Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2000-10-12
2004-08-24
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
Utilizing fluent abradant
C451S041000, C451S056000, C451S059000, C451S072000
Reexamination Certificate
active
06780088
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chemical mechanical polishing apparatus and a method of chemical mechanical polishing using the same, and in particular to those involving a dresser for refreshing the top surface of a polishing pad for polishing an object to be polished, in which the refreshment is effected by pressure-contacting such dresser under rotation to such polishing pad.
2. Description of the Related Art
Chemical Mechanical Polishing (CMP) apparatus is becoming widely used in the planarization of interlayer insulating film for isolating upper and lower wirings as multi-layered wiring structures are increasingly adopted by system LSIs (Large Scale Integrated circuits). Using the chemical mechanical polishing apparatus allows surface roughness of the interlayer insulating film to be suppressed as small as 100 nm or around.
A known chemical mechanical polishing apparatus is such that being typically shown in FIG.
7
. In a chemical mechanical polishing apparatus
10
, a polishing pad
14
is stretched on a turn table
12
; where the polishing pad
14
being made of a material such as polyurethane foam.
Above the polishing pad
14
, a pressurizing head
16
is provided so as to be rotatable and so as to be pressurized against the polishing pad
14
. On the bottom surface of the pressurizing head
16
, a semiconductor wafer
18
as an object to be polished is held by vacuum chucking so as to orient a plane to be polished downward.
Again above the polishing pad
14
and at a position not overlapped with that for the pressurizing head
16
, a dresser
20
is provided so as to be rotatable and so as to be pressurized against the polishing pad
14
. A substrate composing the upper portion of the dresser
20
is made of stainless steel (SUS), the under surface of the substrate is nickel-plated, and diamond grains (#100) are embedded in such plated surface.
A nozzle
22
is positioned above the center portion of the polishing pad
14
, from which polishing fluid is dropwisely supplied to the center portion of the polishing pad
14
. The polishing fluid is spread by the centrifugal force and flows into the interface between the polishing pad
14
and the semiconductor wafer
18
, thereby to be used for polishing the semiconductor wafer
18
.
The polishing fluid comprises a mixture (slurry) of SiO
2
abrasive and a 0.5 wt % KOH solution, and has a primary grain size (size of a single SiO
2
grain) of about 40 nm in diameter and an average grain size (size of an agglomerate composed of a couple of SiO
2
grains for forming siloxane bonds —Si—O—Si—) of approximately 100 nm in diameter.
Polishing of the semiconductor wafer
18
using such a chemical mechanical polishing apparatus
10
begins with making pressure-contact of the rotating pressurizing head
16
with the polishing pad
14
stretched on the rotating turn table
12
, thereby to effect mutual sliding motion between the semiconductor wafer
18
and polishing pad
14
kept under contact. During the polishing of the semiconductor wafer
18
, the polishing fluid is constantly dropped from the nozzle
22
and thus supplied to the interface between the polishing pad
14
and the semiconductor wafer
18
.
The rotating dresser
20
is also pressure-contacted to the polishing pad
14
stretched on the rotating turn table
12
, thereby to effect mutual sliding motion between the dresser
20
and polishing pad
14
kept under contact. This allows constant grinding of the surface of the polishing pad
14
by the dresser
20
so as to keep on creating a fresh surface thereof, which is also referred to as refreshing.
Typical polishing conditions relate to a number of rotation of the pressurizing head
16
of 40 rpm, a pressing force of the pressurizing head
16
against the polishing pad
14
of 58.8 kN/m
2
, a number of rotation of the turn table
12
of 42 rpm, a number of rotation of the dresser
20
of 34 rpm, a pressing force of the dresser
20
against the polishing pad
14
of 50 N/m
2
, an amount of polishing of interlayer insulating film of 1,000 nm, a polishing time of approx. 2 min., and a material of the interlayer insulating film of plasma TEOS (P-TEOS).
Next, parameters representing the polishing properties will be described. Such parameters representing the polishing characteristics relate to polishing uniformity (%) and polishing rate (nm/min).
According to a general method for calculating the polishing uniformity, differences in the film thickness before and after the polishing are measured for 49 points on the semiconductor wafer
18
, maximum value (D
max
)and minimum value (D
min
) of such differences are found and then further difference between these values is obtained (D
max
−D
min
), then the value is divided by an average value (D
ave
) of the differences of the film thickness before and after the polishing measured for the same 49 points multiplied by 2, and the quotient is multiplied by 100, which is expressed by the equation below:
polishing uniformity (%)=(
D
max
−D
min
)×100/(2
×D
ave
)
According to a general method for calculating the polishing rate, the average value (D
ave
: nm) of the differences in the film thickness before and after the polishing measured for 49 points is divided by polishing time (t: min), which is expressed by the equation below:
polishing rate (nm/min)=
D
ave
/t
Now,
FIG. 5
is a graph showing a relation between operating time of the dresser
20
and cumulative operating time of the polishing pad
14
for use in the polishing of the semiconductor wafer
18
. The figure shows the operating time of the dresser
20
on the abscissa and the cumulative operating time of the polishing pad
14
on the ordinate. It is apparent from the figure that the cumulative operating time of the polishing pad
14
in the polishing of the semiconductor wafer
18
sharply increases as the operating time of the dresser
20
increases.
This is probably because wear of the diamond grains embedded in the surface of the dresser
20
resulted in decrease in the amount of wear of the polishing pad
14
, which prolongs the cumulative operating time of the polishing pad
14
used in the polishing of the semiconductor wafer
18
. It is generally defined that the lifetime of the polishing pad
14
ends when the thickness thereof reaches a value 0.8 mm thinner than the initial thickness. Lifetime of the dresser
20
ends when the operating time reaches 300 hours.
However in the conventional chemical mechanical polishing apparatus, a problem resides in that, as shown in
FIG. 8
, the lifetime of the dresser
20
ends too early when the operating time reaches only as short as 100 hours or around, far from 300 hours, since clogs
26
of the polishing fluid are likely to be trapped between the diamond grains
24
on the dresser
20
and thus the polishing performance is ruined. This may result in degraded productivity with the dresser
20
since the dresser
20
needs to be frequently replaced.
Considering the foregoing problems, it is therefore an object of the present invention to provide a chemical mechanical polishing apparatus and a method using thereof, in which the dresser is prevented from being shortened in the lifetime through preventing the clogs of the polishing fluid from being trapped between the diamond grains, and through successfully removing clogs already formed.
SUMMARY OF THE INVENTION
To solve the foregoing problem, a chemical mechanical polishing apparatus of the present invention is such that used for polishing an object to be polished while feeding a polishing fluid between the object to be polished and a polishing pad, and comprises a turn table rotating while holding on a top surface of which the polishing pad; a pressurizing head rotating while holding on a bottom surface of which the object to be polished so as to pressure-contact the object to be polished to the polishing pad; a dresser for refreshing the top surface of the polishing pad by pressure-contacting the bottom surface of which to th
Eley Timothy V.
Sonnenschein Nath & Rosenthal LLP
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