U.S. patent application number 11/768652 was filed with the patent office on 2007-11-08 for hollow cathode sputtering apparatus and related method.
This patent application is currently assigned to ENERGY PHOTOVOLTAICS, INC.. Invention is credited to Alan E. Delahoy, Sheyu Guo.
Application Number | 20070256926 11/768652 |
Document ID | / |
Family ID | 34116223 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070256926 |
Kind Code |
A1 |
Delahoy; Alan E. ; et
al. |
November 8, 2007 |
HOLLOW CATHODE SPUTTERING APPARATUS AND RELATED METHOD
Abstract
The present invention provides an improved hollow cathode method
for sputter coating a substrate. The method of the invention
comprises providing a channel for gas to flow through, the channel
defined by a channel defining surface wherein one or more portions
of the channel-defining surface include at least one target
material. Gas is flowed through the channel wherein at least a
portion of the gas is a non-laminarly flowing gas. While the gas is
flowing through the channel a plasma is generated causing target
material to be sputtered off the channel-defining surface to form a
gaseous mixture containing target atoms that is transported to the
substrate. In an important application of the present invention, a
method for forming oxide films and in particular zinc oxide films
is provided.
Inventors: |
Delahoy; Alan E.; (Rocky
Hill, NJ) ; Guo; Sheyu; (Wallingford, PA) |
Correspondence
Address: |
BROOKS KUSHMAN P.C.
1000 TOWN CENTER
TWENTY-SECOND FLOOR
SOUTHFIELD
MI
48075
US
|
Assignee: |
ENERGY PHOTOVOLTAICS, INC.
276 Bakers Basin Road
Lawrenceville
NJ
08648
|
Family ID: |
34116223 |
Appl. No.: |
11/768652 |
Filed: |
June 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10635344 |
Aug 6, 2003 |
7235160 |
|
|
11768652 |
Jun 26, 2007 |
|
|
|
Current U.S.
Class: |
204/192.1 |
Current CPC
Class: |
H01J 37/342 20130101;
C23C 14/14 20130101; C23C 14/34 20130101; H01J 37/34 20130101; H01J
37/32449 20130101; C23C 14/081 20130101; C23C 14/345 20130101; C23C
14/228 20130101; C23C 14/08 20130101 |
Class at
Publication: |
204/192.1 |
International
Class: |
C23C 14/34 20060101
C23C014/34 |
Claims
1. A method for sputter coating a substrate in a sputter coating
reactor, the method comprising: a) providing a channel for gas to
flow through, the channel defined by a channel defining surface
wherein one or more portions of the channel-defining surface
include at least one target material; b) flowing gas through the
channel wherein at least a portion of the gas is a non-laminarly
flowing gas; and c) generating a plasma, wherein the target
material is sputtered off the channel-defining surface to form a
gaseous mixture containing target atoms that is transported to the
substrate.
2. The method of claim 1 wherein the non-laminarly flowing gas is
formed by turbulence.
3. The method of claim 1 wherein the non-laminarly flowing gas is
formed by flowing a first portion of gas in a first direction and a
second portion of gas in a second direction wherein the first
direction and the second direction are substantially
non-parallel.
4. The method of claim 1 wherein the non-laminarly flowing gas is
formed by flowing the gas through at least two orifices such that
at least two gas streams emerging from the at least two orifices
are flowing in substantially non-parallel directions.
5. The method of claim 1 wherein the non-laminarly flowing gas is
formed flowing the gas through a series of orifices such that
adjacent orifices direct the gas in non-parallel directions.
6. The method of claim 1 wherein the non-laminarly flowing gas is
formed by turbulence with a Reynolds number greater than 2000.
7. The method of claim 1 wherein the channel-defining surface is
part of a cathode.
8. The method of claim 1 wherein the channel has a rectangular
cross section.
9. The method of claim 1 wherein the target material is in
electrical contact with a DC potential, a DC potential with a
superimposed AC potential, or a pulsed DC potential.
10. The method of claim 1 wherein the target material is in
electrical contact with a pulsed DC power source that is an
asymmetric bipolar pulsed DC power supply.
11. The method of claim 1 wherein the at least one target material
comprises a metal or metal alloy.
12. The method of claim 1 wherein the at least one target material
comprises a component selected from the group consisting of zinc,
copper, aluminum, silicon, tin, indium, magnesium, titanium,
chromium, molybdenum, nickel, yttrium, zirconium, niobium, cadmium,
and mixtures thereof.
13. The method of claim 1 wherein the at least one target material
includes a first target material and a second target material, the
first target material being opposite the second and wherein the
first target material and the second target material are the same
or different.
14. The method of claim 13 wherein the first target material and
the second target material comprise a metal or a metal alloy.
15. The method of claim 13 wherein the first target material and
the second target material independently include a component
selected from the group consisting of zinc, copper, aluminum,
silicon, tin, indium, magnesium, titanium, chromium, molybdenum,
nickel, yttrium, zirconium, niobium, cadmium, and mixtures
thereof.
16. The method of claim 13 wherein the at least one target material
includes a third target material and a fourth target material, the
third target material being opposite the fourth target material and
wherein the first target material, the second target material, the
third target material, and the fourth target material are the same
or different.
17. The method of claim 13 wherein the at least one target material
includes a first electrically insulating block and a second
electrically insulating block, the first insulating block being
opposite the second insulating.
18. The method of claim 13 further comprising introducing a
reactive gas into the sputter coating reactor.
19. The method of claim 18 wherein the reactive gas is introduced
at a position located outside of the channel from which the gaseous
mixture emerges.
20. The method of claim 18 wherein the reactive gas contains an
atom selected from the group consisting of oxygen, nitrogen,
selenium, sulfur, iodine, hydrogen, carbon, boron, and phosphorus.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of pending U.S.
application Ser. No. 10/635,344 filed Aug. 6, 2003. This
application is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is related to methods and related
apparatus for depositing films on a substrate by hollow cathode
sputtering. More particularly, the present invention relates to
methods and apparatus for depositing oxide and other films by
hollow cathode sputtering.
[0004] 2. Background Art
[0005] Numerous methods are known for depositing thin films on a
substrate. Such methods include, for example, sputtering, vacuum
evaporation, chemical vapor deposition, and the like. Typical
substrates that are coated with thin films are glass, ceramics, and
silicon wafers. Vacuum evaporation is a low pressure deposition
technique in which a material is vaporized by heating. Vacuum
evaporation is a line of sight deposition technique in which the
vaporized material is then radiated out in straight lines from the
source. Chemical vapor deposition is a thin film deposition
technique in which a reactive gaseous mixture is heated over a
substrate. The elevated temperature causes a chemical reaction to
occur from which a desired film is formed. Chemical vapor
deposition can be undesirable because of contamination of the
deposited films.
[0006] Sputtering is a low pressure deposition process in which a
plasma containing gas ions and electrons is created by the action
of an electric field on gas that is introduced into a deposition
chamber. The electric field may be formed by either a dc or rf
voltage bias. These ions are accelerated towards a target from
which material is removed. This removed material is ultimately
deposited on a nearby substrate. Reactive sputtering is a further
refinement of the sputtering process in which a reactive gas such
as nitrogen, oxygen, hydrogen, H.sub.2O, H.sub.2Se, CH.sub.4,
C.sub.2H.sub.6, C.sub.2H.sub.2, C.sub.2H.sub.4, B.sub.2H.sub.6,
PH.sub.3, CCl.sub.4, CF.sub.4, organic monomers like HMDSO, pyrrole
and the like are introduced into the deposition chamber. These
reactive gases are capable of reacting with the removed target
material to form a compound film on the substrate. Accordingly,
these reactive gases provide one or more atoms that are
incorporated into the film. Reactive sputtering is particularly
useful for depositing doped and undoped metal oxides, nitrides,
carbides, and the like. However, care must be taken in the reactive
sputtering process because such reactive gases may form an
insulating layer on the conductive target thereby reducing film
growth rate.
[0007] The effect of insulating layers on the targets in the
sputtering process is generally alleviated by the use of RF power
to form the plasma. This type of sputtering is referred to as RF
sputtering. It is particularly useful for depositing both
insulating and oxide films, but deposition rates tend to be low. In
the RF sputtering process, a substrate is placed between two
electrodes which are driven by an RF power source. Superimposed on
this applied RF field is a DC potential. This DC potential
advantageously drives the ions toward the target causing some of
the target material to be removed. This removed target material may
then react with a reactive gas. Again the removed material
ultimately coats the substrate.
[0008] A number of sputtering refinements makes this technique even
more desirable for the deposition of insulating and oxide films.
These refinements include unbalanced magnetron sputtering, the
utilization of pulsed dc power, and the use of hollow cathodes. The
utilization of hollow cathode sputtering in a gas flow mode is a
relatively new technique in which an inert gas such as argon is
introduced into a channel in a target cathode. While contained
within this channel a plasma is formed that removes atoms from the
target. These atoms are eventually swept by the gas flow out of the
cathode at which point they may then be reacted with a reactive
gas. The continuous flow of the inert gas prevents (or tends to
prevent) the reactive gas from entering the cathode and thereby
prevents (or tends to prevent) an insulating layer from forming on
the target. Although the prior art hollow cathode processes may
inhibit the formation of an insulating layer on the target, these
processes tend to produce films at unacceptably low growth
rates.
[0009] Accordingly, there exists a need for improved sputtering
methods for depositing thin films and in particular insulating or
oxide thin films with high growth rates and reduced formation of
insulating layers on the targets used in such sputtering
processes.
SUMMARY OF THE INVENTION
[0010] The present invention overcomes the problems of the prior
art by providing in one embodiment an improved method for sputter
coating a substrate. The method of the invention is a hollow
cathode sputtering process which comprises providing a channel for
gas to flow through, the channel defined by a channel defining
surface wherein one or more portions of the channel-defining
surface includes at least one target material. Gas is flowed
through the channel wherein at least a portion of the gas is a
non-laminarly flowing gas. While the gas is flowing through the
channel a plasma is generated causing target material to be
sputtered off the channel-defining surface to form a gaseous
mixture containing target atoms that are transported to the
substrate. In an important application of the present invention, a
method for forming oxide films and in particular zinc oxide films
is provided.
[0011] In another embodiment of the present invention, a
sputter-coating system for coating a substrate is provided. Such a
sputter-coating system will include at least one target material,
an electrode having a channel-defining surface, and a source of
non-laminarly flowing working gas. The channel-defining surface
contains the target material. During operation of the
sputter-coating system, a plasma is generated causing the at least
one target material to be sputtered off the channel-defining
surface. This in turn causes a gaseous reactive composition to form
which is subsequently transported to the substrate.
[0012] The source of non-laminarly flowing gas includes a series of
orifices such that at least two gas streams emerging from the
series of orifices are substantially flowing in non-parallel
directions. The source of non-laminarly flowing gas includes a
series of adjacent orifices that direct the gas in non-parallel
directions. The channel defining surface will typically be part of
the cathode. Moreover, the channel is characterized by a generally
rectangular cross section. The sputter-coating system may have a
first target material and a second target material. The first
target material is preferably opposite the second where the first
target material and the second target material are the same or
different. In such a configuration, the two target materials will
form at least a portion of the side walls of the channel-defining
surface, and in particular the side walls that make up the wider
sides when the channel has a rectangular cross section. Moreover,
the at least one target material optionally includes a third target
material and a fourth target material. The third target material
being opposite the fourth target material. In this instance, the
first target material, the second target material, the third target
material, and the fourth target material may be the same or
different. The target material, which is typically part of the
cathode, is in electrical contact with a DC potential or a DC
potential with a superimposed AC potential. Moreover, the at least
one target material comprises a metal or metal alloy. Suitable
target materials include, but are not limited to, zinc, copper,
aluminum, silicon, tin, indium, magnesium, titanium, chromium,
molybdenum, nickel, yttrium, zirconium, niobium, cadmium, and
mixtures thereof. The sputter-coating system of the present
invention further comprises a source of a reactive gas which is
located at proximate position to the exit of the channel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1A is a schematic demonstrating laminar gas flow in a
hollow cathode with a baffle between the gas nozzle and the channel
defined by the target materials;
[0014] FIG. 1B is a schematic demonstrating laminar gas flow in a
hollow cathode with the gas nozzle between the baffle and the
channel defined by the target materials;
[0015] FIG. 1C is a schematic demonstrating the utilization of
non-laminar gas flow in a hollow cathode by creating a narrow
passage between the gas nozzle and the target materials;
[0016] FIG. 1D is a schematic demonstrating the utilization of
non-laminar gas flow in a hollow cathode by directing the gas flow
into non-parallel directions;
[0017] FIG. 2 is a perspective view of a gas nozzle which
introduces a gas with non-parallel directions into the channel.
[0018] FIG. 3 is a plot of a waveform that may be used to drive a
sputtering system with an asymmetric bipolar pulsed DC power
supply.
[0019] FIG. 4A is a perspective view of a target that is capable of
holding up two target materials separated by two insulating
blocks;
[0020] FIG. 4B is a front view of a target that is capable of
holding up two target materials separated by two insulating
blocks;
[0021] FIG. 4C is a perspective view of a target that is capable of
holding up four target materials;
[0022] FIG. 4D is a perspective view of a target that is capable of
holding up four target materials;
[0023] FIG. 5A is a schematic of an embodiment of the
sputter-coating system of the present invention;
[0024] FIG. 5B is a schematic of the cathode used in the
sputter-coating system of the present invention;
[0025] FIG. 6 is a plot of the deposition rate as a function of
oxygen flow rate for aluminum oxide films deposited from an
aluminum target by the method of the present invention operating
with a power of 300 W, a pressure of 250 mTorr, and an argon flow
rate of 4 slm for the cases of oxygen injection outside the cathode
and oxygen passing through the cathode;
[0026] FIG. 7 is a plot of zinc oxide growth rate as a function of
the argon flow rate for zinc oxide films deposited from a zinc
target by the method of the invention operating with power of 150
W, a pressure of 500 mTorr, and an oxygen flow rate of 150 sccm;
and
[0027] FIG. 8 is a plot of the deposition rate of aluminum oxide
films as a function of oxygen flow rate for non-laminar and laminar
flow by the method of the present invention operating at a power of
300 W, a pressure of 500 mTorr, and argon flow rates of 2 slm and 4
slm. The oxygen is injected outside the cathode.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0028] Reference will now be made in detail to presently preferred
compositions or embodiments and methods of the invention, which
constitute the best modes of practicing the invention presently
known to the inventors.
[0029] In one embodiment of the present invention, a method for
sputter coating a substrate utilizing a hollow cathode in a sputter
coating reactor is provided. The method of the invention comprises
providing a channel (i.e., a cathode channel) for gas to flow
through, the channel defined by a channel defining surface wherein
one or more portions of the channel-defining surface include at
least one target material. Typically, the channel defining surface
is part of the cathode of a sputtering system and has a rectangular
cross section. Gas is flowed through the channel wherein at least a
portion of the gas is a non-laminarly flowing gas. Preferably, this
gas will be an inert gas such as argon. Such inert gases are
sometimes referred to as working gases in that these gases are used
to sputter off material from target surfaces. FIGS. 1 A through D
are schematics illustrating laminar flow and the methods of the
present invention. With reference to FIGS. 1 A and B, gas is
introduced from nozzle 2 into channel 4. Prior to entering channel
4, the gas impinges on baffle 6 which helps in mixing. While the
gas is flowing through channel 4 a plasma is generated causing
target material to be sputtered off the channel-defining surface 8
to form a gaseous mixture containing target atoms that are
transported to substrate 10. With reference to FIG. 1C, a
configuration suitable for small gap cathodes is provided. In this
configuration, non-laminar flow is induced by placing nozzle 2
within channel 4. This causes gas that impinges on baffle 6 to be
forced at a relatively higher velocity through narrow passage 12
which is formed between nozzle 2 and channel-defining surfaces 8.
The higher velocity gas flow close to the target surface is
maintained across the length of the channel from entrance to exit
or across at least part of the channel. With reference to FIG. 1D,
a configuration that is suitable for large gap cathodes is
provided. In this configuration, nozzle 2 is placed in channel 4.
Gas emerging from nozzle 2 is forced to flow through flow directing
shield 14 which directs the gas in a number of non-parallel
directions. It will be appreciated that the flow directing
properties of shield 14 may be built directly into nozzle 2 by
having orifices in nozzle 2 that direct the gas in non-parallel
directions. The requirement that the gas be flowing non-laminarly
is important in achieving the advantages of the present invention.
A preferred way to achieve non-laminar flow is by inducing
turbulence. Typically, turbulent flow is characterized as having a
Reynolds number greater than 2000. A slightly different preferred
way of achieving non-laminar flow is by having different portions
of the gas flow in different directions. In its simplest embodiment
of this concept, a first portion of gas in a first direction and a
second portion of gas is a second direction wherein the first
direction and the second direction are substantially non-parallel.
With reference to FIG. 2 a perspective view of gas nozzle 13 which
introduces a gas into the channel is provided. Typically, the gas
will be introduced into a sputtering reactor through a manifold 15
with a series of orifices 16 from which the gas emerges.
Accordingly, the non-laminarly flowing gas is formed by flowing the
gas through at least two orifices such that at least two gas
streams emerging from the at least two orifices are flowing in
substantially non-parallel directions. In practice, however, the
manifold will contain numerous orifices wherein two adjacent
orifices will direct the gas flow in different non-parallel
directions.
[0030] The target material, which is typically part of the cathode,
is in electrical contact with a DC potential, a DC potential with a
superimposed AC potential, or a pulsed DC potential. The preferred
power source is a pulsed DC power source and in particular an
asymmetric bipolar pulsed DC power supply. An asymmetric bipolar
power is applied between the cathode and anode by adding a reverse
(opposite polarity) voltage pulse to the normal (steady negative)
DC waveform. The resulting waveform is shown in FIG. 3. Typical
sputtering runs at about -400V, so that the positive argon ions
accelerate towards the target biased at -400V, striking and
sputtering the target (sputtering mode). However, in reactive
sputtering, reaction of the gas (oxygen, for example) with the
target material can create an insulating film on the target
surface. Positive charge from the ions builds up on the film
surface and reduces the incoming ion energy because of
electrostatic repulsion. This makes it difficult or impossible to
remove the oxide since sputtering is effectively prevented. If DC
sputtering is attempted, the presence of an insulator on the target
surface leads to arcing. Using the bipolar type of supply described
above, when the polarity is rapidly reversed to about +100V, the
surface charges up to -100V because of the attraction of electrons.
Next, upon returning to sputtering mode, -400V is applied to the
target and the effective voltage on the surface of the oxide is
-500V. Thus, the argon ions are drawn by electrostatic attraction
to the insulators, and strike with extra energy. This helps sputter
off the insulators, reducing target poisoning. The frequency
normally used is from 50 kHz to 250 kHz. The reverse pulse width
can be set anywhere between 0 and 40% of the pulse's duty cycle.
Depending on the target material and the rate of oxide formation,
the use of asymetric bipolar pulsed power may only have limited
effectiveness in removal of insulating layers. Even with the flow
of inert gas through the cathode (laminar or non-laminar), some
backstreaming of the reactive gas (oxygen, say) may occur and
partially oxidize the target surface. Asymmetric bipolar pulsed DC
supplies usually have low energy storage which also reduces arcing.
A similar benefit occurs when a new target is being run for the
first time (burn-in). The time required to stabilize the discharge
is decreased, resulting in faster burn-in. Depending on the power
supply manufacturer, the pulse shape may not be rectangular. This
does not affect the principles described.
[0031] The at least one target material used in the method of the
invention comprises a metal or metal alloy. Suitable target
materials include, but are not limited to, zinc, copper, aluminum,
silicon, tin, indium, magnesium, titanium, chromium, molybdenum,
nickel, yttrium, zirconium, niobium, cadmium, and mixtures
thereof.
[0032] In a preferred variation of the present invention, the
target material includes a first target material and a second
target material. The first target material is preferably opposite
the second where the first target material and the second target
material are the same or different. In such a configuration, the
two target materials will form at least a portion of the side walls
of the channel-defining surface, and in particular the side walls
that make up the wider sides when the channel has a rectangular
cross section. Moreover, the at least one target material
optionally includes a third target material and a fourth target
material. The third target material being opposite the fourth
target material. In this instance, the first target material, the
second target material, the third target material, and the fourth
target material may be the same or different.
[0033] FIGS. 4A through D provide schematics of a water-cooled Cu
cathode fitted with four target pieces (two large side pieces and
two smaller end blocks). With reference to FIGS. 4A and 4B, a
perspective view and a front view of a target that is capable of
holding up to two target materials separated by insulating blocks
is provided. Target 20 consists of plate 22 and plate 24 with are
opposite and face each other. Plate 22 is made from the first
target material and plate 24 is made of the second target material.
Target 20 also consists of insulating blocks 26, 28 which are
opposite and face each other. Insulating end blocks 26, 28 are made
from an electrically insulating material such as Macor (a
machinable ceramic from Corning). Insulating end blocks 26, 28 are
isolated from plates 22, 24 by gaps 30, 32, 34, 36. The gap width
for each of gaps 30, 32, 34, 36 is about 0.5 mm to 1.0 mm. Without
such gaps, the arcs result from a potential difference between the
floating metal film that builds up on the insulator surface during
the sputtering process and the target proper. This metal film
builds up on the insulator close to the target until a discharge
occurs. Once the discharge occurs, arcs continue until the metal
film near the target is burned away. This arc-generating process
then repeats during thin film deposition. With appropriate sizing
of the insulators and target pieces to create a gap, a discharge
between the target and a metal film on the insulator cannot occur
because of the gap spacing. The insulating end blocks make the film
thickness distribution in the direction of the long axis of the
slot more uniform than if additionally metal targets are placed
there. If a back insulator (not shown) is used on the rear of the
cathode for construction purposes, a similar principle is used to
create a gap between the back insulator and the target pieces.
Without the ceramic end blocks, the thickness distribution strongly
peaks near the two ends of the slot. Plates 22, 24 are contained
within cooling jacket 38 through which a coolant such as water
flows to keep the target materials cooled. This figure shows the
water-cooled Cu cathode fitted with four target pieces (two large
side pieces and two smaller end blocks). The exit slot defined by
the inner surfaces of the target pieces is evident. When all four
target pieces are metals, they may butt up against each other as
shown.
[0034] With reference to FIGS. 4C and 4D, a perspective view and a
front view of a target that is capable of holding up to four target
materials are provided. Target 40 consists of wide plate 42 and
wide plate 44 which are opposite and face each other. Wide plate 42
is made from the first target material and wide plate 44 is made of
the second target material. Target 40 also consists of short plate
46 and short plate 48 which are opposite and face each other. Short
plate 46 is optionally made from the third target material and
short plate 48 is optionally made from the fourth target material.
Plates 42, 44, 46, 48 are contained within cooling jacket 50
through which a coolant such as water flows to keep the target
materials cooled.
[0035] The method of the present invention optionally further
includes a step of introducing a reactive gas into the sputter
coating reactor. The reactive gas is introduced into the sputter
coating reactor at a position located outside of the channel from
which the gaseous mixture emerges prior to reaching the substrate.
The reactive gas contains an atom selected from the group
consisting of oxygen, nitrogen, selenium, sulfur, iodine, hydrogen,
carbon, boron, and phosphorus. Suitable reactive gases include, but
are not limited to, molecular oxygen, molecular nitrogen, molecular
hydrogen, H.sub.2O, H.sub.2Se, CH.sub.4, C.sub.2H.sub.6,
C.sub.2H.sub.2, C.sub.2H.sub.4, B.sub.2H.sub.6, PH.sub.3,
CCl.sub.4, CF.sub.4, HMDSO, pyrrole and mixture thereof.
[0036] In a particularly useful application of the method of the
present invention, a method for depositing an oxide film on a
substrate in a sputter coating reactor is provided. This oxide
forming method comprises the following steps:
[0037] a) providing a channel for a working gas to flow through,
the channel defined by a channel-defining surface wherein one or
more portions of the channel-defining surface include at least one
target material;
[0038] b) flowing the working gas through the channel wherein at
least a portion of the working gas flows non-laminarly;
[0039] c) generating a plasma wherein a portion of the target
material is sputtered off the at least one target material to form
a gaseous mixture containing target atoms; and
[0040] d) introducing into the sputter coating reactor a reactive
gas that comprises oxygen, wherein an oxide film is deposited on
the substrate. Preferably, the working gas is an inert gas such as
argon. The reactive gas is introduced at a position located outside
of the channel from which the gaseous mixture emerges prior to
reaching the substrate. The at least one target material comprises
a metal, metal alloy, or a semiconductor. Examples of useful target
materials include, but are not limited to, zinc, copper, aluminum,
silicon, tin, indium, magnesium, titanium, chromium, molybdenum,
nickel, yttrium, zirconium, niobium, cadmium, and mixtures thereof.
Preferred oxide films made by the method include zinc oxide made by
using a target which includes zinc and CrSiOx made from a target
that includes both chromium and silicon, wherein x is a number such
that the valency of Cr and Si are satisfied or partially satisfied.
Transparent electrically conducting oxides that may be made by the
method of the present invention include, for example, ZnO:B (boron
doped zinc oxide), CuAlO.sub.2, CuBO.sub.2, In.sub.2O.sub.3,
In.sub.2O.sub.3:Mo (molybdenum doped indium oxide), ITO (indium tin
oxide), Al.sub.2O.sub.3, or mixtures thereof. In the case of zinc
oxide, the target may also include aluminum so that an aluminum
doped zinc oxide film (ZnO:Al) is formed. Gallium and indium are
also suitable dopants for zinc oxide. In the case of ZnO:B, the
source of the boron atoms is conveniently the gas diborane
(B.sub.2H.sub.6). The diborane may be introduced either externally
or internally to the cathode. External introduction avoids target
memory effects, and is preferred. In the case of CuBO.sub.2, the
boron is preferably introduced by flowing a mixture of the working
gas and diborane through the cathode. Magnesium oxide and aluminum
oxide, which are highly insulating films, may be advantageously
made by the method of the invention. In forming oxide films, the
reactive gas must necessarily include compounds that have an oxygen
atom. Useful examples of such gases include, but are not limited
to, molecular oxygen and H.sub.2O. The present variation of the
method of the invention may include a first, second, third, and
fourth target material as set forth above.
[0041] In another embodiment of the present invention, a method for
depositing a nitride film on a substrate in a sputter coating
reactor is provided. The method of this embodiment comprises
providing a channel for a working gas to flow through, the channel
defined by a channel-defining surface wherein one or more portions
of the channel-defining surface include at least one target
material. The working gas is then flowed through the channel
wherein at least a portion of the working gas flows non-laminarly.
While the working gas is flowing, a plasma is generated wherein a
portion of the target material is sputtered off the at least one
target material to form a gaseous mixture containing target atoms.
Finally, a reactive gas comprising molecular nitrogen is introduced
into the sputter coating reactor, wherein a nitride film is
deposited on the substrate. In one variation of this embodiment the
reactive gas is introduced at a position located outside of the
channel from which the gaseous mixture emerges. In a particularly
preferred variation of this embodiment, the reactive gas is
combined with the working gas (e.g. Ar) while it is flowed through
the channel (i.e., the cathode channel.) The need to mix the
reactive gas and the working gas in the cathode channel is likely
due to the lower reactivity of nitrogen gas compared to oxygen. The
success may relate to the relatively high electrical conductivity
of many metal nitrides. The configuration of the at least one
target material is the same as set forth above. For example, the at
least one target material includes a first target material and a
second target material; and the first target material and the
second target material are the same or different. In this
configuration, the first target material is preferably opposite the
second target material. Moreover, the at least one target material
typically comprises a metal, metal alloy, or semiconductor.
Preferably, the at least one target material comprises a component
selected from the group consisting of zinc, copper, aluminum,
silicon, tin, indium, magnesium, titanium, chromium, molybdenum,
nickel, yttrium, zirconium, niobium, cadmium, vanadium, hafnium,
tungsten, and mixtures thereof. Examples of nitrides that may be
made by the method of this embodiment include titanium nitride,
indium nitride, aluminum nitride, chromium nitride, vanadium
nitride, tungsten nitride, copper nitride, zirconium nitride, or
mixtures thereof.
[0042] With reference to FIG. 5A a schematic of the sputter-coating
system of the present invention is provided. Sputter system 60
includes cathode 62 into which a non reactive gas such as argon is
introduced into injector 64 by tube 66. Cathode 62 is powered by
high voltage power supply 68. Within cathode 62 a gaseous mixture
containing target atoms as set forth above is formed and
transported toward substrate 70. Upon emerging from cathode 62, the
gaseous mixture combines with a reactive gas that is introduced
from manifold 72. Low pressure is maintained within chamber 74 by
the operation of throttle valve 76 and pumping system 78. Moreover,
substrate 70 is heated by heating lamps 80 and transported through
the sputtering system by transport mechanism 82. With reference to
FIG. 5B, a schematic cross-section of cathode 62 is provided.
Cathode 62 includes targets 90, 92 which are made of materials as
set forth above. Targets 90,92 are powered through electrical feed
94. Cathode 62 is cooled via copper cooling block 96 which is water
cooled. Water is introduced into copper cooling block 96 through
teflon tube 98 which snakes through leak tight adapter 100. Teflon
tube 98 attaches to copper cooling block 96 via connector 102.
Similarly, water is removed from copper cooling block 96 through
teflon tube 104 which snakes through leak tight adapter 106. Teflon
tube 104 attaches to copper cooling block 96 via connector 110.
Back section 112 is electrically isolated from cooling section 96
and targets 90, 92 by ceramic insulators 114, 116. Cathode 62 also
includes dark shield 118 and ceramic support 120 which holds
cathode 62 in place. A non-reactive gas such as argon is introduced
into the cathode by inlet 122. The gas then emerges from nozzle
124. Next the gas is redirected by flow directing shield 126 which
causes the gas to flow in non-parallel directions. The gas enters
channel 128 wherein a plasma is generated and material is sputtered
off of targets 90, 92. The resulting gaseous mixture includes
target material atoms which are transported to the substrate.
Reactive gas manifold 130 is positioned near the exit of channel
128. Reactive gas manifold 130 introduces a reactive gas that mixes
with the gaseous mixture that includes the target atoms.
[0043] As set forth for the method described above, the source of
non-laminarly flowing gas includes a series of orifices such that
at least two gas streams emerging from the series of orifices are
substantially flowing in non-parallel directions. The source of
non-laminarly flowing gas includes a series of adjacent orifices
that direct the gas in non-parallel directions. The channel
defining surface will typically be part of the cathode. Moreover,
the channel is characterized by a rectangular cross section. Again,
as described above for the method, the sputter-coating system may
have a first target material and a second target material. The
first target material is preferably opposite the second where the
first target material and the second target material are the same
or different. In such a configuration, the two target materials
will form at least a portion of the side walls of the
channel-defining surface, and in particular the side walls that
make up the wider sides when the channel has a rectangular cross
section. Moreover, the at least one target material optionally
includes a third target material and a fourth target material. The
third target material being opposite the fourth target material. In
this instance, the first target material, the second target
material, the third target material, and the fourth target material
may be the same or different. The target material, which is
typically part of the cathode, is in electrical contact with a DC
potential or a DC potential with a superimposed AC potential.
Moreover, the at least one target material comprises a metal or
metal alloy. Suitable target materials include, but are not limited
to, zinc, copper, aluminum, silicon, tin, indium, magnesium,
titanium, chromium, molybdenum, nickel, yttrium, zirconium,
niobium, cadmium, and mixtures thereof. The sputter-coating system
of the present invention further comprises a source of a reactive
gas which is located at proximate position to the exit of the
channel.
[0044] The following examples illustrate the various embodiments of
the present invention. Those skilled in the art will recognize many
variations that are within the spirit of the present invention and
scope of the claims.
EXAMPLE 1
[0045] Copper films were deposited in accordance to the method of
the present invention at a power of 1000 W, a pressure of 400
mTorr, and an argon flow rate of 4 slm. The resistivities for a
series of copper films for varying substrate conditions is provided
in Table 1. TABLE-US-00001 TABLE 1 Resistivity of copper films film
resistivity deposition conditions (microhm cm) unheated substrate
8.5 bias -30 V, unheated substrate 4.2 bias -15 V, substrate
70.degree. C. 3.9 substrate heated to 70.degree. C. 3.3 bias -30 V,
substrate 70.degree. C. 2.4
EXAMPLE 2
[0046] Aluminum oxide films were deposited by the method of the
invention with a power of 300 W, a pressure of 250 mTorr, and an
argon flow rate of 4 slm. The argon was injected using the
arrangement of FIG. 1C. FIG. 6 is a plot of the deposition rate as
a function of oxygen flow rate. The reactive gas O.sub.2 is used
here for two different cases: O.sub.2 goes through the channel and
O.sub.2 is outside the channel. The deposition rate was measured by
crystal monitor.
EXAMPLE 3
[0047] Zinc oxide films were deposited by the method of the
invention with power of 150 W, a pressure of 500 mTorr, and an
oxygen flow rate of 150 sccm. FIG. 7 is a plot of zinc oxide growth
rate as a function of the argon flow rate for deposition in a
hollow cathode reactor where the argon is introduced
non-turbulently and turbulently. In the case of turbulent flow, the
film growth rate is observed to be significantly greater for all
argon flow rates.
EXAMPLE 4
[0048] Aluminum doped zinc oxide films were deposited by the method
of the invention with the conditions in Table 2. Table 3 provides a
comparison for aluminum doped zinc oxide films made by the method
of the present invention and by RF sputtering. Table 3 demonstrates
that the method of the present invention is capable of depositing
doped zinc oxide films with resistivities that are comparable to RF
sputtering. TABLE-US-00002 TABLE 2 Aluminum doped zinc oxide
deposition conditions. target- oxygen substrate resistivity Power
Pressure flow rate distance (10.sup.-3 ohm- Run (W) (mTorr) (sccm)
(cm) cm) 1 100 300 70 2.0 0.49 2 100 200 70 3.5 1.26 3 100 200 100
3.5 0.49 4 100 200 500 3.5 48 5 100 200 140 3.5 1.5 6 100 100 150
5.5 5.9 7 100 100 250 5.5 large 8 250 300 100 2.5 1.2
[0049] TABLE-US-00003 TABLE 3 Aluminum doped zinc oxide properties.
sheet resistance thickness resistivity Run method
(.OMEGA./.quadrature.) (.mu.m) (10.sup.-3 .OMEGA.-cm) 1 hollow
cathode 13 0.38 0.49 2 hollow cathode 23 0.52 1.19 3 hollow cathode
14 0.9 1.26 4 RF magnetron 5 0.89 0.45 5 RF magnetron 16 0.43 0.69
6 RF magnetron 14 0.63 0.88
EXAMPLE 5
[0050] Aluminum and aluminum oxide films were deposited by the
method of the invention with a power of 300 W, a pressure of 500
mTorr, and argon flow rates of 2 slm and 4 slm. FIG. 8 is a plot of
the aluminum oxide deposition rate as a function of oxygen flow
rate for turbulent and non-turbulent Ar flow. For non-laminar flow,
the gas injector is the type in FIG. 1C and for non-turbulent flow,
the gas injector is the type of FIG. 1A. Again, the growth rates
for all oxygen flow rates is observed to be significantly higher
with turbulent Ar flow. Even for zero oxygen flow, the deposition
rate of pure Al is enhanced by turbulent flow. With the addition of
oxygen, the deposited mass rate increases because of oxygen
incorporation into the film. The mass rate saturates once a fully
oxidized film is formed. The increase in deposition rate with
turbulence is even greater for aluminum oxide than for pure
aluminum. This rate enhancement is of considerable technological
importance. At the lower Ar flow (2 slm) the deposition rate
without turbulent Ar flow is seen to decline with increasing oxygen
flow. This is believed to result from partial penetration of oxygen
into the cathode, resulting in partial oxidation of the target
surface. With turbulent Ar flow, the deposition rate is independent
of oxygen flow. This suggests that turbulence, as well as
increasing the mass of Al that can be moved out of the cathode,
also hinders the back-diffusion of oxygen into the cathode.
EXAMPLE 6
[0051] The transparent conductor ZnO:B was deposited by the method
of the invention using zinc target pieces, turbulent Ar gas
injection (type (c)), an Ar gas flow rate of 2 slm, a power of 300
W, a pressure of 300 mTorr, 120 sccm O.sub.2 supplied from a
manifold external to the cathode and directed at the substrate, and
2 sccm B.sub.2H.sub.6 gas passing through the cathode and mixed
with the Ar. The deposition rate was 20 A/s and the film
resistivity was 1.8.times.10.sup.3 ohm cm.
[0052] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *