U.S. patent application number 11/030260 was filed with the patent office on 2005-07-21 for tantalum and other metals with (110) orientation.
Invention is credited to Wickersham, Charles E. JR..
Application Number | 20050155677 11/030260 |
Document ID | / |
Family ID | 34806906 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050155677 |
Kind Code |
A1 |
Wickersham, Charles E. JR. |
July 21, 2005 |
Tantalum and other metals with (110) orientation
Abstract
Tantalum metal, niobium metal, alloys thereof and other bcc
metals and alloys thereof having a texture of primary or mixed
(110) on the surface and/or throughout the thickness of the metal
is described. Also described are the processes for making the
tantalum metal and other bcc metal with a texture of primary or
mixed (110) and the process of making a sputtering target from the
tantalum metal or other bcc metal with a texture of primary or
mixed (110).
Inventors: |
Wickersham, Charles E. JR.;
(Columbus, OH) |
Correspondence
Address: |
Martha Ann Finnegan, Esq.
CABOT CORPORATION
Billerica Technical Center
157 Concord Road
Billerica
MA
01821-7001
US
|
Family ID: |
34806906 |
Appl. No.: |
11/030260 |
Filed: |
January 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60535164 |
Jan 8, 2004 |
|
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Current U.S.
Class: |
148/422 |
Current CPC
Class: |
C22F 1/18 20130101; C30B
29/02 20130101; C30B 11/00 20130101; C23C 14/3414 20130101; C22C
27/02 20130101 |
Class at
Publication: |
148/422 |
International
Class: |
C22C 027/02 |
Claims
1. A tantalum metal having a texture of primary (110) on the
surface, throughout the thickness, or a combination thereof.
2. The tantalum metal of claim 1, wherein said metal has a) a
texture in which a (100) pole figure, a (111) pole figure, or a
combination thereof has a center peak intensity less than about 15
random or b) a log ratio of (110):(100), (110):(111), or
(110):(100):(111) center peak intensities of greater than about
-4.0, or c) both.
3. (canceled)
4. The tantalum metal of claim 2, wherein said center peak
intensity is from about 0 random to about 10 random.
5. (canceled)
6. The tantalum metal of claim 2, wherein said log ratio is from
about -1.5 to about 7.0.
7. (canceled)
8. The tantalum metal of claim 1, wherein said metal is fully
recrystallized.
9-12. (canceled)
13. The tantalum metal of claim 1, having a purity of from 99.99%
to about 99.999%.
14. A metal alloy comprising the tantalum metal of claim 1.
15. (canceled)
16. A sputtering target comprising the tantalum metal of claim
1.
17. (canceled)
18. A capacitor comprising the tantalum metal of claim 1.
19. (canceled)
20. A resistive film layer comprising the tantalum metal of claim
1.
21. (canceled)
22. An article comprising at least as a component the tantalum
metal of claim 1.
23. (canceled)
24. The tantalum metal of claim 1, wherein the tantalum metal has a
substantially fine and uniform microstructure.
25. (canceled)
26. The tantalum metal of claim 1 comprising an average grain size
of from about 5 to about 125 microns.
27-28. (canceled)
29. The tantalum metal of claim 28, wherein said tantalum metal
includes an average grain size of from about 25 to about 50
microns.
30. The tantalum metal of claim 1, wherein said tantalum metal
comprises grains with an average grain size, wherein 95% of said
grains are less than three times said average grain size.
31-32. (canceled)
33. A process of making a sputtering target from a tantalum metal
of claim 1, comprising casting an ingot having a diameter the same
or greater than the diameter of a finished sputter target and
having a thickness the same as or greater than a finished target,
wherein said casted ingot has a (110) texture.
34-37. (canceled)
38. A process of making a sputtering target from tantalum metal of
claim 1, comprising forming a casted ingot having a diameter
smaller than the diameter of a finished target and then rolling
said casted ingot to form a casted ingot having the diameter of the
finished target, wherein the true strain applied in rolling the
cast ingot is less than 1.0 true strain.
39. (canceled)
40. The process of claim 38, wherein the amount of true strain is
0.5 or less.
41. The process of claim 38, wherein the true strain is from about
0.4 to about 0.5.
42. A method of making the sputter target of claim 16 having a
(110) texture, comprising cutting a plate having a (111) primary
texture wherein the plate is cut into multiple strips; rotating the
cut strips 90 degrees and then joining together the cut strips to
form a mosaic target.
43-48. (canceled)
49. A sputter target comprising a uniform texture of primary or
mixed (110) texture on the surface or throughout, wherein said
tantalum metal is substantially void of (100) and/or (111) textural
bands.
50. The sputter target of claim 49, further comprising a backing
plate.
51. The sputter target of claim 50, wherein an interlayer is
present between said backing plate and sputter target.
52. A process for making the tantalum metal of claim 1, comprising
heating a tantalum feedstock to a temperature above its melting
point to create molten drops; and solidifying said molten drops of
the tantalum in a crucible.
53-57. (canceled)
58. A bcc metal or alloy thereof having a texture of primary (110)
on the surface, throughout the thickness, or a combination
thereof.
59. The bcc metal of claim 58, wherein said metal has a) a texture
in which a (100) pole figure, a (111) pole figure, or a combination
thereof has a center peak intensity less than about 15 random or b)
a log ratio of (110):(100), (110):(111), or (110):(100):(111)
center peak intensities of greater than about -4.0, or c) both.
60-61. (canceled)
62. The bcc metal or alloy thereof of claim 58, wherein said bcc
metal is niobium.
63. The bcc metal or alloy thereof of claim 59, wherein said bcc
metal is niobium.
Description
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of prior U.S. Provisional Patent Application No.
60/535,164 filed Jan. 8, 2004, which is incorporated in its
entirety by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to metals, in particular
tantalum, and products made from tantalum as well as methods of
making and processing the tantalum.
[0003] In the industry, there has always been a desire to form
metals having a uniform texture. With respect to tantalum,
uniformed textured metals are especially desirable due to
tantalum's use as a sputtering target and its use in electrical
components such as capacitors. Tantalum sputtering targets are
gaining increasing commercial importance as the source for the
barrier metallization layer in copper dual-damascene integrated
circuit metallization.
[0004] In sputtering, the crystallographic orientation, also known
as texture, of the material being sputtered has a significant
effect on the process parameters and the deposited film
characteristics. According to Wehner, Phys. Rev. 102, 690 (1956),
incorporated in its entirety herein by reference, in sputtering,
the crystallographic orientation (also known as the texture) of the
material being sputtered has a significant effect on the process
parameters and the deposited film characteristics.
[0005] More recently, tantalum has become an increasingly important
material as a barrier layer in integrated circuit fabrication.
Consequently, there have been a number of publications and patents
pertaining to tantalum sputtering targets with (100) and (111)
crystallographic orientations. For example, Michaluk, (U.S. Pat.
No. 6,348,113 B1), incorporated in its entirety herein by
reference, describes, in part, tantalum-sputtering targets which
can have a (111) crystallographic texture or mixed textures.
[0006] Similarly, there has always been a desire to form higher
purity metals for a variety of reasons. With respect to tantalum,
higher purity metals are especially desirable due to tantalum's use
as a sputtering target and its use in electrical components such as
capacitors. Thus, impurities in the metal can have an undesirable
effect on the properties of the articles formed from the
tantalum.
[0007] When tantalum is processed, the tantalum is obtained from
ore. The ore is subsequently crushed and the tantalum is separated
from the crushed ore through the use of an acid solution. The acid
solution containing the tantalum is then separated from the acid
solution containing niobium and other impurities by density
separation. The acid solution containing the tantalum is then
crystallized into a salt and this tantalum containing salt is then
reacted with pure sodium in a vessel having an agitator typically
constructed of nickel alloy material, wherein tungsten or
molybdenum is part of the nickel alloy. The vessel will typically
be a double walled vessel with pure nickel in the interior surface.
The salt is then dissolved in water to obtain tantalum powder.
However, during such processing, the tantalum powder is
contaminated by contacting various surfaces such as the tungsten
and/or molybdenum containing surfaces. Many contaminants can be
volatized during subsequent melting, except highly soluble
refractory metals (e.g., Nb, Mo, and W). These impurities can be
quite difficult or impossible to remove, thus preventing a very
high purity tantalum product.
[0008] Accordingly, there is a desire to obtain a uniformed
textured tantalum. Also, there is a desire to have a tantalum
product having higher purity, and/or a fine grain size. Qualities
such as fine grain size can be an important property for sputtering
targets made from tantalum since fine grain size can lead to
improved uniformity of thickness of the sputtered deposited film.
Further, other products containing the tantalum having fine grain
size can lead to improved homogeneity of deformation and
enhancement of deep drawability and stretchability which are
beneficial in making capacitors, capacitor cans, laboratory
crucibles, and increasing the lethality of explosively formed
penetrators (EFP's). Uniform texture in tantalum containing
products can increase sputtering efficiency (e.g., greater sputter
rate) and can decrease normal anisotropy (e.g., increased deep
drawability), in preform products.
SUMMARY OF THE PRESENT INVENTION
[0009] A feature of the present invention is to provide a tantalum
metal or other bcc metal having a texture of primary (110) on the
surface, or throughout the thickness, or a combination thereof. The
tantalum metal or other bcc metals are preferably ingot-derived
metals.
[0010] Another feature of the present invention is to provide a
tantalum metal or other bcc metal exhibiting a fine grain structure
with the above texture, which is preferably uniform.
[0011] A further feature of the present invention is to provide an
increased sputtering yield of a metal target.
[0012] An additional feature of the present invention is to provide
a tantalum metal having a close-packed crystallographic plane.
[0013] Another feature of the present invention is to provide
articles, products, and/or components containing the tantalum or
other bcc metal having a texture of primary (110).
[0014] An additional feature of the present invention is to provide
processes to make the tantalum product as well as the articles,
products, and/or components containing the tantalum or other bcc
metal having a texture of primary (110).
[0015] A further feature of the present invention is to provide a
tantalum metal, or other bcc metals having a mixed texture of (110)
on the surface, and/or throughout the thickness of the metal,
wherein the metal is preferably void of textural bands, such as
(100) or (111) textural bands.
[0016] Another feature of the present invention is to provide a
tantalum metal having a mixed texture of (110), on the surface,
and/or throughout the thickness of the metal, wherein the mixed
texture is uniformly distributed throughout the metal.
[0017] Additional features and advantages of the present invention
will be set forth in part in the description which follows, and in
part will be apparent from the description, or may be learned by
practice of the present invention. The objectives and other
advantages of the present invention will be realized and attained
by means of the elements and combinations particularly pointed out
in the description and appended claims.
[0018] To achieve these and other advantages, and in accordance
with the purpose of the present invention, as embodied and broadly
described herein, the present invention relates to tantalum metal
or other bcc metals having a texture of primary (110). The metal
preferably has a fine grain structure and/or uniform texture.
[0019] The present invention further relates to an alloy or mixture
comprising tantalum, wherein the tantalum present in the alloy or
mixture includes a uniform texture. The alloy or mixture (e.g., at
least the tantalum present in the alloy or mixture) also preferably
has a fine grain structure and/or a purity of at least 99.0% and
more preferably at least 99.99%.
[0020] The present invention also relates to tantalum metal, e.g.,
suitable for use as a sputtering target, having a fully
recrystallized grain size with an average grain size of about 150
.mu.m or less and/or having a primary (10)-type texture
substantially throughout the thickness of the tantalum and
preferably throughout the entire thickness of the tantalum metal
and/or having an absence of strong (100) and/or (111) textural
bands throughout the thickness of the tantalum.
[0021] The present invention further relates to forming various
components from the above-mentioned tantalum or other bcc metals by
casting an ingot with a sufficient diameter so as to avoid any
heavy working of the metal so as to maintain the (110) texture in
the ingot. The ingot or subsequent shape can be annealed any number
of times. Final products such as sputtering targets can be then
machined from the unannealed or annealed metal, such as in the
shape of a plate or sheet.
[0022] The present invention also relates to a sputtering target
comprising the above-described tantalum or other bcc metals and/or
alloy. The sputtering target can be formed a variety of ways.
[0023] The present invention further relates to resistive films and
capacitors comprising the above-described tantalum and/or alloys
thereof.
[0024] The present invention also relates to articles, components,
or products which comprise at least in part the above-described
tantalum and/or alloys thereof.
[0025] Also, the present invention relates to a process of making
the above-described tantalum which involves heating the tantalum
feedstock to a temperature above its melting point and solidifying
the molten drops of the tantalum in a crucible.
[0026] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are intended to provide further
explanation of the present invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 illustrates inverse pole figures for a tantalum metal
having a texture of primary (110).
[0028] FIG. 2 illustrates (111), (110), and (100) pole figures for
tantalum sputtering target surface.
[0029] FIG. 3 illustrates a grain map of tantalum plate
predominantly having (110) crystallographic orientation in the
sputtering plane.
[0030] FIG. 4 illustrates grain size distribution for a tantalum
metal having a texture of primary (110) sputtering target.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0031] The present invention relates to a metal having a (110)
texture. The metal, such as tantalum metal, is preferably
ingot-derived metal as opposed to powder metallurgy product. This
texture is preferably a primary (110), and more preferably this
texture is uniform on the surface and/or throughout the thickness
of the metal. More specifically, the present invention relates to
bcc metals, like tantalum metal. In the present invention,
tantalum, which has a body-centered-cubic (bcc) atomic structure,
preferably has a texture of primary (110). Given that the
close-packed plane in tantalum is the (110) crystallographic
orientation, a sputtering target fabricated with a predominately
(110) crystallographic orientation parallel to the sputtering
surface has an improved sputtering performance over the more
typical (100) and (111) orientations. The advantages of using a
tantalum metal having a texture of primary (110) include, but are
not limited to, higher sputtering rate/yield than other principal
orientations, such as the (100) and (111) orientations, and an
improved sputter ejection pattern for improved film uniformity. For
purposes of discussion only, the preferred metal, tantalum and
alloys thereof, shall be discussed below. However, the same
discussion including the various parameters apply equally to other
bcc metals, including niobium, and alloys thereof.
[0032] Preferably, the texture of primary (110) is on the surface
and/or throughout the thickness of the metal. Preferably, the
tantalum metal of the present invention includes an absence of
textural bands. In another embodiment, the present invention
relates to a tantalum metal which includes mixed (110) texture
throughout its thickness, and preferably is substantially void of
(100) and/or
[0033] (111) textural bands.
[0034] The tantalum metal or other bcc metal, can have any purity
such as 95% or greater. Preferably, the purity of the metal is 99%
or greater, 99.95% or greater, 99.99% or greater, and 99.995% or
greater. This purity can exclude gases. Preferably, the tantalum
metal has a purity of at least 99.999% and can range in purity from
about 99.995% to about 99.999% or more. Other ranges include about
99.998% to about 99.999% and from about 99.999% to about 99.9992%
and from about 99.999% to about 99.9995%. The present invention
further relates to a metal alloy which comprises the tantalum
metal, such as a tantalum based alloy or other alloy which contains
the tantalum as one of the components of the alloy.
[0035] The impurities (e.g., metallic impurities) that may be
present in the tantalum metal can be less than or equal to 0.005%
and typically comprise other bcc refractory metals of infinite
solubility in tantalum, such as niobium, molybdenum, and tungsten.
For instance, metallic impurities, like Mo, W, and Nb (in the case
of Ta) can be below (individually or combined) 100 ppm, below 50
ppm, below 20 ppm, below 10 ppm, or even below 5 ppm total. The
oxygen content can be below 100 ppm, below 50 ppm, below 20 ppm, or
below 10 ppm. All other elemental impurities, (including
radioactive elements) whether metal or non-metal can be below a
combined amount of 200 ppm, below 50 ppm, below 25 ppm, or below 10
ppm or even lower and optionally having 50 ppm or less 02, 25 ppm
or less N.sub.2, or 25 ppm or less carbon, or combinations
thereof.
[0036] The tantalum metal and alloys thereof containing the
tantalum metal preferably have a texture which is advantageous for
particular end uses, such as sputtering. In other words, when the
tantalum metal or alloy thereof is formed into a sputtering target
having a surface and then sputtered, the texture of the tantalum
metal in the present invention leads to a sputtering target which
is easily sputtered and, very few if any areas in the sputtering
target resist sputtering. Further, with the texture of the tantalum
metal of the present invention, the sputtering of the sputtering
target leads to a very uniform sputtering erosion thus leading to a
sputtered film which is therefore uniform as well. A texture
capable of resulting in a sputtering target which is easily
sputtered can be a mixture of textures that are uniformly
distributed in the tantalum metal (e.g., (100), (111)), as long as
a (110) texture is present in the mixed texture.
[0037] The grain size of the tantalum metal can also affect the
uniformity of the sputtering erosion and the ease of sputtering.
The tantalum metal of the present invention can have any grain
size. Preferably, the tantalum metal of the present invention
includes an average grain size of about 1,000 microns or less, 750
microns or less, 500 microns or less, 250 microns or less, 150
microns or less, 100 microns or less, 75 microns or less, 50
microns or less, 35 microns or less, 25 microns or less, 20 microns
or less, 15 microns or less, or 10 microns or less. Other grain
sizes that are suitable in the tantalum metal of the present
invention are grain sizes having an average grain size of from
about 5 to about 125 microns. Preferably, the tantalum metal of the
present invention includes an average grain size of from about 10
to about 100 microns. The tantalum metal of the present invention
can include an average grain size of from about 5 to about 75
microns or from 25 to 75 microns, or from about 25 to about 50
microns. Also, in one embodiment, 95% of the grain sizes are 100
microns or less. This can be determined by measuring 500 grain
sizes on a sample. Preferably, 95% of the grain sizes are 75
microns or less. Also, 95% of the grains can be less than 3 times
the average grain size.
[0038] Preferably, the tantalum metal is at least partially
recrystallized, and more preferably at least about 80% of the
tantalum metal is recrystallized and even more preferably at least
about 98% of the tantalum metal is recrystallized. Most preferably,
the tantalum metal is fully recrystallized.
[0039] Also, it is preferred that the tantalum metal have a fine
texture. More preferably the texture is such that the (100) and/or
(111) peak intensity within any 5% incremental thickness of the
tantalum is less than about 15 random, and/or has a natural log
(Ln) ratio of (110):(100) and/or (110):(111) center peak
intensities within the same increment greater than about -4.0
(i.e., meaning, -4.0, -3.0, -2.0, -1.5, -1.0 and so on) or has both
the (100) centroid intensity and the ratio above or has both the
(111) centroid intensity and the ratio above. The center peak
intensity is preferably from about 0 random to about 10 random, and
more preferably is from about 0 random to about 5 random. Other
(100) centroid intensity ranges and/or other (111) centroid
intensity ranges include, but are not limited to, from about 1
random to about 10 random and from about 1 random to about 5
random. Further, the log ratio of (110):(100) center peak
intensities and/or the log ratio of (110):(111) center peak
intensities is from about -4.0 to about 15 and more preferably from
about -1.5 to about 7.0. Other suitable ranges of log ratios,
include, but are not limited to, about -4.0 to about 10, and from
about -3.0 to about 5.0. Most preferably, the tantalum metal of the
present invention includes a grain size and preferred texture with
regard to the (100) and/or the (111) incremental intensity and the
(110):(100) and/or (110):(111) ratio of incremental centroid
intensities. The method and equipment that can be used to
characterize the texture are described in Adams et al., Materials
Science Forum, Vol. 157-162 (1994), pp. 31-42; Adams et al.,
Metallurgical Transactions A, Vol 24A, April 1993-No. 4, pp.
819-831; Wright et al., International Academic Publishers, 137
Chaonei Dajie, Beijing, 1996 ("Textures of Material: Proceedings of
the Eleventh International Conference on Textures of Materials);
Wright, Journal of Computer-Assisted Microscopy, Vol. 5, No. 3
(1993), all incorporated in their entirety by reference herein. In
one embodiment, the tantalum metal has a) an average grain size of
about 50 microns or less, b) a texture in which a (100) pole
figure, a (111) pole figure, or a combination thereof has a center
peak intensity less than about 15 random or c) a log ratio of
(110):(100), (110):(111), or (110):(100):(111) center peak
intensities of greater than about -4.0, or a combination
thereof.
[0040] The tantalum metal of the present invention can be used in a
number of areas. For instance, the tantalum metal can be made into
a sputtering target or into chemical energy (CE) munition warhead
liner which comprises the high purity metal. The metal can also be
used and formed into a capacitor anode or into a resistive film
layer. The tantalum metal of the present invention can be used in
any article or component which conventional tantalum is used and
the methods and means of making the various articles or components
containing the conventional tantalum can be used equally here in
incorporating the tantalum metal into the various articles or
components. For instance, the various components and processing
used in making sputtering targets, such as the backing plate, one
or more interlayers between the target and backing plate, and other
components and design options, described in U.S. Pat. Nos.
5,753,090, 5,687,600, 5,522,535, 6,348,113 B1; 6,619,537;
6,605,199; 6,579,431; 6,451,135; 6,444,104; 6,444,100; 6,283,357;
6,183,686; and 6,183,613, can be used here and these patents are
incorporated in their entirety by reference herein.
[0041] The tantalum of the present invention can be made a number
of ways. The tantalum, such as sputtering targets, having a (110)
crystallographic orientation can be manufactured by cutting the
ingot, such as in the shape of sputtering targets, from ingots such
as formed by electron beam melting. In the process of manufacturing
tantalum with the (110) crystallographic orientation, tantalum
feedstock can be heated to a temperature above its melting point,
preferably to a temperature of about 3000.degree. C. by bombardment
with energetic electrons in an electron beam device. Molten drops
of the tantalum can then be cooled, for example, by contacting the
molten drops with a water-cooled crucible to solidify the tantalum
into an ingot. The crucible is preferably designed so that as
tantalum accumulates in the crucible, the distance between the top
surface of the ingot and the tantalum material source preferably
remains constant. In one example, to maintain a constant distance
between the top surface of the ingot and the tantalum material
source, the crucible can be lowered as the tantalum accumulates in
the crucible. Other methods known to one skilled in the art can
also be used to maintain a constant distance between the top
surface of the ingot and a tantalum material source. Maintaining a
constant distance between the top surface of the ingot and the
tantalum material source allows the ingot length to increase. The
produced ingot typically includes a (110) crystallographic
orientation in the planes perpendicular to the ingot axis.
[0042] In one embodiment, an ingot can be cast by any melting
technique such as electron beam melting to form an ingot having the
desired diameter of a sputter target such as 12.+-.2 to 13.+-.2
inches. Furthermore, the casting of this ingot can have any
thickness (such as the thickness of several sputter targets). For
instance, the thickness of the ingot can be the thickness of one
target or can be any thickness above the thickness of one target
such as several inches or many inches. By this technique, if an
ingot is cast having essentially the diameter of a finished target,
then the ingot can be sliced or cut to form multiple targets having
the desired diameter and thickness of a finished target.
Furthermore, by doing so, the (110) texture is maintained. In
another embodiment, the ingot can be cast using more conventional
EB ingot diameters. For instance, an ingot can be cast having an 11
inch diameter with a thickness, for instance, of 0.563 inch. Then,
this cast ingot can be lightly rolled to form a 13.75 inch diameter
disc with a 0.36 inch thickness. Essentially, this would be the
dimensions of the finished target. This light rolling to form the
finished target would, for instance, use a true strain of about
0.447 which is well below the normal true strain applied to metals
which are on the order of 2.0 to 3.0 true strain. Thus in one
embodiment, the true strain applied in rolling an ingot is
preferably less than 1.0 true strain and more preferably less than
0.5 true strain in order to maintain a strong (110) texture. Thus,
in these embodiments, the casting of the ingot using the desired
mold provides an ingot which can easily be formed into a target
with minimal working of the metal in order to preserve the (110)
texture. Preferably, when the ingot is formed, the ingot is
subjected to very rapid cooling which aids in a more preferred
finer grain size such as on the order of below 500 microns as
described above with respect to the preferred grain sizes.
[0043] In another embodiment, a rolled plate, for instance, having
a (111) texture as, for instance, obtained in Michaluk et al. (U.S.
Pat. No. 6,348,113 B1) can be cut into slices in order to expose
the side edges of the slices. Then, the slices can be rotated 90
degrees in order to expose the cut edges, which provides a (110)
texture. Then, these slices or strips can be connected together by
any manner to form a mosaic sputtering target. For instance, the
cut strips can be 1/2 inch thick. The connecting together of the
various slices can be done by any technique such as mechanical,
welding, adhesives, combinations thereof, and the like. For
instance, the slices can be cut to have a tongue and groove design
or other similar mechanical connecting design to connect each of
the slices together to form a mosaic target.
[0044] The ingot can be subjected to working (e.g., rolling,
forging, and the like), being careful to maintain the preferred
texture. The targets from the ingot can be machined-sputtered so
that the surface of the sputtering target is parallel to the (110)
crystallographic plane. FIG. 1 provides inverse pole figures viewed
from the surface of a sputtering target with a texture of primary
(110) parallel to the sputtering surface.
[0045] FIG. 2 provides (111), (110), and (100) pole figures for the
sputtering target surface. According to FIG. 2, the (110) pole
figure illustrates a strong central peak characteristic of a
predominately (110) texture.
[0046] FIG. 3 provides an image of a circular plate showing grains
in the metal plate. Although the grain size, as illustrated in FIG.
3 is large, reduction of the average grain size can be accomplished
by adjusting the cooling rate during casting and by metal working
the plate with or without annealing (one or more times) to retain
the (110) crystallographic texture.
[0047] FIG. 4 illustrates the grain size distribution for the
tantalum plate with a predominately (110) crystallographic
orientation. According to FIG. 4, 95% of the grains are less than 3
times the average grain size.
[0048] The purity of the sputtering target can be another important
attribute. Given that most impurities in tantalum are vaporized at
the melting point of tantalum, the electron beam melting of
tantalum can purify the tantalum. In one example, a Glow Discharge
Mass Spectroscopic (GDMS) analysis was preformed on the sputtering
target of the present invention to measure the chemical purity of
the sputtering target. The results of the analysis are provided in
Table 1. According to Table 1, the overall purity of the material
is 99.995%. According to Table 1, the major impurities in the
material after the electron beam melting were Fe, Cu, Nb, Mo, and
W.
1TABLE 1 GDMS analysis of (110) oriented Tantalum sputtering
target. Concen- tration Concentration Concentration Element (ppmw)
Element (ppmw) Element (ppmw) Na 0.048 Ca 0.025 Zr 0.003 Mg 0.004
Ti 0.002 Nb 23 Al 0.031 Cr 0.015 Mo 0.35 Si 0.065 Fe 0.69 W 0.16 P
0.007 Co 0.002 Th 0.0003 S 0.007 Ni 0.038 U 0.0006 Cl 0.004 Cu 0.17
K 0.034 As 0.04
[0049] Table 1 indicates that the concentration of all other
metallic impurities were below the GDMS detection limits, meaning
below 10 ppm or even below 5 ppm or below 1 ppm or 0.1 ppm or less,
or 0.01 ppm or less.
[0050] To measure non-metallic impurities, such as oxygen,
nitrogen, hydrogen and carbon, metal fusion and subsequent thermal
conductive or infrared measurement of the quantity of gas evolved
was used. The results of the determined non-metallic impurities are
provided in Table 2. According to Table 2, the oxygen, carbon,
hydrogen and nitrogen levels in the tantalum sputtering target
material of the present invention are also low.
2TABLE 2 Gaseous element analysis of (110) oriented sputtering
target materials. All values are in ppmw. Carbon Oxygen Hydrogen
Nitrogen Sulfur Avg 37 49 5 24 10 Max 59 60 5 44 10 Min 13 26 5 13
10 StDev 23 20 0 17 0
[0051] A refining process, a vacuum melting process, and a thermal
mechanical process can also be used to make the tantalum metal of
the present invention. In this process or operation, the refining
process involves the steps of extracting tantalum metal preferably
in the form a powder from ore containing tantalum and preferably
the ore-containing tantalum selected has low amounts of impurities,
especially, low amounts of niobium, molybdenum, and tungsten. More
preferably, the amount of niobium, molybdenum, and tungsten is
below about 10 ppm, and most preferably is below about 8 ppm. Such
a selection leads to a purer tantalum metal. After the refining
process, the vacuum melting process is used to purge low melting
point impurities, such as alkyde and transition metals from the
tantalum while consolidating the tantalum material into a fully
dense, malleable ingot. Then, after this process, a thermal
mechanical process can be used which can involve a combination of
cold working and annealing of a tantalum.
[0052] The tantalum metal preferably may be made by reacting a
salt-containing tantalum with at least one agent (e.g., compound or
element) capable of reducing this salt to the tantalum metal and
further results in the formation of a second salt in a reaction
container. The reaction container can be any container typically
used for the reaction of metals and should withstand high
temperatures on the order of about 800.degree. C. to about
1,200.degree. C. For purposes of the present invention, the
reaction container or the liner in the reaction container, which
comes in contact with the salt-containing tantalum and the agent
capable of reducing the salt to tantalum, is made from a material
having the same or higher vapor pressure as tantalum at the melting
point of the tantalum. The agitator in the reaction container can
be made of the same material or can be lined as well. The liner can
exist only in the portions of the reaction container and agitator
that come in contact with the salt and tantalum. Examples of such
metal materials which can form the liner or reaction container
include, but are not limited to, metal-based materials made from
nickel, chromium, iron, manganese, titanium, zirconium, hafnium,
vanadium, ruthenium, cobalt, rhodium, palladium, platinum, or any
combination thereof or alloy thereof as long as the alloy material
has the same or higher vapor pressure as the melting point of
tantalum metal. Preferably, the metal is a nickel or a nickel-based
alloy, a chromium or a chromium-based alloy, or an iron or an
iron-based alloy. The liner, on the reaction container and/or
agitator, if present, typically has a thickness of from about 0.5
cm to about 3 cm. Other thicknesses can be used. It is within the
bounds of the present invention to have multiple layers of liners
made of the same or different metal materials described above.
[0053] The salt-containing tantalum can be any salt capable of
having tantalum contained therein such as a potassium-fluoride
tantalum. With respect to the agent capable of reducing the salt to
tantalum and a second salt in the reaction container, the agent
which is capable of doing this reduction is any agent which has the
ability to result in reducing the salt-containing tantalum to just
tantalum metal and other ingredients (e.g. salt(s)) which can be
separated from the tantalum metal, for example, by dissolving the
salts with water or other aqueous sources. Preferably, this agent
is sodium. Other examples include, but are not limited to, lithium,
magnesium, calcium, potassium, carbon, carbon monoxide, ionic
hydrogen, and the like. Typically, the second salt which also is
formed during the reduction of the salt-containing tantalum is
sodium fluoride. Details of the reduction process which can be
applied to the present invention in view of the present application
are set forth in Kirk-Othmer, Encyclopedia of Chemical Technology,
3.sup.rd Edition, Vol. 22, pp. 541-564, U.S. Pat. Nos. 2,950,185;
3,829,310; 4,149,876; and 3,767,456. Further details of the
processing of tantalum can be found in U.S. Pat. Nos. 5,234,491;
5,242,481; and 4,684,399. All of these patents and publications are
incorporated in their entirety by reference herein.
[0054] The above-described process can be included in a multi-step
process which can begin with low purity tantalum, such as
ore-containing tantalum. One of the impurities that can be
substantially present with the tantalum is niobium. Other
impurities at this stage are tungsten, silicon, calcium, iron,
manganese, etc. In more detail, low purity tantalum can be purified
by mixing the low purity tantalum which has tantalum and impurities
with an acid solution. The low purity tantalum, if present as an
ore, should first be crushed before being combined with an acid
solution. The acid solution should be capable of dissolving
substantially all of the tantalum and impurities, especially when
the mixing is occurring at high temperatures.
[0055] Once the acid solution has had sufficient time to dissolve
substantially, if not all, of the solids containing the tantalum
and impurities, a liquid solid separation can occur which will
generally remove any of the undissolved impurities. The solution is
further purified by liquid-liquid extraction. Methyl isobutyl
ketone (MIBK) can be used to contact the tantalum rich solution,
and deionized water can be added to create a tantalum fraction. At
this point, the amount of niobium present in the liquid containing
tantalum is generally below about 25 ppm, and more preferably below
10 ppm or even below 5 ppm.
[0056] Then, with the liquid containing at least tantalum, the
liquid is permitted to crystallize into a salt with the use of
vats. Typically, this salt will be a potassium tantalum fluoride
salt. More preferably, this salt is K.sub.2TaF.sub.7. This salt is
then reacted with an agent capable of reducing the salt into 1)
tantalum and 2) a second salt as described above. This compound
will typically be pure sodium and the reaction will occur in a
reaction container described above. As stated above, the second
salt byproducts can be separated from the tantalum by dissolving
the salt in an aqueous source and washing away the dissolved salt.
At this stage, the purity of the tantalum can be typically 99.50 to
99.99% Ta.
[0057] Once the tantalum powder is extracted from this reaction,
any impurities remaining, including any contamination from the
reaction container, can be removed through melting of the tantalum
powder.
[0058] The tantalum powder can be melted a number of ways such as a
vacuum arc remelt or an electron beam melting. Generally, the
vacuum during the melt will be sufficient to remove substantially
any existing impurities from the recovered tantalum so as to obtain
an acceptably pure tantalum. Preferably, the melting occurs in a
high vacuum such as 10.sup.-4 Torr or more. Preferably, the
pressure above the melted tantalum is lower than the vapor
pressures of the metal impurities in order for these impurities,
such as nickel and iron to be vaporized. The diameter of the cast
ingot should be as large as possible, preferably greater than 91/2
inches. Once the mass of melted tantalum consolidates, the ingot
formed can have a purity of 99.995% or higher and preferably
99.999% or higher. The electron beam processing preferably occurs
at a melt rate of from about 300 to about 800 lbs. per hour using
20,000 to 28,000 volts and 15 to 40 amps, and under a vacuum of
from about 1.times.10.sup.-3 to about 1.times.10.sup.-6 Torr. More
preferably, the melt rate is from about 400 to about 600 lbs. per
hour using from 24,000 to 26,000 volts and 17 to 36 amps, and under
a vacuum of from about 1.times.10.sup.-4 to 1.times.10.sup.-5 Torr.
With respect to the VAR processing, the melt rate is preferably of
500 to 2,000 lbs. per hour using 25-45 volts and 12,000 to 22,000
amps under a vacuum of 2.times.10.sup.-2 to 1.times.10.sup.-4 Torr,
and more preferably 800 to 1200 lbs. per hour at from 30 to 60
volts and 16,000 to 18,000 amps, and under a vacuum of from
2.times.10.sup.-2 to 1.times.10.sup.-4 Torr.
[0059] The tantalum product preferably exhibits a uniform texture
of mixed or primary (110) on the surface, throughout its thickness,
or a combination thereof as measured by electron backscatter
diffraction (EBSD), such as TSL's Orientation Imaging Microscopy
(OIM) or other acceptable means. The resulting tantalum can include
an excellent fine grain size and/or a uniform distribution. The
tantalum preferably has an average recrystallized grain size of
about 150 microns or less, more preferably about 100 microns or
less, and even more preferably about 50 microns or less. Ranges of
suitable average grain sizes include from about 5 to about 150
microns; from about 30 to about 125 microns, and from about 30 to
about 100 microns.
[0060] The resulting tantalum metal of the present invention,
preferably has 10 ppm or less metallic impurities and preferably 50
ppm or less O.sub.2, 25 ppm or less N.sub.2, and 25 ppm or less
carbon. If a purity level of about 99.995 is desired, than the
resulting high purity metal preferably has metallic impurities of
about 50 ppm or less, and preferably 50 ppm or less O.sub.2, 25 ppm
or less N.sub.2, and 25 ppm or less carbon.
[0061] With respect to taking this ingot and forming a sputtering
target, the following process can be used. In one embodiment, the
sputtering target made from the tantalum metal can be made by
mechanically or chemically cleaning the surfaces of the tantalum
metal, wherein the tantalum metal has a sufficient starting
cross-sectional area to permit the subsequent processing steps
described below. Preferably, the tantalum metal has a
cross-sectional area of at least 91/2 inches or more. The plate can
then be mechanically or chemically cleaned and formed into the
sputtering target having any desired dimension. Also, the tantalum
can be annealed at a temperature (e.g., from about 950.degree. C.
to about 1500.degree. C.) and for a time (e.g., from about 1/2 hour
to about 8 hours) to achieve at least partial recrystallization of
the tantalum metal.
[0062] With respect to annealing of the tantalum, preferably this
annealing is in a vacuum annealing at a temperature and for a time
sufficient to achieve complete recrystallization of the tantalum
metal. As indicated above, the tantalum ingot and any form of the
ingot formed afterwards can be annealed one or more times before
and/or after any step mentioned herein. The annealing can be at any
conventional annealing temperature, such as a temperature that
causes at least partial recrystallization and/or alteration in
grain size.
[0063] Another way to process the tantalum metal into sputtering
targets involves mechanically or chemically cleaning one or more
surfaces of the tantalum metal (e.g., the tantalum ingot), wherein
the tantalum metal has a sufficient starting cross-sectional area
to permit any subsequent processing.
[0064] Preferably, the sputtering targets made from the tantalum of
the present invention have the following dimensions: a thickness of
from about 0.080 to about 1.50", and a surface area from about 7.0
to about 1225 square inches. Other dimensions can be made.
[0065] The tantalum preferably has a primary or mixed (110)
texture, and a minimum (100) and/or (111) texture throughout the
thickness of the sputtering target, and is preferably sufficiently
void of (100) and/or (111) textural bands.
[0066] The present invention will be further clarified by the
following examples, which are intended to be purely exemplary of
the present invention.
[0067] The Figures represent analysis done on tantalum metal that
was formed as an ingot by EB melting. The ingot was casted
essentially in the shape of a sputter target.
[0068] Metallurgical Analysis
[0069] Grain size and texture were measured along the longitudinal
or radial directions of samples taken from the cut ingot or casted
ingot. Grain size was measured using ASTM procedure E-112.
[0070] Texture Measurement Technique: A limited number of samples
(chosen based on metallurgical results) were used for texture
analysis. Mounted and polished samples, previously prepared for
metallurgical analysis, were employed as texture samples after
being given a heavy acid etch prior to texture measurement. EBSD
such as Orientation Imaging Microscopy (OIM) was chosen as the
method of texture analysis because of its unique ability to
determine the orientation of individual grains within a
polycrystalline sample. Established techniques such as X-ray or
neutron diffraction would have been unable to resolve any localized
texture variations within the thickness of the tantalum
materials.
[0071] For the analysis, each texture sample was incrementally
scanned by an electron beam (within an SEM) across its entire
thickness; the backscatter Kikuchi patters generated for each
measurement point was then indexed using a computer to determine
the crystal orientation. From each sample, a raw-data file
containing the orientations for each data point within the
measurement grid array was created. These files served as the input
data for subsequently producing grain orientation maps and
calculating pole figures and orientation distribution functions
(ODFs).
[0072] By convention, texture orientations are described in
reference to the sample-normal coordinate system. That is, pole
figures are "standardized" such that the origin is normal to the
plate surface, and the reference direction is the rolling (or
radial) direction; likewise, ODFs are always defined with respect
to the sample-normal coordinate system. Terminology such as "a
(110) texture" means that the (110) atomic planes are
preferentially oriented to be parallel (and the (110) pole oriented
to be normal) with the surface of the plate. In the analyses, the
crystal orientations were measured with respect to the sample
longitudinal direction. Therefore, it was necessary to transpose
the orientation data from the longitudinal to sample-normal
coordinate system as part of the subsequent texture analysis. These
tasks were conducted through use of computer algorithms.
[0073] Grain Orientation Maps: Derived from principles of
presenting texture information in the form of inverse pole figures,
orientation maps are images of the microstructure within the sample
where each individual grain is "color-coded" based on its
crystallographic orientation relative to the normal direction of
the plate of disc from which it was taken. To produce these images,
the crystal axes for each grain (determined along the longitudinal
direction of the texture sample by EBSD such as OIM) were tilted
90.degree. about the transverse direction so to align the crystal
axes to the normal direction of the sample. Orientation maps serve
to reveal the presence of texture bands or gradients through the
thickness on the product; in tantalum, orientation maps have shown
that large, elongated grains identified by optical microscopy can
be composed of several small grains with low-angle grain
boundaries.
[0074] Analysis of the Texture Results: EBSD scans (e.g., OIM
scans) were taken along the thickness of each sample provided. The
orientation maps were visually examined to qualitatively
characterize the texture uniformity through the sample thickness.
To attain a quantifiable description of the texture gradients and
texture bands in the example materials, the measured EBSD data was
partitioned into 20 subsets, with each representing a 5% increment
of depth through the thickness of the sample. For each incremental
data set, a pole figure was first calculated, then (100), (111),
and (110) centroid intensities determined numerically using
techniques reported elsewhere. The equipment and procedures
described in S. Matthies et al., Materials Science Forum, Vol.
157-162 (1994), pp. 1647-1652 and S. Matthies et al., Materials
Science Forum, Vol. 157-162 (1994), pp. 1641-1646 were applied, and
these publications are incorporated in their entirety herein by
reference. The texture gradients can then be described graphically
by plotting the (100), (111), and (110) intensities, as well as the
log ratio of the (100):(110), (100):(111), and (100):(111);(110) as
a function depth of the sample.
[0075] Applicants specifically incorporate the entire contents of
all cited references in this disclosure. Further, when an amount,
concentration, or other value or parameter is given as either a
range, preferred range, or a list of upper preferable values and
lower preferable values, this is to be understood as specifically
disclosing all ranges formed from any pair of any upper range limit
or preferred value and any lower range limit or preferred value,
regardless of whether ranges are separately disclosed. Where a
range of numerical values is recited herein, unless otherwise
stated, the range is intended to include the endpoints thereof, and
all integers and fractions within the range. It is not intended
that the scope of the invention be limited to the specific values
recited when defining a range.
[0076] Other embodiments of the present invention will be apparent
to those skilled in the art from consideration of the present
specification and practice of the present invention disclosed
herein. It is intended that the present specification and examples
be considered as exemplary only with a true scope and spirit of the
invention being indicated by the following claims and equivalents
thereof.
* * * * *