U.S. patent application number 16/849050 was filed with the patent office on 2020-07-30 for method of making a tantalum sputter target and sputter targets made thereby.
The applicant listed for this patent is Tosoh SMD, Inc.. Invention is credited to Matthew Fisher, Eugene Y. Ivanov, Alex Kuhn.
Application Number | 20200240006 16/849050 |
Document ID | 20200240006 / US20200240006 |
Family ID | 1000004781108 |
Filed Date | 2020-07-30 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200240006 |
Kind Code |
A1 |
Ivanov; Eugene Y. ; et
al. |
July 30, 2020 |
METHOD OF MAKING A TANTALUM SPUTTER TARGET AND SPUTTER TARGETS MADE
THEREBY
Abstract
Methods for making Ta sputter targets and sputter targets made
thereby. Ta ingots are compressed along at least two of the x, y,
and z dimensions and then cross rolled in at least one of those
dimensions. A pair of target blanks is then cut from the cross
rolled ingot. The resulting targets have a predominate mix of {100}
and {111} textures and have reduced B {100} and B {100} banding
factors.
Inventors: |
Ivanov; Eugene Y.; (Grove
City, OH) ; Fisher; Matthew; (Columbus, OH) ;
Kuhn; Alex; (Columbus, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tosoh SMD, Inc. |
Grove City |
OH |
US |
|
|
Family ID: |
1000004781108 |
Appl. No.: |
16/849050 |
Filed: |
April 15, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15560733 |
Sep 22, 2017 |
10655214 |
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PCT/US2016/025592 |
Apr 1, 2016 |
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16849050 |
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62145550 |
Apr 10, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B21B 2015/0014 20130101;
B21B 1/026 20130101; C23C 14/3414 20130101; B21B 15/0007 20130101;
H01J 37/3426 20130101; B21B 1/024 20130101; B21B 2015/0021
20130101; C22C 27/02 20130101; C22F 1/18 20130101 |
International
Class: |
C23C 14/34 20060101
C23C014/34; B21B 15/00 20060101 B21B015/00; H01J 37/34 20060101
H01J037/34; B21B 1/02 20060101 B21B001/02; C22C 27/02 20060101
C22C027/02; C22F 1/18 20060101 C22F001/18 |
Claims
1-12. (canceled)
13. A thin film for semiconductor applications created by using the
BCC metal or BCC metal alloy sputter target according to claim 14,
where variation in film thickness uniformity (percent
non-uniformity) is 3.000% or less, and variation in sheet
resistance, within wafers, and between wafers is 4.00% or less.
14. A BCC metal or BCC metal alloy sputter target, the sputter
target comprising a Ta metal or a Ta metal alloy, said target
having a thickness dimension and having a purity of at least 99.5%
and a combined C, O, N, H content of less than about 25 ppm, said
Ta metal or Ta metal alloy having a grain size of from about 50 to
150 microns and mixed texture with no banding throughout the
mid-fraction of said thickness dimension.
15. The BCC metal or BCC metal alloy sputter target as recited in
claim 14, wherein said C, O, N, H content is less than 25 ppm and
said grain size is from about 50 to 150 microns.
16. The BCC metal or BCC metal alloy sputter target as recited in
claim 14, having a purity of 99.995% or greater.
17. The BCC metal or BCC metal alloy sputter target as recited in
claim 14, wherein said target has a predominate mix of {100} and
{111} textures and has reduced {100} and {111} banding factors
wherein each of the B {100} and B {111} banding factors is less
than 5.00%.
18. The BCC metal or BCC metal alloy sputter target as recited in
claim 17, wherein B {100} and B {111} are each less than 4.50%.
19. The BCC metal or BCC metal alloy sputter target as recited in
claim 18, wherein the average of B {100} and B {111} is less than
about 4.00%.
20. The BCC metal or BCC metal alloy sputter target as recited in
claim 18, wherein said target has a {100} mole fraction of about
30%, and a mole {111} fraction of about 27%.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of U.S.
Provisional Patent Application Ser. No. 62/145,550 filed Apr. 10,
2015.
FIELD OF INVENTION
[0002] The present invention relates to BCC metal and BCC metal
alloy sputter targets and to methods of making same wherein banding
at target mid-thickness is reduced compared to prior art methods.
This invention yields a Ta sputtering target that improves film
thickness uniformity, which in turn reduces variation in sheet
resistance.
BACKGROUND
[0003] Conventional Ta and other BCC metal targets display bands of
{111} and {100} crystallographic orientation proximate the
mid-thickness target area. These bands lead to substrate
non-uniformity upon sputtering, through the life of the target.
SUMMARY OF THE INVENTION
[0004] In one exemplary aspect of the invention, a BCC metal or BCC
metal alloy target is prepared. An ingot of the target is provided
with the ingot having a generally cylindrical configuration and
having x, y, and z dimensional directions. The ingot is compressed
in at least two of these dimensional directions and cross rolled in
at least one of the dimensional directions. The resulting ingot is
cut perpendicular to a first of the dimensional directions and
parallel to a second of the dimensional directions to form at least
a pair of target blanks. Each of the target blanks is then cross
rolled.
[0005] In one exemplary embodiment, the ingot is compressed in the
y and z directions and then the ingot is cut into a pair of target
blanks by cutting perpendicular to the z direction and parallel to
the y direction. In some embodiments, the compressing step may
comprise forging. In other embodiments, this forging may be
conducted in the x, y, and z dimensional directions thereby
defining tri-axial forging.
[0006] In other embodiments of the invention, the BCC metal is Ta
or Ta alloy. Sputter targets comprising Ta metal or Ta alloy are
thus provided, and these targets have a thickness dimension and a
purity of at least 99.5% and a combined C, O, N, H content of less
than about 25 ppm. The Ta metal or metal alloy may have a grain
size of from about 50 to 100 microns and a mixed texture with
substantially no gradient throughout the mid-fraction of the
thickness dimension.
[0007] In some embodiments, the sputter target may have a C, O, N,
H content of less than 25 ppm, and the grain size is from about 50
to 150 microns. In some embodiments, the sputter target has a
purity of 99.995% or greater. The targets may be characterized by
having a predominant mix of {100} and {111} textures, and the
target has reduced {100} and {111} banding factors wherein each of
the B {100} and B{111} banding factors is less than 5.00%.
[0008] In other embodiments, the banding factors B {100} and B
{111} are less than about 4.00%. In certain exemplary embodiments,
the target has a {100} mole fraction of about 30% and a {111} mole
fraction of about 27%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1a is a schematic process diagram showing one exemplary
manufacturing scheme in accordance with the invention;
[0010] FIG. 1b is a schematic process diagram showing another
exemplary manufacturing scheme in accordance with the
invention;
[0011] FIG. 2 is a graph showing through target texture of one
sputter target in accordance with the invention. In the graph, the
x direction represents target thickness with the y direction
showing the amount of a given crystallographic orientation present
at particular target thickness locations.
[0012] FIG. 3 is a graph similar to that shown in FIG. 2 except
that this figure illustrates through target texture of a target
prepared via a prior process; and
[0013] FIG. 4 is a graph showing percentage of non-uniformity of
films sputtered at various target power outputs for a comparative
sputter target C-1 and a target made in accordance with the
invention X-1.
DESCRIPTION OF THE INVENTION
[0014] In one embodiment of the invention, an ingot of Ta or Ta
alloy or other BCC metal is obtained. In one embodiment, as shown
in FIG. 1a, the ingot is e-beamed melted and subjected to vacuum
are melting. The centerline of the ingot is defined as the central
z-axis of the original ingot. The billet is turned by 90 degrees
about the x-axis during each the tri-axial forging step. This
tri-axial forging can be repeated several times, in each of them
the height is reduced, and then the billet is swaged back to its
original diameter with the height increasing along the x-axis.
After each swaging step, the billet axis is turned another 90
degrees about the y-axis. The ingot is then vacuum annealed and
followed by a cutting step to produce a double target blank, whose
weight is approximately 2.2 times the final target weight (i.e.,
the double blank itself weighs about 2.2.times. a final target
weight). The target double blanks may be upset forged and clock
rolled. During the upset forging and clock rolling, the center line
of the ingot is maintained in the center of the ingot and parallel
to the compressive forces used during fabrication. After the first
clock rolling step, the target double blank is cut in half
perpendicular to the ingot centerline and parallel to the target
blank surface. The resulting two pieces are subjected to an
additional clock rolling step, followed by a final vacuum anneal.
This processing results in near net shape blanks for usage as a
sputter targets.
[0015] As shown in FIG. 1a, the starting ingot 1 with a central
ingot axis along the z-axis is upset forged parallel to the central
axis to a specific height to form billet 2, which is then rotated
90 degrees about the x-axis. Billet 2 is swaged back to original
diameter of ingot 1, to give billet 3. Compressive forces used to
swage billet 3 are along the y-axis, parallel to the central ingot
axis. The process above is repeated two more times to yield billet
7, with the original dimensions and the same central ingot axis as
ingot 1. Billet 7 is then swaged, with compressive forces along the
y-axis, with increasingly smaller dies to a specified diameter to
yield billet 8. This forging in the x, y, and z directions of the
billet is referred to as "tri-axial" forging. The black arrows in
FIG. 1 indicate the central ingot axis; the red arrows indicate the
direction of the compressive forces used to create the current
ingot morphology. The resulting billet 8 is sectioned into double
target blanks, upset forged and cross or clock rolled as shown at
10 and 11, with compressive forces along the z axis. Then the
billet is cut perpendicular to the z axis and parallel to the y
axis as shown at 12, followed by cross rolling of each resulting
billet half as shown at 13. The resulting two pieces are subjected
to a final vacuum anneal.
[0016] FIG. 1b shows another embodiment in which the billet is
forged in two directions: y and z. Here, the billet is upset forged
along the z axis as shown by the red arrows around billet 2. Billet
2 is swaged back to the original diameter of ingot 1 to give billet
3. Compressive forces used to swage billet 3 are along the y-axis,
perpendicular to the central ingot axis. This process is repeated
three times to give billet 3. Billet 3 is then swaged, with
compressive forces along the y-axis, with increasingly smaller dies
to a specified diameter to yield billet 4. The resulting billet 4
is sectioned into double target blanks, upset forged and cross or
clock rolled as shown at 6 and 7, with compressive forces along the
z axis. Then, the billet is cut perpendicular to the z axis and
parallel to the y axis as shown at 8, followed by cross rolling of
each resulting billet half as shown at 9. The resulting two pieces
are subjected to a final vacuum anneal. In FIGS. 1a and 1b, dot
dash arrows 102f indicate direction of force, and the solid line
arrows 102c1 represent the ingot centerline. For purposes of
simplification, only some of the arrows have reference numerals
applied thereto.
[0017] It is apparent then that in accordance with both embodiments
1a, and 1b, a Ta or Ta alloy (or BCC metal or alloy) target is
prepared by providing a generally cylindrical billet having an x
direction, a y direction perpendicular to the x direction, and a z
direction perpendicular to the plane defined by vectors extending
in the x and y direction. The billet is then compressed along at
least two of these three directions. Recrystallization annealing
may be performed between each forging step and is preferably
conducted after each swaging step and after the final cross or
clock rolling steps.
[0018] Both of the FIGS. 1a and 1b embodiments result in at least a
pair of near net target shape blanks that may be used as suitable
sputter targets after appropriate final machining and/or polishing
steps. Ta and Ta alloy targets are provided wherein the Ta is at
least 99.5% pure and has an interstitial content (C, O, N, H) of
less than about 25 ppm. Ta targets in accordance with the invention
have a uniform grain size of about 50-100 microns and a mixed
homogenous {100}/{111}/{110} texture throughout the thickness of
the blank.
[0019] The texture of one target in accordance with the invention
is shown in FIG. 2. Here, the x direction of the graph represents
target thickness with the y direction representing the amount of
crystallographic orientation present at the particular target
thickness locations. The line 200 depicts {100} texture, line 202
depicts {111} texture and line 204 represents {110} texture. In
FIG. 2, the mole fraction of {100} is 0.300, {111} is 0.278, and
{110} is 0.046. (Each of these is multiplied by 100 to establish
mole % present). The banding factor B is B {100} 3.616% and B {111}
4.138%. Banding factors of less than about 5.00%, for each of the
{100} and {111} are beneficial with B factors of less than about
4.50% being even more preferred. The average B {100} and B {111}
banding for the target is 3.877%, with an average B {100} and B
{111} banding factor of less than about 4.50 being considered as
beneficial. Thus, this target exhibits a predominate mix of {100}
and {111} with substantially no banding. {110} is present in a
small amount.
[0020] The thin film formed by sputtering targets produced in
accordance with this invention, have a variation in film thickness
uniformity (percent non-uniformity) 3.000% or less, and more
preferably 2.000% or less. See FIG. 4. Furthermore, the thin film
formed by sputtering targets produced in accordance with this
invention, have a variation in sheet resistance, within wafers, and
between wafers, 4.00% or less, and more preferably 3.00% or
less.
[0021] One target produced in accordance with the invention had
exemplary sputtering performance, as exhibited in FIG. 4. This
target had a banding factor B {100} 3.798% and B {111} 4.126%, with
an average B {100} and B {111} of 3.962%. This target exhibited an
average percent (for the resulting sputtering film) non-uniformity
of 1.447% , achieving as low as 0.928% through the life of the
target. The percent variation in sheet resistance within wafers was
2.61% on average, achieving as low as 1.77%. It is clear that a
sputtering target with a banding factor less than 5.00% for both
{100} and {111} textures produces exemplary thin film
properties.
[0022] FIG. 3 represents the texture of a conventionally processed
Ta target in accord with the prior art. Line 300 represents {100}
texture; line 302 represents {111} texture; and line 304 represents
{110} texture. Here the {100} mole fraction is 0.163 and {111} is
present in an amount of 0.359. {110} is present in an amount of
0.107. Banding is significant: B {100}=6.039% and B {111}=8.80%
.
[0023] The Ta targets in accordance with the invention exhibit
predominate mixed {100} {111} texture, i.e., both {100} and {111}
textures, when combined, equal greater than 50% mole fraction
(based on 100% mole fraction), and the targets banding factors B
{100} and B {111} are each less than 5.00%. Methods for determining
mole fractions of textures present and banding factors are detailed
in published U.S. Patent Application 2011/0214987, incorporated by
reference herein.
[0024] Recrystallization annealing steps of about 900-1300.degree.
C. may be performed at various times throughout the process and,
for example, may be performed under vacuum conditions after the
final clock rolling steps (e.g., workstations 13 and 9 in FIGS. 1a
and 1b) and prior to or between the other compression steps of the
process. The various cross roll or clock rolling steps may in some
embodiments result in about 70% area reduction.
[0025] Preferably, the BCC metal is Ta, although Nb can also be
mentioned. Ta/Nb alloys may also be treated by the process.
[0026] With regard to quantification of texture components,
variation through thickness, a method was cooperatively developed
by leading tantalum sputter plate suppliers and users that allows
the features to be measured independent of one another. In rolled
tantalum plate, the texture is nominally symmetrical about its
mid-thickness center line and each half (upper and lower) can be
analyzed separately and compared. The through thickness sample is
measured in an SEM with Electron Back Scattered Diffraction
capability and a two dimensional map is collected as an EBSD data
file. The `as-measured` orientation is in the transverse plan and
each data point is rotated to show the texture in the plate normal
orientation (ND). Each data point has a texture orientation and
individual grains can be indexed. The pixel by pixel data is used
in the following analysis.
[0027] The original EBSD data can be converted from multi color
maps representing all possible textures to three primary colors.
The primary colors were chosen because they show up in equal
contrast in a display. Any points that did not index within a
15.degree. cut-off for the three textures being analyzed are
presented as the color gray and do not count in the volume fraction
of analyzed textures (Ftotal).
[0028] For calculation, the entire data set is broken into thin
slices perpendicular to the x direction (thickness direction). The
crystallographic texture is averaged (over the y direction) in each
slice. The width of each slice is the x-step distance. It is
specified as an integer multiple (n-step) of the minimum e-beam
stepping increment in the x direction used to create the pixel map.
Usually an n-step of 1 is used. It can be larger if the e-beam
stepping distance was set very small compared to the grain size.
The EBSD step size should be set to about 1/3 the average linear
intercept (ASTM E112 Grain Size method). The analysis area should
be at least 100 steps wide (RD rolling direction).
[0029] The strengths of the components (100//ND and 111//ND are
normally the two major components in tantalum plate) are measured
as the area percentage of each half thickness, using a 15.degree.
cut-off. For the analysis of a two dimensional EBSD map, only three
texture components are analyzed: {100}, {110}, and {111}. Four
arrays (each of length n-count) are needed to receive the data from
the EBSD input file, i.e., F100, F110, F111, and Ftotal. For each
point in the pixel map, the x-location (thickness direction)
determines the index location for updating calculation arrays:
Index = ` x - location ` x - step ` + 1 ##EQU00001##
[0030] The Euler angles .PHI. and .PHI..sub.2 determine the
location of the target surface normal (Nt) within orientation
space. These two angles, respectively, can range from 0 to
90.degree.. and from 0 to 360.degree.. For each pixel in the data
file, it is necessary to calculate the angle of Nt with each
orientation direction for the relevant texture components. For the
three components, there are 26 angles to calculate. By applying
crystal symmetry operations, the ranges for .PHI. and .PHI..sub.2
can be reduced. The smallest angle found determines the texture
component `candidate`. That angle is compared to the "cut-off"
angle--chosen as 15.degree.. If the angle is less than the
"cut-off" angle the candidate array is incremented (i.e.,
F100(index)=F100(index)+1). The total count array is increments
(Ftotal(index)=Ftotal(index)+1).
[0031] Once the calculation for all of the pixel data points has
been completed as outlined above, the volume fraction of the
texture component has been calculated as a function of depth
direction (x) with a depth resolution of x-step.
[0032] Each texture component is analyzed by moving the window
across the analysis area and collecting the F(hkl) in each window.
The value of F(hkl) is plotted by the location (center of the
window). The data can be smoothed by creating a band or window
larger than x-step and averaging the volume components within the
band or window. The volume fraction data is plotted as the average
value within the band at each x step location.
[0033] Once the area fractions F(hkl) are known from each window
location, the data can be fitted to a line using a least squares
method (linear regression). The slope of the line is the texture
gradient with units of area fraction/distance (%/mm). The gradient
must be calculated for only the half thickness. Both halves of the
sample can be measured to determine the symmetry of the plate.
[0034] For banding, the F(hkl) lines can be fit to a polynomial of
order 4 or less and the average deviation of the data to the
polynomial (absolute value of the difference) is used as the
banding severity number. The polynomial accounts for the
non-linearity of the gradient and avoids over estimating the
banding as a result. Noise is also an issue with the banding
calculation.
[0035] In an EBSB analysis, a very small number of grains are
analyzed compared to traditional X-ray diffraction texture analysis
of individual planes (thousands versus millions). The relatively
low number of grains available for the analysis results in a low
signal to noise ratio. To estimate the noise level, random textures
can be assigned to all the points in the analysis grid (all EBSD
points) and the same analysis completed. A banding number greater
than zero will be the result. By running the noise calculation
multiple times, an average random noise can be determined and
compared to the result from the actual data set. The EBSD
measurement method is powerful but time consuming. To accumulate
data from the same number of grains as traditional XRD would be
impractical. To aid in the analysis, a computer program can be
written to automatically do the calculations from the EBSD data
file and provide the results in graphical form. Such a program was
created and made available to the members working together to
develop the method.
[0036] Having described the invention by reference to various
exemplary embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims.
* * * * *