U.S. patent application number 10/782927 was filed with the patent office on 2005-08-25 for fine grained sputtering targets of cobalt and nickel base alloys made via casting in metal molds followed by hot forging and annealing and methods of making same.
Invention is credited to Ray, Ranjan.
Application Number | 20050183797 10/782927 |
Document ID | / |
Family ID | 34861105 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050183797 |
Kind Code |
A1 |
Ray, Ranjan |
August 25, 2005 |
Fine grained sputtering targets of cobalt and nickel base alloys
made via casting in metal molds followed by hot forging and
annealing and methods of making same
Abstract
Disclosed are sputtering targets and methods for making various
nickel and cobalt base alloys into sputtering targets by melting
the alloys in a vacuum or under a low partial pressure of inert gas
and subsequent casting of the melt as round, square or rectangular
plates in metal molds under vacuum or under low partial pressure of
inert gas are provided. The plates are subsequently preheated and
deformed between two flat dies.
Inventors: |
Ray, Ranjan; (Tucson,
AZ) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, LLP
Suite 850
1615 L Street NW
Washington
DC
20036
US
|
Family ID: |
34861105 |
Appl. No.: |
10/782927 |
Filed: |
February 23, 2004 |
Current U.S.
Class: |
148/556 ;
148/557 |
Current CPC
Class: |
C22C 1/02 20130101; H01J
37/3491 20130101; C22C 19/03 20130101; H01J 37/3426 20130101; C23C
14/3414 20130101; C22C 19/07 20130101; C22F 1/10 20130101; C22C
19/05 20130101 |
Class at
Publication: |
148/556 ;
148/557 |
International
Class: |
C22F 001/10 |
Claims
1. A method of making an article of metallic alloy, comprising the
steps of: melting the metallic alloy under vacuum or partial
pressure of inert gas; pouring the metallic alloy into a metal mold
with a cavity of uniform thickness, wherein the metal mold is made
by machining or casting technique from materials having melting
point in the temperature range 2350.degree. F.-3000.degree. F. and
thermal conductivity between 300-400 Btu/Ft.sup.2/hr/in/.degree. F.
in the temperature range 70-700.degree. F. and ultimate tensile
strength betwen 100 and 200 KSI, solidifying the melted metallic
alloy into a solid body taking the shape of the mold cavity as a
plate of constant thickness; preheating the solidified plate at
temperature below the melting temperature of the metallic alloy;
deforming the preheated plate between two flat dies with the
application of pressure along the thickness direction producing a
plate with reduced but constant thickness; optionally annealing the
deformed plate at temperatures below the melting temperature of the
metallic alloy.
2. The method of claim 1, wherein the mold has a temperature in the
range from 30 to 800.degree. C. when the alloy is poured into the
mold.
3. The method of claim 1, wherein the mold has a temperature in the
range from 200 to 800.degree. C. when the alloy is poured into the
mold.
4. The method of claim 1, wherein the mold has a temperature in the
range from 100 to 500.degree. C. when the alloy is poured into the
mold.
5. The method of claim 1, wherein the mold cavity is round or
square or rectangular with a constant thickness in the range from
0.25 to 2 inch.
6. The method of claim 1, wherein the mold cavity is round or
square or rectangular with a constant thickness in the range from
0.5 to 2 inch.
7. The method of claim 1, wherein the mold cavity is round or
square or rectangular with a constant thickness in the range from
0.5 to 1 inch.
8. The method of claim 1, wherein the solidified plate is preheated
before deformation at temperature in the range from 500 to
2200.degree. F.
9. The method of claim 1, wherein the solidified plate is preheated
before deformation at temperature in the range from 1000 to
2200.degree. F.
10. The method of claim 1, wherein the solidified plate is
preheated before deformation at temperature in the range from 1000
to 2000.degree. F.
11. The method of claim 1, wherein the solidified plate is
preheated before deformation at temperature in the range from 1200
to 1800.degree. F.
12. The method of claim 1, wherein the solidified plate is
preheated before deformation at temperatures in the range from 1200
to 1600.degree. F.
13. The method of claim 1, wherein the preheated plate is pressed
between two flat dies at strain rate in the range from 0.1/second
to 10/second.
14. The method of claim 1, wherein the preheated plate is pressed
between two flat dies at strain rate in the range from 0.5/second
to 10/second.
15. The method of claim 1, wherein the preheated plate is pressed
between two flat dies at strain rate in the range from 1/second to
10/second.
16. The method of claim 1, wherein the preheated plate is pressed
between two flat dies at strain rate in the range from 1/second to
5/second.
17. The method of claim 1, wherein the preheated plate is deformed
between two flat dies undergoing 10-80% reduction in thickness.
18. The method of claim 1, wherein the preheated plate is deformed
between two flat dies to undergo 20-80% reduction in thickness.
19. The method of claim 1, wherein the preheated plate is deformed
between two flat dies to undergo 30-70% reduction in thickness.
20. The method of claim 1, wherein the metallic alloy is a cobalt
base alloy having the composition in weight percent as follows:
Cobalt=Balance Chromium=5 to 20% Tantalum=5 to 15% and inevitable
impurity elements, wherein the impurity elements are less than
0.01% each and less than 0.05% total
21. The method of claim 1, wherein the metallic alloy is a cobalt
base alloy having the composition in weight percent as follows:
Cobalt=Balance Chromium=5-20% Iron=0-15% and inevitable impurity
elements, wherein the impurity elements are less than 0.01% each
and less than 0.05% total.
22. The method of claim 1, wherein the metallic alloy is a cobalt
base alloy having the composition in weight percent as follows:
Cobalt=Balance Chromium=5-20% Platinum=5-15% Boron=0-2% and
inevitable impurity elements, wherein the impurity elements are
less than 0.01% each and less than 0.05% total.
23. The method of claim 1, wherein the metallic alloy is a cobalt
base alloy having the composition in weight percent as follows:
Cobalt=Balance Chromium=0-20% Zirconium=0-5% Niobium=0-5%
Tantalum=0-10% Hafnium=0-10% and inevitable impurity elements,
wherein the impurity elements are less than 0.01% each and less
than 0.05% total.
24. The method of claim 1, wherein the metallic alloy is a nickel
base alloy having the composition in weight percent as follows:
Nickel=Balance Chromium=0-20% Iron=0-10% and inevitable impurity
elements, wherein the impurity elements are less than 0.01% each
and less than 0.05% total.
25. The method of claim 1, wherein the metallic alloy is a nickel
base alloy having the composition in weight percent as follows:
Nickel=Balance Chromium=0-20% Rhodium=0-10% and inevitable impurity
elements, wherein the impurity elements are less than 0.01% each
and less than 0.05% total.
26. The method of claim 1, wherein the metallic alloy is a nickel
base alloy having the composition in weight percent as follows:
Nickel=Balance Chromium=0-20% Tungsten=0-10% and inevitable
impurity elements, wherein the impurity elements are less than
0.01% each and less than 0.05% total.
27. The method of claim 1, wherein the metallic alloy is a nickel
base alloy having the composition in weight percent as follows:
Nickel=Balance Vanadium=0-10% and inevitable impurity elements,
wherein the impurity elements are less than 0.01% each and less
than 0.05% total.
28. The method of claim 1, wherein the metallic alloy has the
composition in weight percent as follows: Nickel=99.95 to
99.99%.
29. A sputtering target made by the method of claim 1.
30. The sputtering target of claim 29, wherein the sputtering
target is a nickel base alloy sputtering target.
31. The sputtering target of claim 29, wherein the sputtering
target is a cobalt base alloy sputtering target.
32. A nickel base or cobalt base alloy sputtering target having a
percentage pass through flux of at least 60%.
33. The sputtering target of claim 32, having a percentage pass
through flux of at least 65%.
34. The sputtering target of claim 32, having a percentage pass
through flux of 65% to 80%.
35. The sputtering target of claim 32, having a percentage pass
through flux of 65% to 75%.
36. The sputtering target of claim 32, wherein the sputtering
target is a nickel base alloy sputtering target.
37. The sputtering target of claim 32, wherein the sputtering
target is a cobalt base alloy sputtering target.
Description
FIELD OF THE INVENTION
[0001] This invention relates to sputter targets and methods of
making same. Sputter targets made of ferromagnetic materials are
critical to thin film deposition in industries such as data storage
and VLSI (very large scale integration)/semiconductors. Magnetron
cathode sputtering is one means of sputtering magnetic thin
films.
BACKGROUND OF THE INVENTION
[0002] The sputtering process involves argon ion bombardment of a
target as a cathode in the presence of an electric field. The
dislodge atoms from the target due to ion bombardment traverse the
enclosure and deposit as a thin film onto a substrate or substrates
maintained at or near anode potential.
[0003] In magnetron cathode sputtering, an arched magnetic field
created by magnets behind the target and formed in a closed loop
over the surface of the sputter target, is superimposed on the
electric field. The closed-loop leakage magnetic field traps
electrons and increases the plasma density adjacent to the surface
of the target, thereby significantly increasing the sputtering
activity.
[0004] The use of magnetron sputtering to deposit thin films of
magnetic target materials is widespread in the electronics
industry, particularly in the fabrication of semiconductor and data
storage devices. Due to the magnetic nature of the target
materials, there is considerable shunting of the applied magnetic
field in the bulk of the target. Erosion of particles from the
sputter target surface generally occurs in a relatively narrow
ring-shaped region corresponding to the shape of the closed-loop
magnetic field. Only the portion of the total target material in
this erosion groove is consumed before the target must be replaced.
The result is that typically only 18-25% of the target material is
utilized. Thus, a considerable amount of material, which is
generally very expensive, is either wasted or must be recycled. (In
the present specification, all compositional percentages are weight
percents unless otherwise indicated). Furthermore, a considerable
amount of sputter deposition equipment "down-time" occurs due to
frequent target replacement.
[0005] Several sputtering processes and apparatus with which the
invention may be usable are disclosed in Bergmann, et al., U.S.
Pat. Nos. 4,889,772 and 4,961,831; Shagun, et al., U.S. Pat. No.
4,961,832; Shimamura, et al., U.S. Pat. No. 4,963,239; Nobutani, et
al., U.S. Pat. No. 4,964,962; Arita, U.S. Pat. No. 4,964,968;
Kusakabe, et al., U.S. Pat. No. 4,964,969 and Hata, U.S. Pat. No.
4,971,674; and the references referred to therein; sputtering
targets are discussed also in Fukaswawa, et al. U.S. Pat. Nos.
4,963,240 and 4,966,676; and Archut, et al., U.S. Pat. No.
4,966,676. These disclosures of sputtering processes and apparatus
as well as sputtering targets are expressly incorporated herein by
reference. Additional background on sputtering is presented by U.S.
Pat. Nos. 6,402,912; 6,494,999, and 6,585,870 expressly
incorporated herein by reference.
[0006] Thin films of a magnetic alloy such as Co--Ni--Pt,
Co--Cr--Ni, Co--Cr--Ta, Co--Cr, Co--Ni--Cr--V, Co--Cr--Pt, or the
like, formed via magnetron sputtering on a substrate are used as
magnetic recording medium in magnetic disks, hard drives,
magneto-optical disks. Recently, various ideas such as increasing
the coercive force of the magnetic film or reducing a noise have
been proposed for the magnetic recording medium to cope with high
density recording.
[0007] The pass through flux (PTF) of a magnetic sputtering target
is defined as the ratio of transmitted magnetic field to the
applied magnetic field. A PTF value of 100% is indicative of a
non-magnetic material where none of the applied field is shunted
through the bulk of the target. The PTF of magnetic target
materials is typically specified in the range of 0 to 100%, with
the majority of commercially produced materials exhibiting values
between 10 to 95%.
[0008] For magnetron sputtering, the magnetic leakage flux (MLF) or
leakage magnetic field at the target surface must be high enough to
start and sustain the plasma. Under normal sputtering conditions,
such as an argon pressure of 5-10 mTorr, the minimum MLF, also
known as pass through flux (PTF), is approximately 150 gauss at the
sputtering surface, and preferably is about 200 gauss for high
speed sputtering. The magnet strength of the cathode sputtering
target in part determines the MLF. The higher the magnet strength,
the higher the MLF. In the case of ferromagnetic sputter targets,
however, the high intrinsic magnetic permeability of the material
effectively shields or shunts the magnetic field from the magnets
behind the target and hence reduces the MLF on the target surface.
This leads to reduced sputtering efficiency.
[0009] Because of high permeability and thus low MLF, ferromagnetic
sputter targets are generally made much thinner than non-magnetic
sputter targets to allow enough magnetic field to be leaked out to
the sputtering surface to sustain the sputtering plasma necessary
for magnetron sputtering. With some ferromagnetic materials,
particularly those with higher permeability, the targets have to be
machined to 0.0625 inch thick or less to achieve an MLF at the
sputtering surface of 150 gauss, and some very high permeability
materials are impossible to magnetron sputter because an MLF of 150
gauss simply cannot be achieved. Thus, not only can these
ferromagnetic targets not simply be made thicker so as to reduce
equipment down-time, they must actually be made thinner.
[0010] In general, the higher the permeability of the ferromagnetic
material, the thinner the sputter target is required to be. Such a
limitation on target thickness, however, leads to a shorter target
life, waste of material and a need for more frequent target
replacement. Furthermore, the high permeability and low MLF of a
ferromagnetic target can cause problems of high impedance, low
deposition rates, narrow erosion grooves, poor film uniformity and
poor film performance. It is thus desirable to provide a high MLF
ferromagnetic sputter target that may be made relatively thick
without sacrificing film integrity.
[0011] It is well known that reducing target material permeability
or increasing the target material PTF promotes less severe erosion
profile, thus enhancing target material utilization during the
sputtering process. This leads to a net reduction in target
material cost per unit sputter fabricated product. Furthermore, the
presence of severe target erosion profiles can also lead to a point
source sputtering phenomena which can result in a deposited thin
film that lacks thickness uniformity. Therefore, in addition to
less severe erosion profile, increasing the PTF of the target
material has the added benefit of increasing the uniformity of the
thickness of the deposited thin film.
[0012] Magnetic target PTF is a strong function of both target
chemistry and the thermo-mechanical techniques utilized during
target fabrication. For alloys that do not possess inherently high
PTF as a result of their stoichiometry, i.e., PTF<85%, it is
possible to increase product PTF by various thermo-mechanical
manipulations during product fabrication. For example, the typical
fabrication of Ni, Co and Co-alloy targets involves casting,
hot-rolling and either heat treatment or cold-rolling or a
combination of heat treatment followed by cold-rolling. It is known
that heat treating and cold-rolling of magnetic target materials
can increase product PTF. Heat treatment of Co--Cr--Ta--(Pt) alloys
below 2200.degree. F. has been shown to increase the PTF by
promoting matrix crystallographic phase transformation from face
centered cubic to hexagonal closed packed as discussed in Chan et
al., Magnetism and Magnetic Materials, Vol. 79, pp. 95-107
(1989).
[0013] It is suggested in Weigert et al., Mat. Sci. and Eng., A
139, p.p. 359-363 (1991), that cold-rolling of an alloy comprising
62-80 atomic % Co, 18-30 atomic % Ni, and 0-8 atomic % Cr
immediately after the hot-rolling step results in an increase in
product PTF. A similar result is disclosed in Uchida et al., U.S.
Pat. No. 5,468,305 for an alloy containing 0.1-40 atomic % Ni,
0.1-40 atomic % Pt, 4-25 atomic % Cr and the remainder Co which is
cold-rolled by not more than a 10% reduction after the hot-rolling
process. Uchida et al. claim that the cold-deformation induced
internal strain in the alloy reduces magnetic permeability.
[0014] High PTF in the ferromagnetic sputtering targets are
generally achieved by heat treatment and/or thermal-mechanical
processing treatments.
[0015] Co alloy targets strongly require the lowering in
permeability. The lowering in permeability is most effective to
enhance the sputtering efficiency of Co alloy targets and it also
greatly contributes to the reduction in cost from the viewpoint of
users.
[0016] Sputtering efficiencies of targets depend on several factors
such as: (a) grain size, (b) grain orientation and texture, and (c)
the homogeneity of dispersion and particle size of second phase
precipitates. Fine grain sizes, finely dispersed second phases in
the matrix and strong texture will enhance sputtering efficiency of
targets.
[0017] The effect of crystallographic orientation of a sputtering
target on sputtering deposition rate and film uniformity has been
described in an article by C. E. Wickersham, Jr., entitled
Crystallographic Target Effects in Magnetron Sputtering in the
J.Vac. Sci. Technol. A5(4), July/August 1987 publication of the
American Vacuum Society.
[0018] However, there is a limit to how fine a grain size, how
strong a texture, and how small a precipitate size can be achieved
with conventional metal processing techniques, i.e., rolling,
forging, for each metal system and alloy.
[0019] Similarly, the development of different textures and
anisotropic properties by rolling is difficult. Desired plane
textures and enhanced properties can be created only along the
rolling direction with accompanying large reductions (see e.g.,
U.S. Pat. Nos. 3,954,516, 4,406,715, 4,609,408, 4,753,692 and
5,079,907). In addition, methods are not available which develop
the required texture and anisotropy at a desired angle relative to
the rolling direction at the rolling plane. Production of
non-oriented textureless or isotropic products by rolling is also a
difficult problem. Moreover, intensive rolling develops strongly
laminated materials that often exhibit anisotropy of material
properties which cannot be eliminated through existing
technologies.
[0020] Grain size reduction in cobalt alloys can be achieved by
thermo-mechanical processing such as hot rolling or hot forging
followed by recrystallization. However, cobalt alloys containing
multiple elements such as chromium, tantalum, nickel, platinum and
boron are difficult to hot work by the conventional ingot
metallurgy route due to segregated microstructures containing
brittle second phases at the grain boundaries. Often the expensive
powder metallurgy route is followed to fabricate these alloys with
desirable fine and homogeneous microstructures.
[0021] To improve the performance of sputtering targets,
manufacturers have used special casting techniques to reduce the
resulting as-cast grain size. Also, hot or cold deformation
followed by recrystallization has been used to reduce the grain
size of the metal to be formed into a sputtering target.
[0022] Grain orientation control has also been suggested. A slow
hot forging technique which produces a predominately <110>
texture is described in U.S. Pat. No. 5,087,297 to Pouliquen.
[0023] Conventional casting, forming, annealing, and forging
techniques have produced sputtering targets with limited minimum
grain sizes. Ultra-fine grains have also been achieved with a
technique known as equal channel angular extrusion (ECAE), but not
in production of sputtering targets. The ECAE process has been a
technical curiosity but has not been used for any known commercial
purpose. It is a method which uses an extrusion die containing two
transversely extending channels of substantially identical cross
section. It is common, but not necessary, to use channels which are
perpendicular to each other, such that a cross section of the
transverse channels forms an "L" shape.
[0024] Thermo-mechanical processing (i.e., various combinations of
heat treatment and mechanical working) is performed on materials to
refine grains and phases, change their aspect ratios, orientation
and distribution, and develop substructures. Intensive plastic
deformation plays an important role in thermo-mechanical materials
processing. Different deformation methods are used for material
processing depending upon the shape and dimensions of the billet
and the initial and final properties of the material. Hot forging
of metals is an advantageous method of producing sputtering
materials for PVD targets. Hot forging also tends to produce a
finer metallurgical grain size. The mechanism for this improved
microstructure is dynamic recrystallization.
[0025] Dynamic recrystallization is a softening process that takes
place during metal deformation at elevated temperatures. This
softening is observed in a large number of metals and alloys and
for numerous deformation processes. Careful analyses of the
deformation behavior, including microstructural investigations,
have shown that there are two broad classes of dynamic
softening.
[0026] The first class is described in the literature as involving
the discontinuous formation of new grains within the deformed
matrix. To be more specific, grains develop during deformation by
nucleation and growth, so that the average dislocation density
drops, leading to significant softening. This type of dynamic
recrystallization is associated with low or medium stacking fault
energy metals (copper, silver, nickel, the austenite phase of
conventional steels, and austenitic stainless steels).
[0027] The second class of softening process is associated with
materials in which dynamic recovery is rapid enough to insure slow
migration of the subgrain boundaries. Such materials undergo
softening by continuous fragmentation of their substructure. This
fragmentation produces a fine grained microstructure, without
involving any nucleation or growth mechanism. For these reasons,
the first broad class is usually referred to as "discontinuous
dynamic recrystallization," while the second is designated as
"continuous dynamic recrystallization."
[0028] Traditionally, forming operations such as forging and
rolling were performed on billets to develop desired
physical/mechanical properties. However, in many respects, such
operations are ineffective. The difficulty in achieving the high
strains necessary for structure and texture formation represents
the greatest limitation in these operations. In order to develop
cumulative strain sufficient to provide grain refinement by
recrystallization during subsequent annealing, it is necessary to
apply a number of successive forging stages along the three
perpendicular axes of a billet (see, e.g., U.S. Pat. Nos. 3,954,514
and 4,721,537). However, such a forging operation may be used only
with billets having approximately equal dimensions along their
three perpendicular axes. The treatment of plates by such a process
results in a marked change of billet dimensions from a plate to a
bar-shape (see, e.g., U.S. Pat. No. 4,511,409). However,
conventional ingots of cobalt base alloys that are used for
applications as ferromagnetic sputtering targets contain coarse,
brittle intermetallic phases and hence are difficult to be deformed
or strained via hot working operations.
[0029] There is a need for an improved cost effective process for
making ferromagnetic sputtering targets with fine and uniform grain
structure based on various cobalt and nickel based alloys suitable
for high efficiency utilization in magnetron sputtering
equipment.
PREFERRED OBJECTS OF THE PRESENT INVENTION
[0030] It is a preferred object of the present invention to rapidly
cast various cobalt and nickel base alloys as plates in reusable
metallic molds having high melting point, high thermal conductivity
and high strength under vacuum or inert gas atmosphere.
[0031] It is another preferred object of the present invention to
produce fine columnar grains parallel to the thickness of the cast
plates by maintaining the thickness of the castings under 2
inch.
[0032] It is another preferred object of the invention to hot forge
the cast plates containing the columnar grains along the thickness
direction at in successive steps.
[0033] It is another preferred object of the invention to carry out
the hot forging operations at certain combinations of temperatures
and strain rates depending on the alloy composition which will
cause deformation of the columnar grains followed by dynamic
recrystallization into fine equiaxed grains.
SUMMARY OF THE INVENTION
[0034] The invention relates to a method for making various
metallic alloys based on cobalt and nickel alloys as plates with
fine grain uniform microstructures that can be machined to final
net shaped sizes for applications as ferromagnetic sputtering
targets with high pass through flux.
[0035] This invention relates to a method for making various
metallic alloys based on cobalt and nickel as plates suitable for
applications as ferromagnetic sputtering targets in magnetron
sputtering equipment. The invention relates to fabrication of the
sputtering targets of cobalt and nickel alloys as follows:
[0036] (a) The alloys are vacuum induction melted and cast as
plates under vacuum with a maximum thickness of 2 inches in
metallic molds having melting points between 2350-3000F, thermal
conductivity between 300-600 Btu/Ft.sup.2/hr/in/F in the range
70-700F and room temperature tensile strength between 100-200
KSI.
[0037] (b) The cast plates are hot forged along the thickness
direction under certain critical combinations of strain rate
ranging between 0.1/second to 10/second and temperature ranging
between 500.degree. F. and 2200.degree. F. and total deformation
ranging between 20-80 %.
[0038] (c) The forged plates are subsequently annealed within
certain ranges of temperatures between 500.degree. F. to
2000.degree. F.
[0039] Depending on the alloy compositions, the columnar grain
structure of the cast plates undergoes dynamic recrystallization
during forging and/or subsequent annealing step into fine,
homogeneous equiaxed grains.
[0040] More particularly, this invention relates to the use of
metallic molds such as certain grades of plain carbon steels,
malleable cast irons and low alloy steels. High melting point
(>2350.degree. F.) and high thermal conductivity (300-400
Btu/Ft.sup.2/hr/in/.degree. F. in the temperature range
70-700.degree. F.) and high ultimate tensile strength (100-200 KSI)
are some of the characteristics of the metallic materials that
render them suitable for use as molds for casting cobalt and nickel
base alloys of as much as 2 inch thickness with fine columnar
grains along the thickness direction in accordance with the scope
of the present invention.
[0041] The present invention has a number of advantages:
[0042] (1) Use of metallic molds having high melting points and
high thermal conductivity leads to formation of columnar grains
parallel to the thickness direction in the cobalt and nickel base
alloys intended for applications as magnetic sputtering target. The
columnar grain structure is critical for achieving equiaxed fine
grains by high strain rate forging induced dynamic
recrystallization. The fine grain structure of the forged and
annealed plates of cobalt and nickel alloys are critical for
improved properties and high efficiency performance of the
sputtering targets compared to the sputtering targets of similar
alloys produced by conventional processes.
[0043] (2) The metallic molds having high strength and high melting
points can be used repeatedly many times thereby reducing
significantly the cost of fabrication of the castings.
[0044] (3) The castings can be made in molds held at room or low
temperatures resulting in finer grain structures and improved
mechanical properties.
[0045] (4) The fine columnar grains of certain cobalt base alloys
containing brittle intermetallic phases are amenable to deformation
by hot forging without fracture or cracks. Large ingots produced by
conventional slow cooling process contains large grains with
brittle intermetallic grain boundary phases and such ingots are
difficult to hot forge at high strain rate necessary to impart
substantial strain energy in the alloy which triggers simultaneous
grain refinement by the mechanism of dynamic recrystallization.
[0046] This invention also relates to a sputtering target made of
alloys, such as various metallic alloys based on cobalt and nickel
alloys, made by the method of the present invention.
[0047] This invention also relates to a nickel base alloy
sputtering target or cobalt base alloy sputtering target having a
percentage PTF (pass through flux) of at least 60%.
[0048] This invention also relates to a nickel base alloy
sputtering target or a cobalt base alloy sputtering target having a
percentage PTF (pass through flux) of at least 65%, for example 65%
to 80% or 65% to 75%.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] A. Metallic Molds
[0050] Certain grades of plain carbon steels, low alloy steels and
malleable cast irons are preferred materials as the main body of
the mold of the present invention for the following reasons:
[0051]
[0052] The metallic alloys have high melting point between
2350.degree. F.-3000.degree. F. and thermal conductivity between
300-400 Btu/Ft.sup.2/hr/.degree. F. in the temperature range
70-700.degree. F. and ultimate tensile strength between 100-200
KSI.
[0053] Other important properties of the above material are high
thermal shock, wear and chemical resistance, and minimum wetting by
liquid metal.
[0054] The typical physical and mechanical properties of metallic
molds suitable for casting cobalt and nickel base alloys in
accordance with the present invention are given in Table 1.
1TABLE 1 Thermal Ultimate Conductivity Tensile Melting Point
BTU/ft.sup.2/ Strength (KSD Material (degrees F.) hr/in/.degree.
F., 70.degree. F. at 70.degree. F. Carbon Steel 2840 325 110 AISI
1118 Carbon Steel 2810 315 120 AISI 1030 Carbon Steel 2790 320 140
AISI 1050 Carbon Steel 2775 310 190 AISI 1080 Carbon Steel 2760 315
180 AISI 1095 Carbon Steel 2756 315 200 AISI 1141 Carbon Steel 2805
325 105 AISI Type B 1211 Carbon Steel 2815 330 105 AISITypeB 1212
Nitriding Steels 2810 360 140 Type 135 Nitriding Steels 2790 360
130 Type N Steel AISI 4130 2775 300 200 Steel AISI 4330 2765 348
200 Steel AISI 4340 2770 350 200 Malleable Cast 2475 354 100 Iron
Pearlitic 80002 Cast Alloy Steel 2495 320 100 Class 105,000 Cast
Alloy Steel 2465 320 100 Class 120,000 Cast Alloy Steel 2440 310
160 Class 150,000 Cast Alloy Steel 2430 300 200 Class 200,000
PERMANICKEL 2580 400 170 Alloy 300
[0055] The chemical compositions of the alloys listed in Table 1
are given in the CRC Handbook of Materials Science, Vol. II, edited
by C. T. Lynch, CRC Press, Inc, Boca Raton, Fla., 1975.
[0056] Parameters referenced in the present specification are
measured according to the following standards unless otherwise
indicated.
[0057] Tensile strength is measured by ASTM E8-96
[0058] Thermal conductivity is measured according to ASTM
C-714.
[0059] B. Molding
[0060] An embodiment of the present invention is a method of making
an article of metallic alloy, comprising the steps of: melting the
metallic alloy under vacuum or partial pressure of inert gas;
pouring the metallic alloy into a mold with a cavity of uniform
thickness, the metallic alloys having melting point between
2350-3000.degree. F. and thermal conductivity between 300-400
Btu/Ft.sup.2/hr/in/.degree. F. in the temperature range
70-700.degree. F. and ultimate tensile strength between 100-200
KSI, solidifying the melted metallic alloy into a solid metallic
body taking the shape of the mold cavity as a plate of constant
thickness; preheating the solidified plate at temperature below the
melting temperature of the metallic alloy; deforming the preheated
plate between two flat dies with the application of pressure along
the thickness direction producing a plate with reduced but constant
thickness; and annealing the deformed plate at temperatures below
the melting temperature of the metallic alloy.
[0061] If molds are made of metallic materials which have thermal
conductivity outside the critical range i.e. <300
Btu/Ft.sup.2/hr/in/.degree. F. and >400
Btu/Ft.sup.2/hr/in/.degree. F. in accordance with the present
invention , the properties of the sputtering targets made via
casting melt in such molds followed by hot forging will be less
than optimum.
[0062] At low thermal conductivity, the metallic melt cast into it
will not cool fast enough to generate predominantly columnar grains
perpendicular to the mold wall and will lead to formation of a
mixture of columnar grains and equiaxed in the solidified casting.
Under the condition, when solidification begins, the melt will
solidify as columnar grains perpendicular to the wall of the mold
followed by formation of equiaxed grains in the center region of
the casting away from the surface. Similarly, when the thermal
conductivity of a specific mold material is greater than 400
Btu/Ft.sup.2/hr/in/.degree. F., solidification will begin with the
formation of very fine equiaxed adjacent to the mold wall followed
by formation of columnar grains. In either condition of thermal
conductivity of the mold materials, a mixture of equiaxed and
columnar grains present in the cast body will result into
non-uniform distribution of strain energy in it during the
subsequent high strain rate forging operation. The strain energy
being stored in the material body as it gets deformed during
forging has to reach a critical value to trigger the subsequent
recrystallization of fine grains. The mixture of equiaxed and
columnar grains in the casting will result in retained strain
energy in some parts of the material body to be below the critical
value necessary for dynamic recrystallization of fine grains. At
the end of the forging operation, the grain structure in the final
product will have, or consist of, a mixture of fine recrystallized
grains and coarse unrecrystallized grains. The properties of the
sputtering targets will be inferior as a consequence of uniform
grain structure.
[0063] The melting point of the material below 2350.degree. F.
makes it unsuitable for use as mold in accordance with the present
invention. Low melting point (<2350.degree. F.) of a mold
material will have a tendency to melt or react with the candidate
cobalt and nickel base alloys having relatively high melting points
(i.e. >2650.degree. F.) when cast into such molds.
[0064] The preferred tensile strength of the metallic mold material
is between 100 and 200 KSI. Some of the candidate metallic mold
materials listed in Table 1 can be heat treated to achieve a
certain combination of tensile strength and elongation (i.e.,
ductility). For example, the plain carbon and alloy steels such as
AISI 1080, AISI 1095, AISI Type B 1211, AISI 4130, AISI 4330 and
AISI 4340 can be heat treated to achieve ultimate tensile strength
in excess of 200KSI at lower than optimum ductility. Under such
conditions of mechanical properties, the mold materials when
subjected to repeated cycles of thermal stress during casting
operations will crack and prematurely fail. When the ultimate
tensile strength is below 100 KSI, the mold material will deform
due to high thermal stress leading to low mold life.
[0065] Typically the melting is done by vacuum induction melting
(VIM).
[0066] Preferably the mold has a temperature in the range from 30
to 300.degree. C. when the alloy is poured into the mold.
Typically, the mold has a temperature in the range from 20 to
400.degree. C. when the alloy is poured into the mold, or the mold
has a temperature in the range from 100 to 200.degree. C. when the
alloy is poured into the mold. Typically the mold cavity is round
or square or rectangular with a constant thickness in the range
from 0.25 to 2 inch, or from 0.5 to 2 inch, or from 0.5 to 1
inch.
[0067] C. Preheating
[0068] Typically, after molding the solidified plate is preheated
before deformation via hot forging at temperature in the range from
500 to 2200.degree. F. or in the range from 1000 to 2200.degree.
F., or in the range from 1000 to 2000.degree. F. or in the range
from 1200 to 1800.degree. F. or in the range from 1200 to
1600.degree. F.
[0069] D. Hot Forging
[0070] The hot forging of plates cast in graphite molds is
primarily carried out in open flat dies in accordance with the
present invention. The optimum forging parameters need to be
determined for each alloy before the actual forging operation is
carried out.
[0071] Flow stress of an alloy at a specific temperature is a
fundamental characteristic of great importance. It is the stress
that must be applied to make the metal deform plastically.
[0072] The control of grain size evolving during the hot forging
process for cobalt and nickel base alloys is achieved by using a
specific set of thermo-mechanical processing conditions. The
starting columnar grain size produced by the casting process
employed in the present invention is critical. Samples machined
from each cast plate are subjected to a series of hot compression
tests over a range of temperatures and strain rates. Hot
compression is carried out to achieve deformation in the range,
10-80% or 20-80% in a single step or a multiple steps at a given
temperature.
[0073] Typically, the preheated plate is pressed between two flat
dies at strain rate in the range from 0.1/second to 10/second, or
in the range from 0.5/second to 10/second, or in the range from
1/second to 10/second, or in the range from 1/second to 5/second.
Typically, the preheated plate is deformed between two flat dies
undergoing 10-80% reduction in thickness, or 20-80% reduction in
thickness, or 30-70% reduction in thickness.
[0074] E. Annealing
[0075] Following hot compressions, the samples are annealed
optionally to induce dynamic recrystallization. The microstructures
including grain size and grain distribution are evaluated after hot
compression and annealing treatments. Based on microstructural
characteristics, the hot forging parameters are determined for each
alloy.
[0076] F. Alloys
[0077] The invention is suitable for fabricating various nickel and
cobalt base alloys which are suitable for applications as
ferromagnetic sputtering targets in magnetron sputtering
systems.
[0078] 1. Cobalt and Cobalt base alloys
[0079] The Co-base alloy used as targets for magnetron cathode
sputtering contains further elements that produce intermetallic
phases dispersed in the matrix. The typical chemistries of such
alloys can be described by the following formula:
Co.sub.1-x-yM.sub.xR.sub.y
[0080] The compositions are in atom percent, wherein M is at least
one of the elements chromium, platinum, nickel, palladium or
similar elements and 0<=x<=0.3, and R is at least one of the
elements tantalum, molybdenum, tungsten, boron, hafnium, niobium,
vanadium or similar elements which promotes the tendency towards
the formation of intermetallic phases and 0.015<=y<=0.20.
[0081] Depending on the manufacturing techniques employed, the
grain boundaries, twin grain boundaries or slip bands of the Co
based matrix are decorated with the elements forming the
intermetallic phase.
[0082] Sputtering targets based on cobalt alloys such as Co--30
Ni--15 Cr (atom percent) are used for magnetic recording media
production to form recording and protection films, respectively.
Poor consumable volume efficiency of Co alloy targets fabricated by
conventional techniques such as ingot casting and hot rolling have
permeability of >200. If the microstructure of cobalt alloys can
be rendered more homogeneous and fine grained, permeability can be
reduced to below 50 leading to 100% increase in target life.
[0083] Cobalt-Iron-Boron is a family of ferromagnetic target alloys
a containing various amounts of Iron (Fe) and Boron (B). Typically
these amounts are approximately 10 at% Fe and 2-5 at% B.
[0084] Various other ternary and multi-component cobalt base alloy
systems for sputtering target applications are listed below:
[0085] Cobalt-Iron
[0086] Cobalt-Iron-Boron
[0087] Cobalt-Iron-Chromium
[0088] Cobalt-Zirconium-Tantalum
[0089] Cobalt-Zirconium-Niobium
[0090] Cobalt-Zirconium-Rhodium
[0091] Cobalt-Platinum
[0092] Cobalt-Chromium-Platinum
[0093] Cobalt-Chromium-Platinum-Tantalum
[0094] Cobalt-Platinum-Boron
[0095] Cobalt-Chromium
[0096] Cobalt-Chromium-Nickel
[0097] Cobalt-Chromium-Tantalum
[0098] Cobalt- Niobium-Hafnium
[0099] Cobalt-Niobium-Titanium
[0100] Cobalt-Niobium-Iron.
[0101] Typically the metallic alloy is a cobalt base alloy having
the composition in weight percent as follows:
[0102] Cobalt=Balance
[0103] Chromium=5 to 20%
[0104] Tantalum=5 to 15%
[0105] and inevitable impurity elements, wherein the impurity
elements are less than 0.01% each and less than 0.05% total
[0106] Another typical metallic alloy is a cobalt base alloy having
the composition in weight percent as follows:
[0107] Cobalt=Balance
[0108] Chromium=5-20%
[0109] Iron=0-15%
[0110] and inevitable impurity elements, wherein the impurity
elements are less than 0.01% each and less than 0.05% total.
[0111] Another typical metallic alloy is a cobalt base alloy having
the composition in weight percent as follows:
[0112] Cobalt=Balance
[0113] Chromium=5-20%
[0114] Platinum=5-15%
[0115] Boron=0-2%
[0116] and inevitable impurity elements, wherein the impurity
elements are less than 0.01% each and less than 0.05% total.
[0117] Another typical metallic alloy is a cobalt base alloy having
the composition in weight percent as follows:
[0118] Cobalt=Balance
[0119] Chromium=0-20%
[0120] Zirconium=0-5%
[0121] Niobium=0-5%
[0122] Tantalum=0-10%
[0123] Hafnium=0-10%
[0124] and inevitable impurity elements, wherein the impurity
elements are less than 0.01% each and less than 0.05% total.
[0125] 2. Nickel and Nickel Alloys
[0126] Nickel and nickel alloy targets are used in magnetron
sputtering process to fabricate thin films on substrates for a
variety of applications such as:
[0127] Corrosion resistant film adherence to non-metals, thin film
resistors, magnetic thin films, disk drives and magnetic random
access memory (MRAM), contact layers and under bond metallization,
ferromagnetic films and diffusion barriers.
[0128] Various ternary and multicomponent nickel base alloy systems
that are currently used as sputtering targets are listed below:
[0129] High purity nickel (3N7 purity)
[0130] Nickel-Chromium.
[0131] Nickel Chromium Iron
[0132] Nickel-Iron-Rhodium
[0133] Nickel-Tungsten
[0134] Nickel-7 weight percent Vanadium
[0135] A typical nickel base alloy has the composition in weight
percent as follows:
[0136] Nickel=Balance
[0137] Chromium=0-20%
[0138] Iron=0- 10%
[0139] and inevitable impurity elements, wherein the impurity
elements are less than 0.01% each and less than 0.05% total.
[0140] Another typical nickel base alloy has the composition in
weight percent as follows:
[0141] Nickel=Balance
[0142] Chromium=0-20%
[0143] Rhodium=0-10%
[0144] and inevitable impurity elements, wherein the impurity
elements are less than 0.01% each and less than 0.05% total.
[0145] The nickel-tungsten alloy systems, typically have, or
consist of, 10 weight percent of tungsten. The tungsten is added to
make the nickel non-magnetic while retaining similar properties to
pure nickel as a thin film.
[0146] A typical metallic alloy is a nickel base alloy having the
composition in weight percent as follows:
[0147] Nickel=Balance
[0148] Chromium=0- 20%
[0149] Tungsten=0-10%
[0150] and inevitable impurity elements, wherein the impurity
elements are less than 0.01% each and less than 0.05% total.
[0151] The nickel-vanadium alloy system, the desirable compositions
are composed of 93 weight % nickel and 7 weight % vanadium. The
vanadium is added to make the nickel non-magnetic while retaining
similar properties to pure nickel as a thin film.
[0152] A typical metallic alloy is a nickel base alloy having the
composition in weight percent as follows:
[0153] Nickel=Balance
[0154] Vanadium=0-10%
[0155] and inevitable impurity elements, wherein the impurity
elements are less than 0.01% each and less than 0.05% total.
[0156] Another suitable material is a nickel base alloy has a
composition in weight percent as follows:
[0157] Nickel=99.95 to 99.99%.
EXAMPLES
Example 1
[0158] Table 2 lists several alloy compositions which are suitable
for fabrication as sputtering targets in accordance with the scope
of the present invention.
2TABLE 2 (compositions are in weight %) Alloy No. Ni Co Cr Fe Ta V
Pt B Other 1 100 2 80 20 3 97 7 4 70 20 10 5 90 10W 6 85 10 5Rh 7
80 10 10Rh 8 90 10 9 90 9 1Boron 10 80 10 10 11 83 12 5Zr 12 90
5Nb, 5Zr 13 90 10 14 80 10 10 15 68 15 12 5 16 84 16 17 15 70 15 18
77 10 13
Example 2
[0159] An alloy having the composition of Co-16 atom % Cr alloy is
cast into metallic molds of several metal alloys as listed in Table
1 according the scope of the sent invention as plates with the
following dimensions: 5.times.5.times.1 inch thick plate. The
following metal alloys are used as molds: AISI 1030, AISI 1095,
AISI 1141, AISI 4130 and AISI 4340.
[0160] The plate are heated to 2100.degree. F. and forged into 0.4
inch thick plates. The forged plates show fine grained
microstructures with homogeneous dispersions of fine second phase
precipitates throughout the primary grains of the matrix. The
forged plates are machined to final thickness of about 0.315 inch
and are analyzed for the percentage PTF (pass through flux). The
results are shown in Table 3 below. Also listed in the same Table 3
the data obtained from sputtering targets having the similar
compositions produced by the conventional process based on ingot
melting, casting and hot rolling. The sputtering targets produced
by the method disclosed in the present invention show higher PTF
values compared to the similar targets produced by the conventional
processes.
3TABLE 3 Final Machined Composition Produced by Thickness (inch) %
PTF Co-16atom % casting in AISI 1050 0.315 67 carbon steel mold
followed by hot forging Co-16atom % casting in AISI 1095 0.315 65
carbon steel mold followed by hot forging Co-16atom % casting in
AISI 1141 0.315 68 carbon steel mold followed by hot forging
Co-16atom % casting in AISI 4130 0.315 69 carbon steel followed by
hot forging Co-16atom % casting in AISI 4340 0.315 66 carbon steel
followed by hot forging Co-16atom % conventional ingot 0.315 55
metallurgy and hot rolling
Example 3
[0161] Several cobalt base alloy compositions as listed in Table 4
below are cast into PERMANICKEL alloy 300 molds according the scope
of the present invention as plates having a thickness ranging
between 1 to 2 inches. PERMANICKEL alloy has the following chemical
composition (weight percent):
[0162] Nickel=98.5, C=0.20, Mn=0.25, Fe=0.30, Si=0.18, Cu=0.13,
Ti=0.40, Mg=0.35
[0163] The plates are heated between 1200.degree. F.-2150.degree.
F. and forged into plates at strain rates ranging between
0.1/second to 10/second with total deformation ranging between 20
to 80%. The forged plates show fine equiaxed grains with
homogeneous dispersions of fine second phase precipitates
throughout the primary grains of the matrix. The forged plates are
machined to final thickness of 0.250 inch and are analyzed for the
percentage PTF (pass through flux). The results are shown in Table
4 below.
4TABLE 4 Composition (atom %) Final machined Thickness (inch) % PTF
Co-10Cr-5Ta 0.250 70 co-13Cr-6Ta 0.250 68 Co-10Cr-15Pt 0.250 70
Co-12Cr-13Pt-10B 0.250 67 Co-10Cr-10Ni 0.250 72 Co-15Cr-15Ni 0.250
69 Co-10Cr-5Nb 0.250 65 Co-13Cr-5Zr 0.250 73 co-12Cr-5Fe 0.250
70
Example 4
[0164] An alloy having the composition of Co-16 atom % Cr is cast
into molds made of Nitriding steel Type 135 and Nitriding steel
type N according the scope of the present invention as plates with
the following dimensions: 5.times.5.times.1 inch.
[0165] The plates are heated to 2100.degree. F. and forged into 0.4
inch thick plates. The forged plate show very fine grain
structures. The forged plates show PTF values in excess of 70%.
Example 5
[0166] An alloy having the composition of Co-14Cr-4Ta (atom %) is
cast into a mold made of Pearlitic 80002 type malleable cast iron
according the scope of the present invention as plates. The plates
are heated to 2100.degree. F. and forged into 0.4 inch thick
plates. The forged plate show very fine grain structures. The
forged plates show PTF values in excess of 70%. The microstructure
of the forged plate is found to be considerable more uniform in
comparison to a sputtering target of the same alloy made by the
conventional process of ingot metallurgy followed by hot
rolling.
Example 6
[0167] An alloy having the composition of Co-16 atom % Cr is cast
into a mold made of different carbon steels as listed in Table 1
such as AISI 1118, A AISI 1030, AISI 1050, AISI 1080, AISI 1095,
AISI 1141, AISI Type B 1211 and AISI type B 1212 according to the
scope of the present invention as plates with the following
dimensions: 5.times.5.times.1 inch. The samples from each of the
cast plates are examined metallographically under an optical
microscope. The microstructure of the samples from the as cast
plates show fine columnar grain structure.
Example 7
[0168] The alloy of Example 6 which is cast into AISI 4340 and AISI
4330 steel molds into plates having the following dimensions 5
inch.times.5 inch.times.1 inch thick. The cylindrical samples
(0.625 inch diameter.times.1 inch long) are machined from the cast
plates and are hot compressed at strain rate of 3/sec at four
different temperatures 2000.degree. F., 1800.degree. F.,
1700.degree. F. and 1600.degree. F. The hot compressed specimens
are analyzed for microstructures. Hot compression at lower
temperatures results into finer microstructures.
Example 8
[0169] A nickel plate with purity of 99.95% is cast into molds made
of the following cast alloy steels: Class 105,000, Class 120,000
and Class 200,000 According to the scope of the present invention
with the following dimensions: 5.times.5.times.1 inch. Samples
sectioned from the cast plates are hot compressed at 3/second
strain rate at various temperatures ranging from 1200.degree. F. to
1800.degree. F.
[0170] The microstructures of the as cast plate as well as hot
compressed specimens are examined. Samples hot compressed at lower
temperatures (1200.degree. F. and 1400.degree. F.) are found to
show finer grain sizes as compared to the as cast plates as well as
the samples hot compressed at temperatures greater than
1400.degree. F.
Example 9
[0171] Several nickel base alloys listed in Table 2 are cast in
PERMANICKEL alloy 300 molds into plates with thickness ranging
between 0.5 to 2 inches. The plates are hot forged at strain rates
between 0.1/second to 10/second at temperatures between
1200.degree. F. and 2200.degree. F. Following forging the plates
are annealed at 1200.degree. F.-2000.degree. F. for 10 minutes to 2
hours. The microstructures of the plates following forging and
annealing consist of uniform fine equiaxed grains with grain size
below 50 microns as a result of dynamic recrystallization.
Example 10
[0172] Several materials listed in Table 5 have been considered as
potential candidates for use as mold materials in accordance with
the present invention. Although the materials listed in Table 5
have desirable mechanical and physical properties, some of the
properties fall outside the critical range of properties such as
thermal conductivity, melting point and ultimate tensile strength
of mold materials in accordance with the present invention.
[0173] Several nickel and cobalt base alloys listed in Table 2 such
as Ni-7 wt % V and Co-10 wt % Cr-10 wt % Ta are melted and cast in
molds made of materials listed in Table 5 as 5.times.5.times.1 inch
thick plate. The plates are hot forged at strain rates between
0.1/second to 10/second at temperatures between 1200.degree. F. and
2200.degree. F. Following forging the plates are annealed at
1200.degree. F.-2000.degree. F. for 10 minutes to 2 hours. The PTF
values of the plates following forging and annealing are measured
to be low i.e. below 50% and hence are determined to be unsuitable
for use as magnetron sputtering targets.
5TABLE 5 Thermal Ultimate Conductivity Tensile Melting Point
BTU/ft.sup.2/hr/ Strength Material (.degree. F.) in/.degree. F.,
70.degree. F. (KSI) at 70.degree. F. Nickel 201 2659 550 59 Nickel
Base 2587 145 120 Hastelloy D Nickel Base 2480 124 160 Monel Alloy
R 500 Nickel Base 2475 88 135 MAR-M-200 Nickel Base 2450 77 100
Incoloy 825 17-4 PH 2710 125 190 Stainless Steel AISI 410 Stainless
2750 172 110 Steel The chemical compositions of the alloys listed
in Table 5 are given in the CRC Handbook of Materials Science, Vol.
II, edited by C.T. Lynch, CRC Press, Inc, Boca Raton, Florida,
1975.
[0174] It should be apparent that in addition to the
above-described embodiments, other embodiments are also encompassed
by the spirit and the scope of the present invention. Thus, the
present invention is not limited by the above-provided description,
but rather is defined by the claims appended hereto.
* * * * *