pad
29
. Since polishing slurry is uniformly supplied between a wafer and the polishing pad, it would be possible to keep a polishing speed constant to thereby enhance uniformity in polishing a wafer.
There has been suggested also a second polishing apparatus in which a polishing pad is composed of porous material in order to enhance uniformity in polishing a wafer.
However, since a wafer having a greater diameter is compressed onto a polishing pad at a greater pressure around a center thereof than a periphery thereof, a polished wafer would have a cross-section like a cross-section of a concave lens, if a wafer is polished in accordance with the above-mentioned first or second polishing apparatuses in which polishing slurry is uniformly supplied to a surface of a wafer, whereas a polished wafer would have a cross-section like a convex lens, if a wafer is polished in accordance with the apparatus illustrated in FIG.
2
.
In order to avoid this problem, Japanese Unexamined Patent Publication No. 5-13389 has suggested a polishing apparatus which has the same structure as that of the above-mentioned first and second polishing apparatus, but is capable of controlling an amount of polishing slurry at a predetermined position of a polishing pad for the purpose of enhancing uniformity in polishing a wafer.
Specifically, the suggested polishing apparatus is formed with a plurality of through-holes through which polishing slurry is supplied onto a surface of a polishing pad, in such a manner that the number of through-holes per a unit area in a region closer to a center of a polishing pad is designed to be greater than the number of through-holes per a unit area in a region closer to a periphery of a polishing pad, or that a through-hole located closer to a center of a polishing pad is designed to have a greater diameter than a diameter of a through-hole located closer to a periphery of a polishing pad.
A diameter of a wafer necessary to be polished is increasing. For instance, a diameter of a wafer to be polished years ago was 6 inches (about 15 cm), but a diameter of a wafer to be polished presently is in the range of 8 to 10 inches (about 20 to about 25 cm). Such a wafer having a great diameter could not be polished by means of such an apparatus as illustrated in
FIG. 2
, because the level block
23
has to have too much area, which results in too high load to the apparatus.
Hence, there has been suggested such a polishing apparatus as illustrated in
FIG. 3A
, in order to avoid the above-mentioned problem. The illustrated apparatus is comprised of a rotatable carrier
2
supporting a wafer
1
at a bottom thereof, a level block
3
, a polishing pad
4
mounted on the level block
3
and positioned in facing relation to the carrier
2
, and a motor
5
for rotating the level block
3
around a rotation axis. The polishing pad
4
is formed with a plurality of through-holes equally spaced from one another.
The wafer
2
is made to rotate, and then, is compressed onto the rotating polishing pad
4
. While the wafer
1
is being polished. While the wafer
2
is being polished, slurry
6
is supplied onto a surface of the polishing pad
4
through the through-holes.
In order to enhance uniformity in polishing the wafer
1
, the level block
3
is rotated by means of the motor
5
in such a manner that the rotation axis of the level block
3
moves along an arcuate path. That is, the level block
3
makes so-called orbital revolution.
FIG. 4
shows a positional relation in orbital revolution between the wafer
1
rotating around a rotation axis A and the polishing pad
4
rotating around a rotation axis B. As illustrated in
FIG. 4
, if viewed from the rotation axis A, the rotation axis B rotates around the rotation axis A.
As mentioned earlier, if a wafer is polished with polishing slurry being supplied onto a surface of a polishing pad through through-holes formed with the polishing pad, there is caused a problem that a wafer is polished to a greater degree in a central region than in a peripheral region, resulting in that a wafer is concave in a central region thereof. If a wafer is non-uniformly polished as mentioned above, an electrically conductive film such as the electrically conductive film
104
illustrated in
FIG. 1D
partially remains non-removed on an insulating film such as the insulating film
102
, resu
Suzuki Mieko
Tsuchiya Yasuaki
Grant Alvin J
Hail III Joseph J.
Hayes & Soloway P.C.
NEC Electronics Corporation
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