U.S. patent application number 11/684523 was filed with the patent office on 2007-09-13 for composite polishing pad.
This patent application is currently assigned to RIMPAD TECH LTD.. Invention is credited to Spencer Preston.
Application Number | 20070212979 11/684523 |
Document ID | / |
Family ID | 38255040 |
Filed Date | 2007-09-13 |
United States Patent
Application |
20070212979 |
Kind Code |
A1 |
Preston; Spencer |
September 13, 2007 |
COMPOSITE POLISHING PAD
Abstract
A polishing pad having an optically clear bottom layer and a
closed cell top layer where the interface between the top and
bottom layers is only a urethane to urethane interface. Grooves may
be machined into the top layer or through the top layer and into
the bottom layer.
Inventors: |
Preston; Spencer; (Manteca,
CA) |
Correspondence
Address: |
SNELL & WILMER L.L.P. (Main)
400 EAST VAN BUREN
ONE ARIZONA CENTER
PHOENIX
AZ
85004-2202
US
|
Assignee: |
RIMPAD TECH LTD.
PO Box 296
Austin
TX
78767
|
Family ID: |
38255040 |
Appl. No.: |
11/684523 |
Filed: |
March 9, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60780773 |
Mar 9, 2006 |
|
|
|
Current U.S.
Class: |
451/6 ;
451/526 |
Current CPC
Class: |
B24B 37/24 20130101;
B24B 37/26 20130101; B24D 11/001 20130101; B24B 37/205
20130101 |
Class at
Publication: |
451/006 ;
451/526 |
International
Class: |
B24D 11/00 20060101
B24D011/00 |
Claims
1. A polishing pad comprising: an optically clear bottom layer; a
closed cell polyurethane top layer; and a plurality of grooves
contained in the top layer.
2. The polishing pad of claim 1 wherein the plurality of grooves
traverse the top layer and are present in at least a portion of the
bottom layer.
3. The polishing pad of claim 1 wherein the optically clear bottom
layer comprises a polyurethane.
4. The polishing pad of claim 1 wherein the top layer has a Shore D
hardness that is greater than the bottom layer.
5. The polishing pad of claim 1 wherein the top layer has a Shore D
hardness of 60.
6. The polishing pad of claim 1 wherein the bottom layer has a
Shore D hardness within a range of 20 to 50.
7. The polishing pad of claim 1 wherein an interface between the
top and bottom layers comprises a urethane to urethane bond.
8. A method for making a polishing pad comprising the steps of:
providing a solid urethane piece having a cavity contained therein
wherein said solid urethane piece comprises a first Shore D
hardness; pouring a liquid urethane formulation into the cavity of
the solid urethane piece wherein the liquid urethane formulation
comprises a hardness formulation having a second Shore D hardness;
allowing the liquid urethane formulation to solidify and cure;
machining the solid urethane piece to a desired thickness; and
machining the solidified liquid urethane formulation to a desired
thickness.
9. The method of claim 8 further comprising the step of machining
grooves into at least one of the solid urethane piece and the
solidified liquid urethane formulation.
10. The method of claim 9 wherein the step of machining grooves
comprises the step of machining grooves into both the solid
urethane piece and the solidified liquid urethane formulation.
11. The method of claim 8 wherein values of the first Shore D
hardness and the second Shore D hardness are distinct from one
another.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to provisional patent
application having Ser. No. 60/780,773, filed Mar. 9, 2006, which
is herein incorporated in its entirety.
FIELD OF INVENTION
[0002] This invention generally relates to polishing pads and
methods for making the same. More particularly, this invention
relates to a composite chemical mechanical polishing (CMP) pad
having a bottom optically clear layer and a closed cell
polyurethane top layer wherein the interface between the two layers
comprises only a urethane to urethane bond.
BACKGROUND OF THE INVENTION
[0003] It is important to obtain specific performance criteria for
the rate of removal of material, the flatness of the polished
object, and other such factors in the field of polishing. These
factors can be greatly impacted by the type of material used to
polish an object. In the semiconductor industry, polishing pads are
often used to polish raw wafers and for performing chemical
mechanical planarization.
[0004] Many polishing methods and polishing materials have been
used for abrading and/or polishing the surface of various materials
and objects. Many materials use grooves contained in their surfaces
and several methods include applying slurry to the grooved
surfaces. However, the goals of planarization uniformity and
consistency during polishing remain high. Accordingly, there is
always a need for improved polishing pads that increase
planarization uniformity and consistency during polishing.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a composite polishing
pad that includes an optically clear bottom layer and a closed cell
polyurethane top layer where the interface between the top and
bottom layers comprises only a urethane to urethane bond. Grooves
may be machined into one or more of the top and bottom layers of
the composite pad.
[0006] The invention is also directed to a method for making a
polishing pad which includes the steps of providing a solid
urethane piece having a cavity contained within it where the solid
urethane piece has a first Shore D hardness, pouring a liquid
urethane formulation into the cavity of the solid urethane piece
where the liquid urethane formulation has a hardness formulation
having a second Shore D hardness, allowing the liquid urethane
formulation to solidify and cure, machining the solid urethane
piece to a desired thickness, and machining the solidified liquid
urethane formulation to a desired thickness. The method may also
include the step of machining grooves into the solid urethane piece
and/or the solidified liquid urethane formulation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] A more complete understanding of the present invention may
be derived by referring to the detailed description and the claims
when considered in connection with the Figures, wherein like
reference numbers refer to similar elements throughout the Figures,
and:
[0008] FIG. 1 is a cross sectional view of the polishing pad of the
present invention;
[0009] FIG. 2 is a top plan view of the polishing pad of the
present invention having grooves with a wafer shown on the surface
of the pad;
[0010] FIG. 3 shows a top plan view of the polishing pad of the
present invention positioned on a clear polishing table using
tape;
[0011] FIG. 4 is a graph showing high edge removal rate; and
[0012] FIG. 5 is a graph showing low edge removal rate.
DETAILED DESCRIPTION
[0013] While the exemplary embodiments herein are described in
sufficient detail to enable those skilled in the art to practice
the invention, it should be understood that other embodiments may
be realized and that logical and mechanical changes may be made
without departing from the spirit and scope of the invention. Thus,
the following detailed description is presented for purposes of
illustration only and not of limitation.
[0014] There are two innovative attributes disclosed in this
invention.
[0015] The first being a CMP pad with 360 degree polishing table
rotation optical accessibility to the wafer surface being polished.
This is accomplished without interrupting the polishing
surface.
[0016] The pad has a top surface which includes a series of
concentric grooves dimensioned to facility the CMP Polishing
process.
[0017] Cross section of the present invention showing the grooves.
The black is the polishing surface consisting of closed cell
polyurethane. The white is optically clear polyurethane.
[0018] The polishing surface (black) is a harder urethane (shrore D
60) than the bottom urethane (Shore D 20-50). The combination of
the two materials make up the top surface of the CMP polishing
pad.
[0019] This type for groove configuration is designed to allow the
normal polishing surface the ability to have independent loading in
the radial direction while maintaining the long range planarization
characteristics in the radial direction.
[0020] This invention is designed to be used with a rotational CMP
polishing tool which has a clear polishing table. The current
invention of the Polishing pad when used with a clear polishing
table is capable of providing 360 degrees of accessibility to the
polishing surface of a wafer while it is being polished.
[0021] FIG. 2 shows a top view of the polishing pad with grooves
with a wafer on the surface. During the polishing the polishing pad
is rotated while the wafer remains stationary rotating on its own
axis.
[0022] The black rings represent the top of the polishing surface
the white rings represent the bottom of the grooves as shown in the
cross section of FIG. 1.
[0023] It can be clearly seen that if the polishing pad is fixed to
a clear polishing table that light can be passed through the table
and through the pad to reflect off the wafer without interrupting
the normal polishing surface. Access to the wafer is 100% of the
time and 360 degrees of table rotation.
[0024] Please note that in FIG. 1 the interface between the closed
cell urethane and the clear urethane is urethane to urethane bonds.
These bonds are formed by pouring a reacted urethane formulation
into a cavity formed in the back side of a solid urethane part of a
different hardness formulation. There is no mold release present to
inhibit the liquid urethane from bonding with the surface it
touches. The liquid urethane is allowed to solidify and completely
cure. The composite material is then machined flat and to the
desired thickness of the clear urethane. The composite is then
thinned to provide the desired thickness of the closed cell
urethane. The grooves are then machined to the desired depth. A
depth which is be greater then the thickness of the closed cell
urethane polishing surface.
[0025] Please note that the top surface of the lower urethane never
sees anything other than the lower surface to the solid urethane in
its solid state.
[0026] Please note there is no means of adhering the dissimilar
materials together other than the natural urethane to urethane
bonds which become permanent. There is no tape involved at the
interface.
[0027] Please note that in one embodiment where the first attribute
is not needed (the light transmissive attribute) the grooves may
not need to penetrate completely through the closed cell urethane
thickness.
[0028] With the Composite pad having groove depths greater than the
closed cell thickness the bottom of the grooves is a clear
elastomeric urethane material capable of transmitting a light beam
through the composite pad without interrupting the normal polishing
surface. The light is then capable of reflecting off the surface of
the wafer being polished and reflected back through the groove to
the clear urethane.
[0029] There are three methods to fix the composite pad to the
clear polishing table:
[0030] The first is to use a double side tape such as 442KW a 3M
product. This tape adheres to the side away from the grooved
surface with one side of the tape and the other side of the tape
adheres to the clear polishing table. The draw back from using the
442KW is that this product is not completely clear and can
interfere with the light beam in both directions. Because of this a
clear double side tape should be used.
[0031] The second method of adhering the composite pad to the clear
polishing table resolves the light transmission problem by
providing the 442KW only to the outer and inner regions of the
polishing pad. Areas where the wafer is not present. The back side
of the composite pad can be machined to provide for a flat surface
with the tape installed.
[0032] With this lamination the light is capable of passing through
the clear table directly to the clear urethane and reflecting off
the wafer to the sensor located below the table.
[0033] A third method of lamination is to install fastening devices
on the back side of the composite pad. These could be snaps, screws
clamps etc that line up with mating fasteners located on the clear
polishing table. With this method the pad is helps secure and is
fixed to the clear polishing table. It is also possible in this
method to apply a light transmission fluid between the composite
pad and the clear table to enhance the light transmission by
eliminating one of the refracting surfaces at the interface.
[0034] Once the pad is fixed to the table the wafer is positioned
to polish the polishing machine dispenses polishing slurry to the
pad. The grooves fill with slurry. This creates irregular light
transmission making it difficult to analyze the reflected light
from the wafer. The composite pad of the present invention
minimizes the effect of the slurry in the grooves by monitoring the
light signal 100% of the polishing time or 360 degrees of table
rotation. With this type of observation it is possible to filter
out the noise from the slurry in the grooves.
[0035] The second attribute of the current invention is to provide
a polishing surface with a hard enough surface to provide a
reference for planarization while also absorbing any out of
perfectly flat topographies that exist in the system. This
configuration of hard polishing surface with a shock absorbing bulk
material is also advantageous in controlling the polishing rate at
the very edge of the wafer.
[0036] Please note the high edge removal rate on the top wafer
profile versus the low edge removal rate on the lower profile.
These wafers were measured at 4 mm edge exclusion. The high edge
removal rate profile was produced without the use of a shock
absorbing composite.
[0037] The low edge removal rate wafer profile was produced with a
shock absorbing composite prototype material.
[0038] Please not the low edge removal rate prototype was repeated
with these 4 wafer profiles.
[0039] Additional attributes. This invention is of benefit on each
attribute alone. That is to say the table does not need to be clear
to take advantage of the independent pressure loading in the
Composite Pad. The lower urethane does not have to be clear to take
advantage of only the independent radial loading. Not all of the
grooves need to penetrate through the closed cell urethane to
provide the edge removal rate control and with in wafer uniformity
benefits disclosed in this invention.
[0040] A composite pad capable of 360 degrees of endpoint detection
monitoring.
[0041] This allows for EPD with slurry in the grooves because the
analysis is continuous and can filter out the slurry noise more
accurately than the current EPD window technology.
[0042] Using a light source mounted below a clear polishing
table.
[0043] This improvement enables #1.
[0044] A composite pad with independent polishing surface pressure
loading in the radial table direction while maintaining the long
range planarization characteristics of a planarizing pad in the
radial direction.
[0045] With in wafer non uniformity can be improved because the
pressure loading is independent in the radial direction. The long
range planarization characteristics do not change. The current
invention composite pad will improve the shorten distance from the
edge of the wafer that a steady state removal rate can be
achieved.
[0046] Elimination of a tape layer to fabricate a composite
pad.
[0047] With no tape layer holding the pad surfaces together the pad
has an elastic behavior. This allows for more consistent response
to loading variations.
[0048] Pad mounting fasteners in the table and mating mounting
fasteners on the pad.
[0049] The fastener idea is an improvement over taping the pad to
the table for ease of removal and enables improved light
transmitting characteristics. It is also possible to provide a
vacuum table for the polishing table and securing the pad to the
table via vacuum. The pad in the case of vacuum can be included in
combination with other fastening devises other than tape.
[0050] The invention has huge improvements to the performance of
the pad for CMP . . . one can control the hardness of the lower
half of the composite pad to control non-uniformity, however there
is no "gluing" the pad together, so the interaction of glue/Mylar
(part of the glue layer)/pad/CMP slurry or water is eliminated. It
allows us to put grooves much deeper into the top layer than on
pads that are first made and then glued together. Also, by
producing this bottom layer of the composite pad in a "clear"
version, one can put grooves deep enough in the top layer to allow
optical transmission (useful for end point lasers in the CMP tool
platen) without causing a disruption of the polishing surface . . .
making the performance uninterrupted by a pad window.
[0051] In the foregoing specification, the invention has been
described with reference to specific embodiments. However, it may
be appreciated that various modifications and changes may be made
without departing from the scope of the invention. The
specification and figures are to be regarded in an illustrative
manner, rather than a restrictive one, and all such modifications
are intended to be included within the scope of invention.
Accordingly, the scope of the invention should be determined by the
appended claims and their legal equivalents, rather than by the
examples given above. For example, the steps recited in any of the
method or process claims may be executed in any order and are not
limited to the order presented.
[0052] Benefits, other advantages, and solutions to problems have
been described above with regard to specific embodiments. However,
the benefits, advantages, solutions to problems, and any element(s)
that may cause any benefit, advantage, or solution to occur or
become more pronounced are not to be construed as critical,
required, or essential features or elements of any or all the
claims. As used herein, the terms "comprises", "comprising", or any
other variation thereof, are intended to cover a non-exclusive
inclusion, such that a process, method, article, or apparatus that
comprises a list of elements does not include only those elements
but may include other elements not expressly listed or inherent to
such process, method, article, or apparatus. Further, no element
described herein is required for the practice of the invention
unless expressly described as "essential" or "critical".
* * * * *