U.S. patent application number 11/860643 was filed with the patent office on 2008-01-17 for low friction planarizing/polishing pads and use thereof.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Maria Ronay.
Application Number | 20080014841 11/860643 |
Document ID | / |
Family ID | 34194332 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080014841 |
Kind Code |
A1 |
Ronay; Maria |
January 17, 2008 |
LOW FRICTION PLANARIZING/POLISHING PADS AND USE THEREOF
Abstract
A polishing pad comprising a polymeric matrix and solid
lubricant particles is useful for planarizing surfaces, and
preventing delamination and scratches.
Inventors: |
Ronay; Maria; (San
Francisco, CA) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W.
SUITE 1100
WASHINGTON
DC
20036
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
34194332 |
Appl. No.: |
11/860643 |
Filed: |
September 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10645493 |
Aug 22, 2003 |
|
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11860643 |
Sep 25, 2007 |
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Current U.S.
Class: |
451/41 |
Current CPC
Class: |
B24D 3/32 20130101; B24B
37/24 20130101; B24D 3/346 20130101 |
Class at
Publication: |
451/041 |
International
Class: |
B24B 1/00 20060101
B24B001/00 |
Claims
1-36. (canceled)
37. A method for planarizing a surface which is formed on a
substrate which comprises providing on the surface to be planarized
a liquid polish slurry composition comprising abrasive particles;
and contacting said surface with a polishing pad that consists of a
polymeric matrix and solid lubricant particles in an amount
sufficient to reduce friction between the pad and surface during
planarizing and optionally at least one auxiliary agent selected
from the group consisting of surfactant, dispersant, stabilizing
agent and polymeric microsphere.
38. The method of claim 1, wherein the solid lubricant particles
comprise fluoropolymers selected from the group consisting of
poly(tetrafluorethylene ((PTFE), fluoroethylene-propylene
copolymers (FEP), perfluoroalkoxy resins (PFA)
ethylene-chlorotrifluoroethylene alternating copolymer (ECTFE),
poly(vinylidene fluoride) PVDE and mixtures thereof.
39. The method of claim 1, wherein the lubricant particles have a
coefficient of friction of 0.03 to about 0.3.
40. The method of claim 1, wherein the solid lubricant particles
have a spherical shape, a cylindrical shape, or a platelet shape,
and optionally contain cut fibers.
41. The method of claim 1, wherein the size of the solid lubricant
particles is about 0.05 to about 18 microns.
42. The method of claim 1, wherein the size of the solid lubricant
particles is about 0.05 to about 0.5 microns.
43. The method of claim 6, wherein the organic fluoropolymers have
a weight average molecular weight of about 1.times.10.sup.5 to
about 5.times.10.sup.5.
44. The method of claim 1, wherein the amount of solid lubricant
particles is about 0.5 to about 30% by weight.
45. The method of claim 1 wherein the amount of solid lubricant
particles is about 0.5 to about 10% by weight.
46. The method of claim 1, wherein the amount of the solid
lubricant particles is about 2 to 3% by weight.
47. The method of claim 1, wherein the solid lubricant particles
are pretreated with a surfactant in an amount sufficient to
disperse the lubricant particles in a planarizing slurry upon being
detached from the pad during planarizing.
48. The method of claim 1, wherein the polymeric matrix comprises
at least one member selected from the group consisting of
polyurethane, polycarbonate, polyamide, polysulfone, polyvinyl
chloride, polyacrylate, polymethacrylate, polyvinylalcohol,
polyester and polyacrylamide.
49. The method of claim 1, wherein the polymeric matrix is
microporous.
50. The method of claim 1, wherein the polymeric matrix is
non-porous.
51. The method of claim 1, wherein the pad surface contains
macroscopic channels before use and microscopic texture during use
to facilitate slurry transport.
52. The method of claim 1, wherein said lubricant particles
comprises at least one member selected from the group consisting of
a binding agent, coupling agent or adhesive promoter.
53. A method according to claim 1, wherein the surface to be
polished is selected from the group consisting of Al, Al alloys,
Cu, Cu alloys, Ag, Ag-alloys, Au, Au alloys, W, W alloys, silicon
oxide, polysilicon, silicon nitride, Ta, Ta alloys, Ti, Ti alloys,
low-k dielectric and combinations thereof.
54. A method according to claim 1, wherein the surface to be
polished contains at least one low-k dielectric selected from the
group consisting low-k porous dielectric, low-k non-porous
dielectric and air bridges and combinations thereof.
55. A method according to claim 18 wherein said low-k dielectric
comprises at least one member selected from the group consisting of
CVD carbon-doped silicon oxide, spin on organo silicate and spin on
organic polymer.
56. A method according to claim 1, wherein said planarizing is
chemical-mechanical polishing (CMP).
Description
TECHNICAL FIELD
[0001] The present invention relates to pads and use thereof. The
pads are especially useful for planarizing and polishing surfaces
in the microelectronics industry. More particularly the present
invention relates to increasing the topological selectivity of
planarizing/polishing pads by providing pads containing a polymeric
matrix and solid lubricant particles. An added advantage of the
pads of the present invention is that the reduced friction between
the pads and surface being planarized/polished e.g.-wafer reduces
delamination (peeling) due to planarization/polishing, which is
particularly important in planarizing conductor lines embedded in
low-k (i.e. low dielectric constant) insulators or porous low-k
insulators or planarizing the insulators themselves. Furthermore,
such pads reduce defects such as scratches.
BACKGROUND OF THE INVENTION
[0002] In microelectronics planarization metal or insulator layers
are deposited conformally into etched trenches of a substrate after
which a need exists to planarize the surface with chemical
mechanical planarization (CMP). With device dimensions becoming
smaller and smaller involving not only narrower conductor and
insulator lines but also thinner and thinner layers both in
front-end, and back-end of the line applications, post CMP
specifications for permissible deviation from perfect planarity are
becoming tighter. The deviation from perfect planarity, referred to
as a step, is detrimental due to depth-of-focus issues in
subsequent lithography steps. Also, this deviation in the case of
oxide polish can lead to field threshold problems in isolation
regions, while in the case of metal planarization can cause shorts
in the next metal level. For devices manufactured in the near
future it is important to achieve a post-planarization step-height
of less than 100 Angstroms on a 100 microns.times.100 microns test
site.
[0003] For example, a shallow trench isolation (STI) structure is
shown in FIG. 1a before planarization. In order to achieve perfect
planarization, a CMP process is required which has a high degree of
topological selectivity meaning that it removes material from the
"up" areas of the wafer, but it does not remove material from the
"down" areas of the wafer until the level of the up area reaches
the level of the down area as shown in FIG. 1b. If material is
removed from the down area before it becomes level with the up
area, "dishing" results i.e. a post CMP step will remain as shown
in FIG. 1b'.
[0004] It is well known that when the pad and wafer are separated
by the slurry layer known as hydrodynamic polishing, shown in FIG.
2a, removal rates are small. Significant polish rates result only
when the planarizing pad is in contact with the wafer. Most
importantly significant removal rates in the down area take place
only when the down area is in contact with the pad as shown in FIG.
2b.
[0005] The present inventor has determined the mechanism believed
responsible for the polishing pad extending into the down area of
the wafer. In particular, the inventor of this application
discovered that the most commonly used prior art polishing pad, the
IC1000 pad, which is a foam polyurethane from Rodel Corporation
develops normal stresses in the direction perpendicular to the
plane of the pad when submitted to a surface torque. The normal
stress is a linear function of the square of the torque. This
normal stress creates an extension of the pad into the down areas
of the wafer, and consequently promotes dishing.
[0006] While the pad exhibits this phenomenon when tested in the
dry condition, when a slurry is applied, the torque, which
represents friction, increases and so, does the normal force and
the pad extension into the down areas of the water.
[0007] The present inventor's U.S. patent Ser. No. 10/295/836,
filed Nov. 18, 2002 and entitled "Polishing Compositions and Use
Thereof" discloses, inter alia, planarizing slurries with reduced
friction by adding organic solid lubricant particles such as
poly(tetrafluoroethylene) (PTFE) to the slurry containing the
abrasive. The disclosure of U.S. Ser. No. 10/295,836 is
incorporated herein by reference.
[0008] The solid lubricant additive reduced the torque i.e.
friction between pad and wafer and eliminated the normal force,
thus the extension of the pad into the down areas of the wafer,
consequently it reduced dishing and provided for improved
planarization.
[0009] Nevertheless, room for improvement exists. For instance,
some dishing can still occur probably due to the hydrodynamic
component of the planarizing process and that component was
increased from adding the PTFE dispersion, the preferred solid
lubricant, to the abrasive slurry, most likely from the additives
used to disperse the PTFE particles. This can be counteracted by
increasing the overfill of the material to be planarized (overfill
is film thickness minus etched step-height as illustrated in FIG.
1), but this is not an advantage. Another obstacle of using solid
lubricant particles in the slurry is that due to the chemical
inertness of PTFE, it is not easy to create a hydrophilic
dispersion to be used with water-base abrasive slurries.
Consequently only a very limited number of vendors commercially
offer such dispersions.
[0010] Also, as discussed above, reducing friction between pad and
wafer is important in addition to improved planarization in
reducing surface damage created during planarization, such as
peeling and scratches, particularly in planarizing conductors over
low-k dielectric insulators or the low-k dielectric insulators
themselves. The current approach is to use very low down force to
reduce friction which results in non-economical removal rates.
SUMMARY OF THE INVENTION
[0011] The present invention provides for improving the topological
selectivity of the polymeric planarizing/polishing pads by
providing pads comprising a polymeric matrix and solid lubricant
particles. This is achievable by the present invention without a
need to alter the polymer matrix, the manufacturing process or
surface micro or macro texture of prior art polishing pads.
[0012] More particularly, an aspect of the present invention
relates to a pad comprising a polymeric matrix and solid lubricant
particles. The solid lubricant particles are typically present in
amounts of about 0.5% to about 30% weight of the pad.
[0013] Another aspect of the present invention relates to a method
for polishing a surface by providing on the surface a liquid slurry
composition comprising abrasive particles; and contacting the
surface with a polishing pad comprising a polymeric matrix and
solid lubricant particles.
[0014] Other objects and advantages of the present invention will
become readily apparent by those skilled in the art from the
following detailed description, wherein it is shown and described
preferred embodiments of the invention, simply by way of
illustration of the best mode contemplated of carrying out the
invention. As will be realized the invention is capable of other
and different embodiments, and its several details are capable of
modifications in various obvious respects, without departing from
the invention. Accordingly, the description is to be regarded as
illustrative in nature and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1a illustrates a shallow trench isolation (STI)
structure before planarization.
[0016] FIG. 1b illustrates the structure after planarization with
high topological selectivity i.e. material is removed from the "up"
area but not from the "down" area until it becomes level with the
up area leading to perfect planarization.
[0017] FIG. 1b.sup.1 illustrates "dishing" which results in case of
low topological selectivity, when material is removed from the down
area before it becomes level with the up area.
[0018] FIG. 2 shows a patterned surface having up and down areas
during planarization when a. the pad does not touch the wafer
referred to as hydrodynamic polishing (FIG. 2a) and [0019] b. when
it does touch the wafer including the bottom surface of the down
area. (FIG. 2b). Wafers are upside down during planarization.
[0020] FIG. 3 illustrates the cross-section of a
planarizing/polishing pad according to the present invention
showing uniformly distributed solid lubricant particles in a porous
pad.
[0021] FIG. 4 illustrates the cross-section of a
planarizing/polishing pad according to the present invention
showing uniformly distributed solid lubricant particles in a
non-porous pad with micro and macro channels on the surface.
BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION
[0022] According to the present invention a planarizing/polishing
pad that contains solid lubricant particles is provided. The solid
lubricant particles enhance the topological selectivity of the
planarizing pad. In addition, by reducing the friction between pad
and wafer the occurrence of thin film delamination and scratching
is reduced. Examples of suitable solid lubricants are organic
fluoropolymers such as poly(tetrafluoroethylene) (PTFE);
fluoroethylene-propylene copolymers (FEP), perfluoroalkoxy resins
(PFA), ethylene-chlorotrifluoroethylene alternating copolymer
(ECTFE) and polyvinylidene fluoride (PVDF). Mixtures of solid
lubricant particles can be employed, if desired.
[0023] The most preferred lubricants are virgin
polytetrafluoroethylene particles. Polytetrafluoroethylene is
preferred because of its very low coefficient of friction
(0.03-0.1) and its chemical inertness. The lubricant particles
typically have a coefficient of friction of about 0.3 or below and
more typically about 0.03 to about 0.3, and even more typically
about 0.03 to about 0.1.
[0024] The lubricant particles may have a spherical shape, or
cylindrical shape or may contain cut fibers or platelets, the most
preferred shape being a spherical shape. The size of the lubricant
particles is typically from about 0.05 to about 18 microns, more
typically about 0.05 to about 0.5 micron. A typical average
particle size is 0.2 micron.
[0025] The organic fluoropolymers typically have a weight average
molecular weight about 1.times.10.sup.5 to about 5.times.10.sup.5,
and more typically about 2.times.10.sup.5 to about
3.times.10.sup.5.
[0026] The solid lubricant particles may be treated with a
surfactant so that if they become detached from the pad in the
course of planarization, they may become dispersed in the
planarizing slurry. The surfactant, when present, is typically
anionic or nonionic. Specific examples of surfactants can be
determined by those of ordinary skill in the art once aware of this
disclosure and need not be discussed to any further extent in this
application.
[0027] If it is desired that the solid lubricant particles are
bonded to the pad material, adhesion to fluoropolymers can be
enhanced by electrochemical treatment as disclosed by U.S. Pat. No.
5,800,858 to Bickford et al. or chemical etch such as
TetraEtch.RTM. (W. L. Gore and Associates). Such treatment may be
followed by the application of a coupling agent, or a coupling
agent maybe used without adhesion promotion. Suitable coupling
agents include bifunctional coupling agents such as compounds
containing a silyl group with either an amine or epoxy group or
both and further a fluorinated hydrocarbon group. An example of a
silylating coupling agent is
N-methyl-N-trimethylsilyltrifluoroacetamide,
(CH.sub.3).sub.3SiN(CH.sub.3)COCF.sub.3.
[0028] The pads in which the solid lubricant particles can be
employed include any of the various types of polishing pad
typically made available for the microelectronics industry and
typically comprise a polymeric matrix. Examples of suitable matrix
materials are polyurethanes including polyester and polyether
urethanes, polycarbonates, polyamide, polysulfone, polyvinyl
chloride, polyacrylates, polymethyacrylates, polyvinylalcohol,
polyester, polyacrylamide, polyaramides, epoxies and derivatives of
epoxies, and combinations of these polymers. The polymeric matrix
can be solid or porous. Examples of pads that can be modified with
the solid lubricant particles according to the present invention
are those disclosed in U.S. Pat. No. 4,927,432 to Budinger et al.,
U.S. Pat. No. 5,900,164 to Budinger et al. and U.S. Pat. No.
5,489,233 to Cook et al; U.S. patent application Ser. No.
09/715,184 to Chen et al. and U.S. patent application Ser. No.
09/668,142, to Chen et al., disclosures of which are incorporated
herein by reference.
[0029] The amount of solid lubricant particles is typically about
0.5% by weight to about 30% by weight, more typically about 0.5% to
about 10% by weight and even more typically about 2 to about 3% by
weight, based upon the total weight of the pad.
[0030] Polishing pads may be made of a uniform material such as
polyurethane or nonwoven fibers impregnated with a synthetic resin
binder, or may be formed from multilayer laminations having
non-uniform physical properties throughout the thickness of the
pad.
[0031] A typical laminated pad may have a plurality of layers, such
as a spongy and resilient microporous polyurethane layer laminated
onto a firm but resilient supporting layer comprising a porous
polyester felt with a polyurethane binder. Polishing pads typically
may have a thickness in the range of 50-80 mils, preferably about
55 mils, and a diameter in the range of 10 to 36 inches, typically
22.5 inches to polish 200 mm diameter wafers and 29.15 inches to
polish 300 mm wafers. Alternatively, the polishing pads may have
belt type geometry.
[0032] To facilitate, slurry transport, polishing pads also may
have macrotextured work surfaces made by surface machining using
various techniques. Polishing pads typically may also have
microtextured surfaces created by conditioning the pads between
wafers.
[0033] The pads are typically formed by adding solid lubricant
particles to the polymer such as a polyurethane along with
auxiliary agents such as surfactants, dispersants, stabilizing
agents and polymeric microspheres.
[0034] The composition is placed in a mold and cured to form the
pad material. If desired, it can then be sliced or dice cut into
the desired size and shape and finally buffed.
[0035] The reagents that form the polyurethane or the resin binder
also may be reacted within a cylindrical container. After forming,
a cylindrically shaped piece of pad material is cut into slices
that are subsequently used as the polishing pad.
[0036] The present pads offer a versatility of properties and
performance required to give a high degree of planarization and
global uniformity to a variety of polished substrates. The pads of
the present invention can be used for polishing aluminum and
aluminum alloys such as Al--Si and Al--Cu, Cu, Cu alloys, Ag,
Ag-alloys, Au, Au alloys, W, W alloys, a variety of adhesion and
diffusion barriers such as Ti, Ti alloys, TiN, Ta, Ta alloys, TaN,
Cr and the like, silicon oxide, polysilicon, silicon nitride, as
well as other metals and alloys, and glasses of various
compositions.
[0037] The present pads are particularly important to polish metal
conductors, liners and diffusion barriers when in conjunction with
low-k (dielectric constant ) insulators representing delicate
structures including air bridges, or planarizing these insulators
themselves. Some low-k materials are CVD carbon-doped silicon
oxide, such as Black Diamond.TM., Coral.TM., SiCOH, their porous
versions such as Black Diamond II and Black Diamond III; porous and
non-porous spin-on organo silicates JSR 5109, 5117 and the like,
and other varieties, such as Shipley Zircon.TM., Nanoglass; porous
and non-porous organic spin-on polymers such as SILK.TM. and porous
SILK.TM.. A low friction pad is imperative for polishing such
future structures.
[0038] The polishing slurries employed can be any suitable CMP
slurries. The slurries typically contain abrasive particles such as
alumina, ceria, silica, titania, zirconia, polymer particles,
organic/inorganic composite particles or combinations thereof. The
abrasives typically have a particle size of about 30 to about 1000
nanometers and preferably about 75 to about 300 nanometers.
[0039] The amount of abrasive particles is typically about 0.1 to
about 20 percent by weight and more typically about 0.3 to about 2
percent of weight.
[0040] The slurry can include other ingredients in addition to the
abrasive, solid lubricant particles and surfactants such as
oxidizing agents, preservatives, anticorrosion agents and the
like.
[0041] Suitable polishing slurries that contain solid lubricant
particles are disclosed in U.S. patent application Ser. No.
10/295,836 to Ronay, disclosure of which is incorporated herein by
reference.
[0042] An advantage of the present invention as compared to
including solid lubricant particles in the slurry is that the
friction of the process can be smaller than with slurries because
larger amounts of solid lubricant particles can be incorporated
into the pad material then into the slurry without reducing the
removal rate to non-economical values.
[0043] An embodiment of a pad, suitable for the semiconductor
industry, is a substantially cylindrical pad having general
dimensions such that it might be used in a polishing apparatus, for
example in the equipment described in the IBM Technical Disclosure
Bulletin, Vol. 15, No. 6, November 1972, pages 1760-1761, the
entire contents of which are incorporated herein by reference.
[0044] The parameters of the polishing or planarizing can be
determined by those skilled in the art, once aware of this
disclosure, without exercising undue experimentation. For instance,
the speed of rotation of the polishing pads and also of the wafer
is about 10 to about 150 rpm and pressure about 2 to 10 psi. A
wafer may be in the range of 100 to 300 mm in diameter.
[0045] The following non-limiting Examples are presented to further
illustrate the present invention.
EXAMPLE 1
[0046] A porous polyurethane pad is provided according to the
method in U.S. Pat. No. 5,900,164 by mixing liquid urethane with a
polyfunctional amine at a proper temperature in the ratio required
by the desired amount of cross-linking. During the "low viscosity
window" hollow elastic polymeric microspheres are blended with the
polymers mixture and 2% by weight of PTFE solid lubricant particles
of 0.2 micron average diameter available under the trade name of
Pinnacle 9003 by Carroll Scientific Inc., are blended applying a
high shear rate mixer. The solid lubricant particles can be added
to the liquid urethane or the liquid urethane-polyfunctional amine
mixture, or the liquid urethane-polyfunctional amine-microspheres
mixture.
[0047] The mixture is transferred during the low viscosity window
to a convention mold and permitted to gel. It is subsequently cured
in an oven, cooled and cut to form polishing pads. FIG. 3 shows the
cross-section of a planarizing pad according to the present
invention showing uniformly distributed solid lubricant particles
in the porous pad. The surface of the pad may be supplied with a
micro-texture or a macro-texture as described in the above
referenced patent in order to facilitate slurry transport during
planarization.
[0048] In FIG. 3, numeral 10 represents the polymer matrix, numeral
12, solid lubricant particles, numeral 14, micropores and numeral
16, the surface of the pad.
EXAMPLE 2
[0049] In producing a non-porous pad the process of Example 1 is
followed except that the hollow microspheres are not added. Thus a
liquid urethane is mixed with a polyfunctional amine at a proper
temperature in a ratio required by the desired amount of
cross-linking. During the "low viscosity window" 3% by weight of
PTFE solid lubricant particles of 0.2 micron average diameter with
the trade name of Pinnacle 9003 by Carroll Scientific Inc. are
blended into the liquid polymer mix applying a high shear rate
mixer. The lubricant particles can be added into the liquid
urethane, or into the liquid urethane-polyfunctional amine
mixture.
[0050] The mixture is transferred during the low viscosity window
to a conventional mold and permitted to gel. It is subsequently
cured in an oven, cooled and cut to form a polishing pad. Since
this pad does not transport slurry well a surface texture providing
macroscopic channels for slurry transport is mechanically produced
on the surface of the pad before use as given in U.S. Pat. No.
5,489,233, which should be consulted for specifics. In addition a
microtexture, produced on the surface of the pad by abrasion at
regular intervals during the use of the pad is also claimed in the
above patent. FIG. 4 shows a non-porous pad with microscopic (20)
and macroscopic (18) flow channels containing solid lubricant
particles (12) according to the present invention. Numeral 10
represents the polymer matrix and numeral 16 the surface of the
pad.
[0051] The foregoing description of the invention illustrates and
describes only the preferred embodiments of the present invention.
However, as mentioned above, it is to be understood that the
invention is capable of being made and used in various other
combinations, modifications, and environments, and is capable of
being changed or modified within the scope of the inventive concept
as expressed herein, commensurate with the above teachings and/or
the skill or knowledge of persons skilled in the relevant art. The
embodiments described hereinabove are further intended to explain
the best modes known of practicing the invention and to enable
others skilled in the art to utilize the invention in such, or
other, embodiments and with the various modifications required by
the particular applications or uses of the invention. Accordingly,
the description is not intended to limit the invention to the form
disclosed herein. Also, it is intended that the appended claims be
construed to include alternative embodiments.
[0052] All publications and patent applications cited in this
specification are herein incorporated by reference as if each
individual publication or patent application were specifically and
individually indicated to be incorporated by reference.
* * * * *