Abrading – Abrading process – Abradant supplying
Reexamination Certificate
2002-07-29
2003-12-09
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Abradant supplying
C451S005000, C451S446000
Reexamination Certificate
active
06659848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to slurry dispensers that dispense slurry to a chemical-mechanical polisher used in semiconductor fabrication and, more particularly, to a slurry dispenser that outputs a filtered slurry to a polisher at a constant flow rate over the lifetime of the filter.
2. Description of the Related Art
A chemical-mechanical polisher is a device that removes excess material from the top surface of a semiconductor wafer. Chemical-mechanical polishers are commonly used to planarize the topography of a wafer, and to form damascene structures that are embedded in an insulation layer on a wafer.
FIG. 1
shows a block diagram that illustrates a conventional chemical-mechanical polisher
100
. As shown in
FIG. 1
, polisher
100
includes a round polish platen
110
, a round pad
112
that is connected to platen
110
, and a slurry dispenser
114
that dispenses a slurry
116
onto pad
112
. Slurry
116
includes water, a number of chemicals, and an abrasive material that has a large number of particles.
In addition, polisher
100
also includes a wafer carrier
120
that holds a wafer
122
so that the top surface of wafer
122
is parallel to the top surface of pad
112
. Polisher
100
further includes a vertical carrier
124
that moves wafer carrier
120
up and down so that the semiconductor materials formed on the top surface of wafer
122
are brought into contact with pad
112
.
In operation, pad
112
is rotated via platen
110
at a high rate of speed, slurry
116
is dispensed to pad
112
, and wafer
122
is rotated via carrier
120
at a high rate of speed and lowered until wafer
122
makes contact with pad
112
. Pad
112
and slurry
116
then remove the materials formed on the top surface of wafer
122
, beginning with the peaks, for as long as pad
112
and wafer
122
remain in contact.
One of the problems with chemical-mechanical polisher
100
is that when oversized particles are present in the abrasive material in slurry
116
, the surface of wafer
122
can become scratched and may affect the polishing removal rate and non-uniformity. With very small line widths, these scratches and degraded process characteristics can destroy or degrade the devices being fabricated on wafer
122
.
One approach to preventing scratches from oversized particles is to add a filter to slurry dispenser
114
that removes the oversized particles from slurry
116
. One problem with filters, however, is that filters increasingly restrict the flow of slurry
116
over time as the filters catch more and more oversized material. Eventually, the filters clog up and the flow of slurry stops.
Changes in the slurry flow rate effect the removal rate of the wafer material that is in contact with the pad which, in turn, makes it difficult to calculate how long the wafer material should remain in contact with the pad. In addition, polishers typically require a minimum slurry flow rate to remove material from a wafer, and prevent damage to the wafer.
As a result, to avoid damaging the wafer, the filter must be replaced before the decreasing slurry flow rate drops below the minimum slurry flow rate. Thus, there is a need for a slurry dispenser that outputs a filtered slurry, indicates when the filter needs to be replaced, and outputs the filtered slurry at a constant flow rate throughout the lifetime of the filter.
SUMMARY OF THE INVENTION
The present invention provides a slurry dispenser that utilizes a filter to remove oversized particles from a slurry to reduce the effects of scratches. In addition, the slurry dispenser of the present invention indicates when the filter needs to be replaced, and maintains a constant flow of slurry through the filter throughout the lifetime of the filter.
A slurry dispenser in accordance with the present invention includes a pump that receives a slurry from a slurry supply, and outputs a pumped slurry. The pump outputs the pumped slurry with a flow rate at a pump speed. The pump speed is controlled by a pump speed control signal.
The slurry dispenser also includes a slurry filter that removes oversized particles from the pumped slurry. The slurry filter has an input and an output. The dispenser additionally includes a flow meter that measures a flow rate of the pumped slurry, and outputs a measured flow signal that indicates a measured flow rate.
Further, the slurry dispenser includes a flow controller that receives the measured flow signal, compares the measured flow rate to a reference set point rate, and controls a value of the pump speed control signal in response to the difference between the measured flow rate and the reference set point rate.
The present invention also includes a method of dispensing slurry onto a pad of a chemical-mechanical polisher that includes the step of pumping a slurry from a slurry supply to output a pumped slurry. The pumped slurry has a flow rate at a pump speed. The pump speed is controlled by a pump speed control signal.
The method also includes the step of filtering the pumped slurry with a filter to remove oversized particles from the pumped slurry. The method additionally includes the steps of measuring a flow rate of the pumped slurry, and outputting a measured flow signal that indicates a measured flow rate.
The method further includes the steps of receiving the measured flow signal, comparing the measured flow rate to a reference set point rate, and controlling a value of the pump speed control signal in response to the difference between the measured flow rate and the reference set point rate.
REFERENCES:
patent: 5635074 (1997-06-01), Stenstrom et al.
patent: 5945346 (1999-08-01), Vanell et al.
patent: 6149508 (2000-11-01), Vanell et al.
Michael S. Wang, “Using a Transducer and a Flowmeter to Determine Slurry Flow Rate and POU Filter Life”, Jul./Aug. 2001 of Micro Magazine, 7 pages.
Craig David Linn
Gautreau Matthew
Hail III Joseph J.
National Semiconductor Corporation
Pickering Mark C.
Thomas David B.
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