U.S. patent application number 09/850934 was filed with the patent office on 2001-09-13 for method and apparatus for supporting and cleaning a polishing pad for chemical-mechanical planarization of microelectronic substrates.
Invention is credited to Elledge, Jason B..
Application Number | 20010021627 09/850934 |
Document ID | / |
Family ID | 23528863 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021627 |
Kind Code |
A1 |
Elledge, Jason B. |
September 13, 2001 |
Method and apparatus for supporting and cleaning a polishing pad
for chemical-mechanical planarization of microelectronic
substrates
Abstract
A method and apparatus for supporting, cleaning and/or drying a
polishing pad used for planarizing a microelectronic substrate. In
one embodiment, the apparatus can include a cleaning head
positioned adjacent a post-operative portion of the polishing pad
to clean and/or dry the rear surface of the polishing pad. The
cleaning head can include a heat source, a mechanical contact
element, and/or orifices that direct fluid and/or gas toward the
rear surface. The apparatus can further include a vessel through
which the rear surface of the polishing pad passes to clean the
rear surface. The apparatus can also include a flow passage in
fluid communication with a region between the polishing pad and a
support pad upon which the polishing pad rests during
planarization. Gas moves through the flow passage toward or away
from an interface region between the polishing pad and the support
pad to draw the polishing pad toward or away from the support
pad.
Inventors: |
Elledge, Jason B.; (Boise,
ID) |
Correspondence
Address: |
Steven H. Arterberry, Esq.
DORSEY & WHITNEY LLP
Suite 3400
1420 Fifth Avenue
Seattle
WA
98101
US
|
Family ID: |
23528863 |
Appl. No.: |
09/850934 |
Filed: |
May 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09850934 |
May 7, 2001 |
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09387190 |
Aug 31, 1999 |
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6244944 |
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Current U.S.
Class: |
451/56 ; 451/299;
451/303; 451/305; 451/306; 451/307; 451/443; 451/444; 451/59 |
Current CPC
Class: |
B08B 3/123 20130101;
B24B 21/04 20130101; B08B 3/022 20130101; B24B 53/017 20130101;
B08B 1/02 20130101; B08B 3/041 20130101; B08B 1/007 20130101 |
Class at
Publication: |
451/56 ; 451/299;
451/303; 451/305; 451/306; 451/307; 451/443; 451/444; 451/59 |
International
Class: |
B24B 001/00 |
Claims
1. An apparatus for removing material from a rear surface of an
elongated polishing pad, the polishing pad having a planarizing
surface opposite the rear surface to planarize a microelectronic
substrate, the polishing pad extending across a platen and having a
post-operative portion movable relative to the platen, the
apparatus comprising a cleaning head positioned proximate to the
post-operative portion of the polishing pad and having at least one
cleaning device operable to remove material from the rear surface
of the post-operative portion of the polishing pad.
2. The apparatus of claim 1 wherein the cleaning device includes a
contact element having a cleaning surface positionable to contact
the rear surface of the post-operative portion of the polishing
pad.
3. The apparatus of claim 1 wherein the cleaning device includes an
orifice coupleable to a fluid source and facing at least partially
toward the rear surface of the polishing pad to direct fluid toward
the rear surface of the polishing pad and remove material from the
rear surface.
4. The apparatus of claim 1 wherein the cleaning device includes a
vessel positioned proximate to the post-operative portion of the
polishing pad and having an opening configured to receive the
post-operative portion of the polishing pad, the vessel having an
interior volume in fluid communication with the opening and
configured to contain a quantity of cleaning liquid sufficient to
contact the rear surface of the polishing pad.
5. The apparatus of claim 1 wherein the polishing pad extends from
a supply roll across the platen to a take-up roll and the cleaning
head includes a body having a first surface toward the platen, a
second surface toward the take-up roll and a slot extending through
the body from the first surface to the second surface to receive
the polishing pad, the body further having a manifold coupled to
the fluid source and coupled to a plurality of orifices positioned
within the slot, each orifice being directed toward the rear
surface of the post-operative portion of the polishing pad.
6. The apparatus of claim 1 wherein the polishing pad moves back
and forth across the platen between a supply roll and a take-up
roll along a travel axis, further wherein the cleaning head
includes a body having a first surface toward the platen, a second
surface toward the take-up roll, and a slot aligned with the travel
axis and extending through the body from the first surface to the
second surface to receive the polishing pad, the body further
having a manifold coupled to the fluid source and coupled to a
plurality of orifices positioned within the slot, the orifices
being arranged in at least one row oriented transverse to the
travel axis, each orifice being directed toward the rear surface of
the post-operative portion of the polishing pad.
7. The apparatus of claim 1 wherein the polishing pad moves back
and forth across the platen between a supply roll and a take-up
roll along a travel axis, further wherein the cleaning head
includes a plurality of orifices arranged in first and second rows
oriented transverse to the travel axis, orifices of the first row
being offset in a direction transverse to the travel axis from
orifices of the second row, the orifices of both the first and
second rows being coupled to a source of heated gas to remove
liquid from the rear surface of the polishing pad by
evaporation.
8. The apparatus of claim 1 wherein the polishing pad moves back
and forth across the platen between a supply roll and a take-up
roll along a travel axis and the cleaning head has an orifice
coupleable to a fluid source and facing at least partially toward
the rear surface of the polishing pad, the orifice including a slot
elongated along an axis generally transverse to the travel
axis.
9. The apparatus of claim 1 wherein the cleaning head has an
orifice facing at least partially toward the rear surface of the
polishing pad and coupled to a source of high vapor pressure
liquid.
10. The apparatus of claim 9 wherein the high vapor pressure liquid
is selected from alcohol and acetone.
11. The apparatus of claim 1 wherein the cleaning head has an
orifice facing at least partially toward the rear surface of the
polishing pad and coupled to a source of gas.
12. The apparatus of claim 11 wherein the gas has a pressure of
from approximately 10 to approximately 100 psi.
13. The apparatus of claim 11 wherein the source of gas includes
air.
14. The apparatus of claim 1 wherein the cleaning head has an
orifice facing at least partially toward the rear surface of the
polishing pad and coupleable to a fluid source, further comprising
a temperature controller in fluid communication with the orifice to
control a temperature of fluid passing through the orifice.
15. The apparatus of claim 14 wherein the temperature controller is
configured to control the temperature of fluid passing through the
orifice to be less than approximately 100 degrees Celsius.
16. The apparatus of claim 1 wherein the polishing pad moves back
and forth across the platen between a supply roll and a take-up
roll along a travel axis, further wherein the cleaning head has a
contact element with the cleaning surface positionable to contact
the rear surface of the post-operative portion of the polishing
pad, the contact element including a generally impermeable blade
elongated along an axis transverse to the travel axis and
positionable to press against the polishing pad and form an at
least approximately liquid tight seal with the polishing pad to
remove liquid from the polishing pad as the polishing pad moves
relative to the cleaning surface.
17. The apparatus of claim 1 wherein the cleaning head has a
contact element with a cleaning surface positionable to contact the
rear surface of the postoperative portion of the polishing pad, the
contact element including an absorbent brush.
18. The apparatus of claim 17 wherein the absorbent brush is
coupled to a heating element to discharge liquid absorbed by the
absorbent brush.
19. The apparatus of claim 1, further comprising a vacuum source in
fluid communication with the polishing pad to draw the polishing
pad against the cleaning surface of the contact element.
20. The apparatus of claim 1 wherein the cleaning head has a
plurality of cleaning surfaces, each being positionable to contact
the rear surface of the polishing pad to remove material from the
rear surface.
21. The apparatus of claim 1 wherein the cleaning head has a first
orifice in fluid communication with a source of pressurized gas and
a second orifice in fluid communication with a source of cleaning
liquid, the first and second orifices being directed toward the
rear surface of the polishing pad.
22. The apparatus of claim 1 wherein the cleaning head has a heat
source positioned proximate to the rear surface of the
post-operative portion of the polishing pad to direct heat toward
the rear surface of the polishing pad and dry the rear surface.
23. An apparatus for planarizing a substrate, comprising: a platen;
an elongated polishing pad having a planarizing surface facing away
from the platen and a rear surface facing opposite the planarizing
surface, the polishing pad being movable relative to the platen to
separate a post-operative portion of the polishing pad from the
platen; a substrate carrier configured to press the microelectronic
substrate against the planarizing surface of the polishing pad; and
a heat source positioned proximate to the rear surface of the
postoperative portion of the polishing pad to direct heat toward
the rear surface of the polishing pad and dry the rear surface.
24. The apparatus of claim 23 wherein the heat source includes a
gas manifold coupled to a source of gas, the manifold having at
least one orifice directed toward the rear surface of the polishing
pad, the heat source further including a temperature controller in
fluid communication with the at least one orifice to control a
temperature of the gas directed through the at least one orifice
toward the rear surface of the polishing pad.
25. The apparatus of claim 23 wherein the heat source includes an
infrared heating element spaced apart from the rear surface of the
polishing pad.
26. An apparatus for planarizing a microelectronic substrate,
comprising: a platen; an elongated polishing pad having a
planarizing surface and a rear surface opposite the planarizing
surface, the polishing pad extending across the platen from a
supply roll to a take-up roll with the rear surface of the
polishing pad facing toward the platen, the polishing pad having a
pre-operative portion between the platen and the supply roll and a
post-operative portion between the platen and the take-up roll; a
substrate carrier positioned proximate to the planarizing surface
of the polishing pad, the substrate carrier having at least one
engaging surface to press the microelectronic substrate against the
planarizing surface of the polishing pad, the substrate carrier
being moveable relative to the polishing pad to remove material
from the microelectronic substrate; and a cleaning head positioned
proximate to the post-operative portion of the polishing pad
between the platen and the take-up roll and having at least one
cleaning surface positionable to contact the rear surface of the
post-operative portion of the polishing pad and/or at least one
orifice coupleable to a fluid source and directed at least
partially toward the rear surface of the polishing pad to remove
material from the rear surface as the polishing pad moves relative
to the platen and the take-up roll.
27. The apparatus of claim 26 wherein the polishing pad moves back
and forth between the supply roll and the take-up roll along a
travel axis and the fluid orifice is elongated along an axis
generally transverse to the travel axis.
28. The apparatus of claim 26 wherein the orifice is coupled to a
source of high vapor pressure liquid.
29. The apparatus of claim 26 wherein the orifice is coupled to a
source of gas.
30. The apparatus of claim 26 wherein the polishing pad moves back
and forth between the supply roll and the take-up roll along a
travel axis, further wherein the cleaning surface includes a
generally impermeable blade elongated along an axis transverse to
the travel axis and positionable to press against the polishing pad
and form an at least approximately liquid tight seal with the
polishing pad to remove liquid from the polishing pad as the
polishing pad moves relative to the cleaning surface.
31. The apparatus of claim 26 wherein the cleaning surface includes
an absorbent brush.
32. The apparatus of claim 26 wherein the orifice is a first
orifice in fluid communication with a source of pressurized gas,
the cleaning head having a second orifice in fluid communication
with a source of cleaning liquid, the second orifice being directed
toward the rear surface of the polishing pad to clean the rear
surface.
33. An apparatus for planarizing a microelectronic substrate,
comprising: a platen; an elongated polishing pad having a
planarizing surface and a rear surface opposite the planarizing
surface, the polishing pad extending across the platen with the
rear surface of the polishing pad facing toward the platen, the
polishing pad having a post-operative portion movable relative to
the platen; a substrate carrier configured to press the
microelectronic substrate against the planarizing surface of the
platen; and a vessel positioned proximate to the post-operative
portion of the polishing pad and having an opening configured to
receive the post-operative portion of the polishing pad, the vessel
having an interior volume in fluid communication with the opening
and configured to contain a quantity of cleaning liquid sufficient
to contact the rear surface of the polishing pad.
34. The apparatus of claim 33, further comprising the liquid
wherein the liquid is selected from water, alcohol and acetone.
35. The apparatus of claim 33, further comprising an ultrasonic
transducer coupled to the vessel to transmit ultrasonic energy to
the interior volume of the vessel.
36. The apparatus of claim 33, further comprising a roller
rotatably positioned within the interior volume of the vessel to
rotate relative to walls of the vessel, the roller being configured
to rotatably engage the polishing pad and guide the polishing pad
through the interior volume of the vessel.
37. The apparatus of claim 33, further comprising a cleaning head
positioned proximate to the post-operative portion of the polishing
pad between the vessel and the platen, the cleaning head having at
least one cleaning surface positionable to contact the rear surface
of the post-operative portion of the polishing pad and/or at least
one orifice coupleable to a fluid source and directed at least
partially toward the rear surface of the polishing pad to remove
material from the rear surface as the polishing pad moves relative
to the platen and the take-up roll.
38. The apparatus of claim 37 wherein the orifice is coupled to a
source of high vapor pressure liquid.
39. The apparatus of claim 37 wherein the orifice is coupled to a
source of gas.
40. The apparatus of claim 37 wherein the polishing pad moves back
and forth across the platen between the supply roll and the take-up
roll along a travel axis, further wherein the cleaning surface
includes a generally impermeable blade elongated along an axis
transverse to the travel axis and positionable to press against the
polishing pad and form an at least approximately liquid tight seal
with the polishing pad to remove liquid from the polishing pad as
the polishing pad moves relative to the cleaning surface.
41. The apparatus of claim 37 wherein the cleaning surface includes
an absorbent brush.
42. An apparatus for planarizing a microelectronic substrate,
comprising: a platen having a support surface; a support pad
positioned on the support surface an elongated polishing pad having
a planarizing surface and a rear surface opposite the planarizing
surface, the polishing pad extending across the support pad and
movable relative to the support pad with the rear surface of the
polishing pad facing the support pad; and a fluid flow passage
coupled to a vacuum source and a pressurized gas source, the flow
passage being in fluid communication with an interface between the
support pad and the rear surface of the polishing pad to move gas
toward and away from the interface.
43. The apparatus of claim 42 wherein the platen has a trench
around a perimeter of the support pad, the trench being in fluid
communication with the fluid flow passage and having an upwardly
facing opening facing toward the rear surface of the polishing pad
to draw the polishing pad toward the support pad when the fluid
flow passage is in fluid communication with the vacuum source and
separate the polishing pad from the support pad when the fluid flow
passage is in fluid communication with the pressurized gas
source.
44. The apparatus of claim 42 wherein the platen has a plurality of
orifices around a perimeter of the support surface and a perimeter
of the support pad, the orifices being in fluid communication with
the fluid flow passage, the orifices having upwardly facing
openings facing toward the rear surface of the polishing pad to
draw the polishing pad toward the support pad when the fluid flow
passage is in fluid communication with the vacuum source and
separate the polishing pad from the support pad when the fluid flow
passage is in fluid communication with the pressurized gas
source.
45. The apparatus of claim 42 wherein the platen has a plurality of
first orifices extending through the support surface and the
support pad has a plurality of second orifices extending
therethrough, each second orifice being aligned with a
corresponding first orifice, the first and second orifices being in
fluid communication with the fluid flow passage, the second
orifices having upwardly facing openings facing toward the rear
surface of the polishing pad to draw the polishing pad toward the
support pad when the fluid flow passage is in fluid communication
with the vacuum source and separate the polishing pad from the
support pad when the fluid flow passage is in fluid communication
with the pressurized gas source.
46. The apparatus of claim 45 wherein the first orifices are spaced
apart from each other by approximately equal distances.
47. The apparatus of claim 42 wherein the platen includes orifices
directed outwardly toward a perimeter of the support pad and in
fluid communication with the fluid flow passage, the orifices
having upwardly facing openings facing toward the rear surface of
the polishing pad to draw the polishing pad toward the support pad
when the fluid flow passage is in fluid communication with the
vacuum source and separate the polishing pad from the support pad
when the fluid flow passage is in fluid communication with the
pressurized gas source.
48. The apparatus of claim 42, further comprising the pressurized
gas source, the pressurized gas source including pressurized
air.
49. The apparatus of claim 42, further comprising a substrate
carrier positioned proximate to the planarizing surface of the
polishing pad, the substrate carrier having at least one engaging
surface to press the microelectronic substrate against the
planarizing surface of the polishing pad, the substrate carrier
being moveable relative to the polishing pad to remove material
from the microelectronic substrate.
50. A method for cleaning a rear surface of a polishing pad having
a planarizing surface opposite the rear surface to planarize a
microelectronic substrate, the method comprising: advancing the
polishing pad over a supporting platen to move a postoperative
portion of the polishing pad away from the platen and expose the
rear surface of the post-operative portion; and removing material
from the rear surface of the post-operative portion of the
polishing pad.
51. The method of claim 50 wherein removing material includes
contacting the rear surface of the post-operative portion with a
cleaning surface.
52. The method of claim 50 wherein removing material includes
directing a fluid jet toward the rear surface of the post-operative
portion of the polishing pad.
53. The method of claim 50 wherein removing material includes
directing heat toward the rear surface of the post-operative
portion to evaporate liquid from the rear surface.
54. The method of claim 50 wherein removing material from the rear
surface of the post-operative portion includes pressing an
absorbent material against the rear surface of the post-operative
portion.
55. The method of claim 50 wherein removing material from the rear
surface of the post-operative portion includes pressing a Generally
impermeable blade against the rear surface to form an at least
approximately liquid tight seal with the rear surface.
56. The method of claim 50 wherein removing material from the rear
surface of the polishing pad includes moving at least one of a
cleaning surface and the polishing pad relative to the other while
the cleaning surface presses against the polishing pad.
57. The method of claim 50 wherein removing material from the rear
surface of the polishing pad includes moving at least one of an
orifice and the polishing pad relative to the other while the
orifice is directed toward the polishing pad and coupled to a
source of fluid.
58. The method of claim 50 wherein removing material from the
polishing pad includes pressing a plurality of cleaning surfaces
against the rear surface of the polishing pad.
59. The method of claim 50 wherein advancing the polishing pad
includes moving the polishing pad along a travel axis, further
comprising directing a fluid jet toward the rear surface through an
elongated slot to extend the fluid jet along an axis transverse to
the travel axis.
60. The method of claim 50 wherein advancing the polishing pad
includes moving the polishing pad along a travel axis, further
wherein removing material from the polishing pad includes directing
a gas through a plurality of orifices arranged transverse to the
travel axis.
61. The method of claim 50 wherein removing material includes
directing a gas jet through an orifice toward the rear surface of
the polishing pad.
62. The method of claim 61 wherein the orifice is a first orifice,
further comprising directing a liquid jet toward the rear surface
of the polishing pad through a second orifice.
63. The method of claim 61 wherein directing the gas jet includes
pressurizing the gas to a pressure of from approximately 10 psi to
approximately 100 psi.
64. The method of claim 61, further comprising selecting the gas
jet to include air.
65. The method of claim 61, further comprising selecting the gas
jet to include an inert gas.
66. The method of claim 50, further comprising controlling a
temperature of a fluid jet directed toward the rear surface of the
polishing pad.
67. The method of claim 66 wherein controlling the temperature of
the fluid jet includes selecting the temperature of the fluid jet
to be less than or equal to approximately 100 degrees Celsius.
68. The method of claim 50 wherein removing material includes
removing liquid from the rear surface of the polishing pad.
69. The method of claim 50 wherein removing material includes
removing solid particulates from the rear surface of the polishing
pad.
70. The method of claim 50, further comprising heating a contact
surface pressed against the rear surface of the polishing pad to
evaporate liquid from the rear surface of the polishing pad.
71. The method of claim 50 wherein the polishing pad extends
downwardly between the platen and the take-up roller, further
wherein removing material from the polishing pad includes directing
a fluid jet downwardly against the rear surface of the polishing
pad.
72. The method of claim 50 wherein removing the material includes
removing liquid with an absorbent brush, further comprising drying
the absorbent brush.
73. The method of claim 50 wherein removing material includes
drying liquid from the rear surface by heating a region adjacent
the rear surface.
74. The method of claim 50 wherein removing material includes
drying liquid from the rear surface by directing heated gas toward
the rear surface.
75. A method for supporting and/or cleaning a rear surface of a
polishing pad facing opposite a planarizing surface of the
polishing pad used for planarizing a microelectronic substrate, the
method comprising: positioning the polishing pad on a support
surface with the rear surface of the polishing pad facing toward
the support surface and the planarizing surface of the polishing
pad facing away from the support surface; and directing a flow of
gas toward an interface region between the rear surface of the
polishing pad and the support surface while the polishing pad is
supported by the support surface.
76. The method of claim 75, further comprising moving the polishing
pad transverse to the support surface while directing the flow of
gas toward the interface region between the rear surface of the
polishing pad and the support surface.
77. The method of claim 75, further comprising moving the polishing
pad transverse to the support surface after directing the flow of
gas toward the interface region between the rear surface of the
polishing pad and the support surface.
78. The method of claim 75 wherein positioning the polishing pad on
the support surface includes disposing the polishing pad on an
upwardly facing surface of a support pad and disposing the support
pad on a platen.
79. The method of claim 75 wherein directing the flow of gas
includes removing material from the rear surface of the polishing
pad.
80. The method of claim 75 wherein directing the flow of gas
includes expelling particulates from the rear surface of the
polishing pad.
81. The method of claim 75 wherein directing the flow of gas
includes drying the rear surface of the polishing pad.
82. The method of claim 75 wherein directing the flow of gas
includes separating the rear surface of the polishing pad from the
support pad.
83. The method of claim 75 wherein directing the flow of gas
includes passing the flow of gas through a trench positioned around
a perimeter of the support pad.
84. The method of claim 75 wherein directing the flow of gas
includes passing the gas through at least one orifice in the
support pad.
85. The method of claim 75, further comprising drawing the gas away
from the region between the rear surface of the polishing pad and
the support pad to draw the polishing pad into engagement with the
support pad.
86. The method of claim 75 wherein removing material includes
directing liquid outwardly from between the polishing pad and the
support pad.
87. The method of claim 75 wherein removing material includes
directing solid particulates outwardly from between the polishing
pad and the support pad.
88. The method of claim 75, further comprising heating the gas
before directing the gas between the polishing pad and the support
pad.
89. A method for cleaning a rear surface of an elongated polishing
pad facing opposite a planarizing surface of the polishing pad used
for planarizing a microelectronic substrate, the method comprising:
moving a post-operative portion of the polishing pad away from a
platen supporting the polishing pad; and immersing the rear surface
of the post-operative portion of the polishing pad in a liquid to
remove material from the rear portion.
90. The method of claim 89 wherein moving a post-operative portion
of the polishing pad includes advancing the polishing pad from a
supply roller, across the platen to a take-up roller.
91. The method of claim 89 wherein immersing the rear surface
includes exposing the rear surface to a liquid selected from
acetone and alcohol.
92. The method of claim 89, further comprising passing ultrasonic
energy into the liquid.
93. The method of claim 89, further comprising: removing the
post-operative portion of the polishing pad from the liquid with a
portion of the liquid remaining engaged with the post-operative
portion; removing at least some of the portion of liquid engaged
with the postoperative portion; and moving the post-operative
portion of the polishing pad into contact with the support pad
after removing at least some of the portion of liquid engaged with
the post-operative portion.
94. The method of claim 93 wherein removing at least some of the
portion of liquid includes contacting the rear surface of the
post-operative portion with an absorbent material.
95. The method of claim 93 wherein removing at least some of the
portion of liquid includes pressing a generally impermeable blade
against the rear surface of the post-operative portion of the
polishing pad to form an at least approximately liquid tight seal
with the polishing pad.
96. The method of claim 93 wherein removing at least some of the
portion of liquid includes evaporating the liquid.
97. The method of claim 93 wherein removing at least some of the
portion of liquid includes directing a gas jet toward the rear
surface of the postoperative portion of the polishing pad.
Description
TECHNICAL FIELD
[0001] The present invention is directed toward methods and
apparatuses for supporting, cleaning and/or drying a polishing pad
used for mechanical and/or chemical-mechanical planarization.
BACKGROUND OF THE INVENTION
[0002] Mechanical and chemical-mechanical planarizing processes
(collectively "CMP") are used in the manufacturing process of
microelectronic devices to form a flat surface on semiconductor
wafers, field emission displays, and many other
microelectronic-device substrates and substrate assemblies. FIG. 1
is a partially schematic, isometric view of a conventional
web-format planarizing machine 10 that has a platen 20. A sub-pad
11 is attached to the platen 20 to provide a flat, solid
workstation for supporting a portion of a web-format polishing pad
16 in a planarizing zone "A" during planarization. The polishing
pad 16 has a rear surface 19 that engages the sub-pad 11 and a
planarizing surface 18 facing opposite the rear surface 19 to
planarize a substrate 12.
[0003] The planarizing machine 10 also has a pad-advancing
mechanism, including a plurality of rollers, to guide, position and
hold the polishing pad 16 over the sub-pad 11. The pad-advancing
mechanism generally includes a supply roller 24, first and second
idler rollers 21a and 21b, first and second guide rollers 22a and
22b, and a take-up roller 23. As explained below, a motor (not
shown) drives the take-up roller 23 and the supply roller 24 to
advance and retract the polishing pad 16 over the sub-pad 11 along
a travel path T-T. The first idler roller 21a and the first guide
roller 22a press an operative portion of the polishing pad 16
against the sub-pad 11 to hold the polishing pad 16 stationary
during operation.
[0004] The planarizing machine 10 further includes a carrier
assembly 30 to translate the substrate 12 over the polishing pad
16. In one embodiment, the carrier assembly 30 has a head 31 to
pick up, hold and release the substrate 12 at appropriate stages of
the planarizing process. The carrier assembly 30 also has a support
gantry 32 and a drive assembly 33 that can move along the gantry
32. The drive assembly 33 has an actuator 34, a drive shaft 35
coupled to the actuator 34, and an arm 36 projecting from the drive
shaft 35. The arm 36 carries the head 31 via a terminal shaft 37.
The actuator 34 orbits the head 31 about an axis B-B (as indicated
by arrow R.sub.1) and can rotate the head 31 about an axis C-C (as
indicated by arrow R.sub.2) to move the substrate 12 over the
polishing pad 16 while a planarizing fluid 17 flows from a
plurality of nozzles 38 in the head 31. The planarizing fluid 17
may be a conventional CMP slurry with abrasive particles and
chemicals that etch and/or oxidize the surface of the substrate 12,
or the planarizing fluid 17 may be a non-abrasive planarizing
solution without abrasive particles. In most CMP applications,
conventional CMP slurries are used on conventional polishing pads,
and planarizing solutions without abrasive particles are used on
fixed-abrasive polishing pads.
[0005] In the operation of the planarizing machine 10, the carrier
assembly 30 presses the substrate 12 against the planarizing
surface 18 of the polishing pad 16 as the carrier head 31 moves the
substrate 12 over the planarizing surface 18. The polishing pad 16
moves across the sub-pad 11 along the pad travel path T-T either
during or between planarizing cycles to change the particular
portion of the polishing pad 16 in the planarizing zone A. For
example, the supply and take-up rollers 24, 23 can drive the
polishing pad 16 between planarizing cycles such that a point P
moves incrementally across the sub-pad 11 to a number of
intermediate locations I.sub.1, I.sub.2, etc. Alternatively, the
rollers 24, 23 may drive the polishing pad 16 between planarizing
cycles such that the point P moves all the way across the sub-pad
11 toward the take-up roller 23 to completely remove a used or
postoperative portion of the polishing pad 16 from the planarizing
zone A. The rollers 24, 23 may also continuously drive the
polishing pad 16 at a slow rate during a planarizing cycle such
that the point P moves continuously across the sub-pad 11 during
planarization.
[0006] The planarizing machine 10 can also include a planarizing
surface cleaner 40 (shown schematically in FIG. 1) positioned
between the platen 20 and the take-up roller 23 to clean the
post-operative portion of the polishing pad 16. The planarizing
surface cleaner 40 can include a brush 41 having bristles that
contact the planarizing surface 18 of the polishing pad 16 and a
liquid dispenser 42 positioned proximate to the brush 41 to
dispense a cleaning liquid on the planarizing surface 18.
Accordingly, the planarizing surface cleaner 40 can clean the
post-operative portion of the polishing pad 16 as it moves off the
platen 20 along the travel path T-T. Once the post-operative
portion of the polishing pad 16 has been cleaned, it can be
translated back onto the platen 20 along the travel path T-T and
into the planarizing zone A for another planarizing cycle.
[0007] One drawback with the apparatus 10 shown in FIG. 1 is that
the rear surface 19 of the polishing pad 16 can become contaminated
with debris (such as liquid and/or particulate matter) during the
planarizing process and/or the cleaning process. The debris can
become trapped between the polishing pad 16 and the sub-pad 11,
causing a local bump or other non-uniformity to form in the
planarizing surface 18. The non-uniformity in the planarizing
surface 18 can create a non-uniformity in the substrate 12 and/or
can cause the polishing pad 16 to wear in a non-uniform manner.
[0008] A further drawback is that liquid on the rear surface 19 of
the polishing pad 16 can form an adhesive bond between the
polishing pad 16 and the sub-pad 11. The adhesive bond can inhibit
relative movement between the polishing pad 16 and the sub-pad 11
when the polishing pad 16 moves along the travel path T-T. In one
conventional method, the idler rollers 21a, 21b and/or the guide
roller 22a move the polishing pad 16 normal to the upper surface of
the sub-pad 11 to break the adhesive bond. However, the action of
the rollers against the polishing pad 16 may not be effective to
separate the polishing pad 16 from the sub-pad 11. Furthermore, if
the polishing pad 16 is dragged over the sub-pad 11, the frictional
contact between the two can abrade particulate matter from the
polishing pad 16 and/or the sub-pad 11, which can cause a bump or
other nonuniformity to form in the planarizing surface 18, as
discussed above.
SUMMARY OF THE INVENTION
[0009] The present invention is directed toward methods and
apparatuses for supporting, cleaning and/or drying a polishing pad
used for mechanical and/or chemical planarization of
microelectronic substrates and substrate assemblies. In one aspect
of the invention, a cleaning head is positioned proximate to a
postoperative portion of the polishing pad to remove material from
a rear surface of the polishing pad that faces opposite a
planarizing surface of the polishing pad. The cleaning head can
have a cleaning device operable to remove liquid and/or particulate
material from the rear surface. For example, the cleaning device
can include a contact element such as an absorbent brush or an
impermeable blade positionable to contact the rear surface of the
post-operative portion of the polishing pad, an orifice facing
toward the rear surface of the polishing pad to provide gas or
liquid to the rear surface, and/or a heat source to dry the rear
surface of the polishing pad. Alternatively, the cleaning head can
include a vessel proximate to the post-operative portion of the
polishing pad. The vessel can have an opening configured to receive
the post-operative portion and an interior volume in fluid
communication with the opening and configured to contain a quantity
of cleaning liquid sufficient to contact the rear surface of the
polishing pad. The vessel can further include an ultrasonic
transducer to transmit ultrasonic energy to the cleaning
liquid.
[0010] In an embodiment in accordance with still a further aspect
of the invention, the polishing pad can be supported on a support
surface, such as a surface of a support pad. Gas or liquid is
directed toward or away from an interface region between the
support surface and the rear surface of the polishing pad to
separate the polishing pad from the support surface, or draw the
polishing pad toward the support surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a partially schematic, front isometric view of a
web-format planarizing machine in accordance with the prior
art.
[0012] FIG. 2 is a partially schematic, partially broken, front
isometric view of a planarizing machine having a cleaning head in
accordance with an embodiment of the invention.
[0013] FIG. 3 is a partially schematic, partially broken, front
isometric view of a planarizing machine having a cleaning head and
a liquid vessel in accordance with another embodiment of the
invention.
[0014] FIG. 4 is a partially schematic, top isometric view of a
portion of a planarizing machine having a platen coupled to a gas
source and a vacuum source in accordance with another embodiment of
the invention.
[0015] FIG. 5 is a partially schematic, top isometric view of a
portion of a planarizing machine having a platen with orifices
coupled to a gas source and a vacuum source in accordance with
another embodiment of the invention.
[0016] FIG. 6 is a partially schematic, top isometric view of a
portion of a planarizing machine having a platen and a support pad
with orifices coupled to a gas source and a vacuum source in
accordance with still another embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention is directed toward methods and
apparatuses for supporting, cleaning and/or drying planarizing
media used to planarize microelectronic substrates and/or substrate
assemblies. Many specific details of certain embodiments of the
invention are set forth in the following description and in FIGS.
2-6 to provide a thorough understanding of such embodiments. One
skilled in the art, however, will understand that the present
invention may have additional embodiments, or that the invention
may be practiced without several of the details described in the
following description.
[0018] FIG. 2 is a partially schematic, side isometric view of
planarizing machine 110 having a polishing pad 116 that passes
through a cleaning head 150 and adjacent a planarizing surface
cleaner 140 in accordance with an embodiment of the invention. The
polishing pad 116 extends from a supply roller 124 across a platen
120 and a support pad 111 to a take-up roller 123, while being
controlled and guided by an idler roller 121 and two guide rollers
122a, 122b generally as was discussed above. The polishing pad 116
has a planarizing surface 118 facing toward a microelectronic
substrate or substrate assembly 112 and a rear surface 119 facing
opposite the planarizing surface 118. A carrier assembly 130
positioned adjacent the polishing pad 116 can include a head 131
having an engaging surface 139 that presses the substrate 112
against the polishing pad 116 during operation. A drive assembly
133 supported by a gantry 132 and including an actuator 134, a
drive shaft 135, an arm 136 and a terminal shaft 137 moves the head
131 relative to the polishing pad 116 to remove material from the
substrate 112. The polishing pad 116 advances from the supply
roller 124 to the take-up roller 123 either between or during
planarizing cycles, in a manner generally similar to that discussed
above.
[0019] The polishing pad 116 includes a pre-operative portion 113
between the supply roller 124 and the platen 120 and a
post-operative portion 114 between the platen 120 and the take-up
roller 123. As the polishing pad 116 advances along the travel path
T-T toward the take-up roller 123, the preoperative portion 113
moves onto the platen 120 to planarize the substrate 112 and the
post-operative portion 114 moves off the platen 120 for cleaning.
Accordingly, the planarizing surface cleaner 140 and the cleaning
head 150 are positioned proximate to the post-operative portion 114
between the platen 120 and the take-up roller 123.
[0020] In one embodiment, the planarizing surface cleaner 140
includes a brush 141 having bristles that engage the planarizing
surface 118 of the polishing pad 116 to remove particulates and
other contaminants from the planarizing surface 118, or the
planarizing surface cleaner 140 can include other cleaning
elements. The planarizing surface cleaner 140 also includes a
liquid dispenser 142 coupled with a conduit 143 to a source of
cleaning liquid (not shown). The liquid dispenser 142 can have
orifices facing toward the planarizing surface 118 to dispense the
cleaning liquid onto the planarizing surface 118. The mechanical
action provided by the brush 141 in combination with the chemical
and/or mechanical action provided by the cleaning liquid clean the
planarizing surface 118 of the post-operative portion 114 before
the post-operative portion 114 returns to the platen 120 along the
travel path T-T for the next planarizing cycle.
[0021] The cleaning head 150 is positioned between the planarizing
surface cleaner 140 and the platen 120 to clean and/or dry the rear
surface 119 of the polishing pad 116 before the post-operative
portion 114 of the polishing pad 116 returns to the platen 120. The
cleaning head 150 can include a body 151 with an upper surface 153,
a lower surface 154 and a slot 152 extending through the body 151
from the upper surface 153 to the lower surface 154, or the
cleaning head 150 can have other configurations to receive the
polishing pad 116. In one embodiment, the cleaning head 150
includes a liquid manifold 170 positioned within the slot 152 and
coupled to a liquid source 174 with a liquid conduit or passage
171. The liquid manifold 170 has one or more liquid orifices 172
pointing toward the rear surface 119 of the polishing pad 116 to
direct the cleaning liquid toward the rear surface 119. In one
aspect of this embodiment, the cleaning liquid has a high vapor
pressure so that it evaporates quickly, leaving the rear surface
119 dry before the post-operative portion 114 of the polishing pad
116 returns to the platen 120. For example, the cleaning liquid can
include acetone, alcohol, or other liquids having a relatively high
vapor pressure. Alternatively, the vapor pressure of the cleaning
liquid may not be particularly high and the rate at which the
polishing pad 116 moves back onto the platen 120 can be reduced (or
the polishing pad 116 can remain in a fixed position) while the
cleaning liquid evaporates from the rear surface 119.
[0022] In one embodiment, the cleaning head 150 includes one or
more gas manifolds 160 to hasten the drying of the rear surface 119
and/or to clean the rear surface 119. In one aspect of this
embodiment, the cleaning head 150 has three gas manifolds 160
(shown as an upper manifold 160a, an intermediate manifold 160b and
a lower manifold 160c) and in other embodiments, the cleaning head
has more or fewer manifolds 160, as will be discussed in greater
detail below. Each gas manifold 160 is coupled via a gas conduit or
passage 161 to a gas source 164 to provide gas to the manifolds
160. The gas source 164 can include any suitable gas, such as air,
or an inert gas, compressed to an elevated pressure of, for
example, between about 10 psi and about 100 psi, or another
suitable pressure.
[0023] Each gas manifold 160 is also in fluid communication with
one or more orifices 162 (shown in FIG. 2 as circular upper
orifices 162a, circular intermediate orifices 162b and an elongated
lower orifice 162c) to direct the gas toward the rear surface 119
of the polishing pad 116. The upper and intermediate orifices 162a,
162b can include discrete circular openings arranged in rows
transverse to the travel direction T-T of the polishing pad 116 or
the orifices 162a, 162b can have other shapes or configurations. In
one embodiment, the upper orifices 162a are offset or staggered
transversely relative to the intermediate orifices 162b to
uniformly distribute the gas over the width of the rear surface
119. In one aspect of this embodiment, the orifices 162a, 162b are
directed at least partially downward so that the gas emitted from
the orifices 162a, 162b forces liquid and/or contaminants
downwardly away from the rear surface 119 as the post-operative
portion 114 moves upwardly back onto the platen 120. Alternatively,
the orifices 162a, 162b can have other orientations.
[0024] In yet a further aspect of this embodiment, the lower
orifice 162c includes a slot elongated in a direction generally
transverse to the travel path T-T and directed at least slightly
downward, as was discussed above. The lower gas manifold 160c is
coupled to a temperature controller 163 to control the temperature
of the gas directed toward the rear surface 119 of the polishing
pad 116. For example, in one embodiment, the temperature controller
163 can control the temperature of the gas be up to and including
approximately 100.degree. C.
[0025] In other embodiments, the temperature controller 163 can
elevate the temperature of the gas to other values that do not
adversely affect the polishing pad 116.
[0026] In still further embodiments, other combinations and
arrangements of the elements discussed above with reference to FIG.
2 can clean and/or dry the rear surface 119 of the polishing pad
116. For example, the cleaning head 150 can include a single row of
orifices 162 or can include more than two rows of orifices 162, any
of which can be coupled to the temperature controller 163.
Alternatively, the cleaning head 150 can include the elongated
orifice 162c in lieu of, rather than in addition to, the circular
orifices 162a, 162b. In another embodiment, the gas manifold(s) 160
can be eliminated, for example, when the liquid manifold 170
provides liquid sufficient to adequately clean the rear surface 119
of the polishing pad 116 and the liquid evaporates before the
post-operative portion 114 moves back onto the platen 120.
Conversely, when the gas provided by the gas manifold(s) 160 is
sufficient to both clean and dry the rear surface 119, the liquid
manifold 170 can be eliminated.
[0027] One feature of an embodiment of the apparatus 110 discussed
above with reference to FIG. 2 is that the cleaning head 150
removes liquid and/or solid contaminants from the rear surface 119
of the polishing pad 116 before the post-operative portion 114 of
the polishing pad 116 returns to the platen 120. An advantage of
this arrangement is that the planarizing surface 118 of the
polishing pad 116 is less likely to have non-uniformities resulting
from contaminants trapped between the polishing pad 116 and the
support pad 111. A further advantage of this arrangement is that
the likelihood for the polishing pad 116 to adhere to the support
pad 111 (due to the presence of liquid between the two) can be
reduced, increasing the ease with which the polishing pad 116 is
moved across the platen 120. This is unlike some conventional
planarizing devices which not only allow liquid and/or solid debris
to accumulate on the rear surface 119 of the polishing pad 116 but
also fail to remove such contaminants before the polishing pad 116
returns to the platen 120.
[0028] FIG. 3 is a partially schematic, partially broken side
isometric view of an apparatus 210 having a cleaning head 250 in
accordance with another embodiment of the invention. The cleaning
head 250 includes a body 251 having a slot 252 through which the
polishing pad 116 passes. In one embodiment, two contact elements
280 (shown as a wiper 280a and an absorbent brush 280b) are
positioned within the slot to remove contaminants from the rear
surface 119 of the polishing pad 116. The contact elements 280 can
be coupled to an actuator 286 that moves the contact elements 280
into and out of engagement with the rear surface 119, or the
contact elements 280 can remain pressed against the rear surface
119. In other embodiments, the cleaning head 250 can include more
or fewer contact elements 280 and/or contact elements 280 in
combination with fluid manifolds and/or gas manifolds, similar to
those discussed above with reference to FIG. 2.
[0029] In one embodiment, the wiper 280a includes an impermeable,
resilient and flexible material, such as rubber or another
elastomer having one or more edges 281 (two are shown in FIG. 3) or
other cleaning surfaces that contact the rear surface 119 of the
polishing pad 116. In a further aspect of this embodiment, the
wiper 280a has vacuum orifices 283 facing toward the rear surface
119 and coupled with a vacuum conduit 282 to a vacuum source (not
shown). When a vacuum is applied to the vacuum orifices 283 via the
vacuum conduit 282, the polishing pad 116 is drawn against the
wiper 280a so that the rear surface 119 contacts the edges 281,
forming an at least partially liquid-tight seal. Alternatively, the
vacuum orifices 283 can be housed in a separate unit (not shown)
adjacent to the wiper 280a. In either case, the edges 281 of the
wiper 280a deflect liquid and/or solid contaminants from the rear
surface 119 as the polishing pad 116 moves upwardly onto the platen
120.
[0030] The cleaning head 250 can include the absorbent brush 280b
in addition to, or in lieu of the wiper 280a. In one embodiment,
the absorbent brush 280b has a cleaning surface that includes any
resilient, compliant and absorbent material (such as polyvinyl
alcohol) to absorb liquid from the polishing pad 116 without
abrading the polishing pad 116. In one aspect of this embodiment,
the absorbent brush 280b has a heating element 285 coupled to an
electrical source (not shown) with electrical leads 284 to remove
moisture from the absorbent brush 280b after the absorbent brush
280b has absorbed moisture from the rear surface 119 of the
polishing pad 116. In other embodiments, other devices (for
example, rollers or forced heated air) discharge moisture from the
absorbent brush 280b. In still another embodiment, the absorbent
brush 280b (or another contact element 280, such as the wiper 280a)
is heated while it is pressed against the polishing pad 116.
[0031] In yet another embodiment, the cleaning head 250 includes
the heating element 285 alone instead of the contact elements 280.
For example, the heating element 285 can include an electric coil
heater or an infrared heater that removes moisture from the rear
surface 119 of the polishing pad without contacting the polishing
pad 116. In one embodiment, the heating element 285 operates in
conjunction with devices that clean the rear surface 119 (such as
the gas manifolds 160 and liquid manifolds 170 discussed above with
reference to FIG. 2) or alternatively the heating element 285
operates independently of the cleaning devices, for example, when
it is desired only to dry the rear surface 119, rather than both
clean and dry the rear surface 119.
[0032] In one embodiment, the cleaning head 250 includes a cleaning
vessel 290 in addition to or in lieu of the planarizing surface
cleaner 140 discussed above with reference to FIG. 2. The cleaning
vessel 290 has an internal volume 292 with an opening 291
configured to receive the polishing pad 116. The internal volume
292 contains a cleaning liquid 293, such as a solvent, to remove
contaminants from the polishing pad 116. In one aspect of this
embodiment, the polishing pad 116 passes around a guide roller 222
submerged in the cleaning liquid 293 to immerse both the
planarizing surface 119 and the rear surface 118 of the polishing
pad 116. Alternatively, the cleaning vessel 290 can include other
devices that immerse the planarizing surface 118 and/or the rear
surface 119. The vessel 290 can also include ultrasonic transducers
294 adjacent to the internal volume 292 to direct ultrasonic energy
into the cleaning liquid 293, increasing the efficacy of the
cleaning liquid 293.
[0033] In one embodiment, the cleaning liquid 293 includes a
relatively high vapor pressure liquid, such as acetone or alcohol,
that evaporates from the polishing pad 116 before the
post-operative portion 114 of the polishing pad 116 returns to the
platen 120. Accordingly, the body 251 of cleaning head 250 can be
eliminated. Alternatively, the vessel 290 can include other liquids
293 (such as water) that do not evaporate as readily as acetone or
alcohol, in which case the contact elements 280, the heating
element 285, and/or the gas manifolds 160 discussed above can
remove excess liquid from the rear surface 119 of the polishing pad
116 before the polishing pad 116 returns to the platen 120.
[0034] One feature of an embodiment of the apparatus 210 shown in
FIG. 3 is that the cleaning vessel 290 cleans the polishing pad 116
without direct mechanical contact other than that resulting from
the roller 222. Accordingly, the likelihood for abrading the
polishing pad 116 during cleaning is reduced when compared with
some conventional devices. The likelihood for abrasion can be
further reduced by drying the polishing pad 116 with the heater 285
or with gas from the gas manifold(s) 160 (FIG. 2) or by allowing
the cleaning liquid 293 to evaporate before the polishing pad 116
returns to the platen 120.
[0035] FIG. 4 is a partially schematic, top isometric view of a
portion of a planarizing apparatus 310 having a platen 320 that
supports the polishing pad 116 (shown in phantom lines) in
accordance with another embodiment of the invention. In one aspect
of this embodiment, the apparatus 310 includes a support pad 311
positioned between the rear surface 119 of the polishing pad 116
and an upwardly facing support surface 322 of the platen 320. The
platen 320 can further include a channel 325 that extends around
the perimeter of the support pad 311 and has an upwardly facing
opening adjacent to the rear surface 119 of the polishing pad 116.
The channel 325 is coupled with a conduit 326 to a pressurized gas
source 327 and a vacuum source 328. A valve 323 in the conduit 326
can be manually or automatically controlled to connect either the
gas source 327 or the vacuum source 328 with the channel 325.
[0036] In operation, the valve 323 is adjusted to connect the
vacuum source 328 with the channel 325 during planarization of the
substrate 112 (FIGS. 2-3). Accordingly, the polishing pad 116 is
drawn tightly against the support pad 311 to prevent unwanted
movement of the polishing pad 116 which can result in
non-uniformities in the substrate 112. When the polishing pad 116
is to be moved relative to the platen 320 (for example, to be
cleaned according to one or more of the methods discussed above
with reference to FIGS. 2-3), the valve 323 is adjusted to couple
the gas source 327 to the channel 325. The gas source 327 pumps a
gas (such as air) through the channel 325 to impinge on the rear
surface 119 of the polishing pad 116 and flow to an interface
region between the polishing pad 116 and the support pad 311. The
pressurized gas separates the polishing pad 116 slightly from the
support pad 311, allowing the polishing pad 116 to be more easily
moved relative to the support pad 311 and the platen 320.
Furthermore, the compressed gas can remove contaminants, such as
liquid or solid debris, from the rear surface 119 of the polishing
pad 116. Accordingly, an advantage of an embodiment of the
apparatus 310 shown in FIG. 4 is that it can clean and dry the rear
surface 119 and/or separate the rear surface 119 from the support
pad 311 for moving the polishing pad 116 relative to the platen
320.
[0037] FIG. 5 is a partially schematic, partially broken top
isometric view of a portion of a planarizing apparatus 410 having a
platen 420 and a support pad 411 that support the polishing pad 116
in accordance with another embodiment of the invention. The platen
420 includes a plurality of orifices 429 arranged around the
perimeter of the support pad 411 and coupled to a plenum 421
positioned within the platen 420. The plenum 421 is coupled via the
conduit 326 to the gas source 327 and the vacuum source 328 in a
manner generally similar to that discussed above with reference to
FIG. 4. Accordingly, the plenum 421 can be selectively coupled to
the gas source 327 and the vacuum source 328 to either expel or
draw in air in a manner generally similar to that discussed above
with reference to FIG. 4.
[0038] FIG. 6 is a partially schematic, partially broken top
isometric view of a portion of an apparatus 510 having a platen 520
and a support pad 511 that support the polishing pad 116 in
accordance with yet another embodiment of the invention. The platen
520 includes a plenum 521 coupled to the gas source 327 and the
vacuum source 328 in a manner similar to that discussed above. The
apparatus 510 further includes a plurality of orifices 529,
including pad orifices 529a extending through the support pad 511
and aligned with a corresponding plurality of platen orifices 529b
extending through a portion of the platen 520 to be in fluid
communication with the manifold 521. The orifices 529 can be
uniformly spaced over the support pad 511, or alternatively, the
orifices can be arranged in other patterns. In a further aspect of
this embodiment, the orifices 529 can point toward the edges of the
support pad 511 and the polishing pad 116 to direct contaminants
outwardly away from the interface region between the support pad
511 and the polishing pad 116. The orifices 529 are selectively
coupled to either the gas source 327 or the vacuum source 328 to
operate in a manner similar to that discussed above with reference
to FIG. 4.
[0039] From the foregoing it will be appreciated that, although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention.
Accordingly, the invention is not limited except as by the appended
claims.
* * * * *