Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2000-06-30
2002-10-22
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
Utilizing fluent abradant
C451S041000, C451S056000, C451S060000, C451S072000, C451S306000, C451S446000
Reexamination Certificate
active
06468134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to chemical mechanical polishing (CMP) systems and techniques for improving the performance and effectiveness of CMP operations. Specifically, the present invention relates to the distribution of micro-abrasive suspension, or slurry, underneath the wafer in CMP operations.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform CMP operations, including polishing, buffing and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from each other by dielectric materials, such as silicon dioxide, for example. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metal line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization, e.g., such as copper.
In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.
FIG. 1A
illustrates an exemplary prior art CMP system
100
. The CMP system
100
in
FIG. 1A
is a belt-type system, so designated because the preparation surface is an endless belt
108
mounted on two drums
114
which drive the belt
108
in a rotational motion as indicated by belt rotation directional arrows
116
. As used herein, the belt
108
should be understood to include a polishing pad or other preparation surface material in addition to any supporting material, such as aluminum, stainless steel or any suitable supporting structural material for holding the pad or other preparation surface. A wafer
102
is mounted on a carrier
104
. The carrier
104
is rotated in direction
106
. The rotating wafer
102
is then applied against the rotating belt
108
with a force F to accomplish a CMP process. Some CMP processes require significant force F to be applied. A platen
112
is provided to stabilize the belt
108
and to provide a solid surface onto which to apply the wafer
102
.
Slurry
118
is introduced upstream of the wafer
102
. In a belt-type CMP system
100
, slurry
118
is commonly introduced in a region that is upstream and off-center from the wafer
102
as illustrated in FIG.
1
A. The movement of the belt
108
carries the slurry
118
to the wafer
102
which is mounted on the carrier
104
and being applied against the belt
108
with a force F as it is being rotated
106
. The rotation
106
of the wafer
102
and the friction of the wafer
102
against the belt
108
further distributes the slurry
118
across and into the polishing pad or other preparation surface of the belt
108
and over the surface of the wafer
102
. In
FIG. 1C
, the effect of the moving belt
108
and the rotating wafer
102
is illustrated. As the slurry
118
approaches the wafer
102
from upstream and off-center, it is distributed across the belt
108
, facilitating the CMP operation and moving beyond the wafer
102
having been distributed across a larger region of the belt
108
. Slurry
118
a
is shown after passing the wafer
102
and having been distributed across the belt
108
during the CMP operation on wafer
102
.
Slurry
118
, as is known, is a water-based suspension consisting of dispersed micro-abrasives, dissolved chemicals and in some cases, lubricants. The fluid properties of the suspension allow for the even distribution of the abrasive material across a surface and enhance the effectiveness of the CMP operation. Both solid abrasives and fluid chemicals, including water, modify the surface properties of interacting objects, thus promoting smooth removal. A section of a typical CMP belt
108
and the porous texture of the polishing pad or other preparation surface is illustrated in FIG.
1
B. As stated above, the belt provides the supporting structure for the polishing pad or other preparation surface. In
FIG. 1B
, the polishing pad surface of the belt
108
is shown as uneven or rough and contributing an abrasiveness. Slurry
118
is distributed over the pad surface
108
, but due to the fluid properties, the micro-abrasives, surface tension, capillary openings in the belt
108
surface blocked by air, and other such factors, the slurry does not penetrate into the surface cavities through the usual distribution method described above.
FIG. 1B
shows capillary openings blocked by air pockets
119
that form in the surface cavities and result in uneven and unstable slurry distribution. Non-uniform slurry distribution can result in less efficient and non-uniform planarization of wafers being processed. Further, if slurry
118
loses the fluid properties due to build-up and drying, then the micro-abrasives collect and “cake” forming chunks of abrasive debris. This abrasive debris, in the extreme, can damage the quality of the semiconductor wafer being processed in a CMP operation. Typically, such debris contributes to non-uniform planarization and wafer defects. In addition to the air pockets
119
shown in
FIG. 1B
, the polishing pad surface
108
can accumulate build-up of dried slurry
118
. As the slurry build-up dries, chunks of abrasive debris form.
One method of removing and preventing build-up on the pad surface
108
is illustrated in
FIG. 1A. A
belt conditioner assembly
110
is mounted down-stream from the wafer
102
. The belt conditioner assembly
110
consists of an abrasive head that is applied against the polishing pad surface
108
to dislodge any abrasive debris that may be on the polishing pad
108
. Further, the belt conditioner assembly
110
renews the surface cavities in the polishing pad
108
to ensure the pad
108
retains its abrasive properties, and the ability to hold and transport slurry into the CMP operation. As the belt continues to rotate, the conditioner assembly
110
provides constant conditioning of the pad
108
during CMP operations. Or, the conditioning assembly
110
can be programmed to condition the pad
108
at intervals according to operator requirements.
The increased complexity of multi-layered semiconductor chips requires more precise and more uniform planarization techniques. CMP is and will remain an integral part of the semiconductor wafer manufacturing process, but must be made more effective and more controllable to meet the increasing demands for more complex fabrication. In view of the foregoing, there is a need for slurry distribution methods and apparatus in CMP operations that are more controllable, that more evenly and uniformly distribute slurry across a preparation surface, and that minimize the risks of damage due to dried slurry and abrasive debris.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing systems and methods for the uniform and even distribution of slurry in a CMP system. The gimbaled roller system and method provide a controllable distribution of slurry to create a more efficient and effective CMP operat
Eley Timothy V.
Lam Research Corporation
Martine & Penilla LLP
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