U.S. patent application number 10/886105 was filed with the patent office on 2005-06-02 for adjustable gap chemical mechanical polishing method and apparatus.
Invention is credited to Ashjaee, Jalal, Basol, Bulent M., Talieh, Homayoun.
Application Number | 20050118932 10/886105 |
Document ID | / |
Family ID | 34622756 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050118932 |
Kind Code |
A1 |
Talieh, Homayoun ; et
al. |
June 2, 2005 |
Adjustable gap chemical mechanical polishing method and
apparatus
Abstract
A polishing apparatus for polishing a surface of wafer is
provided. The apparatus includes a carrier to hold the workpiece.
An array of fluid nozzles are placed across from the surface of the
wafer to provide a gap between the nozzles and the surface of the
workpiece. A polishing pad positioned within the gap and configured
to polish the surface of the workpiece when a fluid is applied from
the plurality of nozzles to push the polishing pad to the
surface.
Inventors: |
Talieh, Homayoun; (San Jose,
CA) ; Ashjaee, Jalal; (Cupertino, CA) ; Basol,
Bulent M.; (Manhattan Beach, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
34622756 |
Appl. No.: |
10/886105 |
Filed: |
July 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60484909 |
Jul 3, 2003 |
|
|
|
Current U.S.
Class: |
451/41 ; 451/285;
451/60 |
Current CPC
Class: |
B24B 37/30 20130101;
B24B 49/16 20130101 |
Class at
Publication: |
451/041 ;
451/060; 451/285 |
International
Class: |
B24B 001/00 |
Claims
We claim:
1. A polishing apparatus for polishing a surface of a workpiece
comprising: a carrier surface configured to hold the workpiece; a
plurality of fluid nozzles placed across from the surface to
provide a gap between the nozzles and the surface of the workpiece;
and a polishing pad positioned within the gap and configured to
polish the surface of the workpiece when a fluid is applied from
the plurality of nozzles to push the polishing pad to the
surface.
2. The polishing apparatus of claim 1, wherein an isolation region
separates fluid nozzles from one another.
3. The polishing apparatus of claim 2, wherein the isolation region
drain the fluid after the step of applying the fluid to the
polishing pad.
4. The polishing apparatus of claim 1, wherein the fluid nozzles
are arranged into a plurality of zones.
5. The polishing apparatus of claim 1, wherein isolation regions
separate zones from one another.
6. The polishing apparatus o f claim 4, wherein the plurality of
zones are circular and disposed concentrically.
7. The polishing apparatus of claim 4 further comprising at least
one regulator associated with each zone and configured to modify
the fluid flow from the nozzles to create a desired fluid flow rate
profile.
8. The polishing apparatus of claim 1 wherein the fluid nozzles are
configured to be moved close to or away from the polishing pad.
9. The polishing apparatus of claim 1, wherein the polishing pad is
configured to be moved with respect to the fluid nozzles.
10. The polishing apparatus of claim 1, wherein the polishing pad
is configured to be moved bilinearly.
11. The polishing apparatus of claim 1, wherein the fluid nozzles
are placed above the surface of the workpiece.
12. The polishing apparatus of claim 1, wherein the polishing pad
is a fixed abrasive pad.
13. The polishing apparatus of claim 1, wherein the polishing pad
is a polymeric pad.
14. The polishing apparatus of claim 1, wherein the surface of the
wafer comprises copper.
15. The polishing apparatus of claim 1, wherein the fluid is
air.
16. A method of polishing a surface of a workpiece surface using a
polishing pad, the method comprising the steps of: placing the
polishing pad within a gap defined between the surface of the
workpiece and an array of nozzles; emitting a fluid from the array
of nozzles to push the polishing pad onto the surface of the
workpiece; and polishing the surface with the polishing pad while
keeping the gap constant.
17. The method of claim 16 further comprising the step of removing
the fluid through the isolation space between the array of
nozzles.
18. The method of claim 16, wherein the step of polishing comprises
establishing a relative motion between the polishing pad and the
surface.
19. The method of claim 16 further comprising the step of reducing
the gap to increase the material removal rate from the surface.
20. The method of claim 19 further comprising the step of
continuing polishing the surface with the polishing pad after the
step of reducing the gap.
21. The method of claim 19, wherein the step of reducing the gap is
performed by moving the array of nozzles close to the surface.
22. The method of claim 19, wherein the step of reducing the gap is
performed by moving the surface close to the array of nozzles.
23. The method of claim 16 further comprising the step of
increasing the gap to decrease the material removal rate from the
surface.
24. The method of claim 23 further comprising the step of
continuing polishing the surface with the polishing pad after the
step of increasing the gap.
25. The method of claim 23, wherein the step of increasing the gap
is performed by moving the array of nozzles away from the
surface.
26. The method of claim 23, wherein the step of increasing the gap
is performed by moving the surface away from the array of
nozzles.
27. The method of claim 18, wherein the array of nozzles includes a
plurality of zones and the step of emitting fluid comprises
emitting fluid with different flow rates from each zone.
28. The method of claim 27 further comprising the step of removing
the fluid through the isolation space between the zones.
29. The method of claim 16 further comprising delivering a
polishing slurry between the surface of the workpiece and the
polishing pad.
30. The method of claim 18, wherein the step of establishing a
relative motion includes moving the polishing pad bi-linearly over
the array of nozzles while rotating the surface of the workpiece on
the polishing pad.
31. The method of claim 16 further comprising the step of
increasing the flow rate of the fluid to increase material removal
rate from the surface.
32. The method of claim 16 further comprising the step of
decreasing the flow rate of the fluid to decrease the material
removal rate from the surface.
33. The method of claim 27, wherein the step of emitting fluid with
different flow rates from each zone comprises emitting fluid with a
flow rate from a zone and emitting fluid with another flow rate
from another zone.
Description
RELATED APPLICATIONS
[0001] This application claims priority from Provisional
Application Ser. No. 60/484,909 filed Jul. 3, 2003 (NT-303-P),
which is incorporated herein by reference.
FIELD
[0002] The present invention relates to manufacture of
semiconductor integrated circuits and, more particularly, to a
method and apparatus for polishing substrates.
BACKGROUND
[0003] Chemical mechanical polishing (CMP) of materials for VLSI
and ULSI applications has important and broad application in the
semiconductor industry. Chemical mechanical polishing is a widely
used technique for planarizing metals and dielectrics as well as
other types of layers on semiconductor wafers. CMP is generally
used to flatten and remove material from surfaces during the wafer
fabrication process, for example, during the wafer fabrication
process, CMP is often used to flatten/polish the profiles that
build up in multilevel metal interconnection.
[0004] In a typical CMP process, a substrate such as a
semiconductor wafer is mounted on a substrate carrier, often called
a head. The wafer surface is pressed against a polishing pad and
moved with respect to the polishing pad. This is typically
performed by rotating the wafer, moving the pad or both. The
polishing pad may be a conventional polishing pad or a fixed
abrasive polishing pad. Conventional or polymeric polishing pads
are usually used with polishing slurries including abrasive
particles and chemically reactive agents. During the CMP process,
the polishing slurry is supplied onto the polishing pad as the
wafer surface is pressed on the pad. The surface of a fixed
abrasive polishing pad typically includes abrasive particles that
are embedded in a matrix or binder material.
[0005] FIG. 1 illustrates an exemplary conventional CMP system 10
that includes a polishing pad 12 to polish a front side of the
wafer 14. A wafer carrier 16 holds the wafer 14 and the polishing
pad can be moved with respect to the wafer. The wafer carrier 16
may include an array of built in pressure zones 18 that are located
behind the wafer. The pressure zones 18 are often formed
concentrically to apply localized pressure to the backside of the
wafer. By applying pressure to the selected locations of the
backside, polishing rate on the corresponding locations of the
front side of the wafer can be changed. During the polishing
process, the wafer carrier 16 is rotated (clockwise or
counter-clockwise) while the pad 12 is moved. A platen 20 with a
flat surface supports the polishing pad 12. Depending on the
pressure distribution profile created on the backside of the wafer,
polishing rate of the corresponding regions on the wafer can be
varied to achieve desired polishing on the wafer. For example, by
increasing the pressure around the center of the backside, higher
polishing rates are obtained at the center of the front side.
However, in such systems, pressures applied by selected pressure
zones onto corresponding selected locations on the wafer are not
entirely independent from one another. Pressure from neighboring
pressure zones may interfere with each other, which situation
affects the local material removal rate and cause undesired poor or
excessive material removal from the front side.
[0006] Therefore, a need exists for a chemical mechanical polishing
(CMP) system that can provide accurate, stable and controllable
polishing rates on a wafer.
SUMMARY
[0007] The present invention provides a polishing system using
fluid from a fluid source to push a polishing pad to a workpiece
surface during the polishing process. A constant gap is kept
between the fluid source and the workpiece surface as the workpiece
surface is polished by the polishing pad.
[0008] In one aspect of the present invention, a polishing
apparatus for polishing a surface of a workpiece is provided. The
apparatus includes a carrier surface configured to hold the
workpiece, a plurality of fluid nozzles placed across from the
surface to provide a gap between the nozzles and the surface of the
workpiece, and a polishing pad positioned within the gap. The
polishing pad is configured to polish the surface of the workpiece
when a fluid is applied from the plurality of nozzles to push the
polishing pad to the surface.
[0009] In another aspect of the present invention, a method of
polishing a surface of a workpiece surface using a polishing pad is
provided. The method includes the steps of placing the polishing
pad within a gap defined between the surface of the workpiece and
an array of nozzles, emitting a fluid from the array of nozzles to
push the polishing pad onto the surface of the workpiece; and
polishing the surface with the polishing pad while keeping the gap
constant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic illustration of a conventional
chemical mechanical polishing apparatus; and
[0011] FIG. 2 is a schematic illustration of an embodiment of a
chemical mechanical polishing system of the present invention.
DETAILED DESCRIPTION
[0012] The present invention provides a CMP system applying fluid
flow from a fluid source to the backside of a polishing pad to
cause the polishing surface of the polishing pad to be forced
against a workpiece surface. During the polishing the workpiece
surface with the polishing pad, the workpiece surface is kept at a
predetermined distance from the fluid source, to achieve chemical
mechanical polishing of the workpiece surface.
[0013] FIG. 2 depicts an exemplary CMP system 100 according to an
embodiment of the invention. The system 100 comprises a fluid
source assembly 102 and a carrier surface 104 to hold a workpiece
106. The workpiece 106 may be a semiconductor wafer. Carrier
surface 104 may be a front surface of a wafer carrier or it may be
any surface against which the backside of a wafer rests. A
polishing pad 108 is positioned between a surface 110 of the wafer
106 and the fluid source assembly 102. The surface 110 of the wafer
may include a conductive layer such as copper or a dielectric layer
such as silicon dioxide layer to be planarized using CMP. The
polishing pad 108 includes a first surface or a process surface 112
and a second surface or a back surface 114. The polishing pad 108
may preferably be tensioned by a tensioning mechanism (not shown).
Process surface 112 of the polishing pad 108 polishes the surface
110 of the wafer 106 during the CMP process, typically with the
help of a process solution or a polishing slurry. A variety of
different polishing pads can be used with the present invention.
For example, the polishing pad can be a fixed abrasive pad or a
more commonly used polymeric pad. The polishing pad 108 may be used
with or without a slurry. The carrier surface 104 of the system 100
may rotate or move the wafer laterally or vertically. In this
embodiment, fluid source assembly 102 is placed above the wafer
106. However, other configurations which place the fluid source
assembly 102 under the wafer is also possible and within the scope
of this invention.
[0014] In this embodiment, the fluid may be gas such as air, or
liquid such as water. During the process, a fluid flow 115 is
applied to the back surface 1 14 of the polishing pad 108. The
application of the fluid flow 115 to the back surface 114 of the
polishing pad 108 is carried out using the fluid source assembly
102. The fluid source assembly may include a plurality of fluid
nozzles 116. The fluid nozzles 116 may be arranged into any
configuration or array with space 118 among them. For example, the
nozzles 116 may form a nozzle array that positions nozzles a
predetermined distance from one another thereby creating the space
118 among them. Alternatively, instead of leaving a space among the
nozzles, holes or openings may be placed among the nozzles to
remove the used fluid from the system. In this approach, the fluid
flow assembly may have surface including nozzles and the openings.
The nozzles 116 may form discrete zones to create a fluid flow rate
distribution profile of the fluid source assembly 102. The zones
may be formed concentrically and each zone may be connected to a
fluid flow controller (not shown) to regulate fluid flow for each
zone. In an alternative embodiment, a space or holes may exist
between the zones. By varying amount of fluid flow rate from the
selected fluid flow zones, a fluid flow rate distribution profile
including different flow rates from different zones may be
generated on the back surface 114 of the polishing pad 108. Fluid
flow rate distribution profile may have high flow rate zones or low
flow rate zones. Depending on the fluid flow rate distribution
profile, polishing rate of the corresponding regions on the wafer
106 may be varied to achieve desired polishing on the surface 110
since more fluid flow from a given zone pushes the process surface
112 to the surface 110 with a higher force at that zone. For
example, by increasing the fluid flow rate from the nozzles around
the center of the fluid source assembly 102, higher polishing rates
is obtained at the center of the surface 110 of the wafer.
[0015] Referring back to FIG. 2, in this embodiment, a first end
117 of the nozzles 116 are aligned with an imaginary plane P which
is nearly parallel to the surface 110 of the wafer. A gap "t" is
left between the first end 117 of the nozzles 116 and the surface
110 of the wafer 106. During the polishing process, the gap "t" is
kept constant. The predetermined height of the gap "t" is important
for the polishing process of the present invention and this height
is adjustable. The gap "t" may be less than 6 millimeters. If the
gap "t" is configured to be large, fluid flow rate must be high to
accomplish the desired polishing rate on the surface 110 of the
wafer 106. However, if the gap "t" is configured to be small,
reduced flow rates can be used to accomplish desired polishing
rates. The gap "t", however, cannot be too small to allow the back
surface 114 of the polishing pad 108 to touch the nozzles 116.
[0016] As shown in FIG. 2, when fluid flow 115 is applied during
the process, the polishing pad 108 moves into a process position
120 within the gap "t" and is forced onto the surface of the wafer
with the applied fluid flow. While the gap is kept constant or
unchanged, any desired fluid flow rate distribution profile can be
applied to the polishing pad 108 to obtain corresponding desired
polishing rates on the surface 110. The space 118 among the nozzles
116 may be used for isolating the nozzles from the neighboring
nozzles and may advantageously provide a passage or a drain for the
exhausted, or used, fluid. Alternately, the used fluid may leave
the system from the edges of the fluid source assembly 102. After
forcing the polishing pad toward the surface of the wafer for the
CMP process, the fluid flow from the nozzles 116 exits the fluid
source assembly 102 through the space 118 among the nozzles 116
without interfering with the fluid flow from the neighboring
nozzles. When the process is over, for example by reaching a
predetermined endpoint, the fluid flow is stopped, which causes the
preferably tensioned polishing pad to return to its original
position within the gap "t".
[0017] Accordingly, the present invention provides a substantially
independent fluid flow for each nozzle, and if the nozzles are
arranged into zones, the present invention provides distinct fluid
flow rate distribution profiles. Such well-defined and independent
fluid flow rate distribution profiles, in turn, establish
well-defined polishing rates on the substrate as the polishing pad
polishes the workpiece surface. In one embodiment, the polishing
pad 108 is statically held in position with respect to the nozzles
116 and the wafer 106 is moved. In another embodiment, the
polishing pad 108 is moved in an orbital direction or a linear
direction with respect to the nozzles 116. In yet another
embodiment, the polishing pad 108 is moved in a bi-linear direction
with respect to the nozzles 116. In all cases the wafer 106 may
also be moved during the polishing process.
[0018] Although various preferred embodiments and the best mode
have been described in detail above, those skilled in the art will
readily appreciate that many modifications of the exemplary
embodiment are possible without materially departing from the novel
teachings and advantages of this invention.
* * * * *