U.S. patent application number 09/841625 was filed with the patent office on 2002-10-31 for nickel-titanium sputter target alloy.
Invention is credited to Gilman, Paul S., Hunt, Thomas J., Koenigsmann, Holger J..
Application Number | 20020159911 09/841625 |
Document ID | / |
Family ID | 25285327 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020159911 |
Kind Code |
A1 |
Koenigsmann, Holger J. ; et
al. |
October 31, 2002 |
NICKEL-TITANIUM SPUTTER TARGET ALLOY
Abstract
The sputter target deposits nickel from a binary alloy. The
binary alloy contains, by weight percent, 9 to 15 titanium and the
balance nickel and incidental impurities. The binary alloy has, by
weight percent, 35 to 50 TiNi.sub.3 needle-like intermetallic phase
and balance .alpha.-nickel phase. The TiNi.sub.3 needle-like
intermetallic phase and .alpha.-nickel phase are formed from a
eutectic decomposition. The .alpha.-nickel phase having a grain
size between 50 and 180 .mu.m. The binary alloy has a Curie
temperature of less than or equal to a temperature of 25.degree. C.
and exhibits paramagnetic properties at temperatures of 25.degree.
C. or lower.
Inventors: |
Koenigsmann, Holger J.;
(Congers, NY) ; Gilman, Paul S.; (Suffern, NY)
; Hunt, Thomas J.; (Peekskill, NY) |
Correspondence
Address: |
PRAXAIR, INC.
LAW DEPARTMENT - M1 557
39 OLD RIDGEBURY ROAD
DANBURY
CT
06810-5113
US
|
Family ID: |
25285327 |
Appl. No.: |
09/841625 |
Filed: |
April 25, 2001 |
Current U.S.
Class: |
420/451 ;
148/409; 148/556 |
Current CPC
Class: |
C23C 14/3414 20130101;
C22C 19/03 20130101 |
Class at
Publication: |
420/451 ;
148/556; 148/409 |
International
Class: |
C22C 019/03 |
Claims
I claim:
1. A sputter target for depositing nickel comprising a binary alloy
consisting essentially of, by weight percent, about 9 to 15
titanium and the balance nickel and incidental impurities, the
binary alloy having, by weight percent, about 35 to 50 TiNi.sub.3
needle-like intermetallic phase and balance .alpha.-nickel phase,
the TiNi.sub.3 needle-like intermetallic phase and .alpha.-nickel
phase being formed from a eutectic decomposition, the
.alpha.-nickel phase having a grain size between about 50 and 180
.mu.m and the binary alloy having a Curie temperature of less than
or equal to a temperature of about 25.degree. C. and exhibits
paramagnetic properties at temperatures of about 25.degree. C. or
lower.
2. The sputter target of claim 1, wherein the binary alloy contains
about 9.5 to 12 titanium.
3. The sputter target of claim 1, wherein the .alpha.-nickel phase
has a grain size of about 70 to 100 microns.
4. The sputter target of claim 1, wherein the .alpha.-nickel phase
contains between about 10 and 40 percent of each of the
crystallographic orientations (111), (200), (220) and (311).
5. A method of forming a binary nickel-titanium sputter target
blank comprising the steps of: casting a binary alloy into an
ingot, the ingot consisting essentially of, by weight percent,
about 9 to 15 titanium and the balance nickel and incidental
impurities, the binary alloy having, by weight percent about 35 to
50 TiNi.sub.3 intermetallic phase and balance .alpha.-nickel phase;
dissolving the TiNi.sub.3 intermetallic phase into a single
.alpha.-nickel phase at a temperature of at least about
1000.degree. C.; hot working the ingot at a temperature between
about 1000.degree. C. and the ingot melting temperature to form the
target blank, to reduce thickness of the ingot by at least fifty
percent and to reduce grain size of the .alpha.-nickel phase; and
cooling the target blank to precipitate needle-like TiNi.sub.2
intermetallic phase in an .alpha.-nickel phase matrix, the grain
size of the .alpha.-nickel phase matrix being between about 50 and
180 .mu.m and the binary alloy having a Curie temperature of less
than or equal to a temperature of about 25.degree. C. and exhibits
paramagnetic properties at temperatures of about 25.degree. C. or
lower.
6. The method of claim 5, wherein the nickel and titanium are
vacuum melted and cast under an atmosphere pressure of less than or
equal to about 5 mTorr.
7. The method of claim 5, wherein hot working occurs at a
temperature in the range of about 1050 to 1150.degree. C.
8. A method of forming a binary nickel-titanium sputter target
comprising the steps of: casting a binary alloy into an ingot, the
ingot consisting essentially of, by weight percent, about 9 to 15
titanium and the balance nickel and incidental impurities, the
binary alloy having, by weight percent, about 35 to 50 TiNi.sub.3
intermetallic phase and balance .alpha.-nickel phase; dissolving
the TiNi.sub.3 intermetallic phase into a single .alpha.-nickel
phase at a temperature of at least about 1000.degree. C.; hot
rolling the ingot at a temperature between about 1050 and
1150.degree. C. to form the target blank, to reduce thickness of
the ingot by at least fifty percent and to reduce grain size of the
.alpha.-nickel phase grain size; maintaining temperature of the
ingot at a temperature of between about 1050 and 1150.degree. C.
during the rolling; and cooling the target blank to precipitate
needle-like TiNi.sub.3 intermetallic phase in an .alpha.-nickel
phase matrix, the grain size of the .alpha.-nickel phase matrix
being between about 50 and 180 .mu.m and the binary alloy having a
Curie temperature of less than or equal to temperatures of about
25.degree. C. and exhibits paramagnetic properties at temperatures
of about 25.degree. C. or lower.
9. The method of claim 8, wherein the nickel and titanium are
vacuum melted and cast under an atmosphere pressure of about 5
mTorr or less.
10. The process of claim 8 wherein the hot rolling includes
multiple passes of less than about 1.3 mm reduction.
11. The process of claim 10 wherein the reduction per pass is
between about 0.5 and 1 mm per pass.
12. The process of claim 10 wherein the maintaining of the
temperature consists of reheating the ingot to the temperature
between about 1050 and 1150.degree. C. before each hot rolling
pass.
13. The method of claim 8 wherein the hot rolling occurs in a
single direction.
14. The method of claim 8 including the additional step of
machining the target blank to produce a sputter target.
Description
FIELD OF THE INVENTION
[0001] This invention relates to nickel-titanium alloy sputter
targets for use with magnetron sputtering systems to deposit
nickel.
BACKGROUND OF THE INVENTION
[0002] With magnetron sputtering, magnets are located behind the
cathode target in a manner as to cause closed magnetic field loops
to cut through the cathode. A portion of the magnetic field loop is
located adjacent the front face of the cathode. The combination of
magnetic field and electric field causes electrons to spiral in
long confined paths giving rise to a very dense plasma immediately
adjacent to the face of the target material. This dense plasma
facilitates an increased yield of material sputtered from the
target.
[0003] One limitation to magnetron sputtering, however, is that
this technique is not amenable to the deposition of ferromagnetic
materials. A target of ferromagnetic material acts as a shunt and
prevents magnetic field lines from cutting through the target and
being located, as required, in front of the target. Therefore,
materials such as iron and nickel cannot generally be magnetron
sputtered. In order to light and maintain a plasma during the
sputtering of ferromagnetic materials, such as pure nickel, it
usually is necessary to limit the thickness of the nickel target to
usually less than 3 mm. This thin target, however, provides only
limited source material and thereby reduces the useful life of the
target.
[0004] Some limited success in the magnetron sputtering of magnetic
nickel has been achieved by using specially fabricated targets in
which a thin layer of the ferromagnetic material plates onto a
non-ferromagnetic base material. The layer is thin enough so as not
to completely shunt the magnetic field, but again, the target is
now very expensive and the source has a severely limited lifetime
due to the reduced amount of source material.
[0005] The Curie temperature varies over a wide range for various
materials. By properly forming an alloy of the ferromagnetic nickel
with one or more other elements, the Curie temperature can be
reduced from that of pure nickel to a temperature lower than the
desired sputtering temperature. For example, Nanis, in U.S. Pat.
No. 5,405,646, disclose binary systems of platinum, palladium,
molybdenum, vanadium, silicon, titanium, chromium, aluminum,
antimony, manganese and zinc. Similarly, Wilson, in U.S. Pat. No.
4,159,909, discloses the use of platinum, copper and tin to render
nickel paramagnetic at room temperature. As far as known, targets
manufactured from these alloys have not received widespread
acceptance in the marketplace.
[0006] In addition, adding about 7 weight percent vanadium to
nickel lowers the Curie temperature for obtaining paramagnetic
properties at room temperature. The Curie temperature is the lowest
temperature before spontaneous magnetization occurs. The Curie
temperature separates the disordered paramagnetic phase from the
ordered ferromagnetic phase. Stated in another way, at temperatures
below a material's Curie temperature, that material is strongly
magnetic or ferromagnetic. For temperatures at and above the Curie
temperature, the magnetic properties disappear.
[0007] With its shift in Curie temperature, Ni-7 V (wt. %) has
become the standard composition for use with direct current
magnetron sputtering systems to deposit magnetic nickel.
Nickel/vanadium (Ni/V) serves as a barrier/adhesion layer for
under-bump metals to support flip chips, or C4 (collapsed,
controlled, chip connection) assemblies. The flip chips allow high
I/O counts, good speed and electrical performance, thermal
management, low profile, and the use of standard surface mount and
production lines for assembly. Unfortunately, Ni/V target materials
are susceptible to high impurity concentrations and to cracking
during fabrication of the target blanks. Moreover, Ni/V films can
suffer problems during subsequent etching procedures.
[0008] Because magnetic nickel is a highly desirable thin film for
many microcircuit and semiconductor device applications, there is a
need to develop a method for sputtering high purity magnetic nickel
that does not suffer the above disadvantages.
SUMMARY OF THE INVENTION
[0009] The sputter target deposits nickel from a binary alloy. The
binary alloy contains, by weight percent, 9 to 15 titanium and the
balance nickel and incidental impurities. The binary alloy has, by
weight percent, 35 to 50 TiNi.sub.3 needle-like intermetallic phase
and balance .alpha.-nickel phase. The TiNi.sub.3 needle-like
intermetallic phase and .alpha.-nickel phase are formed from a
eutectic decomposition. The .alpha.-nickel phase has a grain size
between 50 and 180 .mu.m. The binary alloy has a Curie temperature
of less than or equal to a temperature of 25.degree. C. and
exhibits paramagnetic properties at temperatures of 25.degree. C.
or lower.
[0010] The method forms a binary nickel-titanium sputter target
blank by first casting a binary alloy of the above composition into
an ingot. The binary alloy has, by weight percent, 35 to 50
TiNi.sub.3 intermetallic phase and balance .alpha.-nickel phase.
Then, dissolving the TiNi.sub.3 intermetallic phase into a single
.alpha.-nickel phase at a temperature of at least 1000.degree. C.
prepares the alloy for hot working. Hot working the ingot at a
temperature between 1000.degree. C. and the ingot melting
temperature forms the target blank, reduces the thickness by at
least fifty percent and reduces the .alpha.-nickel phase grain size
to between 50 and 180 .mu.m. Finally, cooling the target blank
precipitates a needle-like TiNi.sub.3 intermetallic phase in a
.alpha.-nickel phase matrix to form the final microstructure.
DETAILED DESCRIPTION
[0011] The present invention provides the specific alloying
concentration for this binary alloy with a method of preparing
targets that facilitates magnetron sputtering of nickel. Magnetron
sputtering of nickel can be accomplished by using a binary nickel
alloy target material having a properly selected titanium alloying
concentration in order that the alloy has a Curie temperature at or
below room temperature (25.degree. C.), thereby making the material
paramagnetic at room temperature.
[0012] A series of incremental tests determined that about 9 weight
percent was the minimum amount of titanium necessary to make the
alloy paramagnetic at room temperature. For purposes of this
specification, all composition's units are expressed in weight
percent, unless specifically noted otherwise. This alloy allows the
thickness of the target to be increased significantly as compared
to a pure nickel target, thereby decreasing the sputtering cost per
wafer. With the lower Curie temperature, the alloy is
non-ferromagnetic at the sputtering temperature, and is therefore
amenable to magnetron sputtering.
[0013] Alloying about 9 to 15 weight percent titanium with the
balance nickel and incidental impurities produces a sputtering
target with paramagnetic properties at room temperature.
Advantageously, the alloy contains about 9.5 to 12 weight percent
titanium. Most advantageously, the alloy has a nominal composition
of about ten weight percent. In addition, advantageously, limiting
impurities to less than 0.1 percent provides commercially pure
properties. Most advantageously, the target contains less than 0.01
percent impurities.
[0014] The melting of the nickel and titanium source material
advantageously occurs under a vacuum or protective atmosphere. Most
advantageously, a vacuum furnace, such as a semi-continuous vacuum
melter (SCVM) can melt the source material in a steel, graphite or
ceramic mold. Advantageously, the vacuum is about
1.0.times.10.sup.-4 mTorr to about 10.0 mTorr.
[0015] Advantageously, the binary alloy casting occurs under an
atmosphere pressure of less than about 5 mTorr. For example, vacuum
atmospheres having a pressure of about 1 mTorr to about 5 mTorr are
effective for limiting uncontrolled oxidation of the melt. In
addition, pouring into molds having a low pressure protective
atmosphere is another procedure for limiting oxidation. To maintain
low impurities, it is important to cast the alloy under a
controlled atmosphere such as under a protective argon, helium or
other Group VIII gas or combination of gases. For example, a low
pressure argon atmosphere of about 0.1 to about 0.7 atm, such as
about 0.3 atm has been found to provide adequate protection to the
melt and the ingot upon pouring.
[0016] After the molten alloy is cast into a mold, the alloy cools
and solidifies into an "as cast" structure of TiNi.sub.3
intermetallic phase and balance .alpha.-nickel phase. This as-cast
structure is unacceptable for sputtering targets.
[0017] To process the alloy, the alloy is first heated for a
sufficient period of time and temperature to dissolve the
TiNi.sub.3 intermetallic phase into an .alpha.-nickel phase. If the
TiNi.sub.3 intermetallic phase remains during deformation, the
ingot cracks. Temperatures between about 1000.degree. C. and
melting are sufficient to dissolve the intermetallic. Most
advantageously, a furnace heats the alloy to a temperature between
about 1050 and 1150.degree. C. In addition, the process
advantageously heats the ingot for at least one hour and most
advantageously at least two hours, to ensure the dissolution of the
intermetallic phase.
[0018] After dissolving the intermetallic phase, hot working the
ingot with at least a fifty percent reduction in thickness breaks
the .alpha.-nickel grains into a suitable size. Advantageously, hot
working occurs at temperatures between about 1000.degree. C. and
melting to prevent cracking. Most advantageously, the process hot
works the ingot at a temperature between about 1050 and
1150.degree. C.
[0019] Advantageously, the hot working consists of hot rolling the
ingot into a target blank. Most advantageously, the hot rolling is
in a single direction to lower the likelihood of cracking. In
addition, maintaining the ingot at a temperature between about
1000.degree. C. and melting during rolling also serves to hold the
intermetallic phase in solution and reduce the likelihood of
cracking during rolling. Most advantageously, the hot rolling
includes reheating between each rolling pass to maintain
temperature--during experimentation, reheating between only every
other pass resulted in cracking.
[0020] Advantageously, the process relies upon multiple passes with
each hot rolling pass being less than about 0.05 inch (1.3 mm). For
example, multiple passes of about 0.02-0.05 inch (0.5 to 1.3 mm)
are effective. Most advantageously, the reduction per pass is
between about 0.5 and 1 mm. In addition, having at least ten
reduction passes within this range ensures the production of
uniform .alpha.-nickel grains.
[0021] After hot working, cooling the target blank precipitates
about 35 to 50 weight percent needle-like TiNi.sub.3 intermetallic
phase in an .alpha.-nickel phase matrix. Advantageously, the alloy
contains about 35 to 45 weight percent needle-like TiNi.sub.3
intermetallic phase. Most advantageously, the alloy contains about
38 to 42 weight percent needle-like TiNi.sub.3 intermetallic phase.
The .alpha.-nickel phase grain size is between about 50 and 180
.mu.m. Most advantageously, the grain size is between about 70 and
100 .mu.m. In addition to this relatively small grain size, the
alloy advantageously contains relatively equiaxed grains of
.alpha.-nickel phase. Most advantageously, the .alpha.-nickel phase
has between 10 and 40 percent of each of the following four
crystallographic orientations: (111), (200), (220), and (311).
After cooling, machining the target blank produces a sputter target
having excellent sputtering characteristics.
EXAMPLE
[0022] First, vacuum melting 10 weight percent titanium balance
nickel at a pressure of 5.0 mTorr in a zirconia crucible purified
the alloy. Then casting the melt into a 5.5.times.15.5.times.1.5
inch (14.times.39.times.3.8 cm) graphite ingot mold produced the
binary nickel/titanium alloy target. Pouring in a protective argon
atmosphere, at a pressure of 0.3 atm protected the alloy from
oxidation.
[0023] After solidification and cooling to room temperature, the
cast ingot was removed. Then heating the ingot to a temperature of
1100.degree. C. for four hours prepared the ingot for hot rolling.
Hot rolling the ingot at a temperature of 1100.degree. C. from 1.5
inch (3.8 cm) thickness down to 0.5 inches (1.3 cm) converted the
as cast structure to a grain size of 90 .mu.m. Specifically,
rolling the ingot in the short direction with a reduction of 0.04
inches (0.10 cm) per pass formed the target blank. Reheating the
ingot to 1100.degree. C. after each pass maintained the
intermetallic phase in solution and prevented cracking. The target
blank contained 14, 32, 35 and 19 percent of the (111), (200),
(220) and (311) crystallographic orientations, respectively. Then
machining the rolled blank produced a finished target having a
Curie temperature below 25.degree. C.
[0024] Sputter targets fabricated from the binary nickel alloys of
the present invention have a Curie temperature that is at or below
room temperature. The sputter targets of the present invention can
be magnetron sputtered at or above room temperature, and the binary
alloy exhibits paramagnetic properties at room temperature. Thus,
nickel-titanium can be deposited from a sputter target without
complete shunting of the magnetic field. The targets of the present
invention can be made with greater thicknesses than pure nickel
sputter targets, thereby providing a greater target life. Methods
for fabricating the binary alloy targets also allow for a
crack-free sputter target with a small-uniform grain size to be
produced at relatively low cost. While exemplary methods of
fabrication have been described for each binary alloy, it should be
understood that binary alloy targets of the present invention may
be fabricated by other now known or hereafter developed techniques,
which are within the ordinary skill of one in the art.
[0025] While the present invention has been illustrated by the
description of embodiments thereof, and while the embodiments have
been described in considerable detail, they are not intended to
restrict or in any way limit the scope of the appended claims to
such detail. Additional advantages and modifications will readily
appear to those skilled in the art. The invention in its broader
aspects is therefore not limited to the specific details,
representative apparatus and method and illustrative examples shown
and described. Accordingly, departures may be made from such
details without departing from the scope or spirit of applicants'
general inventive concept.
* * * * *