Method and apparatus for polishing semiconductor substrate

A polishing pad is adhered to the top surface of a flat polishing pad holder of a platen. A substrate holding head for holding and rotating a semiconductor substrate is provided above the platen. The semiconductor substrate is rotated and pressed against the polishing pad on the platen. A slurry is supplied in a prescribed amount from a slurry supply pipe onto the polishing pad. A slat-like slurry pushing member for pushing the slurry to a central portion of the platen is provided slidably over the polishing pad. The slurry pushing member is fixed so that an inner portion thereof in a radial direction of the platen is downstream of an outer portion thereof in the radial direction of the platen in the direction of rotation of the platen during polishing.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for polishing a 
semiconductor substrate whereby chemical mechanical polishing (CMP) is 
performed with respect to a semiconductor substrate of silicon or the like 
to flatten a surface thereof. 
From the 1990s, CMP technology for polishing semiconductor substrates of 
silicon or the like has shown increasing tendencies toward single-wafer 
processing as the semiconductor substrates processed by CMP have had 
larger diameters on the order of 10 cm or more, resulting in an increased 
amount of slurry consumed per wafer. 
By way of example, a conventional apparatus for polishing a semiconductor 
substrate will be described below with reference to the drawings. 
FIG. 22 schematically shows the construction of the conventional polishing 
apparatus, in which is shown a platen 11 including: a substrate holder 11a 
made of a rigid material and having a flat surface; a rotary shaft 11b 
extending vertically downwardly from the back surface of the substrate 
holder 11a; and rotating means (not shown) for rotating the rotary shaft 
11b. To the top surface of the substrate holder 11a of the platen 11 is 
adhered a polishing pad 12. Above the platen 11 is provided a substrate 
holding head 14 which holds and rotates a semiconductor substrate 13. The 
semiconductor substrate 13 is rotated and pressed against the polishing 
pad 12 on the platen 11 by the substrate holding head 14. A slurry 15 
containing abrasive grains (extremely fine powder for polishing) is 
dropped in a prescribed amount from a slurry supply pipe 16 onto the 
polishing pad 12 so as to supply the abrasive grains to the space between 
the polishing pad 12 and the semiconductor substrate 13. 
In the polishing apparatus thus constructed, the polishing pad 12 supplied 
with the slurry 15 is rotated by rotating the platen 11 and the 
semiconductor substrate 13 is pressed against the rotating polishing pad 
12 by the substrate holding head 14 so that a surface of the semiconductor 
substrate 13 is polished. 
In this process, if the surface of the semiconductor substrate 13 is 
rugged, the polishing rate is increased at projecting portions of the 
semiconductor substrate 13 since their contact pressure with the polishing 
pad 12 is high. On the other hand, the polishing rate is reduced at 
recessed portions of the semiconductor substrate 13 since their contact 
pressure with the polishing pad 12 is low. Consequently, the surface of 
the semiconductor substrate 13 becomes less rugged and more smooth. 
However, the above polishing apparatus have the following problems. 
When a consideration is given to the amount of supplied slurry and the 
polishing rate, the polishing rate increases with increases in the amount 
of supplied slurry 15 and eventually becomes constant when the amount of 
supplied slurry reaches a given value. Accordingly, the amount of slurry 
15 normally supplied onto the polishing pad 12 is slightly larger than the 
given value with which the polishing rate becomes constant. 
However, since the slurry 15 is supplied onto the rotating polishing pad 12 
as described above, the slurry 15 is caused to flow to the peripheral 
portion of the polishing pad 12 by a centrifugal force accompanying the 
rotation of the platen 11. When the amount of slurry 15 becomes smaller 
than the given value, the polishing rate is reduced. To compensate for the 
reduction in the polishing rate, the pressure for pressing the 
semiconductor substrate 13 against the polishing pad 12 should be 
increased. However, the increased pressure induces dishing or like 
phenomenon, which causes such a problem as the degradation of polishing 
properties. Hence, the slurry should constantly be supplied in an amount 
slightly larger than the given value with which the polishing rate becomes 
constant, so that the cost of the slurry accounts for a considerable 
proportion of the cost of polishing. 
To solve the problem, there have been proposed an apparatus and method for 
polishing wherein a slurry on a polishing pad is prevented from flowing 
out by a partition board enclosing the polishing pad, as disclosed in U.S. 
Pat. No. 4,910,155. 
According to the apparatus and method for polishing, however, foreign 
matters such as tips of polishing pad generated at the polishing are 
accumulated on the polishing pad. Also, water supplied onto the polishing 
pad to clean up a semiconductor substrate after polishing or perform 
dressing (the conditioning of the surface of the polishing pad) as well as 
the slurry is prevented from flowing out, resulting in unfavorable 
variations in the concentration of the slurry, which changes the polishing 
properties. 
SUMMARY OF THE INVENTION 
In view of the foregoing, an object of the present invention is to provide 
a method and apparatus for polishing a semiconductor substrate wherein a 
cleaning liquid supplied onto a polishing pad is removed from the top 
surface thereof, while a slurry supplied onto the polishing pad is held 
thereon. 
A first apparatus for polishing a semiconductor substrate according to the 
present invention comprises: a platen having a flat surface and rotating 
around a shaft vertical to the flat surface; a polishing pad disposed on 
the flat surface of the platen; slurry supplying means for supplying a 
slurry onto the polishing pad; substrate holding means for holding a 
semiconductor substrate and pressing it against the polishing pad; and 
slurry pushing means for pushing, to a central portion of the platen, the 
slurry supplied onto the polishing pad and caused to flow to a peripheral 
portion of the platen by a centrifugal force accompanying the rotation of 
the platen. 
In the first apparatus for polishing a semiconductor substrate, the slurry 
flowing to the peripheral portion of the platen due to a centrifugal force 
accompanying the rotation of the platen is pushed back to the central 
portion of the platen by the slurry pushing means to be reused in the 
polishing of the semiconductor substrate, so that the amount of consumed 
slurry is reduced. 
In the first apparatus for polishing a semiconductor substrate, the slurry 
pushing means is preferably a pushing plate held over the polishing pad to 
push, to the central portion of the platen, the slurry brought in contact 
therewith by the centrifugal force accompanying the rotation of the 
platen. The arrangement permits the pushing plate to push back, to the 
central portion of the platen, the slurry brought in contact therewith by 
the centrifugal force accompanying the rotation of the platen. Thus, the 
amount of consumed slurry can be reduced by the simple and cost-effective 
method wherein the pushing plate is provided above the polishing pad. 
Preferably, the pushing plate is positioned to intersect a radial direction 
of the platen such that an inner portion of the pushing plate in the 
radial direction of the platen is downstream of an outer portion of the 
pushing plate in the radial direction of the platen in the direction of 
rotation of the platen during polishing. In the arrangement, the slurry 
flowing to the peripheral portion of the platen while rotating with the 
rotation of the platen is caused to change its direction by the pushing 
plate and flows back to the central portion of the platen while rotating. 
This enables the slurry to be smoothly returned to the central portion of 
the platen and efficiently reused. 
In this case, the direction in which the slurry flows can be determined 
based on the speed of the slurry relative to the pushing plate and on a 
change in velocity vector accompanying a change in kinetic energy caused 
by a collision of the slurry with the pushing plate. By optimizing the 
configuration, position, and orientation of the pushing plate in 
consideration of the rotation speed of the platen, the viscosity of the 
slurry, and the surface roughness of the polishing pad, the effect of 
pushing back the slurry to the central portion of the platen can surely be 
achieved. 
Preferably, the pushing plate is provided rotatable in a direction opposite 
to the rotation of the platen during polishing. When the pushing plate is 
rotated in the direction opposite to the rotation of the platen during 
polishing, the cleaning liquid on the polishing pad is pushed to the 
outside of the platen by the back surface of the pushing plate, so that 
the cleaning liquid is removed from the top surface of the polishing pad 
in a short period of time. 
Preferably, the pushing plate is provided to have a spacing equal to or 
smaller than the thickness of a layer of the slurry supplied onto the 
polishing pad between the pushing plate itself and a top surface of the 
polishing pad. The arrangement permits the pushing plate to come in 
contact with the slurry and push it back to the central portion of the 
platen, while keeping the pushing plate from contact with the polishing 
pad. Consequently, powder does not result from the friction between the 
pushing plate and the polishing pad. 
Preferably, the pushing plate is made of a flexible material and provided 
such that a back surface of the pushing plate is in contact with a top 
surface of the polishing pad. In the arrangement, the lower portion of the 
pushing plate is deformed to follow the configuration of the top surface 
of the polishing pad so that no space is formed between the back surface 
of the pushing plate and the top surface of the polishing pad. 
Consequently, the slurry is pushed back to the central portion of the 
platen and reused more efficiently. 
Preferably, the pushing plate has a slurry collecting portion for 
collecting the slurry at an outer portion thereof in a radial direction of 
the platen and a slurry pushing portion for pushing the slurry collected 
by the slurry collecting portion to the central portion of the platen at 
an inner portion thereof in the radial direction of the platen. In the 
arrangement, the slurry flowing to the peripheral portion can be collected 
more positively by the slurry collecting portion and the slurry collected 
by the slurry collecting portion can be pushed back to the central portion 
of the platen by the slurry pushing member. Accordingly, the amount of 
slurry flowing out of the top surface of the polishing pad can further be 
reduced, resulting in more efficient reuse of the slurry. 
Preferably, a plurality of pushing plates are spaced along the periphery of 
the platen. The arrangement further reduces the amount of slurry flowing 
out of the top surface of the polishing pad, resulting in more efficient 
reuse of the slurry. On the other hand, the cleaning liquid on the 
polishing pad is removed through the space between the pushing plates. 
In the first apparatus for polishing a semiconductor substrate, the slurry 
pushing means is preferably gas ejecting means for ejecting a gas for 
pushing the slurry on the polishing pad to a central portion of the 
platen. By controlling the flow rate and pressure of the gas ejected from 
the gas ejecting means in the arrangement, the slurry can be pushed 
properly back to the central portion of the platen depending on flow 
characteristics such as the amount and viscosity of the slurry. On the 
other hand, the cleaning liquid can be removed smoothly from the top 
surface of the polishing pad by halting the ejection of the gas. 
Preferably, a plurality of gas ejecting means are provided along the 
periphery of the platen. With the arrangement, the amount of slurry 
flowing out of the top surface of the polishing pad is further reduced, 
resulting in more efficient reuse of the slurry. 
In the first apparatus for polishing a semiconductor substrate, the slurry 
pushing means is preferably a rotary member provided in contact with or 
slightly spaced from a top surface of the polishing pad and rotating in a 
direction opposite to the rotation of the platen. In the arrangement, the 
slurry flowing to the peripheral portion of the platen while rotating with 
the rotation of the platen is brought in contact with the outer 
circumferential surface of the rotary member rotating in the direction 
opposite to the rotation of the platen and caused to flow to the central 
portion of the platen along the outer circumferential surface. The slurry 
thus smoothly returned to the central portion of the platen can be reused 
efficiently. 
More preferably, the rotary member has a projecting portion on the outer 
circumferential surface thereof. In the arrangement, the slurry flowing to 
the peripheral portion of the platen with the rotation of the platen is 
caused to flow back to the central portion of the platen by the projecting 
portion provided on the outer circumferential surface of the rotary 
member. Accordingly, the amount of slurry flowing out of the top surface 
of the polishing pad can further be reduced, resulting in more efficient 
reuse of the slurry. 
A second apparatus for polishing a semiconductor substrate according to the 
present invention comprises: a platen having a flat surface and rotating 
around a shaft vertical to the flat surface; a polishing pad disposed on 
the flat surface of the platen; slurry supplying means for supplying a 
slurry onto the polishing pad; substrate holding means for holding a 
semiconductor substrate and pressing it against the polishing pad; and a 
slurry holding member provided on an edge portion of the platen such that 
an inner portion of the slurry holding member in a radial direction of the 
platen is downstream of an outer portion of the slurry holding member in 
the radial direction of the platen in the direction of rotation of the 
platen during polishing so as to hold the slurry supplied onto the 
polishing pad and caused to flow to a peripheral portion of the platen by 
a centrifugal force accompanying the rotation of the platen on the 
polishing pad. 
In the second apparatus for polishing a semiconductor substrate, the slurry 
flowing to the peripheral portion of the platen while rotating with the 
rotation of the platen is caused to change its direction by the slurry 
holding member and held on the polishing pad to be reused in the polishing 
of the substrate. Thus, the amount of consumed slurry can be reduced by 
the simple and cost-effective method. 
In the second apparatus for polishing a semiconductor substrate, a 
plurality of slurry holding members are preferably spaced along the 
periphery of the platen. The arrangement further reduces the amount of 
slurry flowing out of the top surface of the polishing pad, resulting in 
more efficient reuse of the slurry. On the other hand, the cleaning liquid 
on the polishing pad is removed through the space between the slurry 
holding members. 
Of the plurality of slurry holding members, adjacent ones are more 
preferably overlapping in the radial direction of the platen. The 
arrangement further reduces the amount of slurry flowing out of the 
polishing pad, resulting in more efficient reuse of the slurry. 
In the second apparatus for polishing a semiconductor substrate, the slurry 
holding member is preferably provided movable upwardly, downwardly, or 
outwardly from the polishing pad and the substrate holding member is 
provided movable in a plane in parallel with the polishing pad while 
holding the semiconductor substrate. 
After the slurry holding member is moved upwardly, downwardly, or outwardly 
from the polishing pad, the slurry holding member is moved in a plane in 
parallel with the polishing pad such that at least a part of the 
semiconductor substrate protrudes from the polishing pad to reduce the 
adhesion of the polishing pad to the semiconductor substrate. Thus, the 
semiconductor substrate can easily be unloaded from the top surface of the 
polishing pad. 
A first method of polishing a semiconductor substrate according to the 
present invention comprises: a slurry supplying step of supplying a slurry 
onto a polishing pad disposed on a flat surface of a platen rotating 
around a shaft vertical to the flat surface; a substrate polishing step of 
polishing a semiconductor substrate by pressing it against the polishing 
pad; and a slurry pushing step of pushing, to a central portion of the 
platen, the slurry supplied onto the polishing pad and caused to flow to a 
peripheral portion of the platen by a centrifugal force accompanying the 
rotation of the platen. 
According to the first method of polishing a semiconductor substrate, the 
slurry flowing to the peripheral portion of the platen due to a 
centrifugal force accompanying the rotation of the platen is pushed back 
to the central portion of the platen to be reused in the polishing of the 
substrate, so that the amount of consumed slurry is reduced. 
In the first method of polishing a semiconductor substrate, the slurry 
pushing step preferably includes a step of pushing the slurry on the 
polishing pad to the central portion of the platen by means of a pushing 
plate held over the polishing pad. With the arrangement, the slurry 
flowing to the peripheral portion of the platen due to the centrifugal 
force accompanying the rotation of the platen is pushed back to the 
central portion of the platen to be reused in the polishing of the 
semiconductor substrate, so that the amount of consumed slurry is reduced. 
In the first method of polishing a semiconductor substrate, the slurry 
pushing step preferably includes a step of pushing the slurry on the 
polishing pad to the central portion of the platen by means of the pushing 
plate positioned to intersect a radial direction of the platen such that 
an inner portion of the pushing plate in the radial direction of the 
platen is downstream of an outer portion of the pushing plate in the 
radial direction of the platen in the direction of rotation of the platen 
during polishing. With the arrangement, the slurry flowing to the 
peripheral portion of the platen while rotating with the rotation of the 
platen is caused to flow back to the central portion of the platen while 
being rotated by the pushing plate. The slurry thus smoothly returned to 
the central portion of the platen can be reused efficiently. 
In the first method of polishing a semiconductor substrate, the slurry 
pushing step preferably includes a step of pushing the slurry supplied 
onto the polishing pad to the central portion of the platen by means of 
the pushing plate provided to have a spacing equal to or smaller than the 
thickness of a layer of the slurry on the polishing pad between the 
pushing plate itself and a top surface of the polishing pad. The 
arrangement permits the pushing plate to push the slurry in contact 
therewith back to the central portion of the platen, while keeping the 
pushing plate from contact with the polishing pad, so that powder does not 
result from the friction between the pushing plate and the polishing pad. 
In the first method of polishing a semiconductor substrate, the slurry 
pushing step preferably includes a step of pushing the slurry on the 
polishing pad to the central portion of the platen by means of the pushing 
plate made of a flexible material and provided such that a back surface 
thereof is in contact with a top surface of the polishing pad. With the 
arrangement, the lower portion of the pushing plate is deformed in 
accordance with the configuration of the top surface of the polishing pad 
so that no space is formed between the back surface of the pushing plate 
and the top surface of the polishing pad. Consequently, the slurry is 
pushed back to the central portion of the platen and reused more 
efficiently. 
Preferably, the first method of polishing a semiconductor substrate, 
further comprises a cleaning-liquid removing step of removing a cleaning 
liquid supplied onto the polishing pad by rotating the platen in a 
direction opposite to the rotation of the platen during polishing. When 
the platen is rotated in the direction opposite to the rotation of the 
platen during polishing, the pushing plate relatively rotates in the 
direction opposite to the rotation of the platen, so that the cleaning 
liquid on the polishing pad is pushed to the outside of the platen by the 
back surface of the pushing plate. Accordingly, the cleaning liquid can be 
removed from the top surface of the polishing pad in a short period of 
time. 
In the first method of polishing a semiconductor substrate, the slurry 
pushing step preferably includes a step of ejecting a gas toward a central 
portion of the platen to push the slurry on the polishing pad to the 
central portion of the platen. By controlling the flow rate and pressure 
of the gas ejected toward the central portion of the platen in the 
arrangement, the slurry can be pushed properly back to the central portion 
of the platen depending on flow characteristics such as the amount and 
viscosity of the slurry. On the other hand, the cleaning liquid can be 
removed smoothly from the top surface of the polishing pad by halting the 
ejection of the gas. 
In the first method of polishing a semiconductor substrate, the slurry 
pushing step preferably includes a step of pushing the slurry on the 
polishing pad to the central portion of the platen by means of a rotary 
member provided in contact with or slightly spaced from a top surface of 
the polishing pad and rotating in a direction opposite to the rotation of 
the platen. With the arrangement, the slurry flowing to the peripheral 
portion of the platen while rotating with the rotation of the platen 
collides with the outer circumferential surface of the rotary member and 
is caused to flow back to the central portion of the platen along the 
outer circumferential surface. The slurry thus smoothly returned to the 
central portion of the platen can be reused efficiently. 
A second method of polishing a semiconductor substrate according to the 
present invention comprises: a slurry supplying step of supplying a slurry 
onto a polishing pad disposed on a flat surface of a platen rotating 
around a shaft vertical to the flat surface; a substrate polishing step of 
polishing a semiconductor substrate by pressing it against the polishing 
pad; and a slurry holding step of holding the slurry supplied onto the 
polishing pad and caused to flow to a peripheral portion of the platen by 
a centrifugal force accompanying the rotation of the platen on the 
polishing pad by means of a slurry holding member fixed to an edge portion 
of the platen such that an inner portion of the slurry holding member in a 
radial direction of the platen is downstream of an outer portion of the 
slurry holding member in the radial direction of the platen in the 
direction of rotation of the platen during polishing. 
According to the second method of polishing a semiconductor substrate, the 
slurry flowing to the peripheral portion of the platen while rotating with 
the rotation of the platen is caused to change its direction by the slurry 
holding member and flows back to the central portion of the platen while 
rotating. Accordingly, the slurry can be held positively on the polishing 
pad and reused efficiently. Thus, the amount of consumed slurry can be 
reduced by the simple and cost-effective method. 
In the second method of polishing a semiconductor substrate, the slurry 
holding step preferably includes a step of holding the slurry on the 
polishing pad by means of a plurality of slurry holding members spaced 
along the periphery of the platen. The arrangement further reduces the 
amount of slurry flowing out of the top surface of the polishing pad, 
resulting in more efficient reuse of the slurry, while the cleaning liquid 
on the polishing pad is removed through the space between the slurry 
holding members. 
In the second method of polishing a semiconductor substrate, the slurry 
holding step preferably includes a step of holding the slurry on the 
polishing pad by means of the plurality of slurry holding members of which 
adjacent ones are overlapping in the radial direction of the platen. The 
arrangement further reduces the amount of slurry flowing out of the top 
surface of the polishing pad, resulting in more efficient use of the 
slurry. 
Preferably, the second method of polishing a semiconductor substrate 
further comprises a cleaning-liquid removing step of removing a cleaning 
liquid supplied onto the polishing pad by rotating the platen in a 
direction opposite to the rotation of the platen during polishing. When 
the platen is rotated in the direction opposite to the rotation of the 
platen during polishing, the slurry holding member relatively rotates in 
the direction opposite to the rotation of the platen, so that the cleaning 
liquid on the polishing pad is pushed to the outside of the platen by the 
back surface of the slurry holding member. Accordingly, the cleaning 
liquid can be removed from the top surface of the polishing pad in a short 
period of time. 
Preferably, the second method of polishing a semiconductor substrate 
further comprises: a slurry-holding-member moving step of moving the 
slurry holding member upwardly, downwardly, or outwardly from the 
polishing pad; and a substrate moving step of moving the semiconductor 
substrate in a plane in parallel with the polishing pad such that at least 
a part of the semiconductor substrate thrusts out from the polishing pad. 
The arrangement reduces the adhesion of the polishing pad to the 
semiconductor substrate so that the semiconductor substrate is easily 
unloaded from the top surface of the polishing pad.

DETAILED DESCRIPTION OF THE INVENTION 
Below, polishing methods and polishing apparatus according to the 
individual embodiments of the present invention will be described with 
reference to the drawings. 
(First Embodiment) 
FIG. 1 is a schematic perspective view of a polishing apparatus according 
to a first embodiment of the present invention, in which is shown a platen 
11 including: a polishing-pad holder 11a made of a rigid material and 
having a flat surface; a rotary shaft 11b extending vertically downwardly 
from the back surface of the polishing-pad holder 11a; and rotating means 
(not shown) for rotating the rotary shaft 11b. To the top surface of the 
polishing-pad holder 11a is adhered a polishing pad 12 made of 
polyurethane or like material. Above the platen 11, there is provided a 
substrate holding head 14 which holds and rotates a semiconductor 
substrate 13. The semiconductor substrate 13 is rotated and pressed 
against the polishing pad 12 on the platen 11 by the substrate holding 
head 14. A slurry 15 containing abrasive grains is dropped in a prescribed 
amount from a slurry supply pipe 16 onto the polishing pad 12 and supplied 
to the space between the polishing pad 12 and the semiconductor substrate 
13 by rotating the platen 11 and the substrate holding head 14. 
The first embodiment is characterized in that a compressed-air supply pipe 
17 for ejecting a compressed air to the top surface of the polishing pad 
12 is provided as slurry pushing means over the periphery of the polishing 
pad 12. An ejection hole 17a of the compressed-air supply pipe 17 is 
opened to face the center of rotation of the platen 11. The ejection hole 
17a has a diameter of, e.g., about 3 mm and the flow speed of the 
compressed air ejected from the ejection hole 17a is set at about 5 
m/second. With the arrangement, the compressed air ejected from the 
ejection hole 17a of the compressed-air supply pipe 17 is supplied from 
the slurry supply pipe 16 to the top surface of the polishing pad 12 to 
push the slurry 15 directed to the peripheral portion by a centrifugal 
force accompanying the rotation of the platen 11 back to the central 
portion of the platen 11. As a result, the slurry 15 reciprocates between 
the central and peripheral portions of the platen 11 to equally provide 
the abrasive grains over the top surface of the semiconductor substrate 
13. 
The diameter of the ejection hole 15a and the flow speed of the compressed 
air are not limited to the foregoing. Any diameter and any speed may be 
selected properly provided that the slurry 15 on the polishing pad 12 is 
pushed back to the central portion of the platen 11. Although the ejection 
hole 17a of the compressed-air supply pipe 17 is opened to face the center 
of rotation of the platen 11, it may face any direction provided that the 
gas ejected from the ejection hole 17a is capable of causing the slurry 15 
on the polishing pad 12 to flow to the center of rotation of the platen 
11. 
The number of ejection holes 17a of the compressed-air supply pipe 17 is 
not particularly limited. However, a plurality of, e.g., 5 or 6 ejection 
holes 17a are preferably provided. 
Although the first embodiment has used the compressed air as the gas to be 
ejected, similar effects are achieved by using any other gas. However, an 
inert gas such as a nitrogen gas is preferably ejected depending on the 
type of the slurry, since the inert gas exhibits chemical stability to the 
slurry. 
Although the slurry 15 contains the abrasive grains in the above first 
embodiment, the slurry 15 may be a liquid containing no abrasive grain. 
Any flowable slurry may be used extensively. The same shall apply to each 
of the embodiments which will be described below. 
(Second Embodiment) 
FIGS. 2 and 3 schematically show the construction of a polishing apparatus 
according to a second embodiment of the present invention, of which FIG. 2 
is a perspective view and FIG. 3 is a plan view. 
The second embodiment comprises: a platen 11; a polishing pad 12; a 
substrate holding head 14; and a slurry supply pipe 16, similarly to the 
first embodiment. A semiconductor substrate 13 is rotated and pressed 
against the polishing pad 12 on the platen 11. A slurry 15 is supplied in 
a prescribed amount from the slurry supply pipe 16 onto the polishing pad 
12. 
The second embodiment is characterized in that a slat-like slurry pushing 
member 18 made of, e.g., polyurethane foam is provided as the slurry 
pushing means for pushing the slurry 15 to the central portion of the 
platen 11 by sliding over the polishing pad 12. As shown in FIG. 3, the 
slurry pushing member 18 is fixed such that an inner portion 18a thereof 
in a radial direction of the platen 11 is positioned downstream (forward) 
of an outer portion 18b thereof in the radial direction of the platen 11 
in the direction of rotation of the platen 11 during polishing. 
Specifically, the slurry pushing member 18 is fixed such that the tangent 
L to the circle S centering around the center of rotation of the platen 11 
and the slurry pushing member 18 intersect each other to form an angle of 
120.degree. therebetween. 
With the arrangement, the slurry 15 supplied from the slurry supply pipe 16 
onto the polishing pad 12 and caused to flow to the outside of the platen 
11 by a centrifugal force accompanying the rotation of the platen 11 is 
returned to the central portion of the platen 11 by the surface of the 
slurry pushing member 18, evenly spread over the polishing pad 12, and 
supplied to the semiconductor substrate 13. In the case of removing a 
cleaning liquid such as water from the top surface of the polishing pad 
12, the removal is promoted if the platen 11 is rotated in the direction 
opposite to the rotation of the platen 11 during polishing, since the 
cleaning liquid is brought in contact with the back surface of the slurry 
pushing member 18 by the rotation of the platen 11 in the opposite 
direction. 
The length and angle of the slurry pushing member 18 may be selected 
properly provided that the slurry pushing member 18 returns the slurry 15 
on the polishing pad 12 to the central portion of the platen 11. 
Although the angle between the slurry pushing member 18 and a radius of the 
platen 11 is invariable in the second embodiment, the angle between the 
slurry pushing member 18 and a radius of the platen 11 may be variable 
such that the slurry 15 is returned efficiently to the central portion of 
the platen 11 depending on the viscosity of the slurry 15 and on the 
rotation speed of the platen 11. 
Although the slurry pushing member 18 is fixed, it may be rotated in a 
direction relatively opposite to the rotation of the platen 11 during 
polishing. In this case, it is necessary to provide the slurry pushing 
member 18 of such a length in such a position as to prevent the slurry 
pushing member 18 from colliding with the substrate holding head 14. In 
the arrangement, the cleaning liquid supplied onto the polishing pad 12 
can be removed efficiently by the back surface of the slurry pushing 
member 18. 
The material of the slurry pushing member 18 is not limited to polyurethane 
foam but any other material may be used instead. However, the use of a 
soft material such as one containing polyethylene, polypropylene, 
polystyrene, polyvinyl chloride, or Teflon as the main component or rubber 
such as butadiene rubber is particularly preferred, since the slurry 
pushing member 18 made of such a material is deformed to follow the 
surface configuration of the polishing pad 12, as shown in FIG. 4. 
There may be provided a space sufficiently large to permit the slurry 15 to 
be returned to the central portion of the platen 11 (space with a height 
equal to or less than the thickness of the layer of the slurry 15) between 
the slurry pushing member 18 and the polishing pad 12 so that the slurry 
pushing member 18 is kept from rubbing against the polishing pad 12. The 
arrangement is preferred since it is free from powder resulting from the 
rubbing of the slurry pushing member 18 against the polishing pad 12. 
FIGS. 5(a) to 5(d) and FIGS. 6(a) to 6(d) show variations of the slurry 
pushing member 18 in terms of the configuration and number thereof. As 
shown in the drawings, the configuration and number of the slurry pushing 
members 18 are not limited but can be changed properly depending on the 
viscosity of the slurry 15 and the rotation speed of the platen 11. As 
shown in FIG. 5(b) or 5(c), the slurry pushing member 18 may be curved 
such that the outer portion thereof in the radial direction of the platen 
11 has the function of collecting the slurry 15 and that the inner portion 
thereof in the radial direction of the platen 11 has the function of 
pushing the collected slurry 15 toward the substrate holding head 14. 
Below, a polishing method using the polishing apparatus according to the 
second embodiment will be described with reference to FIGS. 7. 
Initially, as shown in FIG. 7(a), the semiconductor substrate 13 is 
attached to the substrate holding head 14 with a face to be polished 
facing downward. 
Next, as shown in FIG. 7(b), the slurry 15 is supplied from the slurry 
supply pipe 16 onto a portion of the polishing pad 12 corresponding to the 
near-central portion of the platen 11, while the platen 11 and the 
substrate holding head 14 are rotated counterclockwise (CCW). As a result, 
the slurry 15 is caused to flow to the peripheral portion of the polishing 
pad 12 by a centrifugal force accompanying the rotation of the platen 11 
to be supplied to the interface between the semiconductor substrate 13 and 
the polishing pad 12. 
As shown in FIG. 7(c), the slurry 15 on the polishing pad 12 tends to flow 
toward the outside of the polishing pad 12 due to the centrifugal force 
accompanying the rotation of the platen 11. However, the slurry 15 is 
brought in contact with the slurry pushing member 18 in one complete 
rotation of the platen 11 and returned to the central portion of the 
polishing pad 12 to be reused in the polishing of the semiconductor 
substrate 13. 
When the polishing of the semiconductor substrate 13 is completed, a 
cleaning liquid such as water is supplied onto the polishing pad 12 to 
clean the surface to be polished of the semiconductor substrate 13 and 
remove the slurry 15 from the top surface of the polishing pad 12. 
Thereafter, the platen 11 is rotated clockwise (CW) to remove the slurry 
remaining on the platen 11 and polishing pad 12. As a result, the cleaning 
liquid is pushed to the outside of the polishing pad 12 so that the 
cleaning liquid is removed more efficiently than in the case where the 
slurry pushing member 18 is not provided. 
Although the platen 11 and the substrate holding head 14 are rotated after 
the slurry 15 is supplied in the foregoing polishing method, the timing of 
rotating the platen 11 and the substrate holding head 14 and the timing of 
supplying the slurry 15 can be changed as necessary provided that the 
slurry 15 is supplied prior to the rotation of the platen 11. 
Although the platen 11 is rotated CCW during polishing and CW during the 
removal of the cleaning liquid, the polishing effect by the slurry 15 
remains substantially the same even when the platen 11 is continuously 
rotated CCW during the removal of the cleaning liquid, except for a slight 
reduction in the speed at which the cleaning liquid is removed. 
The slurry 15 may be supplied onto a portion other than the portion of the 
polishing pad 12 corresponding to the near-central portion of the platen 
11 provided that it is interior to the outer end of the slurry pushing 
member 18. 
(Third Embodiment) 
FIG. 8 is a perspective view schematically showing the construction of the 
polishing apparatus according to a third embodiment of the present 
invention. The third embodiment comprises: a platen 11; a polishing pad 
12; a substrate holding head 14; and a slurry supply pipe 16, similarly to 
the first embodiment. A semiconductor substrate 13 is rotated and pressed 
against the polishing pad 12 on the platen 11. A slurry 15 is supplied in 
a prescribed amount from the slurry supply pipe 16 onto the polishing pad 
12. 
The third embodiment is characterized in that a circular rotary member 21 
as rotatable slurry pushing means is provided in close contact with or 
slightly spaced from the top surface of the polishing pad 12 on the side 
opposite to the substrate holding head 14. The diameter of the rotary 
member 21 is determined to be larger than the diameter of the substrate 
holding head 14. The rotary member 21 partially projects from the edge of 
the polishing pad 12. The rotary member 21 rotates in the direction 
opposite to the rotation of the platen 11 during polishing, while rotating 
in the same direction as the rotation of the platen 11 during the removal 
of the cleaning liquid or the like. 
Thus, as shown in FIG. 9, the slurry 15 supplied from the slurry supply 
pipe 16 onto the polishing pad 12 and directed to the peripheral portion 
of the platen 11 by a centrifugal force accompanying the rotation of the 
platen 11 is brought in contact with the outer circumferential surface of 
the rotary member 21, returned to the central portion of the platen 11 
along the outer circumferential surface of the rotary member 21, and 
evenly spread over the polishing pad 12 to be supplied to the 
semiconductor substrate 13. The arrow above the polishing pad 12 in FIG. 9 
conceptually indicates the flow direction of the slurry 15 during 
polishing. In this case, although the slurry 15 is formed into a swell 15a 
by the surface tension thereof on the peripheral portion of the polishing 
pad 12, the swell 15a is eventually pushed back to the central portion of 
the platen 11 during the rotation of the rotary member 21 since the rotary 
member 21 partially projects from the edge of the polishing pad 12. 
In removing the cleaning liquid from the top surface of the polishing pad 
12, on the other hand, the removal of the cleaning liquid is promoted 
since the cleaning liquid flows to the outside of the platen 11 along the 
outer circumferential surface of the rotary member 21 rotating in the same 
direction as the platen 11. 
The plan configuration of the rotary member 21 is not limited to a circle. 
The provision of projecting portions 21a on the outer circumferential 
surface of the rotary member 21 enhances the effect of pushing the slurry 
15 back to the central portion of the platen 11 along the outer 
circumferential surface of the rotary member 21 rotating in the direction 
opposite to the rotation of the platen 11. Although the dedicated rotary 
member 21 is provided as the slurry pushing means in the third embodiment, 
a rotary member of the same configuration as that of the substrate holding 
head 14 may be provided in place of the dedicated rotary member 21. 
(Fourth Embodiment) 
FIGS. 11 and 12 schematically show the construction of a polishing 
apparatus according to a fourth embodiment of the present invention, of 
which FIG. 11 is a perspective view and FIG. 12 is a plan view. 
The fourth embodiment comprises: a platen 11; a polishing pad 12; a 
substrate holding head 14; and a slurry supply pipe 16, similarly to the 
first embodiment. A semiconductor substrate 13 is rotated and pressed 
against the polishing pad 12. A slurry 15 is supplied in a prescribed 
amount from the slurry supply pipe 16 onto the polishing pad 12. 
The fourth embodiment is characterized in that the diameter of the 
polishing pad 12 is smaller than that of the platen 11 so that the 
polishing pad 12 is disposed on the central portion of the platen 11. On 
the other hand, a plurality of slat-like slurry holding members 19 made 
of, e.g., polyvinyl chloride are provided as slurry holding means along 
the outer circumferential surface of the polishing pad 12 to hold the 
slurry 15 on the polishing pad 12. Each of the slurry holding members 19 
has such a height that the top position thereof is higher in level than 
the top surface of the polishing pad 12 and is positioned so that the 
inner portion thereof in a radial direction of the platen 1 is downstream 
of the outer portion thereof in the radial direction of the platen 1 in 
the direction of rotation of the platen 1 during polishing. Specifically, 
the slurry holding member 19 is fixed so that an angle of about 30 degrees 
is formed between the slurry holding member 19 and a tangent to the outer 
circumferential surface of the polishing pad 12. 
As a general rule in the second embodiment, the slurry pushing member 18 
does not rotate in conjunction with the polishing pad 12 so that the 
slurry 15 is pushed back to the central portion of the platen 11. As a 
general rule in the fourth embodiment, on the other hand, the slurry 
holding members 19 rotate in conjunction with the polishing pad 12 so that 
the slurry 15 is stored on the polishing pad 12. Specifically, the slurry 
15 supplied from the slurry supply pipe 16 onto the polishing pad 12 and 
directed to the peripheral portion of the platen 11 by a centrifugal force 
accompanying the rotation of the platen 11 changes its direction in 
collision with the slurry holding members 19 and is stored on the 
polishing pad 12. Consequently, the slurry 15 is evenly spread over the 
polishing pad 12 when it is supplied to the semiconductor substrate 13. 
The proper length and angle of the slurry holding member 19 can be selected 
such that the slurry 15 is held on the polishing pad 12. If any adjacent 
two of the holding members 19 are provided to overlap in the radial 
direction of the platen 11, the slurry 15 can be held more positively. 
The slurry holding member 19 may be provided on the polishing pad 12, not 
on the peripheral portion 11c of the platen 11. 
The material of the slurry holding members 19 is not limited to polyvinyl 
chloride. Any other material can be used instead, similarly to the second 
embodiment. 
FIGS. 13(a) to 13(d) show variations of the configuration, placement angle, 
and number of the slurry holding member 19. As shown in the drawings, the 
configuration, placement angle, and number of the slurry holding member 19 
are not particularly limited and can be varied properly depending on the 
viscosity of the slurry 15 and on the rotation speed of the platen 11. In 
other words, the slurry holding member 19 may be curved. 
Below, a polishing method using the polishing apparatus according to the 
fourth embodiment will be described with reference to FIGS. 14(a) and 
14(b) and FIGS. 15(a) and 15(b). 
Initially, as shown in FIGS. 14(a), the semiconductor substrate 13 is 
attached to the substrate holding head 14 with a surface to the polished 
facing downward and pressed against the polishing pad 12. 
Next, as shown in FIG. 14(b), the slurry 15 is supplied from the slurry 
supply pipe 16 onto a portion of the polishing pad 12 corresponding to the 
near-central portion of the platen 11, followed by the clockwise (CW) 
rotation of the platen 11 and substrate holding head 14. As a result, the 
slurry 15 flows toward the outside of the polishing pad 12 due to the 
centrifugal force accompanying the rotation of the platen 11 to be 
supplied to the interface between the semiconductor substrate 13 and the 
polishing pad 12. 
As shown in FIG. 15(a), the slurry 15 on the polishing pad 12 tends to flow 
toward the outside of the polishing pad 12 due to the centrifugal force 
accompanying the rotation of the platen 11, comes into contact with the 
inner surface of each slurry holding member 19, flows upstream in the 
direction of rotation of the platen 11 (from the outer portion of each 
slurry holding member 19 in the radial direction of the polishing pad 12 
to the inner portion of the slurry holding member 19 in the radial 
direction of the polishing pad 12) along the inner surface of the slurry 
holding member 19, and then moves to the outer portion of the subsequent 
slurry holding member 19 in the radial direction of the polishing pad 12. 
By repeatedly performing the foregoing flowing movement, the slurry 15 is 
held on the polishing pad 12 and reused in the polishing of the 
semiconductor substrate 13. 
When the polishing of the semiconductor substrate 13 is completed, a 
cleaning liquid such as water is supplied onto the polishing pad 12 to 
clean the polished surface of the semiconductor substrate 13 and rinse the 
slurry 15 out of the top surface of polishing pad 12. Thereafter, the 
platen 11 is rotated counterclockwise (CCW) to remove the cleaning liquid 
or the like remaining on the platen 11 and on the polishing pad 12. As a 
result, the cleaning liquid 20 exhibits a flowing movement in the 
direction opposite to the flowing movement of the slurry 15 described 
above as shown in FIG. 15(b), so that the cleaning liquid 20 is removed 
more efficiently than in the case where no slurry holding member 19 is 
provided. 
Although the platen 11 is rotated CW during the polishing of the 
semiconductor substrate 13 and CCW during the removal of the cleaning 
liquid 20, the platen 11 is rotated CCW during the polishing of the 
semiconductor substrate 13 and CW during the removal of the cleaning 
liquid 20 in the case where the orientation in which the slurry holding 
member 19 is placed is radially reversed. 
(Fifth Embodiment) 
FIG. 16(a) is a schematic perspective view of a polishing apparatus 
according to a fifth embodiment of the present invention. 
As shown in FIG. 16(a), the fifth embodiment also comprises a platen 11, a 
polishing pad 12, a substrate holding head 14, and a slurry supply pipe 
16, similarly to the first embodiment. A semiconductor substrate 13 is 
rotated and pressed against the polishing pad 12 on the platen 11. A 
slurry 15 is supplied in a prescribed amount from the slurry supply pipe 
16 onto the polishing pad 12. In FIG. 16(a), the drawing of a 
polishing-pad holder 11a of the platen 11 is omitted. 
The fifth embodiment is characterized in that a ring-shaped vertically 
movable member 22 moving vertically relative to the platen 11 and rotated 
by rotating means other than the rotating means for the platen 11 is 
provided on the outside of the polishing-pad holder 11a of the platen 11. 
On the vertically movable member 22, a plurality of slat-like slurry 
holding members 19 having the same configuration as in the fourth 
embodiment is provided as the slurry holding means along the outer 
circumferential surface of the polishing pad 12 to hold the slurry 15 on 
the polishing pad 12. The slurry holding members 19 move vertically 
relative to the polishing pad 12 as the vertically movable member 22 moves 
vertically. The slurry holding member 19 is held such that the top 
position thereof becomes higher in level than the surface of the polishing 
pad 12 during polishing and that the top position thereof becomes lower in 
level than the surface of the polishing pad 12 during cleaning. 
The fifth embodiment is also characterized in that an arm 14a of the 
substrate holding head 14 performs a rotary movement over the surface of 
the polishing pad 12. 
The two-dimensional arrangement of the slurry holding members 19 is the 
same as in the fourth embodiment so that the slurry 15 supplied from the 
slurry supply pipe 16 onto the polishing pad 12 and directed to the 
peripheral portion of the platen 11 by the centrifugal force accompanying 
the rotation of the platen 11 changes its direction in collision with the 
slurry holding members 19 and is stored on the polishing pad 12. As a 
result, the slurry 15 is evenly spread over the polishing pad 12 before it 
is used in the polishing of the semiconductor substrate 13. 
Below, a polishing method using a polishing apparatus according to the 
fifth embodiment will be described with reference to FIGS. 16(a) and 16(b) 
and FIGS. 17(a) and 17(b). 
Initially, the semiconductor substrate 13 is attached to the substrate 
holding head with a surface to be polished facing downward and pressed 
against the polishing pad 12. 
Next, the slurry 15 is supplied from the slurry supply pipe 16 onto a 
portion of the polishing pad 12 corresponding to the near-central portion 
of the platen 11, followed by individual rotations of the platen 11 and 
the substrate holding head 14. As a result, the slurry 15 flows toward the 
outside of the polishing pad 12 due to a centrifugal force accompanying 
the rotation of the platen 11 and is supplied to the interface between the 
semiconductor substrate 13 and the polishing pad 12. In this case, the 
slurry 15 on the polishing pad 12 tends to flow toward the outside of the 
polishing pad 12 due to the centrifugal force accompanying the rotation of 
the platen 11, charges its flow direction in collision with the slurry 
holding member 19, is stored on the polishing pad 12, and evenly spread 
over the polishing pad 12 before it is used to polish the semiconductor 
substrate 13. 
When the polishing of the semiconductor substrate 13 is completed, the 
vertically movable member 22 is moved downward relative to the platen 11, 
as shown in FIG. 16(b). 
Next, as shown in FIGS. 17(a) and 17(b), the arm 14a of the substrate 
holding head 14 is rotated along the surface of the polishing pad 12 so 
that a part of the substrate holding head 14 and therefore a part of the 
semiconductor substrate 13 thrust out from the polishing pad 12. 
Consequently, the adhesion of the polishing pad 12 to the semiconductor 
substrate 13 is reduced to permit easy removal of the semiconductor 
substrate 13 from the polishing pad 12. 
FIGS. 18(a) and 18(b) show another structure in which the substrate holding 
head 14 is moved along the surface of the polishing pad 12. The substrate 
holding head 14 is held by a horizontal movable member 23 moving 
horizontally in parallel with the surface of the polishing pad 12. 
When the polishing of the semiconductor substrate 13 is completed, the 
vertically movable member 22 is moved downward relative to the platen 11 
as shown in FIG. 16(b) and then the horizontal movable member 23 is moved 
horizontally as shown in FIGS. 18(a) and 18(b) to move the substrate 
holding head 14 along the surface of the polishing pad 12. Consequently, a 
part of the substrate holding head 14 and therefore a part of the 
semiconductor substrate 13 thrust out from the polishing pad 12, so that 
the semiconductor substrate 13 is removed easily from the top surface of 
the polishing pad 12. 
(Sixth Embodiment) 
FIG. 19 schematically shows the plan configuration of a polishing apparatus 
according to a sixth embodiment of the present invention. 
As shown in FIG. 19, the sixth embodiment also comprises a platen 11, a 
polishing pad 12, a substrate holding head 14, and a slurry supply pipe 
16, similarly to the first embodiment. A semiconductor substrate 13 is 
rotated and pressed against the polishing pad 12 on the platen 11. A 
slurry 15 is supplied in a prescribed amount from the slurry supply pipe 
16 onto the polishing pad 12. In FIG. 19, the drawing of a polishing-pad 
holder 11a of the platen 11 is omitted. 
The sixth embodiment is characterized in that a ring-shaped rotary member 
24 rotated in a plane vertical to the surface of the polishing pad 12 by 
rotating means other than the rotating means for the platen 11 is provided 
outside the polishing-pad holder 11a of the platen 11. The drawing of a 
mechanism for rotating the rotary member 24 is omitted here. On the rotary 
member 24, a plurality of slat-like slurry holding members 19 having the 
same configuration as in the fourth embodiment are provided as the slurry 
holding means along the outer circumferential surface of the polishing pad 
12 to hold the slurry 15 on the polishing pad 12. The slurry holding 
member 19 rotates relative to the polishing pad 12 with the rotation of 
the rotary member 24. The slurry holding member 19 is held so that the top 
position thereof becomes higher in level than the surface of the polishing 
pad 12 during polishing. 
An arm 14a of the substrate holding head 14 is provided to perform a rotary 
movement over the surface of the polishing pad 12, similarly to the fifth 
embodiment. 
The two-dimensional arrangement of the slurry holding member 19 is the same 
as in the fourth embodiment so that the slurry 15 supplied from the slurry 
supply pipe 16 and directed to the peripheral portion of the platen 11 by 
a centrifugal force accompanying the rotation of the platen 11 changes its 
direction in collision with the slurry holding member 19 and is stored on 
the polishing pad 12. As a result, the slurry 15 is evenly spread over the 
polishing pad 12 before it is used in the polishing of the semiconductor 
substrate 13. 
Below, a polishing method using the polishing apparatus according to the 
sixth embodiment will be described with reference to FIGS. 19 and 20. 
Initially, as shown in FIG. 19, the slurry 15 is supplied from the slurry 
supply pipe 16 onto a portion of the polishing pad 12 corresponding to the 
near-central portion of the platen 11, while the platen 11 and the 
substrate holding head 14 are rotated individually. As a result, the 
slurry 15 flows toward the outside of the polishing pad 12 due to the 
centrifugal force accompanying the rotation of the platen 11 and is 
supplied to the interface between the semiconductor substrate 13 and the 
polishing pad 12. In this case, the slurry 15 on the polishing pad 12 
tends to flow to the outside of the polishing pad 12 due to the 
centrifugal force accompanying the rotation of the platen 11 but changes 
its direction in collision with the slurry holding member 19 and is stored 
on the polishing pad 12. As a result, the slurry 15 is evenly spread over 
the polishing pad 12 before it is used in the polishing of the 
semiconductor substrate 13. 
When the polishing of the semiconductor substrate 13 is completed, the 
rotary member 24 is rotated in a plane vertical to the surface of the 
polishing pad 12, as shown in FIG. 20, and then the arm 14a of the 
substrate holding head 14 is rotated over the surface of the polishing pad 
12 so that a part of the substrate holding head 14 and therefore a part of 
the semiconductor substrate 13 thrust out from the polishing pad 12, 
similarly to the fifth embodiment. Consequently, the adhesion of the 
polishing pad 12 to the semiconductor substrate 13 is reduced to permit 
easy removal of the semiconductor substrate 13 from the polishing pad 12. 
As shown in FIGS. 18(a) and 18(b), the substrate holding head 14 may be 
held by a horizontal movable member 23 moving horizontally in parallel 
with the surface of the polishing pad 12 so that a part of the substrate 
holding head 14 and therefore a part of the semiconductor substrate 13 
thrust out from the polishing pad 12. 
FIG. 21 shows respective relationships between the amounts of supplied 
slurry and the polishing rates in the case where polishing is performed by 
using the polishing apparatus according to the individual embodiments of 
the present invention and in the case where polishing is performed by 
using the conventional polishing apparatus. Although the amount of 
supplied slurry required to maintain a sufficient polishing rate is L0 in 
the conventional embodiment, the present invention requires L1, which is 
smaller than L0, to maintain a polishing rate on the same order as in the 
conventional embodiment.