Abrading – Machine – Rotary tool
Reexamination Certificate
1998-08-28
2001-12-18
Scherbel, David A. (Department: 3723)
Abrading
Machine
Rotary tool
C451S527000, C451S528000, C451S530000, C451S921000
Reexamination Certificate
active
06331137
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the planarization of semi-conductor wafers and, more specifically to a polishing pad having a cross-sectional open area which varies with distance from the initial pad surface
BACKGROUND OF THE INVENTION
Chemical-mechanical polishing (CMP) is a widely used means of planarizing silicon dioxide as well as other types of surfaces on semiconductor wafers. Chemical mechanical polishing typically utilizes an abrasive slurry disbursed in an alkaline or acidic solution to planarize the surface of the wafer through a combination of mechanical and chemical action.
FIG. 1
illustrates one type of chemical mechanical polishing (CMP) system. The CMP system
100
includes a rotatable circular platen or table
102
on which a polishing pad
104
is mounted. A single or multi-head polishing device
106
is positioned above the table
102
. The polishing device
106
has a single or multiple rotating carrier heads
108
to which wafers can be secured typically through the use of vacuum pressure. Typically, the polishing pad
104
includes a bottom pad
110
mounted on the platen
102
and a top pad
112
mounted on the bottom pad
110
. Typically, the top pad
112
is adhered to the bottom pad
110
using a glue. The bottom pad
110
serves as a damper and typically is formed from foam or felt. The top pad
112
generally contacts the wafer for polishing and is typically formed from polyurethane.
In use, the platen
102
is rotated and an abrasive slurry is disbursed onto the polishing pad
104
of the platen
102
. Once the slurry has been applied to the polishing pad
104
, the rotating carrier heads
108
move downward to press their corresponding wafers against the polishing pad
104
. As the wafer is pressed against the polishing pad
104
, the surface of the wafer is mechanically and chemically polished. Between polishing runs, the polishing pad
104
is typically conditioned. Conditioning typically includes applying a conditioning tool, such as a diamond impregnated steel plate, to the top pad
112
to remove expired surface and expose fresh pad material.
A significant goal relating to chemical-mechanical polishing techniques is the maintenance of substantially uniform removal rate over the entire surface of a given wafer. The uniformity or nonuniformity of a wafer is typically measured using the relationship: &sgr;/R, where R is the average removal amount over a number of different locations on a wafer and &sgr; is the standard deviation of the removal amounts. The polishing uniformity of a polishing pad may also be measured using the relationship &sgr;/R for wafers polished by the pad over time. By way of example,
FIG. 2
is a graph illustrating polishing uniformity as a function of pad life for a typical polishing pad. As can be seen, the polishing uniformity typically starts poorly in a period of time known as the break-in period. This typically results from the pad polishing the center of a wafer slower or faster than the edges. After the break-in period, the polishing uniformity reaches an optimum level and flattens out for a period of time. This time period is commonly referred to as the useful life of the pad. At the end of the useful life, the polishing uniformity declines, again usually resulting from the pad polishing wafer centers faster or slower than the edges.
SUMMARY OF THE INVENTION
The present invention generally provides a polishing pad having a cross-sectional open area which varies with depth from the pad surface. This can, for example, allow the open area of the pad to vary with pad life and increase the polishing uniformity and/or extend the useful life of the pad.
A polishing pad, in accordance with one embodiment of the invention, includes a pad having an outer surface and defining a cross-sectional open area which varies with distance from the outer surface. The cross-sectional open area of the pad may increase and/or decrease moving away from the outer pad surface. In some cases, the cross-sectional open area of the pad varies uniformly with depth over the entire pad. In other cases, certain regions of the pad may define local cross-sectional open areas which vary differently.
A method of polishing wafers, in accordance with an embodiment of the invention, includes providing a polishing pad having an outer surface and defining a cross-sectional open area which varies with distance from the outer surface. One or more wafers are polished using the polishing pad at a first cross-sectional open area. A portion of the polishing pad is then removed to expose a second cross-sectional open area different than the first cross-sectional open area, and one or more wafers are polished at the second cross-sectional open area. The removal of portions of the polishing pad typically occurs through conditioning of the pad between one or more polishing runs.
The above summary of the present invention is not intended to describe each illustrated embodiment or implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.
REFERENCES:
patent: 5020283 (1991-06-01), Tuttle
patent: 5297364 (1994-03-01), Tuttle
patent: 5441598 (1995-08-01), Yu et al.
patent: 5645469 (1997-07-01), Burke et al.
patent: 5655951 (1997-08-01), Meikle et al.
patent: 5725420 (1998-03-01), Torii
patent: 5853317 (1998-12-01), Yamamoto
patent: 5876271 (1999-03-01), Oliver
patent: 5882251 (1999-03-01), Berman et al.
patent: 5984769 (1999-11-01), Bennett et al.
patent: 0 304 645 A2 (1989-03-01), None
Raeder Christopher H.
Shipley Kevin
Advanced Micro Devices Inc
Nguyen George
Scherbel David A.
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