U.S. patent application number 14/089019 was filed with the patent office on 2014-06-19 for depositing lithium metal oxide on a battery substrate.
This patent application is currently assigned to FRONT EDGE TECHNOLOGY, INC.. The applicant listed for this patent is FRONT EDGE TECHNOLOGY, INC.. Invention is credited to Kai Wei NIEH, Weng-Chung WANG.
Application Number | 20140166471 14/089019 |
Document ID | / |
Family ID | 40405691 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140166471 |
Kind Code |
A1 |
WANG; Weng-Chung ; et
al. |
June 19, 2014 |
DEPOSITING LITHIUM METAL OXIDE ON A BATTERY SUBSTRATE
Abstract
A method of depositing lithium metal oxide on a battery
substrate in a sputtering chamber comprising a substrate support,
first and second sputtering targets each comprising lithium metal
oxide, and first and second electrodes about the backside surfaces
of the first and second sputtering targets respectively. In the
method, a substrate is placed on the substrate support, sputtering
gas maintained at a pressure and energized by applying an
alternating voltage of AC power to the first and second electrodes
so that each electrode is alternately either an anode or a cathode.
The alternating voltage can be applied within a frequency range
while also applying a time varying magnetic field about each of the
surfaces of the first and second targets.
Inventors: |
WANG; Weng-Chung; (Rowland
Heights, CA) ; NIEH; Kai Wei; (Monrovia, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FRONT EDGE TECHNOLOGY, INC. |
Baldwin Park |
CA |
US |
|
|
Assignee: |
FRONT EDGE TECHNOLOGY, INC.
Baldwin Park
CA
|
Family ID: |
40405691 |
Appl. No.: |
14/089019 |
Filed: |
November 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11849959 |
Sep 4, 2007 |
8628645 |
|
|
14089019 |
|
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Current U.S.
Class: |
204/192.17 |
Current CPC
Class: |
H01M 4/139 20130101;
C23C 14/352 20130101; H01M 4/1391 20130101; H01M 10/0585 20130101;
C23C 14/08 20130101; H01M 4/0426 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
204/192.17 |
International
Class: |
H01M 4/04 20060101
H01M004/04 |
Claims
1. A method of depositing lithium metal oxide on a battery
substrate, in a sputtering chamber comprising (i) a substrate
support, (ii) first and second sputtering targets each comprising a
sputtering surface of lithium metal oxide and having a backside
surface, and (iii) a first electrode about the backside surface of
the first sputtering target and a second electrode about the
backside surface of the second sputtering target, the method
comprising: (a) placing one or more substrates on the substrate
support in the sputtering chamber; (b) maintaining a sputtering gas
at a pressure in the sputtering chamber; (c) energizing the
sputtering gas by applying an alternating voltage of AC power to
the first and second electrodes so that each electrode is
alternately either an anode or a cathode, the alternating voltage
being applied at a frequency of between about 10 and about 100 kHz;
and (d) applying a time varying magnetic field about each of the
sputtering surfaces of the first and second targets.
2. A method according to claim 1 wherein the time varying magnetic
field comprises a rotational frequency.
3. A method according to claim 2 wherein the rotational frequency
is between about 0.005 and about 0.1 Hz.
4. A method according to claim 1 comprising providing a magnetron
behind each sputtering target, the magnetron comprising first and
second magnets that have different magnetic fluxes or magnetic
field orientations.
5. A method according to claim 1 wherein the sputtering chamber
comprises a cathode formed by binding a sputtering target to a
magnetron, and wherein (d) comprises rotating the magnetron.
6. A method according to claim 5 comprising mounting a
cylindrically shaped target to a cylindrically shaped
magnetron.
7. A method according to claim 1 wherein the sputtering chamber
comprises a cathode formed by binding a sputtering target to a
magnetron comprising a rotatable magnet assembly, and wherein (d)
comprises rotating the magnet assembly.
8. A method according to claim 1 comprising applying the
alternating voltage at at least one of (i) a frequency of from
about 20 to about 80 kHz, and (ii) a power level of from about 3 kW
to about 10 kW.
9. A method according to claim 1 wherein the substrate support is
electrically isolated from a sputtering chamber wall and from the
first and second sputtering targets and wherein (a) comprises
applying to the substrate support, a biasing voltage that is at
least one of (i) a pulsed voltage, (ii) from about -20V to about
-200V, and (iii) has a duty cycle from 10% to 90%.
10. A method according to claim 1 wherein the lithium metal oxide
comprises lithium cobalt oxide, lithium nickel oxide, lithium
manganese oxide, lithium iron oxide, lithium cobalt nickel oxide,
or a mixtures of transition metals.
11. A method according to claim 1 wherein the lithium metal oxide
consists essentially of lithium cobalt oxide.
12. A method of depositing lithium cobalt oxide on a battery
substrate in a sputtering chamber comprising (i) a substrate
support, (ii) first and second sputtering targets each comprising a
sputtering surface of lithium cobalt oxide and having a backside
surface, and (iii) a first electrode about the backside surface of
the first sputtering target and a second electrode about the
backside surface of the second sputtering target, the method
comprising: (a) placing one or more substrates on the substrate
support in the sputtering chamber; (b) maintaining a sputtering gas
at a pressure in the sputtering chamber; (c) energizing the
sputtering gas by applying an alternating voltage of AC power to
the first and second electrodes so that each electrode is
alternately either an anode or a cathode, the alternating voltage
being applied at a frequency of between about 10 and about 100 kHz;
and (d) applying a time varying magnetic field about each of the
sputtering surfaces of the first and second targets, the time
varying magnetic field comprising a rotational frequency of between
about 0.005 and about 0.1 Hz.
13. A method according to claim 12 comprising providing a magnetron
behind each sputtering target, the magnetron comprising first and
second magnets that have different magnetic fluxes or magnetic
field orientations.
14. A method according to claim 12 wherein the sputtering chamber
comprises a cathode formed by binding a sputtering target to a
magnetron, and wherein (d) comprises rotating the magnetron.
15. A method according to claim 12 wherein the sputtering chamber
comprises a cathode formed by binding a sputtering target to a
magnetron comprising a rotatable magnet assembly, and wherein (d)
comprises rotating the magnet assembly.
16. A method according to claim 12 comprising applying the
alternating voltage at at least one of a frequency of from about 20
to about 80 kHz and a power level of from about 3 kW to about 10
kW.
17. A method of depositing lithium cobalt oxide on a battery
substrate in a sputtering chamber comprising (i) a substrate
support, (ii) first and second sputtering targets that each have a
sputtering surface consisting essentially of lithium cobalt oxide,
and (iii) a first electrode about the first sputtering target and a
second electrode about the second sputtering target, the method
comprising: (a) placing one or more substrates on the substrate
support in the sputtering chamber; (b) maintaining a sputtering gas
at a pressure in the sputtering chamber; (c) energizing the
sputtering gas by applying an alternating voltage of AC power to
the first and second electrodes so that each electrode is
alternately either an anode or a cathode, the alternating voltage
being applied at a frequency of between about 10 and about 100 kHz;
(d) providing a magnetron about each of the first and second
sputtering targets, each magnetron comprising a first magnet having
a first magnetic flux or first magnetic field orientation, and one
or more peripheral magnets having a second magnetic flux or second
magnetic field orientation; and (e) applying a time varying
magnetic field about each of the sputtering surfaces of the first
and second targets, the time varying magnetic field comprising a
rotational frequency of between about 0.005 and about 0.1 Hz.
Description
CROSS REFERENCE
[0001] The present application is a continuation of U.S. patent
application Ser. No. 11/849,959, filed on Sep. 4, 2007, which is
incorporated herein by reference in its entirety.
BACKGROUND
[0002] Thin film batteries are used to supply energy in
applications requiring a small size, high specific energy or
density, or resistance to environmental degradation. Common
applications include, for example, portable electronics, medical
devices, and outer space systems. A thin film battery typically
comprises a substrate that supports a stack of thin films that can
include one or more of a current collector, cathode, anode and
electrolyte, the thin films typically having a thickness of less
than 100 microns. The thin films can be formed on the substrate by
conventional fabrication processes, such as for example, physical
or chemical vapor deposition (PVD or CVD), oxidation, nitridation,
electron beam evaporation, and electroplating processes.
[0003] A lithium ion, thin film battery typically includes a
cathode of a lithium-based material such as LiCoO.sub.x, and in
these batteries, increasing the thickness of this cathode film
increases the energy density of the battery. The thicker cathode
film provides greater charge retention and faster charging and
discharging rates. For example, specific energy levels of at least
250 Whr/L can be achieved using a cathode film having a thickness
of 5 microns or higher, as for example is taught in commonly
assigned U.S. patent application Ser. No. 11/007,362 entitled "THIN
FILM BATTERY AND METHOD OF MANUFACTURE" which is incorporated by
reference herein, and in its entirety. The cathode film can be
deposited as an amorphous or microcrystalline film in a single pass
deposition process, and thereafter, crystallized by heating the
film; or deposited in a sequence of thin films to form a thicker
cathode comprising a stack of films.
[0004] However, conventional sputtering processes have several
limitations, which include relatively slow cathode film deposition
rates that make it economically difficult to manufacture thick
cathode films. For example, conventional radio frequency magnetron
sputtering processes often result in deposition rates of around 0.2
microns per hour. Increasing the sputter deposition rates can
result in plasma arcing which affects the quality of deposited
films. These processes also require an impedance matching network
to match the impedance of magnetron and power supply to increase
plasma stability and efficiency. However, it is also often
difficult to identify the correct impedance matching
parameters.
[0005] Thus it is desirable to have a process for depositing
relatively thick cathode films in a short time to provide a battery
having relatively higher energy density or specific energy. There
is also a need for depositing such cathode films with decreased
electrical contact resistances while still maintaining good
deposition rates. There is further a need for depositing lithium
cobalt oxide without arcing or impedance matching problems.
SUMMARY
[0006] A method of depositing lithium metal oxide on a battery
substrate in a sputtering chamber comprising (i) a substrate
support, (ii) first and second sputtering targets each comprising a
sputtering surface of lithium metal oxide and having a backside
surface, and (iii) a first electrode about the backside surface of
the first sputtering target and a second electrode about the
backside surface of the second sputtering target. In the method,
one or more substrates is placed on the substrate support, and
sputtering gas is provided at a pressure in the sputtering chamber.
The sputtering gas is energized by applying an alternating voltage
of AC power to the first and second electrodes so that each
electrode is alternately either an anode or a cathode, the
alternating voltage being applied at a frequency of between about
10 and about 100 kHz. A time varying magnetic field is applied
about each of the sputtering surfaces of the first and second
targets.
[0007] In one version, the deposition method uses first and second
sputtering targets that each comprise lithium metal oxide
comprising lithium cobalt oxide, lithium nickel oxide, lithium
manganese oxide, lithium iron oxide, lithium cobalt nickel oxide,
or a mixtures of transition metals. For example, the first and
second sputtering targets can each consist essentially of lithium
cobalt oxide.
[0008] In another version, the method further comprises applying a
time varying magnetic field comprising a rotational frequency of
between about 0.005 and about 0.1 Hz. In still other versions, each
magnetron comprises a first magnet having a first magnetic flux or
first magnetic field orientation, and a second magnet having a
second magnetic flux or second magnetic field orientation.
DRAWINGS
[0009] These features, aspects and advantages of the present
invention will become better understood with regard to the
following description, appended claims, and accompanying drawings,
which illustrate examples of the invention. However, it is to be
understood that each of the features can be used in the invention
in general, not merely in the context of the particular drawings,
and the invention includes any combination of these features,
where:
[0010] FIG. 1A is a sectional side view of an embodiment of a thin
film battery comprising a battery cell on a substrate;
[0011] FIG. 1B is a sectional side view of another embodiment of a
battery comprising a first battery cell on a first surface of a
substrate and a second battery cell on a second surface;
[0012] FIG. 2 is a top plan view of a thin film battery showing a
plurality of battery cells on a single surface of the
substrate;
[0013] FIG. 3A is a top plan schematic view of an embodiment of a
twin magnetron deposition chamber;
[0014] FIG. 3B is a sectional side schematic view of the twin
magnetron deposition chamber of FIG. 3A;
[0015] FIGS. 4A and 4B are plots of the X-ray diffraction pattern
of a deposited lithium cobalt oxide film before and after
annealing, respectively; and
[0016] FIG. 5 is a plot of the energy capacity versus current for
an embodiment of a thin film battery.
DESCRIPTION
[0017] An embodiment of a thin film battery 20 comprising a single
battery cell 22 enclosed on one side by the substrate 24, is
illustrated in FIG. 1A. The battery 20 can also have single or
multiple battery cells 22a,b on opposing surfaces of a substrate
24, as illustrated for example in FIG. 1B. A further embodiment of
a battery 20 comprising a plurality of battery cells 22a-c on a
planar surface 26 of a substrate 24 is illustrated in FIG. 2.
[0018] Referring back to FIG. 1A, the battery cell 22 comprises a
plurality of battery component films 30. The battery component
films 30 are typically formed on an adhesion layer 32 but can also
be formed directly on the substrate 24. The battery component films
30 cooperate to form a battery capable of receiving, storing, and
discharging electrical energy. The films 30 can be employed in a
number of different arrangements, shapes, and sizes. The battery
component films 30 includes at least a pair of electrode films on
either side of an electrolyte film 40. The electrode films can
include one or more of a cathode current collector film 34, a
cathode film 38 an anode film 42, and an anode current collector
film 44, which are all inter-replaceable. For example, the battery
20 can include (i) a pair of cathode and anode films or a pair of
current collector films, (ii) both the anode/cathode films and the
current collector films, or (iii) various combinations of these
films, for example, a cathode film and an anode and anode current
collector film but not a cathode current collector film, and so on.
The exemplary versions of the battery 20 illustrated herein are
provided to demonstrate features of the battery and to illustrate
their processes of fabrication; however, it should be understood
that these exemplary battery structures should not be used to limit
the scope of the invention, and alternative battery structures as
would be apparent to those of ordinary skill in the art are within
the scope of the present invention.
[0019] Referring to FIG. 1B, the battery 20 can include a first
battery cell 22a on a first planar surface 26 of the substrate 24,
and a second battery cell 22b on a second planar surface 27 of the
same substrate 24. Each battery cell 22a,b comprises a plurality of
battery component films 30a,b that include one or more adhesion
films 32a,b; first or cathode current collector films 34a,b;
cathode films 38a,b; electrolyte films 40a,b; anode films 42a,b;
and second or anode current collector films 44a,b. This version of
the battery 20 with two opposing cells 22a,b can be formed using
the same processes used to form the battery 20 with the single cell
22 (FIG. 1A), by flipping over the substrate 24 to form the battery
film components 30b of the second battery cell 22b, during or after
processing of the first battery cell 30a. Alternatively, the
battery film components 30b of the second battery cell 22b can be
formed simultaneously with the battery film components 30a of cell
22a, using chambers having multiple process zones, an exemplary
version of which is described in copending U.S. patent application
Ser. No. 11/681,754, filed Mar. 2, 2007, which is incorporated
herein by reference and in it's entirety.
[0020] The battery component films 30 are formed on a battery
substrate 24 to fabricate a battery 20 in several fabrication
steps, which can be performed separately or as a combination of
steps. In a first step, a suitable substrate 24 is selected, the
substrate 24 being a dielectric having sufficient mechanical
strength to support battery component films 30, and typically
having a surface suitable for the deposition of thin films.
Suitable substrates 24 can be made from, for example, ceramics such
as aluminum oxide or silicon dioxide; metals such as titanium and
stainless steel; semiconductors such as silicon; or even polymers.
One desirable substrate comprises a crystalline sheet formed by
cleaving the planes of a cleavable crystalline structure. The
cleavable crystalline structure splits along definite planes to
create flat surfaces, and can include (i) basal cleavage crystals
having cleavage planes parallel to the base of a crystal or to the
plane of the lateral axes; (ii) cubic cleavage crystals having
cleavage planes parallel to the faces of a cube, (iii) diagonal
cleavage crystals which has cleavage planes parallel to a diagonal
plane; (iv) lateral cleavage crystals which have cleavage planes
parallel to the lateral planes; (v) octahedral, dodecahedral, or
rhombohedral cleavage crystals in which cleavage occurs parallel to
the faces of an octahedron, dodecahedron, or rhombohedron
(respectively); and (vi) prismatic cleavage crystals in which
cleavage occurs parallel to a vertical prism. The crystalline
cleaving structure can be, for example, mica or graphite. Mica can
be split into thin crystal sheets having thicknesses of less than
about 100 microns or even less than about 25 microns, as described
in a U.S. Pat. No. 6,632,563 "THIN FILM BATTERY AND METHOD OF
MANUFACTURE", filed on Sep. 9, 2000, which is incorporated by
reference herein and in its entirety. In one version, an array of
substrates 24 that each comprise a mica sheet is used in the
fabrication process. Each mica sheet can be a rectangle which is
sized, for example, having dimensions from about 10 mm to about 200
mm.
[0021] The substrate 24 of mica or other materials, can optionally
be annealed to temperatures sufficiently high to clean the
deposition surface, such as the cleavage plane surface, by
burning-off contaminants and impurities, such as organic materials,
water, dust, and other materials formed or deposited on the planar
surfaces 26, 27 of the substrate 24; or even heated to temperatures
high enough to remove any water of crystallization present within
the substrate. The annealing temperatures can be from about 150 to
about 600.degree. C., even at least about 400.degree. C., or even
at least about 540.degree. C. The annealing process can be
conducted in an oxygen-containing gas, such as oxygen or air, or
other gas environments, for about 10 to about 120 minutes, for
example, about 60 minutes. The cleaning process can also be
conducted in an oxygen plasma containing cleaning step. Suitable
annealing and other cleaning processes are described, for example,
in U.S. patent application Ser. No. 11/681,754 which is
incorporated by reference herein and in its entirety.
[0022] After the substrate cleaning and annealing step, a plurality
of battery component films 30 are deposited on the surfaces 26, 27
of the substrate 24 to form battery cells 22 that can generate or
store electrical charge. The component films 30 are typically
formed using a PVD sputter deposition process, under controlled
process conditions and in one or more sputtering chambers.
[0023] In one exemplary fabrication method, one or more battery
component films 30 are deposited onto the battery substrate 24
using a sputtering chamber 100, as shown, for example, in FIGS. 3A
and 3B. The chamber 100 comprises a circular sidewall 108, a
chamber ceiling 110 and a lower wall 112 which surrounds and
encloses a process zone 114. The chamber sidewall 108 can be
electrically isolated from the chamber ceiling 110 and the lower
wall 112 and can even be electrically grounded. The chamber walls
are typically composed of stainless steel, steel or aluminum. In
one version, the sputtering chamber 100 is separated from a loading
chamber by a slit valve 115 for passage and transport of substrates
24 into and out of the chamber 100. The slit valve 115 can lead to
a dry box 117 for loading the substrates 24. Substrates 24 are
placed onto a substrate holding fixture which is then carried into
the sputtering chamber by a conveyer, the substrate holding fixture
is electrically isolated from the chamber walls.
[0024] One or more substrate supports 104, or 104a,b, are
positioned about the peripheral edge of the chamber 100 for
receiving substrates 24. The substrate supports 104 or 104a,b are
oriented to face inward and towards a radially inward region 116 of
the chamber 100. In one version, the substrate supports 104 can be
moved during sputter processing, thereby allowing the substrates 24
to be rotated about the periphery of the sputtering chamber 100 or
even around a circumference that encloses the plurality of
sputtering targets 102 a-d. Rotation of the substrates 24 during
processing increases the deposition uniformity. In a further
version, the substrate support 104 is electrically isolated from
the chamber sidewall 108 and sputtering targets 102. The substrate
supports 104 can be biased at a negative voltage relative to the
plasma, or even relative to the time averaged potential of the
cathodes. The negatively biased substrate support 104 serves to
attract the positively charged ions and sputtered material from the
plasma zone 114. In one version the substrate supports 104 are
biased by a biasing power supply. The biasing power supply provides
a pulsed DC voltage bias of from about -5 to about -200 V or even
about -40 V between the substrate supports 104 and the radially
inward region 116 of the chamber 100. The pulsed biasing voltage
has a duty cycle of from about 10% to about 90%, or even about 30%.
The substrate support 104 can also include a heater and heating
control circuitry to maintain the substrate 24 at an appropriate
processing temperature. In one version the substrate 24 is
maintained at a temperature of from about 50 to about 200.degree.
C. during processing.
[0025] A plurality of sputtering targets 102 are mounted in the
radially inward region 116 of the chamber 100. The sputtering
targets 102 can comprise lithium metal oxide, such as for example,
lithium cobalt oxide, lithium nickel oxide, lithium manganese
oxide, lithium iron oxide, or even lithium oxides comprising
mixtures of transition metals such as for example, lithium cobalt
nickel oxide. The sputtered target material deposits onto a
plurality of battery substrates 24 in the chamber. The targets 102
comprise an even number of targets such as for example two, four,
six or even ten or more targets. In one version, the number of
targets 102 and the size of the chamber 100 is scaleable to
accommodate a larger batch of substrates 24 for processing. The
sputtering targets 102 can be rectangular or cylindrical. The
cylindrically shaped targets are mounted to cylindrically shaped
magnetrons 106. These magnetrons 106 can be configured to
self-rotate during the deposition process, exposing fresh
sputtering surface and reducing localized heating of the attached
targets 102, thereby increasing the target lifespan, in on-time
plasma hours, by from 15% to 70%.
[0026] One or more magnetrons 106 are provided in the radially
inward region 116 of the chamber 100. The magnetrons 106 are
capable of generating a time varying magnetic field at a particular
location in the chamber 100. Each magnetron 106 comprises a set of
rotatable magnets or electromagnets. The magnetron 106 can be a
single structure or a set of structures. In one version, the
magnetron 106 includes a first rotatable magnet assembly 146a which
is rotated behind a backside surface of a first sputtering target
102a, and a second rotatable magnet assembly 146b which is rotated
behind the backside surface of a second sputtering target 102b.
[0027] The rotatable magnet assembly comprises a magnet that is
capable of being rotated about a central axis. In the version shown
in FIG. 3B a first magnet 148 having a first magnetic flux or
magnetic field orientation, and one or more peripheral magnets 150
having a second magnetic flux or magnetic field orientation are
mounted to a support plate 152. The support plate 152 is rotated by
an axle 154 that is powered by a motor (not shown). In one version,
the ratio of the first magnetic flux to the second magnetic flux is
at least about 1:2, for example, from about 1:3 to about 1:8, or
even about 1:5. This allows the magnetic field from the peripheral
magnets 150 to extend deeper into the chamber 100. For example, the
second magnetic field orientation can be generated by positioning
the peripheral magnets 150 so that their polarity direction is
opposite to the polarity direction of the central magnets 150. In
one embodiment, the first and second rotatable magnet assemblies
146a,b are rotated at a rotational frequency of between about 0.005
and about 0.1 Hz, whereby a time varying magnetic field is provided
about the surface of the first and second targets 102.
[0028] The magnetron 106 can also be connected to an AC power
source 118 that provides an alternating voltage to excite the
sputtering gas within the chamber 100. When the chamber comprises
twin magnetrons 106a,b, the power source 118 serves to bias the
twin magnetrons 106a,b relative to each other. For example, when
the first magnetron 106a is on a negative potential relative to the
second magnetron 106b, the first magnetron 106a acts as the
sputtering cathode, while the second magnetron 106b acts as an
anode. In the present example, the magnetrons 106 are powered with
an AC voltage that is between 200V and 1200V and has a power of
between 1 kW and 20 kW. During processing the momentary cathode
generates secondary electrons which are accelerated towards the
anode and neutralize positive surface charges having been built up
in insulating areas during the negative half cycle. The magnetrons
106 can be mounted to the chamber ceiling 110 or lower wall 112.
Typically, a sputtering target is attached to each magnetron 106.
The magnetron 106 transmits the voltage to the attached sputtering
target 102, and the sputtering gas between the AC biased targets
102 is excited. In one version, the chamber 100 comprises twin
magnetrons which are each connected to a target 102.
[0029] In one embodiment, twin magnetrons 106a,b are operated by a
voltage or current maintained at a mid-frequency level, which is a
frequency of from about 10 to about 100 kHz. It has been found that
the mid-frequency sputtering process desirably reduces or
eliminates co-excitation modes that would otherwise occur between
the twin magnetrons 106. Absence of the co-excitation mode results
in reduced arcing of the sputtering targets 102, thereby increasing
the lifespan of the targets 102, and also improving the quality of
the deposited films. Arcing is often initiated by electrical
breakdown of the insulating layer on the magnetron cathode.
However, application of a mid-frequency power from a mid-frequency
AC power source 118 to a twin-magnetron arrangement, reduces
charging up of the insulating layer and resultant plasma process
instabilities. For targets 102 comprising lithium cobalt oxide,
sputtered films can be produced in this manner without arcing over
almost the entire lifetime of the target 102. Thus higher power
levels can be applied to the sputtering targets 102. As a result,
the deposition process is more continuous and results in high
quality films and higher deposition throughput. For example, the
mid-frequency dual magnetron process provides a deposition rate of
from about 0.2 to about 4 microns/hour.
[0030] The chamber 100 also has a plurality of cathodes 120, as
shown for example in FIGS. 3A and 3B. Each cathode 120 is formed by
binding a target 102 to a magnetron 106, which provides an
unbalanced magnetic field about the surface of the target 102 and
results in a more continuous bombardment of the target during
sputtering.
[0031] The chamber 100 can further include a plurality of ion
sources 122 that are capable of supplying ionized gas for in-situ
active cleaning and activation of the substrates 24. In the
embodiment shown in FIG. 3A, the ion sources 122 are located
adjacent to the targets 102. For example, the ion sources 122 can
be located within a radially inward region 116 of the chamber 100,
or even between the targets 102. During the cleaning process, a
cleaning gas is provided to the chamber 100 such as for example,
argon and oxygen. A voltage is supplied between the radially inward
region of the chamber 116 and the substrate supports 104, such that
the cleaning gas ions are drawn towards and bombard the surface of
the substrate 24. Typical ion-source cleaning processes are erosive
to, and can decrease the lifespan of, the sputtering target 102. In
one embodiment, a fixture (not shown) covering half of the surface
of a target 102 can be rotated to first and second orientations
within the chamber 100. In the first orientation, the exposed part
of the targets 102 face the substrates 24 for film deposition and
in the second orientation, the exposed part of the targets 102
faces the center for in-situ active substrate cleaning, thereby
decreasing target contamination.
[0032] The chamber 100 is connected to a gas supply 123, gas
distributor 126 and gas exhaust 130, which supply and control the
pressure and concentration of process gas within the chamber 100.
The process gas mixture is controlled by first evacuating the
chamber 100 and then introducing controlled amounts of process gas
into the chamber 100. In one version the chamber 100 is evacuated
to a pressure of less than about 5.times.10.sup.-5 Torr or even
less than about 2.times.10.sup.-5 Torr prior to introduction of the
sputtering gas. Sputtering process gas is introduced into the
chamber and maintained at a pressure of from about 1.1 to about 15
mTorr. In one version the sputtering gas comprises argon and
oxygen. The argon provides stable plasma and oxygen can prevent
oxygen loss in the targets or the deposited films during the
process. The sputtering argon gas is maintained in the chamber 100
at a pressure of from about 1 to about 10 mTorr. The sputtering
oxygen gas is maintained in the chamber 100 at a pressure of from
about 0.1 to about 5 mTorr.
[0033] The twin magnetrons are connected to a power source 118,
such as for example, an AC power supply 134. The AC power supply
134 and provides an alternating voltage having a wave form that is
approximately sinusoidal and that has a frequency in the
mid-frequency range of between about 10 and about 100 kHz, or even
about 40 kHz. During processing, the power supply 134 energizes the
process gas by applying a voltage bias across the first and second
magnetrons 106a,b at a frequency of from about 10 to about 100 kHz,
or even from about 20 to about 80 kHz. The voltage bias can also be
applied at a power level of at least about 1 kW, or even at a power
level of from about 3 kW to about 20 kW. In one exemplary process,
the power supply 134 supplies a power density to the surface of the
targets 102 that is at least 0.1 W/cm.sup.2 or even between about
0.1 W/cm.sup.2 and about 20 W/cm.sup.2.
[0034] The chamber 100 is controlled by a controller 119 that
comprises program code having instruction sets to operate
components of the chamber 100 to process substrates 24 in the
chamber 100. For example, the controller 119 can comprise a
substrate positioning instruction set to operate a substrate
transport mechanism to position a substrate 24 in the chamber 100;
a gas flow control instruction set to operate the flow control
valves 125 to set a flow of gas to the chamber 100; a gas pressure
control instruction set to operate the exhaust 130 to maintain a
pressure in the chamber 100; power supply control instruction sets
such as a gas energizer control instruction set to operate the
electrode power supply 134 to set a gas energizing power level and
a DC power supply control instruction set to operate a DC power
supply 121 to provide a DC voltage bias to the substrate support
104; a temperature control instruction set to control temperatures
in the chamber 100; and a process monitoring instruction set to
monitor the process in the chamber 100, for example by monitoring
temperatures or pressure via one or more sensors 137 that are
within the chamber.
[0035] The mid-frequency twin magnetron sputtering process is
particularly efficient at deposition of lithium cobalt oxide films
and can provide deposition rates of between 0.2 and 4 microns per
hour. The sputtering rate is sensitive to adjustments in power,
processing gas pressure and DC bias voltage. In one exemplary
process, two or four LiCoO.sub.2 targets are installed in the
chamber. The substrate is placed in the chamber which is pumped
down to below 5.times.10.sup.-5 Torr. A suitable substrate 24
comprises a 35 mm.times.62 mm sheet of mica. Process gas, such as
for example, argon and oxygen, are introduced into the chamber 100
to serve as the sputtering gas. The sputtering gas comprising argon
is maintained in the chamber 100 at a pressure from about 1 to
about 10 mTorr and in one version about 2 mTorr, and oxygen is
maintained at the pressure of from 0.1 to 5 mTorr and in one
version about 0.75 m Torr. Sputtering is performed by applying an
0.1 to 20 W/cm.sup.2 power density to each target 102 and a pulsed
DC voltage bias of between -5 and -100 V or even about -40 V
between the substrate supports 104 and the radially inward region
116 of the chamber 100. The duty cycle is between 10% and 90%, even
at 30%. The substrate 24 is maintained at a temperature of from
about 50 to about 200.degree. C. during processing. In one version
the voltage bias is applied for a sufficient time to deposit a
lithium cobalt oxide film having a thickness of from about 0.25 to
about 0.75 of the total thickness of a stack of films formed on the
substrate 24.
[0036] The deposition rates obtained from the mid-frequency twin
magnetron process were found to be higher than the deposition rates
obtained by conventional sputtering processes, as illustrated by
the following examples:
Example I
[0037] Four LiCoO.sub.2 targets were installed in the chamber 100 a
mica substrate was placed in the chamber onto a substrate support
104 in the chamber 100. The chamber 100 was pumped down to
2.times.10.sup.-5 Torr prior to introduction of the sputtering gas.
Sputtering gas comprising argon and oxygen were introduced into the
chamber 100. The argon gas was maintained in the chamber 100 at a
pressure of about 8.2 mTorr and the oxygen gas was maintained in
the chamber 100 at a pressure of about 0.75 mTorr. Sputtering was
performed by applying an oscillating voltage bias between the
targets, the oscillation having a frequency of about 40 kHz. The
power applied to each pair of targets was about 3 kW, and with a
density of about 3.5 W/cm.sup.2. A pulsed DC voltage bias of about
-40 V was applied between the substrate support 104 and the
radially inward region 116 of the chamber 100 with a duty cycle of
about 30%. The substrate 24 was maintained at a temperature of
about 120.degree. C. during processing. The as-deposited lithium
cobalt oxide film had a thickness of 3.5 microns after 5 hours
deposition. The deposition rate was found to be about 0.7 microns
per hour. The volume deposition rate per kilowatt hour was about
0.050 cm.sup.3/kWhr.
Example II
[0038] For comparison, a conventional RF sputtering process and
deposition rate for lithium cobalt oxide film with a single
magnetron chamber are presented.
[0039] A single LiCoO.sub.2 target was installed in the chamber and
a substrate was placed onto a substrate support in the chamber. The
chamber was pumped down to 1.times.10.sup.-5 Torr prior to
introducing the sputtering gas. A process gas comprising argon and
oxygen were introduced into the chamber. The argon gas was
maintained in the chamber at a pressure of about 8.2 mTorr and the
oxygen gas was maintained in the chamber at a pressure of about
0.75 mTorr. Sputtering was performed by applying an oscillating
voltage bias to the target, with a frequency of about 13.5 MHz. A
power density of 1.8 W/cm.sup.2 was thereby applied to the target.
The substrate 24 was maintained at a temperature of about
120.degree. C. during processing. The as-deposited lithium cobalt
oxide film had a thickness of 2 microns after 5 hours deposition.
The deposition rate of the conventional RF system was found to be
about 0.4 microns/hr. The volume deposition rate per kilowatt hour
was about 0.016 cm.sup.3/kWhr. In addition, the RF deposition
process was limited in the amount of power that could be applied to
the target because the system was prone to arcing at higher power
densities.
[0040] As supported in the examples above, the volume deposition
rate per kilowatt hour of the dual-magnetron mid-frequency process
was found to be 3.1 times higher than the volume deposition rate
per kilowatt hour of the RF process.
[0041] The deposited film can be annealed to reduce or even
eliminate point defects in the crystal lattice by heating the
substrate 24 to a temperature that is sufficient for annealing for
example, to a temperature of from about 200 to about 500.degree. C.
The substrate 24 can be annealed in-situ by direct heating from a
temperature controlled substrate support 104 or by radiation
heating from an infrared radiation source (not shown). In another
embodiment, the substrate 24 is removed and annealed in a separate
chamber or even outside the chamber environment.
[0042] Unexpectedly and surprisingly, LiCoO.sub.x films deposited
using a mid-frequency, dual magnetron process were found to anneal
sufficiently well at a temperature of only about 400.degree. C., as
compared to a previous anneal temperature of about 540.degree. C.
for the conventionally deposited film. It is believed that this
reduction in the temperature of annealing is because the
as-deposited film contains fewer lattice defects. The reduction in
lattice defects may be caused by a higher plasma density during the
mid-frequency twin-magnetron deposition process, which may break
down the sputtered material into smaller pieces.
Example III
[0043] A LiCoO.sub.x film fabricated according to the present
method and without an additional annealing step comprises
LiCoO.sub.2 which is crystalline with a strong (012) preferred
orientation and with a smaller amount of (003) oriented grains.
FIG. 4A shows a typical x-ray two theta diffraction pattern 138 of
the as-deposited LiCoO.sub.2 film. The large peak 140, located at a
scattering angle of about 39.degree., and the smaller peak 142,
located at a scattering angle of about 19.degree., show that the
film is highly crystalline and with a (012) and (003) preferred
orientation. The substrate was slightly tilted when taking x-ray
diffraction in order to suppress the diffraction peaks from an
underlying mica substrate to better reveal the crystalline
properties of the LiCoO.sub.2 film. It is believed that the
crystalline material was deposited due to a combination of plasma
heating, oxygen activation and plasma enhanced nucleation and
growth processes. The as deposited crystalline material was a good
cathode material.
Example IV
[0044] Optionally, the film formed on the substrate may be annealed
at 150 to 600.degree. C. to further improve the quality of the
cathode film. An x-ray diffraction pattern 136 of crystalline
LiCoO.sub.2 film after annealing at 400.degree. C. for 10 hours is
shown in FIG. 4B. The larger intensity peak 148, located at a
scattering angle of about 37.5.degree. shows a strong (101)
preferred orientation and the smaller intensity peak 150, located
at a scattering angle of about 40.degree. shows a small amount of
(012) oriented grains. The annealing step was found to increase the
battery capacity by 10 to 20%, increase the charge and discharge
current by more than 50%, and improve the resistance to moisture.
It is believed that these attributes arise from the elimination of
point defects and the reduction of electrical contact resistances
in the cathode material.
Example V
[0045] In one version, the area of the battery is 2.9 cm.sup.2. The
mica substrate is 20 microns thick, and overall thickness of the
battery is around 50 microns. The battery is sealed with Surlyn
(epoxy) for temporary protection against the oxidizing environment.
FIG. 5 shows the discharge curves of four test batteries, each
comprising a LiCoO.sub.x film deposited by the method described
above (with 400.degree. C. annealing). The curves indicate that the
higher the discharge current, the lower the capacity, which is
consistent with previous data obtained from LiCoO.sub.x film
batteries formed using an RF deposition process. This Surlyn sealed
battery has an energy density of around 62.4 wh/l.
[0046] While a particular sequence of process steps is described to
illustrate an embodiment of the process, it should be understood
that other sequences of process steps can also be used as would be
apparent to one of ordinary skill in the art.
[0047] The above methods or other deposition methods can be used to
deposit one or more of the component films 30, which in one
embodiment include an adhesion film 32. The adhesion film 32 is
deposited on the planar surface 26 of the substrate 24 to improve
adhesion of overlying battery component films 30 (FIG. 1A). The
adhesion film 32 can comprise a metal or metal compound, such as
for example, aluminum, cobalt, titanium, other metals, or their
alloys or compounds thereof; or a ceramic oxide such as, for
example, lithium cobalt oxide. Exemplary process conditions for
deposition of a titanium adhesion film 32 comprise: argon
maintained at a pressure of 2 mTorr; DC (direct current) sputtering
plasma at a power level of 1 kW, a deposition time of 30 seconds, a
titanium target size of 5.times.20 inches, and a
target-to-substrate distance of 10 cm. In the version shown in FIG.
1B, after deposition of a first adhesion film 32a on the first
planar surface 26 of the substrate 24, the substrate 24 is flipped
over and a second adhesion film 32b is deposited on the second
planar surface 27 which forms the other side of the substrate. The
adhesion film 32 can be deposited on the substrate 24 not only to
cover the area under the subsequently deposited battery cells 22a-c
and their battery component films 30 but also the area 36 extending
beyond the battery component films 30, as described in
aforementioned U.S. patent application Ser. No. 11/681,754. The
adhesion film 32 is typically deposited in a thickness of from
about 100 to about 1500 angstroms.
[0048] A cathode current collector film 34 is formed on the
adhesion film 32 to collect the electrons during charge and
discharge process. The cathode current collector film 34 typically
comprises a conductor such as, for example, aluminum, platinum,
silver or gold or even the same metal as the adhesion film 32 in a
thickness that is sufficient to provide the desired electrical
conductivity. The first current collector film 34 typically has a
thickness that is from about 0.05 microns to about 2 microns. The
cathode current collector film 34a-c can be formed as a pattern of
features 68a-c, as illustrated in FIG. 2, that each comprise a
spaced apart discontinuous region that covers a small region of the
adhesion film 32. The features 68a-c are over the covered regions
71a-c of the adhesion film 32, and adjacent to the features 68a-c
are exposed regions 70a-c of the adhesion film 32. To deposit the
patterned film 34a-c, a patterned mechanical mask is placed on top
of the substrate 24, and a first current collector film 34 of
platinum is deposited by DC magnetron sputtering to form the
features 68a-c between the patterned mask regions. Exemplary
process conditions for argon sputter deposition of a platinum
cathode current collector film 34a-c comprise a gas pressure of 5
mTorr to form a DC plasma at a power level of 40 Watts for 10
minutes.
[0049] After forming the features 68a-c on the adhesion film 32,
the adhesion film with its covered regions 71a-c below the
patterned features 68a-c and exposed surface regions 70a-d, is then
exposed to an oxygen-containing environment and heated to
temperatures of from about 200.degree. C. to about 600.degree. C.,
for example, about 400.degree. C., for about an hour, to oxidize
the exposed regions 70a-d of titanium that surround the deposited
platinum features but not the titanium regions covered and
protected by the platinum features. The resultant structure,
advantageously, includes not only the non-exposed covered regions
71a-c of adhesion film 32 below the features 68a-c of the current
collector film 38, but also oxygen-exposed or oxidized regions
70a-d which form non-conducting regions that electrically separate
the plurality of battery cells 22a-c formed on the same substrate
24.
[0050] A cathode film 38 comprising an electroactive material is
then formed over the current collector film 34. In one version, the
cathode film 38 is composed of lithium metal oxide, such as for
example, lithium cobalt oxide, lithium nickel oxide, lithium
manganese oxide, lithium iron oxide, or even lithium oxides
comprising mixtures of transition metals such as for example,
lithium cobalt nickel oxide. Other types of cathode films 38 that
may be used comprise amorphous vanadium pentoxide, crystalline
V.sub.2O.sub.5 or TiS.sub.2. In one example, the cathode film 38
comprises crystalline lithium cobalt oxide, which in one version,
has the stoichiometric formula of LiCoO.sub.2. The cathode film 38
can be fabricated in a single continuous deposition step or using a
multiple sequential deposition and stress reducing annealing step
that is performed at a temperature of between about 150 and
600.degree. C. Typically, the cathode film 38 or cathode film stack
has a thickness of at least about 5 microns, or even at least about
10 microns. In one exemplary embodiment, the cathode film 38 is
deposited using a twin-magnetron, mid-frequency sputtering process,
as described above. The twin-magnetron mid-frequency process is
particularly well suited for deposition of the cathode film 38
because of it's comparatively high sputtering rates for lithium
metal oxides. The cathode film 38 can also be annealed in a defect
reducing step to temperatures of from about 150 to about
700.degree. C., for example, by about 400.degree. C., to further
improve the quality of the cathode film 38 by reducing the amount
of defects.
[0051] An electrolyte film 40 is formed over the cathode film 38.
The electrolyte film 40 can be, for example, an amorphous lithium
phosphorus oxynitride film, also known as a LiPON film. In one
embodiment, the LiPON has the stoichiometric form
Li.sub.xPO.sub.yN.sub.z in an x:y:z ratio of about 2.9:3.3:0.46. In
one version, the electrolyte film 40 has a thickness of from about
0.1 micron to about 5 microns. This thickness is suitably large to
provide sufficiently high ionic conductivity and suitably small to
reduce ionic pathways to minimize electrical resistance and reduce
stress.
[0052] An anode film 42 formed over the electrolyte film 40. The
anode film 42 can be the same material as the cathode film 38, as
already described. A suitable thickness is from about 0.1 micron to
about 20 microns. In one version, anode film 42 is made from
lithium which is also sufficiently conductive to also serve as the
anode current collector film, and in this version the anode film 42
and anode current collector film 44 are the same. In another
version, the anode current collector film 44 is formed on the anode
film 42, and comprises the same material as the cathode current
collector film 34 to provide a conducting surface from which
electrons may be dissipated or collected from the anode film 42.
For example, in one version, the anode current collector film 44
comprises a non-reactive metal such as silver, gold, platinum, in a
thicknesses of from about 0.05 microns to about 5 microns.
[0053] After the deposition of all the battery component films 30,
a variety of protective layers or electrically conducting layers
can be formed over the battery component films 30 to provide
protection against environmental elements. In one example, the
protective layer comprises a plurality of polymer and ceramic
layers that are superimposed on each other. In another example, a
portion of the cathode current collector film 34 or anode current
collector film 44 that extends out from under a battery cell 22
forms a contact portion that is used to connect the battery cell 22
or the battery 20 to the external environment. This contact portion
is coated with an electrically conducting barrier layer. The layers
can protect the battery cell 22 during pulsed laser cutting of the
individual battery cells from an array of cells formed on a larger
mica substrate. For example, the electrically conducting barrier
layer is formed in a thickness sufficiently large to prevent the
pulsed laser beam from penetrating therethrough.
[0054] The thin film battery 20 can also be fabricated to provide a
plurality of battery cells 22a-c on a single substrate 24. The
battery cells 22a-c can be arranged horizontally across a single
substrate surface 26 or fabricated on the front surface 26 and
backside surface 27 of a battery substrate 24 to substantially
increase the energy density and capacity of the battery cell 22.
Suitable battery configurations, protective layers, and packaging,
are described in for example, U.S. patent application Ser. No.
11/090,408, filed on Mar. 25, 2005, entitled "THIN FILM BATTERY
WITH PROTECTIVE PACKAGING" by Krasnov et al., which is incorporated
by reference herein and in its entirety.
[0055] While a particular sequence of process steps and chamber
configuration is described to illustrate an embodiment of the
process, it should be understood that other sequences of process
steps can also be used as would be apparent to one of ordinary
skill in the art. For example the order of deposition of the
component films 30 can be interchanged or other films can be
deposited on top of or in between films of the battery 20. Also,
other configurations of the chamber 100 are possible for example
the chamber can have more pairs of cathodes 120, such as 3, 4, or
more. Therefore, the spirit and scope of the appended claims should
not be limited to the description of the preferred versions
contained herein.
* * * * *