U.S. patent application number 10/218872 was filed with the patent office on 2003-04-24 for method of altering and preserving the surface properties of a polishing pad and specific applications therefor.
This patent application is currently assigned to Exigent, Inc.. Invention is credited to Obeng, Yaw S., Yokley, Edward M..
Application Number | 20030077436 10/218872 |
Document ID | / |
Family ID | 27500347 |
Filed Date | 2003-04-24 |
United States Patent
Application |
20030077436 |
Kind Code |
A1 |
Obeng, Yaw S. ; et
al. |
April 24, 2003 |
Method of altering and preserving the surface properties of a
polishing pad and specific applications therefor
Abstract
The present invention is directed, in general, to an improved
material and method of planarizing a surface on a semiconductor
wafer and, more specifically, to a method of altering the
properties of polymers, preferably thermoplastic foam polymers,
used in polishing applications. The chemical and mechanical
properties thermoplastic foam substrates can be transformed by
inorganic, inorganic-organic, and or organic-organic grafting
techniques, such that the polymer foam is endowed with new set of
properties that more desirable and suitable for polishing.
Inventors: |
Obeng, Yaw S.; (Orlando,
FL) ; Yokley, Edward M.; (Pembroke Pines,
FL) |
Correspondence
Address: |
HITT GAINES & BOISBRUN P.C.
P.O. BOX 832570
RICHARDSON
TX
75083
US
|
Assignee: |
Exigent, Inc.
Winter Park
FL
|
Family ID: |
27500347 |
Appl. No.: |
10/218872 |
Filed: |
August 14, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10218872 |
Aug 14, 2002 |
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09994407 |
Nov 27, 2001 |
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60250299 |
Nov 29, 2000 |
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60295315 |
Jun 1, 2001 |
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60304375 |
Jul 10, 2001 |
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Current U.S.
Class: |
428/304.4 |
Current CPC
Class: |
B24B 49/003 20130101;
Y10T 428/249952 20150401; B24B 37/013 20130101; Y10T 428/249991
20150401; B24B 37/24 20130101; B24D 3/26 20130101; B24D 18/009
20130101; Y10T 428/31786 20150401; Y10T 428/31507 20150401; Y10T
428/31743 20150401; B29K 2105/04 20130101; Y10T 428/249987
20150401; B29C 44/56 20130101; Y10T 428/249953 20150401; B29C 59/14
20130101; Y10T 428/31725 20150401; Y10T 428/31551 20150401; B24B
49/16 20130101; B24D 18/0063 20130101; B24B 37/042 20130101; Y10T
428/24999 20150401; Y10T 428/31765 20150401 |
Class at
Publication: |
428/304.4 |
International
Class: |
B32B 003/26 |
Claims
What is claimed is:
1. A polymer comprising: a thermoplastic foam substrate having a
modified surface thereon; and a grafted surface on said modified
surface.
2. The polymer as recited in claim 1 wherein said thermoplastic
foam substrate is selected from the group consisting of:
polyurethane; polyolefin; and polyvinyl esters.
3. The polymer as recited in claim 1 wherein said thermoplastic
foam substrate is selected from the group consisting of: polyurea;
polycarbonate; aliphatic polyketone; polysulfone; aromatic
polyketone; 6,6 nylon; 6,12 nylon; and polyamide.
4. The polymer as recited in claim 1 wherein said thermoplastic
foam substrate is selected from the group consisting of:
thermoplastic rubber; and melt-processible rubber.
5. The polymer as recited in claim 1 wherein said thermoplastic
foam substrate is selected from the group consisting of:
polypropylene; polyethylene; crosslinked polyethylene; ethylene
vinyl acetate; and polyvinylacetate.
6. The polymer as recited in claim 1 wherein said modified surface
is modified by a primary plasma reactant selected from a group of
inert gas plasmas consisting of: Helium; Neon; and Argon.
7. The polymer as recited in claim 1 wherein said grafted surface
includes an inorganic metal oxide surface.
8. The polymer as recited in claim 7 wherein said inorganic metal
oxide surface is created by exposure to a secondary plasma reactant
selected from a group of reactive agents consisting of: titanium
esters; tantalum alkoxides; manganese acetate; manganese alkoxide;
manganese acetate; manganese acetylacetonate aluminum alkoxides;
alkoxy aluminates; zirconium alkoxides; alkoxy zirconates;
magnesium acetate; and magnesium acetylacetonate.
9. The polymer as recited in claim 7 wherein said inorganic metal
oxide surface is created by exposure to a secondary plasma reactant
selected from a group of reactive agents consisting of: titanium
esters plus water; titanium esters plus alcohols; titanium esters
plus ozone; alkoxy silanes plus ozone; and alkoxy silanes plus
ammonia.
10. The polymer as recited in claim 1 wherein said grafted surface
includes a controlled wetability surface.
11. The polymer as recited in claim 10 wherein said controlled
wetability surface is created by exposure to a secondary plasma
reactant selected from a group of reactive agents consisting of:
water; aliphatic alcohols; and aliphatic polyalcohols.
12. The polymer as recited in claim 10 wherein said controlled
wetability surface is created by exposure to a secondary plasma
reactant selected from a group of reactive agents consisting of:
hydrogen peroxide; ammonia; and oxides of nitrogen.
13. The polymer as recited in claim 10 wherein said controlled
wetability surface is created by exposure to a secondary plasma
reactant selected from a group of reactive agents consisting of:
hydroxylamine solution; and sulfur hexafluoride.
14. The polymer as recited in claim 1 wherein said grafted surface
on said thermoplastic foam substrate includes an organic grafted
surface.
15. The polymer as recited in claim 14 wherein said organic grafted
surface is created by exposure to a secondary plasma reactant
selected from a group of reactive agents consisting of: allyl
alcohols; allyl amines; allyl alkylamines, where the alkyl groups
contain 1-8 carbon atoms; allyl ethers; secondary amines, where the
alkyl groups contain 1-8 carbon atoms; alkyl hydrazines, where the
alkyl groups contain 1-8 carbon atoms; acrylic acid; methacrylic
acid; acrylic acid esters containing 1-8 carbon; methacrylic esters
containing 1-8 carbon; vinyl pyridine; vinyl esters.
16. A method for preparing a polymer comprising the steps of:
providing a thermoplastic foam substrate; exposing said substrate
to an initial plasma reactant to produce a modified surface
thereon; and exposing said modified surface to a secondary plasma
reactant to create a grafted surface on said modified surface.
17. The method for preparing the polymer as recited in claim 16
wherein said substrate is selected from the group consisting of:
polyurethane; polyolefin; and polyvinyl esters.
18. The method for preparing the polymer as recited in claim 16
wherein said substrate is selected from the group consisting of:
polyurea; polycarbonate; aliphatic polyketone; polysulfone;
aromatic polyketone; 6,6 nylon; 6,12 nylon; and polyamide.
19. The method for preparing the polymer as recited in claim 16
wherein said substrate is selected from the group consisting of:
thermoplastic rubber; and melt-processible rubber.
20. The method for preparing the polymer as recited in claim 16
wherein said substrate is selected from the group consisting of:
polypropylene; polyethylene; crosslinked polyethylene; ethylene
vinyl acetate; and polyvinylacetate.
21. The method for preparing the polymer as recited in claim 16
wherein said primary plasma reactant is selected from the group of
inert gas plasmas consisting of: Helium; Neon; and Argon.
22. The method for preparing the polymer as recited in claim 16
wherein said grafted surface includes an inorganic metal oxide
surface.
23. The method for preparing the polymer as recited in claim 22
wherein said inorganic metal oxide surface is created by exposure
of said modified surface to said secondary plasma reactant selected
from the group of reactive agents consisting of: titanium esters;
tantalum alkoxides; manganese acetate; manganese alkoxide;
manganese acetate; manganese acetylacetonate aluminum alkoxides;
alkoxy aluminates; zirconium alkoxides; alkoxy zirconates;
magnesium acetate; and magnesium acetylacetonate.
24. The method for preparing the polymer as recited in claim 22
wherein said inorganic metal oxide surface is created by exposure
of said modified surface to said secondary plasma reactant selected
from the group of reactive agents consisting of: titanium esters
plus water; titanium esters plus alcohols; titanium esters plus
ozone; alkoxy silanes plus ozone; and alkoxy silanes plus
ammonia.
25. The method for preparing the polymer as recited in claim 16
wherein said grafted surface includes a controlled wetability
surface.
26. The method for preparing the polymer as recited in claim 25
wherein said controlled wetability surface is created by exposure
of said modified surface to said secondary plasma reactant selected
from the group of reactive agents consisting of: water; aliphatic
alcohols; and aliphatic polyalcohols.
27. The method for preparing the polymer as recited in claim 25
wherein said controlled wetability surface is created by exposure
of said modified surface to said secondary plasma reactant selected
from the group of reactive agents consisting of: hydrogen peroxide;
ammonia; and oxides of nitrogen.
28. The method for preparing the polymer as recited in claim 25
wherein said controlled wetability surface is created by exposure
of said modified surface to said secondary plasma reactant selected
from the group of reactive agents consisting of: hydroxylamine
solution; and sulfur hexafluoride.
29. The method for preparing the polymer as recited in claim 16
wherein said grafted surface includes an organic surface.
30. The method for preparing the polymer as recited in claim 29
wherein said organic grafted surface is created by exposure of said
modified surface to said secondary plasma reactant selected from
the group of reactive agents consisting of: allyl alcohols; allyl
amines; allyl alkylamines, where the alkyl groups contain 1-8
carbon atoms; allyl ethers; secondary amines, where the alkyl
groups contain 1-8 carbon atoms; alkyl hydrazines, where the alkyl
groups contain 1-8 carbon atoms; acrylic acid; methacrylic acid;
acrylic acid esters containing 1-8 carbon; methacrylic esters
containing 1-8 carbon; vinyl pyridine; vinyl esters.
31. A method of manufacturing a polishing pad, comprising:
providing a thermoplastic foam substrate; forming a thermoplastic
foam body by a process including: exposing said thermoplastic foam
substrate to an initial plasma reactant to produce a modified
surface thereon; and exposing said modified surface on said
thermoplastic foam substrate to a secondary plasma reactant to
create a grafted surface on said modified surface; and forming a
polishing pad from said thermoplastic foam body suitable for
polishing a semiconductor wafer or integrated circuit using said
grafted surface.
32. The method of manufacturing the polishing pad as recited in
claim 31 wherein said thermoplastic foam substrate is provided by
extruding a thermoplastic foam substrate from an extrusion
apparatus to form said thermoplastic foam substrate.
33. The method of manufacturing the polishing pad as recited in
claim 31 wherein said thermoplastic foam substrate is selected from
the group consisting of: polyurethane; polyolefin; and polyvinyl
esters.
34. The method of manufacturing the polishing pad as recited in
claim 31 wherein said thermoplastic foam substrate is selected from
the group consisting of: polyurea; polycarbonate; aliphatic
polyketone; polysulfone; aromatic polyketone; 6,6 nylon; 6,12
nylon; and polyamide.
35. The method of manufacturing the polishing pad as recited in
claim 31 wherein said thermoplastic foam substrate is selected from
the group consisting of: thermoplastic rubber; and melt-processible
rubber.
36. The method of manufacturing the polishing pad as recited in
claim 31 wherein said thermoplastic foam substrate is selected from
the group consisting of: polypropylene; polyethylene; crosslinked
polyethylene; ethylene vinyl acetate; and polyvinylacetate.
37. The method of manufacturing the polishing pad as recited in
claim 31 wherein said primary plasma reactant is selected from the
group of inert gas plasmas consisting of: Helium; Neon; and
Argon.
38. The method of manufacturing the polishing pad as recited in
claim 31 wherein said grafted surface includes an inorganic metal
oxide surface.
39. The method of manufacturing the polishing pad recited in claim
38 wherein said inorganic metal oxide surface is created by
exposure of said modified surface to said secondary plasma reactant
selected from the group of reactive agents consisting of: titanium
esters; tantalum alkoxides; manganese acetate; manganese alkoxide;
manganese acetate; manganese acetylacetonate aluminum alkoxides;
alkoxy aluminates; zirconium alkoxides; alkoxy zirconates;
magnesium acetate; and magnesium acetylacetonate.
40. The method of manufacturing the polishing pad recited in claim
38 wherein said inorganic metal oxide surface is created by
exposure of said modified surface to said secondary plasma reactant
selected from the group of reactive agents consisting of: titanium
esters plus water; titanium esters plus alcohols; titanium esters
plus ozone; alkoxy silanes plus ozone; and alkoxy silanes plus
ammonia.
41. The method of manufacturing the polishing pad as recited in
claim 38 wherein said grafted surface on said thermoplastic foam
substrate includes a controlled wetability surface.
42. The method of manufacturing the polishing pad as recited in
claim 41 wherein said controlled wetability surface is created by
exposure of said modified surface to said secondary plasma reactant
selected from the group of reactive agents consisting of: water;
aliphatic alcohols; and aliphatic polyalcohols.
43. The method of manufacturing the polishing pad as recited in
claim 41 wherein said controlled wetability surface is created by
exposure of said modified surface to said secondary plasma reactant
selected from the group of reactive agents consisting of: hydrogen
peroxide; ammonia; and oxides of nitrogen.
44. The method of manufacturing the polishing pad as recited in
claim 41 wherein said controlled wetability surface is created by
exposure of said modified surface to said secondary plasma reactant
selected from the group of reactive agents consisting of:
hydroxylamine solution; and sulfur hexafluoride.
45. The method of manufacturing the polishing pad as recited in
claim 31 wherein said grafted surface includes an organic grafted
surface.
46. The method of manufacturing the polishing pad as recited in
claim 45 wherein said organic grafted surface is created by
exposure of said modified surface to said secondary plasma reactant
selected from the group of reactive agents consisting of: allyl
alcohols; allyl amines; allyl alkylamines, where the alkyl groups
contain 1-8 carbon atoms; allyl ethers; secondary amines, where the
alkyl groups contain 1-8 carbon atoms; alkyl hydrazines, where the
alkyl groups contain 1-8 carbon atoms; acrylic acid; methacrylic
acid; acrylic acid esters containing 1-8 carbon; methacrylic esters
containing 1-8 carbon; vinyl pyridine; vinyl esters.
47. A polishing apparatus comprising: a mechanically driven carrier
head; a polishing platen, said carrier head being positionable
against said polishing platen to impart a polishing force against
said polishing platen; and a polishing pad attached to said
polishing platen and including a polishing body comprising a
material wherein said material is a thermoplastic foam substrate
having a modified surface thereon; and a grafted surface on said
modified surface.
48. The polishing apparatus as recited in claim 47 wherein said
thermoplastic foam substrate is selected from the group consisting
of: polyurethane; polyolefin; and polyvinyl esters.
49. The polishing apparatus as recited in claim 47 wherein said
thermoplastic foam substrate is selected from the group consisting
of: polyurea; polycarbonate; aliphatic polyketone; polysulfone;
aromatic polyketone; 6,6 nylon; 6,12 nylon; and polyamide.
50. The polishing apparatus as recited in claim 47 wherein said
thermoplastic foam substrate is selected from the group consisting
of: thermoplastic rubber; and melt-processible rubber.
51. The polishing apparatus as recited in claim 47 wherein said
thermoplastic foam substrate is selected from the group consisting
of: polypropylene; polyethylene; crosslinked polyethylene; ethylene
vinyl acetate; and polyvinylacetate.
52. The polishing apparatus as recited in claim 47 wherein said
modified surface is modified by a primary plasma reactant selected
from a group of inert gas plasmas consisting of: Helium; Neon; and
Argon.
53. The polishing apparatus as recited in claim 47 wherein said
grafted surface includes an inorganic metal oxide surface.
54. The polishing apparatus as recited in claim 53 wherein said
inorganic metal oxide surface is created by exposure to a secondary
plasma reactant selected from a group of reactive agents consisting
of: titanium esters; tantalum alkoxides; manganese acetate;
manganese alkoxide; manganese acetate; manganese acetylacetonate
aluminum alkoxides; alkoxy aluminates;, zirconium alkoxides; alkoxy
zirconates; magnesium acetate; and magnesium acetylacetonate.
55. The polishing apparatus as recited in claim 53 wherein said
inorganic metal oxide surface is created by exposure to a secondary
plasma reactant selected from a group of reactive agents consisting
of: titanium esters plus water; titanium esters plus alcohols;
titanium esters plus ozone; alkoxy silanes plus ozone; and alkoxy
silanes plus ammonia.
56. The polishing apparatus as recited in claim 47 wherein said
grafted surface includes a controlled wetability surface.
57. The polishing apparatus as recited in claim 56 wherein said
controlled wetability surface is created by exposure to a secondary
plasma reactant selected from a group of reactive agents consisting
of: water; aliphatic alcohols; and aliphatic polyalcohols.
58. The polishing apparatus as recited in claim 57 wherein said
controlled wetability surface is created by exposure to a secondary
plasma reactant selected from a group of reactive agents consisting
of: hydrogen peroxide; ammonia; and oxides of nitrogen.
59. The polishing apparatus as recited in claim 56 wherein said
controlled wetability surface is created by exposure to a secondary
plasma reactant selected from a group of reactive agents consisting
of: hydroxylamine solution; and sulfur hexafluoride.
60. The polishing apparatus as recited in claim 47 wherein said
grafted surface on said thermoplastic foam substrate includes an
organic grafted surface.
61. The polishing apparatus as recited in claim 60 wherein said
organic grafted surface is created by exposure to a secondary
plasma reactant selected from a group of reactive agents consisting
of: allyl alcohols; allyl amines; allyl alkylamines, where the
alkyl groups contain 1-8 carbon atoms; allyl ethers; secondary
amines, where the alkyl groups contain 1-8 carbon atoms; alkyl
hydrazines, where the alkyl groups contain 1-8 carbon atoms;
acrylic acid; methacrylic acid; acrylic acid esters containing 1-8
carbon; methacrylic esters containing 1-8 carbon; vinyl pyridine;
vinyl esters.
Description
CROSS-REFERENCE TO PROVISIONAL APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/250,299 entitled, "SUBSTRATE POLISHING DEVICE
AND METHOD," to Edward M. Yokley, filed on Nov. 29, 2000; U.S.
Provisional Application No. 60/295,315 entitled, "A METHOD OF
ALTERING PROPERTIES OF A POLISHING PAD AND SPECIFIC APPLICATIONS
THEREFOR," to Yaw S. Obeng and Edward M. Yokley, filed on Jun. 1,
2001; and U.S. Provisional Application No. 60/304,375 entitled, "A
METHOD OF ALTERING PROPERTIES OF A THERMOPLASTIC FOAM POLISHING PAD
AND SPECIFIC APPLICATIONS THEREFOR," to Yaw S. Obeng and Edward M.
Yokley, filed on Jul. 10, 2001, which are commonly assigned with
the present invention and incorporated herein by reference as if
reproduced herein in its entirety.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention is directed to polishing pads used for
creating a smooth, ultra-flat surface on such items as glass,
semiconductors, dielectric/metal composites, magnetic mass storage
media and integrated circuits. More specifically, the present
invention relates to grafting and preserving the grafted surface of
polymers, preferably thermoplastic foam polymers, thereby
transforming their mechanical and chemical properties to create
more suitable polishing pads therefrom.
BACKGROUND OF THE INVENTION
[0003] Chemical-mechanical polishing (CMP) is used extensively as a
planarizing technique in the manufacture of VLSI integrated
circuits. It has potential for planarizing a variety of materials
in IC processing but is used most widely for planarizing
metallizied layers and interlevel dielectrics on semiconductor
wafers, and for planarizing substrates for shallow trench
isolation.
[0004] In trench isolation, for example, large areas of field oxide
must be polished to produce a planar starting wafer. Integrated
circuits that operate with low voltages, i.e., 5 volts or less, and
with shallow junctions, can be isolated effectively with relatively
shallow trenches, i.e., less than a micron. In shallow trench
isolation (STI) technology, the trench is backfilled with oxide and
the wafer is planarized using CMP. The result is a more planar
structure than typically obtained using LOCOS, and the deeper
trench (as compared with LOCOS) provides superior latch up
immunity. Also, by comparison with LOCOS, STI substrates have a
much reduced "birds' beak" effect and thus theoretically provide
higher packing density for circuit elements on the chips. The
drawbacks in STI technology to date relate mostly to the
planarizing process. Achieving acceptable planarization across the
full diameter of a wafer using traditional etching processes has
been largely unsuccessful. By using CMP, where the wafer is
polished using a mechanical polishing wheel and a slurry of
chemical etchant, unwanted oxide material is removed with a high
degree of planarity.
[0005] Similarly, integrated circuit fabrication on semiconductor
wafers require the formation of precisely controlled apertures,
such as contact openings or "vias," that are subsequently filled
and interconnected to create components and very large scale
integration (VLSI) or ultra large scale integration (ULSI)
circuits. Equally well known is that the patterns defining such
openings are typically created by optical lithographic processes
that require precise alignment with prior levels to accurately
contact the active devices located in those prior levels. In
multilevel metallization processes, each level in the multilevel
structure contributes to irregular topography. In three or four
level metal processes, the topography can be especially severe and
complex. The expedient of planarizing the interlevel dielectric
layers, as the process proceeds, is now favored in many state of
the art IC processes. Planarity in the metal layers is a common
objective, and is promoted by using plug interlevel connections. A
preferred approach to plug formation is to blanket deposit a thick
metal layer on the interlevel dielectric and into the interlevel
windows, and then remove the excess using CMP. In a typical case,
CMP is used for polishing an oxide, such as SiO.sub.2,
Ta.sub.2O.sub.5, W.sub.2O.sub.5. It can also be used to polish
nitrides such as Si.sub.3N.sub.4, TaN, TiN, and conductor materials
used for interlevel plugs, such as W, Ti, TiN.
[0006] CMP generally consists of the controlled wearing of a rough
surface to produce a smooth specular finished surface. This is
commonly accomplished by rubbing a pad against the surface of the
article, or workpiece, to be polished in a repetitive, regular
motion while a slurry containing a suspension of fine particles is
present at the interface between the polishing pad and the
workpiece. Commonly employed pads are made from felted or woven
natural fibers such as wool, urethane-impregnated felted polyester
or various types of filled polyurethane plastic.
[0007] A CMP pad ideally is flat, uniform across its entire
surface, resistant to the chemical nature of the slurry and have
the right combination of stiffness and compressibility to minimize
effects like dishing and erosion. In particular, there is a direct
correlation between lowering Von Mises stress distributions in the
pad and improving polishing pad removal rates and uniformity. In
turn, Von Mises stresses may be reduced though the controlled
production of pad materials of uniform constitution, as governed by
the chemical-mechanical properties of the pad material.
[0008] CMP pad performance optimization has traditionally involved
the empirical selection of materials and use of macro fabrication
technologies. For example, a pad possessing preexisting desirable
porosity or surface texture properties may be able to absorb
particulate matter such as silica or other abrasive materials. Or,
patterns of flow channels cut into the surface of polishing pads
may improve slurry flow across the workpiece surface. The reduction
in the contact surface area effected by patterning also provides
higher contact pressures during polishing, further enhancing the
polishing rate.
[0009] Alternatively, intrinsic microtextures may be introduced
into pads by using composite or multilayer materials possessing
favorable surface textures as byproduct of their method of
manufacture. Favorable surface microtextures may also be present by
virtue of bulk non-uniformities' introduced during the
manufacturing process. When cross-sectioned, abraded, or otherwise
exposed, these bulk non-uniformities become favorable surface
microtextures. Such inherent microtextures, present prior to use,
may permit the absorption and transport of slurry particles,
thereby providing enhanced polishing activity without the need to
further add micro- or macrotextures.
[0010] There are, however, several deficiencies in polishing pad
materials selected or produced according to the above-described
empirical techniques. Pads made of layers of polymer material may
have thermal insulating properties, and therefore unable conduct
heat away from the polishing surface, resulting in undesirable
heating during polishing. Numerous virgin homogenous sheets of
polymers such as polyurethane, polycarbonate, nylon, polyureas,
felt, or polyester, have poor inherent polishing ability, and hence
not used as polishing pads. In certain instances, mechanical or
chemical texturing may transform these materials, thereby rendering
them useful in polishing.
[0011] However, polyurethane based pads, currently in widespread
use, are decomposed by the chemically aggressive processing
slurries by virtue of the inherent chemical nature of urethane.
This decomposition produces a surface modification in and of itself
in the case of the polyurethane pads.
[0012] Yet another approach involves modifying the surface of CMP
polishing pads materials to improve the wetability of the pad
surface, the adhesion of surface coatings, and the application
performance of these materials. Plasma treatment of polishing pad
materials is one means to functionalize and thereby modify
polishing pad surfaces. However, the simple functionalization of
pad surfaces by plasma treatment is known to be a temporary effect,
with spontaneous loss of functionalization after one to two days.
While some success in the preservation of functionalized pad
surfaces has been obtained for fluorinated polymeric surfaces, this
has not been demonstrated for other polymeric surfaces, and in
particular, thermoplastics.
[0013] Accordingly, what is needed in the art is an improved
process for functionalizing and preserving a semiconductor wafer
thermoplastic polishing pad surface, thereby providing a rapid rate
of polishing and yet reducing scratches and resultant yield loss
during chemical/mechanical planarization.
SUMMARY OF THE INVENTION
[0014] To address the deficiencies of the prior art, the present
invention, in one embodiment, provides a polymer, preferably
thermoplastic foam polymer, comprising a thermoplastic foam
substrate having a modified surface thereon and a grafted surface
on the modified surface.
[0015] In another embodiment, the present invention provides a
method for preparing a polymer, preferably a thermoplastic foam
polymer. The method comprises the steps of providing a
thermoplastic foam substrate, exposing the substrate to an initial
plasma reactant to produce a modified surface thereon, and exposing
the modified surface to a secondary plasma reactant to create a
grafted surface on the modified surface.
[0016] Yet another embodiment provides a method of manufacturing a
polishing pad. The method comprises providing a thermoplastic foam
substrate, and then forming a thermoplastic foam polishing body
with a grafted surface by including those steps described above. A
polishing pad is then formed from the thermoplastic foam polishing
body that is suitable for polishing a semiconductor wafer or
integrated circuit using the grafted surface.
[0017] In still another embodiment, the present invention provides
a polishing apparatus. This particular embodiment includes a
mechanically driven carrier head, a polishing platen, and a
polishing pad attached to the polishing platen. The carrier head is
positionable against the polishing platen to impart a polishing
force against the polishing platen. The polishing pad includes a
polishing body comprising a material wherein the material is a
thermoplastic foam polymer.
[0018] The foregoing has outlined, rather broadly, preferred and
alternative features of the present invention so that those skilled
in the art may better understand the detailed description of the
invention that follows. Additional features of the invention will
be described hereinafter that form the subject of the claims of the
invention. Those skilled in the art should appreciate that they can
readily use the disclosed conception and specific embodiment as a
basis for designing or modifying other structures for carrying out
the same purposes of the present invention. Those skilled in the
art should also realize that such equivalent constructions do not
depart from the spirit and scope of the invention in its broadest
form.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] For a more complete understanding of the invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawing, in which:
[0020] FIG. 1 illustrates a polishing apparatus, including a
polishing pad fabricated using a thermoplastic foam polymer made
according to the present invention.
DETAILED DESCRIPTION
[0021] Conditions have been discovered for producing a polymer,
preferably thermoplastic foam polymer, having desirable polishing
properties. The thermoplastic foam polymer, for example, comprises
a thermoplastic foam substrate having a modified surface and a
grafted surface on the modified surface. This polymer is produced,
for example, by subjecting a thermoplastic foam substrate to a
first plasma treatment to produce a modified surface, thereby
allowing the grafting of various functional groups onto the
substrate's modified surface in a second plasma treatment. Such
treatments are facilitated using inert gas plasmas such Helium,
Neon or Argon. The thermoplastic foam polymers of the present
invention may also be produced using more reactive plasma gases,
such as oxygen. In certain embodiments, the functional effects of
grafting decline over a period of three to twenty days, as
determined by water contact angle measurements, while in other
embodiments these functional effects are preserved. The polymers of
the present invention are ideally suited for use as pads in CMP
applications.
[0022] It is believed that exposing polymers, such as thermoplastic
foam substrates, to an initial plasma reactant creates ruptured
single bonds, existing on the polymer surface regime as excited
states. Due to the low mobility and limited vibrational degrees of
freedom within the polymer matrix, these triplet sites lack the
ability to undergo intersystem crossing and return to ground state
for short periods of time. Based on the ability of the plasma
surface to show large macro effects, excited state sites are likely
present in abundance at the modified surface.
[0023] The excited state sites generated by exposing polymers, such
as thermoplastic foam polymers, to the initial plasma reactant are
thought to provide an attractive base on which to selectively graft
polymerized numerous inorganic and organic materials. The modified
surface of the polymer incorporating such functional groups is
designated as a grafted surface. Such grafted surfaces are
particularly useful in CMP processes due to the grafting process's
ability to introduce very fine hard groups onto the grafted
surface, which is then incorporated into a polishing pad. Such pads
may enable the use of reduced or no abrasive slurries, which may
improve thermal management. Additionally, the grafting process
produces thermoplastic foam polymers with certain desirable
physical and chemical properties, such as controlled wetability
surfaces, and renders such grafted surfaces permanent. Still other
thermoplastic foam polymers may contain grafted functional groups
that change the nanoscale morphology of a pad surface, while
leaving the bulk properties of the thermoplastic polymer relatively
intact.
[0024] As noted above, polymers, such as thermoplastic polymers are
produced according to the present invention by a process whereby a
thermoplastic foam substrate is exposed to primary and secondary
plasma mixtures introduced into a conventional plasma generating
apparatus. In certain embodiments, the thermoplastic foam substrate
is preferably composed of polyurethane, polyolefin or polyvinyl
esters. Alternative embodiments of the thermoplastic foam substrate
may be, for example, polyurea, polycarbonate, aliphatic polyketone,
polysulfone, aromatic polyketone, 6,6 nylon, 6,12 nylon or
polyamide. In other preferred embodiments, the substrate may be
thermoplastic rubber or melt-processible rubber. However
embodiments where the substrate is composed of closed-cell
polypropylene, polyethylene, crosslinked polyethylene, ethylene
vinyl acetate, or polyvinylacetate are also within the scope of the
present invention.
[0025] One skilled in the art will be familiar with reagents
suitable for producing conventional primary plasma mixtures. For
instance, conventional mixtures often include noble gases such as
Helium, Neon or Argon; or ammonia, oxygen, or water. In the present
invention, the plasma treatment is continued in the presence of a
secondary plasma mixture to graft various functional groups onto
the polymer surface, depending on the secondary plasma reactant
used.
[0026] One group of such secondary plasma reactants are
oxygen-containing organometallic reactants that produce a grafted
surface that includes an inorganic metal oxide. In such
embodiments, the secondary plasma mixture typically includes a
transition metal such as titanium, manganese, or tantalum. However,
any metal element capable of forming an oxygen containing
organometallic compound and capable of being grafted to the polymer
surface is suitable. Silicon may also be employed as the metal
portion of the organometallic secondary plasma mixture. In these
embodiments, the organic portion of the organometallic reagent may
be an ester, acetate, or alkoxy fragment. The secondary plasma
reagent may optionally include ozone, alkoxy silanes, water,
ammonia, alcohols, mineral sprits or hydrogen peroxide. For
example, in preferred embodiments, the secondary plasma reactant
may be composed of titanium esters, tantalum alkoxides, including
tantalum alkoxides wherein the alkoxide portion has 1-5 carbon
atoms; manganese acetate solution in water; manganese alkoxide
dissolved in mineral spirits; manganese acetate; manganese
acetylacetonate; aluminum alkoxides; alkoxy aluminates; zirconium
alkoxides, wherein the alkoxide has 1-5 carbon atoms; alkoxy
zirconates; magnesium acetate; and magnesium acetylacetonate. Other
embodiments are also contemplated for the secondary plasma
reactant, for example, alkoxy silanes and ozone, alkoxy silanes and
ammonia, titanium esters and water, titanium esters and alcohols,
or titanium esters and ozone.
[0027] Another group of secondary plasma reactants produce grafted
surfaces having super hydrated, controlled wetability, and designed
alkalinity surface properties. For example, in preferred
embodiments, the secondary plasma reactant may be composed of
water, aliphatic alcohols, or aliphatic polyalcohols. In other
embodiments, the secondary plasma reactant may be hydrogen
peroxide, ammonia, or oxides of nitrogen. Yet other embodiment
include hydroxylamine solution, hydrazine, sulfur hexafluoride as
the secondary plasma reactant. One skilled in the art, however,
will recognize that other similar materials, including other
organic alcohols or polyalcohols, may produce these desired surface
properties when grafted onto the polymer's surface, and thus, art
within the scope of the present invention.
[0028] Yet another group of secondary plasma reactants result in
organic grafted surfaces. For example, in preferred embodiments,
the secondary plasma reactant may be composed of allyl alcohols;
allyl amines; allyl alkylamines, where the alkyl groups contain 1-8
carbon atoms; allyl ethers; secondary amines, where the alkyl
groups contain 1-8 carbon; alkyl hydrazines, where the alkyl groups
contain 1-8 carbon atoms; acrylic acid; methacrylic acid; acrylic
acid esters containing 1-8 carbon atoms; methacrylic esters
containing 1-8 carbon atoms; or vinyl pyridine, and vinyl esters,
for example, vinyl acetate.
[0029] The conditions of plasma treatment via Radio Frequency Glow
Discharge (RFGD) must be carefully chosen to avoid damaging the
grafted layer, and to achieve long-lasting grafts. For example,
high power plasmas may cause polymer surfaces to crack. See e.g.,
Owen, M. J. & Smith, P. J. in POLYMER SURFACE MODIFICATION:
RELEVANCE TO ADHESION, 3-15 (K. L. Mittal, ed., 1995), incorporated
herein by reference as if reproduced herein in its entirety. As
further illustrated in experiments described below, the exact
grafting conditions depend on factors including the type of polymer
specimen, radio frequency and power, and the identity of the
primary and secondary plasma reactants. However, typical preferred
plasma-grafting process conditions include exposing the
thermoplastic foam substrate to a primary plasma reactant treatment
time (TT-1) from about 30 s to about 30 min, in a reaction chamber
having a pressure ranging from about 130 to about 340 mTorr, and
plasma back pressure (PBP) ranging from about 140 to about 200
mTorr. Subsequent exposure of the modified substrate surface to the
secondary plasma reactant for similar treatment times (TT-2) and
pressures also include a diluting inert gas, where the inert gas to
secondary plasma reactant ratio typically ranges from about 1:1 to
about 3:1, the dilutant inert gas being introduced into the
reaction chamber at a flow rate of about 0.03 to about 1.0 standard
liters per min (SLM). The amount of secondary reactant monomer in
the gas stream is governed by the monomer vapor pressure (MBP), and
the monomer reservoir temperature (MRT), typically ranging from
about 20 to about 75.degree. C. The resulting pressure in the
reaction chamber during grafting (GP) may range from about 135 to
about 340 mTorr, and out gas back pressure (OGBP) may range from
about 55 to 70 mTorr. Throughout, the RDGD electrode may be
maintained at a constant value within the range of room temperature
to about 100.degree. C. One of ordinary skill in the art
understands that conditions outside of the above-cited ranges may
also be used to produce the subject matter of the present
invention.
[0030] Polishing pads in certain embodiments of the present
invention may be manufactured by first melting a thermoplastic
polymer pellets in an extrusion apparatus such as a melt extruder,
and blowing gas into the melt to form a thermoplastic foam
substrate. The substrate may be formed into pads by techniques well
known to those skilled in the art, such as laser cutting or die
cutting. The substrate is next formed into a thermoplastic foam
polishing body by first exposing the substrate to an initial plasma
reactant to produce a modified surface and then exposing the
modified surface to a secondary plasma reactant to create a grafted
surface on the modified surface. Finally, the polishing body may be
incorporated into a pad such that the grafted surface is
suitability situated to polish a semiconductor wafer or integrated
circuit.
[0031] Polishing pads may be employed in a variety of CMP polishing
apparatus 150, one embodiment of which is displayed in FIG. 1. The
thermoplastic foam polymers of the present invention may be
incorporated into a polishing body 100 that includes a base pad
110, where a thermoplastic foam polymer 120 forms a polishing
surface located over the base pad 110. Optionally, a first adhesive
material 130, such as acrylate-based, silicone-based, epoxy or
other materials well known to those skilled in the art, may be used
to couple the base pad 110 to the thermoplastic foam polymers 120.
The polishing pads thus formed may also have a second adhesive
material 140, well known to those skilled in the art, applied to
the platen side. The polishing pad may then be cleaned and packaged
for use.
[0032] With continuing reference to FIG. 1, the polishing body 100
may then be employed in a variety of CMP processes by incorporation
into a polishing apparatus 150. The polishing apparatus 150
typically includes a conventional mechanically driven carrier head
160, a conventional carrier ring 170, a conventional polishing
platen 180, and a polishing pad that includes the polishing body
100 comprising the thermoplastic foam polymer 120 of the present
invention, attached to the polishing platen 180, optionally using
the second adhesive 140. The substrate to be polished 185,
typically a wafer, may be attached to the carrier ring with the aid
of a third a conventional adhesive 190. The carrier head 160 is
then positioned against the polishing platen 180 to impart a
polishing force against the polishing platen 180, typically a
repetitive, regular motion of the mechanically driven carrier head
160, while providing an appropriate conventional slurry mixture.
Optionally, in certain embodiments of the thermoplastic foam
polymer 120, the slurry may be omitted.
[0033] With continuing reference to FIG. 1, in such polishing
processes, a substrate 185 may be polished by positioning the
substrate 185, having at least one layer, on to the above-described
polishing apparatus 150, and polishing the layer against the
thermoplastic foam polymer 120 of the present invention. In one
embodiment, the substrate 185 has at least one layer of material
that is a metal layer. In particular embodiments, the metal layer
may be is copper or tungsten. In another embodiment, the substrate
185 may be a silicon, polysilicon or dielectric material located on
a semiconductor wafer. Thermoplastic foam polymers 120 of the
present invention are particularly suited for polishing in shallow
trench isolation (STI), interlevel dielectrics, and metal
interconnects in integrated circuit fabrication or other
fabrication techniques where large areas of field oxide, other
dielectrics or metal must be removed from the wafer to produce a
planar surface prior to subsequent processing. The thermoplastic
foam polymers 120 of the present invention are also desirable for
polishing metalization materials such as W, Ti, Cu, Al, and other
metals as well as nitrides or barrier materials such as
Si.sub.3N.sub.4, TaN, TiN.
EXPERIMENTS
[0034] Measurements of solvent contact angles provides a
particularly useful means to measure to extent and stability of
grafts providing controlled wetability surfaces. Wetability,
typically measured by measuring the contact angle of a water
droplet, provides an indication of surface energy. A hydrophilic
surface having a high surface energy will have a low contact angle.
Thermoplastic foam polymers made according to the present invention
were examined for changes in water contact angle, by comparing pre-
and post-plasma treatment angles, typically for several days
following plasma treatment, using commercial instruments (Rame-Hart
Goniometer, Mountain Lakes, N.J.; and Accu-Dyne-Test Marker Pen,
Diversified Enterprises, Claremont, N.H.).
[0035] Several such experiments were performed using approximately
2" by 2" sheets of 0.125" thick thermoplastic elastomer foam
(Santoprene.RTM. D-40; Advanced Elastomer Systems, LP, Akron,
Ohio). The Santoprene.RTM. D-40 sheets were manually cleaned with
an aqueous/isopropyl alcohol solution, and then placed in the
reaction chamber of a conventional commercial RFGD plasma reactor
having a temperature controlled electrode configuration (Model
PE-2; Advanced Energy Systems, Medford, N.Y.).
[0036] In one experiment, for comparison purposes, plasma treatment
consisted of exposing the Santoprene.RTM. D-40 substrate to only a
primary plasma reactant, comprising Helium:Oxygen, 60:40, for 10
minutes, with the reaction chamber maintained at 230 mTorr
pressure, the electrode temperature maintained below about
100.degree. C. and using a RF operating power of 2500 Watts.
Surface modification was confirmed by the observation of an
increased hydrogen and oxygen content to a depth of 100 Angstroms,
as measured by Electron Spectroscopy Chemical Analysis (ESCA).
[0037] While the pre-treatment water contact angle of the
Santoprene.RTM. D-40 substrate was 98.degree., the immediate
post-treatment angle was 25.degree.. The contact angle, however,
subsequently rose to and stabilized at 60.degree. by 6 days after
treatment. Similar results were obtained in a second experiment,
when the Santoprene.RTM. D-40 substrate was exposed to a primary
plasma reactant of 100% ammonia. The water contact angle was
40.degree. immediately following plasma treatment, but
progressively rose to and stabilized at 80.degree. by 6 days
post-treatment.
[0038] In a third experiment, the plasma treatment of the
Santoprene.RTM. D-40 substrate was commenced by introducing the
primary plasma reactant, Argon, for 30 seconds within the reaction
chamber maintained at 350 mTorr. The electrode temperature was
maintained at 30.degree. C., and an RF operating power of 300 Watts
was used. Subsequently, the secondary reactant was introduced for
either 10 or 30 minutes at 0.10 SLM and consisted of either
Tetraethoxy Silane (TEOS), Titanium Alkoxide (TYZOR), Allyl-Alcohol
(Allyl-OH), or Allyl-Amine (ALLYL-NH.sub.2)vapor mixed with He or
Ar gas (TABLE 1). In this, and analogous experiments described
below, the amount of secondary reactant in the gas stream was
governed by the vapor back pressure (BP) of the secondary reactant
monomer at the monomer reservoir temperature (MRT; 50.+-.10.degree.
C.). The monomer-carrier gas mixture was further diluted with a
separate stream of either argon or helium in the reactor chamber.
The pre-and post-plasma treatment water contact angles, shown in
TABLE 1, reveal substantially lower immediate post-treatment
contact angles as compared to previously described Santoprene.RTM.
D-40 substrates treated with the primary plasma reactant only.
1TABLE 1 Immediate Seven Day Pre- Post- Post- Secondary Treatment
Treatment Treatment Plasma Contact Contact Contact Reactant TT-2
(min) Angle (.degree.) Angle (.degree.) Angle (.degree.) TYZOR 10
98 0 36 TYZOR 30 98 0 65 TEOS 30 98 0 90 Allyl-OH 30 98 0 90
Allyl-NH.sub.2 30 98 65 75
[0039] Similar results were obtained in a fourth experiment, where
Santoprene.RTM. D-40 was exposed to a primary plasma reactant of
Argon mixture for 30 second at 100 mTorr and 50 Watts RF power,
with the electrode maintained at 40.degree. C., and was exposed to
a secondary plasma reactant of 100% ammonia. The pre-treatment
water contact angle of 98.degree. was reduced to 40.degree.
immediately following treatment, with the angle increasing to and
stabilizing at 60.degree. by 6 days post-treatment.
[0040] In a fifth experiment using Santoprene.RTM. D-40 as the
substrate, plasma treatment was commenced by introducing the
primary plasma reactant, Helium, for 10 minutes with the reaction
chamber maintained at 350 mTorr pressure, the electrode temperature
below about 100.degree. C. and RF operating power of 3500 Watts was
used. This was followed by a second 10 minute plasma treatment
under the same conditions while introducing a secondary plasma
reactant containing tetraethoxyorthosilicate at 0.10 SLM into the
gas stream. The immediate post-treated surface modified
thermoplastic foam substrate had a water contact angle of
0.degree., as compared to 92.degree. for the pre-treated
substrate.
[0041] In a sixth experiment, 1 inch by 1 inch sheets of 0.063 inch
thick cross-linked polypropylene foam (type TPR, from Merryweather
Foams Inc., Anthony, N. Mex.) was plasma treated under the same
conditions as described for Experiment 5. The immediate
post-treated surface modified thermoplastic foam substrate had a
water contact angle of 0.degree., as compared to 90.degree. for the
pre-treated substrate.
[0042] By careful manipulation of the plasma treatment conditions,
the grafts can be preserved for longer periods, as indicated by the
stability of water contact angle changes. This is illustrated by a
seventh series of experiments conducted on the above-described
polypropylene sheets having dimensions of 6 inch by 6 inch by 0.125
inch thickness, under the plasma treatment conditions presented in
Table 2. Cold BP (Cold Back Pressure) is measured with the RF power
off, while PBP (Power Back Pressure) is with the RF power on. In
experiments 12 and 13, PBP was not recorded (n.r.).
2TABLE 2 Ar dilutant Flow Cold Grafting Sample TT-1 OGBP Rate BP
PBP GP MRT RF Power Number (min) (mTorr) (SLM) (mTorr) (mTorr)
(mTorr) (.degree. C.) (Watts) 1 1 60 0.03 120 140 200 50 50 2 1 60
0.03 120 140 300 50 50 3 1 65 0.10 190 207 280 70 50 4 1 65 0.03
120 150 250 50 100 5 1 70 0.03 125 160 320 50 100 6 1 70 0.03 125
160 200 55 100 7 1 60 0.10 180 200 245 50 100 8 1 60 0.10 180 200
340 55 100 9 1 60 0.03 105 125 150 60 50 10 1 55 0.03 105 125 220
50 50 11 1 60 0.01 90 105 130 75 50 12 0 55 0.03 110 n.r. 135 21 50
13 1 55 0.03 110 n.r. 165 60 50
[0043] As shown in Table 3, post-treated substrates produced under
the conditions described in Table 2 retained their low water
contact angles for at least 10 days of exposure to laboratory
atmospheric conditions.
3TABLE 3 Sample Pre-treatment Post-treatment Contact Angle
(.degree.) Number Contact Angle (.degree.) 0 days 3 days 7 days 10
days 1 90 45 47 50 50 2 90 58 65 67 65 3 90 80 73 73 76 4 90 30 42
45 45 5 90 80 75 75 77 6 90 70 73 73 76 7 90 70 80 75 76 8 90 68 70
75 76 9 90 75 77 77 75 10 90 75 77 77 76 11 90 48 52 59 62 12 90 70
77 75 65 13 90 73 78 75 80
[0044] In an eighth experiment, the polishing efficiency of a pad
manufactured according to this invention was compared to a
conventional polishing pad. A polishing pad was prepared by
exposing Aliplast.RTM. (JMS Plastic Supplies, Neptune, N.J.; Type
6A: medium foam density and hardness 34 Shore A), a thermoplastic
heat moldable cross-linked polyethylene closed-cell foam, to the
above-described grafting process. Specifically, secondary plasma
reactants, containing either Allyl-Alcohol, or Allyl-Amine,
Tetraethoxy Silane (TEOS), or tetraisopropyl-titanate (TYZOR TPT)
monomers, were grafted onto the modified Aliplast.RTM. substrate,
under conditions similar to Sample number 4 shown in Table 1, to
produce pads designated as A32AA, A32AN, A32S, and A32T,
respectively. The blanket Copper (Cu) polishing properties of pads
fashioned from these polymers were compared to the untreated
Aliplast.RTM. substrate (designated A32), and to a commercially
available IC1000/SUBA IV pad stack (Rodel, Phoenix, Ariz.).
[0045] The comparison was performed using an CETR CMP simulator
(Center For Tribology, Inc., Campbell, Calif. Conditions for
thermal oxide polishing include using a down force of 3 psi; table
speeds of 0.8 m/min; and a conventional slurry comprising K1501 and
polishing time of 5 min. Conditions for copper polishing include
using a down force of 3 psi; table speeds of 0.8 m/min; and a
conventional slurry comprising Cabot EP-5001 containing 3% hydrogen
peroxide and adjusted to a pH of about 4, and polishing time of 5
min. Plasma Enhanced Tetraethylorthosilicate (PE-TEOS) 5,000 .ANG.
wafers having a deposited 20,000 .ANG. copper surface and an
underlying 250 .ANG. thick tantalum barrier layer were used for
test polishing.
[0046] Cu removal rates for the A32AA, A32AN and A32T pads were
about 10,000; 7,500; and 7,200 .ANG./min, respectively. The
corresponding Ta removal rates were only 216, 215 and 175
.ANG./min, respectively. In comparison, the untreated A32 pad
removed Cu at a rate of about 3,200 .ANG./min. The high selectivity
of the grafted Aliplast.RTM. pads for Cu polishing compared to
Tantalum (Ta) polishing may be expressed by the ratio of Cu to Ta
removal rates. For the A32AA, A32AN and A32T pads, the selectivity
ratio was about 46, 35 and 41, respectively. In comparison, the Cu
and Ta removal rates of an IC1000/SUBA IV pad stack were about
5,700 .ANG./min and about 170 .ANG./min, respectively, giving a
Cu:Ta selectivity of about 34.
[0047] Although the present invention has been described in detail,
those skilled in the art should understand that they can make
various changes, substitutions and alterations herein without,
departing from the spirit and scope of the invention in its
broadest form.
* * * * *