Abrading – Accessory – Dressing
Reexamination Certificate
1999-11-18
2001-12-04
Hail, III, Joseph J. (Department: 3723)
Abrading
Accessory
Dressing
C451S041000, C451S056000, C451S287000, C451S288000, C451S443000, C451S444000
Reexamination Certificate
active
06325709
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention generally relates to a chemical mechanical polishing process used in semiconductor manufacturing and, more particularly, to a pad conditioner used to remove build up of residue and slurry from an abrasive polishing pad during a chemical and mechanical polishing process of a semiconductor wafer.
(2) Description of Prior Art
Semiconductor fabrication often uses a combination of chemical and mechanical polishing (CMP) 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.
FIGS. 1
a
and
1
b
illustrate schematically the current art for the CMP process.
FIG. 1
a
shows a cross section of the CMP process, while
FIG. 1
b
shows a more simplified top view. The wafer (not shown) is contained laterally by a wafer carrier
106
. To facilitate thin film planarization, uniform pressure is applied mechanically from above to the carrier
106
holding the wafer firmly against the polishing pad
100
. The polishing table
102
and polishing pad
100
are rotated at a set speed about axis A
2
by adjusting the polishing table drive mechanism
104
. The carrier drive mechanism
108
will rotate the wafer carrier
106
about axis A
1
at a second predetermined speed. During the CMP process an abrasive and chemical slurry
116
is dispensed through a spigot
110
. During the polishing operation residue from the wafer and particles in the slurry
116
build up in pores of the pad
100
. Over time this reduces the thin film removal rate and can result in yield loss. For this reason, the pad is periodically conditioned. The conditioner
112
typically having a diamond abrasive crystal electroplated to the lower surface (not shown) is pressed against the pad
100
while being moved radially across the pad
100
and rotated about axis A
3
by the conditioner drive mechanism
114
. This conditioning operation can be performed while a wafer is being polished, but often is performed as a separate step with de-ionized (DI) water applied to the pad. The conditioning process is only performed when needed because constant contact of the conditioner
112
and pad
100
would cause the pad
100
to wear out prematurely.
Referring now to
FIG. 2
illustrating in cross section the current art for pad conditioning. Here a conditioner
112
having a flat, diamond abrasive crystal lower surface
118
is pressed against the pad
100
. The diamond crystals
118
are usually electroplated to a nickel alloy conditioner
112
. Unfortunately, this arrangement causes the conditioning to occur non-uniformly which in turn results in non-uniform material removal from the wafer. The non-uniform conditioning is caused by two factors. The first factor is due to the increased friction at the leading (left) edge of the conditioner
112
. This additional friction results from the relative motion between the pad
100
and conditioner
112
. The second factor is that, due to the shape of the conditioner
112
, the slurry (not shown) used during the conditioning process (typically DI water) will not reach the center of the conditioner
112
. One other problem with this pad conditioning method is that the low pH slurry attacks the diamond crystals
118
causing particles to fall off and subsequently scratch the wafers.
Other approaches attempt to address problems with pad conditioning and maintaining polishing uniformity. U.S. Pat. No. 5,605,499 to Sugiyama et al. teaches a method using a specific polishing pad along with an oscillating conditioning tool which has a shape designed to conform to the shape of the backing film used on the wafer carrier. U.S. Pat. No. 5,667,433 to Mallon teaches a method using keys to locking the conditioner in place thereby eliminating slippage of the conditioner. U.S. Pat. No. 5,823,854 to Chen teaches a method utilizing an automated measuring process to determine when the polishing pad needs conditioning. U.S. Pat. No. 5,904,615 to Jeong et al teaches a method using a disc or cup shaped conditioner while providing ultrasonic vibration to the conditioner. U.S. Pat. No. 5,906,754 to Appel et al teaches a method where polishing and conditioning are performed simultaneously. There are three embodiments of this invention using conditioners with a lower surface having triangular teeth, rectangular teeth and dimples, respectively.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a CMP process which polishes the wafer equally across the wafer surface by circumventing the problems caused by non-uniform pad conditioning. In doing this, material removal at the edge of the wafer will be equal to that at the center resulting in even planarization of thin film semiconductor material.
Another object of the present invention is to provide an improved mechanism for uniform conditioning of the polishing pad used in CMP.
Another object of the present invention is to extend the life of the polishing pad used during the polishing process.
Yet another object of the present invention is the reduction in friction between the leading edge of the conditioner and the polishing pad.
A further object of the present invention is equal distribution of slurry under the conditioning surface of the conditioner.
Another object of the present invention is to provide an improved method of bonding the diamond crystals to the lower surface of the polishing pad.
A still further object of the present invention is to provide an improved method for uniform conditioning of the polishing pad used in CMP by using a conditioner with a convex lower surface.
These objects are achieved by using a conditioner with a convex lower surface covered by diamond crystal abrasive surface. The modification in shape reduces the friction between the pad and conditioner and also allows the slurry to reach the center of the conditioner. This results in a more uniformly conditioned surface which then yields more uniformly polished wafers.
REFERENCES:
patent: 5885137 (1999-09-01), Ploessl
patent: 5954570 (1999-09-01), Yano et al.
patent: 6001008 (1999-12-01), Fujimori et al.
Nanda Arun Kumar
Quek Ser Wee
Chartered Semiconductor Manufacturing Ltd
Hail III Joseph J.
McDonald Shantese
Pike Rosemary L. S.
Saile George O.
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