Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-06-22
2002-07-16
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S286000, C451S287000, C451S288000, C451S289000
Reexamination Certificate
active
06419558
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method, and particularly, to the apparatus and the method for polishing semiconductor wafers based on a chemical mechanical polishing (CMP) technique. The present invention also relates to a backing plate and a backing film used by the polishing apparatus.
2. Description of the Related Art
FIG. 1A
is a top view showing a polishing apparatus according to a related art and
FIG. 1B
is a side view showing the same. The polishing apparatus is used for semiconductor device manufacturing for polishing and planarizing the steps in the surface of a semiconductor wafer due to devices and interconnections formed thereon. A disk-like surface plate
8
has a shaft
10
rotated by a driver (not shown). A polishing cloth
7
made of for example, polyurethane foam is attached to the top of the surface plate
8
. A port
11
supplies abrasive
12
onto the polishing cloth
7
. A wafer base
13
is arranged above the surface plate
8
. The bottom of the wafer base
13
holds a wafer. The wafer base
13
has a shaft
9
, which is connected to a pressing unit (not shown) and a rotating unit (not shown). The pressing unit presses the wafer against the polishing cloth
7
. The rotating unit rotates the wafer in the same direction as the rotating direction of the surface plate
8
.
FIG. 2
is a sectional view showing the wafer base
13
and the vicinity thereof. The wafer base
13
is made of a head
6
, backing plate
4
, a backing film
2
, and a guide
5
. The head
6
is driven by the shaft
9
and rotates above the surface plate
8
. The head
6
is pushed down by the pressing unit through the shaft
9
. The head
6
uniformly presses the wafer
1
against the polishing cloth
7
through the backing plate
4
. To flatly polish the wafer
1
, an interface of the backing plate
4
with the backing film
2
is processed flat. The back film
2
is resilient so that the backing plate
4
may evenly press the wafer
1
against the polishing cloth
7
. Even if dust is present between the wafer
1
and the backing film
2
, the backing film
2
is flexible to contain the dust so that a surface of the wafer
1
to be polished may evenly be pushed against the polishing cloth
7
. The guide
5
prevents the wafer
1
from moving away from the backing film
2
. An end face of the guide
5
that faces the polishing cloth
7
is higher than the polished surface of the wafer
1
with respect to the polishing cloth
7
. When the wafer
1
is set on the polishing cloth
7
, the end face of the guide
5
is away from the polishing cloth
7
. When the wafer
1
is pressed against the polishing cloth
7
, the backing film
2
and polishing cloth
7
are compressed and the end face of the guide
5
comes in contact with and presses the polishing cloth
7
.
With this arrangement the port
11
feeds the abrasive
12
onto the polishing cloth
7
that is rotated The wafer
1
set under the backing film
2
is rotated and pushed by the wafer base
13
toward the polishing cloth
7
so that the surface of the wafer
1
contacting with the polishing cloth
7
is polished.
Polishing rates and their uniformity on a thermal oxidation film formed on the surface of an 8-inch silicon wafer will be explained. The wafer has LSIs formed on the surface thereof The size of each LSI is dependent on a step-and-repeat technique used to form the LSIs and is usually 1-cm square. To improve the yield and quality of LSIs on each wafer, polishing rates within the wafer must be as uniform as possible.
FIG. 3
shows polishing rates measured at different measurement points on a wafer. The wafer is a silicon wafer of 200 mm in diameter and has a thermal oxidation film to be polished with the wafer being pressed against the polishing cloth
7
and the guide
5
being away from the polishing cloth
7
. The measurement points
1
to
7
are set along a straight line passing through the notch and center of the. wafer and are away from the center of the wafer by 96 mm, 80 mm, 40 mm, 0 mm, 40 mm, 80 mm, and 96 mm, respectively. Namely, the measurement points
1
and
7
are at the periphery of the wafer, and the measurement point
4
is at the center thereof. Polishing rates measured at the points
1
and
7
are each about 1.7 times greater than that measured at the point
4
.
FIG. 4
shows polishing rates measured at different measurement points with the guide
5
being pressed against the polishing cloth
7
when polishing a thermal oxidation film formed on a silicon: wafer of 200 mm in diameter. The measurement points
1
to
7
are the same as those of FIG.
3
. Polishing rates at the peripheral measurement points
1
and
7
are about 20% smaller than those at the other measurement points. Compared wit
FIG. 3
,
FIG. 4
shows an improvement in the uniformity of polishing rates on the wafer, and therefore, it can be said that pressing the guide
5
against the polishing cloth
7
is advantageous. This, however, may deteriorate the quality of LSIs formed at the periphery of the wafer below criteria because the peripheral polishing rates are about 20% smaller than the others.
SUMMARY OF THE INVENTION
The reason why the peripheral polishing rates are lower than the others will be examined.
FIG. 5
is a partly see-trough top view showing essential parts of a polishing apparatus. A polishing cloth
7
is circular, 600 mm in diameter, and about 4 mm in thickness. When polishing a wafer
1
, the polishing cloth
7
is rotated counterclockwise at about 30 rpm. A guide
5
is a cylinder having an inner diameter of about 202 mm. When polishing the wafer
1
, the guide
5
is rotated counterclockwise at about 30 rpm. The wafer
1
is circular, 200 mm in diameter, and about 0.8 mm in thickness. When being polished, the wafer
1
is pushed against a backing film
2
(not shown) that revolves with the guide
5
. At this time, the wafer
1
slightly slides on the backing film
2
and rotates counterclockwise at a speed slower than 30 rpm. Under this situation, the wafer
1
is shifted toward a right part of the ring
5
, and a gap
16
of about 2 mm is formed between the guide
5
and the left edge of the wafer
1
. In connection with this, two cases will be examined.
(1) A first case is that the guide
5
is away from the polishing cloth
7
even after the wafer
1
is pressed against the polishing cloth
7
.
FIGS. 6A
,
6
B, and
6
C are sectional views taken along a line I—I of FIG.
5
. In
FIG. 6A
, the wafer
1
is not pressed against the polishing cloth
7
, and the polishing cloth
7
and a wafer base
13
are not rotated yet. A gap
15
between the guide
5
and the polishing cloth
7
is set to be in the range of 0.3 mm to 0.5 mm so that the guide
5
is away from the polishing cloth
7
after the wafer
1
is pressed against the polishing cloth
7
and so that the wafer
1
may not escape from the guide
5
even when the polishing cloth
7
and wafer base
13
are rotated.
In
FIG. 6B
, a shaft
9
is thrust to press the wafer
1
against the polishing cloth
7
. The wafer
1
compresses the polishing cloth
7
, and the backing film
2
on the wafer
1
is also compressed evenly.
In
FIG. 6C
, the polishing cloth
7
and wafer base
13
are rotated from the condition of FIG.
6
B. The polishing cloth
7
moves right ward in
FIG. 6C
, and therefore, the wafer
1
is shifted toward the right part of the guide
5
and the polishing cloth
7
at the edge of the wafer
1
is deformed due to rotation. In particular, the polishing cloth
7
at the left edge of the wafer
1
rises and is compressed further than FIG.
6
B. At this time, the left edge of the wafer
1
is pushed more strongly than the remaining part thereof by the polishing cloth
7
, to increase a polishing rate at the left edge.
The reason why polishing rates at the periphery of a wafer is about 1.7 times greater than those at the other parts in
FIG. 3
is because the periphery of the wafer is pushed more strongly than the other parts by the polishing cloth
7
Kato Nobuhiro
Watanabe Tomoharu
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Hail III Joseph J.
Kabushiki Kaisha Toshiba
McDonald Shantese
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