U.S. patent application number 11/336980 was filed with the patent office on 2007-07-26 for magnetic sputter targets manufactured using directional solidification.
This patent application is currently assigned to Heraeus, Inc.. Invention is credited to Anirban Das, Jun Hui, Bernd Kunkel, David Long, Abdelouahab Ziani.
Application Number | 20070169853 11/336980 |
Document ID | / |
Family ID | 37909762 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070169853 |
Kind Code |
A1 |
Kunkel; Bernd ; et
al. |
July 26, 2007 |
Magnetic sputter targets manufactured using directional
solidification
Abstract
A sputter target includes a metal alloy having a target surface,
a rear surface and a thickness between the target and rear
surfaces. The target surface and rear surface are outer surfaces of
the metal alloy. The metal alloy has a thickness direction
substantially along the thickness. The target surface is
substantially normal to the thickness direction. The metal alloy
has a single substantially homogenous microstructural zone across
substantially the entire thickness. The metal alloy further
includes dendrites. The dendrites at the target surface are
oriented along substantially one direction, and the dendrites at a
center plane of the metal alloy are oriented along substantially
the same one direction. A sputter target may include a metal alloy
which is a cobalt (Co) based, and may have a [0001] hexagonal
close-packing (HCP) direction oriented substantially normal to the
target surface. The sputter target may be formed by directional
solidification at near-equilibrium temperature conditions by
withdrawing the metal alloy at a first rate through a temperature
gradient. The sputter target is for forming one or more magnetic
layers on a substrate for, among other purposes, data storage.
Inventors: |
Kunkel; Bernd; (Phoenix,
AZ) ; Long; David; (Chandler, AZ) ; Ziani;
Abdelouahab; (Chandler, AZ) ; Das; Anirban;
(Tempe, AZ) ; Hui; Jun; (Maricopa, AZ) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
18191 VON KARMAN AVE.
SUITE 500
IRVINE
CA
92612-7108
US
|
Assignee: |
Heraeus, Inc.
Chandler
AZ
|
Family ID: |
37909762 |
Appl. No.: |
11/336980 |
Filed: |
January 23, 2006 |
Current U.S.
Class: |
148/425 ;
420/435 |
Current CPC
Class: |
C22C 19/07 20130101;
B22D 27/045 20130101; C22C 19/007 20130101; C23C 14/3414
20130101 |
Class at
Publication: |
148/425 ;
420/435 |
International
Class: |
C22C 19/07 20060101
C22C019/07 |
Claims
1. A sputter target comprising: a metal alloy having a target
surface, a rear surface and a thickness between the target surface
and the rear surface, the target surface and rear surface being
outer surfaces of the metal alloy, the metal alloy having a single
substantially homogenous microstructural zone across substantially
the entire thickness.
2. The sputter target of claim 1, wherein the sputter target is
formed by solidification at near-equilibrium temperature conditions
by withdrawing the metal alloy at a first rate through a
temperature gradient.
3. The sputter target of claim 1, wherein the metal alloy includes
a plurality of dendrites, and substantially all of the plurality of
dendrites are preferentially oriented along a growth direction.
4. The sputter target of claim 1, wherein the metal alloy includes
a first plurality of dendrites oriented substantially along a first
dendrite direction at the target surface, a second plurality of
dendrites oriented substantially along a second direction at a
center plane of the metal alloy; and the first dendrite direction
being substantially parallel to the second dendrite direction.
5. The sputter target of claim 1, wherein the metal alloy includes
dendrites, wherein shapes of a substantial portion of the dendrites
at the target surface are substantially similar to shapes of a
substantial portion of the dendrites at a center plane of the metal
alloy.
6. The sputter target of claim 5, wherein the substantial portion
of the dendrites at the target surface occupies an area of about
1.0 square millimeter or greater, and the substantial portion of
the dendrites at the center plane of the metal alloy occupies an
area of about 1.0 square millimeter or greater.
7. The sputter target of claim 1, wherein the metal alloy includes
dendrites, wherein sizes of a substantial portion of the dendrites
at the target surface are substantially similar to sizes of a
substantial portion of the dendrites at a center plane of the metal
alloy.
8. The sputter target of claim 7, wherein the substantial portion
of the dendrites at the target surface occupies an area of about
1.0 square millimeter or greater, and the substantial portion of
the dendrites at the center plane of the metal alloy occupies an
area of about 1.0 square millimeter or greater.
9. The sputter target of claim 1, wherein the metal alloy includes
cobalt (Co), greater than 0 and as much as about 5 atomic percent
tantalum (Ta), and greater than 0 and as much as about 5 atomic
percent zirconium (Zr).
10. The sputter target of claim 1, wherein the sputter target is
for forming one or more magnetic layers on a substrate for data
storage.
11. A sputter target comprising: a metal alloy having a target
surface, a rear surface and a thickness between the target surface
and the rear surface, the target surface and rear surface being
outer surfaces of the metal alloy, the metal alloy having
dendrites, the dendrites at the target surface oriented along
substantially one direction, the dendrites at a center plane of the
metal alloy oriented along substantially the same one
direction.
12. The sputter target of claim 11, wherein the metal alloy is
formed by directional solidification.
13. The sputter target of claim 11, wherein the metal alloy
includes at least one of the following: cobalt (Co), nickel (Ni)
and iron (Fe).
14. The sputter target of claim 11, wherein the metal alloy
includes at least one of the following: cobalt (Co), iron (Fe),
nickel (Ni), chromium (Cr), platinum (Pt), boron (B), copper (Cu),
gold (Au), titanium (Ti), vanadium (V), yttrium (Y), zirconium
(Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), rhodium (Rh),
lanthanum (La), hafnium (Hf), tantalum (Ta), tungsten (W) and
iridium (Ir).
15. The sputter target of claim 11, wherein the metal alloy
includes cobalt (Co), greater than 0 and as much as about 5 atomic
percent tantalum (Ta), and greater than 0 and as much as about 5
atomic percent zirconium (Zr).
16. The sputter target of claim 11, wherein the dendrites are
preferentially oriented along a growth direction.
17. The sputter target of claim 11, wherein the sputter target is
for forming one or more magnetic layers on a substrate for data
storage.
18. The sputter target of claim 11, wherein the metal alloy has a
magnetic property.
19. A sputter target comprising: a metal alloy which is a cobalt
(Co) based alloy, the metal alloy having a target surface, a rear
surface and a thickness between the target surface and the rear
surface, the target surface and rear surface being outer surfaces
of the metal alloy, the target surface being substantially normal
to the thickness direction, a [0001] hexagonal close-packing (HCP)
direction of the metal alloy oriented substantially normal to the
target surface.
20. The sputter target of claim 19, wherein the sputter target is
formed by directional solidification.
21. The sputter target of claim 19, wherein a pass through flux of
the sputter target is greater than about 10%.
22. The sputter target of claim 19, wherein the [0001] hexagonal
close-packing (HCP) direction of the metal alloy is oriented
between 0.degree. and 10.degree. of a direction normal to the
target surface.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to sputter targets
and, in particular, relates to sputter targets with improved
microstructural homogeneity and pass through flux ("PTF"), and to
the products produced therefrom such as thin film magnetic
media.
BACKGROUND OF THE INVENTION
[0002] Cathodic sputtering processes are widely used for the
deposition of thin films of material onto desired substrates. In
particular, thin film magnetic media can be manufactured using a
cathodic sputtering process. Concomitant with the ever increasing
demand for improved magnetic storage media has been an increasing
need for thin films of magnetic media with improved magnetic
characteristics and uniformity. To obtain thin films with these
desired attributes, it is necessary to use sputter targets with
improved microstructural homogeneity.
[0003] One approach to improving the microstructural homogeneity of
sputter targets is a process using vacuum induction melting and
ingot solidification, followed by thermo-mechanical working. These
techniques are limited in effectiveness due to the increased
manufacturing time required by thermo-mechanical working processes,
such as rolling and heat treatment. Moreover, these processes may
significantly limit the yield of sputter targets composed of
low-ductility alloys, as the risk of ingot cracking during the
thermo-mechanical working is higher with these difficult-to-roll
alloys. Further, any deviation from the rolling and heat treatment
process window can result in un-precedent microstructural
non-homogeneity across the target thickness (e.g., along the
sputter direction).
[0004] Additionally, for adequate material removal and deposition
during the cathodic sputtering process, the PTF of the applied
magnetic field through the sputter target is critical. A lower PTF
necessitates a higher voltage/power compensation to sputter the
target and hence limit its maximum utilization. The techniques to
improve PTF made by standard solidification practices followed by
thermo-mechanical working discussed above suffer from drawbacks of
high expense, long processing time, and low yield.
[0005] What is needed is a sputter target with improves
microstructural homogeneity and PTF. The present invention
satisfies this need and provides other advantages.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, a sputter target
is provided that has improved microstructural homogeneity and
higher PTF than was previously possible. The sputter target is
formed by directionally solidifying a metal alloy at
near-equilibrium temperature conditions by withdrawing the metal
alloy at a first rate through a temperature gradient. A sputter
target thus manufactured has a single substantially homogenous
microstructural zone substantially across its entire thickness.
[0007] According to one embodiment, the present invention is a
sputter target including a metal alloy. The metal alloy has a
target surface, a rear surface and a thickness between the target
surface and the rear surface. The target surface and rear surface
are outer surfaces of the metal alloy. The metal alloy has a single
substantially homogenous microstructural zone across substantially
the entire thickness.
[0008] According to another embodiment, a sputter target of the
present invention includes a metal alloy having a target surface, a
rear surface and a thickness between the target surface and the
rear surface. The target surface and rear surface are outer
surfaces of the metal alloy. The metal alloy has dendrites. The
dendrites at the target surface are oriented along substantially
one direction, and the dendrites at a center plane of the metal
alloy are oriented along substantially the same one direction.
[0009] According to another embodiment, a sputter target of the
present invention includes a metal alloy which is a cobalt (Co)
based alloy. The metal alloy has a target surface, a rear surface
and a thickness between the target surface and the rear surface.
The target surface and rear surface are outer surfaces of the metal
alloy. The target surface is substantially normal to the thickness
direction. A [0001] hexagonal close-packing (HCP) direction of the
metal alloy is oriented substantially normal to the target
surface.
[0010] Additional features and advantages of the invention will be
set forth in the description below, and in part will be apparent
from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the structure particularly pointed
out in the written description and claims hereof as well as the
appended drawings.
[0011] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The accompanying drawings, which are included to provide
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention. In the drawings:
[0013] FIG. 1 depicts a sputter target according to one embodiment
of the present invention;
[0014] FIG. 2 depicts a partial view of a target surface of a
sputter target according to one aspect of the present
invention;
[0015] FIG. 3 depicts a partial cross-sectional view of a sputter
target according to another aspect of the present invention;
[0016] FIG. 4 depicts a partial view of a target surface of a
sputter target according to yet another aspect of the present
invention;
[0017] FIG. 5 depicts a partial view of a center plane of a sputter
target according to yet another aspect of the present
invention;
[0018] FIG. 6 illustrates a directionally-solidified metal alloy
according to yet another aspect of the present invention;
[0019] FIG. 7 illustrates a partial view of a target surface of a
sputter target;
[0020] FIG. 8 illustrates a partial view of a center plane of a
sputter target; and
[0021] FIG. 9 depicts a sputter target according to another
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] In the following detailed description, numerous specific
details are set forth to provide a full understanding of the
present invention. It will be obvious, however, to one ordinarily
skilled in the art that the present invention may be practiced
without some of these specific details. In other instances,
well-known structures and techniques have not been shown in detail
not to obscure the present invention.
[0023] Referring to FIG. 1, a sputter target in accordance with one
embodiment of the present invention is illustrated. A sputter
target 100 includes a metal alloy. The metal alloy has a target
surface such as a target surface 101, a rear surface such as a rear
surface 103, and a side surface such as a side surface 104. The
metal alloy further has a thickness such as thickness 102 between
target surface 101 and rear surface 103, and further has a
thickness direction 106 substantially along the thickness 102.
Target surface 101 is an outer surface of the metal alloy and is
substantially normal to thickness direction 106. Side surface 104
is also an outer surface of the metal alloy. Rear surface 103 is an
outer surface of the metal alloy and is substantially normal to
thickness direction 106 or substantially parallel to target surface
101. According to one embodiment of the present invention, the
metal alloy has a single substantially homogenous microstructural
zone across substantially the entire thickness 102, as described
more fully below. According to another embodiment of the present
invention, a sputter target such as sputter target 100 may further
include a center plane such as a center plane 105, disposed between
target surface 101 and rear surface 103. In the present exemplary
embodiment of FIG. 1, the metal alloy of sputter target 100 is
Co-5Ta-5Zr.
[0024] Directional solidification is a solidification process that
enables solidification structures (e.g., the dendrites) to
preferentially grow and stabilize along specific orientations
(e.g., the growth or solidification direction) homogenously across
the entire melt. During directional solidification, a crucible such
as, for example, a ceramic investment mold, containing the melt
(e.g., the molten metal or metal alloy to be solidified) is pulled
at a specific withdrawal rate through a furnace or induction
heating device in which a controllable, uniform thermal gradient is
maintained across the entire melt during its directional
solidification. When solidification occurs at a near-equilibrium
temperature condition, the microstructural features are
preferentially oriented along the solidification direction (i.e.,
the direction opposite to the withdrawal direction). Directionality
or anisotropy in microstructural appearance as well as
crystallographic orientation can significantly lead to performance
anisotropy with respect to both structural and functional
properties (viz. magnetic).
[0025] This preferential orientation is illustrated in FIG. 2,
which depicts a close-up view of region A of target surface 101 of
sputter target 100 of FIG. 1, in which microstructural features
such as microstructural features 111 and 112 of target surface 101
can be seen. FIG. 2 shows a typical microstructure of the
directionally solidified Co-5Ta-5Zr alloy. A typical biphasic
microstructure is observed, with the brighter phase constituting
Co, Ta and Zr, whereas the darker phase predominantly constitutes
Co and Ta. The dendritic phase is preferentially oriented along the
growth direction. As a result of this preferential orientation of
the microstructural features, the evolved solidification
microstructure is substantially homogenous across the
solidification direction (i.e., the growth direction). Due to the
uniform thermal gradient experienced by the entire melt during the
directional solidification process, the microstructural features
with respect to the shape and size of the solidified dendritic
phase are observed to be substantially identical or similar both at
the target surface 101 of the metal alloy and at a center plane 105
of the metal alloy, indicating microstructural homogenization
(e.g., a single substantially homogenous microstructural zone)
across substantially the entire thickness 102 of sputter target
100. FIG. 3, which depicts a partial cross-sectional view of region
B of sputter target 100, illustrates this substantially homogenous
microstructural zone 110 along thickness direction 106. Uniformly
oriented dendritic structures are observed across the target
thickness.
[0026] The microstructural homogeneity of a sputter target improves
the microstructural homogeneity of the coating created by
sputtering the target. A sputter target of the present invention
may be used for sputtering one or more magnetic layers on a
substrate for data storage. Alternatively, a sputter target of the
present invention may be used for sputtering conductive layers on
semiconductor substrates, for sputtering optical thin films, or for
nearly any other sputtering application.
[0027] Region C of target surface 101 and region D of center plane
105 of sputter target 100 of FIG. 1 are illustrated in FIGS. 4 and
5, respectively. According to one embodiment, sputter target 100
may include dendrites, such as dendrites 205 and 206. Dendrites 205
at a target surface 101 are oriented along substantially one
direction 401 (e.g., the growth direction), and dendrites 206 at a
center plane 105 of the metal alloy are oriented along
substantially the same one direction 401 (e.g., the growth
direction).
[0028] Turning now to FIG. 6, a metal alloy 600 directionally
solidified according to one aspect of the present invention is
illustrated. According to one aspect of the present invention,
metal alloy 600 may comprise two or more metals, including, by way
of example and without limitation, two or more of cobalt (Co), iron
(Fe), nickel (Ni), chromium (Cr), platinum (Pt), boron (B), copper
(Cu), gold (Au), titanium (Ti), vanadium (V), yttrium (Y),
zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru),
rhodium (Rh), lanthanum (La), hafnium (Hf), tantalum (Ta), tungsten
(W), or iridium (Ir). According to another aspect of the present
invention, metal alloy 600 may comprise one or more metals.
[0029] According to yet another embodiment, metal alloy 600 may
include a broad range of low moment (Cr content>18 atomic
percent) and high moment (Cr content<18 atomic percent) cobalt
alloys for magnetic layers in Longitudinal magnetic recording, such
as, for example, Co-(5-25)Cr-(5-25)Pt-(5-20)B-(1.5-7.5)Cu or Au
atomic percent and/or (1.5-7.5)X atomic percent where X.dbd.Ti, V,
Y, Zr, Nb, Mo, Ru, Rh, La, Hf, Ta, W or Ir.
[0030] According to yet another embodiment, metal alloy 600 may be
a cobalt (Co) based alloy for sputtering interlayers in
Longitudinal magnetic recording, with a compositional range of, for
example, Co-(5-30)Cr, Co-(5-30)Cr-(2-15)Ta.
[0031] According to still other embodiments of the present
invention, metal alloy 600 may be a cobalt-, iron-, or nickel-based
alloy for sputtering soft magnetic underlayers and APC
(Anti-parallel coupled pinned layers) for perpendicular magnetic
recording, with compositions such as, for example, Co--Ta--Zr,
Co--Nb--Zr; Fe--Co--B, Fe--Co--Cr--B, Fe--Co--Ni--B, Co--Fe,
Ne--Fe, and Ni--Mn in any possible elemental ratio.
[0032] According to another aspect of the present invention, metal
alloy 600 may include cobalt (Co), greater than 0 and as much as
about 5 atomic percent tantalum (Ta), and greater than 0 and as
much as about 5 atomic percent zirconium (Zr).
[0033] According to the present exemplary embodiment, metal alloy
600 is a cobalt-based alloy, such as, for example, Co-5Ta-5Zr.
According to another aspect, a metal alloy is a metal-based alloy
or a metal compound.
[0034] Metal alloy 600 is withdrawn in a withdrawal direction [001]
through a furnace or induction heating device in which a
controllable, uniform thermal gradient is maintained across the
entire melt during its directional solidification. When
solidification occurs at near-equilibrium temperature conditions
during directional solidification, the low temperature hexagonal
close-packing (HCP) cobalt (Co) phase stabilization is favored. The
relative proportion of the HCP Co phase is therefore increased with
respect to the face-centered cubic (FCC) Co phase. As a
consequence, the [0001] HCP direction (i.e., the surface normal to
the basal HCP planes) preferentially orients itself to the surface
601 of the metal alloy at an angle of about 54.degree.. The highest
pass through flux (PTF) can be achieved if the basal hexagonal
texture is parallel to the magnetic lines of force 602 that occur
during sputtering. Therefore, by machining the metal alloy 600 to
create a target surface at 36.degree. with respect to surface 601
of metal alloy 600 (e.g., by cutting along line 603), the [0001]
direction can be made normal to a target surface of a sputter
target machined from metal alloy 600, thereby greatly increasing
the PTF of a sputter target thus manufactured.
[0035] Table 1, below, illustrates the advantage in PTF of a
sputter target according to one embodiment of the present invention
when compared to a sputter target that has been solidified with
vacuum induction melting and ingot casting and subsequently
thermo-mechanically worked. TABLE-US-00001 TABLE 1 Directionally
Solidified Thermo-Mechanically Sputter Target Worked Sputter Target
Composition Co--5Ta--5Zr Co--6Ta--4Zr PTF 15% 5%
[0036] The microstructures of a target surface and of a center
plane of a thermo-mechanically worked sputter target with the
composition Co-6Ta-4Zr are illustrated in FIGS. 7 and 8,
respectively. In contrast to a sputter target of the present
invention, the substantial differences in the microstructure with
respect to the orientation, shape and size of the solidified
dendritic phases 701 and 801 are observed at a target surface
(depicted in FIG. 7) and at a center plane (depicted in FIG. 8) of
the sputter target. At the target surface, the microstructure of
the primary dendritic phase (e.g., the darker structures) are more
columnar and thinner than at the center plane, where the primary
phase microstructure is more coarse and equiaxed. In neither plane
is a preferential orientation along a growth direction
observed.
[0037] In comparing FIGS. 3 and 4, it is apparent that sizes of a
substantial portion of the dendrites 205 at a target surface 101 of
a sputter target 100 of the present invention are substantially
similar to sizes of a substantial portion of the dendrites 206 at a
center plane 105 of a sputter target 100 of the present invention.
In comparing FIGS. 7 and 8, it is apparent that sizes of a
substantial portion of the dendrites 701 at a target surface of a
thermo-mechanically worked sputter target are substantially
dissimilar to sizes of a substantial portion of the dendrites 801
at a center plane of a thermo-mechanically worked sputter
target.
[0038] In further comparing FIGS. 3 and 4, it is apparent that
shapes of a substantial portion of the dendrites 205 at a target
surface 101 of a sputter target 100 of the present invention are
substantially similar to shapes of a substantial portion of the
dendrites 206 at a center plane 105 of a sputter target 100 of the
present invention. In comparing FIGS. 7 and 8, it is apparent that
shapes of a substantial portion of the dendrites 701 at a target
surface of a thermo-mechanically worked sputter target are
substantially dissimilar to shapes of a substantial portion of the
dendrites 801 at a center plane of a thermo-mechanically worked
sputter target.
[0039] According to one aspect of the present invention, the
substantial portion of the dendrites at the target surface occupies
an area of about 1.0 square millimeter or greater (e.g., a square
with sides of 1.0.times.10.sup.-3 m), and the substantial portion
of the dendrites at the center plane of the metal alloy occupies an
area of about 1.0 square millimeter or greater (e.g., a square with
sides of 1.0.times.10.sup.-3 m).
[0040] Turning now to FIG. 9, a sputter target according to yet
another embodiment of the present invention is illustrated. Sputter
target 900 includes a metal alloy which is a cobalt (Co) based
alloy. The metal alloy has a target surface such as target surface
901, a side surface such as a side surface 904 and a rear surface
such as a rear surface 903. The metal alloy also has a thickness
between the target surface 901 and rear surface 903, such as
thickness 902. The metal alloy further has a thickness direction
906 substantially along thickness 902. Target surface 901 and rear
surface 903 are outer surfaces of the metal alloy and are
substantially normal to thickness direction 906. Side surface 904
is an outer surface of the metal alloy. The metal alloy further has
a [0001] hexagonal close-packing (HCP) direction (i.e, the surface
normal to the basal HCP planes) oriented at an angle .theta. with
respect to target surface 901. According to one aspect of the
present invention, the [0001] HCP direction of the metal alloy is
oriented between 0.degree. and 10.degree. of a direction normal to
the target surface 901. According to another aspect of the present
invention, the [0001] HCP direction of the metal alloy is oriented
substantially normal to the target surface 901.
[0041] While the sputter targets illustrated in FIGS. 1 and 9 have
been shown with planar target surfaces and rear surfaces, it will
be apparent to one skilled in the art that sputter targets within
the scope of the present invention may be made in a variety of
other shapes. For example, and not by way of limitation, a sputter
target of the present invention may be configured as a rotatable
sputter target in the form of a cylindrical solid, where the target
surface and rear surface are defined as the portions of the
cylinder that face towards and away from, respectively, a substrate
to be coated. Alternatively, a sputter target of the present
invention may be configured to have a grooved or otherwise textured
target surface, or may have a non-planar target surface exhibiting
smooth or stepped curvature.
[0042] While the present invention has been particularly described
with reference to the various figures and embodiments, it should be
understood that these are for illustration purposes only and should
not be taken as limiting the scope of the invention. There may be
many other ways to implement the invention. Many changes and
modifications may be made to the invention, by one having ordinary
skill in the art, without departing from the spirit and scope of
the invention.
* * * * *