Extended guide rings with built-in slurry supply line

Details Extended guide rings with built-in slurry supply line Extended guide rings with built-in slurry supply line

1999-09-13

2001-01-30

Scherbel, David A. (Department: 3723)

Abrading

Machine

Rotary tool

C451S288000, C451S285000, C451S060000

Reexamination Certificate

active

06179694

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention generally relates to a semiconductor wafer carrier and, more particularly to methods of improving the apparatus used in holding a semiconductor wafer during a chemical mechanical polishing (CMP) process.
(2) Description of Prior Art
Semiconductor fabrication often uses a combination of chemical and mechanical polishing to reduce the thickness and planarize a thin film coating on a wafer. Typically, the wafer is placed in a polishing head and makes contact with a rotating polishing pad having a slurry applied thereto. Often the polishing head holding the wafer also rotates making the planarization process more uniform.
FIG. 1
illustrates a cross section of the current art for the polishing process. The wafer
14
is held in place laterally by the extension ring
20
. To facilitate thin film planarization, uniform pressure is applied mechanically from above to the carrier
18
holding the wafer
14
firmly against the polishing pad
12
. To aid in maintaining uniform pressure to the wafer
14
, a thin backing film
16
is usually attached to the carrier
18
. The polishing table
10
and polishing pad
12
are rotated at a set speed, while often, the carrier
18
, backing film
16
, and wafer
14
rotate at a second set speed. During automated loading and unloading, the wafer is held onto the carrier by vacuum pressure via passages
22
.
Using the current methods of CMP to polish a wafer, less material is removed from the edge of the wafer than from the center. This is due to a phenomenon known as “pad rebound” or “waving phenomenon” and results in non-functioning devices on the wafer edge.
FIG. 2
a
shows a magnified cross section of the edge of the wafer
14
, the polishing pad
12
, the carrier
18
, the backing film
16
and extension ring
20
. When the wafer
14
is pressed downward onto the pad
12
, a stress concentration
38
occurs just inside the outer edge of the extension ring
20
as the pad
12
is pressed against the extension ring
20
and wafer
30
. This results in the pad
12
rebounding away from the extension ring
20
and wafer
14
. This is illustrated by the exaggerated dip
39
in the pad
12
.
FIG. 2
b
shows graphically the result of the pad rebound phenomenon. The extension ring is typically 3 to 4 mm wide. A portion of the pad rebound (~3 to 4 mm from the edge of the extension ring
12
) occurs under the extension ring (region
32
). Because of the pad rebound, material removal rate at the interface
30
between the ring and wafer is approximately at a minimum. The material removal rate increases toward the center of the wafer
14
, and becomes constant at ~6 to 7 mm (region
37
) inside the edge of the extension ring (2 to 4 mm from the edge of the wafer). Unfortunately, the edge of the wafer (region
34
) has a higher material removal rate and is therefore unusable.
Other approaches attempt to address problems with pad rebound during polishing. U.S. Pat. No. 5,795,215 to Guthrie et al. teaches a method using different pressures applied to the carrier and extension ring. U.S. Pat. No. 5,876,273 to Yano et al teaches a method using a pressure-absorbing member between the carrier and extension ring. This member allows movement of the extension ring with respect to the carrier while maintaining uniform pressure on the wafer. Another embodiment has a circular plate surrounding the wafer. U.S. Pat. No. 5,785,584 to Marmillion et al teaches a method utilizing a raised section on the polishing pad. U.S. Pat. No. 5,635,083 to Breivogel et al teaches a method whereby an air pillow under the wafer holds it flat against the polishing pad. It also utilizes different pressures on the carrier and wear ring to minimize pad rebounding. U.S. Pat. No. 5,876,271 to Oliver teaches a method whereby slurry is applied to the wafer surface though a plurality of holes in the surface of the polishing pad. U.S. Pat. No. 5,851,140 to Barns et al. teaches a method using a flexible carrier plate providing an air pillow that maintains uniform pressure on the wafer during CMP.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a carrier mechanism which polishes the wafer equally across the wafer surface by circumventing the problems caused by “pad rebound” or “waving phenomenon” during polishing.
Another object of the present invention is to equalize the pressure against the pad across the entire surface of the wafer, resulting in even planarization of thin film semiconductor material.
Yet another object of the present invention is to provide an improved mechanism for positioning semiconductor wafers during polishing.
Another object of the present invention is the reduction in slurry usage during the polishing process.
These objects are achieved by two improvements of the wafer carrier head over the prior art. The first improvement uses a wider extension ring. This results in the pad rebound phenomenon occurring only under the extension ring, allowing the applied pressure to be uniform across the wafer. The second improvement directs the polishing slurry to the pad/wafer interface through passageways in the extension ring. This alleviates problems of getting slurry to contact the wafer while using the wider extension ring, and results in a reduction in slurry usage.


REFERENCES:
patent: 5476414 (1995-12-01), Hirose et al.
patent: 5569062 (1996-10-01), Karlsrud
patent: 5584751 (1996-12-01), Kobayashi et al.
patent: 5635083 (1997-06-01), Breivogel et al.
patent: 5785584 (1998-07-01), Marmillion et al.
patent: 5795215 (1998-08-01), Guthrie et al.
patent: 5851140 (1998-12-01), Barns et al.
patent: 5876271 (1999-03-01), Oliver
patent: 5876273 (1999-03-01), Yano et al.
patent: 5902173 (1999-05-01), Tanaka
patent: 6059638 (2000-05-01), Crevasse et al.

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