U.S. patent application number 12/235427 was filed with the patent office on 2009-01-22 for copper sputtering targets and methods of forming copper sputtering targets.
Invention is credited to Frank A. Alford, Stephane Ferrasse, Vladimir M. Segal, Susan D. Strothers, William B. Willett, Chi tse Wu, Wuwen Yi.
Application Number | 20090020192 12/235427 |
Document ID | / |
Family ID | 23848035 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090020192 |
Kind Code |
A1 |
Segal; Vladimir M. ; et
al. |
January 22, 2009 |
Copper Sputtering Targets and Methods of Forming Copper Sputtering
Targets
Abstract
The invention includes a copper-comprising sputtering target.
The target is monolithic or bonded and contains at least 99.99%
copper by weight and has an average grain size of from 1 micron to
50 microns. The copper-comprising target has a yield strength of
greater than or equal to about 15 ksi and a Brinell hardness (HB)
of greater than about 40. The invention includes copper alloy
monolithic and bonded sputtering targets consisting essentially of
less than or equal to about 99.99% copper by weight and a total
amount of alloying element(s) of at least 100 ppm and less than 10%
by weight. The targets have an average grain size of from less than
1 micron to 50 microns and have a grain size non-uniformity of less
than about 15% standard deviation (1-sigma) throughout the target.
The invention additionally includes methods of producing bonded and
monolithic copper and copper alloy targets.
Inventors: |
Segal; Vladimir M.; (Howell,
MI) ; Yi; Wuwen; (Veradale, WA) ; Ferrasse;
Stephane; (Veradale, WA) ; Wu; Chi tse;
(Veradale, WA) ; Strothers; Susan D.; (Spokane,
WA) ; Alford; Frank A.; (Veradale, WA) ;
Willett; William B.; (Spokane, WA) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD, P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Family ID: |
23848035 |
Appl. No.: |
12/235427 |
Filed: |
September 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10614807 |
Jul 9, 2003 |
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12235427 |
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09465492 |
Dec 16, 1999 |
6878250 |
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10614807 |
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Current U.S.
Class: |
148/536 ;
148/684; 148/685 |
Current CPC
Class: |
C23C 14/3414 20130101;
B21C 23/001 20130101 |
Class at
Publication: |
148/536 ;
148/684; 148/685 |
International
Class: |
C22F 1/08 20060101
C22F001/08 |
Claims
1-78. (canceled)
79. A method of forming a copper-comprising sputtering target,
comprising: providing a Cu billet having a purity of at least
99.99% copper; hot-forging the Cu billet at a temperature of
greater than 300.degree. C. with a reduction in height of at least
about 40% to form a forged block; water quenching the forged block;
performing an extrusion process comprising: at least four passes of
the forged block through equal channel angular extrusion (ECAE);
and a heat-treatment comprising one or both of intermediate
annealing between at least some of the at least four passes, and
heating ECAE die to a temperature of from about 125.degree. C. to
about 225.degree. C. during the extrusion process; after extrusion
process, cold-rolling to a reduction of less than 90% to form a
blank, and forming the blank into a target.
80. The method of claim 79 further comprising solutionizing the
forged block prior to water quenching, the solutionizing comprising
heating the forged block to a temperature of at least about
500.degree. C. and maintaining the temperature for at least about
60 minutes.
81. The method of claim 79 wherein the extrusion process comprises
intermediate annealing at a temperature of from about 125.degree.
C. to about 225.degree. C. for greater than about 1 hour.
82. The method of claim 79 further comprising heating the blank to
recrystallize the copper and form a final grain distribution within
the blank, the final grain distribution having an average grain
size of from about 1 to about 20 microns; wherein the forming the
blank into a target forms a monolithic target.
83. The method of claim 79 wherein the forming the blank into a
target comprises forming a bonded target.
84. The method of claim 83 wherein the forming the bonded target
comprises bonding the target to a backing plate, the bonding being
conducted at a temperature of less than or equal to about
3250.degree. for a time of less than about 4 hours, the bonding
comprising at least one of hipping, roll cladding, soldering and
diffusion bonding.
85. The method of claim 84 wherein the bonding comprises diffusion
bonding to form a bond having a bond yield strength of from at
least about 10 ksi to about 15 ksi.
86. The method of claim 79 wherein the average grain size is from 1
micron to about 50 microns.
87. The method of claim 86 wherein the average grain size is from 5
microns to about 20 microns.
88. The method of claim 79 wherein a uniform grain size
distribution exists throughout an entirety of the blank, the
uniform grain size having a standard deviation of less than 15%
(1-sigma).
89. The method of claim 88 wherein the grain size uniformity
standard deviation is less than about 10% (1-sigma).
90. The method of claim 79 wherein the Cu billet has a purity of at
least about 99.999% copper.
91. The method of claim 79 wherein the Cu billet has a purity of at
least about 99.9999% copper.
92. The method of claim 79 wherein the Cu billet has a purity of at
least about 99.99995% copper.
93. The method of claim 79 wherein the at least four passes
consists of from tour to six passes.
94. A method of forming a copper alloy sputtering target,
comprising: providing a Cu billet consisting essentially of less
than 99.99% copper and at least one alloying element selected from
the group consisting of Cd. Ca, Au, Ag, Be, Li, Mg Al, Pd, Hg, Ni,
in, Zn, B, Ga, Mn, Sn, Ge, W, Cr, O, Sb, Ir, P, As, Co, Te, Fe, S,
Ti, Zr, Sc, and Hf, a total amount of the at least one alloying
element present in the Cu billet being at least 100 ppm and less
than 10% by weight; hot-forging the Cu billet at a temperature of
greater than 300.degree. C. with a reduction in height of at least
about 40% to form a forged block; performing an extrusion process
comprising: at least four passes of the forged block through equal
channel angular extrusion (ECAE); and a heat-treatment comprising
one or both of heating ECAE die during the extrusion process, and
intermediate annealing at a temperature of from about 120.degree.
C. to about 325.degree. C., for a time of at least 1 hour between
at least some of the at least four passes; after the extrusion
process, cold-rolling to a reduction of less than about 90% to form
a blank; and forming the blank into a target.
95. The method of claim 94 wherein the extrusion process comprises
heating the ECAE die to a temperature of from about 125.degree. C.
to about 325.degree. C.
96. The method of claim 94 further comprising solutionizing b
forged block by heating to a temperature of at least about
500.degree. C. and maintaining the temperature for at least about
60 minutes prior to the extrusion process.
97. The method of claim 94 wherein the at least four passes
consists of from four to six passes.
98. The method of claim 94 wherein during and after the extruding
process the method utilizes only temperatures less than or equal to
350.degree. C., and wherein the forming the blank into a target
comprises forming a monolithic target.
99. The method of claim 94 wherein the forming the blank into a
target comprises forming a bonded target.
100. The method of claim 99 further comprising performing a full
static recrystallization treatment conducted at a temperature of
from about 250.degree. C. to about 500.degree. C. for a time of
from about 1 hour to about 8 hours, prior to the forming the bonded
target.
101. The method of claim 99 further comprising performing a full
static recrystallization treatment conducted at a temperature of
from about 250.degree. C. to about 500.degree. C. for a time of
from about 1 hour to about 8 hours after the forming the bonded
target.
102. The method of claim 99 wherein the forming the bonded target
comprises bonding the target to a backing plate, the bonding being
conducted at a temperature of less than or equal to about
500.degree. C. for a time of less than or equal to about 4 hours,
the bonding comprising at least one of hipping, roll cladding,
soldering, explosive bonding, frictionless forging and diffusion
bonding.
103. The method of claim 99 wherein the bonding comprises diffusion
bonding to form a bond having a bond yield strength of from at
least about 10 ksi to about 15 ksi.
104. The method of claim 94 wherein the average grain size is from
1 micron to about 20 microns.
105. The method of claim 104 wherein the average grain size is from
about 5 microns to about 10 microns.
106. The method of claim 94 wherein the average grain size is less
than 1 micron.
107. The method of claim 94 wherein a uniform grain size
distribution exists throughout an entirety of the blank, the
uniform grain size having a standard deviation of less than 15%
(1-sigma).
108. The method of claim 107 wherein the grain size uniformity
standard deviation is less than about 10% (1-sigma).
109. The method of claim 94 further comprising, prior to the
extruding process, performing an aging treatment at a temperature
of less than about 500.degree. C. to form precipitates having an
average precipitate size of less than or equal to about 0.5 micron.
Description
RELATED PATENT DATA
[0001] This patent is a continuation in part of U.S. patent
application Ser. No. 09/465,492 which was filed on Dec. 16, 1999
and which is herein incorporated by reference. This patent further
claims benefit of priority under 35 U.S.C. .sctn.119 to U.S.
Provisional Patent Ser. No. 60/396,544, which was filed Jul. 16,
2002, and to U.S. Provisional Patent Serial No. Not Yet Assigned,
entitled Copper Sputtering Targets and Methods of Forming Copper
Sputtering Targets, which was filed May 15, 2003.
TECHNICAL FIELD
[0002] The invention pertains to copper-comprising monolithic
sputtering targets and copper-comprising bonded sputtering targets.
The invention additionally pertains to methods of forming
copper-comprising monolithic and bonded sputtering targets.
BACKGROUND OF THE INVENTION
[0003] High-purity copper sputtering targets and copper alloy
sputtering targets are currently used in a variety of applications
including, for example, fabrication of integrated circuits. The
quality of copper-comprising structures such as interconnects and
thin films can depend upon sputtering performance of the target.
Various factors of a sputtering target can influence the target's
sputtering performance including: average grain size and grain size
uniformity of the target material; crystallographic
orientation/texture of the target material; structural and
compositional homogeneity within the target; and the strength of
the target material. Typically, a smaller average grain size is
associated with an increased strength of material. Additionally,
the amount of alloying can affect strength and hardness of target
materials, with increased alloying typically resulting in increased
target strength.
[0004] Due to the low strength of high-purity copper (greater than
99.99% copper by weight) conventional high-purity copper sputtering
targets are typically formed as bonded targets. A bonded copper
sputtering target can have a high-purity copper target bonded to a
backing plate comprising a relatively high strength material such
as, for example, aluminum. However, the high temperatures utilized
during bonding of the copper target to the backing plate often
results in abnormal grain growth resulting in non-uniformity of
microstructure and an increase in overall average grain size.
Conventional high-purity copper targets typically have an average
grain size greater than 50 microns which can result in relatively
low yield strength. The resulting grain size and structural
non-uniformity of conventionally formed high-purity copper
sputtering targets can detrimentally affect the quality of
sputter-deposited high-purity copper films and interconnects.
[0005] In addition to the resulting large grain size and anomalous
grain growth that can result during bonding processes, diffusion
bonded copper targets are often plagued by problems such as burn
through and short target life. Additionally, bonding processes can
be complicated and time consuming.
[0006] One approach to increasing grain size uniformity and
enhancing strength of copper materials for sputtering target
purposes is to alloy the copper with one or more "alloying"
elements. However, since the presence of alloying elements affects
the resistivity of copper, it can be desirable to limit the total
amount of alloying elements within a target material to no greater
than 10 percent by weight. For particular applications such as
copper thin films and interconnects, where a resistivity comparable
to that of high-purity copper is desired, the amount of alloying
should be limited to less than or equal to 3% by weight. Another
draw back to alloying can be potential defects such as formation of
second phase precipitates or segregation.
[0007] Although treatment of conventional materials for reduction
or removal of precipitates or segregation defects may be possible
in some instances, such treatment typically includes high
temperatures which can result in extremely large grain sizes
(greater than 150 microns). Alternatively, a partial reduction of
second phase precipitates or segregation defects present in
conventional materials can be obtained in some instances utilizing
conventional rolling and/or forging techniques. However, the
remaining defects can still affect the quality of sputtered films.
Currently, conventional processing to form copper alloys having
less than or equal to 3% by weight of alloying elements result in
targets typically having an average grain size of over 30 microns,
commonly over 50 microns, and having second phase precipitates
therein.
[0008] It is desirable to develop methods to produce copper
sputtering targets and copper alloy sputtering targets having
improved sputtering performance.
SUMMARY OF THE INVENTION
[0009] In one aspect the invention encompasses a copper-comprising
sputtering target. The target contains at least 99.99% copper by
weight and has an average grain size of from 1 micron to 50
microns. The copper-comprising target has a yield strength of
greater than or equal to about 15 ksi and a Brinell hardness (HB)
of greater than about 40.
[0010] In one aspect the invention encompasses a copper alloy
sputtering target consisting essentially of less than or equal to
about 99.99% copper by weight and at least one alloying element
selected from the group consisting of Cd, Ca, Au, Ag, Be, Li, Mg,
Al, Pd, Hg, Ni, In, Zn, B, Ga, Mn, Sn, Ge, W, Cr, O, Sb, Ir, P, As,
Co, Te, Fe, S, Ti, Zr, Sc, Si, Mo, Pt, Nb, Re and Hf. The target
has a total amount of alloying elements of at least 100 ppm and
less than 10% by weight. The target also has an average grain size
of from 1 micron to 50 microns and a grain size uniformity having a
standard deviation throughout the target of less than about 15% of
1-sigma.
[0011] In one aspect the invention encompasses a method of forming
a monolithic sputtering target. A copper billet consisting
essentially of copper and less than or equal to 10% by weight of a
total amount of one or more alloying elements is heated to a
temperature of at least about 900.degree. F. and maintained at that
temperature for at least about 45 minutes. The billet is hot forged
with a reduction in height of at least about 50% to form a forged
block and the block is cold rolled to a reduction of at least about
60% to form a blank. The blank is heated to induce
recrystallization and to form a fine grain distribution having an
average grain size less than about 100 microns. The blank is
subsequently formed into a monolithic target shape.
[0012] In one aspect the invention encompasses a method of forming
a copper-comprising sputtering target from a copper-billet having a
purity of at least 99.99% copper. The billet is hot forged at a
temperature of greater than 300.degree. C. with a reduction in
height of at least 40% to form a forged block. The forged block is
water quenched and subjected to an extrusion process comprising at
least 4 passes of the forged block through equal channel angular
extrusion (ECAE). An optional solutionizing process can be
conducted after the forging, followed by water quenching and the
ECAE. Intermediate annealing is performed between at least some of
the ECAE passes and, after completion of ECAE processing the block
is cold rolled to a reduction of less than 90% to form a blank. The
blank can be heat treated and subsequently formed into a sputtering
target.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Preferred embodiments of the invention are described below
with reference to the following accompanying drawings.
[0014] FIG. 1 is a flowchart diagram depicting a general overview
of processing methods according to one aspect of the present
invention.
[0015] FIG. 2 illustrates a square billet at an initial processing
step according to the invention.
[0016] FIG. 3 is a diagrammatic cross-sectional view of a material
being treated with an equal channel angular extrusion
apparatus.
[0017] FIG. 4 shows a comparison of yield strength and ultimate
tensile strength of various copper and copper alloys processed
utilizing equal channel angular extrusion relative to standard 6N
copper having a grain size of 40 microns and relative to various
backing plates.
[0018] FIG. 5 is an image EBSD/SEM map of grain size distribution
and texture for a 99.9999% copper material (6N) after equal channel
angular extrusion and subsequent annealing at 250.degree. C. for 5
hours according to one aspect of the invention.
[0019] FIG. 6 shows the grain area distribution for the material
imaged in FIG. 5. The average grain size of the material is about 6
microns.
[0020] FIG. 7 shows the resulting average grain size as a function
of annealing treatment as measured by EBSD and optical microscopy.
The annealing treatments were performed on a copper material
containing copper alloyed with 0.53 weight % Mg which had been
subjected to 6 passes of equal channel angular extrusion through
route D.
[0021] FIG. 8 shows the EBSD/SEM map of the Cu 0.53 wt % Mg ECAE
material of FIG. 7 after annealing at 300.degree. C. for 2
hours.
[0022] FIG. 9 is an EBSD/SEM map of the grain structure of the Cu
0.53 wt % Mg material of FIG. 7 after annealing at 450.degree. C.
for 1.5 hours.
[0023] FIG. 10 shows an image of the FIG. 9 material obtained
utilizing optical microscopy.
[0024] FIG. 11 is a diagram depicting sampling of a target for
grain size and texture measurement according to one aspect of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] This disclosure of the invention is submitted in furtherance
of the constitutional purposes of the U.S. Patent Laws "to promote
the progress of science and useful arts" (Article 1, Section
8).
[0026] The invention encompasses monolithic high-purity copper
sputtering targets, bonded high-purity copper sputtering targets,
monolithic copper alloy sputtering targets bonded copper alloy
sputtering targets, and methods of producing such targets. For
purposes of the present description, high-purity copper can refer
to copper or a copper material having at least 99.99% copper by
weight. The invention encompasses high-purity targets having from
at least 99.99% to 99.99995% copper by weight. Additionally, the
use of the term "monolithic" refers to a target that is utilized
for sputtering without being bonded to a backing plate.
[0027] Bonded or monolithic high-purity targets according to the
invention can have an average grain sizes of from less than 1
micron to less than or equal to about 100 microns, preferably less
than 50 microns. In some instances, methods of the invention can be
utilized to produce monolithic or bonded targets having an average
grain size of from 1 to about 30 microns. Monolithic and bonded
targets of high-purity copper according to the invention can, in
particular instances, preferably have an average grain size of from
1 micron to about 20 microns, such as for example, from about 5
microns to about 10 microns.
[0028] High-purity targets of the invention can have a grain size
uniformity across a sputtering surface of the target and/or
throughout the entire target, the uniformity of grain size being
such that a standard deviation (1-sigma) less than or equal to
about 15% (also referred to as less than 15% non-uniformity). In
particular instances the uniformity can reflect a standard
deviation of less than or equal to 10% (1-sigma).
[0029] High-purity copper sputtering targets of the invention can
have a yield strength that is at least about 10% greater than a
target having a substantially identical elemental composition with
an average grain size of 50 microns, and in some instances at least
10% greater than a target having a substantially identical
elemental composition with an average grain size of 30 microns. For
purposes of the present description the phrase "substantially
identical elemental composition" can refer to a material having no
detectable composition differences. The yield strength imparted to
targets by the methods described below can typically be greater
than or equal to about 15 ksi.
[0030] The high-purity copper targets of the invention can have an
ultimate tensile strength of at least 15% greater than a target
having a substantially identical elemental composition with an
average grain size of 50 microns, and in some instances the
ultimate tensile strength can be at least 15% greater than a target
having a substantially identical elemental composition with an
average grain size of 30 microns. Additionally, the hardness of the
high-purity copper targets can be at least 15% greater than a
target having a substantially identical elemental composition with
an average grain size of 30 microns. In particular instances,
high-purity targets of the invention can have a Brinell hardness of
greater than about 40 HB, and in particular instances greater than
about 60 HB.
[0031] In particular aspects, the high-purity copper sputtering
targets of the invention can have a purity of 99.99% (4N) or
greater. For purposes of the present description, all percentages
and included amounts are by weight unless specifically indicated
otherwise. In some aspects the high-purity target can preferably
comprise 99.999% (5N) copper, can preferably comprise 99.9999% (6N)
copper, or can preferably comprise 99.99995% (6N5) copper.
[0032] Bonded high-purity copper targets of the present invention
can comprise the high-purity copper target diffusion bonded to a
backing plate. In particular instances the bonded target can have a
diffusion bond yield strength of greater than 10 ksi, preferably
greater than or equal to about 15 ksi, and in particular instances
can have a bond yield strength greater than or equal to about 30
ksi. Alternatively, the target can be bonded to a backing plate
utilizing an alternative bonding method comprising, for example,
one or more of hipping, roll cladding, soldering, explosive
bonding, and frictionless forging. The alternative bonding method
can preferably bond the high-purity copper target to the backing
plate to produce a bond having a yield strength of greater than or
equal to about 10 ksi.
[0033] A backing plate for utilization in bonded targets of the
present invention can preferably be an aluminum or CuCr backing
plate. As will be understood by those skilled in the art,
alternative backing plate materials may also be utilized as
appropriate.
[0034] The invention encompasses copper alloy sputtering targets
that comprise less than or equal to about 99.99% copper by weight.
Preferably, the copper alloy sputtering targets of the invention
can consist essentially of less than or equal to about 99.99%
copper by weight and at least one alloying element selected from
the group consisting of Cd, Ca, Au, Ag, Be, Li, Mg, Al, Pd, Hg, Ni,
In, Zn, B, Ga, Mn, Sn, Ge, W. Cr, 0, Sb, Ir, P, As, Co, Te, Fe, S,
Ti, Zr, Sc, Si, Pt, Nb, Re, Mo, and Hf. In particular instances,
the at least one alloying element can preferably be selected from
Ag, Al, In, Zn, B, Ga, Mg, Sn, Ge, Ti and Zr. A total amount of the
at least one alloying element present in the target can preferably
be from at least about 100 ppm by weight to less than about 10% by
weight. In some instances, the at least one alloying element can
preferably be present at from at least 1000 ppm to less than about
3%, more less than about 2%, by weight.
[0035] Copper alloy sputtering targets according to the invention
can, in particular aspects, have an average grain size of less than
1 micron. Alternatively, the copper alloy sputtering target can
comprise an average grain size of from 1 micron to about 100
microns, preferably less than 50 microns. In some aspects, the
copper alloy target can preferably have a grain size of from 1 to
30 microns. Applications of the methods of the invention can, in
some instances produce the target to have an average grain size of
less than or equal to 20 microns, and in particular aspects from
about 5 microns to about 10 microns. Additionally, copper alloy
targets of the invention can have a grain size uniformity
throughout the target and or across the sputtering surface of the
target. In particular aspects, the average grain size throughout
the target can have a grain size non-uniformity of less than 15%
(referring to a standard deviation (1-sigma) in grain size of less
than or equal to about 15%, and in particular instances can have a
standard deviation (1-sigma) of less than or equal to about 10%
(non-uniformity of less than or equal to 10%).
[0036] Copper alloy sputtering targets according to the invention
can have a Brinell hardness of at least about 40 HB. In some
instances, targets of the invention can have a hardness of greater
than or equal to about 60 HB. Additionally, the copper alloy
targets can have a hardness uniformity across a sputtering surface
and/or throughout the target. For example, in particular instances
the hardness throughout a copper alloy target can have a standard
deviation (1-sigma) of less than about 5% (in other words, the
target can have a non-uniformity of less than 5%). In particular
instances, the hardness uniformity can have a standard deviation of
less than about 3.5% (1-sigma).
[0037] Copper alloy targets of the invention can be monolithic or
in alternative embodiments can be bonded, Bonded copper alloy
targets of the invention can be bonded to a backing plate by
diffusion bonding or alternatively by a method utilizing one or
more of hipping, roll cladding, soldering, explosive bonding,
frictionless forging and other appropriate bonding techniques.
Where the copper alloy target is bonded, the bond can have a bond
yield strength of greater than about 10 ksi and preferably greater
than about 15 ksi.
[0038] Processing of copper materials in accordance with methods of
the invention can produce copper targets having a texture ranging
from extremely weak (close to random) to extremely strong,
depending upon the processing routes utilized (discussed below).
For purposes of the present description, the term "copper" (as used
in the terms "copper target", "copper material", "copper billet",
etc.), can generally refer to either a high-purity copper or a
copper alloy. An exemplary copper target having a weak texture in
accordance with the invention can have a crystal grain orientation
distribution function (ODF) of less than or equal to about fifteen
times random. In particular instances the target can have an
extremely weak texture, characterized by an ODF less than about
five times random.
[0039] The copper target can comprise a primary grain orientation
wherein the term "primary" refers to a grain orientation that is
present in the target in greater abundance than any single
alternative grain orientation. It is noted that the term "primary"
does not necessarily mean that a majority of the grains are present
in this orientation. Rather, the term "primary" means that there is
no single alternative orientation present in greater abundance
within the target. In particular aspects, the methodology of the
invention can be utilized to produce targets having a primary grain
orientation other than (220).
[0040] Alternative processing in accordance with the invention can
produce copper targets having a less random texture. The invention
encompasses processing which can induce strong textures in the
copper articles produced, where the term "strong texture" can refer
to a material having an ODF above about 15 times random. Targets of
the invention can additionally be produced to have an extremely
strong texture characterized by an ODF above 20 times random. In
particular instances the targets of the invention can preferably
have a predominant grain orientation other than (220).
[0041] The size of copper targets produced utilizing methods in
accordance with the invention is not limited to particular values.
Additionally, the targets can be produced in a variety of shapes
such as for example, circular or rectangular. Due to the increased
strength of the materials produced by the methods described
relative to conventional methods, larger copper target sizes can be
produced relative to those produced by conventional methodologies.
As discussed above, conventional copper targets are bonded to a
backing plate to provide sufficient strength. The high strength of
the materials of the invention can be especially advantageous since
the increased strength can reduce or prevent warping of the target
during fabrication and or sputtering processes. The methodology
allows monolithic (non-bonded) copper targets to be utilized and
allows larger target sizes for both bonded and monolithic targets.
Bonded or monolithic targets of the invention can be produced for a
variety of sputtering applications, including but not limited to
200 mm wafer processing and 300 mm wafer processing.
[0042] Although the targets and methods of the invention are
described with specific reference to copper and copper alloys, it
is to be understood that the invention encompasses alternative
materials, including high-purity metals and alloy materials.
Exemplary alternative materials to which application of the
described methodology can be particularly advantageous include
aluminum, aluminum alloys, titanium, titanium alloys, tantalum,
tantalum alloys, nickel, nickel alloys, molybdenum, molybdenum
alloys, gold, gold alloys, silver, silver alloys, platinum and
platinum alloys. The listed alloys can preferably comprise less
than or equal to 10% alloying element(s), by weight. As will be
understood by those skilled in the art, the temperatures and other
values indicated for methodology described below with respect to
copper materials can be adjusted based upon particular composition
to which the methodology will be applied.
[0043] Methodology of the invention is described generally with
reference to FIG. 1. In an exemplary processing scheme 10 a
material to be processed to form a sputtering target is provided in
an initial processing step 100. The initial material can be
provided in the form of a billet such as the exemplary billet 12
depicted in FIG. 2. Referring to FIG. 2, billet 12 can comprise a
lower face 14, an upper face 16 and can comprise a thickness of
material between lower face 14 and upper face 16 indicated as
T.sub.1. Billet 12 can be a square or rectangular shape as
indicated in FIG. 2 or alternatively can comprise a cylindrical or
other shape (not shown). Billet 12 can preferably comprise a cast
material, although alternative billet materials are contemplated.
In embodiments where a high-purity target is desired, it can be
particularly preferred that billet 12 be a cast material since cast
materials can be provided in very pure form. The targets produced
by methodology of the invention typically have a composition that
is substantially identical to the composition of the billet; where
substantially identical refer to materials having no detectable
composition differences.
[0044] The texture of the material of billet 12 can influence the
texture and/or the difficulty in achieving a desired final texture
of the article produced in accordance with the invention.
Accordingly, billet 12 can be provided to have an initial texture
that can favor production of the texture desired in the copper
target. It can be advantageous to provide billet 12 having a strong
texture where a strong texture is desired in the final article. It
is to be noted however, that alternative methodology of the
invention can be utilized to produce a weak or extremely weak
texture from a billet having a strong texture. Additionally, a
billet having a weak texture can be processed in accordance with
methodology of the invention to produce a target having a strong or
extremely strong texture. A billet having a particular primary or
predominant grain orientation can be processed to produce a target
having the same or a differing primary of predominant grain
orientation, or to having no single predominant grain
orientation.
[0045] In particular aspects, billet 12 can comprise a high-purity
copper material having at least 99.99% copper by weight. In
particular applications, billet 12 can consist essentially of
copper having a 99.99% purity (4N), having a 99.999% purity (5N),
having a 99.9999% purity (6N), or having a purity which exceeds 6N,
for example 99.9999% copper by weight. The invention also
encompasses processes where billet 12 comprises an alternative
high-purity metal such as aluminum, gold, silver, titanium
tantalum, nickel, platinum or molybdenum.
[0046] Billet 12 can alternatively comprise less than 99.99% copper
or less than 99.99% of any of the alternative metals indicated
above. For ease of description, billet 12 will henceforth be
referred to as a copper billet although it is to be understood that
the invention encompasses alternative metals and their alloys. In
some aspects of the invention, copper billet 12 can preferably
consist essentially of less than 99.99% copper and at least one
alloying element selected from the group consisting of Cd, Ca, Au,
Ag, Be, Li, Mg, Al, Pd, Hg, Ni, In, Zn, B, Ga, Mn, Sn, Ge, W, Cr,
O, Sb, Ir, P, As, Co, Te, Fe, S, Ti, Zr, Sc, Si, Pt, Nb, Re, Mo,
and Hf. A total amount of alloying element(s) in the copper billet
can preferably be from at least 100 ppm by weight to less than or
equal to about 10% by weight. In particular aspects, the copper
billet can preferably comprise from at least 1000 ppm to less than
or equal to about 3% alloying element(s), or more preferably less
than or equal to about 2% total alloying element(s), by weight. In
particular embodiments the alloying elements can preferably
comprise one or more of Ag, Al, In, Zn, B, Ga, Mg, Sn, Ge, Ti and
Zr.
[0047] Referring again to FIG. 1, the copper billet provided in
step 100 can be subjected to a preliminary treatment 200.
Preliminary treatment 200 can comprise at least one of
homogenizing, solutionizing and hot forging. As will be understood
by those skilled in the art, appropriate temperatures for
conducting solutionizing, homogenizing or hot forging can depend
upon the specific composition of billet 12. In particular aspects,
the invention preferably comprises hot forging during preliminary
treatment 200 to form a forged block. Hot forging of copper billet
12 can be conducted a temperature of at least about 300.degree. C.,
and can preferably be conducted at a temperature of at least about
500.degree. C., The hot forging can preferably reduce the initial
thickness of billet 12 (T.sub.1 of FIG. 2) at least about 40% and
in particular instances preferably at least about 50%.
[0048] During the preliminary treatment, hot forging can optionally
be preceded by or followed by additional heat treatment which can
comprise solutionizing and/or homogenizing of the copper material
Heat treatment can be conducted at a temperature sufficient to
induce solutionization and/or homogenization to occur in the
particular composition being treated. This
solutionizing/homogenizing temperature can preferably be maintained
for a time sufficient to maximize the solutionization and/or
homogenization of the composition. It is to be noted that
temperatures sufficient for solutionizing or homogenizing can
result in grain growth producing a grain size above the desired
range of less than about 100 microns. Accordingly, conventional
methods which attempt to achieve smaller grain sizes tend to
minimize solutionizing or homogenizing treatments. However,
methodology according to the present invention allows post
homogenizing/solutionizing reduction in grain size thereby
achieving the benefits of both the solutionizing/homogenizing
treatment and small grain size. It can be advantageous to
solutionize and or homogenize during preliminary treatment step 200
to dissolve any precipitates and/or particles present in the copper
billet. Homogenizing can additionally decrease or eliminate
chemical segregation within billet 12.
[0049] Preliminary treatment processes of the present invention are
not limited to particular ordering of homogenizing, soiutionizing
and/or hot forging treatments. In particular aspects, preliminary
treatment 200 can comprise homogenizing of the copper billet
followed by hot forging and subsequent solutionizing. In other
instances, solutionizing is conducted followed by hot forging.
Exemplary preferred preliminary treatments are set forth below in
descriptions of exemplary preferred embodiments of the
invention.
[0050] In some instances where hot forging is conducted during
preliminary treatment 200, the preliminary treatment can
additionally include quenching following, and preferably
immediately following hot forging. Although alternative quenching
techniques can be utilized it can be preferable to utilize water
quenching.
[0051] In particular embodiments, hot forging can comprise an
initial heating and one or more subsequent re-heating events may be
conducted. The height reduction produced during each forging event
between the initial heating and each subsequent re-heating can vary
depending on factors such as the particular composition and forging
temperature utilized. Any quenching that is conducted can
preferably occur only after the final reheating. Exemplary
reheating can comprise one or more reheating of the forged block to
a temperature of 1400.degree. F. for at least about ten minutes
subsequent to the initial hot forging.
[0052] In addition to the processes described above, preliminary
treatment 200 can optionally comprise aging treatment. Where the
preliminary treatment comprises aging, billet 12 is preferably
processed into a forged block prior to aging. More preferably,
aging can be conducted as the final processing in the pretreatment
stage. In particular instances, aging can be utilized to induce
formation of fine precipitates within the copper material. Such
induced precipitates can have an average diameter of less than
about 0.5 microns. In particular applications, it can be
advantageous to induce precipitates by aging since such
precipitates can promote development of fine and uniform grains
during subsequent processing and can stabilize the grain structures
so produced.
[0053] The hot forged and/or solutionized block formed during
preliminary treatment 200 can subsequently undergo alternative
processing as shown in FIG. 1. In one aspect, the processed block
can be subjected to equal channel angular extrusion (ECAE)
processing 310 to form a target blank. Referring to FIG. 3, such
illustrates an exemplary ECAE device 20. Device 20 comprises a mold
assembly 22 that defines a pair of intersecting channels 24 and 26.
Intersecting channels 24 and 26 are identical or at least
substantially identical in cross section, with the term
"substantially identical" indicating that the channels are
identical within acceptable tolerances of an ECAE apparatus. In
operation, a billet 28 (which can be the forged block described
above) is extruded through channels 24 and 26. Such extrusion
results in plastic deformation of the billet by simple shear, layer
after layer, in a thin zone located at the crossing plane of the
channels. Although it can be preferable that channels 24 and 26
intersect at an angle of about 90%, it is to be understood that an
alternative tool angle can be utilized (not shown). A tool angle
(channel intersect angle) of about 90.degree. can be preferable
since an optimal deformation (true shear strain) can be
attained.
[0054] ECAE can introduce severe plastic deformation in the forged
block material while leaving the dimension of the block unchanged.
ECAE can be a preferred method for inducing severe strain in a
metallic material in that ECAE can be utilized at low loads and
pressures to induce strictly uniform and homogenous straining.
Additionally, ECAE can achieve a high deformation per pass (true
strain .epsilon.=1.17); can achieve high accumulated strains with
multiple passes through an ECAE device (at N=4 passes,
.epsilon.=4.64); and can be utilized to create various
textures/microstructures within materials by utilizing different
deformation routes (i.e. by changing an orientation of the forged
block between passes through an ECAE device).
[0055] In an exemplary method of the present invention, ECAE is
conducted at a strain rate and processing temperature sufficient to
obtain desired microstructures (for example a weak texture and
small grain size) within a copper billet or forged block, and to
generate a uniform stress-strain state throughout the billet. The
copper material can be passed through an ECAE apparatus several
times, and with numerous routes and at a temperature which can
correspond to cold or hot processing of the material. A preferred
route to utilize with multiple passes through ECAE apparatus 20 can
be the "route D", which corresponds to a constant 90.degree. billet
rotation before each successive pass. Since the ECAE route can
affect structural orientation produced during dynamic
recrystallization, one or more particular routes can be chosen for
deformation passes to induce a desired orientation in the processed
material.
[0056] In particular applications, the forged block processed in
step 200 is subjected to at least four ECAE passes in process 310.
Typically, ECAE processing 310 comprises from four to eight passes,
and can preferably comprise from four to six passes. Such exemplary
number is generally found sufficient to promote grain refinement to
sub-micron size by mechanically induced dynamic recrystallization
(where sub-micron refers to an average grain size of less than 1
micron).
[0057] Typically, ECAE passes one through three each successively
creates defects (micro-bands; shear bands, arrays of dislocations,
etc.). During these initial passes, thermodynamic rearrangement can
occur creating cells and sub-grains and initiating mis-orientation
of grain boundaries. The texture strength of the material prior to
ECAE can affect the strength that is produced during the initial
three passes, with strong initial textures typically becoming
randomized after a greater number of passes relative to materials
having a weak initial texture. Subsequent passes (i.e. the fourth
pass and any additional passes); create a dynamically
recrystallized sub-micron grain size by inducing an increase in the
number of high angle boundaries. During the dynamic
recrystallization, the newly created grains gradually acquire a
weaker texture and become increasingly equiaxed.
[0058] In some applications, heating of ECAE apparatus die can be
utilized to heat billet 28 during the ECAE passes. The die can
preferably be heated to less than the lowest temperature which can
produce static recrystallization of the copper material being
processed (alternatively referred to as the minimum
recrystallization temperature), and can more preferably be heated
to a temperature of from about 125.degree. C. to about 350.degree.
C.
[0059] During ECAE processing 310, intermediate annealing can
optionally be performed between some or all of the ECAE passes.
Intermediate annealing can be performed below the beginning
temperature of static recrystallization, at or near the beginning
temperature of static recrystallization (defined as the lowest
temperature which begins to induce recrystallization of the
material being processed) or within the range of temperature for
full static recrystallization of the composition. The temperature
at which the intermediate anneal is conducted can influence the
size and orientation of crystal grains and can therefore be
utilized to promote a desired texture in a given instance.
[0060] Intermediate annealing at temperatures which can produce
full static recrystallization can allow increased weakening of
textures to occur during subsequent ECAE passes. Annealing at
temperatures below the beginning temperature of static
recrystallization can produce recovery (stress relief) which can
also result in changes in texture strength and orientation. The
reorientation effect can be maximal when sub-crystallization
temperature annealing is performed between one or more of the
initial four passes, and can become less marked when performed
between passes subsequent to the fourth pass. Intermediate
annealing at the beginning temperature of static recrystallization
can result in both change in texture (strength and/or orientation)
and some recrystallization. Repeated intermediate annealing between
successive passes can have an enhanced effect relative to the
effects described for individual annealing events.
[0061] In particular applications of the present invention it can
be preferable to conduct any intermediate annealing at a
temperature and for a time less than those which can result in
static recrystallization of the material being processed. It can be
advantageous to conduct intermediate annealing at temperatures
lower than those which can induce static recrystallization to
minimize surface cracking and enhanced microstructural uniformity.
Where the forged block being subjected to ECAE comprises
high-purity copper, intermediate annealing can preferably be
conducted at temperatures of from about 125.degree. C. to about
225.degree. C., and for a time of longer than about 1 hour. This
can allow ECAE processing 310 to produce a high-purity copper
material having extremely uniform and small grain sizes, for
example, averaging from submicron grain sizes to about 20
microns.
[0062] In aspects of the invention where the forged block material
comprises a copper alloy, sub-crystallization temperature
intermediate annealing performed during ECAE processing 310 can
preferably comprise temperatures from about 150.degree. C. to about
325.degree. C., such temperature preferably being maintained for at
least 1 hour. This sub-recrystallization temperature annealing
treatment can produce copper alloy material having an average grain
size of less than 1 micron.
[0063] The high-purity copper and copper alloy materials produced
by the ECAE methods described above can have an improved hardness
relative to materials produced by conventional processing
techniques. The resulting hardness for 6N copper and various copper
alloys processed in accordance with the methodology of the
invention relative to the corresponding materials prior to ECAE are
indicated in Table 1. FIG. 4 compares the yield strengths and
ultimate tensile strengths for high-purity copper and various
copper alloys processed in accordance with methodology of the
invention, relative to 6N copper having a grain size of 40 microns
and relative to various baking plate materials.
TABLE-US-00001 TABLE 1 Effects of ECAE treatment on material grain
size and hardness Pre-ECAE Post-ECAE Post-ECAE Material (grain
Hardness average grain Hardness Increase in size 30-50 .mu.m
(Vickers) size (Vickers) Hardness 6N Copper 48.44 HV 5 .mu.m 72.2
HV 49% 6N Cu + 0.8% Ag 73.02 HV 4 .mu.m 89.88 HV 23% 6N Cu + 0.8%
Ag 73.02 HV 0.35 .mu.m 172.4 HV 136% 6N Cu + 0.5% Sn 75 HV 4 .mu.m
104.56 HV 39.4% 6N Cu + 0.5% Sn 75 HV 0.35 .mu.m 182 HV 142%
[0064] After preliminary treatment 200, copper materials can
undergo an alternative processing route 330 comprising a rolling
process to produce the target blank, as shown in FIG. 1. Rolling
treatment 330 preferably comprises subjecting the forged block
produced by preliminary treatment 220 to cold rolling with a total
reduction of at least 60% and preferably from 60% to 85%. The cold
rolling can comprise greater than four passes, preferably greater
than eight passes and more preferably from eight to sixteen passes.
During the overall rolling process, each of an initial four passes
is preferably conducted to reduce the thickness of the block by
from about 5% to about 6% for each pass. Additionally it can be
preferable that a final four of the rolling passes each produce
reduction of thickness of from about 10% to about 20%. The
relatively small reductions during the initial four passes can
alleviate or prevent cracking during the rolling process. The
rolling can produce a small grain size in the resulting cold rolled
high-purity copper or copper alloy material.
[0065] Alternative to the processing route above, processing route
320 can be conducted as shown in FIG. 1. Route 320 utilizes a
combination of cold rolling and equal channel angular extrusion
techniques. In aspects of the invention where processing
alternative 320 is utilized, it can be preferable to subject the
hot forged block produced by preliminary treatment 200 to ECAE and
a subsequent cold rolling treatment. It is to be understood
however, that the invention contemplates performing cold rolling
prior to ECAE, or both prior to and subsequent to ECAE.
[0066] The ECAE portion of process 320 can comprise the ECAE
processing methods described above. The ECAE extruded material can
subsequently be cold rolled to a reduction of less than about 90%
to form a blank. In particular instances, the cold rolling portion
of route 320 can preferably produce a reduction of at least about
60%. The cold rolling processing of ECAE extruded material can
comprise the rolling process described above with respect to
rolling processing 330. In particular aspects, route 320 can
combine the rolling with forging to produce the total reduction of
at least 60% and less than 90%. Alternatively, a forging process
can be utilized in an absence of rolling to produce the desired
reduction of from 60% to 90%.
[0067] It can be advantageous to combine ECAE with a subsequent
rolling and/or forging process since such processing can induce a
desired grain orientation into the copper material. The induced
orientation can comprise a primary grain orientation or can
comprise a predominant grain orientation. Rolling and/or forging
can be used to create strong or extremely strong textures within
the copper articles of the invention. In some aspects, the strong
textures created by the post-ECAE rolling/forging will be other
than (220) texture.
[0068] The resulting blank comprising copper or copper alloy
material can undergo a final target formation processing 500 and
can optionally undergo an additional heat treatment 400 prior to
the final target formation 500 as shown in FIG. 1. Optional heat
treatment process 400 can comprise conducting an annealing
treatment at a temperature and time less than those that can induce
onset of static recrystallization. The low temperature anneal also
referred to as recovery anneal, is conducted below the minimum
temperature of static recrystallization. Recovery annealing or
optional absence of anneal can be advantageous for maintaining
extremely small grain size. Such low temperature or absence of
anneal can result in a blank having an average grain size of less
than about 1 micron.
[0069] Alternatively, the blank can be subjected to a temperature
equal to or exceeding the minimum temperature to induce
recrystallization for a time sufficient to form a final grain
distribution within the blank. Although static recrystallization
can increase the grain size, the increase can be minimized by
conducting the anneal close to the minimum temperature for
recrystallization for a minimum time to produce the desired amount
of recrystallization (partial or full recrystallization). For
copper alloys, the recrystallization annealing can preferably
conducted at a temperature of from about 350.degree. C. to about
500.degree. C. for a time period of from about 1 hour to about 8
hours. For high purity copper, the recrystallization annealing is
preferably conducted at a temperature of from about 225.degree. C.
to about 300.degree. C. for a time period of from about 1 hour to
about 4 hours.
[0070] FIGS. 5 and 6 show the grain size and distribution for 6N
copper having an average grain size of about 6 microns produced
using ECAE and subsequent annealing at 250.degree. C. for 5 hours
in accordance with methodology of the invention. FIG. 7 shows the
evolution of grain size as a function of anneal treatment for
copper alloyed with 0.53% Mg which has been subjected to six passes
of ECAE through route D prior to the anneal. FIG. 8 shows the grain
size and distribution for the copper/0.53% Mg alloy of FIG. 7 after
annealing at 300.degree. C. for 2 hours. FIGS. 9 and 10 show the
grain size and distribution for the copper/0.53% Mg alloy of FIG. 7
after annealing at 450.degree. C. for 1.5 hours, analyzed using
EBSD/SEM (FIG. 9) and by optical microscopy (FIG. 10).
[0071] It is to be noted that the blanks produced in alternate step
310, 320 or 330 can be subjected to an aging treatment (not shown)
either in an absence of heat treatment step 400, or after heat
treatment 400. Where aging is utilized, the aging can preferably be
performed at a temperature less than about 500.degree. C. As
indicated above it can be advantageous to perform an aging step to
increase the strength of the copper or copper alloy blank by
inducing fine precipitates having an average precipitate size of
less than about 0.5 microns.
[0072] The high-purity copper or copper alloy blank produced by
methods of the present invention can be subjected to final target
formation 500 to produce a monolithic target or alternatively to
produce a bonded target (where "bonded target" refers to a
sputtering target bonded to a support such as a backing plate).
[0073] Where the final target formed in process 500 will be a
monolithic target, final target formation can comprise, for
example, machining of the blank to produce the desired target
shape. Where a target produced by methodology of the invention will
be utilized for semiconductor wafer processing, final formation
step 500 can comprise production of a target which has a size
appropriate for processing of 200 mm wafers or for processing of
300 mm wafers. An exemplary monolithic copper or copper or copper
alloy target in accordance with the invention which can be utilized
for example, for processing of a 200 mm semiconductive wafer can
have a 13.7 inch sputtering surface diameter, a 16.6 inch opposing
surface (backside) diameter, and a thickness of about 0.89 inches.
A corresponding target which can be utilized for processing of 300
mm wafers can have a 17.5 inch sputtering surface diameter, a 20.7
inch backside diameter, and a thickness of about 1.0 inch. The
monolithic targets formed by methodology of the present invention
can preferably be planar targets although other target shapes are
contemplated as well as alternative sizes.
[0074] Monolithic targets produce in accordance with methodology of
the invention can preferably have grain sizes of less than or equal
to about 50 microns in order to maximize target strength.
Monolithic targets of the invention having submicron grain size can
have a yield strength, ultimate tensile strength (UTS) and hardness
at least about 50% greater than targets having a substantially
identical composition with an average grain size of 30 microns.
Monolithic copper targets produced according to the invention which
have an average grain size of from 1 to less than about 20 microns
can have a strength enhancement of at least 10% over conventional
copper targets. For extremely large monolithic targets or in
applications where maximum target strength is desired, a monolithic
target can preferably be produced in an absence of heat treatment
step 400. Accordingly, the resulting monolithic target can retain
the small grain size produced in the preceding processing. For
example, where a submicron grain size is produced utilizing rolling
and or ECAE, the submicron grain size can be maintained in the
final monolithic target to maximize the target strength. In an
alternative aspect, heat treatment step 400 can be utilized during
processing to produce the monolithic target which can produce a
final grain distribution resulting in an average grain size of from
about 1 micron to about 20 microns in the resulting monolithic
target.
[0075] Where the target produced in step 500 will be a bonded
target, the target formation can comprise a bonding step in
addition to any machining that is performed to form the desired
target shape. The bonding process can involve bonding the blank
formed by the previous processing methods to a support such as a
backing plate. Exemplary backing plates can comprise, for example,
aluminum and/or copper. Exemplary backing plate materials are CuCr,
Al 2024 and Al 6061 T4. The bonding process can comprise one or
more of hipping, rolling, cladding, soldering, explosive bonding,
frictionless forging, diffusion bonding, or alternative methods
known to those skilled in the art. The bonding can produce a bond
having a yield strength of at least about 10 ksi. In particular
instances, the bonding produces a bond strength greater than or
equal to about 15 ksi and in specific applications, produces a bond
strength equal to or exceeding 30 ksi.
[0076] The various processing methods described above can be
utilized to produce copper articles having extremely uniform and
small grain sizes. Often, the grain sizes produced can average from
submicron grains to about. This small grain size allows very high
bonding strength to be obtained since high temperature bonding
methods can be utilized. Where a bonded target will be produced,
heating (heat treatment 400) can be combined with the bonding in
the target formation process.
[0077] Bonding of high-purity copper targets according to methods
of the invention can preferably be conducted at a temperature of
less than or equal to about 325.degree. C. for a time of less than
or equal to about 4 hours to minimize grain growth in the target.
Although some grain growth may occur during high temperature
bonding processes, the initial extremely fine grain size allows
some grain growth to occur without resulting in the larger grain
sizes observed in targets formed utilizing conventional processing
methods. A resulting grain size of from 1 to about 20 microns in
the final bonded targets of the invention allow strength
enhancement of at least 10% over conventional copper targets.
[0078] Formation of bonded copper alloy targets can preferably be
conducted at a temperature and time less than those that produce
full static recrystallization. Such bonding can preferably comprise
conducting bonding at temperature of less than about 400.degree. C.
for 4 hours and more preferably less than 350.degree. C. for 1-4
hours. Utilizing these bonding conditions, the copper alloy target
can be formed to have an average grain size of less than 1
micron.
[0079] Alternatively, bonding can comprise a temperature which can
result in recrystallization of the copper alloy. During bonding
that comprises temperatures above the minimum temperature of static
recrystallization for the specific alloy, it can be desirable to
minimize the temperature and time of bonding to thereby minimize
grain growth. Recrystallization that occurs during bonding can
preferably be such that the resulting average grain size produced
in the copper alloy is from 1 to about 20 microns. Such heat
treatment for full recrystallization can preferably be conducted at
a temperature of from about 200.degree. C. for at least about 1
hour and preferably between 350.degree. C. and 500.degree. C. for a
time of greater than 1 hour.
[0080] As an alternative to combining the heating and bonding
processes, a heat treating can be conducted either prior to the
bonding step (i.e. heat treatment 400) or subsequent to the bonding
step. It can be advantageous to combine bonding and heat treatment
to enhance bond strength and recrystallize the copper or copper
alloy material.
[0081] The bonded copper and bonded copper alloy targets formed in
accordance with the methodology of the invention can have increased
bond strength relative to bonded targets formed utilizing
conventional methods. Diffusion bonding can be preferred for
bonding targets to backing plates in some aspects of the invention.
Where the grain size of the target blank is submicron, a very high
strength diffusion bond can be produced due to enhanced diffusivity
of the ultrafine grains. The resulting diffusion bond can have a
yield strength of 15 ksi or above, which in some instances can
equal or exceed 30 ksi. Additional advantages of bonded copper and
copper alloy targets of the invention relative to conventional
targets include improved resistance to target warping, reduced
arcing. Utilization of the targets of the invention for sputtering
applications can provide an improved quality of film having fewer
particles incorporated therein and can provide better uniformity of
film thickness and therefore an improved resistance uniformity.
Additionally, utilization of targets formed in accordance with
methodology of the invention for semiconductor processing provides
improved wafer to wafer uniformity of film thickness and
resistance.
[0082] Monolithic high-purity copper and copper alloy targets
formed in accordance with methodology of the Invention can have a
lifetime which is at least 30% longer and typically 40% longer
relative to conventional bonded copper and copper alloy targets
formed utilizing alternative methodologies. The ability to achieve
monolithic copper targets allows avoidance of debonding (separation
from the backing plate) that can occur with conventional bonded
targets. The monolithic targets according to the invention
additionally have increased resistance to target warping, reduction
of arcing, reduced particle generation in thin films sputtered from
such targets, enhanced uniformity of film thickness and
resistivity. Additionally, monolithic targets in accordance with
the invention have improved wafer to wafer consistency of film
thickness and uniformity of resistivity.
[0083] The examples presented below are exemplary preferred
embodiments of the invention. It is to be understood that the
invention contemplates additional embodiments and is not intended
to be limited to the specific examples presented.
Example 1
Production of High-Purity Copper Monolithic Sputtering Targets
[0084] An as-cast copper billet of 6N purity having a 6 inch
diameter and a length of 11 inches, is heated and maintained at a
temperature of about 990.degree. F. for about 60 minutes in an air
oven. The billet is then hot forged, utilizing silica or graphite
foil during forging, to a final height reduction of from 55-75% and
is immediately water quenched. The forged block is then cold-rolled
using 16 passes, quenching after an initial 8 passes, with a total
reduction of from about 60% to about 80%. Cracking is prevented
during the cold-rolling by conducting each of the initial four
passes to produce a reduction of from about 5% to about 6% per
pass. Passes 13-16 are conducted to produce from about 10% to about
11% reduction per pass to achieve a small grain size. After
cold-rolling, the blank is recrystallized by heating to about
480.degree. F. for about 120 minutes. The blank is machined to
produce the final target. The resulting high-purity copper
monolithic target has an average grain size of less than 50 microns
with a uniform grain distribution throughout the target.
[0085] FIG. 11 illustrates sampling locations utilized for analysis
of the resulting monolithic target. The target has a thickness of
0.89 inches. The grain size measured at each point indicated at the
sputtering surface, and the average thereof is given in Table
2.
TABLE-US-00002 TABLE 2 Grain size measurements at target surface
Location 1 2 3 4 5 6 7 8 9 Ave Grain size 38 45 45 38 38 53 38 38
53 43
The grain size measured for the indicated point of the depth planes
of FIG. 11 are given in Table 3, along with the average of such
measured values. Table 4 indicates the texture determined for the
indicated target points identified in FIG. 11.
TABLE-US-00003 TABLE 3 Grain size measurements at indicated points
within the target Depth 2 4 5 7 Ave 0.250'' 53 38 45 45 45.3
0.460'' 45 38 45 45 43.3 0.700'' 45 45 45 45 45
TABLE-US-00004 TABLE 4 Texture of target microstructure at
indicated points Depth Location (111) (200) (220) (113) 0.00'' 2
24.0% 20.9% 25.0% 30.1% 4 23.9% 22.3% 23.7% 30.1% 5 21.5% 20.6%
26.2% 31.7% 7 23.5% 20.5% 24.2% 31.7% 0.250'' 2 22.5% 16.9% 30.8%
29.7% 4 24.6% 16.7% 28.7% 30.2% 5 18.0% 15.2% 39.4% 27.5% 7 24.5%
15.2% 31.2% 28.0% 0.460'' 2 21.5% 17.6% 35.1% 25.8% 4 19.0% 17.6%
42.4% 21.0% 5 16.8% 15.9% 41.2% 26.2% 7 20.5% 17.2% 33.1% 29.3%
0.700'' 2 21.9% 20.5% 26.0% 31.6% 4 23.0% 20.8% 25.8% 30.4% 5 22.2%
20.8% 27.2% 29.8% 7 22.4% 22.4% 21.1% 34.0%
[0086] An additional example of a high-purity target is formed as
indicated in the preceding example with the exception that ECAE is
included in the processing. The ECAE is performed prior to the
cold-rolling to reduce the grain size from that present in the
as-cast billet. The resulting target is analyzed as indicated above
for the previous example. The target had an average grain size of
less than 15 microns throughout the target.
Example 2
Production of Copper Alloy Monolithic Sputtering Targets
[0087] Copper alloy billets having less than 10% of Ag, Sn, Al, or
Ti are heated and maintained at a temperature of about 900.degree.
F. to about 1500.degree. F. for about 45 minutes. The billets are
then hot forged to produce a final reduction of at least about 50%.
Some of forged billets (depending on the alloy) are reheated for at
least 10 minutes during the forging. After the final forging, the
forged billets are immediately water quenched. The forged blocks
are cold-rolled to a reduction of at least about 60% to form a
blank which is recrystallized by heating to a temperature of from
about 750.degree. F. to about 1200.degree. F. for 120 minutes. The
recrystallized blanks are machined to form monolithic targets. Each
of the targets has an average grain size of from about 15 microns
to about 50 microns.
[0088] A specific target having copper alloyed with 0.3 atomic % Al
was formed from a billet having a six inch diameter and a length of
11 inches. The billet was initially heated for 1 hour at
1400.degree. F. and was initially forged to a height of 6 inches.
After the initial forging, the billet was reheated for 15 minutes
at 1400.degree. F. and was subsequently forged to a height of 3
inches. After final forging, the forged block was immediately water
quenched. Cold rolling consisting of 17 passes was then conducted
according to the rolling plan shown in Table 5 to form a rolled
blank.
[0089] After rolling the blank was annealed at about 825.degree. F.
for about 120 minutes and formed into the final monolithic target.
Analysis of the target surface (in accordance with the surface
points shown in FIG. 11) revealed a homogenous composition and an
average grain size of 37 microns. The grain size non-uniformity was
8.6% (1-sigma).
TABLE-US-00005 TABLE 5 Rolling Plan for Cu-0.3 at % Al Direction
.DELTA. Height Height % Pass (degree) (inches) (inches) Reduction 1
0 0.1 2.9 3.3 2 135 0.1 2.8 3.4 3 270 0.1 2.7 2.6 4 45 0.1 2.6 3.7
5 180 0.1 2.5 3.8 6 315 0.1 2.4 4.0 7 90 0.1 2.3 4.2 8 225 0.1 2.2
4.3 9 0 0.13 2.07 5.9 10 135 0.13 1.94 6.2 11 270 0.13 1.81 6.7 12
45 0.13 1.68 7.1 13 180 0.13 1.55 7.7 14 315 0.13 1.42 8.3 15 90
0.13 1.29 9.1 16 225 0.13 1.16 10.0 17 One free pass
Example 3
Production of Copper Alloy Diffusion Bonded Sputtering Targets
[0090] Copper alloy billets are provided and processed as described
in example 2 with the exception that the cold-rolling was conducted
to a reduction of at least about 50%. The cold-rolled blanks are
bonded to CuCr backing plates at a bonding temperature of about
450.degree. C. for about 120 minutes. Recrystallization of the
alloy occurs during the bonding. The bonded targets have a grain
size of less than about 30 microns and a bond strength of up to
about 30 ksi.
Example 4
Production of High-Purity Copper Sputtering Targets Utilizing
ECAE
[0091] Copper billets of cast copper having a purity of at least
99.9999% are provided. The high-purity copper billets are
hot-forged at a temperature of least about 500.degree. C. with a
reduction in height of at least about 40% to form forged blocks.
The forged blocks are solutionized by heating the blocks to a
temperature of at least about 500.degree. C. which is maintained
for at least about 1 hour. The solutionized blocks are water
quenched immediately after the heat treatment and are extruded
utilizing from four to six passes of equal channel angular
extrusion (ECAE) in accordance with route D (90 degree rotation of
the blocks between successive passes) to produce a sub-micron
microstructure. Intermediate annealing at a temperature of from
about 125.degree. C. to about 225.degree. C., and for a time of at
least about 1 hour is performed between some or all of the ECAE
passes. The extruded high-purity copper blocks are cold-rolled to a
reduction of at least 60% to form target blanks which are formed
into either monolithic or bonded targets.
[0092] The blanks for monolithic targets are machined to produce
the final target. Direct machining of the blanks produces targets
having submicron grain size. Recrystallization is performed to
produce monolithic targets having an average grain size of from 1
micron to about 20 microns.
[0093] The blanks for bonded targets are diffusion bonded to a
backing plate. Diffusion bonding is conducted at a temperature
below 350.degree. C. for less than 4 hours. The bond yield strength
is greater than about 15 ksi. The bonded targets have grain sizes
of from submicron to about 20 microns. The submicron targets have a
strength enhancement of about 50% relative to conventional targets.
The bonded targets having a grain size of from 1 to about 20
microns have a strength enhancement of at least 10% relative to
conventional copper targets. The grain size at various locations
(see FIG. 11 for sampling information) throughout the 6N copper
target after diffusion bonding at 250.degree. C. for 2 hours is
shown in Table 6. The average grain size is 11.37 microns with a
standard deviation of 6.97% (1-sigma).
TABLE-US-00006 TABLE 6 Grain size (.mu.m) for the 6N diffusion
bonded target Top Middle Bottom Location Plane Plane plane 1 13 11
11 2 11 13 11 3 11 11 11 4 13 11 11 5 11 11 11 6 11 11 13 7 11 11
13 8 11 11 11 9 11 11 11
[0094] Table 7 gives the three-point hardness measurements obtained
from the top surface and bottom surface of the target of Table 6.
The average hardness is 53.3 HB with a standard deviation of 2.18%
(1-sigma).
TABLE-US-00007 TABLE 7 Hardness (HB) of the 6N diffusion bonded
target Location Top Plane Bottom Plane 1 53.4/55.1/53.4
51.8/51.8/50.3 2 50.3/51.8/51.8 53.4/53.4/51.8 3 53.4/55.1/51.8
53.4/53.4/53.4 4 53.4/55.1/53.4 50.3/51.8/51.8 5 55.1/55.1/53.4
51.8/51.8/51.8 6 53.4/55.1/53.4 51.8/53.4/50.3 7 55.1/55.1/53.4
53.4/53.4/51.8 8 53.4/53.4/51.8 51.8/53.4/51.8 9 53.4/53.4/51.8
53.4/53.4/51.8
Example 5
Production of Copper Alloy Sputtering Targets Utilizing ECAE
[0095] Copper billets containing copper alloyed with from 1000 ppm
to less than or equal to about 10% of Ag, Al, In, Zn, B, Ga, Mg,
Sn, Ge, Ti or Zr are provided. The billets are hot forged at a
temperature of at least about 500.degree. C. with a reduction of
height of at least about 40% to form a forged blocks. The forged
blocks are solutionized by heating the forged blocks to a
temperature of at least about 500.degree. C. and maintaining the
temperature for at least about 1 hour to form a solutionized block.
The solutionized blocks are water quenched immediately after
solutionizing.
[0096] The solutionized blocks are extruded by performing from four
to six passes of ECAE. The solutionized blocks are rotated 90
degrees between each of the passes in accordance with route D.
Intermediate annealing is conducted for at least one hour at a
temperature of from about 150.degree. C. to about 325.degree. C.
between some passes through ECAE. The ECAE extruded blocks are
cold-rolled to a reduction of at least about 60% to form a copper
alloy blank.
[0097] A first monolithic copper alloy target is produced by
machining a copper alloy blank produced as described to form a
monolithic target. The first monolithic target has an average grain
size of less than 1 micron. Additionally, the first monolithic
copper alloy target has a yield strength, ultimate tensile strength
(UTS) and hardness at least about 50% greater than a target having
a substantially identical elemental composition with an average
grain size of 30 micron.
[0098] A second monolithic copper alloy target is produced by
heat-treating a copper alloy blank produced as described above. The
heat treatment is conducted at a temperature of 350.degree. C. for
about 1 hour. The second target has an average grain size of from 1
micron to about 20 microns, has a substantial absence of
precipitates (where substantial absence of precipitates refers to
an absence of detectible precipitates), and has an absence of
detectable segregation and a maximum void size of less than 1
micron.
[0099] A first bonded copper alloy target is produced by diffusion
bonding a copper alloy blank produced as described, to a backing
plate. The diffusion bonding is conducted at a temperature of less
than 350.degree. C. for from one to four hours. The first bonded
alloy target has an average grain size of less than 1 micron.
[0100] A second bonded copper alloy target is produced by diffusion
bonding a copper alloy blank produced as described above to a
backing plate at a bonding temperature of from about 350.degree. C.
to about 500.degree. C. for at least one hour. The second bonded
copper alloy target is fully recrystallized and has an average
grain size of from about 1 micron to about 20 microns.
[0101] In compliance with the statute, the invention has been
described in language more or less specific as to structural and
methodical features. It is to be understood, however, that the
invention is not limited to the specific features shown and
described, since the means herein disclosed comprise preferred
forms of putting the invention into effect. The invention is,
therefore, claimed in any of its forms or modifications within the
proper scope of the appended claims appropriately interpreted in
accordance with the doctrine of equivalents.
* * * * *