U.S. patent application number 10/383477 was filed with the patent office on 2004-06-10 for method and polishing pad design enabling improved wafer removal from a polishing pad in a cmp process.
This patent application is currently assigned to Ebara Technologies. Invention is credited to Moloney, Gerard, Reyes, Alejandro, Saldana, Ernesto, Walsh, Cormac.
Application Number | 20040108063 10/383477 |
Document ID | / |
Family ID | 32474217 |
Filed Date | 2004-06-10 |
United States Patent
Application |
20040108063 |
Kind Code |
A1 |
Reyes, Alejandro ; et
al. |
June 10, 2004 |
Method and polishing pad design enabling improved wafer removal
from a polishing pad in a CMP process
Abstract
The invention provides a chemical mechanical polishing pad and
method that enables improved wafer removal from the polishing pad
after completion of chemical mechanical polishing of the wafer.
Inventors: |
Reyes, Alejandro; (San Jose,
CA) ; Moloney, Gerard; (Milpitas, CA) ; Walsh,
Cormac; (Sunnyvale, CA) ; Saldana, Ernesto;
(San Jose, CA) |
Correspondence
Address: |
SQUIRE, SANDERS & DEMPSEY L.L.P
600 HANSEN WAY
PALO ALTO
CA
94304-1043
US
|
Assignee: |
Ebara Technologies
51 Main Avenue
Sacramento
CA
|
Family ID: |
32474217 |
Appl. No.: |
10/383477 |
Filed: |
March 7, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60430947 |
Dec 4, 2002 |
|
|
|
Current U.S.
Class: |
156/345.12 ;
257/E21.23 |
Current CPC
Class: |
H01L 21/02024 20130101;
B24B 37/26 20130101 |
Class at
Publication: |
156/345.12 |
International
Class: |
C23F 001/00 |
Claims
What is claimed is:
1. A chemical mechanical polishing pad, comprising: a top surface
having a structure that forms a vacuum between the pad and a wafer
during chemical mechanical polishing; and at least one venting
inlet capable of releasing the vacuum when the wafer is located
over the venting inlet.
2. The pad of claim 1, wherein the structure includes a plurality
of perforations.
3. The pad of claim 1, wherein the structure includes a plurality
of grooves.
4. The pad of claim 1, wherein the at least one venting inlet is
connected to atmospheric pressure.
5. The pad of claim 1, wherein the at least one venting inlet
extends from the periphery of the top surface towards the center of
the top surface.
6. The pad of claim 1, wherein the at least one venting inlet is
angled relative to a diameter of the pad.
7. The pad of claim 1, wherein the at least one venting inlet
passes through the full depth of the polishing pad.
8. The pad of claim 1, wherein the at least one venting inlet
passes through a portion of the depth of the polishing pad.
9. The pad of claim 1, wherein the at least one venting inlet has a
sloped surface.
10. The pad of claim 1, wherein the at least one venting inlet
tunnels through the pad to connect with the top surface of the
pad.
11. The pad of claim 1, wherein the at least one venting inlet
tunnels underneath the pad to connect with the top surface of the
pad and wherein a platen forms a bottom surface of the at least one
venting inlet.
12. A method for removing a wafer from a polishing head after
chemical mechanical polishing, comprising: applying a vacuum to a
backside of the wafer; moving the polishing head retaining the
wafer so that the wafer is positioned over a venting inlet of a
polishing pad; releasing the vacuum from the backside of the wafer;
and removing the wafer from the polishing head.
13. The method of claim 12, wherein the polishing pad has a top
surface having a plurality of perforations.
14. The method of claim 12, wherein the polishing pad has a top
surface having a plurality of grooves.
15. The method of claim 12, wherein the venting inlet is connected
to atmospheric pressure.
16. The method of claim 12, wherein the venting inlet extends from
the periphery of a top surface of the pad towards a center of the
top surface.
17. The method of claim 12, wherein the venting inlet is angled
relative to a diameter of the pad.
18. The method of claim 12, wherein the venting inlet passes
through the full depth of the polishing pad.
19. The method of claim 12, wherein the venting inlet passes
through a portion of the depth of the polishing pad.
20. The method of claim 12, wherein the venting inlet has a sloped
surface.
21. The method of claim 12, wherein the venting inlet tunnels
through the pad to connect with a top surface of the pad.
22. The method of claim 12, wherein the venting inlet tunnels
underneath the pad to connect with a top surface of the pad and
wherein a platen forms a bottom surface of the venting inlet.
23. The method of claim 12, wherein the method is performed in the
order recited.
24. The method of claim 12, wherein the moving is performed before
the applying.
25. A method for removing a wafer from a polishing head after
chemical mechanical polishing, comprising: applying a vacuum to a
backside of the wafer; moving the polishing head retaining the
wafer to a periphery of a polishing pad; rotating the polishing pad
so that a venting inlet of the polishing pad is positioned under
the wafer; releasing the vacuum from the backside of the wafer; and
removing the wafer from the polishing head.
26. The method of claim 25, wherein the polishing pad has a top
surface having a plurality of perforations.
27. The method of claim 25, wherein the polishing pad has a top
surface having a plurality of grooves.
28. The method of claim 25, wherein the venting inlet is connected
to atmospheric pressure.
29. The method of claim 25, wherein the venting inlet extends from
the periphery of a top surface of the pad towards a center of the
top surface.
30. The method of claim 25, wherein the venting inlet is angled
relative to a diameter of the pad.
31. The method of claim 25, wherein the venting inlet passes
through the full depth of the polishing pad.
32. The method of claim 25, wherein the venting inlet passes
through a portion of the depth of the polishing pad.
33. The method of claim 25, wherein the venting inlet has a sloped
surface.
34. The method of claim 25, wherein the venting inlet tunnels
through the pad to connect with a top surface of the pad.
35. The method of claim 25, wherein the venting inlet tunnels
underneath the pad to connect with a top surface of the pad and
wherein a platen forms a bottom surface of the venting inlet.
36. The method of claim 25, wherein the method is performed in the
order recited.
37. The method of claim 25, wherein the moving is performed before
the applying.
Description
PRIORITY REFERENCE TO PRIOR APPLICATIONS
[0001] This application claims benefit of and incorporates by
reference U.S. patent application serial No. 60/430,947, entitled
"Method And Polishing Pad Design Enabling Improved Wafer Removal
From The Polishing Pad In A CMP Process," filed on Dec. 4, 2002, by
inventors Alejandro Reyes, Gerard Moloney, Cormac Walsh, and
Ernesto Saldana.
TECHNICAL FIELD
[0002] This invention relates generally to chemical mechanical
polishing (CMP), and more particularly, but not exclusively,
provides a CMP polishing pad and method for improving the removal
of a wafer from a polishing pad after CMP.
BACKGROUND
[0003] CMP is a combination of chemical reaction and mechanical
buffing. A conventional CMP system includes a polishing head with a
retaining ring that holds and rotates a substrate (also referred to
interchangeably as a wafer) against a polishing pad surface
rotating in the same direction. The polishing pad can be made of
cast and sliced polyurethane (or other polymers) with a filler or a
urethane coated felt.
[0004] During rotation of the substrate against the polishing pad,
a slurry of silica (and/or other abrasives) suspended in a mild
etchant, such as potassium or ammonium hydroxide, is dispensed onto
the polishing pad. The combination of chemical reaction from the
slurry and mechanical buffing from the polishing pad removes
vertical inconsistencies on the surface of the substrate, thereby
forming an extremely flat surface.
[0005] In order to reduce operating costs and human intervention
into the CMP system there has been a push to use CMP consumables
with a longer operating life. An example of one of these
consumables is what is referred to within the industry is a
perforated polishing pad. An example of a perforated polishing pad
is a polishing pad 130a as shown in FIG. 1 and FIG. 2 (not to
scale). The polishing pad 130a has a plurality of holes or
perforations 170 spread uniformly over the surface of the polishing
pad 130a. The perforations 170 act to distribute slurry locally
during CMP when the polishing pad 130a is compressed.
[0006] However, one of the drawbacks of the perforated pad 130a is
the difficulty of lifting a wafer from the pad after polishing. The
holes 170 in the pad 130a act as suction cups and the vacuum force
applied through the polishing head to the back side of the wafer
can not easily overcome this suction force between the front side
of the wafer and the pad.
[0007] For example, FIG. 1 shows a conventional CMP system 100a
with a perforated polishing pad 130a. The polishing pad 130a rests
on a platen 140 on a turn table 150. The polishing head 180
includes a carrier 120 and a retaining ring 110 that retains a
wafer 160 during CMP and can also include other components not
shown. After CMP is complete, a vacuum force is applied to a
backside of the wafer 160 (i.e., the side of the wafer 160 facing
the carrier 120) and the polishing head 180 lifts the wafer 160 off
of the polishing pad 130a.
[0008] Applying the vacuum to the backside of the wafer 160 causes
the wafer 160 to bow since the edge of the wafer is sealed against
the pad at points 165. This bowing of the wafer 160 causes a
secondary vacuum force between the pad 130a and the wafer 160
thereby making it more difficult for the polishing head 180 to lift
the wafer 160.
[0009] One solution to this deficiency to improve the ease of
removing the wafer 160 from the polishing head 180 after CMP
includes moving the polishing head 180 and wafer 160 over the edge
of the polishing pad 130a to relieve the vacuum force between the
polishing pad 130a and the wafer 160. However, this can lead to
increased wafer defects and scratches as the edge of the polishing
pad 130a entraps polishing debris that can damage the wafer 160.
Further, moving the wafer 160 to the edge of the polishing pad 130a
can lead to breakage of the wafer 160 since this leads to uneven
stress distribution on the wafer 160 as a portion of the wafer is
overhanging the polishing pad 130a prior to liftoff.
[0010] Therefore, a new polishing pad and method are needed that
overcome the above-mentioned shortcomings while substantially
decreasing the chance of wafer damage.
SUMMARY
[0011] Embodiment of the invention provides a chemical mechanical
polishing pad and method of using the same to ease removal of a
wafer from the pad after completion of CMP. The pad includes a top
surface and at least one venting inlet. The top surface has a
structure that forms a vacuum between the pad and a wafer during
chemical mechanical polishing. The at least one venting inlet
releases the vacuum when the wafer is located over the venting
inlet. In one embodiment of the invention, the structure includes
perforations. In another embodiment, the structure includes
grooves.
[0012] An embodiment of the method starts with the applying of a
vacuum to a backside of the wafer. After applying the vacuum, a
polishing head retaining the wafer is moved to a periphery of the
polishing pad. The polishing pad is then rotated so that at least
one venting inlet passes underneath the wafer, thereby releasing
the vacuum between the pad and the wafer. The vacuum on the
backside of the wafer is then released and wafer removed from the
polishing head.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Non-limiting and non-exhaustive embodiments of the present
invention are described with reference to the following figures,
wherein like reference numerals refer to like parts throughout the
various views unless otherwise specified.
[0014] FIG. 1 is a diagram illustrating a conventional CMP
system;
[0015] FIG. 2 is a diagram illustrating a conventional perforated
polishing pad;
[0016] FIG. 3 is a diagram illustrating a perforated polishing pad
according to an embodiment of the invention;
[0017] FIG. 4A-FIG. 4E are diagrams illustrating cross-sections of
polishing pads according to different embodiments of the
invention;
[0018] FIG. 5 is a diagram illustrating a CMP system using the
perforated polishing pad of FIG. 3; and
[0019] FIG. 6 is a flowchart illustrating a method of CMP using the
perforated polishing pad of FIG. 3.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0020] The following description is provided to enable any person
of ordinary skill in the art to make and use the invention, and is
provided in the context of a particular application and its
requirements. Various modifications to the embodiments will be
readily apparent to those skilled in the art, and the principles
defined herein may be applied to other embodiments and applications
without departing from the spirit and scope of the invention. Thus,
the present invention is not intended to be limited to the
embodiments shown, but is to be accorded the widest scope
consistent with the principles, features and teachings disclosed
herein.
[0021] FIG. 3 is a diagram illustrating a perforated polishing pad
130b according to an embodiment of the invention. The polishing pad
130b is circular in shape with a thickness between about 50 and
about 80 mils. The polishing pad 130b can comprise a plurality of
planar layers. The diameter of the polishing pad 130b can range
from about 66 centimeters to about 81 centimeters. The polishing
pad 130b can be made of cast and sliced polyurethane (or other
polymers) with a filler or a urethane coated felt. It will be
appreciated by one of ordinary skill in the art that the polishing
pad 130b can have a thickness or diameter greater than or smaller
than the thickness and diameter ranges described above. Further,
the polishing pad 130b can also be made of other materials than
described above.
[0022] The polishing pad 130b includes a plurality of perforations
170 spread uniformly across a planar top and a planar bottom
surface of the polishing pad 130b. In an alternative embodiment,
the polishing pad 130b may include grooves in place of or in
addition to the perforations 170 in the top surface of the
polishing pad 130b. In another embodiment of the invention, the
polishing pad 130b can include any structures that tend to form a
vacuum force between the wafer 160 and the polishing pad 130b.
[0023] The polishing pad 130b also includes four angled venting
inlets 300 that are distributed along on the periphery of the
polishing pad 130b and extend inwards from the edge of the
polishing pad 130b towards the center of the polishing pad 130b.
The venting inlets 300 can be evenly or unevenly distributed along
the top surface of the polishing pad 130b.
[0024] Each venting inlet 300 includes a mouth 310 at the periphery
of the polishing pad 130b and a terminus 320 at an interior end of
the venting inlet 300 thereby forming an axial length there
between. The axial length of the venting inlets 300 should not
extend any farther than necessary to ensure venting of the vacuum
between the polishing pad 130b and the wafer 160 after CMP and so
that the venting inlets 300 do not extend underneath the wafer 160
during CMP as that could lead to an uneven wafer removal profile.
The terminus 320 can comprise any shaped ending, including an oval
ending, a flat ending, a circular ending, a spherical ending,
etc.
[0025] The venting inlets 300 can have a width of about 5 to about
10 mm with a length of about 20 mm. The width of the venting inlets
300 are preferably minimized to limit wafer 160 deflection but
large enough so that residual water or other fluids from the CMP
process do not help maintain a seal and stop the vacuum from
venting though the venting inlets 300. The venting inlets 300 can
travel through the full thickness of the polishing pad 130b or only
travel through a portion (e.g., 10 mils) of the full thickness
(e.g., 50 mils) of the polishing pad 130b. The venting inlets 300
are angled along the top surface of the polishing pad 130b at about
45 degrees from the edge of the polishing pad 130b. The venting
inlets 300 are angled so as to increase water and/or other fluid
removal from the venting inlets via centrifugal force. It will be
appreciated by one of ordinary skill in the art that the venting
inlets 300 can also be straight (i.e., perpendicular to the edge of
the polishing pad 130b) or be angled at other than 45 degrees from
the edge of the polishing pad 130b. In addition, it will be
appreciated that the polishing pad 130b can have fewer (i.e., 1) or
additional venting inlets 300. For example, in one embodiment of
the invention, the polishing pad 130b has 24 venting inlets
300.
[0026] FIG. 4A-FIG. 4E are diagrams illustrating cross-sections of
polishing pads 130b according to different embodiments of the
invention. In one embodiment shown in FIG. 4A, a polishing pad
130b.1 has at least one venting inlet 300.1 that extends inwards
from a mouth 310.1 at the periphery of the polishing pad 130b.1 to
a terminus 320.1 at an inner end of the venting inlet 300.1. The
venting inlet 300.1 is planar and parallel to a top surface and a
bottom surface of the polishing pad 130b.1. Further, the venting
inlet 300.1 only extends through a portion of the thickness of the
polishing pad 130b.1, specifically, from the top surface of the
polishing pad 130b.1 to a depth of, for example, about 20 mils in a
polishing pad having a thickness of 50 mils.
[0027] FIG. 4B illustrates a cross-section of another polishing pad
130b.2 that has at least one venting inlet 300.2 that extends
inwards from a mouth 310.2 at the periphery of the polishing pad
130b.2 to a terminus 320.2 at an inner end of the venting inlet
300.2. The venting inlet 300.2 only extends through a portion of
the thickness of the polishing pad 130b.2, specifically, from the
top surface of the polishing pad 130b.2 to a sloped surface 400
having a first depth at the terminus 320.2 and second depth, which
is greater than the first depth, at the mouth 310.2. For example,
the first depth can be about 20 mils and the second depth can be
about 30 mils. The sloped surface 400 enables increased water or
other fluid removal from the venting inlet 130b.2 due to
gravity.
[0028] FIG. 4C illustrates a cross-section of another polishing pad
130b.3 that has at least one venting inlet 300.3 that extends
inwards from a mouth 310.3 at the periphery of the polishing pad
130b.3 to a terminus 320.3 at an inner end of the venting inlet
300.3. The venting inlet 300.3 extends through the full depth of
the polishing pad 130b.3.
[0029] FIG. 4D illustrates a cross-section of another polishing pad
130b.4 that has at least one venting inlet 300.4 that tunnels
inwards and under the pad 130b.4 from a mouth 310.4 at the
periphery of the polishing pad 130b.4 to a terminus 320.4 on a top
surface of the polishing pad 130b.4 at an inner end of the venting
inlet 300.4. The venting inlet 300.4 uses a top surface of the
platen 140 as a bottom surface of the venting inlet 300.4.
[0030] FIG. 4E illustrates a cross-section of another polishing pad
130b.5 that has at least one venting inlet 300.5 that tunnels
inwards and upwards from a mouth 310.5 at the periphery of the
polishing pad 130b.5 to a terminus 320.5 on a top surface of the
polishing pad 130b.5 at an inner end of the venting inlet 300.5.
The sloped surface of the venting inlet 300.5 increases the rate of
water or other fluid removal from the pad 130b.5 due to gravity.
Alternatively, the venting inlet 300.5 can include a flat
surface.
[0031] FIG. 5 is a diagram illustrating a CMP system 100b capable
of using the perforated polishing pad 130b (i.e., any of 130b.1 to
130b.5). The polishing pad 130b rests on a platen 140 on a turn
table 150. The polishing head 180 includes a carrier 120 and a
retaining ring 110 that retains a wafer 160 during CMP and can
include other components not shown. After CMP is complete, a vacuum
force is applied to a backside of the wafer 160 and the polishing
head 180 moves the wafer 160 towards the periphery of the polishing
pad 130b so that the wafer 160 overhangs a venting inlet 130 (but
does not overhang the periphery of the polishing pad 130b).
[0032] The venting inlet 300 enables the venting of air between the
polishing pad 130b and the wafer 160, thereby releasing any vacuum
forces between the polishing pad 130b and the wafer 160.
Accordingly, the polishing head 180 can then pick up the wafer 160
without the risk of damage to the wafer 160 that is associated with
conventional polishing pads.
[0033] In an embodiment in which the polishing pad 130b has only a
single venting inlet 300, the polishing head 180 must move the
wafer 160 to the periphery of the polishing pad 130b having the
venting inlet 300. Alternatively, the polishing pad 130b can be
rotated so that the venting inlet 300 passes beneath the wafer 160.
However, in an embodiment in which the polishing pad 130b has a
plurality of venting inlets 300, the polishing head 180 need only
move the wafer 160 to the periphery of the polishing pad 130b to
ensure that the wafer 160 overlaps one or more venting inlets 300.
Accordingly, there is no need to move the wafer to a specific
section of the periphery of polishing pad 130b or to rotate the
polishing pad 130b.
[0034] FIG. 6 is a flowchart illustrating a method 600 of CMP using
the perforated polishing pad 130b. First, chemical mechanical
polishing is completed (610) using the polishing pad 130b. Next, a
vacuum is applied (620) to the backside of the wafer 160. The
polishing head 180 and wafer 160 are then moved (630) to the
periphery of the polishing pad 130b. In another embodiment of the
invention, the moving (630) can take place before the applying
(620).
[0035] If necessary, the polishing pad 130b is then rotated (640)
so that at least one venting inlet 300 passes underneath the wafer
160 so as to release any vacuum formed between the wafer 160 and
the polishing pad 130b. If the polishing pad 130b has a plurality
of venting inlets 300, then rotation (640) may not be needed since
moving (630) the head 180 and wafer 160 to the periphery of the
polishing pad 130b is sufficient for passing the wafer 160 over a
venting inlet 300.
[0036] After rotating (640) or moving (630), the polishing head 180
and wafer 160 are lifted (650) from the polishing pad 130b. As the
vacuum between the wafer 160 and the polishing pad 130b has been
released, the polishing head 180 and wafer 160 are relatively
easily lifted from the polishing pad 130b, thereby limiting the
stress on the wafer 160. The polishing head 180 is then moved (660)
to a wafer unload position and a vacuum is released (670) from the
backside of the wafer 160. The wafer 160 is then removed (680) from
the polishing head 180. The method 600 then ends.
[0037] The foregoing description of the illustrated embodiments of
the present invention is by way of example only, and other
variations and modifications of the above-described embodiments and
methods are possible in light of the foregoing teaching. For
example, the venting inlets 300 can be perpendicular or angled with
respect to the edge of the polishing pad 130b. The embodiments
described herein are not intended to be exhaustive or limiting. The
present invention is limited only by the following claims.
* * * * *