U.S. patent application number 11/825854 was filed with the patent office on 2008-01-17 for method of making sputtering target and target produced.
This patent application is currently assigned to Howmet Corporation. Invention is credited to Tyrus W. Hansen, Michael G. Launsbach.
Application Number | 20080011392 11/825854 |
Document ID | / |
Family ID | 39033456 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080011392 |
Kind Code |
A1 |
Launsbach; Michael G. ; et
al. |
January 17, 2008 |
Method of making sputtering target and target produced
Abstract
Method of making a sputtering target includes the steps of
melting a metallic target material, controlling the temperature of
the melted target material in a manner that the melted target
material has almost no superheat, introducing the melted target
material into a mold having interior walls forming a mold cavity in
the shape of the desired target, and solidifying the melted target
material in the mold by extracting heat therefrom at a rate to
solidify it to form a sputtering target having a cellular
nondendritic microstructure uniformly throughout the target. A
sputtering target is provided comprising a metallic target material
having a substantially equiaxed, cellular nondendritic
microstructure uniformly throughout the target.
Inventors: |
Launsbach; Michael G.;
(Yorktown, VA) ; Hansen; Tyrus W.; (New Era,
MI) |
Correspondence
Address: |
Mr. Edward J. Timmer
P.O. Box 770
Richland
MI
49083-0770
US
|
Assignee: |
Howmet Corporation
|
Family ID: |
39033456 |
Appl. No.: |
11/825854 |
Filed: |
July 9, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60831521 |
Jul 17, 2006 |
|
|
|
Current U.S.
Class: |
148/538 ;
148/400; 148/425; 164/120; 164/121; 164/47 |
Current CPC
Class: |
C23C 14/3414 20130101;
C22C 19/07 20130101; B22D 27/04 20130101; B22D 21/025 20130101 |
Class at
Publication: |
148/538 ;
148/400; 148/425; 164/120; 164/121; 164/047 |
International
Class: |
C22C 19/07 20060101
C22C019/07; B22D 27/04 20060101 B22D027/04; B22D 27/09 20060101
B22D027/09 |
Claims
1. Method of making a sputtering target, including the steps of
melting a metallic target material, controlling the temperature of
the melted target material in a manner that the melted target
material has almost no superheat, introducing the melted target
material into a mold having interior walls forming a mold cavity in
the shape of the desired target, and solidifying the melted target
material in the mold by extracting heat therefrom at a rate to
solidify it to form a sputtering target having a cellular
nondendritic microstructure uniformly throughout the target.
2. The method of claim 1 including heating the mold before
introducing the melted target material to a high enough elevated
mold temperature to prevent substantial columnar grain formation
directly adjacent interior walls of the mold
3. The method of claim 1 wherein the temperature of the melted
target material is controlled within 0 to 20 degrees F. of the
melting point of the target material.
4. The method of claim further including hot isostatic pressing the
solidified sputtering target.
5. The method of claim 1 wherein heat is extracted at a rate to
produce an ASTM grain size of 3 or less in the as-cast sputtering
target.
6. The method of claim 1 wherein the mold comprises a ceramic,
graphite, or metallic mold.
7. The method of claim 1 wherein the temperature of the melted
target material is controlled by reducing power supplied to an
induction coil.
8. The method of claim 1 including solidifying the target material
to a target shape that requires minimal machining.
9. The method of claim 1 wherein the target material comprises a
cobalt based alloy including an alloying element selected from the
group consisting of boron, chromium, platinum, tantalum, ruthenium,
niobium, copper, vanadium, silicon, silver, gold, iron, aluminum,
zirconium, and nickel.
10. A sputtering target, comprising a metallic target material
having a substantially equiaxed, cellular nondendritic
microstructure uniformly throughout the target.
11. The target of claim 8 having a grain size of ASTM 3 or
less.
12. The target of claim 8 which is densified by hot isostactic
pressing.
13. The target of claim 10 which comprises a cobalt based alloy
including an alloying element selected from the group consisting of
boron, chromium, platinum, tantalum, ruthenium, niobium, copper,
vanadium, silicon, silver, gold, iron, aluminum, zirconium, and
nickel.
Description
[0001] This application claims benefits and priority of U.S.
provisional application Ser. No. 60/831,521 filed Jul. 17,
2006.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of making a
sputtering target and, in particular, to a method of casting a
metallic sputtering target to have an equiaxed, cellular,
non-dendritic microstructure.
BACKGROUND OF THE INVENTION
[0003] A current process employed to make metallic sputtering
targets comprises crushing a slab of the metallic material,
screening and sorting the crushed particles to appropriate particle
sizes, hot isostatic pressing (HIP'ing) particles of certain sizes
in an evacuated, sealed can to from a target body, and then
machining the HIP'ed body to produce the desired target shape.
[0004] Another method currently used to make a large molybdenum
sputtering target is to cold isostatic press (CIP) Mo powder,
sinter the cold pressed body to reduce the oxygen content, and then
hot roll the sintered body to a flat plate or disk of desired
length/width/thickness. The plate or disk then is machined to final
tolerance.
[0005] These processes involve numerous processing steps and
considerable cost to make the sputtering target.
SUMMARY OF THE INVENTION
[0006] The present invention provides a method for making a fine
grain, cast sputtering target. The present invention provides in an
embodiment a method of making a sputtering target by melting a
metallic target material, controlling the temperature of the melted
target material in a manner that the melted target material has
almost no superheat, introducing the melted target material into a
mold having interior walls forming a mold cavity in the shape of
the desired target, and solidifying the melted target material in
the mold by extracting heat therefrom at a rate to solidify it to
form a sputtering target having substantially equiaxed, cellular
nondendritic microstructure uniformly throughout the target. The
mold optionally can be heated to a high enough elevated mold
temperature that prevents substantial columnar grain formation
directly adjacent interior walls of the mold
[0007] The present invention also provides in another embodiment a
metallic sputtering target having a substantially equiaxed,
cellular nondendritic microstructure uniformly throughout the
target. The sputtering target can be used in the as-cast condition
without further post-cast treatments other than finish machining or
after the as-cast target is hot isostatically pressed to densify
the as-cast target.
[0008] The invention is advantageous to provide a cast sputtering
target without the need for numerous processing steps employed in
the art and to provide a sputtering target with beneficial
microstructural properties for sputtering.
[0009] The invention also provides grain size control of the
target, reduces manufacturing lead times from material selection to
target manufacture, and increased material selection flexibility
such as more alloying options.
[0010] Other advantages, features, and embodiments of the present
invention will become apparent from the following description.
DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic perspective view of a melted target
material in a crucible ready for casting into a steel or ceramic
mold.
DESCRIPTION OF THE INVENTION
[0012] The present invention provides a method of making a
sputtering target comprising a metallic target material. The
metallic target material can comprise a metal or an alloy of two or
more metals. For purposes of illustration and not limitation, the
target material can comprise molybdenum, tungsten, and other metals
and high temperature melting alloys such as nickel based, chromium
based, cobalt based, iron based, tantalum based, molybdenum based,
tungsten based, and other alloys materials. For purposes of
illustration and not limitation, a target alloy can comprise a
cobalt based alloy including an alloying element selected from the
group consisting of boron, chromium, platinum, tantalum, ruthenium,
niobium, copper, vanadium, silicon, silver, gold, iron, aluminum,
zirconium, and nickel. For example, the target can comprise cobalt
based alloys including, but not limited to, a Co--Ta--Zr alloy,
Co--Ta--B alloy, Co--Cr--Pt--B alloy, Co--Cr--Pt--B--Cu alloy and
others. Such target metals or alloys can be obtained commercially
from raw materials suppliers with the appropriate purity for
particular sputtering target applications. The target metals or
alloys are supplied in the form of briquets, powder, chunks,
etc.(shown as INPUT: ALLOY CONTROL in FIG. 1).
[0013] Referring to FIG. 1, an embodiment of the invention involves
melting the selected metallic (metal or alloy) target material TM
in a crucible C or other appropriate melting vessel using an
appropriate melting process such as vacuum induction melting (VIM)
or electron beam (EB) melting. The crucible or melting vessel can
be selected in dependence on the particular metal or alloy to be
melted. Melting can be conducted in an inert atmosphere or in
vacuum (shown as FURNACE ENVIRONMENT VACUUM) in the event the
particular metal or alloy to be melted requires such melting
conditions. Where the metal or alloy requires an inert atmosphere
or vacuum during melting, conventional vacuum induction melting
equipment (shown as VIM MELTING SYSTEM) can be employed.
[0014] A particular conventional vacuum induction melting furnace
used in the Example employs a melting crucible that pours directly
into an underlying mold M. However, the invention envisions use of
a pouring vessel, such as a pouring crucible, optionally as an
intermediate vessel between the melting vessel and the mold to be
cast.
[0015] Preferably, the melted target material in the melting vessel
or in the pouring vessel is held in a substantially quiescent state
to allow any low density non-metallic inclusions to float to the
surface where they can be disposed of or eliminated from the melt.
For example, when vacuum induction melting is used to melt a charge
of target material, a susceptor such as graphite can be placed
between the induction coil IC and the melting vessel such that the
susceptor is heated and in turn heats the charge and such that the
melted target material is not stirred. Alternately, very high
frequencies or resistance heating may be employed to achieve the
same results.
[0016] Furthermore, use of a bottom pouring crucible allows melted
target material to be introduced into a mold without entraining the
floating non-metallic inclusions on the melt surface. Alternately,
a teapot crucible can be used to block non-metallic inclusions
floating on the melt from entering the mold. Other techniques for
minimizing the amount of non-metallic inclusions entering the mold
are described in U.S. Pat. No. 4,832,112 which is incorporated in
its entirety herein by reference.
[0017] The invention further involves controlling the temperature
of the melted target material TM in the melting or pouring vessel
in a manner that the melted target material has almost no superheat
prior to introduction into the mold. The temperature of the melted
target material is reduced to remove up to substantially all of the
superheat in the melted target material. This reduced temperature
should be substantially uniform throughout the melted target
material and, for most target materials, is controlled to be within
0 degree to 20 degrees F. above the measured melting point of the
particular metal or alloy target material, although the range may
be adjusted in dependence on the particular target metal or alloy.
The measured melting point can be determined as described in U.S.
Pat. No. 4,832,112.
[0018] The temperature of the melted target material in the melting
vessel can be reduced by gradually reducing the power or energy
supplied to the melting furnace in which the melting vessel is
located. For example, when the charge of target material is melted
by vacuum induction melting as described in the example below, the
electrical power supplied to the induction coil IC can be gradually
reduced to reduce the temperature of the melted target material so
that substantially all of the superheat is removed prior to
introduction of the melted target material into the mold. The
temperature of the melted material can be measured (shown as
TEMPERATURE MEASUREMENT) using the infrared pyrometer shown or
other temperature measuring device.
[0019] The mold M can include a metal or ceramic mold that includes
interior walls defining a mold cavity having the shape of the
desired sputtering target. Typical shapes of sputtering targets
that can be made include, but are not limited to, plates of
rectangular, square or other polygonal shape and circular
discs.
[0020] Except when making investment cast sputtering targets, the
invention envisions optionally generating turbulence in the melted
target material after it is introduced into the mold. For most
target materials, it is sufficient to pour the melted target
material directly into the mold. The turbulence alternately can be
imparted to the melted target material in the mold by
electromagnetic stirring, mechanical stirring, and comminuting the
melt as it is poured in to the mold such as by breaking the melt
into multiple streams or droplets as it enters the mold as
described in U.S. Pat. No. 4,832,112.
[0021] In accordance with the invention, the melted target material
is solidified in the mold by extracting heat therefrom at a rate to
obtain a substantially equiaxed, cellular, nondendritic grain
structure throughout the sputtering target. The as-solidified
(as-cast)sputtering target preferably has an equiaxed, cellular
ASTM grain size of 3 or less throughout the sputtering target. The
rate of heat extraction is controlled to achieve such equiaxed,
cellular grain structure. In some instances, the initial
temperature gradient between the melted target material and the
relatively cold mold is sufficiently high to produce a zone of
dendritic columnar grains at the interface. The invention envisions
optionally heating the mold to a high enough elevated mold
temperature (shown as Controlled Preheat Process and PREHEATED
MOLD) that prevents substantial columnar grain formation directly
adjacent interior walls of the mold. The solidified target has a
net or near net shape of the desired target and requires only
minimal machining prior to use as a target.
[0022] As the aspect ratio of the mold increases, it is
increasingly important to extract heat more rapidly from the
solidifying target material to maintain the fine grain size and
associated cellular microstructure and to minimize the increasing
tendency for porosity and possible segregation. Improved heat
extraction can be facilitated by the previously disclosed
comminution of the melted target material as it is poured into the
mold.
[0023] In the event the solidified, as-cast sputtering target has
some porosity, this porosity can be removed by various techniques
including by hot isostatic pressing (HIP'ing) the as-cast
sputtering target using conventional hot isostatic gas pressing
processes whose parameters of gas pressure, temperature and time
will depend on the particular target metal or alloy employed.
Control and removal of as-cast porosity of the sputtering target is
described in U.S. Pat. No. 4,832,112.
[0024] For purposes of further illustrating the invention and not
limiting it in any way, a rectangular sputtering target having
dimensions of 27 inches length by 4.25 inches width by 0.2 inches
thickness can be cast in a conventional preheated ceramic
investment mold, which is positioned in a lower chamber of a
conventional vacuum induction furnace. The preheated investment
mold will include a mold cavity that closely replicates the desired
shape of the sputtering target. The target metal or alloy
comprising for example a cobalt based alloy of the type described
above can be heated in an upper chamber of the furnace under vacuum
conditions below 10 microns to a temperature about 20-50 degrees F.
above its melting point to melt it in a zirconia crucible. Power to
the induction coil of the furnace can be gradually reduced until
the melted target material is within 0 to 20 degrees F. of the
melting point. The melted target material then can be poured into
the mold which can contain a constriction at the top of the mold
that forces rapid local solidification at the center line of the
mold cavity. This can prevent the formation of interconnected
porosity at the center line and allowed densification of the
as-cast sputtering target, when necessary, by HIP'ing the target at
2100 degrees F. at 29 KSI gas pressure for 1 hour. The resultant
HIP'ed sputtering target exhibits a fine grain, equiaxed cellular
grain structure.
[0025] Although certain embodiments of the invention have been
described above, those skilled in the art will appreciate that the
invention is not limited to these embodiments and that
modifications and changes can be made therein without departing
from the spirit and scope of the invention as set forth in the
appended claims.
* * * * *