U.S. patent application number 12/319754 was filed with the patent office on 2010-07-15 for method for making composite sputtering targets and the tartets made in accordance with the method.
Invention is credited to Scott Campbell.
Application Number | 20100178525 12/319754 |
Document ID | / |
Family ID | 42319298 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100178525 |
Kind Code |
A1 |
Campbell; Scott |
July 15, 2010 |
Method for making composite sputtering targets and the tartets made
in accordance with the method
Abstract
Composite sputtering targets are made by hot pressing metal or
metal containing powders into a backing plate which can be
comprised of a different material with a depression formed in a
surface or can be a used sputtering target of the same or different
material. The depression corresponds to the erosion pattern of a
target having the same geometry. The depression can be formed for
example, by machining. The backing plate is loaded into a graphite
die and covered with the sputtering material to form an assembly. A
ram is added and the assembly with the ram is loaded into a hot
press which is taken to an appropriate pressure and temperature
under vacuum to form a composite sputtering target having a
sputtering zone of densified sputtering material.
Inventors: |
Campbell; Scott;
(Worthington, OH) |
Correspondence
Address: |
HUDAK, SHUNK & FARINE, CO., L.P.A.
2020 FRONT STREET, SUITE 307
CUYAHOGA FALLS
OH
44221
US
|
Family ID: |
42319298 |
Appl. No.: |
12/319754 |
Filed: |
January 12, 2009 |
Current U.S.
Class: |
428/551 ;
419/19 |
Current CPC
Class: |
B22F 2998/10 20130101;
Y10T 428/12049 20150115; B22F 2999/00 20130101; B22F 3/14 20130101;
B22F 7/08 20130101; B22F 2999/00 20130101; B22F 2003/247 20130101;
B22F 2998/10 20130101; B22F 3/14 20130101; B22F 3/24 20130101; B22F
2201/20 20130101; B22F 3/14 20130101 |
Class at
Publication: |
428/551 ;
419/19 |
International
Class: |
B22F 3/14 20060101
B22F003/14 |
Claims
1. A method of manufacturing composite sputtering targets
comprising the steps of: (a) providing a backing plate having a
geometry and a surface which includes a depression, (b) placing the
backing plate into a graphite die designed to accommodate a
geometry of the backing plate, (c) adding a sputtering material to
the graphite die on top of the backing plate to from a die assembly
(d) placing a graphite die ram into the die assembly so that the
ram contacts the sputtering material, (e) placing the die assembly
and ram into an hydraulic press and pressing the graphite die ram
into graphite die to a specific pressure, (e) placing the compacted
die assembly and ram into a vacuum hot press furnace chamber and
contacting the die ram with the hydraulic ram of the hot press, (g)
sealing and evacuating the vacuum hot press furnace chamber to a
vacuum level of between about 200 and 50 mTorr, (h) heating the
vacuum hot press furnace chamber and contents to a pre-determined
temperature and applying pressure to the graphite die ram via the
hydraulic press ram, (i) lowering the pressure on the ram, and
cooling and raising the vacuum level of the hot press vacuum
furnace chamber, and (j) removing the die assembly and ram from the
vacuum hot press furnace.
2. The method of claim 1 further including the step of removing a
composite sputtering target pre-form from the graphite die.
3. The method of claim 2 including the further step of machining
the surface of the composite sputtering target pre-form.
4. The method of claim 3 wherein the machining step includes one or
more of diamond grinding and electrodynamic machining.
5. The method of claim 1, wherein the backing plate comprises a
material that is a refractory metal or alloy that is mechanically
and chemically compatible with the sputtering material.
6. The method of claim 5 wherein the backing plate material
comprises is Mo, Ta, or Nb.
7. The method of claim 1, wherein said sputtering material is
comprises pure Ru, Rh, Pd, Re, Os, Ir, Pt or mixtures of Ru, Rh,
Pd, Re, Os, Ir, Pt or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt, with
transition metals, or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt, with
transition metals and oxides or mixtures of Ru, Rh, Pd, Re, Os, Ir,
Pt with oxides.
8. The method of claim 1, wherein the sputtering material is
comprised of precious metals or precious metal alloys or mixtures
with other metals or metal alloys or metal oxides.
9. The method of claim 1, wherein the composite sputtering target
geometry is circular, rectangular, delta, or oval shaped.
10. The method of claim 1, wherein the composite sputtering target
is comprised of more than one section requiring a multi-tile
sputtering target design.
11. The method of claim 1, including the further step of forming
the depression in the backing plate.
12. The method of claim 11 including the further step of
calculating the erosion pattern of a used sputtering target having
a geometry which corresponds to the geometry of the composite
sputtering target, using that erosion pattern to calculate an
optimal shape for the depression, and forming the depression to
correspond to the optimal shape in a surface of the backing plate
by machining the backing plate.
13. The method of claim 1 in which the backing plate is a used
sputtering target.
14. The method of claim 1 in which the backing plate is comprised
of a material which is different than the sputtering material.
15. The method of claim 1, wherein a barrier material is used, and
the material of the barrier material is inserted between the
sputtering material and backing plate so as to prevent adverse
reactions between the precious metal containing material and the
machined backing plate material.
16. The method of claim 15, wherein the barrier material is
comprised of one or more of Nb, Ta, Mo of one of more of a foil, a
powder or a coating.
17. A method of manufacturing composite sputtering target including
a sputtering material comprising the steps of: (a) selecting a
backing plate material that is chemically and mechanically
compatible with the sputtering material, (b) forming a groove in
the backing plate material that approximates the erosion groove of
a spent sputtering target to form a backing plate having a geometry
including a top surface, (c) placing the backing plate into a
graphite hot press die designed to accommodate the geometry of the
backing plate, (d) adding a predetermined amount of powder of the
sputtering material onto the top surface of the backing plate so as
to as to fill the groove and cover the top surface of the backing
plate to form a graphite die backing plate assembly, (e) vibrating
the graphite die backing plate assembly so as to evenly distribute
the sputtering material powder over the top surface of the backing
plate and thus form a top surface of the sputtering material
powder, (f) placing a graphite die ram having a top surface and
bottom surface into the graphite die so that the bottom surface of
the ram contacts the top surface of the sputtering material powder
to form an assemblage of the graphite die backing plate assembly
and the graphite die ram, (g) placing the assemblage into an
hydraulic press and pressing the graphite die ram to a
predetermined pressure so as to compact the sputtering material
powder into the backing plate groove and unto the surface of the
machined backing plate to from a compacted assemblage, (h) placing
the compacted assemblage into a vacuum hot press furnace chamber
and lowering the hydraulic ram of the hot press onto the graphite
die ram so as to contact the top surface of the die ram, (i)
sealing and evacuating the vacuum hot press furnace chamber to a
vacuum level of between about 200 and about 50 mTorr, (j) heating
the vacuum hot press furnace chamber and contents to a
pre-determined temperature suitable for the densification of the
sputtering material powder into a solid, dense form, (k) applying
pressure to the graphite die ram via the hydraulic press ram to a
pre-determined pressure suitable for the densification of the
sputtering material powder into a solid, dense form, (l) holding
the assemblage at the applied temperature and pressure for a
pre-determined amount of time suitable for the densification of the
sputtering material powder into a solid, dense form to form a
sputtering target pre-form, (m) releasing the pressure on the
hydraulic press ram, and cooling and releasing the vacuum level of
the hot press vacuum furnace chamber, (n) removing the assemblage
from the vacuum hot press furnace and removing the composite
sputtering target pre-form from the graphite die, (o) finishing the
surface of the composite sputtering target pre-form to obtain a
composite sputtering target.
18. The method of claim 17, wherein the backing plate comprises a
material that is a refractory metal or alloy that is mechanically
and chemically compatible with the sputtering material.
19. The method of claim 18 wherein the backing plate material
comprises is Mo, Ta, or Nb.
20. The method of claim 17, wherein said sputtering material is
composed of pure Ru, Rh, Pd, Re, Os, Ir, Pt or mixtures of Ru, Rh,
Pd, Re, Os, Ir, Pt or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt, with
transition metals or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt, with
transition metals and oxides or mixtures of Ru, Rh, Pd, Re, Os, Ir,
Pt with oxides such as TiO.sub.2.
21. The method of claim 17, wherein the sputtering material is
composed of precious metals or precious metal alloys.
22. The method of claim 21 wherein the sputtering material is Ag or
Au or mixtures of Ag or Au with other metals or metal alloys or
metal oxides.
23. The method of claim 17, wherein the composite sputtering target
has a geometry which is circular, rectangular, or delta shaped.
24. The method of claim 17, wherein the composite sputtering target
is composed of more than one section requiring a multi-tile
sputtering target design.
25. The method of claim 17, wherein a spent composite sputtering
target is used as the backing plate to produce the composite
sputtering target.
26. The method of claim 17, wherein a spent composite sputtering
target is used a plurality of times as the backing plate to produce
the composite sputtering target.
27. The method of claim 17, wherein a barrier material or other
material chemically and mechanically compatible with the sputtering
material and the backing plate material is inserted between the
precious metal containing material and the machined backing
plate.
28. The method of claim 27, wherein the barrier material is
inserted between the sputtering material and the backing plate
material by the use of foils, powders or coatings composed of the
barrier material.
29. A method of increasing the production efficiency of a
sputtering material comprising the steps of: forming a sputtering
target perform by (a) providing a backing plate having a geometry
which includes a surface which provides a depression, (b) placing
the backing plate into a graphite die designed to accommodate the
geometry of the backing plate, (c) adding a sputtering material to
the graphite die on top of the backing plate to from a die assembly
(d) placing a graphite die ram into the die assembly so that the
ram contacts the sputtering material, (e) placing the die assembly
and ram into an hydraulic press and pressing the graphite die ram
into the graphite die to a specific pressure to form a compacted
die assembly, (f) placing the compacted die assembly and ram into a
vacuum hot press furnace chamber and contacting the die ram with
the hydraulic ram of the hot press, (g) sealing and evacuating the
vacuum hot press furnace chamber to a vacuum level of between about
200 and 50 mTorr, (h) heating the vacuum hot press furnace chamber
and contents to a pre-determined temperature and applying pressure
to the graphite die ram via the hydraulic press ram, (i) lowering
the pressure on the hydraulic press ram and cooling and releasing
the vacuum level of the hot press vacuum furnace chamber, (j)
removing the compacted die assembly and ram from the vacuum hot
press furnace, (k) removing a composite sputtering target pre-form
from the graphite die to form a composite sputtering target, using
the composite sputtering target for a sputtering process to form a
used composite sputtering target; and using the used composite
sputtering target as a backing plate to form a new composite
sputtering target.
30. The method of claim 29 including the further step of machining
the surface of the composite sputtering target pre-form to obtain
specified physical dimensions of the composite sputtering
target.
31. The method of claim 30 wherein the machining step includes one
or more of diamond grinding and electrodynamic machining.
32. The method of claim 30, wherein the backing plate comprises a
material that is the sputtering material or Mo, Ta, or Nb.
33. The method of claim 30, wherein said sputtering material is
composed of pure Ru, Rh, Pd, Re, Os, Ir, Pt or mixtures of Ru, Rh,
Pd, Re, Os, Ir, Pt or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt, with
transition metals, or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt, with
transition metals, and oxides such as TiO.sub.2 or mixtures of Ru,
Rh, Pd, Re, Os, Ir, Pt with oxides.
34. A composite sputtering target comprised of a backing plate
which is one or more of Mo, Ta, and Nb, and a sputtering zone which
is composed of pure Ru, Rh, Pd, Re, Os, Ir, Pt or mixtures of Ru,
Rh, Pd, Re, Os, Ir, Pt or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt,
with transition metals, or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt,
with transition metals and oxides or mixtures of Ru, Rh, Pd, Re,
Os, Ir, Pt with oxides, the sputtering zone being a densified area
of sputtering material chemically, thermally and electrically
consolidated with the backing target, and the sputtering target
having a suitable geometry for use in a sputtering process.
35. The composite sputtering target of claim 34, wherein a barrier
material comprised of Nb, Ta, Mo, is inserted between the
sputtering material and backing plate so as to prevent adverse
reactions between the precious metal containing material and the
machined backing plate material.
36. The composite sputtering target of claim 34 wherein the
configuration of the sputtering zone is formed by calculating the
erosion pattern of a used sputtering target having a geometry which
corresponds to the geometry of the composite sputtering target and
using that erosion pattern to calculate the sputtering zone.
Description
FIELD OF THE INVENTION
[0001] The invention relates to composite sputtering target
assemblies made by hot pressing metal or metal containing powders
into a metal backing plate. More particularly, the invention
relates to a method of making a hot pressed composite sputtering
target assembly that reduces the amount of relatively expensive
materials such as precious metal containing materials required to
prepare the target by confining these materials to the area of the
target utilized in the sputtering process. The invention further
relates to the target, which is produced by the method.
BACKGROUND OF THE INVENTION
[0002] Thin layers of many materials may be deposited on a
substrate material by a process known as DC-magnetron sputtering. A
typical sputtering system includes a means for generating a high
energy plasma that removes the material to be deposited from the
surface of a source forming a vapor of that material that condenses
on the surface of the desired substrate. In such a system, the
source of the material to be deposited on the substrate is called a
sputtering target. A sputtering target can be composed solely of
the material to be deposited or in some cases the material to be
deposited is formed into an object called a sputtering target tile
that is joined to a dissimilar material called the sputtering
target backing plate and the entire assembly is called the
sputtering target. The choice of sputter target construction
depends on the sputtering system used, the physical and electrical
properties of the material to be deposited, and the expense of the
material to be deposited.
[0003] In the sputtering process, the high energy plasma
continuously erodes the surface of the sputtering target material
forming a depression known as an "erosion groove" in the surface of
the sputtering target. This erosion groove is commonly referred to
in the thin film industry as the "racetrack" due to its unique
shape. Eventually, the erosion groove becomes deep enough that
further sputtering of the target material is impractical and at
that point the sputtering target is considered "spent".
[0004] In typical sputtering processes only 20-40% of the target
material is utilized and the remaining target material is either
discarded or recycled by remelting or refining. Customarily
precious metal targets are recycled to capitalize on the value of
the sputtering target material. The recycling process increases the
amount of precious metal needed to practice a sputtering process
considerably since the spent target is tied up in being re-melted
and/or refined before it is made available to be made into a new
target. It often takes several weeks, or even months to render the
remaining material from a spent target available and in addition,
there is a significant material loss in the recycling process.
[0005] While for most materials used in the sputtering process
recycling is economically feasible, this is not necessarily the
case for relatively expensive materials such as those that contain
precious metals such as Pt, Ru, Pd, Os, Ir, Rh, and Re or
combinations of precious metals and other metals or metal oxides.
In this case the cost and the amount of material loss from the
recycling processes are substantial enough to warrant a significant
change in the way precious metal containing sputtering targets are
manufactured.
[0006] In accordance with the present invention, a method to reduce
the amount of precious metal containing materials used in the
precious metal containing sputtering target manufacturing process
is to confine the precious metal containing material to the actual
area where it is consumed; the sputtering erosion groove. It is
conceivable to reduce the amount of precious metal containing
material used to manufacture a target by greater than 40% by
restricting the precious metal containing material to the erosion
groove area of the sputtering target. A way to achieve this goal is
to manufacture a composite sputtering target whereby the precious
metal containing material is formed into a shape similar to the
shape of the sputtering erosion groove and applied to a backing
plate composed of a relatively inexpensive material specially
machined to accommodate the shape of the erosion groove of the
sputtering process. Moreover, as the present invention does not
require that a spent target go through a refining process, it
results in a significant reduction in the inventory of precious
metal used for sputtering (and especially in a reduction of the
material that is tied up in spent targets which are not serving in
production capacity, but instead is undergoing the recycling
process.).
[0007] Prior art does teach that composite sputtering target
assemblies can be advantageously fabricated by powder metallurgical
processes. One such process is disclosed in Mueller, U.S. Pat. No.
5,397,050, dated Mar. 14, 1995, which describes a method of
producing a composite sputtering target assembly consisting of a
tungsten-titanium alloy target and a titanium backing plate. The
titanium backing plate is placed in a metal can and
tungsten-titanium powder is placed on top of the titanium backing
plate in the can. The can containing the powder and backing plate
is hot isostatic pressed (HIP'ed) forming a composite sputtering
target. However, since the process involves HIP'ing powder
contained within a metal can, it is relatively costly due to the
use of expensive canning materials, machining, canning as well as
HIP procedures and equipment which add to manufacturing cost. In
addition, the expensive target material is not confined to the
sputtering area of the target, thus the amount of the expensive
target material used to form this type of sputtering target is not
significantly reduced.
[0008] Another such method is disclosed in Stellrecht, U.S. Pat.
No. 5,963,778, dated Mar. 14, 1999 in which a composite target is
fabricated using powder metallurgical processes and which attempts
to confine the expensive sputtering material to the sputtering area
of the target. However, like the previous invention, the process
used to prepare the composite target is HIP'ing and thus, the same
cost implications described above apply.
[0009] Sandlin et al. disclose a method to refurbish spent
sputtering targets in U.S. Pat. No. 7,175,802 whereby new
sputtering material is applied to a spent sputtering target by
filling the sputtering erosion groove with the new material. This
process is also accomplished using HIP'ing. The invention does not
confine the expensive sputtering material to the sputtering area of
the target, but does reuse the spent target instead of recycling
it. However, there still remains a considerable amount of expensive
material in use that is not used in the sputtering process leading
to a still relatively high cost of ownership. In addition, the
disclosed process requires the spent targets to be thoroughly
immersed in the powder of the expensive material that requires
removal and recycling after pressing.
[0010] The present invention provides an efficient and relatively
low cost method of producing composite sputtering target assemblies
whereby the precious metal containing sputtering material is
confined to the sputtering area of the target assembly. This is
achieved by applying the precious metal containing sputtering
material to a backing plate assembly of a substantially lower cost
material that has a cavity machined into its surface that
approximates the sputtering erosion groove of spent targets.
Additionally, the process can be applied such that the erosion
groove of a spent target is filled using the process of the present
invention. In this instance, the spent target becomes the backing
plate, and does not require additional machining to form a form for
the newly added precious material.
[0011] Furthermore, the composite target of the present invention
is fabricated using vacuum hot pressing that utilizes re-usable
graphite dies instead of single-use metal cans and the amount of
precious metal containing material powder used in the forming
process is greatly reduced. The result is a composite sputtering
target that requires at least 50% less of the expensive material
than a target produced purely of the precious metal containing
material. The process significantly reduces amount of precious
metal that needs to be dedicated to a sputtering process since it
eliminates side lining of the spent target material into the
recycling portion of the production cycle of precious material used
in sputtering targets. This advantage results in a tremendous and
unforeseen increase in the efficiency of the precious material
dedicated to the sputtering process.
SUMMARY OF THE INVENTION
[0012] In accordance with the invention, there is provided a method
of making a sputtering target assembly that confines precious metal
containing sputtering target materials to the sputtering area of
the target thereby reducing the amount of precious metal containing
sputtering material required to produce the sputtering target
assembly, and further increases the efficiency of the material
dedicated to the sputtering process, and thus reduces the cost of
ownership of the sputtering target assembly as well as the capital
investment needed for the sputtering process. The method involves
providing a backing plate of a relatively inexpensive material,
that is chemically and mechanically compatible with the precious
metal containing sputtering material, with a depression in the
surface, (which can in the first instance be machined into the
backing plate) that corresponds to the sputtering erosion pattern
observed in used sputtering targets, placing the backing plate into
a graphite die shaped to accommodate the geometry (i.e., the size
and shape) of the backing plate, filling the depression in the
backing plate with a powder of the precious metal containing
sputtering material, then placing a graphite ram on top of the
powder layer. The die containing the backing plate powder
assemblage is then placed in a vacuum hot press to consolidate and
densify the precious metal containing sputtering target material
powder into the backing plate depression. Not only does vacuum hot
pressing consolidate and densify the precious metal containing
sputtering target material, the hot pressing also facilitates the
formation of a strong inter-metallic bond between the precious
metal containing sputtering material and the backing plate material
creating a strong mechanical attachment as well as an intimate
electrical and thermal conduction path between the precious metal
containing sputtering target material and the backing plate. After
hot pressing, a minimal amount of machining may be required to
obtain the required dimensional specifications for the particular
sputtering target design.
[0013] In a preferred embodiment of the invention, a method of
making a precious metal containing sputtering target assembly
comprises 1) providing backing plate including a surface having a
depression; 2) placing the backing plate into the cavity of a
graphite die set prepared to accommodate the geometry backing
plate; 3) forming a die assemblage by placing a sputtering material
into the cavity in contact with the depression so as to completely
cover the surface of the backing plate to a predetermined depth; 4)
placing a graphite ram into the cavity of the assemblage so as to
contact the top of the sputtering material; 5) placing the ram and
die assemblage into the chamber of a vacuum hot press furnace and
pressing them in vacuum at a sufficient pressure and a sufficient
temperature for a sufficient period of time in order to densify and
consolidate the sputtering material into the depression in the
backing plate so as to form a sputtering target perform, and
subsequently reducing the pressure on the ram to zero, cooling or
allowing the hot press furnace chamber to cool to ambient
temperature, and raising or allowing the vacuum level to go to
ambient pressure once the furnace has cooled; 6) removing and
optionally machining of the sputtering target pre-form to obtain a
composite sputtering target. In a further advantageous embodiment
of the invention, the backing plate is comprised of a material
which differs from the sputtering target material and is comprised
of one or more of molybdenum, niobium, tantalum or other refractory
metals or alloys. Advantageously, the depression at least
corresponds to the sputtering erosion pattern of a used sputtering
target. More preferably, the depression corresponds to the erosion
pattern of a spent target (i.e. a target that has been used to the
point at which it is no longer acceptable for further use.) Further
it is preferred that the sputtering material is a powder comprising
precious metal or a mixture of precious metal powders, or a mixture
of precious metal powders and non-precious metal powders, or a
mixture of precious metal powders, non precious metal powders, and
metal oxide powders. In an additional preferred aspect of the
invention, the graphite die is of a geometry determined for the
particular sputtering target assembly design being produced.
[0014] Suitable sputtering material include powders of pure Ru, Rh,
Pd, Re, Os, Ir, Pt or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt or
mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt, with transition metals such
as Co, Cr, Ni, Fe, or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt, with
transition metals such as Co, Cr, Ni, Fe, and oxides such as
TiO.sub.2 or mixtures of Ru, Rh, Pd, Re, Os, Ir, Pt with oxides
such as TiO.sub.2. In the presently preferred embodiment, a pure Ru
powder is as used sputtering material and pure Mo is used for the
backing plate. In an alternative embodiment, the backing plate is
composed of pure Nb metal. In another alternative embodiment, the
backing plate is composed of pure Ta.
[0015] The present invention results in a savings of at least 25%,
preferably at least 35% and most preferably at least 40% or more of
the sputtering material needed for a sputtering target assembly as
compared to the prior art solid sputtering target. As an example, a
precious metal containing sputtering target of a rectangular
geometry can be prepared using this invention with only 50% of the
precious metal material requirement of a precious metal containing
sputtering target prepared using only the precious metal containing
material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 represents a cross-sectional view of a used precious
metal containing sputtering target with a rectangular or circular
geometry;
[0017] FIG. 2 represents a top view of a used precious metal
containing sputtering target with a rectangular geometry;
[0018] FIG. 3 represents a top view of a used precious metal
containing sputtering target with a circular geometry;
[0019] FIG. 4 represents a cross-sectional view of a backing plate
containing a depression that corresponds to the sputtering erosion
pattern for targets with either a rectangular or circular
geometry;
[0020] FIG. 5 represents a cross-sectional view of a first
embodiment of this invention for a precious metal containing
sputtering target with either a rectangular or a circular
geometry;
[0021] FIG. 6 represents a hot pressing die assemblage prior to hot
pressing for consolidating sputtering material into a depression in
the surface of a backing plate.; and
[0022] FIG. 7 represents the hot pressing die assemblage of FIG. 6
after hot pressing.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention relates to a method of making a
composite sputtering target which is comprised of a backing plate
and a sputtering zone which has been incorporated into a depression
in the backing plate so as to provide a sputtering target assembly
with sputtering material substantially only where is will be used
in the sputtering process. In one embodiment, the backing plate is
a used target of the same material that is added as the sputtering
material. In this embodiment, the used target has a top surface
with a depression that has been eroded during the sputtering
process. This depression is filled with new sputtering material
that is uniaxially pressed under vacuum at a suitable temperature
and for a suitable time to cause the additional material to bond
with the used target so that it can be used in the process as a
substitute for the original target. In a second embodiment, the
backing plate is a different material, such as a less expensive
material that will bond with the sputtering material and provide
chemical, thermal and electrical properties that are suitable to
allow the composite target to be substituted for a target made
exclusively from the sputtering material. In this embodiment, the
backing plate included in FIGS. 1-3 illustrate the appearance of a
spent precious metal containing sputtering target of rectangular or
circular geometry. FIG. 1 describes the cross-section of a spent or
used precious metal containing sputtering target 10, showing the
depth and shape of the sputtering erosion groove 12. The erosion
groove, 12, represented in FIG. 1 is consistent with erosion
grooves found in precious metal containing sputtering targets that
have either a rectangular or circular geometry. FIG. 2 shows the
top view of a spent precious metal sputtering target 20 of
rectangular geometry, showing the shape of the sputtering erosion
groove 22. FIG. 3 shows the top view of a precious metal containing
sputtering target of circular geometry, 30, showing the shape of
the sputtering erosion groove 32. An examination of these drawings
shows that a considerable amount of precious metal sputtering
material is left in the used target with as little as 25% of the
material actually used in the sputtering process.
[0024] The present invention reduces the amount of precious metal
containing material in a sputtering target by confining the
precious metal containing material to the areas consumed in the
sputtering process. This invention achieves this by using a backing
plate, which in one embodiment is composed of a relatively
inexpensive material, such as Mo, Ta, Nb, or other refractory
metals and alloys, that is mechanically and chemically compatible
with the precious metal containing material. FIG. 4 illustrates a
cross sectional view of a backing plate 40, that has a top surface
41 with a depression 42 or in this case, a groove. The depression
can be the wear path or erosion groove of a used target in the
event that the backing plate comprises a used or spent target. In a
different embodiment, the depression 42 can be a groove machined
into the top surface, 41 of the backing plate. The groove, which
corresponds to or approximates the geometry of the sputtering
erosion groove, is illustrated in FIG. 1. The geometry of the
erosion groove is used to determine the configuration of the
depression. Preferably, this information is used to maximize the
configuration of the depression to balance the amount of sputtering
target so that as small a volume of sputtering material as possible
can be used while allowing the target to be configured to maximize
the production life of the target. FIG. 5 illustrates the cross
section of a composite sputtering target 50 where the precious
metal containing sputtering material 51 forms a sputtering zone 52
which is mostly confined to the sputtering area of the composite
sputtering target and most of the volume of the precious metal
containing sputtering targets is composed of backing plate material
53. A savings of more than 50% in the amount of precious metal
containing material required to produce a precious metal containing
sputtering target can be achieved by this invention.
[0025] An example of how to produce this invention is illustrated
in FIGS. 6 and 7. As shown in FIG. 6, the refractory metal or alloy
backing plate 60 having a surface including a machined groove 62 is
placed inside a graphite hot press die 64 with the grooved surface
up. Then a specified amount of sputtering material 66 is poured
into the die on top of the backing plate 60 and the assemblage 65
is vibrated for a specified amount of time to evenly settle the
powder onto the surfaces of the backing plate. After vibrating the
assemblage, a graphite hot press die ram 67 is placed into the die
cavity until it contacts the surface of the sputtering material.
The assemblage 65 is then placed in a hydraulic press and
pressurized to a preset pressure for a specific amount of time to
compact the powder onto the surfaces of the backing plate. After
compaction, the assemblage is placed inside the furnace chamber of
a vacuum hot press (not shown in the drawing). The ram of a
hydraulic press that passes through the furnace chamber is lowered
until it makes contact with the top of the hot press die ram. The
furnace chamber is then sealed and is evacuated to between 50 to
200 mTorr. The assemblage is heated in the furnace chamber to a
temperature between 800.degree. and 1000.degree. C. and at that
point pressure is applied to the hot press die ram via the
hydraulic press ram in contact with it. The initial pressure
applied is between 5 and 20 tons. As the assemblage is heated up to
a temperature between 1400.degree. and 1900.degree. C., preferably
between 1500.degree. and 1550.degree. C., ram pressure is slowly
increased to a pressure between 10 and 200 tons; the ultimate ram
pressure depending upon the size and geometry of the precious metal
containing sputtering target being manufactured. The assemblage 65
is held at temperature and ram pressure for between 15 and 240
minutes; preferably between 20 and 60 minutes. After this time has
elapsed, both the ram pressure and temperature are decreased until
the assemblage 65 reaches ambient temperature and pressure and the
vacuum level is raised to ambient pressure once the furnace has
cooled to ambient temperature.
[0026] FIG. 7 illustrates the cross section of the assemblage 70
illustrated in FIG. 6 after hot pressing has been completed. As can
be seen in the drawing, the sputtering material has been
consolidated into the machined groove of the backing plate 73 to
form a sputtering zone 74 which has a density of greater than 95%
of the theoretical density of the sputtering material. The precious
metal containing sputtering target pre-form composed of the
consolidated sputtering material and backing plate 73 is removed
from the hot press die 75, after the removal of the graphite die
ram 77. The pre-form is then machined to final dimensions using CNC
milling, diamond grinding, or electrical discharge machining
(EDM).
[0027] In some applications in which the carbon content of the
precious metal containing material must be maintained at an
extremely low level, the internal surfaces of the graphite die and
the bottom of the graphite die ram can be lined with Mo or an other
refractory metal foil to prevent the diffusion of carbon from the
graphite die parts into the precious metal containing material.
[0028] Another advantage in using this invention is that when the
sputtering target is spent, the spent target can be used to produce
a new sputtering target using the process described above where the
spent target is substituted for the refractory metal or alloy
backing plate containing the machined groove in the process. By
doing so the amount of precious metal containing sputtering
material used in the process is further reduced and the cost of the
refractory metal or alloy backing plate containing the machined
groove is eliminated. The process of reusing the spent composite
sputtering target can be repeated numerous times.
[0029] Yet another advantage in using this invention to produce
precious metal containing sputtering targets is realized when the
oxygen content of the precious metal containing material must be
kept extremely low. During the hot pressing process oxygen is
removed from the precious metal containing material due to its
exposure to the graphite die under vacuum which provides an
extremely reducing atmospheric condition within the graphite die
even when the die surface are lined with Mo or other refractory
metals. This reducing condition is capable of reducing the oxygen
content of the precious metal containing material to below
specified levels even when the oxygen content of the starting
precious metal containing material exceeds said specification. This
feature, which is not encountered on other processes such as hot
isostatic pressing (HIP'ing) where the precious metal containing
material is isolated from reducing conditions by containment in a
sealed metal can, provides for the use of precious metal containing
materials with a wide range of starting oxygen contents leading to
great flexibility in precious metal material sourcing, thus
reducing costs.
[0030] The following examples illustrate specific embodiments of
the invention and are not to be considered as limiting the
invention in any manner.
EXAMPLE 1
[0031] A 2.03'' diameter by 0.31'' thick circular Ru composite
sputtering target was fabricated with a Mo backing plate using the
disclosed invention. Using a lathe, a 2.03'' diameter by 0.25''
thick piece of Mo was machined in such a way as to provide a cavity
concentric with the diameter of the Mo piece with a depth of
0.115'' deep and top diameter of 1.84'' and a bottom diameter of
1.55'' (forming a frustum shape). The machined Mo piece was placed
into a graphite hot press die and 100 grams of Ru powder was poured
into the die cavity so as to fill the cavity in the Mo piece and
cover the top of it. A graphite die ram was then placed into the
die cavity and lowered onto the top of the Ru powder.
[0032] The die assemblage was subsequently placed in a hydraulic
press and pressed to a few hundred pounds of load to pre-compress
the Ru powder. Then the die assemblage was placed into a vacuum hot
press and processed at 1525.degree. C. for 0.5 hours at 500 psi at
a vacuum level of 200 mTorr. After hot pressing the Ru/Mo composite
piece was removed from the hot press and the surfaces machined to
facilitate visual inspection.
[0033] A visual inspection of the part indicated that the Ru and Mo
bonded together during the hot pressing process without reacting
significantly with one another indicating chemical compatibility.
Furthermore, no cracks in either material were noted, indicating
mechanical compatibility. The composite part was then placed in an
EDM machine and sectioned so as to inspect the cross section of the
composite. Visual and microscopic inspection reveal that no
significant reaction occurred and no cracking or gaps were present
in the composite further indicating chemical and mechanical
compatibility between the two materials.
[0034] To check the density of the Ru portion of the composite, a
section of the composite piece was placed in the EDM machine and a
piece of Ru free of Mo with dimensions of 0.701'' by 0.537'' by
0.185'' thick was cut out of the composite. The density was
determined using the physical dimensions and the weight of the
piece. The density of the Ru piece cut from the Ru/Mo composite was
found to be 98.9% of the theoretical density of Ru; a density
suitable for precious metal containing sputtering target
applications.
[0035] The amount of Ru used to make this composite sputtering
target was 100 grams which is less than 50% of the amount required,
202 grams, to make a pure Ru sputtering target of the same
geometry.
EXAMPLE 2
[0036] A 2.03'' diameter by 0.31'' thick circular Ru composite
sputtering target was fabricated with an Nb backing plate using the
disclosed invention. Using a lathe, a 2.03'' diameter by 0.25''
thick piece of Nb was machined in such a way as to provide a cavity
concentric with the diameter of the Nb piece with a depth of
0.115'' deep and top diameter of 1.84'' and a bottom diameter of
1.55'' (forming a frustum shape). The machined Nb piece was placed
into a graphite hot press die and 100 grams of Ru powder was poured
into the die cavity so as to fill the cavity in the Mo piece and
cover the top of it. A graphite die ram was then placed into the
die cavity and lowered onto the top of the Ru powder.
[0037] The die assemblage was subsequently placed in a hydraulic
press and pressed to a few hundred pounds of load to pre-compress
the Ru powder. Then the die assemblage was placed into a vacuum hot
press and processed at 1525.degree. C. for 0.5 hours at 500 psi at
a vacuum level of 200 mTorr. After hot pressing the Ru/Nb composite
piece was removed from the hot press and the surfaces machined to
facilitate visual inspection.
[0038] A visual inspection of the part indicated that the Ru and Nb
bonded together during the hot pressing process with out reacting
significantly with one another indicating chemical compatibility.
Furthermore, no cracks in either material were noted, indicating
mechanical compatibility. The composite part was then placed in an
EDM machine and sectioned so as to inspect the cross section of the
composite. Visual and microscopic inspection reveal that no
significant reaction occurred and no cracking or gaps were present
in the composite further indicating chemical and mechanical
compatibility between the two materials.
[0039] The amount of Ru used to make this composite sputtering
target was 100 grams which is less than 50% of the amount required,
202 grams, to make a pure Ru sputtering target of the same
geometry.
EXAMPLE 3
[0040] A 2.03'' diameter by 0.31'' thick circular Ru composite
sputtering target was fabricated with a Ta backing plate using the
disclosed invention. Using a lathe, a 2.03'' diameter by 0.25''
thick piece of Ta was machined in such a way as to provide a cavity
concentric with the diameter of the Ta piece with a depth of
0.115'' deep and top diameter of 1.84'' and a bottom diameter of
1.55'' (forming a frustum shape). The machined Ta piece was placed
into a graphite hot press die and 100 grams of Ru powder was poured
into the die cavity so as to fill the cavity in the Ta piece and
cover the top of it. A graphite die ram was then placed into the
die cavity and lowered onto the top of the Ru powder.
[0041] The die assemblage was subsequently placed in a hydraulic
press and pressed to a few hundred pounds of load to pre-compress
the Ru powder. Then the die assemblage was placed into a vacuum hot
press and processed at 1525.degree. C. for 0.5 hours at 500 psi at
a vacuum level of 200 mTorr. After hot pressing the Ru/Ta composite
piece was removed from the hot press and the surfaces machined to
facilitate visual inspection.
[0042] A visual inspection of the part indicated that the Ru and Ta
bonded together during the hot pressing process with out reacting
significantly with one another indicating chemical compatibility.
Furthermore, no cracks in either material were noted, indicating
mechanical compatibility. The composite part was then placed in an
EDM machine and sectioned so as to inspect the cross section of the
composite. Visual and microscopic inspection reveal that no
significant reaction occurred and no cracking or gaps were present
in the composite further indicating chemical and mechanical
compatibility between the two materials.
[0043] The amount of Ru used to make this composite sputtering
target was 100 grams which is less than 50% of the amount required,
202 grams, to make a pure Ru sputtering target of the same
geometry.
EXAMPLE 4
[0044] A 2.03'' diameter by 0.31'' thick circular Ru composite
sputtering target was fabricated with a Ti backing plate using the
disclosed invention. Using a lathe, a 2.03'' diameter by 0.25''
thick piece of Ti was machined in such a way as to provide a cavity
concentric with the diameter of the Ti piece with a depth of
0.115'' deep and top diameter of 1.84'' and a bottom diameter of
1.55'' (forming a frustum shape). The machined Ti piece was placed
into a graphite hot press die and 100 grams of Ru powder was poured
into the die cavity so as to fill the cavity in the Ti piece and
cover the top of it. A graphite die ram was then placed into the
die cavity and lowered onto the top of the Ru powder.
[0045] The die assemblage was subsequently placed in a hydraulic
press and pressed to a few hundred pounds of load to pre-compress
the Ru powder. Then the die assemblage was placed into a vacuum hot
press and processed at 1525.degree. C. for 0.5 hours at 500 psi at
a vacuum level of 200 mTorr. After hot pressing the Ru/Ti composite
piece was removed from the hot press and the surfaces machined to
facilitate visual inspection.
[0046] A visual inspection of the part indicated that the Ru and Ti
bonded together during the hot pressing process however there was
evidence of reaction between the two materials with slight erosion
of the Ti along the edges of the piece indicating possible chemical
incompatibility. No cracks in either material were noted,
indicating possible mechanical compatibility. The composite part
was then placed in an EDM machine and sectioned so as to inspect
the cross section of the composite. Visual and microscopic
inspection revealed that significant reaction occurred between the
two materials leaving a gap between the Ru and the Ti pieces
further indicating chemical incompatibility between the two
materials under the conditions used to process the composite. If Ti
is to be used as a backing plate, a barrier material such as Mo,
Nb, Ta, or other material that is chemically and mechanically
compatible with both Ru and Ti could be inserted between the Ti
backing plate and Ru powder load. The barrier material could be in
the form of a foil, powder layer or coating applied with such
methods as sputtering, flame spraying, or plasma spraying or other
coating techniques.
EXAMPLE 5
[0047] A ruthenium/niobium composite part was prepared that was
7.07'' long by 2.30'' wide by 0.5'' thick by pressing ruthenium
powder into a Nb backing plate 7.07'' long by 2.30'' wide by
0.400'' thick containing a groove that was 1.77'' wide at the top
and 1.05'' wide at the bottom and 0.233'' deep running along the
length of the backing plate. The plate was placed in a graphite die
and filled with 715 grams of ruthenium powder which filled the
groove and covered the backing plate. A die ram was place into the
graphite die so that it would make contact with the ruthenium
powder and the die pre-pressed before insertion into a vacuum hot
press which was larger than the vacuum hot press used in the first
four examples. In the vacuum hot press the die was heated to
1600.degree. C. and 26 tons of pressure was applied to the die ram.
The die and contents were held under these conditions for four
hours before cooling to room temperature. A higher density was
achieved for this example and the following example than in the
first four examples by holding the parts at temperature for a
longer period of time. An evaluation of the ruthenium in the groove
of the composite part indicated that the relative density of the
ruthenium was 99% of the theoretical density of ruthenium which is
12.41 g/cc. Then an approximation of an erosion groove was machined
into the surface of the ruthenium portion of the composite along
the length to a maximum depth of 0.200''. The composite was placed
back into the graphite die and filled with 400 grams of ruthenium
powder, which filled the groove and covered the composite part. A
die ram was place into the graphite die so that it would make
contact with the ruthenium powder and the die pre-pressed before
insertion into a vacuum hot press. In the vacuum hot press the die
was heated to 1600.degree. C. and 26 tons of pressure was applied
to the die ram. The die and contents were held under these
conditions for four hours before cooling to room temperature. An
evaluation of the ruthenium pressed into the simulated erosion
groove of the composite part indicated that the relative density of
the ruthenium was 99% of the theoretical density of, which is 12.41
g/cc. These results indicate the possibility of reusing spent
ruthenium/niobium composite sputtering targets to produce new
ruthenium/niobium sputtering targets.
EXAMPLE 6
[0048] Two spent ruthenium target pieces each measuring
7.07.times.1.09.times.0.25'' with a target erosion groove of
roughly triangular shape and about 0.24'' deep eroded along the
length of each strip were placed in a graphite hot press die. 500
grams of ruthenium powder was poured into the graphite die in such
a way as to fill the erosion grooves and completely cover the strip
pieces. A die ram was place into the graphite die so that it would
make contact with the ruthenium powder and the die pre-pressed
before insertion into a vacuum hot press. In the vacuum hot press
the die was heated to 1600.degree. C. and 20 tons of pressure was
applied to the die ram. The die and contents were held under these
conditions for four hours before cooling to room temperature. After
hot pressing, the resultant part was characterized for density and
found to be 98% dense relative to a ruthenium x-ray density of
12.41 g/cc. Upon microscopic examination, the interface between the
spent target and the new material was not discernable without
extensive chemical etching. These results indicated that spent
ruthenium sputtering targets could be refilled with new ruthenium
and used for sputtering operations.
[0049] While in accordance with the patent statutes the best mode
and preferred embodiment have been set forth, the scope of the
invention is not intended to be limited thereto, but only by the
scope of the attached claims.
* * * * *