Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1998-07-13
2001-03-27
Hail, III, Joseph J. (Department: 3725)
Abrading
Abrading process
Glass or stone abrading
C451S287000, C451S288000
Reexamination Certificate
active
06206758
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a chemical-mechanical polishing machine. More particularly, the present invention relates to a method for increasing the working life of a retainer ring used in a chemical-mechanical polishing machine.
2. Description of Related Art
In the fabrication of semiconductor devices, planarizing a wafer surface is an important process before high-density microlithographic techniques can be carried out. Planarization is necessary because only when surface topographic variations are removed can diffraction of light be avoided, and, consequently, transfer of a highly accurate pattern be achieved. Currently, the two main techniques for planarizing a wafer surface include spin-on-glass (SOG) and chemical-mechanical polishing (CMP). However, ever since semiconductor fabrication has reached the sub-half micron stage, spin-on-glass technique is insufficient for providing the degree of planarity necessary for a wafer. This leaves chemical-mechanical polishing as the only means for global planarization of very large scale integration (VILSI) or even ultra large scale integration (LJLSI) circuits. Since chemical-mechanical polishing is such an important planarization techniques, various semiconductor manufacturers and research organizations are participating in the development of CN/tp techniques in order to get a head start in the field.
FIGS. 1A and 1B
are respective top-view and side-view of the components of a conventional chemical-mechanical polishing machine. Components of a chemical-mechanical polishing machine include: a polishing table
10
; a polishing pad
13
on top of the polishing table
10
; a carrier
21
and a retaining ring
20
for grabbing a wafer
12
; a spinning axle
11
for rotating the carrier
21
, a transporting pipe
14
for transporting slurry
19
to the polishing pad
13
; and a pump
15
for pumping the slurry
19
through the transporting pipe
14
. When chemical-mechanical polishing starts, the polishing table
10
and the axle
11
will both rotate separately in a predefined direction, as shown by arrows
18
a
and
18
b
in
FIGS. 1A and 1B
. Carrier
21
grabs the back of the wafer
12
, which is retained in place by the retaining ring
20
. The wafer
12
is pressed with its front face
17
onto the polishing pad
13
. Slurry
19
running through the transporting pipe
14
driven by the pump
15
is constantly dropping onto the polishing pad
13
. Polishing is achieved through chemical reaction between the chemical reagent inside the slurry
19
and the silicon on the front face
17
of the wafer
12
. The chemical reaction produces an easy-to-polish layer on the front face
17
. Moreover, abrasive particles inside the slurry
19
also offer some assistance in removing the protruding parts in the easy-to-polish layer. Therefore, by repeating the above chemical reaction and mechanical polishing action, a surface of high planarity can be obtained. In general, chemical-mechanical polishing is a process that uses mechanical polishing together with chemical reaction through special chemical reagents to smooth out and planarize a highly irregular wafer surface.
FIG. 2
is a cross-sectional view showing the location of pocket depth in a wafer holding assembly. As shown in
FIG. 2
, one end of a retaining ring
20
is connected to the periphery of the lower surface of a carrier
21
. A wafer is fixed in position by the carrier
21
and the retaining ring
20
. In
FIG. 2
, the pocket depth
22
refers to the distance from the front face
17
of the wafer
12
to the other end of the retaining ring
20
. During chemical-mechanical polishing operation, a pocket depth
22
of about 0.3 mm must be maintained so that the slurry on the polishing pad
13
can execute the best possible polishing action.
However, the retaining ring
20
is also be worn away under repeated cycles of chemical reaction and mechanical polishing action. In general, a newly installed retaining ring
20
has a thickness of about 6.35 mm. When the thickness of the retaining ring
20
has worn down to about 5.6 mm, pocket depth
22
can no longer be adjusted to about 0.3 mm. Under such circumstances, the old retaining ring
20
has to be replaced. Normally, a new retaining ring
20
is able to polish roughly between 1500 to 2000 wafers before its working life is finished. Because the retaining ring is made from a rather expensive ceramic material, any method that can increase the working life of the retaining ring can save considerable operating costs.
In light of the foregoing, there is a need to develop a method for increasing the working life of a retaining ring.
SUMMARY OF THE INVENTION
Accordingly, the present invention is to provide a method for increasing the working life of an expensive retaining ring used in a chemical-mechanical polishing machine so that the operating cost of a CMP machine can be reduced. The method is to add a pad between the retaining ring and the carrier in the wafer holding assembly. The extra pad is able to prevent unwanted slippage of the retaining ring and evenly spread out pressure on the wafer. Therefore, useful life of the retaining ring is extended.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for increasing the working life of a retaining ring. The method is used in a chemical-mechanical polishing machine that has a carrier and a retaining ring. The carrier and the retaining ring are used for grabbing a wafer firmly when the chemical-mechanical polishing machine is in operation. The method of increasing the working life of the retaining ring includes placing an additional pad between the carrier and the retaining ring. Therefore, when the wafer is being polished, the retaining ring is protected from slippage that may result in unnecessary wear.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 3791457 (1974-02-01), Hanser et al.
patent: 4025136 (1977-05-01), Ballendux
patent: 4408636 (1983-10-01), Karpenko
patent: 4562946 (1986-01-01), Ryan
patent: 4813600 (1989-03-01), Schultz et al.
patent: 5002418 (1991-03-01), McCown et al.
patent: 5862902 (1999-01-01), Howrie
Lai Chien-Hsin
Lin Juen-Kuen
Peng Peng-Yih
Hail III Joseph J.
Hong William
Huang Jiawei
J.C. Patents
United Microelectronics Corp.
LandOfFree
Method for increasing working life of retaining ring in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for increasing working life of retaining ring in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for increasing working life of retaining ring in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2436475