U.S. patent application number 10/870260 was filed with the patent office on 2004-12-23 for method and design for sputter target attachment to a backing plate.
Invention is credited to Wickersham, Charles E. JR..
Application Number | 20040256226 10/870260 |
Document ID | / |
Family ID | 33539269 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040256226 |
Kind Code |
A1 |
Wickersham, Charles E. JR. |
December 23, 2004 |
Method and design for sputter target attachment to a backing
plate
Abstract
A method of assembling the components of a sputter cathode
assembly via thermal expansion of projections provided on one
assembly member to provide thermal contact to the other assembly
member, and the sputter cathode formed thereby are described. The
method forms a temporary mechanical attachment of component members
that ends when the components are cooled below the predetermined
contact temperature. The method optionally includes mechanically
interlocking the assembly components together.
Inventors: |
Wickersham, Charles E. JR.;
(Columbus, OH) |
Correspondence
Address: |
Martha Ann Finnegan, Esq.
Cabot Corporation
157 Concord Road
Billerica
MA
01821-7001
US
|
Family ID: |
33539269 |
Appl. No.: |
10/870260 |
Filed: |
June 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60480196 |
Jun 20, 2003 |
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Current U.S.
Class: |
204/298.01 ;
204/298.02 |
Current CPC
Class: |
C23C 14/3407 20130101;
H01J 37/3435 20130101 |
Class at
Publication: |
204/298.01 ;
204/298.02 |
International
Class: |
C25B 009/00; C25B
011/00; C25B 013/00 |
Claims
What is claimed is:
1. A method of forming a sputter assembly, comprising: positioning
a first assembly member having a mating surface with a plurality of
projections having side walls, and a second assembly member having
a mating surface with a plurality of corresponding grooves having
side walls, whereby said projections are received in said grooves,
wherein gaps are present between the side walls of said projections
and the side walls of said grooves; and heating said first assembly
member or said second assembly member or both, whereby thermal
expansion causes contacting of the side walls of said projections
and the side walls of said grooves at a contact temperature to form
a temporary mechanical attachment between said first assembly
member and said second assembly member.
2. The method of claim 1, further comprising mechanically
interlocking said first assembly member and said second assembly
member.
3. The method of claim 2, wherein said mechanically interlocking is
achieved by rotating said first assembly member and said second
assembly member relative to one another.
4. The method of claim 1, further comprising providing at least one
mechanical interlock on said mating surfaces.
5. The method of claim 1, wherein said positioning comprises
rotating said first assembly member and said second assembly member
relative to one another, whereby said projections are received in
said grooves.
6. The method of claim 1, wherein said first assembly member
comprises a sputter target, and said second assembly member
comprises a backing plate.
7. The method of claim 1, wherein said first assembly member
comprises an electrode, and said second assembly member comprises a
sputter target.
8. The method of claim 1, wherein said first assembly member or
said second assembly member is a sputter target, and wherein said
sputter target has a rectangular shape.
9. The method of claim 1, wherein said first assembly member or
said second assembly member is a sputter target comprising cobalt,
titanium, copper, aluminum, tantalum, niobium, nickel, molybdenum,
zirconium, hafnium, gold, silver, or alloys thereof.
10. The method of claim 1, wherein said first assembly member or
said second assembly member is an electrode comprising copper,
aluminum, titanium, molybdenum, niobium, alloys thereof, or
steel.
11. The method of claim 1, wherein said first assembly member
comprises a backing plate that is bonded to a sputter target, and
wherein said second assembly member comprises an electrode.
12. The method of claim 11, wherein said backing plate comprises
aluminum, chromium, copper, tantalum, titanium, alloys thereof, or
steel.
13. The method of claim 1, wherein said first assembly member
comprises an electrode, and wherein said second assembly member
comprises a backing plate that is bonded to a sputter target.
14. The method of claim 13, wherein said backing plate comprises
copper, aluminum, titanium, alloys thereof, or steel.
15. The method of claim 1, wherein said heating comprises
sputtering.
16. The method of claim 1, wherein said projections are
cylindrical, or combinations thereof.
17. The method of claim 1, wherein said projections comprise
concentric rows.
18. The method of claim 1, wherein said grooves comprise a groove
channel.
19. The method of claim 1, wherein said grooves comprise concentric
groove channels.
20. The method of claim 1, wherein said gaps include predetermined
dimensions such that said contact occurs substantially
simultaneously for each of said projections.
21. The method of claim 1, wherein said gaps include predetermined
dimensions such that said contact temperature is from about 30 to
about 300.degree. C.
22. The method of claim 1, wherein said mating surfaces are placed
in thermal contact by said mechanical attachment.
23. A sputter assembly comprising: a first assembly member having a
mating surface with a plurality of projections having side walls;
and a second assembly member having a mating surface with a
plurality of corresponding grooves having sidewalls, wherein said
projections are received in said grooves, and wherein the side
walls of said projections and the side walls of said grooves are
adapted to form a temporary mechanical attachment between said
first assembly member and said second assembly member at a contact
temperature.
24. The sputter assembly of claim 23, further comprising a
mechanical interlock for interlocking said first assembly member
and said second assembly member.
25. The sputter assembly of claim 23, wherein said first assembly
and said second assembly are adapted to be mechanically interlocked
by rotation of said mating surfaces relative to each other.
26. The sputter assembly of claim 24, wherein said mechanical
interlock is formed on said mating surfaces for interlocking said
first assembly member and said second assembly member.
27. The sputter assembly of claim 26, wherein said mechanical
interlock includes a trapezoid shaped recess adapted to receive a
trapezoid shaped protrusion.
28. The sputter assembly of claim 26, wherein said mechanical
interlock includes a "T" shaped recess adapted to receive a "T"
shaped protrusion.
29. The sputter assembly of claim 26, wherein said mechanical
interlock includes an "L" shaped recess adapted to receive an "L"
shaped protrusion.
30. The sputter assembly of claim 26, wherein said mechanical
interlock includes a triangular shaped recess adapted to receive a
triangular shaped protrusion.
31. The sputter assembly of claim 23, wherein said projections are
adapted to be received in said grooves by rotation of said first
assembly member and said second assembly member relative to one
another.
32. The sputter assembly of claim 23, wherein said first assembly
member comprises a sputter target, and said second assembly member
comprises a backing plate.
33. The sputter assembly of claim 23, wherein said first assembly
member comprises an electrode, and said second assembly member
comprises a sputter target.
34. The sputter assembly of claim 23, wherein said first assembly
member or said second assembly member is a rectangular shaped
sputter target.
35. The sputter assembly of claim 23, wherein said first assembly
member or said second assembly member is a sputter target
comprising cobalt, titanium, copper, aluminum, tantalum, niobium,
nickel, molybdenum, zirconium, hafnium, gold, silver, or alloys
thereof.
36. The sputter assembly of claim 23, wherein said first assembly
member or said second assembly member is an electrode comprising
copper, aluminum, titanium, molybdenum, niobium, alloys thereof, or
steel.
37. The sputter assembly of claim 23, wherein first assembly member
comprises a backing plate that is bonded to a sputter target, and
wherein said second assembly member comprises an electrode.
38. The sputter assembly of claim 37, wherein said backing plate
comprises aluminum, copper, tantalum, titanium, alloys thereof, or
steel.
39. The sputter assembly of claim 37, wherein said backing plate is
bonded to said sputter target by explosion bonding, diffusion
bonding, friction welding, press fitting, resistance welding,
soldering, brazing, or welding.
40. The sputter assembly of claim 23, wherein said first assembly
member comprises an electrode, and wherein said second assembly
member comprises a backing plate that is bonded to a sputter
target.
41. The sputter assembly of claim 40, wherein said backing plate
comprises aluminum, copper, tantalum, titanium, alloys thereof, or
steel.
42. The sputter assembly of claim 40, wherein said backing plate is
bonded to said sputter target by explosion bonding, diffusion
bonding, friction welding, press fitting, resistance welding,
soldering, brazing, or welding.
43. The sputter assembly of claim 23, wherein said thermal
expansion is achieved by sputtering said sputtering target
assembly.
44. The sputter assembly of claim 23, wherein said projections are
cylindrical, rectangular, or any combinations thereof.
45. The sputter assembly of claim 23, wherein said projections
comprise concentric rows.
46. The sputter assembly of claim 23, wherein said grooves comprise
a groove channel.
47. The sputter assembly of claim 23, wherein said grooves comprise
concentric groove channels.
48. The sputter assembly of claim 23, wherein each of said
projections contacts a respective groove substantially
simultaneously.
49. The sputter assembly of claim 23, wherein said contact
temperature is from about 30 to about 300.degree. C.
50. The sputter assembly of claim 23, wherein said mating surfaces
are adapted to be placed in thermal contact by said mechanical
attachment.
51. The sputter assembly of claim 23, wherein a gap exists between
said side walls of said grooves and said side walls of said
projections when said grooves and said projections are at a
temperature that is less than said contact temperature.
52. The sputter assembly of claim 51, wherein each of said gaps are
adapted to close simultaneously by thermal expansion of said side
walls of said projections, said side walls of said grooves, or
both.
Description
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) of prior U.S. Provisional Patent Application No.
60/480,196 filed Jun. 20, 2003, which is incorporated in its
entirety by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to sputtering components. More
particularly, the present invention relates to a mechanical method
of joining the components of a sputter cathode assembly.
[0003] In the sputter application field, sputtering is widely used
for depositing a film or thin layer of material from a sputter
target onto a desired substrate. A sputter cathode assembly
including the sputter target and an electrode can be placed
together with an anode in a sputtering device or chamber filled
with an inert gas. The desired substrate is positioned in the
chamber near the anode with a receiving surface of the substrate
oriented normally to a path between the sputter cathode assembly
and the anode. A high voltage electric field is applied across the
sputter cathode assembly and the anode, creating an electrical
field that ionizes the inert gas and propels it toward the sputter
target surface. Bombardment of the sputter target surface by the
ions of inert gas dislodges material from the sputter target, which
material is then deposited on the receiving surface of the
substrate to form a thin layer or film.
[0004] Typically, a sputter cathode assembly includes a sputter
target and an electrode in thermal and electrical contact. For
instance, a metal target or metal target blank (e.g., tantalum,
titanium, aluminum, copper, cobalt, tungsten, etc.) is bonded onto
an electrode or a backing plate, such as a backing plate flange
assembly such as copper, aluminum, or alloys thereof. To achieve
the necessary thermal and electrical contact between the assembly
components, the target and the backing plate can be permanently
attached to each other by a metallurgical bond such as by diffusion
bonding, explosion bonding, friction welding, press fitting, epoxy
cement, and the like.
[0005] The differential thermal expansion between the target
material and the backing plate material which occurs when bonding
is accomplished at elevated temperatures by diffusion bonding,
friction welding, explosion bonding and the like, can generate very
high levels of mechanical stress in the metal bodies. The
mechanical stress often causes deflection of the sputter target and
can cause the bond to fail so that the sputter target separates
from the backing plate during the elevated temperatures attained
during the sputtering process. The strain on the interface between
the sputter target and the backing plate when relatively high
temperatures are used to form the bond is proportional to the
difference in linear thermal expansion coefficients between the
target and backing plate multiplied by the bonding temperature and
multiplied by the radial dimension of the target, or:
.epsilon.=R(.alpha.1-.alpha.2).DELTA.T (Eq. 1)
[0006] where .epsilon. is the strain at a point a distance R from
the target center, .alpha.1 and .alpha.2 are the linear thermal
expansion coefficients of the target and backing plate,
respectively, and .DELTA.T is the difference between the bonding
temperature and room temperature. Generally, all units are metric
and temperatures are .degree. C. From Eq. 1, it can be seen that as
the target size increases the strain on the bond will increase. In
addition, the higher the bonding temperature, the higher the
strain. Finally, strain increases as the difference between the
thermal expansion coefficients of the target and backing plate
increases. Thus, controlling strain, .epsilon., presents a
particular challenge for large area sputter cathode assemblies that
are needed to coat a relatively large-area substrate, such as for a
flat glass panel to be used in a flat panel display of a computer
monitor or a television screen.
[0007] Another disadvantage to permanently attaching the sputter
cathode assembly members by a metallurgical bond is that separating
the assembly members is typically achieved in a destructive manner,
such as machining or chemical etching. The backing plate flange
assembly typically contains features, e.g., bolt holes, alignment
marks, and/or an o-ring groove, that are difficult and expensive to
machine. When the sputter target of the sputter cathode assembly is
spent or otherwise deemed unusable, the entire assembly is
typically returned to the processor for recycling. In assemblies in
which the flange is made from the same material as the sputter
target, the flange and the target are typically converted to powder
or other form suitable for remelting. Otherwise, the flange is
typically removed from the target and reprocessed separately. In
either case, the flange is destroyed even though it and its
machined features are often in a near-perfect, or at least usable
condition.
[0008] A conventional method used to control the strain produced
from bonding sputter targets to the electrode for large flat panel
display targets is to use a low melting point solder or braze
material. Although solder or low temperature brazing techniques
reduce net strain via a comparatively low bonding temperature, T,
the bond strength achieved can be insufficient for large sputter
targets. Thus, to reduce R, multi-piece target construction in the
form of several target tiles bonded to the electrode is used to
maintain the strain from differential thermal expansion during
cool-down from solder bonding below the failure point for the
solder. By using a multi-piece construction, the differential
thermal expansion stress, .epsilon., is reduced. However, the
solder can intrude the joints between the multi-piece target
segments of the assembly and thus becomes a source of arcing and
particle emission (i.e., contamination) during sputtering. Also,
the sputtering behavior of the edges of the individual target tiles
may differ from that of the bulk of the target array, resulting in
a deposited film having diminished thickness uniformity. A
schematic diagram of a typical large rectangular sputter cathode
assembly with multi-piece sputter target construction is provided
in FIG. 1.
[0009] While the use of solder and brazing techniques avoids the
recovery and recycle issues described above for metallurgically
bonded components, change-out of a spent target of a soldered
sputter cathode assembly nevertheless requires the entire assembly
to be removed from the sputtering chamber so that the assembly can
be heated to the soldering temperature. Likewise, use of sputter
targets of different sputter materials require change-out of the
entire sputter cathode assembly. This makes change-out of a sputter
target a costly and time-consuming process.
[0010] Accordingly, a need exists for a sputter cathode assembly in
which the bonding-induced strain at the interface between the
sputter target and the electrode is less than that of conventional
permanently bonded sputter cathode assemblies. A need also exists
for a sputter cathode assembly whose components can be easily
recovered for recycling or re-use. A further need exists for a
sputter cathode assembly that avoids the undesirable arcing and
contamination issues associated with soldered and multi-target
sputter cathode assemblies. Yet a further need exists for a sputter
cathode assembly in which the spent sputter target can be readily
removed and replaced without having to remove the electrode from
the sputtering chamber.
SUMMARY OF THE PRESENT INVENTION
[0011] It is therefore a feature of the present invention to
provide a sputter cathode assembly for which the debonding issue is
avoided by providing a fail-safe bond between the assembly
components.
[0012] Another feature of the present invention is to provide a
sputter cathode assembly in which the assembly components can be
separated from each other by nondestructive means and the recovered
usable components can be reused and/or recycled.
[0013] A further feature of the present invention is to provide a
sputter cathode assembly, especially a large-area sputter cathode
assembly, that avoids the undesirable arcing and contamination
issues that are present in conventional soldered sputter cathode
assemblies of multi-target construction.
[0014] Yet another feature of the present invention is to provide a
sputter cathode assembly in which the sputter target component can
be readily removed and replaced without the need to also remove the
electrode from the sputtering chamber.
[0015] Additional features and advantages of the present invention
will be set forth in part in the description that follows, and in
part will be apparent from the description, or may be learned by
practice of the present invention. The objectives and other
advantages of the present invention will be realized and attained
by means of the elements and combinations particularly pointed out
in the description and appended claims.
[0016] To achieve these and other advantages, and in accordance
with the purposes of the present invention, as embodied and broadly
described herein, the present invention relates to a sputter
cathode assembly that includes a first assembly member having a
mating surface with a plurality of projections having side walls;
and a second assembly member having a mating surface with a
plurality of corresponding grooves having sidewalls, wherein the
projections are received in said grooves, and wherein thermal
expansion causes contacting of the side walls of the projections
and the side walls of the grooves at a contact temperature to form
a temporary mechanical attachment between the first and second
assembly members. The sputter cathode assembly optionally includes
a mechanical interlock for interlocking the first and second
assembly members together.
[0017] The present invention further relates to a method of forming
a sputter cathode assembly that includes bonding an interlayer or
backing plate to a sputter target which is then temporarily
attached to an electrode by thermal expansion at the backing
plate/electrode interface so that non-metallic sputter target
materials can be used in the sputter cathode assembly.
[0018] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are intended to provide a further
explanation of the present invention, as claimed.
[0019] The accompanying drawings, which are incorporated in and
constitute a part of this application, illustrate various aspects
of the present invention and together with the description, serve
to explain the principles of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic diagram of a multi-piece large area
rectangular sputter cathode assembly.
[0021] FIG. 2 is a schematic diagram of one version of the sputter
cathode assembly of the present invention with exploded
cross-sectional views of a version of the mechanical interlock and
a version of the projection/groove attachment.
[0022] FIG. 3 is a schematic diagram of a method of forming a
sputter cathode assembly according to one embodiment of the present
invention.
[0023] FIG. 4 is graph showing theoretical sputter target
temperature changes with sputtering power density for sputter
cathode assemblies designed to make contact at 50.degree. C. and at
80.degree. C.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0024] A method of forming a sputter cathode assembly according to
the present invention includes positioning a first assembly member
having a mating surface with a plurality of projections having side
walls, and a second assembly member having a mating surface with a
plurality of corresponding grooves having side walls, whereby the
projections are received in the grooves, wherein gaps are present
between the side walls of the projections and the side walls of the
grooves; and heating the first assembly member or the second
assembly member or both, whereby thermal expansion causes
contacting of the side walls of the projections and the side walls
of the grooves at a contact temperature to form a temporary
mechanical attachment between the first assembly member and the
second assembly member. The method optionally includes mechanically
interlocking the first assembly member and the second assembly
member together.
[0025] In more detail, the sputter cathode assembly as described
above, includes two components or assembly members, i.e., a sputter
target and an electrode. The sputter target member and the
electrode can be any suitable target grade and electrode grade
materials. With respect to the target materials to be attached by
the method of the present invention, examples include, but are not
limited to, tantalum, niobium, cobalt, titanium, copper, aluminum,
and alloys thereof. Examples of electrode materials include, but
are not limited to, copper, or a copper alloy, tantalum, niobium,
cobalt, titanium, aluminum, molybdenum, and alloys thereof, such as
TaW, NbW, TaZr, NbZr, TaNb, NbTa, TaTi, NbTi, TaMo, NbMo, and the
like, or steel. No limitation exists as to the type of materials
used in the sputter target and the electrode. In the present
invention, the target material to be attached to the electrode can
be conventional target grade material, for instance as described in
U.S. Pat. No. 6,348,113, incorporated in its entirety herein by
reference. The purity, texture, and/or grain size and other
properties, including size and the like are not critical to the
present invention. The powder used to make the target grade plate
as well as the target itself can have any purity with respect to
the metal. For instance, the purity can be 99% or greater such as
from about 99.5% or greater and more preferably 99.95% or greater
and even more preferably 99.99% or greater, or 99.995% or greater
or 99.999% or greater. The target grade plate can have any suitable
grain size (e.g., average grain sizes of less than 300 microns,
less than 100 microns, less than 50 microns, less than 20 microns)
and/or texture. For instance, the texture can be random, a primary
(111) texture, or a primary (100) texture that can be on the
surface or throughout the entire thickness of the target.
Preferably, the texture is uniform. Also, the target can have a
mixed (111):(110) texture throughout the surface or throughout the
entire thickness of the target. In addition, the target can be
substantially void of textural banding, such as substantially void
of (100) textural banding. The present invention provides a method
of making a sputter cathode assembly with any type of sputter
target and electrode.
[0026] The sputter target and the electrode can have any shape
and/or dimensions, as described, for example, in U.S. patent
application No. 60/450,196 filed Feb. 25, 2003, which is
incorporated in its entirety herein by reference. For instance, the
sputter target can be circular, rectangular, or can be any other
geometric shape suitable for sputtering. The size or surface area
of the sputter target can be any suitable size, including
conventional sizes or the sizes described below. Preferably, the
sputter target and the electrode are substantially of the same
shape and the same dimensions. Optionally, the electrode can have
dimensions in excess of the dimensions of the target, or,
alternatively the target grade plate can have dimensions in excess
of the dimensions of the electrode. In a preferred embodiment, both
the target and the electrode are substantially rectangular or
circular in shape, having a length of from about 1 ft or less to
about 5 ft or more, and a width of from about 1 ft or less to about
5 ft or more, or diameters of from 6 inches or less to 5 feet or
more. Any dimensions or ranges therein can be used. Other shapes of
the target grade plate and the electrode can have similar surface
areas. Other dimensions for the sputter cathode assembly include
sputter surface areas of greater than 1.5 m.sup.2. Preferred
sputter surface areas are from about 1.5 to about 10 m.sup.2 and
more preferably from about 2 to about 6 m.sup.2. Another way to
describe one aspect of the invention is a sputter cathode assembly
in which the attached target/electrode has a rectangular dimension
of 1.5 m or greater for the length and 1.5 m or greater for the
width or if the assembly plate is circular, a circular diameter of
at least 1.5 m. Preferred dimensions are 1.5 to about 3 m in length
and from about 1.5 to about 3 m in width. Similarly, the circular
diameter can be from about 1.5 to about 3 m or more. As indicated
above, with such large sputter surface areas, the need for mosaic
sputter targets or a series of sputter targets placed next to each
other can be avoided or minimized. By using a single target or less
targets to form the mosaic, a more uniform sputtered thin film can
be achieved for a variety of uses including the capacitor area,
plasma screen area, and the like. Furthermore, the sputter cathode
assembly can be a hollow cathode magnetron sputter target and can
be other forms of sputter targets such as planar magnetron
assemblies incorporating stationary or rotating permanent or
electrode magnets.
[0027] The thicknesses of the electrode and the target material can
be any suitable thickness used for forming sputter cathode
assemblies. Alternatively, the electrode and the target material or
other metal plate to be attached to the electrode can be any
suitable thickness for the desired application. Examples of
suitable thicknesses of the electrode and of the target material
include, but are not limited to, an electrode with a thickness of
from about 0.25 or less to about 2 inches or more in thickness, and
targets with a thickness ranging from about 0.06 inches to about 1
inch or greater.
[0028] The target member used to practice the present invention
includes two opposing sides, a sputter surface, and a mating
surface. The electrode member used to practice the present
invention includes two opposing sides, a mating surface and a back
surface. Preferably, the back surface is adapted to be water
cooled. The assembly described in U.S. Pat. No. 5,676,803,
incorporated in its entirety by reference, can be used in the
present invention. An attachment interface is defined by an area
between the mating surfaces of the target member and the electrode
member. The temporary mechanical attachment between the assembly
members by the method of the present invention preferably results
in substantial contact between the mating surfaces such that
thermal and electrical contact is made between assembly
members.
[0029] When the thermal expansion coefficient of the sputter target
material is large, the sputter target can be attached directly to
the electrode. Examples of materials with comparatively large
thermal expansion coefficients include aluminum and its alloys, and
copper and its alloys. However, other sputter target materials of
practical interest have low thermal expansion coefficients and
therefore, can be difficult to attach directly. Examples of these
materials include tantalum, tungsten, niobium, cobalt and titanium.
For these materials, a high thermal expansion material can be
bonded to the sputter target material and this backing plate
material can have projections or grooves formed in this bonded
layer. Methods for bonding this backing plate material to the
target material include diffusion bonding, explosion bonding,
soldering, friction welding, welding and press fitting. Any
conventional bonding technique can be used. The schematic diagram
provided in FIG. 2 shows a backing plate material between the
sputter target and the electrode.
[0030] According to one embodiment of the present invention, the
sputter cathode assembly includes a backing plate and/or an
interlayer disposed between the sputter target and the electrode.
As stated above, the backing plate is preferably bonded to the
mating surface of the sputter target by any conventional method
such as explosion bonding, diffusion bonding, friction welding,
press fitting, resistance welding, soldering, braising, or welding.
As such, the backing plate surface which makes contact with the
electrode by attachment therewith according to the present
invention, is the mating surface which defines an attachment
interface along with the mating surface of the electrode. The
backing plate assembly member can be any suitable material,
including, but not limited to, zirconium, titanium, copper,
aluminum, chromium, tantalum, niobium, silver, and alloys thereof,
or steel. As used herein, the description of the features formed in
the mating surface of the sputter target according to a method of
the present invention, also refers to the mating surface of the
optional backing plate assembly member.
[0031] The sputter cathode assembly members of the present
invention can be made from materials having dissimilar coefficients
of thermal expansion. Grooves can be formed in the mating side of
the assembly member (i.e., target, electrode, or backing plate)
having a thermal expansion coefficient that is greater or less than
that of the material from which the assembly member having the
projections formed thereon. Grooves can be formed on the mating
surface of the sputter target, the backing plate, or the electrode,
by any suitable method including machining and/or milling. The
grooves can be formed to have a lengthwise dimension so that an
extended groove track, or channel is formed. Preferably, the groove
channel is annular so as to form a continuous recessed track. One
or more groove channels can be formed in the mating surface.
Multiple groove channels can be arranged concentrically.
[0032] The opening of the groove channel is adapted to receive the
projections on the assembly member having the projections. That is,
the groove opening is of a sufficient dimension and shape to allow
the projection to pass into the opening. Interior to the opening of
the grooves, the diameter of the grooves can increase, decrease, or
remain constant. The interior of the grooves can be any shape
and/or volume. Groove shapes can be regular or irregular. A
cross-section of a groove can generally form a square, rectangle,
"T", "L", semi circle, truncated triangle, cusp, bowtie, and the
like. Also, as to an assembly member having more than one groove
channel, the shape of any of the groove channels can be dissimilar.
Also any one groove channel can vary in shape along the length of
the groove channel. The grooves can be any depth such as from about
0.01 inch or less to about 0.5 inch or more and, preferably, from
about 0.025 inch to about 0.075 inch.
[0033] Projections can be formed in the mating surface of any
assembly member, i.e., the sputter target, the electrode, or the
backing plate. The projections can be formed in the mating surface
of the assembly member by any suitable method including machining
and milling. The projection has a distal end and an opposing
proximal end that is attached at the mating surface of the assembly
member. The distal end is of such a shape and a dimension as to
permit the projection to enter the opening of the corresponding
groove in the groove-containing assembly member. The projection can
be of any size or shape. A cross-section of a projection can
generally form a rectangle, triangle, or other suitable shape. The
projection can be of any regular or irregular shape. The projection
can be in the shape of a cylinder, cone, truncated cone, cube,
cuboid, pyramid, ovaliscue, wedge, etc.
[0034] The projections are arranged on the mating side of the
assembly member such that the projections can be mated with a
corresponding groove on the mating side of another assembly member.
Notably, the groove-containing member may include a larger number
of groove channels than the number of projections on the
projection-containing member. That is, every groove need not have a
corresponding projection. The projections can be spaced apart as
desired. For example, the projections can be spaced so close to one
another in a row so as to approximate a continuous ridge. Multiple
projections can be arranged in rows. Preferably, the projections
are arranged circularly. Multiple rows of projections can be used
to mate with the grooves in the groove-containing member.
Preferably, multiple rows of projections are arranged
concentrically. The shape and dimension of any one projection in a
row can be similar or dissimilar to other projections in the same
row. Likewise, concentric rows of projections can contain
projections of similar or dissimilar shape and dimension. The
height of the projection measured from its proximal end to its
distal end can be from about 0.01 inch or less to about 0.5 inch or
more, and preferably from about 0.05 inch to about 0.2 inch. The
projection can be any cross-section such as from about 0.0001
square inch to about 0.25 square inch. Preferably, the projection
is made from a high strength copper-zirconium, copper-chromium, or
copper-zinc alloy.
[0035] Preferably, once the thermal contact grooves and projections
are formed, the sputter target can be attached to the electrode by
rotating the target about the center line so that the preferred
four corners of the target are outside of the electrode. The target
is then moved into the electrode so that the grooves and
projections mesh. The target is then rotated so that the target is
aligned or in registration with the electrode. FIG. 3 provides a
schematic diagram of one target attachment method. Positioning the
first assembly member and the second assembly member involves
aligning one adjacent to the other so that each projection has a
corresponding groove into which the projection is received.
Preferably, the projections are fully received within the grooves
such that the mating surfaces of the first and second assembly
member are placed in substantial contact. Preferably, positioning
includes rotating the first assembly member and the second assembly
member relative to one another, whereby the projections are
received in the grooves.
[0036] Heating the first assembly member, the second assembly
member, or both, can be by any method, and is preferably achieved
by the sputtering process. Heating can be from any temperature, and
is preferably from an ambient temperature or a room temperature.
Heating of an assembly member can be to any temperature below the
melting point of the assembly member. Preferably, at the ambient
temperature, a gap is present between at least one side wall of a
projection and at least one side wall of each groove. Heating is
preferably to a temperature whereby thermal expansion causes
contacting of the side walls of the projections and the side walls
of the grooves at a contact temperature. The contact temperature is
the temperature at which the projections on the first assembly
member make contact from thermal expansion with the grooves in the
second assembly member. Prior to the target reaching the contact
temperature, the target temperature increases rapidly with
increasing sputtering power density. Prior to contact being
achieved, heat transfer between the target and electrode is
marginal. However, once contact is achieved, the area of the
contact provides good heat transfer between the target and the
preferably water-cooled electrode. The rate of temperature rise in
the target is then greatly reduced so that a stable target
temperature is maintained. The change in target temperature with
sputtering power for two contact temperatures, 50.degree. C. and
80.degree. C., is provided in FIG. 4.
[0037] Contacting of the side walls of the projections and the side
walls of the grooves preferably forms a temporary mechanical
attachment between the first assembly member and the second
assembly member. Preferably, the location and the dimensions of the
grooves and the projections are predetermined such that each groove
and its corresponding projection make contact due to thermal
expansion during heating of the first assembly member, the second
assembly member, or both. More preferably, the location and
dimensions of the grooves and the projections are predetermined
such that each groove and its corresponding projections make
contact due to thermal expansion at the same contact temperature.
The predetermined location and dimension of each projection/groove
combination can be determined by the thermal expansion equation for
the target material. For example, at room temperature (e.g.,
20.degree. C.), the gap between the projection and the groove is
given by: D=R .alpha.(T.sub.c-20), where R is the radial distance
of the projection/groove from the assembly center, .alpha. is the
thermal expansion coefficient of the projection material, and
T.sub.c is the temperature at which contact occurs between the side
walls of the projections and the side walls of the grooves.
Preferably, the electrode is actively cooled during the sputtering
process, such that it maintains a temperature near about 20.degree.
C. Table 1 provides relative gap dimension data for
projections/grooves at various radii (R) from the assembly center,
and at various contact temperatures (T.sub.c) for a C18200 Cu--Cr
alloy target interlayer, having an expansion coefficient (.alpha.)
of 1.76E-05 ppm/C.
1 TABLE 1 Contact Temperature (.degree. C.) 50 80 120 150 200
Radius (cm) Gap (mm) 1 0.005 0.011 0.018 0.023 0.032 5 0.026 0.053
0.088 0.114 0.158 10 0.053 0.106 0.176 0.229 0.317 20 0.106 0.211
0.352 0.458 0.634 50 0.264 0.528 0.880 1.144 1.584
[0038] Contacting of the side walls of the projections and the side
walls of the grooves at the contact temperature preferably forms a
temporary mechanical attachment between the first assembly member
and the second assembly member. Preferably the gaps present between
the side walls have predetermined dimensions such that contact
between the side walls occurs substantially simultaneously for each
projection. Preferably, the gaps include predetermined dimensions
such that the contact temperature is from about 30 to about
300.degree. C. or more. This temperature range is just one possible
range. The type of metal used will determine the best temperature
range. For instance, an increase in the contact temperature can
decrease the yield strength of the side wall materials, thus lower
contact temperatures are preferable. The contact temperature for
the target assembly is preferably a temperature at which the stress
created at the contact surfaces of the side walls is less than the
yield stress for the side wall materials. Preferably, the temporary
mechanical attachment places the mating surfaces of the assembly
members in thermal contact. The first assembly member can be a
sputter target, and the second assembly member can be a backing
plate. The first assembly member can be an electrode, and the
second assembly member can be a sputter target. Alternatively, the
first assembly member can be a backing plate that is bonded to a
sputter target, and the second assembly member can be an electrode.
Furthermore, the first assembly member can be an electrode, and the
second assembly member can be a backing plate that is bonded to a
sputter target. By cooling or allowing the assembly members to cool
to temperatures below the contact temperature, contact between the
sidewalls of the projections/grooves is lost, causing the temporary
mechanical attachment to end. At such time, the sputter target can
be nondestructively removed from the electrode. Another sputter
target can then be attached to the electrode by a method of the
present invention.
[0039] According to one embodiment of the present invention, the
method of forming a sputter cathode assembly further includes
mechanically interlocking the first assembly member and the second
assembly member together. Mechanically interlocking can be achieved
before, during, or after positioning of the first and second
assembly members such that the projections are received in the
grooves. Preferably, mechanically interlocking occurs
simultaneously with positioning of the first and second assembly
members. Preferably, mechanically interlocking includes rotating
the first assembly member and the second assembly member relative
to one another. To achieve mechanical interlocking, at least one
mechanical interlock can be provided on the mating surfaces. The
mechanical interlock can be formed on the mating surfaces by any
suitable method such as milling or machining. Mechanically
interlocking the first and second assembly members can place the
mating surfaces in electrical, thermal, or physical contact.
Preferably, mechanically interlocking is sufficient to maintain
physical contact between the mating surfaces until the heating of
the sputter cathode assembly forms a temporary mechanical
attachment between the assembly members. The mechanical interlock
can be formed of any combination of a recess formed in one mating
surface and a corresponding protrusion formed in the other mating
surface such that surfaces of the recess and the protrusion are
abutting, thereby creating an interlock. For example, the
mechanical interlock can include a trapezoid shaped recess adapted
to receive a trapezoid shaped protrusion. The mechanical interlock
can include a "T" shaped recess adapted to receive a "T" shaped
protrusion. The mechanical interlock can include an "L" shaped
groove adapted to receive an "L" shaped protrusion. Also, the
mechanical interlock can include a triangle shaped recess adapted
to receive a triangular shaped protrusion. Preferably, the mating
surfaces contain both protrusions and recesses.
[0040] In one embodiment of the present invention, the mechanical
interlock features are provided at one or more corners of
rectangular assembly members so that mechanical interlocking is
achieved by positioning the assembly members such that their center
lines are offset, and then rotating one or the other assembly
member or both to bring the rectangular assembly members in
substantial registration. In the process, the protrusions are
inserted and received into the corresponding recesses and the
assembly members thereby interlocked. In one embodiment of the
present invention, mechanical interlock features are provided in
the center regions of the assembly members. In this particular
embodiment, the recess includes an opening slot that is large
enough to permit the protrusion to enter into the recess when the
mating surfaces are placed adjacent to one another, and such that
the protrusion is then rotated to a final position within the
recess by rotating the assembly members relative to each other.
Preferably, mechanical interlocking allows the assembly members to
be fixed together at their mating surfaces without separating
during handling, or upon placement within a sputtering chamber in a
vertical or suspended horizontal position, for example. A schematic
diagram of the trapezoid groove and protrusion for forming the
mechanical interlock is provided in FIG. 2.
[0041] The previously described versions of the present invention
have may advantages, including that in assembling large rectangular
sputter assemblies using thermal expansion contact to provide
thermal contact between the sputter target and the electrode, no
soldering is required and the target can be replaced without
removing the electrode from the sputtering system. This greatly
reduces the time required to change targets. In addition, this
assembly method allows the target to be of a single piece
construction which greatly reduces target arcing during sputtering,
thereby reducing defects in the deposited film.
[0042] Other embodiments of the present invention will be apparent
to those skilled in the art from consideration of the present
specification and practice of the present invention disclosed
herein. It is intended that the present specification and examples
be considered as exemplary only with a true scope and spirit of the
invention being indicated by the following claims and equivalents
thereof.
* * * * *