U.S. patent application number 10/163620 was filed with the patent office on 2003-12-11 for high-ptf sputtering targets and method of manufacturing.
Invention is credited to Bartholomeusz, Michael, Deodutt, Anand, Kunkel, Bernd, Zhang, Wenjun.
Application Number | 20030228238 10/163620 |
Document ID | / |
Family ID | 29710011 |
Filed Date | 2003-12-11 |
United States Patent
Application |
20030228238 |
Kind Code |
A1 |
Zhang, Wenjun ; et
al. |
December 11, 2003 |
High-PTF sputtering targets and method of manufacturing
Abstract
A target for a deposition apparatus is formed by blending at
least two different types of powders together and consolidating the
powders with a powder metallurgy process to form a billet. The
target is then formed from the billet. The target includes a first
material phase having a first PTF and a second material phase
having a second PTF higher than the first PTF. The second PTF is
also higher than a PTF of a material having the same chemistry as
the target.
Inventors: |
Zhang, Wenjun; (Gilbert,
AZ) ; Kunkel, Bernd; (Phoenix, AZ) ; Deodutt,
Anand; (Gilbert, AZ) ; Bartholomeusz, Michael;
(Phoenix, AZ) |
Correspondence
Address: |
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Family ID: |
29710011 |
Appl. No.: |
10/163620 |
Filed: |
June 7, 2002 |
Current U.S.
Class: |
419/30 ; 428/523;
G9B/5.304 |
Current CPC
Class: |
B22F 3/15 20130101; B22F
3/1208 20130101; G11B 5/851 20130101; C23C 14/3414 20130101; H01J
37/3426 20130101; B22F 2998/10 20130101; B22F 1/0003 20130101; B22F
2998/10 20130101; Y10T 428/31938 20150401; B22F 1/0003
20130101 |
Class at
Publication: |
419/30 ;
428/523 |
International
Class: |
B22F 001/00 |
Claims
What is claimed is:
1. A target for a deposition apparatus, comprising: a first
material phase having a first PTF; and a second material phase
having a second PTF, the second PTF being higher than the first
PTF.
2. The target according to claim 1, wherein the target has a
chemistry differing from chemistries of both the first and second
material phases.
3. The target according to claim 2, wherein the second PTF is
higher than a PTF of a material having a same chemistry as the
target.
4. The target according to claim 1, wherein a chemistry of the
target is that for a soft magnetic material.
5. The target according to claim 4, wherein the target has a
thickness greater than 3 mm, a diameter greater than 50 mm, and a
PTF of the target is greater than 5%.
6. The target according to claim 5, wherein a PTF of the target is
greater than 20%.
7. The target according to claim 6, wherein the chemistry of the
target includes at least 40 atomic% of Fe or Ni.
8. The target according to claim 7, wherein the chemistry of the
target does not include Co.
9. The target according to claim 5, wherein a PTF of the target is
greater than 50%.
10. The target according to claim 9, wherein the chemistry of the
target includes at least 40 atomic% of Co and does not include Fe
and Ni.
11. The target according to claim 1, wherein the average grain-size
of the target is less than 500 microns.
12. The target according to claim 11, wherein the average
grain-size of the target is less than 200 microns.
13. The target according to claim 1, wherein the first and second
phases consist essentially of elemental phases.
14. The target according to claim 1, wherein the first and second
phases consist essentially of alloy phases.
15. The target according to claim 1, wherein one of the first and
second phases is an elemental phase and another of the first and
second phases is an alloy phase.
16. The target according to claim 1, wherein the target has a
density greater than 80% of theoretical.
17. The target according to claim 16, wherein the target has a
density greater than 95% of theoretical.
18. The target according to claim 1, wherein the target is formed
by powder metallurgy.
19. A method of forming a target for a deposition apparatus,
comprising the steps of: blending at least two different types of
elemental of alloy powders together; consolidating the powders with
a powder metallurgy process to form a billet; and forming the
target from the billet.
20. The method according to claim 19, wherein the at least two
powders consist essentially of elemental powders.
21. The method according to claim 19, wherein the at least two
powders consist essentially of alloy powders.
22. The method according to claim 19, wherein one of the at least
two powders is an elemental powder and another of the at least two
powders is an alloy powder.
23. The method according to claim 19, wherein the consolidation of
the powders is by isostatic pressing.
24. The method according to claim 19, wherein the consolidation of
the powders is by uniaxial pressing.
25. The method according to claim 19, wherein the aggregate
diameter of each of the powders is less than 500 microns.
26. The method according to claim 25, wherein the aggregate
diameter of each of the powders is less than 200 microns.
27. The method according to claim 19, wherein the target includes a
first material phase having a first PTF and a second material phase
having a second PTF, and the second PTF is higher than the first
PTF.
28. The method according to claim 27, wherein the target has a
chemistry differing from chemistries of both the first and second
material phases.
29. The method according to claim 28, wherein the second PTF is
higher than a PTF of a material having a same chemistry as the
target.
30. The method according to claim 19, wherein a chemistry of the
target is that for a soft magnetic material.
31. The method according to claim 30, wherein the target has a
thickness greater than 3 mm, a diameter greater than 50 mm, and a
PTF of the target is greater than 5%.
32. The method according to claim 31, wherein a PTF of the target
is greater than 20%.
33. The method according to claim 32, wherein the chemistry of the
target includes at least 40 atomic% of Fe or Ni.
34. The method according to claim 33, wherein the chemistry of the
target does not include Co.
35. The method according to claim 31, wherein a PTF of the target
is greater than 50%.
36. The method according to claim 35, wherein the chemistry of the
target includes at least 40 atomic% of Co and does not include Fe
and Ni.
37. The method according to claim 19, wherein the target has a
density greater than 80% of theoretical.
38. The method according to claim 37, wherein the target has a
density greater than 95% of theoretical.
39. A method of forming a magnetic disk, comprising the steps of:
providing a substrate of the magnetic disk; and depositing material
from a target onto the substrate, wherein the target includes a
first material phase having a first PTF and a second material phase
having a second PTF, the second PTF higher than the first PTF.
40. The method according to claim 39, wherein the target has a
chemistry differing from chemistries of both the first and second
material phases.
41. The method according to claim 39, wherein a chemistry of the
target is that for a soft magnetic material.
42. The method according to claim 39, wherein the target is formed
by powder metallurgy.
43. A disk drive, comprising: a magnetic disk; wherein the magnetic
disk is formed by depositing material from a target onto a
substrate of the magnetic disk, the target includes a first
material phase having a first PTF and a second material phase
having a second PTF, the second PTF higher than the first PTF.
44. The disk drive according to claim 43, wherein the target has a
chemistry differing from chemistries of both the first and second
material phases.
45. The disk drive according to claim 43, wherein a chemistry of
the target is that for a soft magnetic material.
46. The method according to claim 43, wherein the target is formed
by powder metallurgy.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to the manufacturing of
magnetic disks for hard disk drives and, more specifically, to
sputter targets having a high-PTF for use in manufacturing the
magnetic disks.
BACKGROUND OF THE INVENTION
[0002] A hard disk drive (HDD) stores and retrieves data on
magnetic disks within the HDD. The surfaces of each magnetic disk
are a laminate structure comprised of several different layers of
magnetic and non-magnetic materials coated on an Al or
glass-composite substrate. The resultant media layer provides the
magnetic medium for read/write/erase cycles. The disk or disks are
fixed to a rotating spindle and can spin at speeds sufficient to
create a cushion of air on the disk surface. This cushion of air
provides a bearing surface for an aerodynamically designed head to
"fly" in very close proximity to media surfaces of the disks to
access different locations.
[0003] The HDD uses the head on each media surface to perform the
write, erase and read functions on the disk. The head has two basic
active components, and these components are the write element and
the read sensor. The write element can basically be described as an
electromagnet that includes a coil wrapped around a pole structure.
As electrical current is passed through the coil, the current
induces a magnetic field into the pole structure. The pole
structure includes a gap that physically presents itself to the
media surface of the disk. When the magnetic field is induced into
the pole structure, flux energy jumps the gap in the pole structure
creating a field that projects out of the head device and onto the
media surface. This write field causes a specific alignment of the
magnetic domains in the media surface called a transition. Through
elaborate encoding schemes, the HDD will "write" data patterns onto
the media surfaces of the disk.
[0004] The read sensor in the head accomplishes data retrieval, or
reading. The read sensor is a magneto-resistive (MR) device that
includes several layers of ferromagnetic and anti-ferromagnetic
materials. As the read sensor is positioned over a written
transition on the media, the sensor's MR effect creates a change in
resistance proportional to the "sensed" field strength of the
transition on the media surfaces. This change in resistance is
electrically interpreted as a data bit and, through elaborate
decoding schemes, is translated into data.
[0005] Hard and soft magnetic materials are extensively used in the
architecture of both media and head components of a HDD. Magnetic
materials exhibit a hysteric behavior, and the magnetization of a
ferromagnetic material increases with increasing applied magnetic
field until saturation is achieved. After saturation has been
achieved, the magnetization of the material remains relatively
constant even with additional increases in applied field. After
saturation, however, a decrease in the applied field to zero does
not reduce the materials magnetization to zero. Instead, the
magnetized material maintains a remnant field that is lower than
the value of saturation magnetization. Ferromagnetic materials can
thus be made into permanent magnets. For these reasons,
ferromagnetic materials are chosen for long-term data storage
applications (i.e., HDD).
[0006] Ferromagnetic materials can be described as magnetically
soft or hard. Typically, for data storage applications, high and
low values of remnant magnetization as respectively associated with
soft and hard magnetic materials. Ferromagnetic materials will
alternatively be referred to as soft or hard magnetic
materials.
[0007] Typically for data storage applications, low and high values
of magnetic coercivity are associated with soft and hard magnetic
materials. Soft magnetic materials tend to have values of magnetic
coercivity between several Oersteds to several hundred Oersteds,
whereas hard magnetic materials have values of magnetic coercivity
between several thousand to tens of thousand Oersteds. (For
example, soft magnetic materials may have a coercivity ranging from
5-2000 and hard magnetic materials may have a coercivity ranging
from 2000-100,000.
[0008] A large portion of media and head components are
manufactured using physical vapor deposition (PVD) or sputtering
processes, specifically magnetron sputter deposition. PVD is a
process that deposits thin films of material onto a substrate. The
substrate is placed in close proximity to the material source
(target) in a vacuum chamber, and the material source is biased
with a negative voltage (cathode) while the substrate is positively
biased (anode). Predominantly neutral (uncharged) Ar gas is
introduced into the sputter chamber, and the acceleration of a few
incidental charged Ar ions and electrons towards the cathode and
anode, respectively, results in collisions with the prevailing Ar
gas cloud resulting in an escalation (avalanching) of the Ar
ionization phenomena. The accelerating Ar ions collide with the
target surface with sufficient energy to eject target surface
atoms. The ejected target atoms traverse the space between target
and substrate and deposit on the substrate. This process results in
the atom-by-atom creation of thin films on the substrate.
[0009] In magnetron sputtering, which is the predominant method
employed in the data storage media industry, the ionization of Ar
gas can be further enhanced by placing a magnetic array behind the
target. The magnetic field, which must be of sufficient strength to
transmit through the target, acts in conjunction with the
prevailing electric field to focus electrons in a region near the
target surface. This results in multiple and more efficient
ionization by electrons of Ar atoms and improves the deposition
rate of target atoms onto the substrate.
[0010] Due to the magnetic nature of magnetic target alloys,
however, there is considerable shunting of the applied magnetic
field in the bulk of the target. This results in reduced target
utilization due to focussing of the transmitted magnetic field in
the erosion groove formed as a result of the shunting and an upper
limit on operable magnetic target thickness due to the requirement
of sufficient passage of magnetic flux through the bulk of the
target to initiate the sputtering process. Both these effects are
exacerbated with decreasing Pass-Through-Flux (PTF) capability. The
presence of severe target erosion profiles also promotes a point
source sputtering phenomena that can result in less than optimum
deposited film thickness uniformity.
[0011] The PTF of a magnetic target is defined as the ratio of
transmitted magnetic field to applied magnetic field. A PTF value
of 100% is indicative of a non-magnetic material in which none of
the applied field is shunted through the bulk of the target. The
PTF of magnetic target materials is typically specified in the
range of 0 to 100%, with the majority of commercially produced
materials exhibiting values between 1 to 80%.
[0012] There are several different techniques for measuring product
PTF. One technique involves placing a 4.4 (.+-.0.4) kilogauss bar
magnet in contact with one side of the target material and
monitoring the transmitted field using an axial Hall probe in
contact with the other side of the target material. The maximum
value of the magnetic field transmitted through the bulk of the
target divided by the applied field strength in the absence of the
target between the magnet and probe (maintained at the same
distance apart as when the target was between them) is defined as
the PTF. PTF can be expressed as either a fraction or a percent.
Another technique for measuring PTF involves using a horseshoe
magnet and a transverse Hall probe. This technique, unless
otherwise stated, has been used in obtaining the PTF values
described in the present application. A more detailed description
of the measurement technique itself can be found in ASTM Standard F
1761.
[0013] The PTF measurement techniques are constructed to
realistically approximate the applied magnetic flux occurring in an
actual magnetron-sputtering machine. Therefore, PTF measurements
correlate to a target material's performance during magnetron
sputtering. Magnetic material PTF and permeability are not mutually
exclusive. Rather, an inverse correlation typically exists between
PTF and maximum permeability of magnetic materials. Values of
material magnetic permeability can be very precisely determined by
using vibrating-sample-magnetometer (VSM) techniques in accordance
with ASTM Standard A 894-89. Descriptions of sample geometry and
calculation of the appropriate demagnetization factors for
permeability determination are also well known in the art, as
described by Bozarth, Ferromagnetism, p. 846.
[0014] Vacuum induction melting (VIM) processes have been used in
the prior art to form both hard and soft ferromagnetic materials
for use in targets. Although the prior art describes techniques for
raising PTF in hard-magnetic materials typically used in the data
storage industry, there is a notable absence in the prior art of
high-PTF processing techniques for soft-magnetic materials,
particularly as applied to magnetron sputtering thin-film
electronic applications. Soft-magnetic materials used in magnetron
sputtering applications in the data storage and electronics
industry can broadly be described as comprising three alloy
families: Co-based, Ni-based and Fe-based.
[0015] CoA--(Fe, Ta, Nb, Zr, B)B
[0016] NiA--(Fe, Nb, Cu, V, Cr, Mo) B
[0017] FeA--(Al, Si, Ta, B, C, Co, Cr, Ni, Ir, Rh, V) B
[0018] For each of these families, one or more of alloying
additions (shown in parentheses) can be added up to a total
concentration not to exceed 60 atomic %. Thus, the subscript B
ranges between 0 to 60 atomic % of one or more of the alloying
additions described, and the subscript A constitutes the remainder
such that A and B add up to a total of 100 atomic %.
[0019] Through the use of conventional VIM techniques,
soft-magnetic materials are formed having microscopic and
macroscopic chemistries (or compositions) that are identical. VIM
processing involves the casting of material inside a vacuum
chamber. The starting materials, which are formulated to achieve
desired alloy chemistry, are placed into a crucible composed of
refractory material. The starting materials typically constitutes
flakes, powders and alloy re-melt of the various constituent
elements. A coil surrounds the crucible, and an alternating
electrical current flows through the coil at a controlled frequency
to create a voltage potential. The material in the crucible short
circuits this potential and is subject to resistive heating via
current flow. Once liquid, the material is poured (cast) into a
metallic or ceramic mold and allowed to solidify and cool. The
solid cast material is referred to as an ingot, and can be
subjected to further thermo-mechanical processes, if necessary, to
achieve material densification or specific microstructural
properties. Thermo-mechanical processing typically constitutes
various combinations of hot rolling, warm rolling, forging and
annealing.
[0020] As previously discussed, a problem with VIM processing of
soft-magnetic materials is that a very low-PTF material is
produced. The PTF values typically range from between 1% to 10%.
PTF values greater than 10% are not achievable for target materials
with thickness values between 3 mm to 7 mm. This is particularly
true for the Ni and Fe-based soft-magnetic materials. For a select
number of Co-based soft-magnetic alloys (typically not containing
any Fe or Ni alloying additions), it is, however possible to
achieve values of PTF in excess of 10%, (usually 20% to 50%), for
the thickness ranges specified above using VIM techniques. There
is, therefore, a need for a high-PTF soft-magnetic material and a
method of manufacturing the same.
SUMMARY OF THE INVENTION
[0021] These and other needs are met by the present invention,
which in accord with one aspect provides a target for use in a
deposition apparatus. The target includes a first material phase
having a first PTF and a second material phase having a second PTF
higher than the first PTF. The second PTF is also higher than a PTF
of a material having the same chemistry as the target. The
chemistry of the target differs from chemistries of both the first
and second material phases, and the chemistry of the target is that
for a soft magnetic material. The target is formed by powder
metallurgy.
[0022] In certain aspects of the invention, the target has a
thickness greater than 3 mm, a diameter greater than 50 mm, and a
PTF of the target is greater than 5%. The PTF of the target can be
greater than 20% when the chemistry of the target includes at least
40 atomic % of Fe or Ni and does not include Co. The PTF of the
target can be greater than 50% when the chemistry of the target
includes at least 40 atomic% of Co and does not include Fe and
Ni.
[0023] In other aspects of the inventions, the average grain-size
of the target is less than 500 microns or less than 200 microns.
Also, the first and second phases are elemental phases or alloy
phases. Alternatively, one of the first and second phases is an
elemental phase and another of the first and second phases is an
alloy phase. The target can have a density greater than 80% of
theoretical or greater than 95% of theoretical.
[0024] In another embodiment of the invention, a target for a
deposition apparatus is formed by blending at least two different
types of powders together and consolidating the powders with a
powder metallurgy process to form a billet. The consolidation of
the powders can be by isostatic pressing or uniaxial pressing. The
target is then formed from the billet. The target includes a first
material phase having a first PTF and a second material phase
having a second PTF higher than the first PTF. The second PTF is
also higher than a PTF of a material having the same chemistry as
the target. The chemistry of the target is that for a soft magnetic
material.
[0025] In other aspects of the invention, the powders consist of
elemental powders or alloy powders. Alternatively one of the
powders is an elemental powder and another of the powders is an
alloy powder. The aggregate diameter of each of the powders is less
than 500 microns or less than 200 microns.
[0026] In still another embodiment of the invention, a method of
forming a magnetic disk is provided. The method includes depositing
material from a target onto a substrate of the magnetic disk. The
target includes a first material phase having a first PTF and a
second material phase having a second PTF higher than the first
PTF. The chemistry of the target differs from chemistries of both
the first and second material phases, and the chemistry of the
target is that for a soft magnetic material. The target is formed
by powder metallurgy.
[0027] In yet another embodiment of the invention, a disk drive is
provided. The disk drive includes a magnetic disk formed by
depositing material from a target onto a substrate of the magnetic
disk. The target includes a first material phase having a first PTF
and a second material phase having a second PTF higher than the
first PTF. The chemistry of the target differs from chemistries of
both the first and second material phases, and the chemistry of the
target is that for a soft magnetic material. The target is formed
by powder metallurgy.
[0028] Additional advantages of the present invention will become
readily apparent to those skilled in this art from the following
detailed description, wherein only an exemplary embodiment of the
present invention is shown and described, simply by way of
illustration of the best mode contemplated for carrying out the
present invention. As will be realized, the present invention is
capable of other and different embodiments, and its several details
are capable of modifications in various obvious respects, all
without departing from the invention. Accordingly, the drawings and
description are to be regarded as illustrative in nature, and not
as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Reference is made to the attached drawings, wherein elements
having the same reference numeral designations represent like
elements throughout, and wherein:
[0030] FIG. 1 is a flow chart of a process flow to form a high-PTF
target in accordance with one aspect of the invention;
[0031] FIG. 2a illustrates the microstructure of a conventionally
manufactured NiFeNb alloy;
[0032] FIG. 2b illustrates the microstructure of a high-PTF NiFeNb
alloy manufactured in accordance with one aspect of the
invention;
[0033] FIG. 3a illustrates the microstructure of a high-PTF FeAlSi
alloy manufactured in accordance with one aspect of the invention
using elemental phases; and
[0034] FIG. 3b illustrates the microstructure of a high-PTF FeAlSi
alloy manufactured in accordance with one aspect of the invention
using alloy phases.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0035] According to the invention, a method of manufacturing
high-PTF soft-magnetic material is provided. The invention is also
applicable to the manufacture of high-PTF hard magnetic materials.
The invention is especially applicable to the manufacture of very
brittle hard magnetic materials where PTF enhancement by use of
standard wrought processing is difficult or impossible. In
addition, novel sputtering targets formed by the high-PTF materials
are also provided. Such sputtering targets can be used in PVD
manufacturing processes of a magnetic disk. Furthermore, the
sputtering targets can also be used to form a disk in a HDD.
[0036] A high-PTF material according to aspects of the invention
includes at least two different material phases (or types of
grains). At least one of the material phases has a first PTF
characteristic, and at least one of the other material phases has a
PTF characteristic lower than the first PTF characteristic. The
high-PTF material for a particular type of alloy can alternatively
be defined as being macro-alloyed and micro-unalloyed (or partially
micro-unalloyed). As defined, the chemistry (or composition) of
individual grains of the high-PTF material can differ substantially
from the chemistry of the aggregate composition of the high-PTF
material. The individual grains, besides having different
chemistries, can also have substantially different PTF
characteristics. Furthermore, the PTF characteristic of at least
one of the material phases (or type of grains) can be higher than
the aggregate PTF characteristic of a conventionally-formed
material for use in the body of a sputtering target.
[0037] By providing at least two material phases with at least one
the material phases having a higher PTF characteristic, the
high-PTF material phase provides higher PTF flux paths for magnetic
fields to pass through the body of the target. This effect is
increased as the percentage of higher PTF phase(s) within the body
increases. The effect is also increased when the distribution of
higher PTF phase or phases within the body is such that an
uninterrupted high PTF flux path through the body is provided. The
high PTF characteristics of the material can also be explained by
the reduction or elimination of low PTF compound or solid solution
phases in the microstructure of the body.
[0038] The high-PTF material, therefore, macroscopically possesses
the desired soft-magnetic phase chemistry, but microscopically is
comprised of a combination of distinct elemental and/or alloy
phases that do not possess the low-PTF characteristics of the
aggregate composition. Because the PVD process (or magnetron
sputtering), in which the high-PTF material can be used, is an
atom-by-atom deposition process, the thin-film phase being
deposited regains the equilibrium soft-magnetic phase chemistry
macroscopically represented by the target material. Therefore, the
high-PTF material allows for optimization of the magnetron sputter
manufacturing process via target PTF maximization, while preserving
the formation of the requisite soft-magnetic phase chemistry on the
resultant thin-film device.
[0039] The invention is not limited as to the manner in which the
at least two material phases of the high-PTF material is provided
as described herein. For example, this structure can also be
provided by mechanical joining of the different phases, (i.e., make
the target of one phase, and mechanically embed chips of the other
phase in the matrix). Another method for providing the high-PTF
material is known as powder metallurgy. Powder metallurgy and
powder metallurgy derivatives are well known in the art of material
processing, and the invention is not limited as to a particular
variation. During the powder metallurgy process, the body is formed
using elemental and/or alloy powders, which are processed at
conditions that promote densification of the resultant product.
This process is accomplished without complete interdiffusion and
reaction of the elemental and/or alloy powders such that at least
one high-PTF phase is provided and the amount of low-PTF phases is
reduced.
[0040] One exemplary method of using powder metallurgy is
illustrated in FIG. 1. In step 10, the powder parameters of the raw
materials are selected to promote homogeneous blending of the
elemental and/or alloy powders and to optimize final product
properties. Examples of powder parameters include size,
distribution, morphology and purity. Although not limited in this
manner, in certain aspects of the invention, the aggregate
diameters of the powders are less than 200 micrometers, and in
other aspects, the aggregate diameters of the powders are less than
500 micrometers.
[0041] After the powders are received in step 20, the powders are
blended together in step 30. Numerous techniques exist that can be
used to efficiently blend and homogenize elemental powders. In some
cases, mechanical pre-alloying can also be used. Examples of
techniques to blend and homogenize the powders include ball
milling, v-blending, tubular blending, and attritor milling.
[0042] In step 40, following the blending process, the powders can
be canned in preparation for consolidation. For example, a
container is filled with the powder, evacuated under heat to ensure
the removal of any moisture or trapped gasses present, and then
sealed. Although the geometry of the container is not limited in
any manner, the container can possess a near-net shape geometry
with respect to the final material configuration. The encapsulated
material can be consolidated via uniaxial or isostatic pressing.
Although not limited in this manner, the temperatures can range
from ambient temperature to about 1500.degree. C.
[0043] In step 50, the blended powders can be subject to
consolidation, for example, via Hot-Isostatic-Pressing (HIP). A HIP
unit is typically a cylindrical pressure vessel large enough to
house one or more containers. The inner walls of the vessel can be
lined with resistance heating elements, and the pressure can be
controlled by the introduction of inert gas within the container.
The consolidation of the blended powders can also use hot/warm
uniaxial or isostatic pressing. Multi step uniaxial/isostatic
pressing at different temperatures (including room) and at
different pressures (with ramp-rate control for both temperature
and pressure) may be utilized depending on the alloy system and
powder specifics under consideration.
[0044] Depending upon the complexity of the cycle, total hold times
during uniaxial/isostatic pressing typically vary from about 1 to
about 12 hours. For data storage soft-magnetic materials, pressures
of about 5 to about 40 ksi (preferably 10-20 ksi) at temperatures
between about 5000 to about 1500.degree. C. (preferably
600-900.degree. C.), are typically employed to ensure densities
greater than about 98% of theoretical although in other aspects of
the invention densities greater than 80% of theoretical can be
provided. High density advantageously ensures that material micro
arching and defect generation does not compromise data storage
media yields during a PVD manufacturing process. In at least one
aspect of the invention, the hold times are between about 2 to
about 6 hours at temperatures between about 400.degree. C. and
about 1000.degree. C. and at pressures between about 10 and about
20 ksi.
[0045] Consolidation can also be facilitated by roll compaction of
the previously described container or can, or by sintering of the
alloy and/or elemental powders without the application of an
applied pressure. After consolidation, the billet can be further
thermo-mechanically processed to achieve further optimization of
properties, such as PTF. For example, straight warm-rolling a
rectangular billet, or cylindrical target section at temperatures
less than 800.degree. C. for reduction ratios in excess of 2%,
preferably between 5% to 20%, can promote noticeable improvements
in target PTF.
[0046] In step 60, after consolidation, the solid material form
(billet) is removed from the encapsulation can, and a slice of the
billet can then be sent to be tested as to various properties of
the billet. As with VIM processing, the billet can be subjected to
optional thermo-mechanical processing to further manipulate the
microstructural and macro-magnetic properties of the target. Also,
in steps 70, 80, and 90, the final shape and size of the sputter
targets can be formed, for example, by processes such as grind,
waterjet, mill, and lathe. In step 100, the target can be cleaned
and subjected to a final inspection.
[0047] Some soft-magnetic materials are optimally manufactured
using blended elemental powders, while others use alloy powders.
Although not limited in this manner, alloy powders are typically
fabricated using gas atomization. In gas atomization, VIM
processing can be employed to generate molten metal that is poured
through a nozzle and atomized by a stream of inert gas. The
atomized material spheroidizes and rapidly cools to form an alloy
powder aggregate. Another method of fabricating alloy powders is to
conventionally cast an ingot of the target material, crush it, and
sieve it to yield powders of the desired size and morphology.
[0048] As previously discussed, good densification is desirable to
minimize defect generation during the PVD process. The scale and
crystal structure of the blended phases can also have an impact on
media properties by impacting the angle of atomic ejection during
the PVD process. Material design paradigms can be developed on an
individual basis for specific applications. For example, with Ni-Fe
soft-magnetic alloys in the GMR read sensor (read-component of data
storage head device), oxygen impurity content can be advantageously
minimized to mitigate adverse compromise of the GMR effect. In
contrast, oxygen content in the range of several thousand ppm may
be beneficial in the same Ni--Fe alloy that is used as a part of a
data-storage media device. In the media application, oxygen
impurity content may serve to positively impact the wetting
characteristics between the soft-magnetic film and seed-layer (i.e.
Ti, Ru, Pt, etc.) to promote beneficial media performance effects
associated with grain-size refinement.
[0049] Although not limited to the characteristics described below,
a target formed from the inventive methodology can possess the
following magnetic and microstructural characteristics. The data
described is for cylindrical targets with thickness between 3 to 7
mm and diameters between 50 to 200 mm. However, the general
applicability of the data is not constrained by these target
dimensional ranges. The PTF can exceed 5%, as measured using the
ASTM technique, and a preferred range of PTF is between 20% and
70%. For Co-based alloys with no Fe or Ni alloying additions, the
preferred PTF range can be further increased to be between 50% and
90%. The average particle-size and grain-size can typically be less
than 500 microns, and preferably less than 200 microns. The
microstructure of target constitutes an assembly of elemental
phases, an assembly of alloy phases, or some combination of
elemental and alloy phases. Typically, interdiffusion between the
different phases will be kept to a minimum to avoid the formation
of the equilibrium low-PTF soft-magnetic phase. However, in certain
situation, limited interdiffusion can be engineered to improve
phase cohesion (such as for reasons of ductility), or to impact the
macromagnetic properties of the target for reasons other than PTF
maximization. The targets typically have densities greater than 80%
of theoretical, and preferably greater than 95% of theoretical.
[0050] By increasing the PTF of the target, a less severe erosion
profile can be provided during sputtering of the target. This
increases target material utilization and subsequently contributes
to a reduction in material cost. A higher PTF also enables the use
of thicker targets, which reduce the frequency that the target is
changed during thin-film device manufacture, and the reduction in
apparatus downtime caused by frequent target changes can reduce
component manufacturing costs. Also, increasing target material PTF
has the added benefit of increasing deposited film thickness
uniformity by reducing point source sputtering phenomena.
EXAMPLE 1
[0051] For comparative purposes, targets using a Ni-15.6Fe-3.2Nb
alloy were manufactured using both conventional processing and
processing according to aspects of the invention, as previously
discussed.
[0052] Target Formed by Conventional Process
[0053] The conventionally formed targets were formed using vacuum
induction melting of an ingot of the specified alloy chemistry. The
ingot was then roll-processed to form a plate at temperatures
between 900 and 1200.degree. C. The rolling process was conducted
to ensure a fine dynamically recrystallized grain morphology and
full material densification. The net reduction ratio exceeded 60%
where the reduction ratio=((ingot thickness-plate thickness)/ingot
thickness). A cylindrically-shaped target having a thickness of 5
mm and a diameter of 180 mm was machined from the rolled plate.
[0054] The PTF of the conventionally formed target was measured at
four equally spaced locations (one measurement per quadrant) and at
a radial position halfway between the center of the target and the
outer diameter using the previously-described ASTM measurement
technique. The microstructure of the conventionally formed target,
as characterized by crystallite grain-size, was measured using
standard optical metallographic techniques known in the art. The
microstructure of the conventional formed target using a
Ni-15.6Fe-3.2Nb alloy is illustrated in FIG. 2A. The results of the
PTF and grain-size measurements are as follows:
[0055] Average PTF=1%
[0056] Average grain-size=45 micrometers
[0057] Although conventional processing can form a target with a
moderately fine-grained microstructure, which is very desirable for
optimum deposited film thickness uniformity, the macro-magnetic PTF
is very low. Under achievable cathode-voltage and gas-pressure
conditions in the sputter chamber for magnetron sputtering, the PVD
process can usually only be initiated when the PTF values of the
target exceed 20% to 30%. Thus, the conventionally formed target
will unlikely fire and sputter in a stable manner at a thickness of
5 mm. Although a thinner target will be more likely to fire and
sputter in a stable manner, reducing the target thickness further
has a detrimental impact on production through-put and costs during
HDD component manufacturing. This results in the higher frequency
of target changes during manufacturing to account for a reduced
amount of material available for sputtering.
[0058] Target Formed by Process According to the Invention
[0059] The manufacturing of the Ni-15.6Fe-3.2Nb target with the
process according to the invention involved using elemental Ni, Fe
and Nb powders, each having an average diameter less than 150
micrometers. The powders were blended to achieve homogeneous
mixing, encapsulated, evacuated, and hot-isostatic-pressed at
between about 600 and about 900.degree. C. at a pressure between
about 10 and about 20 ksi for hold times between about 2 to about 6
hours. After hot-isostatic-pressing, the fully consolidated or
fully dense material was machined to yield a cylindrically-shaped
target having a thickness of 5 mm and a diameter of 180 mm.
[0060] The PTF of the target was measured at four equally spaced
locations (one measurement per quadrant) and at a radial position
halfway between the center of the target and the outer diameter
using the previously-described ASTM measurement technique, which
was identical to the method used to measure the PTF of the
conventionally formed target. The microstructure of the
conventionally formed target, as characterized by crystallite
grain-size, was measured using scanning electron microscopy (SEM)
techniques. The microstructure of the conventional formed target
using a Ni-1 5.6Fe-3.2Nb alloy is illustrated in FIG. 2B. The SEM
was utilized for improved contrast capability to show the
multi-elemental phases of the target. The results of the PTF and
grain-size measurements are as follows:
[0061] Average PTF=32%
[0062] Average grain size=13 micrometers
[0063] The process according to the invention formed a target
having a very fine grain-size, which can be important for obtaining
good deposited film thickness uniformity, and the grain-size of the
target formed by the process according to the invention is
considerably finer than that of the target formed by conventionally
processing. Furthermore, in contrast to the conventionally formed
target, which had a PTF of 1%, the PTF of the target formed by the
process according to the invention is significantly higher at 32%.
Thus, the target formed by the process according to the invention
can fire and sputter in a stable manner at a thickness of 5 mm. The
use of the target formed by the process according to the invention
can therefore be used during HDD component manufacturing, and
therefore, results in a less pronounced sputter erosion groove,
greater uniformity of deposited film thickness, and better overall
material utilization.
[0064] The processing technique according to the invention yields
higher values of target PTF than that of the conventional
technique, in part, because the blended elemental/alloy phases
typically possess higher individual values of PTF than the
compound/alloy phase. Thus, an applied magnetic field will find
more available "higher-PTF" flux paths through the blended
elemental/alloy phases than through a conventional single-phase
having a uniformly low-PTF. Ni and Fe individually exhibit higher
values of PTF than the combined Ni--Fe soft-magnetic phase.
Furthermore, since Nb is not noticeably magnetic (paramagnetic) at
operable PVD temperatures, Nb exhibits excellent high-PTF
characteristics (PTF =100%). Thus, the elemental combination and
consolidation of Ni, Fe and Nb to form an elementally blended
target possessing a nominal Ni-15.6Fe-3.2Nb composition possess a
higher PTF value than a conventionally formed target having a
single Ni-15.6Fe-3.2Nb soft-magnetic phase.
EXAMPLE 2
[0065] For comparative purposes, targets using Fe-30.5Co-11B,
Fe-9.7Al-16.5Si and Ni-19Fe alloys (in atomic %) were manufactured
using both conventional processing and processing according to an
aspect of the invention.
[0066] Target Formed by Conventional Process
[0067] For the Fe-30.5Co-11B and Ni-19Fe alloys, targets were
formed using vacuum induction melting of an ingot of the specified
alloy chemistry. The ingot was then roll-processed to form a plate
at temperatures between 900 and 1200.degree. C. The rolling process
was conducted to ensure a fine dynamically recrystallized grain
morphology and full material densification. The net reduction ratio
exceeded 60% where the reduction ration=((ingot thickness-plate
thickness)/ingot thickness). A cylindrically-shaped target having a
thickness of 5 mm and a diameter of 180 mm was machined from the
rolled plate.
[0068] Due to the excessive brittleness of the Fe-9.7Al-16.5Si
material, this material could not be roll-processed after vacuum
induction melting. Thus, for this material, the target was machined
from the as-cast ingot, and this is a conventional practice for
manufacturing a target from this particular material. The cooling
rate after conventional casting of Fe-9.7Al-16.5Si product was
closely controlled to insure that the as-cast ingot did not
catastrophically fracture.
[0069] The PTF of the conventionally formed target was measured at
four equally spaced locations (one measurement per quadrant) and at
a radial position halfway between the center of the target and the
outer diameter using the previously-described ASTM measurement
technique.
[0070] Target Formed by Process According to the Invention
[0071] The manufacturing of the Fe-30.5Co-11B target with the
process according to the invention involved using elemental Fe, Co
and B powders, each having an average diameter less than 150
micrometers. The powders were blended to achieve homogeneous
mixing, encapsulated, evacuated, and hot-isostatic-pressed at
between about 700 and about 1200.degree. C. at a pressure between
about 12 and about 25 ksi for hold times between about 2 to about 6
hours. After hot-isostatic-pressing, the fully consolidated or
fully dense material was machined to yield a cylindrically-shaped
target having a thickness of 5 mm and a diameter of 180 mm.
[0072] The manufacture of the Ni-19Fe target using the process
according to the invention involved using elemental Ni and Fe
powders, each having an average diameter less than 150 micrometers.
The powders were blended to achieve homogeneous mixing,
encapsulated, evacuated, and hot-isostatic-pressed at between about
700 and about 1200.degree. C. at a pressure between about 12 and
about 25 ksi for hold times between about 2 to about 6 hours. After
hot-isostatic-pressing, the fully consolidated or fully dense
material was machined to yield a cylindrically-shaped target having
a thickness of 5 mm and a diameter of 180 mm.
[0073] The manufacture of the Fe-9.7Al-16.5Si target using the
process according to the invention involved using elemental Fe, Al
and Si powders, each having an average diameter less than 150
micrometers. The powders were blended to achieve homogeneous
mixing, encapsulated, evacuated, and hot-isostatic-pressed at
between about 300 and about 600.degree. C. at a pressure between
about 15 and about 30 ksi for hold times between about 4 to about 8
hours. After hot-isostatic-pressing, the fully consolidated or
fully dense material was machined to yield a cylindrically-shaped
target having a thickness of 5 mm and a diameter of 180 mm.
[0074] The PTF of the target was measured at four equally spaced
locations (one measurement per quadrant) and at a radial position
halfway between the center of the target and the outer diameter
using the previously-described ASTM measurement technique, which
was identical to the method used to measure the PTF of
conventionally formed targets.
[0075] Table 1 below shows the significant increase in PTF from the
conventionally formed targets to targets formed using the process
according to the invention.
1TABLE 1 Chemistry (atomic %) PTF (Conventional) PTF (New)
Fe-30.5Co-11B 2% 20% Fe-9.7A1-16.5Si 4% 49% Ni-19Fe 1% 22%
[0076] As previously stated in Example 1, a target formed from the
process according to the invention and having a higher PTF value
will reduce thin-film manufacturing costs by maximizing material
utilization of the target. The less severe erosion groove
associated with higher-PTF values promotes greater utilization of
available material, and the greater possible thickness of the
target promotes longer target utilization and, therefore, less
frequent target changes in the sputter tool. Furthermore, the less
severe erosion groove geometry associated with the high-PTF targets
enhances the uniformity of deposited film-thickness.
[0077] The Fe-9.7Al-16.5Si alloy is an example of why targets
formed with the process according to the invention yield higher-PTF
values. Al and Si are non-magnetic elemental phases at operable PVD
temperatures. Thus, a significant portion of the target's
microstructure possesses non-magnetic elemental phases that allows
for more available higher-PTF flux paths for magnetic fields to
pass through the body of the target. In contrast, the entire
microstructure of the conventionally formed target consists of a
low-PTF Fe-9.7Al-16.5Si soft-magnetic compound phase.
[0078] The same rationale applies to the other two alloys found in
Table 1. With Ni 19Fe, both Ni and Fe are soft-magnetic elemental
phases; however, the individual values of PTF for Ni and Fe are
higher than that of the Ni-19Fe compound phase. Thus, targets with
multiple phases formed by the process according to the invention
have a higher aggregate PTF than the conventionally formed
single-phase targets.
EXAMPLE 3
[0079] The targets formed discussed in previous examples using the
process according to the invention were all manufactured using
elemental powder phases. However, these targets can also be formed
with a blend of elemental/alloy or alloy/alloy phases. For example,
the Fe-30.5Co-11B alloy of Example 2 can be manufactured using
individual Fe, Co and B elemental phases, or alternatively, by
using an elemental Fe phase in conjunction with a Co--B alloy
phase. The Co--B alloy phase can be formed, for example, by
gas-atomization, melting, or crushing. Similarly, the
Fe-9.7Al-16.5Si target formed using the process according to the
invention can comprise of individual Fe, Al and Si elemental phases
or a combination of an elemental-Al and a Fe-Si phase.
[0080] Although not limited to the reasons described below, there
are many reasons to engage in complex element/alloy phase blending
during using the process according to the invention. Different
elemental and alloy phases have different impurity characteristics;
and thus, the flexibility of combining elemental and alloy phases
together to form a nominal composition provides an improved ability
to microstructurally design specific target impurity profiles to
enhance thin-film performance characteristics.
[0081] For example, as previously noted, oxygen is potentially a
beneficial impurity in soft-magnetic materials for data storage
media applications. In contrast, oxygen needs to be minimized in
data storage GMR sensor applications. However, by custom-designing
impurity profiles using element/alloy phase blending, targets can
be provided that use the process according to the invention and
include all of the benefits associated with the process.
[0082] Another reason for complex element/alloy phase blending is
that some of the all elemental-phase additions to soft-magnetic
alloys are electrically insulating (i.e., B, C, Si). These
insulative elemental phases, when embedded in a conductive metallic
matrix, may promote micro-arching and material "spitting" onto the
thin film device being fabricated. Spitting is an undesirable
defect-generating phenomenon in the PVD manufacture of thin-film
devices. However, alloying of the insulating phases can mitigate
the phenomenon of spitting during PVD processing.
[0083] For example, the formation of a Fe-9.7Al-16.5Si target using
the process according to the invention can use an elemental Al
phase in combination with a Fe--Si phase. This combination can
result in thin-film yield improvement during the PVD fabrication
process. For this particular chemistry, the Si is distributed in a
Fe matrix in a much more refined format (substitutionally,
interstitially or precipitately) and is, therefore, less likely to
exhibit micro-arching and spitting characteristics during a
magnetron PVD process.
[0084] A SEM micrograph of a Fe-9.7Al-16.5Si target manufactured by
the process according to the invention using Fe, Al and Si
elemental phases is shown in FIG. 3A. FIG. 3B is a SEM micrograph
of a Fe-9.7Al-16.5Si target manufactured by the process according
to the invention using an Fe elemental-phase blended with
gas-atomized Fe--Al and Fe--Si alloy-phases. For both processes,
the powders were blended to achieve homogeneous mixing,
encapsulated, evacuated, and hot-isostatic-pressed at between about
300 and about 600.degree. C. at a pressure between about 15 and
about 30 ksi for hold times between about 4 to about 8 hours. After
hot-isostatic-pressing, the fully consolidated or fully dense
material was machined to yield a cylindrically-shaped target having
a thickness of 5 mm and a diameter of 180 mm. The PTF of the
targets were measured at four equally spaced locations (one
measurement per quadrant) and at a radial position halfway between
the center of the target and the outer diameter using the
previously-described ASTM measurement technique. The PTF of the
elemental/alloy blend is 35% and is slightly lower than that of the
PTF of 49% for the pure elemental blend.
EXAMPLE 4
[0085] For comparative purposes, targets using a Co-4Nb-5Zr alloy
(in atomic %) were manufactured using both conventional processing
and processing according to an aspect of the invention. It is known
that Co-based soft-magnetic alloys, with no Fe or Ni alloying
additions, exhibit the highest PTF capability using either
conventional processing or processing according to the
invention.
[0086] Target Formed by Conventional Process
[0087] The conventionally formed targets were formed using vacuum
induction melting of an ingot of the specified alloy chemistry. The
ingot was then roll-processed to form a plate at temperatures
between 950 and 1200.degree. C. The rolling process was conducted
to ensure a fine dynamically recrystallized grain morphology and
full material densification. The net reduction ratio exceeded 60%
where the reduction ration=((ingot thickness-plate thickness)/ingot
thickness). In a subsequent step, the hot-rolled plate was
thermo-mechanically processed as described in U.S. Pat. No.
6,123,783, to Bartholomeusz, et al., incorporated herein by
reference. A cylindrically-shaped target having a thickness of 5 mm
and a diameter of 180 mm was then machined from the
thermo-mechanically processed plate.
[0088] The PTF of the conventionally formed target was measured at
four equally spaced locations (one measurement per quadrant) and at
a radial position halfway between the center of the target and the
outer diameter using the previously-described ASTM measurement
technique.
[0089] Target Formed by Process According to the Invention
[0090] The manufacture of the Co-4Nb-5Zr target with the process
according to the invention involved using elemental Co, Nb and Zr
powders, each having an average diameter less than 150 micrometers.
The powders were blended to achieve homogeneous mixing,
encapsulated, evacuated, and hot-isostatic-pressed at between about
800 and about 1400.degree. C. at a pressure between about 5 and
about 15 ksi for hold times between about 1 to about 4 hours. After
hot-isostatic-pressing, the fully consolidated or fully dense
material was thermo-mechanically processed as described in U.S.
Pat. No. 6,123,783, to Bartholomeusz, et al. A cylindrically-shaped
target having a thickness of 5 mm and a diameter of 180 mm was then
machined from the thermo-mechanically processed plate.
[0091] The PTF of the target was measured at four equally spaced
locations (one measurement per quadrant) and at a radial position
halfway between the center of the target and the outer diameter
using the previously-described ASTM measurement technique, which
was identical to the method used to measure the PTF of
conventionally formed target.
[0092] The PTF values of the conventionally formed target and the
target manufactured by the process according to the invention are
39% and 56%, respectively. The PTF value of 39% indicates that even
conventionally formed Co-based soft-magnetic materials (not
containing Fe or Ni as alloying additions) can exhibit reasonably
high values of PTF. However, as previously demonstrated, forming
the targets with the process according to the invention still
results in significantly enhanced PTF performance of the alloy
under consideration. This example further demonstrates that PTF
enhancing techniques applied to Co and Ni based materials are also
effective in enhancing the PTF of the elemental Co and Ni
constituent phases contained within a target formed using the
process according to the invention.
[0093] In the examples discussed above, the PTF test and geometries
of the targets have been maintained as consistently as possible
because the absolute PTF value of soft-magnetic materials can
exhibit a dependency on the relative geometry between target and
magnet and the nominal strength of the magnet utilized. Therefore,
although the absolute values of PTF for targets formed using the
conventional process and the process according to the invention can
vary as a function of the method utilized to measure PTF, targets
manufactured using the process according to the invention have
higher values of PTF than targets formed using identical alloys but
by conventional processing.
[0094] As an example, two targets of Ni-19Fe were manufactured
using identical processes with the first target being 6 mm thick
with a 76 mm diameter and the second target also being 6 mm thick
but with a 152 mm diameter. For both targets, a 4.4 kilogauss
magnet, possessing a 6.5 mm by 26 mm cross section, was placed in
contact with the center of one face of each target. An axial Hall
probe was then placed at the center of the opposite face. The PTF
measured values for the 76 mm and 152 mm diameter targets were
respectively 30% and 15%. Thus, this test demonstrates that a
target (76 mm) with a smaller relative amount of soft-magnetic
target material can be saturated by an applied magnetic filed to
yield a higher net PTF.
[0095] In another test using the 152 mm target, the target was
placed on an actual PVD magnetron cathode. At target-to-cathode
distances of 10 and 15 mm, the maximum PTF on the opposing face of
the 152 mm target was measured at 60% and 20%, respectively. Thus,
this test demonstrates the impact of applied magnetic field
strength on the net PTF of soft-magnetic materials.
[0096] The present invention can be practiced by employing
conventional materials, methodology and equipment. Accordingly, the
details of such materials, equipment and methodology are not set
forth herein in detail. In the previous descriptions, numerous
specific details are set forth, such as specific materials,
structures, chemicals, processes, etc., in order to provide a
thorough understanding of the present invention. However, it should
be recognized that the present invention can be practiced without
resorting to the details specifically set forth. In other
instances, well known processing structures have not been described
in detail, in order not to unnecessarily obscure the present
invention.
[0097] Only an exemplary aspect of the present invention and but a
few examples of its versatility are shown and described in the
present disclosure. It is to be understood that the present
invention is capable of use in various other combinations and
environments and is capable of changes or modifications within the
scope of the inventive concept as expressed herein.
* * * * *