U.S. patent application number 11/880847 was filed with the patent office on 2009-01-29 for ultra-high purity nipt alloys and sputtering targets comprising same.
This patent application is currently assigned to Heraeus, Inc.. Invention is credited to Carl Derrington, Jun Hui, Bernd Kunkel, ShinHwa Li, David Long.
Application Number | 20090028744 11/880847 |
Document ID | / |
Family ID | 40020262 |
Filed Date | 2009-01-29 |
United States Patent
Application |
20090028744 |
Kind Code |
A1 |
Hui; Jun ; et al. |
January 29, 2009 |
Ultra-high purity NiPt alloys and sputtering targets comprising
same
Abstract
A method of making a NiPt alloy having an ultra-high purity of
at least about 4N5 and suitable for use as a sputtering target,
comprises steps of: heating predetermined amounts of lesser purity
Ni and Pt at an elevated temperature in a crucible to form a NiPt
alloy melt, the crucible being composed of a material which is
inert to the melt at the elevated temperature; and transferring the
melt to a mold having a cavity with a surface coated with a release
agent which does not contaminate the melt with impurity elements.
The resultant NiPt alloy has a very low concentration of impurity
elements and is subjected to cross-directional hot rolling for
reducing thickness and grain size.
Inventors: |
Hui; Jun; (Maricopa, AZ)
; Li; ShinHwa; (Chandler, AZ) ; Long; David;
(Chandler, AZ) ; Derrington; Carl; (Tempe, AZ)
; Kunkel; Bernd; (Phoenix, AZ) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
18191 VON KARMAN AVE., SUITE 500
IRVINE
CA
92612-7108
US
|
Assignee: |
Heraeus, Inc.
Chandler
AZ
|
Family ID: |
40020262 |
Appl. No.: |
11/880847 |
Filed: |
July 23, 2007 |
Current U.S.
Class: |
420/456 ; 164/72;
420/468 |
Current CPC
Class: |
C22C 1/02 20130101; C22C
5/04 20130101; C22C 30/00 20130101; C22F 1/14 20130101; Y02P 10/25
20151101; C22C 19/03 20130101; C22C 1/03 20130101; C22F 1/10
20130101; C22B 9/003 20130101; C23C 14/3414 20130101; Y02P 10/253
20151101; C22B 23/06 20130101; C22C 1/023 20130101 |
Class at
Publication: |
420/456 ; 164/72;
420/468 |
International
Class: |
C22C 19/03 20060101
C22C019/03; B22C 3/00 20060101 B22C003/00; C22C 5/04 20060101
C22C005/04 |
Claims
1. A method of making an ultra-high purity NiPt alloy of at least
4N5 purity, comprising steps of: (a) heating predetermined amounts
of lesser purity Ni and Pt at an elevated temperature in a crucible
to form a NiPt alloy melt, said crucible being composed of a
material which is inert to said melt at said elevated temperature;
and (b) transferring said melt to a mold having a cavity with a
surface coated with a release agent which does not contaminate said
melt with impurity elements.
2. The method according to claim 1, wherein: step (a) comprises
heating at a temperature from about 1455 to about 1650.degree. C.
to form said NiPt alloy melt.
3. The method according to claim 1, wherein: step (a) comprises
heating predetermined amounts of lesser purity Ni and Pt in Ni:Pt
atomic ratios ranging from about 99:1 to about 20:80.
4. The method according to claim 1, wherein: step (a) comprises
vacuum induction melting (VIM).
5. The method according to claim 1, wherein: step (a) comprises
forming said NiPt alloy melt in a crucible composed of yttria
stabilized zirconia (YSZ).
6. The method according to claim 1, wherein: step (a) comprises
purifying said NiPt alloy melt by removing impurity-containing slag
which forms at an upper surface of said melt.
7. The method according to claim 1, wherein: step (a) comprises
purifying said NiPt alloy melt by evaporation of impurities from
said melt.
8. The method according to claim 1, wherein: step (b) comprises
directly transferring said melt to said mold without use of a
tundish.
9. The method according to claim 1, wherein: step (b) comprises
directly transferring said NiPt alloy melt to a mold composed of
graphite and having a cavity coated with Al.sub.2O.sub.3 release
agent.
10. The method according to claim 1, further comprising steps of:
(c) removing an ingot of solidified NiPt alloy from said mold; and
(d) subjecting said ingot to thermo-mechanical rolling for reducing
thickness and grain size of said NiPt alloy.
11. The method according to claim 10, wherein: step (d) comprises
alternate rolling in straight and cross directions.
12. The method according to claim 11, wherein: step (d) comprises
re-heating said NiPt alloy during said straight direction
rolling.
13. A 4N5 ultra-high purity NiPt alloy fabricated by the process
according to claim 12.
14. A 4N5 ultra-high purity NiPt alloy having a Si concentration of
<1 ppm, a B concentration of <0.2 ppm, a Ca concentration of
<0.05 ppm, an Al concentration of <0.1 ppm, and a total
impurity concentration of <50 ppm.
15. The NiPt alloy as in claim 14, having a Ni:Pt atomic ratio in
the range from about 99:1 to about 20:80.
16. The NiPt alloy as in claim 14, having with a grain size from
about 200 to about 300 .mu.m.
17. A sputtering target comprising the 4N5 ultra-high purity NiPt
alloy of claim 16.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates generally to ultra-high
purity NiPt alloys, their manufacturing methodology, and to
sputtering targets comprising same. The ultra-high purity NiPt
sputtering targets afforded by the present disclosure are
especially useful in the manufacture of high integration density
semiconductor devices.
BACKGROUND OF THE DISCLOSURE
[0002] Development of new technologies for use in the semiconductor
integrated circuit (IC) industry is driven by "Moore's Law", i.e.,
which postulates doubling of the areal density of transistors
roughly every 18 months, with the resultant size reduction of
electronic devices leading to lower cost with increased
profitability, more functions, and faster device speeds. Currently,
manufacturing technology is transitioning from 90 m feature sizes,
e.g., transistor gate length and pitch-to-pitch line width, to 65
nm and lower. The reduction in feature size necessitates
development of new materials, e.g., semiconductors and materials
used in transistor formation and processing.
[0003] Recently, there has been much interest in various approaches
with the aim or goal of developing new semiconductor materials
which provide increased speeds of electron and hole flow
therethrough, thereby permitting fabrication of semiconductor
devices, such as integrated circuit (IC) devices with higher
operating speeds, enhanced performance characteristics, and lower
power consumption. One such material which shows promise in
attaining the goal of higher device operating speeds is termed
"strained silicon".
[0004] According to this approach, a very thin, tensilely strained,
crystalline silicon (Si) layer is grown on a relaxed, graded
composition SiGe buffer layer several microns thick, which SiGe
buffer layer in turn is formed on a suitable crystalline substrate,
e.g., a Si wafer or a silicon-on-insulator (SOI) wafer. Strained Si
technology is based upon the tendency of the Si atoms, when
deposited on the SiGe buffer layer, to align with the greater
lattice constant (spacing) of the Si and Ge atoms therein (relative
to pure Si). As a consequence of the Si atoms being deposited on a
substrate (SiGe) comprised of atoms which are spaced further apart,
they "stretch" to align with the underlying Si and Ge atoms,
thereby "stretching" or tensilely straining the deposited Si layer.
Electrons and holes in such strained Si layers have greater
mobility than in conventional, relaxed Si layers with smaller
inter-atom spacings, i.e., there is less resistance to electron
and/or hole flow. For example, electron flow in strained Si may be
up to about 70% faster compared to electron flow in conventional
Si.
[0005] Transistor devices (e.g., CMOS devices) formed with such
strained Si layers exhibit operating speeds which are substantially
faster than those of equivalent devices formed with conventional
Si. However, stable, low resistivity contact materials are not
currently available for use with the strained lattice semiconductor
material of the transistor source and drain regions. Specifically,
Co-based and Ti-based silicides typically utilized as contacts with
90 nm (and above) feature sizes are not suitable for use with
feature sizes of 65 nm and below.
[0006] As a consequence of the unsuitability of Co-based and
Ti-based silicides, NiPt-silicide contact technology has been
developed for use in fabricating transistors with feature sizes of
65 nm and below formed on strained lattice semiconductor
substrates. However, currently available practices/technologies are
incapable of providing the ultra-high purity NiPt alloy materials
necessary for use as sputtering targets utilized for NiPt
deposition in the manufacture of high performance, strained
semiconductor IC devices with feature sizes of 65 nm and below.
[0007] Another recent approach for transitioning from 90 nm feature
sizes to 65 nm and lower, e.g., 45 nm and lower, involves use of
high k dielectric gate oxide materials and metal-silicide contact
metallization, such as hafnium oxide-based high k dielectric
materials and NiSi contact metallization. In this regard, NiSi
offers several advantages vis-a-vis earlier metal silicides such as
CoSi.sub.2 and TiSi.sub.2, including lower resistivities, reduced
Si consumption during silicidation, and formation at lower process
temperatures. A currently promising fabrication scheme utilizing
NiSi, termed "FUSI" (short for "fully silicided" gate), involves
performing source/drain ("S/D") silicidation prior to gate
patterning and silicidation. However, the use of NiSi in FUSI and
other high k gate oxide process schemes for feature size reduction
poses challenges arising from poor thermal stability at process
integration temperatures and high diffusivity.
[0008] In view of the foregoing, there exists a need for improved
Ni-based materials suitable for use as silicided gate contact
metallization in FUSI and other fabrication schemes for the next
generation of semiconductor IC devices, as well as ultra-high
purity NiPt alloy materials suitable for use as sputtering targets
in the manufacture of high performance, strained semiconductor IC
devices with feature sizes of 65 nm and below, and improved
manufacturing technology therefor.
SUMMARY OF THE DISCLOSURE
[0009] An advantage of the present disclosure is a method of making
ultra-high purity NiPt alloys.
[0010] Another advantage of the present disclosure is ultra-high
purity NiPt alloys.
[0011] Yet another advantage of the present invention is sputtering
targets comprising ultra-high purity NiPt alloys with uniform grain
size distribution.
[0012] Additional advantages and features of the present disclosure
will be set forth in the disclosure which follows and in part will
become apparent to those having ordinary skill in the art upon
examination of the following or may be learned from the practice of
the present disclosure. the advantages may be realized and obtained
as particularly pointed out in the appended claims.
[0013] According to an aspect of the present disclosure, the
foregoing and other advantages are achieved in part by an improved
method of making a NiPt alloy having an ultra-high purity of at
least about 4N5, comprising steps of:
[0014] (a) heating predetermined amounts of lesser purity Ni and Pt
at an elevated temperature in a crucible to form a NiPt alloy melt,
the crucible being composed of a material which is inert to the
melt at the elevated temperature; and
[0015] (b) transferring the melt to a mold having a cavity with a
surface coated with a release agent which does not contaminate the
melt with impurity elements.
[0016] According to embodiments of the present disclosure, step (a)
comprises heating at a temperature from about 1455 to about
1650.degree. C. to form the NiPt alloy melt; heating predetermined
amounts of lesser purity Ni and Pt in Ni:Pt atomic ratios ranging
from about 99:1 to about 20:80; forming the melt by a process
comprising vacuum induction melting (VIM) in a crucible composed of
yttria stabilized zirconia (YSZ); and purifying the NiPt alloy melt
by removing impurity-containing slag which forms at an upper
surface of the melt and/or by evaporation of impurities from the
melt.
[0017] In accordance with embodiments of the present disclosure,
step (b) comprises directly transferring said melt to the mold
without use of a tundish; the mold being composed of graphite and
having a cavity coated with Al.sub.2O.sub.3 release agent.
[0018] According to embodiments of the present disclosure, the
method further comprises steps of: (c) removing an ingot of
solidified NiPt alloy from the mold; and (d) subjecting the ingot
to thermo-mechanical rolling for reducing thickness and grain size
of the NiPt alloy, wherein step (d) comprises alternate rolling in
straight and cross directions and re-heating the NiPt alloy during
the straight direction rolling.
[0019] Another aspect of the present disclosure is a 4N5 ultra-high
purity NiPt alloy fabricated by the above process.
[0020] Still another aspect of the present disclosure is a 4N5
ultra-high purity NiPt alloy having a Si concentration of <1
ppm, a B concentration of <0.2 ppm, a Ca concentration of
<0.05 ppm, an Al concentration of <0.1 ppm, and a total
impurity concentration of <50 ppm, wherein the Ni:Pt atomic
ratio is in the range from about 99:1 to about 20:80, and the grain
size ranges from about 200 to about 300 .mu.m.
[0021] Yet another aspect of the present disclosure is an improved
sputtering target comprising the above 4N5 ultra-high purity NiPt
alloy.
[0022] Additional advantages of the present disclosure will become
readily apparent to those skilled in this art from the following
detailed description, wherein only the preferred embodiments of the
present disclosure are shown and described, simply by way of
illustration of the best mode contemplated for practicing the
present disclosure. As will be realized, the disclosure is capable
of other and different embodiments, and its several details are
capable of modification in various obvious respects, all without
departing from the spirit of the present disclosure. Accordingly,
the drawings and description are to be regarded as illustrative in
nature, and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The following detailed description of the embodiments of the
present disclosure can best be understood when read in conjunction
with the following drawings, in which:
[0024] FIGS. 1 (A) and 1 (B) are photomicrographs respectively
showing the grain structures of a straight-rolled NiPt alloy formed
according to conventional (prior) practice with grain sizes in the
400-500 .mu.m range and a cross-rolled NiPt alloy formed according
to the present disclosure with grain sizes in the 200-300 .mu.m
range.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0025] The present disclosure addresses and overcomes the problems
associated with the inability of currently available
practices/technologies to provide the ultra-high purity NiPt alloy
materials necessary for use as sputtering targets utilized in the
manufacture of high performance semiconductor IC devices with
feature sizes of 65 nm and below, including devices formed on
strained semiconductor substrates and/or with gate structures
comprising Ni-silicide contact metallization and high k gate
oxides.
[0026] Briefly stated, according to key features of the present
disclosure, ultra-high purity NiPt alloys (i.e. of 4N5 purity and
higher), with Ni:Pt atomic ratios from about 99:1 to about 20:80,
suitable for use in the fabrication of sputtering targets useful,
inter alia, in the manufacture of the above-mentioned high
performance semiconductor IC devices, are formed by a process
comprising vacuum induction melting (VIM) of raw materials of
lesser impurity (e.g., 3N Ni and 3N5 Pt), followed by
casting/molding to form an ingot which is then subjected to
thermo-mechanical processing, e.g., cross-directional hot rolling,
to reduce the thickness and grain size, and provide a uniform grain
size distribution across the surface of the ultimately formed
sputtering target. According to the present disclosure, melting and
casting/molding procedures are employed which avoid contamination
resulting from the melting process. The resultant NiPt alloys have
very low B and Si impurity levels, each well below that of the
starting (raw) materials, as well as substantially reduced levels
of a number of other impurity elements.
[0027] In more detail, it was determined/noted that quantities of
B, Al, Si, Ca, and other elements were introduced into NiPt ingots
formed by conventional processing methodology. Specifically, B was
identified as arising from the BN release agent utilized with
graphite molds, which BN can react with molten Ni. Consequently,
according to the instant process methodology, an alternate release
agent, e.g., Al.sub.2O.sub.3, is utilized to protect the graphite
mold.
[0028] It was also determined/noted that the traces of Al, Ca, and
Si found in the NiPt ingots formed by conventional processing
methodology were derived from the Al.sub.2O.sub.3 crucible utilized
for melting of the constituent raw material(s). Further,
Al.sub.2O.sub.3-based crucibles, which are stable at melting
temperatures below about 1600.degree. C., are not stable when
subjected to the high temperatures utilized in forming molten NiPt,
and consequently may shed particles of Al.sub.2O.sub.3 to the melt
or emit particles of its bonding material (Si). Therefore,
according to the instant process methodology for forming ultra-high
purity NiPt alloys, a crucible formed of a material which is
substantially inert to molten NiPt under the above temperature
conditions utilized for forming the NiPt melt, e.g.,
yttria-stabilized zirconia (YSZ), is substituted for the
conventional Al.sub.2O.sub.3-based crucible.
[0029] It was further determined/noted that another possible source
of Al, Ca, and Si impurities/contaminants is the tundish
conventionally employed for guiding a pour stream of molten NiPt
from a crucible to a casting mold. According to the present
disclosure, therefore, the necessity of a tundish is eliminated by
selection/use of a mold cavity allowing for direct transfer of the
NiPt melt from the crucible to the mold, thereby eliminating
possible contamination from the tundish.
[0030] The ability of the presently disclosed methodology to
provide ultra-high purity (e.g., 4N5) NiPt alloys with
significantly reduced concentrations of Si, B, Ca, and Al, as well
as significantly reduced total impurity levels and uniformly
distributed fine grain sizes will now be demonstrated by reference
to the following illustrative, but non-limitative, example of the
presently disclosed methodology.
EXAMPLE
[0031] Square blocks of 3N5 purity Ni and 3N Pt shot in a Ni/Pt
atomic ratio of 95:5 were placed in a YSZ crucible and subjected to
vacuum induction melting (VIM) at a temperature of about
1600.degree. C. for about 1-1.5 hrs. to form a NiPt alloy melt. The
melt was purified by pouring off any slag which formed on the top
and/or by evaporation of impurities under the vacuum atmosphere.
The melt was then poured, without the use of a tundish, into a
graphite mold lined with an Al.sub.2O.sub.3 mold release agent and
solidified into a NiPt alloy ingot.
[0032] Results of full element glow discharge mass spectroscopy
("GDMS") studies of targets comprised of NiPt alloys formed
according to the conventional and present methodology are given in
Table I below, wherein the column heading "Customer desired
specification" refers to a specification of a semiconductor IC
manufacturer for impurity levels of NiPt sputtering targets and the
other column headings "Conventional (prior) process" and "Instant
process" respectively designate impurity content of NiPt alloy
sputtering targets fabricated according to conventional methodology
as described above and according to the instantly disclosed
methodology.
TABLE-US-00001 TABLE I Customer desired Conventional specification,
(prior) process, Instant process, Element ppm ppm ppm Ag <0.1
<1 <0.1 Al <0.5 <50 <0.1 B <0.2 <100 <0.2 C
<50 <100 <0.2 Ca <0.5 <10 <0.05 Cl <0.5 <10
<0.05 Co <3 <50 <3 Cr <1 <50 <1 Cu <2
<50 <1 Fe <6 <50 <6 H <10 <50 <10 Mg <5
<50 <0.1 N <30 <50 <30 O <50 <100 <100 S
<1 <50 <0.5 Si <1 <200 <1 Zn <0.1 <50
<0.1 Zr <20 <50 <1 Total impurities, <50 <1000
<50 ppm
[0033] It is apparent from the data of Table I that high
concentrations of Si, B, Ca, and Al can be present in the
conventionally fabricated sputtering targets, with total impurity
levels exceeding 1000 ppm, and that the concentrations of Si, B,
Ca, and Al of the ultra-high purity NiPt alloy formed by the
presently disclosed methodology are significantly lower than those
formed according to conventional practice, and in some instances
are lower than required by customer specification. For example, the
Si concentration is <1 ppm, as compared with <200 ppm in the
conventionally prepared NiPt alloy, and comparable to the customer
specification of <1 ppm; the B concentration is <0.2 ppm, as
compared with <100 ppm in the conventionally prepared alloy, and
comparable to the customer specification of <0.2 ppm; the Ca
concentration is <0.05 ppm, as compared with <10 ppm in the
conventionally prepared alloy, and better than the customer
specification of <0.5 ppm; and the Al concentration is <0.1
ppm, as compared with <50 ppm in the conventionally prepared
alloy, and better than the customer specification of <0.5
ppm.
[0034] The total impurity concentration of the NiPt alloy produced
by the present process is <50 ppm, comparable to the customer
desired specification value, and substantially lower than the
<1000 ppm of NiPt alloys produced by the conventional (prior)
methodology. The present methodology thereby meets a requirement
for 4N5 ultra-high purity NiPt alloys for use in fabricating
sputtering targets suitable for high performance semiconductor IC
device manufacture.
[0035] The resultant ultra-high purity NiPt ingot was then
subjected to a more aggressive thermo-mechanical roll schedule than
is conventional, in order to achieve a greater reduction in
thickness and grain size, with a more uniform distribution of grain
size than provided by prior methodologies, which aggressive roll
schedule comprises alternate rolling in straight and cross
directions, with re-heating during the straight direction rolling.
In contrast with prior hot rolling processes involving straight
direction rolling, which can provide a total thickness reduction of
about 60% at temperatures in the range 2000-3000.degree. F., the
cross-directional rolling according to the present methodology
provides a total thickness reduction of about 75% at comparable
temperatures in the range 2000-3000.degree. F.
[0036] The increased thickness reduction afforded by the instant
methodology forces more grains to experience dynamic
recrystallization at the elevated deformation temperature.
Photomicrographs, as shown in FIGS. 1 (A) and 1 (B), indicate that
the grain sizes are reduced from the 400-500 .mu.m range when hot
rolling is performed according to the prior straight direction
rolling process to the 200-300 .mu.m range when hot rolling is
performed according to the cross-direction rolling process. In
addition, grain sizes are more uniformly distributed across the
surface of the rolled plate when hot rolling is performed according
to the cross-direction rolling process, and the Vicker's hardness
for NiPt alloys formed according to the present methodology is
greater than that for NiPt alloys produced according to the
conventional methodology. For example, for Ni-5 at. % Pt alloys,
the Vicker's hardness H.sub.v for alloys formed by the present
methodology is in the range 150-370, whereas the Vicker's hardness
H.sub.v for alloys formed by the conventional methodology is in the
range 100-370.
[0037] The resultant rolled plates formed by the cross-directional
hot rolling process can be cut to a desired size and mounted, in
conventional fashion, to a backing plate for use as a sputtering
target.
[0038] In summary, notable advantages afforded by the process
methodology according to the present disclosure vis-a-vis
conventional technology for forming NiPt alloys and sputtering
targets include:
[0039] 1. substantially reduced levels of Si, B, Ca, and Al;
[0040] 2. total impurity levels well within the requirements for
meeting 4N5 ultra-high purity;
[0041] 3. reduced grain size with uniform grain size
distribution;
[0042] 4. increased Vicker's hardness;
[0043] 5. ability to melt/cast lower grades of Ni and Pt into
ultra-high purity NiPt alloys; and
[0044] 6. readily practiced melting/casting process methodology not
requiring special equipment or capital investment, which
melting/casting process is significantly less costly than powder
metallurgy processing, particularly for alloys with high Pt
content.
[0045] In the previous description, numerous specific details are
set forth, such as specific materials, structures, reactants,
processes, etc., in order to provide a better understanding of the
present disclosure. However, the present disclosure can be
practiced without resorting to the details specifically set forth.
In other instances, well-known processing materials and techniques
have not been described in detail in order not to unnecessarily
obscure the present disclosure.
[0046] Only the preferred embodiments of the present disclosure and
but a few examples of its versatility are shown and described in
the present disclosure. It is to be understood that the present
disclosure is capable of use in various other combinations and
environments and is susceptible of changes and/or modifications
within the scope of the disclosed concept as expressed herein.
* * * * *