U.S. patent application number 10/349761 was filed with the patent office on 2004-07-22 for noble metal contacts for plating applications.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Herchen, Harald.
Application Number | 20040140217 10/349761 |
Document ID | / |
Family ID | 32712775 |
Filed Date | 2004-07-22 |
United States Patent
Application |
20040140217 |
Kind Code |
A1 |
Herchen, Harald |
July 22, 2004 |
Noble metal contacts for plating applications
Abstract
Apparatus for electrochemical plating, comprising a support ring
and a plurality of inwardly directed shanks extended from an inner
circumference of the ring, wherein each of the shanks comprises a
contacting tip brazed to the distal end the shank.
Inventors: |
Herchen, Harald; (Los Altos,
CA) |
Correspondence
Address: |
Applied Materials, Inc.
Patent Counsel
P.O. Box 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
32712775 |
Appl. No.: |
10/349761 |
Filed: |
January 22, 2003 |
Current U.S.
Class: |
204/622 ;
257/E21.175 |
Current CPC
Class: |
C25D 17/001 20130101;
H01L 21/2885 20130101 |
Class at
Publication: |
204/622 |
International
Class: |
C25B 009/02 |
Claims
What is claimed is:
1. Apparatus for electrochemical plating, comprising: a support
ring; a plurality of contacting tips disposed radially inwards of
the support ring; and a plurality of shanks, each of the shanks
having a first end coupled to the support ring and a second end
brazed to a respective one of the contacting tips.
2. The apparatus of claim 1, wherein the support ring and the
shanks are formed from a single piece of the same material.
3. The apparatus of claim 1, wherein the shanks are bonded to the
support ring.
4. The apparatus of claim 1, wherein the shanks are formed from
stainless steel.
5. The apparatus of claim 1, wherein the shanks are formed from a
metal forming a protective oxide layer when exposed to a plating
solution.
6. The apparatus of claim 5, wherein the metal is tantalum or
niobium.
7. The apparatus of claim 1, wherein the contacting tip is brazed
to a bottom of the shank.
8. The apparatus of claim 1, wherein the contacting tip is brazed
to a sidewall of the shank.
9. The apparatus of claim 1, wherein the contacting tip further
comprises: a first portion having a first end brazed to a sidewall
of the shank and extending inward to a second end; and a second
portion extending upward from the second end of the first portion
to a contact surface adapted to support a substrate thereon.
10. The apparatus of claim 1, wherein the support ring comprises a
coating protecting the ring from a plating solution.
11. The apparatus of claim 10, wherein the coating comprises at
least one layer of a polytetrafluoroethylene-based material.
12. The apparatus of claim 1, wherein the contacting tip is formed
from a platinum/indium alloy comprising about 85% of platinum and
about 15% of indium.
13. The apparatus of claim 1, wherein the contacting tip is brazed
using a palladium/cobalt alloy comprising about 65% of palladium
and about 35% of cobalt.
14. The apparatus of claim 1, wherein the contacting tip has a
length of about 0.5 to 10 mm, a width of about 0.05 to 1 mm, and a
thickness of at least about 0.5 mm.
15. The apparatus of claim 1, wherein the shank of the contact has
a length of about 2 to 10 mm, a width of about 0.5 to 10 mm, and a
thickness of about 0.2 to 1 mm.
16. The apparatus of claim 1, wherein the contacting tip is
fabricated from at least two noble metals.
17. Apparatus for electrochemical plating, comprising: a support
ring; a plurality of electrically conductive shanks coupled to the
support ring and having a distal end extending radially inward of
an inner circumference of the support ring; and a plurality of
electrical contact elements, each contact element having a first
portion brazed to the distal end of a respective one of the
plurality of shanks and a second portion extending radially inward
and upward of the first end to a contact tip that is adapted to
support a substrate thereon.
18. A method of fabricating a support ring of an apparatus for
electrochemical plating, comprising: providing a conductive body
having an annular inner portion; forming a concentric groove in the
annular inner portion; depositing a brazing material into the
groove; positioning on the brazing material a ring formed from a
contacting tip material; heating the brazing material to braze the
ring to the annular inner portion; and machining the annular inner
portion and the ring to form a plurality of contacts.
19. The method of claim 18, wherein each contact of said plurality
of contacts comprises a shank and a contacting tip.
20. The method of claim 19, wherein the shanks are formed from
stainless steel, tantalum, or niobium.
21. The method of claim 18, wherein the ring comprises a
platinum/indium alloy having about 85% of platinum and about 15% of
indium.
22. The method of claim 18, wherein the brazing material comprises
palladium/cobalt alloy having about 65% of palladium and about 35%
of cobalt.
23. The method of claim 18, wherein machining removes portions of
the annular inner portion and the ring between the adjacent
contacts.
24. The method of claim 18, wherein machining is electrical
discharge machining.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to semiconductor
substrate processing systems. More specifically, the present
invention relates to an apparatus for performing an electrochemical
plating process in a semiconductor substrate processing system.
[0003] 2. Description of the Related Art
[0004] In ultra large scale integration integrated circuit (IC)
devices (i.e., devices having more than one million logic gates),
the multilevel interconnects are formed by filling the interconnect
features (i.e., trenches, vias, and the like) with a metal, such as
copper (Cu), aluminum (Al), and the like. Copper is the wiring
material of choice in the interconnecting networks of advanced IC
devices. In addition to superior electrical conductivity, copper is
more resistant than aluminum (Al) to electromigration that, in
operation, may destroy a thin film conductive line that carries an
electrical current.
[0005] As dimensions of the interconnect features decrease and the
aspect ratios increase, a void-free metal fill using conventional
metallizing techniques, such as chemical vapor deposition (CVD),
physical vapor deposition (PVD), and the like, becomes increasingly
difficult. As a result thereof, during manufacturing of advanced IC
devices, electrochemical plating (ECP) has emerged as a
production-worthy process for metallizing interconnect
features.
[0006] The ECP process is, generally, a two-step process. During a
first step, a seed layer (e.g., copper seed layer) is formed upon
the interconnect features, as well as elsewhere on the substrate.
The seed layer may extend from a device surface (i.e., plating
surface) of the substrate around the beveled edges to a backside
(i.e., non-plating) surface of the substrate. Generally, the seed
layer is deposited using a CVD, PVD, evaporation, and the like
process. Then, during a second step, the substrate is exposed to a
plating solution, while an electrical bias is simultaneously
applied between the substrate and an anode electrode positioned
within the plating solution. The plating solution is rich in ions
of the metal to be plated onto the substrate (i.e., copper) and, as
such, the electrical bias causes ions of such metal to be urged out
of the plating solution and deposited onto the seed layer.
[0007] The electrical bias is provided to the substrate using a
plurality of electrical contacts. Typically, the same contacts are
also used to provide a support to the substrate during the ECP
process. Generally, such contacts are collectively bonded to a
conductive support ring and engage the seed layer of the substrate.
In operation, the electrical contacts apply a voltage to the seed
layer, creating a current path through the plating solution. Such
current path has an associated electrical resistance. The
contacting surface of the tip of the electrical contact (i.e.,
portion of the contact having a contact with the seed layer) erodes
as a result of exposure to the plating solution. Similarly, the
resistance of the current path changes when a mechanical and
electrical interface formed between the tip and a shank of the
contact is degraded by the plating solution.
[0008] In the prior art, to extend longevity of the electrical
contacts, the contacting tip may be coated with a protective layer
of noble metals, such as platinum (Pt), indium (In), and the like,
or with a layer of an alloy of such metals. Generally, the
contacting tip is attached to a shank of the contact using
fasteners, such as screws and the like. Still, the electrical
contacts of the prior art have limited service life and variable
contact resistance, e.g., due to the thinness of the protective
coating, deterioration of the interface between the tip and shank
of the contact, and the like. The changes in the contact resistance
of the electrical contact result in the non-uniformity of the film
plated upon the substrate and may cause the ECP process to be
defective.
[0009] Therefore, there is a need in the art for an improved
electrical contact that provides an electrical bias to a substrate
during an electrochemical plating process.
SUMMARY OF THE INVENTION
[0010] The present invention is an apparatus for electrochemical
plating, comprising a support ring having a plurality of inwardly
directed shanks extended from an inner circumference of the ring,
wherein each of the shanks comprises a contacting tip brazed to the
distal end the shank.
[0011] In one embodiment, the contacting tip is formed from a
platinum/iridium alloy and is brazed to the shank using a
palladium/cobalt alloy. In another embodiment, the shanks are
formed from a metal, such as niobium (Nb), tantalum (Ta), and the
like, that oxidizes in a plating solution and produces a protective
oxide layer upon the shank.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0013] FIG. 1 is a schematic, partial perspective and sectional
view of an exemplary plating apparatus according to one application
of the present invention;
[0014] FIGS. 2A and 2B are, respectively, schematic,
cross-sectional and top plan views of an exemplary support ring
according to one embodiment of the present invention;
[0015] FIGS. 3-5 are schematic, cross-sectional views of contacts
of the support ring of FIGS. 2A, 2B according to embodiments of the
present invention; and
[0016] FIGS. 6A-6F illustrate an exemplary support ring at
different steps of fabricating the contacts of FIG. 3 according to
one embodiment of the present invention.
[0017] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
[0018] It is to be noted, however, that the appended drawings
illustrate only exemplary embodiments of this invention and are
therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
DETAILED DESCRIPTION
[0019] The present invention is an apparatus for providing an
electrical bias to a substrate in a processing system performing an
electrochemical plating process. The apparatus (e.g., support ring)
comprises a conductive annular body supplied with a plurality of
flexible current-carrying electrical contacts. The contacts are a
part of or conductively bonded to the support ring. Each contact
comprises a shank and a contacting tip that is brazed to the shank.
In operation, the contacting tips engage a peripheral portion of
the substrate. A plurality of such flexible electrical contacts may
be formed using, e.g., a pre-formed ring of the platinum/iridium
alloy that is brazed into the support ring and then machined to
define the individual contacts.
[0020] In one embodiment, the contacting tips are formed from an
alloy comprising at least two noble metals (e.g., a
platinum/iridium (Pt/in) alloy and the like). In another
embodiment, shanks are formed from a metal, such as niobium (Nb),
tantalum (Ta), and the like, that oxidizes in a plating solution
and produces a protective oxide layer upon the shank.
[0021] FIG. 1 is a schematic, partial perspective and sectional
view of an exemplary electrochemical plating (ECP) apparatus 100
utilizing a support ring 150 with flexible electrical contacts 156
according to one embodiment of the present invention. FIGS. 2A and
2B are, respectively, schematic, cross-sectional and top plan views
of the support ring 150. For best understanding of the invention,
the reader should refer simultaneously to FIGS. 1, 2A and 2B. The
images in FIGS. 1, 2A and 2B are simplified for illustrative
purposes and are not depicted to scale.
[0022] The ECP apparatus 100 generally includes a head assembly
102, a substrate securing assembly 110, and a plating bath assembly
161. The head assembly 102 is attached to a base 104 using a
support arm 106. In operation, the head assembly 102 defines the
position and movements of the substrate securing assembly 110 that
places a substrate 120 in a plating solution 165 for plating.
[0023] The plating bath assembly 161 includes an inner basin 167
that is contained within a larger outer basin 163, and an anode
assembly 170. A plating solution (electrolyte) 165 is supplied to
the inner basin 167 through an inlet 166 at a bottom 169 of the
basin. The inlet 166 is generally connected to a supply line to a
reservoir (not shown) for the plating solution 165. The outer basin
163 collects the plating solution from the inner basin 167 and
drains the solution through a fluid drain 168 back to the
reservoir.
[0024] The anode assembly 170 is positioned within a lower region
of the inner basin 167 and provided with a diffusion plate 172
(e.g., a porous ceramic member or the like) positioned above the
anode assembly 170. An electrical connection to the anode assembly
170 is provided using an anode contact 174 formed from a conductive
material that is insoluble in the plating solution (e.g., platinum,
platinum-coated steel, and the like).
[0025] The anode contact 174 extends through the bottom 169 and is
coupled to an anode terminal of an electrical power supply (not
shown), while a cathode terminal of the power supply is coupled to
a support ring 150 (see discussion in reference to the substrate
securing assembly 110 below). As such, the power supply provides an
electrical bias between the anode assembly 170 and the substrate
120. In operation (i.e., when a substrate 120 is immersed into the
plating solution), in response to the bias, an electrical ionic
current (represented by current flux lines 180) flows from the
anode assembly 170 to a plating surface 122 of the substrate 120.
The electrical ionic current deposits the plating material onto the
surface 122 and, as such, metallized the interconnecting features
on the substrate 120.
[0026] The substrate securing assembly 110 comprises a mounting
plate 146, a thrust plate 144, a seal plate 142, a housing 116, and
a support ring 150. The substrate securing assembly 110 may also
comprise an optional inflatable bladder assembly or o-ring (not
shown) that applies an evenly distributed downward force to a
non-plating surface 124 of a substrate 120. The mounting plate 146
and thrust plate 144 couple the substrate securing assembly 110 to
the head assembly 102.
[0027] The support ring 150 comprises a plurality of flexible
electrical contacts 156 that support the substrate 120. The
contacts 156 are disposed around an inner circumference of the
support ring 150 in a circular pattern and extend from the
circumference substantially radially inward. Each contact 156
comprising a shank 301 and a contacting tip 316. Generally, the
contacting tips 316 engage the substrate 120 around the edge of the
substrate. In the depicted embodiment, the shank 301 extends from a
midpoint 320 of the support ring 150 that is thicker than the
shank. In other embodiments, the shank 301 may be coplanar with
either an upper surface 322 or a bottom surface 324 of the support
ring 150.
[0028] The support ring 150 is further supplied with an optional
protective coating 130 to protect the contacts 156 from the plating
solution 165. The protective coating 130 may comprise at least one
layer of material that is chemically resistant to the plating
solution, e.g., polytetrafluoroethylene-based material, such as
AFLON.RTM., TEFZEL.RTM., KALREZ.RTM., VITON.RTM., and the like.
Such materials are available from AG Fluoropolymers USA, Inc.,
Pennsylvania and other suppliers. Alternatively, the housing 116
may also be provided with such protective coating (not shown).
[0029] Generally, the housing 116 is formed from an electrically
conductive material (e.g., stainless steel) coated with an
insulator. As such, the housing 116 may be used to couple the
support ring 150 to the power supply that facilitates the plating
process. Therefore, electrical power (e.g., in a form of a
controlled DC current) may be supplied to the contacts 156 by
coupling the power supply either to the housing 116 or directly to
the support ring 150. The contact 156 conducts an electrical
current from the support ring 150 to a seed layer deposited on the
substrate 120. Generally, the electrical current is supplied to the
contacts 156 cooperatively. Alternatively, the current may be
supplied to groups of the contacts, or to individual contacts that
are electrically isolated one from another.
[0030] The support ring 150 may further comprise scallops (not
shown) that are disposed along the bottom surface 324 of the ring
to increase uniformity of the flux towards the plating surface 122
of the substrate 120. Such scallops are described in commonly
assigned U.S. patent application Ser. No. 10/278,527, filed Oct.
22, 2002, which is incorporated herein by reference.
[0031] FIGS. 3-5 depict schematic, cross-sectional views of
exemplary embodiments of contacts of the support ring 150. For best
understanding of these embodiments, the reader should
simultaneously refer to FIGS. 3-5. The images in FIGS. 3-5 are
simplified for illustrative purposes and are not depicted to scale.
Those skilled in the art will understand that the scope of the
invention is not limited to such exemplary embodiments.
[0032] FIG. 3 depicts a flexible contact 350 where the contacting
tip 316 is brazed into a recess 314 at the distal end of the shank
301. Accordingly, FIG. 4 depicts a flexible contact 450 where the
contacting tip 316 is brazed to a sidewall 328 of the shank 301,
and FIG. 5 depicts a flexible contact 550 where the contacting tip
316 is supplied with a shoulder 330 that is brazed to a sidewall
502 of the shank 301.
[0033] In depicted embodiments, the support ring 150 and the shanks
301 are formed from a single piece of material, such as a stainless
steel (e.g., steel "302") and the like. In an alternative
embodiment, the stainless steel shanks 301 may be bonded to the
support ring 150 using, e.g., welding, brazing, and the like.
Further, the protective coating 130 is applied to protect, in
operation, the contacts and support ring from the plating solution.
In a further alternative embodiment, the shanks 301 may be formed
from such a metal (e.g., niobium (Nb), tantalum (Ta), and the like)
that will oxidize in the plating solution 165 and produce a
protective oxide layer (not shown) upon the shank. When the support
ring 150 comprised such oxidized shanks, the protective coating 130
is considered optional.
[0034] The shank 301 has a length and cross-sectional form factor
that are selected such that the contact 156 provides support and
electrical contact to the substrate 120, however, causes no damage
to the surface of the substrate. In one exemplary embodiment, a
length 306, thickness 308, and width 309 of the shank 301 are about
2 to 10 mm, 0.2 to 1 mm, and 0.5 to 10 mm, respectively. In this
embodiment, the contacting tip 316 has a length 310 (measured on a
contact surface 313), thickness 312 (measured from a surface 311 of
the shank 301 to the contact surface 313), and width 315 of about
0.05 to 1 mm, 0.1 to 1 mm, and 0.5 to 10 mm, respectively. In the
depicted embodiment, the width 309 of the shank 301 and the width
315 of the contacting tip 316 are the same, however, in other
embodiments, the widths 309 and 315 may be different.
[0035] A number of the contacts 156 may vary, for example,
according to a diameter and weight of the substrate 120. In one
particular embodiment, to support a 300 mm silicon (Si) wafer, the
support ring 150 and the shanks 301 were formed from a single piece
of stainless steel "302", and the support ring comprised 500
contacts 350. Each shank was 4 mm long, 0.8 mm thick, and 0.5 mm
wide and comprised a contacting tip that was 0.2 mm long, 0.4 mm
thick, and 0.5 mm wide.
[0036] The contacting tip 316 may be formed from an alloy that
comprises at least two noble metals (e.g., platinum/indium (Pt/in)
alloy having about 85% of platinum and about 15% of indium) and
then bonded to the shank 301. In one embodiment, the contacting tip
316 is brazed to the shank 301 using, e.g., a palladium/cobalt
(Pd/Co) alloy comprising about 65% of palladium and about 35% of
cobalt.
[0037] In operation, the plating solution may cause corrosion of a
contact, as well as corrosion and electrical degradation of the
contacting tip and interface between the tip and shank. However, in
the contacts 156, the entire contacting tip 316 is formed from a
chemically resistant alloy and then brazed to the shank 301 using
also a chemically resistant alloy. Brazing facilitates a high
quality mechanical and electrical interface between the tip and
shank. Additionally, in embodiment shown in FIG. 5, a position of a
brazed interface is moved away from a contact surface 313 of the
contacting tip 316 and, as such, from the plating solution. In each
embodiment, the shank is covered with the protective coating 130,
as discussed above. In an alternative embodiment, the shank 301 may
be formed from such a metal (e.g., tantalum or niobium) that, when
exposed to the plating solution, develops a protective oxide layer
on the shank in lieu of using a separate protective coating 130. As
such, in either embodiment, the contacts 156 provide greater
longevity (service life), reliability, and performance (e.g.,
stability ands low value of electrical resistance) than other
contacts used in the ECP apparatuses.
[0038] FIGS. 6A-6F depict a support ring at different steps of
fabricating the contacts of FIG. 3 according to one embodiment of
the present invention. In operation, uniform contact resistance
promotes uniform plating thickness. As such, a process of
fabricating the contacts intends to ensure that the contacts being
formed have uniform contact resistance. The views in FIGS. 6B-6E
are taken along a centerline 6-6 in FIG. 6A. For best understanding
of this embodiment of the invention, the reader should
simultaneously refer to FIGS. 6A-6F. The images in FIGS. 6A-6F are
simplified for illustrative purposes and are not depicted to
scale.
[0039] FIG. 6A depicts a top plan view of a support ring 450 before
the process of fabricating the contacts begins. The support ring
450 comprises an outer region 402 and inner region 404. In the
depicted embodiment, the regions 402 and 404 are formed from an
annular piece of a conductive material, e.g., stainless steel
"302". The outer region 402 is thicker than the inner region 404.
In one embodiment, the inner region 404 has a thickness 412 that is
equal to the thickness of a contact 428 being formed, while a width
414 of the inner region 404 is generally greater than a length 411
of the contact (discussed in reference to FIG. 6E below).
Generally, the inner region 404 is disposed at a midpoint 406 of
the outer region 402 (discussed in reference to FIG. 6B below).
Alternatively, the inner region 404 may be coplanar (not shown)
with either upper (408) or bottom (410) surface of the outer region
402.
[0040] FIG. 6B depicts a portion of the support ring 450 after a
groove 416 is formed in the distal portion of the inner region 404.
In one embodiment, the groove 416 has a depth 418 of about 0.3 to
0.1 mm and a width 420 of about 0.5 to 10 mm. Generally, the groove
416 is adapted to receive a pre-formed ring 426 (discussed in
reference to FIG. 6D below).
[0041] FIG. 6C depicts a schematic, cross-sectional view of a
portion of the support ring 450 having a brazing material 422
placed and melted in the groove 416. A melting temperature of the
brazing material is below melting temperatures of materials of the
support ring 450 and contacting tip (discussed in reference to FIG.
6D below). When melted, the brazing material forms a layer 424 in
the groove 416. In one embodiment, the brazing material comprises a
palladium/cobalt alloy having about 65% of palladium and about 35%
of cobalt. Such brazing material wets stainless steel "302" (inner
region 404) and platinum/indium alloy (ring 426) and possesses high
corrosion resistance to the plating solution, high purity, and a
low vapor pressure at the brazing temperature. The palladium/cobalt
alloy has a melting temperature of approximately 1220 degrees
Celsius that is substantially below the melting temperature of the
stainless steel "302" (approximately 1620 degrees Celsius).
[0042] FIG. 6D depicts a schematic, cross-sectional view of a
portion of the support ring 450 after the pre-formed ring 426 is
positioned in the groove 416 on a layer 424 of melted brazing
material 472. In one embodiment, the ring 426 fits into the groove
416. The pre-formed ring 426 comprises, for example, a
platinum/indium alloy having about 85% of platinum and about 15% of
indium. Such alloy has a melting temperature of approximately 2230
degrees Celsius.
[0043] When heated above its melting temperature (i.e., above of
approximately 1220 degrees Celsius), the platinum/indium alloy wets
a bottom surface 415 of the groove 416 and a bottom surface 428 of
the pre-formed ring 426. In the depicted embodiment, a width 440 of
the pre-formed ring 426 is selected to fit into the groove 416 and
a height 444 of the ring is selected such that a height 442 of an
exposed portion of the ring is equal to that of the contacting tip
425 (discussed in reference to FIG. 6E below).
[0044] After the platinum/indium alloy is then cooled below its
melting temperature, the alloy bonds the pre-formed ring 426 to the
groove 426. The brazing process develops a high strength mechanical
and high quality electrical interface between the pre-formed ring
426 and inner region 402. After brazing the pre-formed ring 426
into the groove 416, an extending inwardly portion of the inner
region 404 (portion 430) is generally machined off to prevent, in
operation, shielding of the edge of the substrate from the plating
solution. Alternatively, the annular portion 430 may be removed
using an EDM process (discussed in reference to FIGS. 6E and 6F
below). In a further embodiment, the pre-formed ring 426 may also
be machined, e.g., the edges and upper surface of the ring may be
rounded or polished, and the like.
[0045] FIGS. 6E and 6F depict, respectively, schematic,
cross-sectional and top plan views of a portion of the support ring
450 after a contact 428 is formed in the inner region 404. The
contact 428 may be formed using, for example, an electric discharge
machining (EDM) technique and the like. The EDM process removes
portions 446, 448, and the like of the inner region 404 between the
adjacent contacts (e.g., contacts 428a, 428b, and 428c). In a
further embodiment, the EDM process provides surface finishing to
the contacts and/or contacting tips.
[0046] After the EDM process, the remaining portions of the inner
region 404 and ring 426 form shanks 432 (e.g., shanks 432a, 432b,
and 432c) and contacting tips 425 (e.g., contact tips 425a, 425b,
425c). The EDM process continues until all contacts 428 of the
support ring 450 are fabricated as described above.
[0047] Those skilled in the art will appreciate that the contacts
shown in FIGS. 4 and 5 may be fabricated using techniques that are
similar to the described above in reference to the contact of FIG.
3. Similarly, to fabricate the contacts 428 having the tantalum or
niobium shanks 432, the inner portion 404 of the support ring 450
may be formed from tantalum or niobium, respectively.
[0048] While foregoing is directed to the illustrative embodiment
of the present invention, other and further embodiments of the
invention may be devised without departing from the basic scope
thereof, and the scope thereof is determined by the claims that
follow.
* * * * *