U.S. patent application number 14/626256 was filed with the patent office on 2017-07-20 for method and systems to control optical transmissivity of a polish pad material.
The applicant listed for this patent is Thomas West, Inc.. Invention is credited to Pepito Galvez, Suli Holani, Peter McKeever, Gary Quigley, Thomas West.
Application Number | 20170203411 14/626256 |
Document ID | / |
Family ID | 53797297 |
Filed Date | 2017-07-20 |
United States Patent
Application |
20170203411 |
Kind Code |
A9 |
West; Thomas ; et
al. |
July 20, 2017 |
Method and Systems to Control Optical Transmissivity of a Polish
Pad Material
Abstract
A method and systems for controlling optical transmissivity of a
polish pad material are provided. The method and systems may
include adjusting control parameters to determine the optical
transmissivity of a polish pad material. The control parameters may
also include pre-processing controls, casting controls, and/or
curing controls. Methods and systems also provided for assembling a
polish pad that controls the optical transmissivity of the polish
pad. Additionally, a polish pad with a controlled optical
transmissivity is provided.
Inventors: |
West; Thomas; (Portola
Valley, CA) ; Quigley; Gary; (Loomis, CA) ;
Galvez; Pepito; (San Jose, CA) ; McKeever; Peter;
(Redwood City, CA) ; Holani; Suli; (Sunnyvale,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thomas West, Inc. |
Sunnyvale |
CA |
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20150231766 A1 |
August 20, 2015 |
|
|
Family ID: |
53797297 |
Appl. No.: |
14/626256 |
Filed: |
February 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13854856 |
Apr 1, 2013 |
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14626256 |
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61942457 |
Feb 20, 2014 |
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61619328 |
Apr 2, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 37/22 20130101;
B24D 13/14 20130101; B24B 37/205 20130101; B24D 11/001 20130101;
B24B 37/24 20130101 |
International
Class: |
B24D 13/14 20060101
B24D013/14; B24D 11/00 20060101 B24D011/00 |
Claims
1. A method for controlling an optical transmissivity of a polish
pad material, comprising: adjusting control parameters to determine
an optical transmissivity of the polish pad material; wherein the
control parameters comprise at least one of pre-processing
controls, casting controls, and curing controls.
2. The method of claim 1, further comprising selecting chemical
ingredients for forming the polish pad material.
3. The method of claim 2, wherein: the selecting is based in part
on at least one of a ratio of hard to soft segments of the chemical
ingredients; and a mass of the chemical ingredients.
4. The method of claim 2, wherein the chemical ingredients include
at least one of a cross-linker, a chain extender, and a
plasticizer.
5. The method of claim 2, wherein the selecting of the chemical
ingredients is a function of polymer structure, the polymer
structure being at least one of isocyanate type, isomer structure,
and polyol type.
6. The method of claim 2, further comprising mixing the chemical
ingredients to result in an even dispersion within a mixture of the
chemical ingredients.
7. The method of claim 6, wherein the control parameters comprise
the pre-processing controls; and the pre-processing controls
including at least one of controlling a first temperature of the
chemical ingredients individually before the mixing and controlling
a second temperature of the chemical ingredients during the
mixing.
8. The method of claim 7, wherein the controlling of the at least
one of the first temperature and the second temperature includes
controlling a rate of temperature change.
9. The method of claim 2, further comprising adding a material with
a lower density than the chemical ingredients to the chemical
ingredients.
10. The method of claim 9, wherein the material with a lower
density includes microspheres.
11. The method of claim 1, wherein the control parameters comprise
the casting controls; and the casting controls including at least
one of a temperature and a pressure of the polish pad material
during a casting operation.
12. The method of claim 11, wherein the casting controls include
the temperature; and the temperature includes controlling a rate of
temperature change.
13. The method of claim 1, wherein the casting controls include
centrifugal force from rotating the polish pad material in a
cylinder, a thickness variation of the polish pad material being a
function of centrifugal force from the rotating the polish pad
material in the cylinder.
14. The method of claim 1, wherein the control parameters comprise
the curing controls; and the curing controls include at least one
of a time, a temperature, and a pressure of the polish pad material
during curing.
15. The method of claim 14, wherein the temperature includes a rate
of temperature change.
16. A method for assembling a polish pad that controls an optical
transmissivity of the polish pad, comprising: arranging a first
polymer precursor for a sub-pad in at least one mold in a
centrifugal caster; rotating the centrifugal caster to form the
sub-pad; arranging a second polymer precursor for a top-pad in the
mold on top of the sub-pad; and adjusting control parameters of at
least one of the first polymer precursor, the rotating the
centrifugal caster, and the second polymer precursor.
17. The method of claim 16, further comprising forming at least one
window in the sub-pad to facilitate optical transmission of light
through the top-pad using at least one of a mold, laser machining,
and mechanical machining.
18. A polish pad with a controlled optical transmissivity,
comprising: a top-pad layer comprising a polymer layer, the polymer
layer being substantially homogeneous and having a low total
thickness variation, being absent of voids, and being substantially
transmissive to visible light; and a sub-pad layer comprising
materials of different densities and at least one window.
19. The polish pad of claim 18, wherein at least one of the
materials of different densities includes microspheres.
20. The polish pad of claim 18, wherein the at least one window
contains a second polymer, a transmissivity of the second polymer
being greater than a transmissivity of the sub-pad.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This U.S. patent application claims the benefit of U.S.
Provisional Patent Application No. 61/942,457 filed on Feb. 20,
2014. This U.S. patent application is related to U.S. patent
application Ser. No. 13/854,856 filed on Apr. 1, 2013, and U.S.
Provisional Patent Application No. 61/619,328, filed on Apr. 2,
2012, which are incorporated by reference herein in their entirety
for all purposes.
FIELD OF THE INVENTION
[0002] The present disclosure relates generally to polishing pads.
More specifically, the present disclosure relates to methods for
controlling the optical transmissivity of a polish pad
material.
SUMMARY
[0003] A method and systems for controlling an optical
transmissivity of a polish pad material may include adjusting
control parameters to determine an optical transmissivity of the
polish pad material and may further include pre-processing
controls, casting controls, and/or curing controls. The method may
also include selecting chemical ingredients for forming the polish
pad material that may be based in part on a ratio of hard to soft
segments of the chemical ingredients and/or a mass of the chemical
ingredients. The chemical ingredients may include a cross-linker, a
chain extender, and/or a plasticizer. Selecting chemical
ingredients may be a function of polymer structure that may be
isocyanate type, isomer structure, and/or polyol type.
[0004] In various exemplary embodiments, the method includes mixing
the chemical ingredients to result in an even dispersion within a
mixture of the chemical ingredients. The control parameters may
include pre-processing controls that may include at least one of
controlling a first temperature of the chemical ingredients
individually before mixing and controlling a second temperature of
the chemical ingredients during mixing. The controlling of the
first temperature and/or the second temperature may include
controlling a rate of temperature change.
[0005] The selecting chemical ingredients for forming the polish
pad material may include adding a material with a lower density
than the chemical ingredients to the chemical ingredients. The
material with a lower density may be microspheres.
[0006] In various exemplary embodiments, the control parameters
include the casting controls that include a temperature and/or a
pressure of the polish pad material during a casting operation. The
casting temperature controls may include controlling a rate of
temperature change. The casting controls may also include
centrifugal force from rotating the polish pad material in a
cylinder, a thickness variation of the polish pad material may be a
function of centrifugal force from rotating the polish pad material
in a cylinder.
[0007] The control parameters may additionally include curing
controls and the curing controls may include time, temperature,
and/or pressure of the polish pad material during curing. The
temperature control of the curing controls may include a rate of
temperature change.
[0008] The methods and systems of the present technology include a
method for assembling a polish pad that controls the optical
transmissivity of the polish pad. The method may include arranging
a first polymer precursor for a sub-pad in a mold in a centrifugal
caster, rotating the centrifugal caster to form the sub-pad,
arranging a second polymer precursor for a top-pad in the mold on
top of the sub-pad, and adjusting control parameters of the first
polymer precursor, the rotating of the centrifugal caster, and/or
the second polymer precursor. The method may further include
forming a window in the sub-pad to facilitate optical transmission
of light through the top-pad using a mold, laser machining, and/or
mechanical machining.
[0009] Embodiments of the present technology include a polish pad
with a controlled optical transmissivity including a top-pad layer
with a polymer layer being substantially homogeneous and having a
low total thickness variation, being absent of voids, and being
substantially transmissive to visible light. The polish pad may
also include a sub-pad layer with materials of different densities
and may include a window. The materials of different densities may
include microspheres and the window may contain a second polymer
with the transmissivity of the second polymer being greater than a
transmissivity of the sub-pad.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic diagram illustrating a casting system,
according to an example embodiment.
[0011] FIG. 2 is a schematic diagram illustrating a cross-section
of an example polymer pad, according to an example embodiment.
[0012] FIG. 3 is a schematic diagram illustrating a cross-section
of the example drum and showing an example mold insert and window,
according to an example embodiment.
[0013] FIG. 4 is a flow chart illustrating an example method for
making a multilayer polishing pad, according to an example
embodiment.
DETAILED DESCRIPTION
[0014] Polishing (also referred to as planarizing) is a process
step which is commonly used in the manufacture of semiconductor,
hard disk drive and optical products. The polishing process used
for the manufacture of semiconductor devices generally consists of
rubbing a substrate against a polymer pad, or vice versa. A
chemical solution, usually containing fine particles (the slurry),
is present at the interface between the substrate and the polymer
pad.
[0015] Polishing may also be referred to as Chemical Mechanical
Planarization (CMP). Polymer polish pads used for CMP may use
closed cell polyurethane materials, while some polish pads used for
CMP employ open cell polyurethane materials. Additionally, fiber
impregnated with polymer (e.g. felt materials), or polymers
combined with abrasives may be utilized. The surface of such pads
may contain a micro texture. The micro texture may complement the
conditioning process and ultimately the polish performance of the
pad. Inconsistencies in this inherent micro structure may lead to
deviations in the polish performance of the pad. For this reason,
pad manufacturers have worked to refine pad manufacturing processes
to reduce such variation in their products. In contrast, a solid
homogenous polymer polish pad contains no inherent micro structure,
and instead it typically relies on the conditioning process to
impart a micro texture to the pad surface. Polish pads may have one
or more layers. For cases where the polish pad has more than one
layer, the polishing surface is called the top-pad and the other
layer(s) are referred to as the sub-pad or sub-pad stack. A polish
pad including at least a single polish layer, which does not
contain open or closed cell structures, or cell structures that are
dissolved with polish slurry, is often referred to as a solid
pad.
[0016] Polish endpoint detection for a CMP process has evolved from
a "look and see" model to an in situ system that avoids
interruption of the polishing/planarizing process. The two dominant
endpoint detection systems are 1) optical endpoint detection, and
2) motor current/torque endpoint detection. To enable the use of an
optical endpoint detection system on a polisher tool, the polish
pad to be used with such a system must contain a region through
which light can be transmitted. This region on the pad needs to
align with the location of the endpoint detection system on the
polishing tool. Typically, this region on the pad through which
light is transmitted is called a window. A variety of methods are
used to impart a window into the polishing pad. They include
creating an aperture on the top and inserting a transparent
material. Another method used is to polymerize a transparent
material in the cut out window area of the top-pad. In all cases, a
corresponding aperture needs to be created in the sub-pad layers.
In many cases, a transparent plug material will be inserted into
the aperture created in the sub-pad layers to provide support to
the window in the top-pad material.
[0017] Light as used herein is not limited to visible wavelengths,
and may have a wavelength anywhere between 190 nm to 3500 nm.
Transparent as used herein includes translucent, and in particular
includes any non-zero transmissivity for a particular
wavelength.
[0018] With the development of solid polish pads, transmission of
light through the pad is possible and effective for endpoint
detection. Light reflection, absorption, and scattering in
non-solid pads reduce signal intensity below usable levels for
endpoint detection. Optical transmissivity is a preferred exemplary
embodiment, and references herein to transmissivity include, but
are not limited to, optical transmissivity. According to the
present technology, the transmissivity of a polish pad may be
controlled, and therefore may be tuned to particular requirements.
By adjusting the input process parameters of the casting and
polymerization system, the optical transmission of the resulting
polish pad material may be controlled. Representative, but not
exclusive parameters that may be adjusted include selecting
chemical ingredients for the polymer mixture. Further, the control
parameters of the casting and polymerization system may be
adjusted, including temperature and pressure, and, in the case of a
centrifugal caster, the speed of rotation.
[0019] Light transmission through polymers is affected by the
degree of crystallinity of the polymer. Amorphous polymers are
characterized by a random, disordered tangle of polymer chains.
Crystalline polymers have a higher degree of order resulting from
alignment of chains within folded or stacked chain regions. While
there are some polymers that are completely amorphous, most
polymers have at least some crystalline regions.
[0020] The crystalline regions within a polymer have a different
refractive index than the amorphous regions, leading to refraction
and scattering of light passing through the polymer. For this
reason, amorphous polymers are frequently transparent, while
crystalline polymers are translucent or opaque.
[0021] Some polymers tend to be amorphous (e.g. polycarbonate,
poly(methyl methacrylate), polystyrene) and some tend to be
crystalline (e.g. nylon, polypropylene). However, most polymers can
take on different degrees of crystallinity depending on the polymer
structure (e.g. chain length, degree of cross-linking, presence of
side groups, etc.). An example of this is polyethylene, where more
amorphous versions (e.g. Low-Density Polyethylene (LDPE), Linear
Low-Density Polyethylene (LLDPE)) are transparent, while more
crystalline versions (e.g. High-Density Polyethylene (HDPE)) are
translucent.
[0022] Embodiments of the present technology use processing
conditions to vary the degree of crystallinity. For example, slow
cooling of molten thermoplastics gives more time for crystalline
structures to form, while a rapid quench freezes in the amorphous
orientations present in the melt. Mechanical processes, such as
extrusion or blow molding, apply directional forces and tend to
orient the polymer chains and increase crystallinity.
[0023] Exemplary embodiments of the present technology use these
behaviors to control transparency of the polymers used for
polishing pad materials. The vast majority of pads are inherently
unsuitable for use as a window material due to the scattering and
absorption caused by the pores or other fillers used to control the
mechanical properties of the pad. In these cases, an alternate
window material that is optimized for transmission, but does not
confer good polishing characteristics, is added separately to the
pad.
[0024] Various embodiments of the present technology use the
chemical structure of polyurethane. Configurations present in
polyurethane elastomers used for polishing pads show two distinct
regions are present within the polymer chains: the hard, rigid
segment formed by the reacted isocyanate (e.g. urethane) and chain
extension groups, and, the soft, flexible segment formed by the
polyols (e.g. polyethers, polyesters). The hard segment tends to
form ordered, crystalline regions due to strong hydrogen bonds
between urethane groups, while the soft segments remain
amorphous.
[0025] Embodiments of the present technology use the ratio of hard
to soft segments present in the polyurethane to control the degree
of structure within a polymer and to influence transparency. This
ratio also affects many other properties including the mechanical
behavior of the polymer, so changes are carefully considered
against the overall requirements of the polymer for the polishing
pad. Beyond a simple modification of the hard/soft segment ratio,
other modifications to the polymer structure including the
isocyanate type (e.g. MDI, TDI, etc.) isomer structure (e.g.
2,4-Toluene diisocyanate vs. 2,6-Toluene diisocyanate), polyol type
(e.g. polyether, polyester), and selection of cross-linkers and
chain extenders are used in various embodiments to influence the
degree of transparency of the cast polyurethane.
[0026] In various embodiments of the present technology, the
processing conditions influence transparency. In the case of
polyurethane, the temperature at which the components are reacted
has a very strong effect on the transparency, since the process
temperature influences both the tendency of the chains to orient,
and the time available for oriented structures to form by
influencing the kinetics of the reaction. Control of the polymer
precursor and mold/caster temperatures to within about
.+-.1.degree. C. is used with the present technology to maintain
consistent results for some polymer types and transmissivity
levels.
[0027] Embodiments of the present technology use the family of
thermoset plastics. For a given polymer composition, altering
control parameters like temperature, centrifugal force and cure
conditions (e.g. time, temperature, pressure, etc.) results in
changes to transmission characteristics of the CMP pad material
made using the thermoset plastic. The capability to control
transmission and the sensitivity to the parameters, control
transmission depends on the chemistry of the thermoset plastics
used. For example, a .+-.1.degree. C. change in temperature may
cause transmissivity to change from 30% to 45%. Using a different
chemistry polymer and/or polymer precursor may increase or decrease
this sensitivity.
[0028] Exemplary embodiments use the thickness of material which is
molded (i.e. polymerized) to control the transmissivity of a CMP
pad. For exothermic processes, when polymerization starts, the
energy increases in the mixture, and therefore the temperature
increases. Typically, the thicker the material, the lower the
transmissivity, though it is possible for the opposite to be true.
As the material that is used for a CMP pad is thinned, the
transmission will typically increase, within limits. If the
material that is molded has a high transmission level, then the
transmission level may decrease slightly, remain unchanged, or will
only increase slightly when the material is thinned. For example, a
material with 100% transmission (i.e. transparent) cannot be
increased to more than 100%. Controlling the Total Thickness
Variation (TTV) may be important in the context of controlling an
optical transmission property of a polish pad material, since the
thickness of the material may correlate with transmissivity.
Therefore, to control the optical transmission, for example, to a
specific percentage between 0% and 100% may require that the
variation in thickness be very low. Low TTV may be obtained using
centrifugal casting methods discussed in U.S. patent application
Ser. No. 13/854,856 filed Apr. 1, 2013, entitled "Methods and
Systems for Centrifugal Casting of Polymer Polish Pads and
Polishing Pads Made by the Methods", and a low TTV helps control
optical transmission properties.
[0029] In various exemplary embodiments, the preparation of the raw
materials for manufacturing a polymer polish pad require
significant control to ensure that consistent raw material ratios
are input into the mixture. For example, the raw materials may need
to be heated separately before mixing. In addition, the raw
materials may preferably be mixed thoroughly to result in even
dispersion within the mixture.
[0030] In some embodiments, a solid homogenous polymer polish pad
or polish pad layer may be produced, for example, by centrifugal
casting. Production of a solid homogenous polymer sheet by
centrifugal casting enables the manufacture of a polish pad that is
free of voids. The temperature and speed (in Rotations Per Minute
(RPM)) of a centrifugal caster used to make a polish pad or polish
pad layer may be altered depending on the desired pad or pad layer
characteristics, including transmissivity. In addition or
separately, the type of polymer precursor being used may also be
varied to modify the transmissivity.
[0031] In various exemplary embodiments of the present technology,
a centrifugal casting system and method allows the formation of a
thin sheet of solid homogenous polymer with low total thickness
variation. A thin sheet of polymer (for example, polyurethane) can
be easily converted to a solid polymer polish pad or pad layer
which is absent of voids or pores. The presence of voids or pores
typically impacts transmissivity.
[0032] In exemplary embodiments, heating during centrifugal casting
is performed by heating elements that surround or are adjacent to
the casting drum. Such heating elements heat the drum and/or the
air in the drum. Typically, the drum is pre-heated prior to
introduction of the polymer precursor. Additional steps may be
added to the casting operation to improve product properties and/or
to modify or tune transmissivity of the resulting CMP pad.
[0033] FIG. 1 is a schematic diagram illustrating spin casting
system 100 including centrifugal caster 102 and polymer container
104. Polymer container 104 contains polymer mixture 106. Polymer
container 104 may include a mixing apparatus and include jackets,
which may be a heated element having conduits for heated fluid to
flow through, and/or electrical heating elements. Polymer mixture
106 may be a polymer mixture that will phase separate into multiple
layers under centrifugal force. Polymer mixture 106 may be one
polyurethane mixture with microspheres (or a similar less dense
material) added to change the density of the mixture.
[0034] Polymer mixture 106 may be poured from polymer container 104
into pouring spout 108 that directs polymer mixture 106 into drum
110 of centrifugal caster 102 while drum 110 is spinning around
axis 112 in rotational direction 114. Polymer mixture 106 may
spread out to form polymer sheet 116 on an interior surface of drum
110 due to centrifugal force. In the case of drum 110, polymer
sheet 116 may be cylindrical in shape. Drum 110 may spin, and may
have a diameter such that at whatever rotational velocity drum 110
turns, the centrifugal force experienced by polymer mixture 106
after introduction into drum 110 is sufficient to create a uniform
thickness of polymer sheet 116, and to additionally cause phase
separation. Phase separation may occur under centrifugal force and
may cause polymer mixture 106 to separate into a pure polymer layer
and a polymer layer infused with microspheres.
[0035] Drum 110 may be heated. Drum 110 may have a smooth interior
drum face, or alternatively may have a textured drum face that
improves the performance of adhesives used in the polishing pad,
that provides grooves to a surface of a polish pad made according
to the method, and/or that facilitates the separation and/or
forming of a polish pad from a cured and casted polymer sheet
formed by the method.
[0036] By adjusting the process parameters associated with the
operation above, including the type and ratios of the polymer
precursors, heating (of precursors, polymer mixtures, drum casters,
and/or polymerization or casting conditions), and/or drum
rotational speed (in the case of a centrifugal caster), the
transmissivity of the polish pad created during the process may be
adjusted and controlled. The transmissivity may vary depending on
the wavelength of the light, and therefore the transmissivity may
be adjusted as a function of wavelength. Higher transmissivity may
help endpoint detection performance for certain polish
applications.
[0037] FIG. 2 is a schematic diagram illustrating a cross-section
of polymer pad 200 including dense polymer layer 204 (also referred
to as hard pad 204) and porous polymer layer 202 (also referred to
as sub-pad 202). Polymer pad 200 may be cut out or punched out of
polymer sheet 116. The removed polymer pad 200 includes sub-pad 202
and hard pad 204. Hard pad 204 is formed from dense polymer layer
204 while sub-pad 202 is formed from porous polymer layer 202. Both
hard pad 204 and sub-pad 202 may be used for polishing. Although
the solid side (hard pad 204) is conventionally used for polishing,
the porous side (sub-pad 202, though for this use it would not be a
sub-pad) may be used. Sub-pad 202 may have pores that are packed
extremely tight, allowing for higher compressibility. The closed
cell nature of the pores will prevent CMP process liquids from
wicking through the sub-pad. Light 210 may be projected at sub-pad
202 and may pass through polymer pad 200 as transmitted light 212.
Light 212 may represent an attenuated version of light 210 due to
transmission loss caused by reflection, absorption, and/or
diffraction in one or both of sub-pad 202 and hard pad 204. Light
212 may reflect off of a wafer and may be detected directly, may be
reflected and detected, and/or may be transmitted up through hard
pad 204 and sub-pad 202. The reflection of light 212 may be used to
determine the endpoint of a CMP process.
[0038] Additionally, sub-pad 202 may have one or more windows,
which may be formed during the pad polymerization or casting
process via molds (see below), or by machining or punching holes in
the sub-pad after forming. The holes may be filled with transparent
plugs, or may be left as voids. The transmissivity of polymer pad
200, with or without windows or voids in sub-pad 202, may be
anywhere from 0% to 100% in any particular wavelength, and may
typically be 30% to 40%. By adjusting any of the parameters
discussed herein, the transmissivity may also be adjusted. The
present technology may be used to obtain a high degree of control
over the optical transmission properties of a polish pad
material.
[0039] FIG. 3 is a schematic diagram illustrating drum 110 with
mold insert 300 lining the interior wall of drum 110 of a
centrifugal caster. Mold insert 300 may be any thermally stable and
chemically compatible material such as, but not limited to, a
polymer, metal or ceramic sheet lining the interior of the drum
110. The mold insert may be made from materials such as, but not
limited to, Teflon, HDPE, Thermoplastic or PTFE. The use of a
release agent with the mold insert may help ease the removal of the
cast polymer. Mold insert 300 may have at least one mold of a
polishing pad, with the number of molds depending on the size of
drum 110 and the size of the polishing pad. The mold of mold insert
300 may be a single mold or a plurality of molds, which may be
fixed or removable and which may have a fixed or a variable
distance from an axis to vary an amount of centrifugal force
experienced by the polymer during the casting process. The mold or
molds of mold insert 300 may form an outline of a CMP pad, and may
have a textured surface in regard to drum 110. For example, mold
insert 300 may have four molds on the sheet that lines drum 110,
thus potentially producing four polishing pads in one casting. In
this embodiment, a polymer mixture may be poured into each mold
individually, which will eliminate the need to cut or punch out the
polishing pad from a polymer sheet. Alternatively, mold insert 300
may cause polymer mixture to flow into the shape of the CMP pad and
prevent or avoid material flowing into the interstitial areas,
thereby preventing waste. Through these exemplary methods, waste
can be reduced. Window molds 310 may be one or more window molds
formed in mold insert 300 to form one or more windows in a CMP pad.
Window molds 310 may be positioned in any advantageous manner.
Additionally, the window panels themselves may be made using the
present technology to modify the transmissivity of the window, and
to thereby modify the transmissivity of the CMP pad having the
window.
[0040] In an exemplary process, a sub-pad may be formed by casting
using mold insert 300 and window molds 310, with the prepolymer
used to form the sub-pad filling mold insert 300 up to the level of
a top of window molds 310. After completing the casting of the
sub-pad, a subsequent pour of the same or different prepolymer into
mold insert 300 covering the sub-pad and covering window molds 310
may form a top-pad. The top-pad may be tuned to have a particular
transmissivity, and after curing, may bond to the sub-pad without
the use of a pressure sensitive adhesive (PSA) and without further
manipulation. The CMP pad made by this method may have a window
slot in the sub-pad and a translucent or transparent top-pad, and
therefore may have a complete window without the need to align the
sub-pad and the top-pad during production.
[0041] In a further exemplary process, window molds 310 may be
eliminated, and the process reduced to a single pour operation,
when transparent or translucent microspheres are used in the
prepolymer cursor. In this manner, phase separation may occur
during centrifugal casting of the CMP pad, and the microspheres may
migrate to a top layer of the CMP pad to form a sub-pad. The
prepolymer itself and the casting conditions may be adjusted as
discussed herein to create a translucent or transparent CMP pad,
and the translucent or transparent microspheres may enable the
sub-pad also to be translucent. Some loss of transmissivity is
likely due to the refraction and/or diffraction of light off and/or
through the microspheres.
[0042] In still further exemplary embodiments, the present
technology may enable a production process that eliminates the need
to align a window in a sub-pad with a window in a top-pad, thereby
streamlining the production of a CMP pad. Conventionally, windows
through a top-pad have been used in an optical endpoint detection
system, and may include a transparent panel or plug material that
is bonded to the sides of a cut-out of the top-pad. The sub-pad may
also have a cut-out which may or may not include a transparent
plug. A pressure-sensitive adhesive (PSA) layer may be interposed
between the top-pad and the sub-pad to attach the two pads. By
making the top-pad substantially transparent (also referred to
herein as translucent or transmissive), a sub-pad may be made with
a window or windows, or alternatively also substantially
transparent or translucent. Bonding such a sub-pad to a transparent
top-pad would not require alignment of two windows, and therefore
may be considered self-aligning. For example, in the case of the
sub-pad having window(s), the windows may be formed by punching the
sub-pad after application of a PSA layer, thereby causing the
punching to form window(s) in the PSA layer aligned with the
window(s) of the sub-pad automatically.
[0043] FIG. 4 is a process flow diagram showing a method 400
according to the present technology using polyurethane. However,
the method is also applicable to other polymers, as discussed
herein. As shown in FIG. 4, the method 400 may commence at
operation 402, which indicates to select the chemical ingredients.
From operation 402, the flow proceeds to operation 404, which
indicates to adjust the control parameters, including temperature,
pressure, casting material thickness and mass. From operation 404,
the flow proceeds to operation 406, which indicates to optionally
form at least one aperture or multiple apertures in a sub-pad to
facilitate the optical transmission of light through a top-pad
material using molds, laser machining, or mechanical machining. The
process flow ends after operation 406.
[0044] A polymer casting system may involve mixing a prepolymer
(also referred to as a precursor) with a chain extender and a
plasticizer. A chain extender, such as MOCA, may be added to the
prepolymer at a molar ratio of around 1:1 with the unreacted
isocyanate. For example, a mixing ratio of 0.95:1 for the MOCA to
unreacted isocyanate may be used. The prepolymer may be TDI or MDI
system. Alternatively, diisocyanates or other polyisocyanates may
be reacted with a polyol of choice. In another embodiment, a harder
polyurethane mixture may be dispensed into the cylinder and cured
before dispensing a softer polyurethane mixture into the cylinder.
All of the process conditions, including the type and amount of
polymer, and type and amount of microspheres, may be modified to
adjust the transmissivity of the CMP pad.
[0045] While this technology is susceptible of embodiment in many
different forms, there is shown in the drawings and will herein be
described in detail several specific embodiments with the
understanding that the present disclosure is to be considered as an
exemplification of the principles of the technology and is not
intended to limit the technology to the embodiments
illustrated.
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