Abrading – Work holder
Reexamination Certificate
1999-09-20
2001-06-26
Hail, III, Joseph J. (Department: 3723)
Abrading
Work holder
C451S041000, C451S044000, C438S431000, C438S631000, C438S694000, C438S695000
Reexamination Certificate
active
06251000
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a substrate holder for holding a substrate to be polished, such as a semiconductor wafer or a liquid crystal substrate, for use in a chemical/mechanical polishing (CMP) process to planarize the surface of the substrate. The present invention also relates to a method for polishing a substrate by pressing the substrate against a polishing pad and to a method for fabricating a semiconductor device by utilizing the CMP technique.
For the last decade since 1990, the diameters of CMP-processable substrates of various types, such as semiconductor wafers and liquid crystal substrates, have continued to increase. In particular, the diameter of a semiconductor wafer used to be 20-plus centimeters, but has recently reached 30 cm. On the other hand, single-wafer polishing is going to replace multi-wafer polishing day by day. Also, the feature size of a pattern formed on a semiconductor wafer has been drastically reduced over the past few years to 0.5 &mgr;m or less. Under the circumstances such as these, it has become more and more necessary to planarize a semiconductor wafer, for example, even more uniformly by the polishing process.
Hereinafter, a conventional substrate polisher for use in a CMP process and a method for polishing a substrate will be described with reference to FIG.
12
.
FIG. 12
illustrates an overall arrangement for a conventional substrate polisher. As shown in
FIG. 12
, a platen
1
a
, made of a rigid material with a flat surface, is attached to the top of a drive shaft
1
b
extending vertically downward from the lower surface of the platen
1
a
. The platen
1
a
and the drive shaft
1
b
are driven by a motor (not shown). An elastic polishing pad
2
is attached to the upper surface of the platen
1
a
. Polishing slurry
4
is supplied through a slurry supply tube
3
during polishing by a predetermined amount.
A substrate holder
100
for holding a substrate
5
to be polished thereon is provided over the polishing pad
2
. The substrate
5
is pressed against the pad
2
while being rotated by the substrate holder
100
.
In this polisher, the pad
2
is rotated along with the platen
1
a
, while the substrate
5
, held by the substrate holder
100
, is also rotated and pressed against the pad
2
with the slurry
4
supplied through the slurry supply tube
3
onto the pad
2
. As a result, the surface of the substrate
5
to be polished continuously receives pressure from the polishing pad
2
at a certain relative velocity and is polished.
If the surface of the substrate
5
to be polished has some roughness, then such roughness can be reduced through this polishing process and the substrate
5
has its surface planarized. This is because convex portions of the surface are more likely to be polished since the contact pressure between those portions and the pad
2
is relatively high and the relative polishing rate also increases. On the other hand, concave portions thereof are hardly polished because the concave portions hardly come into contact with the polishing pad
2
, or should such contact happen, the resulting contact pressure therebetween is relatively low.
As described above, when chemical/mechanical polishing is carried out, the entire surface of a semiconductor wafer should be polished and planarized even more uniformly recently. To meet this demand, a substrate holder such as that disclosed in Japanese Laid-Open Publication No. 8-339979 was proposed.
FIG. 13
illustrates a substrate holder
100
A according to a first prior art example disclosed in Japanese Laid-Open Publication No. 8-339979 identified above. As shown in
FIG. 13
, the substrate holder
100
A for holding a substrate
5
to be polished thereon and pressing the substrate
5
against a polishing pad
2
is disposed over the polishing pad
2
attached to the upper surface of a platen
1
a.
The substrate holder
100
A according to the first prior art example includes a drive shaft
101
, a disklike substrate-holding head
102
, a ringlike seal member
103
made of an elastic body and a ringlike guide member
104
. The substrate-holding head
102
is integrated with the drive shaft
101
at the lower end thereof. The seal member
103
is secured to the lower surface of the substrate-holding head
102
in a peripheral region thereof. And the guide member
104
is secured around the outer periphery of the seal member
103
on the lower surface of the substrate-holding head
102
. A fluid path
105
runs through the drive shaft
101
and the substrate-holding head
102
. Pressurized fluid or air is introduced through the upper end of the fluid path
105
, passed through the lower end of the path
105
and then supplied into a space
106
, which is formed by the substrate-holding head
102
, seal member
103
and substrate
5
. The pressurized fluid, which has been supplied into the space
106
, presses the substrate
5
against the polishing pad
2
. As a result, the substrate
5
is polished.
FIG. 14
illustrates a substrate holder
100
B according to a second prior art example. As shown in
FIG. 14
, the substrate holder
100
B includes a drive shaft
101
, a disklike substrate-holding head
102
, a back pad
108
made of an elastic body and a ringlike guide member
104
. The substrate-holding head
102
is integrated with the drive shaft
101
at the lower end thereof. The back pad
108
is secured to the lower surface of the substrate-holding head
102
. And the guide member
104
is secured around the outer periphery of the back pad
108
on the lower surface of the substrate-holding head
102
. In this configuration, if the pressure inside a fluid path
105
, which runs through the substrate-holding head
102
, is reduced, then the substrate
5
is held tight on the substrate-holding head
102
. On the other hand, if the pressure inside the fluid path
105
is increased, then the substrate
5
is released from the substrate-holding head
102
. Also, when the substrate-holding head
102
, which is holding the substrate
5
thereon, is pressed against the polishing pad
2
, the substrate
5
is polished.
FIGS.
15
(
a
) and
15
(
b
) illustrate a relationship between the distance from the center of the substrate and the polishing rate where the substrate is polished using the substrate holders according to the first and second prior art examples. As can be seen from FIGS.
15
(
a
) and
15
(
b
), the polishing rate abruptly increases in the outer edge region of the substrate
5
.
The present inventors carried out intensive research to find out why the polishing rate abruptly increased in the outer edge region of the substrate
5
that had been polished using the substrate holders according to the first and second prior art examples. As a result, we reached the following conclusion.
As shown in
FIG. 16
, during the polishing process of the substrate
5
, the substrate-holding head
102
is rotating in the direction as indicated by the arrow B while being pressed downward against the polishing pad
2
as indicated by the arrow A. Accordingly, the polishing pad
2
, which is usually made of an elastic body such as foamed polyurethane or a non-woven fabric, receives the forces applied in the respective directions A and B from the substrate
5
and the guide member
104
. Thus, portions of the polishing pad
2
, which come into contact with the respective outer edges of the substrate
5
and the guide member
104
, are likely to form protrusions
2
a
and
2
b
. And the respective regions near the outer edges of the substrate and the guide member
4
receive high pressure as a result of rebounding of the protrusions
2
a
and
2
b
of the polishing pad
2
as indicated by arrows C representing rebounding force in FIG.
16
. It is probably because the region near the outer edge of the substrate
5
receives much pressure from the protrusion
2
a
that the polishing rate in the outer edge region of the substrate
5
is a lot higher than that in the center region of the substrate
5
.
Thus, a proposed substrate holder includes resp
Ikenouchi Katsuyuki
Miyoshi Yuichi
Murakami Tomoyasu
Hail III Joseph J.
Matsushita Electric - Industrial Co., Ltd.
McDonald Shantese
Nixon & Peabody LLP
Robinson Eric J.
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