U.S. patent application number 14/282832 was filed with the patent office on 2014-11-13 for transparent conductive oxides.
The applicant listed for this patent is DEMARAY, LLC. Invention is credited to R. Ernest Demaray, Mukundan Narasimhan.
Application Number | 20140332371 14/282832 |
Document ID | / |
Family ID | 33490597 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140332371 |
Kind Code |
A1 |
Demaray; R. Ernest ; et
al. |
November 13, 2014 |
TRANSPARENT CONDUCTIVE OXIDES
Abstract
A method of deposition of a transparent conductive film from a
metallic target is presented. A method of forming a transparent
conductive oxide film according to embodiments of the present
invention include depositing the transparent conductive oxide film
in a pulsed DC reactive ion process with substrate bias, and
controlling at least one process parameter to affect at least one
characteristic of the conductive oxide film. The resulting
transparent oxide film, which in some embodiments can be an
indium-tin oxide film, can exhibit a wide range of material
properties depending on variations in process parameters. For
example, varying the process parameters can result in a film with a
wide range of resistive properties and surface smoothness of the
film.
Inventors: |
Demaray; R. Ernest; (Portola
Valley, CA) ; Narasimhan; Mukundan; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DEMARAY, LLC |
PORTOLA VALLEY |
CA |
US |
|
|
Family ID: |
33490597 |
Appl. No.: |
14/282832 |
Filed: |
May 20, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10850968 |
May 20, 2004 |
8728285 |
|
|
14282832 |
|
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|
60473379 |
May 23, 2003 |
|
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Current U.S.
Class: |
204/192.29 |
Current CPC
Class: |
C23C 14/0042 20130101;
C23C 14/086 20130101; H01B 13/0026 20130101; C23C 14/0036
20130101 |
Class at
Publication: |
204/192.29 |
International
Class: |
H01B 13/00 20060101
H01B013/00; C23C 14/00 20060101 C23C014/00; C23C 14/08 20060101
C23C014/08 |
Claims
1. A method of forming a transparent conductive oxide film,
comprising: depositing the transparent conductive oxide film in a
pulsed DC reactive ion process with substrate bias; and controlling
at least one process parameter to provide at least one
characteristic of the conductive oxide film at a particular
value.
2. The method of claim 1, wherein controlling at least one process
parameter includes controlling the oxygen partial pressure.
3. The method of claim 1, wherein the transparent conductive oxide
film includes indiuim-tin oxide.
4. The method of claim 1, wherein the at least one characteristic
includes sheet resistance.
5. The method of claim 1, wherein the at least one characteristic
includes film roughness.
6. The method of claim 5, wherein the transparent conductive oxide
film includes an indium-tin oxide film and the film roughness is
characterized by R.sub.a less than about 10 nm with Rms of less
than about 20 nm.
7. The method of claim 4, wherein the bulk resistance can be varied
between about 2.times.10.sup.-4 micro-ohms-cm to about 0.1
micro-ohms-cm.
8. The method of claim 1, wherein the at least one process
parameter includes a power supplied to a target.
9. The method of claim 1, wherein the at least one process
parameter includes an oxygen partial pressure.
10. The method of claim 1, wherein the at least one process
parameter includes bias power.
11. The method of claim 1, wherein the at least one process
parameter includes deposition temperature.
12. The method of claim 1, wherein the at least one process
parameter includes an argon partial pressure.
13. The method of claim 1, further including supplying a metallic
target.
14. The method of claim 1, further including supplying a ceramic
target.
15. The method of claim 1, wherein the transparent conductive oxide
film is doped with at least one rare-earth ions.
16. The method of claim 15, wherein the at least one rare-earth
ions includes erbium.
17. The method of claim 15, wherein the at least one rare-earth
ions includes cerium.
18. A method of depositing a transparent conductive oxide film on a
substrate, comprising: placing the substrate in a reaction chamber;
adjusting power to a pulsed DC power supply coupled to a target in
the reaction chamber; adjusting an RF bias power coupled to the
substrate; adjusting gas flow into the reaction chamber; and
providing a magnetic field at the target in order to direct
deposition of the transparent conductive oxide film on the
substrate in a pulsed-dc biased reactive-ion deposition process,
wherein the transparent conductive oxide film exhibits at least one
particular property.
19. The method of claim 18, wherein at least one particular
property of the transparent conductive oxide film is determined by
parameters of the pulsed-dc biased reactive ion deposition
process.
20. The method of claim 19, wherein the at least one particular
property includes resistivity of the transparent conductive oxide
film.
21. The method of claim 19, wherein the transparent conductive
oxide film includes an indium-tin oxide film.
22. The method of claim 19, wherein the parameters include oxygen
partial pressure.
23. The method of claim 19, wherein the parameters include bias
power.
24. The method of claim 18, wherein the target can include at least
one rare-earth ions.
25. The method of claim 24, wherein the at least one rare-earth
ions includes erbium.
26. The method of claim 24, wherein the at least one rare-earth ion
includes cerbium.
Description
RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application 60/473,379, "Transparent Conductive Oxides from a
Metallic Target," by R. Ernest Demaray and Mukundan Narasimhan,
filed on May 23, 2003, herein incorporated by reference in its
entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention is related to deposition of oxides on
a substrate and, in particular, deposition of transparent
conductive oxides.
[0004] 2. Discussion of Related Art
[0005] Transparent conductive oxides have a wide variety of uses,
including applications to solar cells, organic light emitting
diodes (OLEDs), electric field devices, current devices (i.e. touch
screens), energy efficient windows, conductive anti-reflective
devices, electromagnetic interference shields, heaters, transparent
electrodes, coatings for cathode ray tube (CRT) displays, to name
only a few. Another important application is for touch sensitive
MEMS devices, such as those used, for example, in fingerprint
sensors and such. In many cases, the electrical properties of the
conducting film is of great importance.
[0006] Specifically, for OLED applications, films deposited with
current technologies are generally rough, resulting in stress
risers and field concentration issues, that can cause leakage.
Further, asperities in the resulting film can induce lifetime
dependent defects in nearest neighbor films that can shorten device
lifetimes. Additionally, the brightness of the emergent light from
the OLED can be reduced.
[0007] Transparent conductive oxides have been deposited from
ceramic targets by RF magnetron sputtering. However, the surface of
properties of the resulting films often include nodules or
asperites which can cause arcing, defects, surface roughness, and
other deleterious effects in the resulting film. Additionally,
ceramic targets tend to be more expensive to produce than metallic
targets.
[0008] Previous attempts at deposition of transparent conductive
oxides, for example indium tin oxide (ITO), with metallic targets
have presented numerous problems, including small process windows,
problems in process controllability, a disappearing anode effect,
and particle deposition on the film. Such attempts have been
abandoned. Deposition with ceramic targets has also been difficult,
including problems with particles, nodule formation, and arching
during deposition. In both cases, film smoothness has presented
major difficulties. Additionally, control of film parameters such
as, for example, resistivity and transparency has been
difficult.
[0009] Therefore, there is need for cost effective deposition of
smoother layers of transparent conductive oxides with greater
control over layer properties such as resistivity and
transparency.
SUMMARY
[0010] In accordance with the present invention, a method of
depositing of a transparent conductive film from a metallic target
is presented. A method of forming a transparent conductive oxide
film according to embodiments of the present invention includes
depositing the transparent conductive oxide film in a pulsed DC
reactive ion process with substrate bias, and controlling at least
one process parameter to provide at least one characteristic of the
conductive oxide film at a particular value.
[0011] A method of depositing a transparent conductive oxide film
on a substrate according to some embodiments of the invention,
then, includes placing the substrate in a reaction chamber,
adjusting power to a pulsed DC power supply coupled to a target in
the reaction chamber, adjusting an RF bias power coupled to the
substrate, adjusting gas flow into the reaction chamber, and
providing a magnetic field at the target in order to direct
deposition of the transparent conductive oxide film on the
substrate in a pulsed-dc biased reactive-ion deposition process,
wherein the transparent conductive oxide film has a particular
characteristic.
[0012] The resulting transparent oxide film, which can be deposited
according to some embodiments of the present invention, can be an
indium-tin oxide (ITO) film. An ITO film can have a wide range of
material properties depending on variations in process parameters.
For example, varying the process parameters according to some
embodiments of the present invention can result in a wide range of
resistive properties and surface smoothness of the film.
[0013] These and other embodiments of the invention are further
discussed below with reference to the following figures.
SHORT DESCRIPTION OF THE FIGURES
[0014] FIGS. 1A and 1B illustrate a pulsed-DC biased reactive ion
deposition apparatus that can be utilized in the methods of
depositing according to the present invention.
[0015] FIG. 2 shows an example of a target that can be utilized in
the reactor illustrated in FIGS. 1A and 1B
[0016] FIG. 3A shows an Atomic Force Microscopy (AFM) image of an
indium-tin-oxide (ITO) process according to some embodiments of the
present invention.
[0017] FIG. 3B shows an Atomic Force Microscopy (AFM) image of
another ITO process deposited using a process according to some
embodiments of the present invention.
[0018] FIG. 4 shows the variation of bulk resistivity of an ITO
layer according to some embodiments of the present invention as a
function of the oxygen flow for two different target powers before
and after a 250.degree. C. anneal in vacuum.
[0019] FIG. 5 shows the variation of the sheet resistance of an ITO
layer according to some embodiments of the present invention as a
function of the oxygen flow used for two different target powers
before and after a 250.degree. C. anneal in vacuum.
[0020] FIG. 6 shows the target current and voltage (min and max) as
a function of oxygen flow.
[0021] FIG. 7 shows the thickness change in layers of ITO according
to embodiments of the present invention as a function of oxygen
flow.
[0022] FIG. 8 illustrates the relationship between oxygen flow and
oxygen partial pressure for a metallic target.
[0023] FIGS. 9A-9D illustrate the smoothness of transparent
conductive oxides deposited with ceramic targets according to the
present invention.
[0024] In the figures, elements having the same designation have
the same or similar function.
DETAILED DESCRIPTION
[0025] Deposition of materials by pulsed-DC biased reactive ion
deposition is described in U.S. patent application Ser. No.
10/101,863, entitled "Biased Pulse DC Reactive Sputtering of Oxide
Films," to Hongmei Zhang, et al., filed on Mar. 16, 2002.
Preparation of targets is described in U.S. patent application Ser.
No. 10/101,341, entitled "Rare-Earth Pre-Alloyed PVD Targets for
Dielectric Planar Applications," to Vassiliki Milonopoulou, et al.,
filed on Mar. 16, 2002. U.S. patent application Ser. No. 10/101,863
and U.S. patent application Ser. No. 10/101,341 are each assigned
to the same assignee as is the present disclosure and each is
incorporated herein in their entirety. Deposition of oxide
materials has also been described in U.S. Pat. No. 6,506,289, which
is also herein incorporated by reference in its entirety.
Transparent oxide films are deposited utilizing processes similar
to those specifically described in U.S. Pat. No. 6,506,289 and U.S.
application Ser. No. 10/101,863.
[0026] FIG. 1A shows a schematic of a reactor apparatus 10 for
sputtering material from a target 12 according to the present
invention. In some embodiments, apparatus 10 may, for example, be
adapted from an AKT-1600 PVD (400.times.500 mm substrate size)
system from Applied Komatsu or an AKT-4300 (600.times.720 mm
substrate size) system from Applied Komatsu, Santa Clara, Calif.
The AKT-1600 reactor, for example, has three deposition chambers
connected by a vacuum transport chamber. These Komatsu reactors can
be modified such that pulsed DC power is supplied to the target and
RF power is supplied to the substrate during deposition of a
material film.
[0027] Apparatus 10 includes target 12 which is electrically
coupled through a filter 15 to a pulsed DC power supply 14. In some
embodiments, target 12 is a wide area sputter source target, which
provides material to be deposited on a substrate 16. Substrate 16
is positioned parallel to and opposite target 12. Target 12
functions as a cathode when power is applied to it and is
equivalently termed a cathode. Application of power to target 12
creates a plasma 53. Substrate 16 is capacitively coupled to an
electrode 17 through an insulator 54. Electrode 17 can be coupled
to an RF power supply 18. A magnet 20 is scanned across the top of
target 12.
[0028] For pulsed reactive dc magnetron sputtering, as performed by
apparatus 10, the polarity of the power supplied to target 12 by
power supply 14 oscillates between negative and positive
potentials. During the positive period, the insulating layer on the
surface of target 12 is discharged and arcing is prevented. To
obtain arc free deposition, the pulsing frequency exceeds a
critical frequency that can depend on target material, cathode
current and reverse time. High quality oxide films can be made
using reactive pulse DC magnetron sputtering as shown in apparatus
10.
[0029] Pulsed DC power supply 14 can be any pulsed DC power supply,
for example an AE Pinnacle plus 10K by Advanced Energy, Inc. With
this DC power supply, up to 10 kW of pulsed DC power can be
supplied at a frequency of between 0 and 350 KHz. The reverse
voltage can be 10% of the negative target voltage. Utilization of
other power supplies can lead to different power characteristics,
frequency characteristics and reverse voltage percentages. The
reverse time on this embodiment of power supply 14 can be adjusted
between 0 and 5 .mu.s.
[0030] Filter 15 prevents the bias power from power supply 18 from
coupling into pulsed DC power supply 14. In some embodiments, power
supply 18 can be a 2 MHz RF power supply, for example a Nova-25
power supply made by ENI, Colorado Springs, Colo.
[0031] In some embodiments, filter 15 can be a 2 MHz sinusoidal
band rejection filter. In some embodiments, the band width of the
filter can be approximately 100 kHz. Filter 15, therefore, prevents
the 2 MHz power from the bias to substrate 16 from damaging power
supply 18.
[0032] However, both RF and pulsed DC deposited films are not fully
dense and may have columnar structures. Columnar structures can be
detrimental to thin film applications. By applying a RF bias on
wafer 16 during deposition, the deposited film can be densified by
energetic ion bombardment and the columnar structure can be
substantially eliminated.
[0033] In the AKT-1600 based system, for example, target 12 can
have an active size of about 675.70.times.582.48 by 4 mm in order
to deposit films on substrate 16 that have dimension about
400.times.500 mm. The temperature of substrate 16 can be held at
between -50.degree. C. and 500.degree. C. The distance between
target 12 and substrate 16 can be between about 3 and about 9 cm.
Process gas can be inserted into the chamber of apparatus 10 at a
rate up to about 200 sccm while the pressure in the chamber of
apparatus 10 can be held at between about 0.7 and 6 millitorr.
Magnet 20 provides a magnetic field of strength between about 400
and about 600 Gauss directed in the plane of target 12 and is moved
across target 12 at a rate of less than about 20-30 sec/scan. In
some embodiments utilizing the AKT 1600 reactor, magnet 20 can be a
race-track shaped magnet with dimensions about 150 mm by 600
mm.
[0034] FIG. 2 illustrates an example of target 12. A film deposited
on a substrate positioned on carrier sheet 17 directly opposed to
region 52 of target 12 has good thickness uniformity. Region 52 is
the region shown in FIG. 1B that is exposed to a uniform plasma
condition. In some implementations, carrier 17 can be coextensive
with region 52. Region 24 shown in FIG. 2 indicates the area below
which both physically and chemically uniform deposition can be
achieved, for example where physical and chemical uniformity
provide refractive index uniformity. FIG. 2 indicates region 52 of
target 12 that provides thickness uniformity is, in general, larger
than region 24 of target 12 providing thickness and chemical
uniformity. In optimized processes, however, regions 52 and 24 may
be coextensive.
[0035] In some embodiments, magnet 20 extends beyond area 52 in one
direction, for example the Y direction in FIG. 2, so that scanning
is necessary in only one direction, for example the X direction, to
provide a time averaged uniform magnetic field. As shown in FIGS.
1A and 1B, magnet 20 can be scanned over the entire extent of
target 12, which is larger than region 52 of uniform sputter
erosion. Magnet 20 is moved in a plane parallel to the plane of
target 12.
[0036] The combination of a uniform target 12 with a target area 52
larger than the area of substrate 16 can provide films of highly
uniform thickness. Further, the material properties of the film
deposited can be highly uniform. The conditions of sputtering at
the target surface, such as the uniformity of erosion, the average
temperature of the plasma at the target surface and the
equilibration of the target surface with the gas phase ambient of
the process are uniform over a region which is greater than or
equal to the region to be coated with a uniform film thickness. In
addition, the region of uniform film thickness is greater than or
equal to the region of the film which is to have highly uniform
optical properties such as index of refraction, density,
transmission or absorptivity.
[0037] Target 12 can be formed of any materials. Typically metallic
materials, for example, include combinations of In and Sn.
Therefore, in some embodiments, target 12 includes a metallic
target material formed from intermetallic compounds of optical
elements such as Si, Al, Er and Yb. Additionally, target 12 can be
formed, for example, from materials such as La, Yt, Ag, Au, and Eu.
To form optically active films on substrate 16, target 12 can
include rare-earth ions. In some embodiments of target 12 with rare
earth ions, the rare earth ions can be pre-alloyed with the
metallic host components to form intermetallics. See U.S.
application Ser. No. 10/101,341. Typical ceramic target materials
include alumina, silica, alumina silicates, and other such
materials.
[0038] In some embodiments of the invention, material tiles are
formed. These tiles can be mounted on a backing plate to form a
target for apparatus 10. A wide area sputter cathode target can be
formed from a close packed array of smaller tiles. Target 12,
therefore, may include any number of tiles, for example between 2
to 20 individual tiles. Tiles can be finished to a size so as to
provide a margin of non-contact, tile to tile, less than about
0.010'' to about 0.020'' or less than half a millimeter so as to
eliminate plasma processes that may occur between adjacent ones of
tiles 30. The distance between tiles of target 12 and the dark
space anode or ground shield 19 in FIG. 1B can be somewhat larger
so as to provide non contact assembly or to provide for thermal
expansion tolerance during process chamber conditioning or
operation.
[0039] As shown in FIG. 1B, a uniform plasma condition can be
created in the region between target 12 and substrate 16 in a
region overlying substrate 16. A plasma 53 can be created in region
51, which extends under the entire target 12. A central region 52
of target 12 can experience a condition of uniform sputter erosion.
As discussed further below, a layer deposited on a substrate placed
anywhere below central region 52 can then be uniform in thickness
and other properties (i.e., dielectric, optical index, or material
concentrations). In addition, region 52 in which deposition
provides uniformity of deposited film can be larger than the area
in which the deposition provides a film with uniform physical or
optical properties such as chemical composition or index of
refraction. In some embodiments, target 12 is substantially planar
in order to provide uniformity in the film deposited on substrate
16. In practice, planarity of target 12 can mean that all portions
of the target surface in region 52 are within a few millimeters of
a planar surface, and can be typically within 0.5 mm of a planar
surface.
[0040] Reactive gases that provide a constant supply of ionic
oxygen to keep the target surface oxidized can be provided to
expand the process window. Some examples of the gases that can be
utilized for controlling surface oxidation are CO.sub.2, water
vapor, hydrogen, N.sub.2O, fluorine, helium, and cesium.
Additionally, a feedback control system can be incorporated to
control the oxygen partial pressure in the reactive chamber.
Therefore, a wide range of oxygen flow rates can be controlled to
keep a steady oxygen partial pressure in the resulting plasma.
Other types of control systems such as target voltage control and
optical plasma emission control systems can also be utilized to
control the surface oxidation of the target. As shown in FIG. 1A,
power to target 12 can be controlled in a feedback loop at supply
14. Further, oxygen partial pressure controller 20 can control
either oxygen or argon partial pressures in plasma 53.
[0041] In some embodiments, transparent conductive oxides can be
deposited on various substrates utilizing an inidium-tin (In/Sn)
metallic target. A series of depositions on glass in accordance
with the present invention is illustrated in Table I. The
parameters in the process column of Table I are in the format
(pulsed DC power/RF bias power/pulsing frequency/reverse
time/deposition time/Ar flow (sccms)/O.sub.2 flow (sccms)). An
indium-tin (In/Sn: 90%/10% by weight) target using a
reactive-pulsed DC (RPDC) process such as that described in U.S.
application Ser. No. 10/101,863 was utilized. A power supply with 2
MHz RF bias applied to substrate 16 was utilized in the process.
Along with the process parameters for each of the separate
depositions, each defined by a "Slot" number in the first column,
the target voltage, and target current ranges for each of the
depositions is also listed.
[0042] Table 2 shows the results obtained by using the process
parameters in Table 1. The results include the sheet resistance,
thickness, bulk resistivity, and refractive indices of the
resulting films. Again, the first column indicates the slot number
of the deposition. The process for each slot number is reiterated
in column 2 of Table 2. The sheet resistance of selected ones of
the films resulting from the deposition is listed in the third
column and the uniformity of the sheet resistance is indicated in
the fourth column. The thickness of the film and its uniformity of
each of the films deposited by the indicated process is indicated
in the fifth and sixth columns. The bulk resistance of selected
ones of the films, .rho., is also indicated. Additionally, the
refractive index taken at 632 nm is indicated along with the film
uniformity of that index. The comments section of Table 2 indicates
whether the resulting film is transparent, translucent, or metallic
in character.
[0043] FIG. 3A shows the Atomic Force Microscopy (AFM) image of an
ITO film produced by the process identified in slot #5 in tables 1
and 2. That process, with particularly low oxygen flow rates (24
sccm), produced a rough film with an Ra of about 70 .ANG. and an
Rms of about 90 .ANG.. The film also appears to be metallic with
this particular oxygen flow and the film roughness is high. Such a
film could be applicable to large surface area requirements, for
example solar cell applications. Wile not being limited by any
particular theory, it is suspected that the roughness of this film
reflects the sub-stoichiometric nature of the film caused by
insufficient oxygen flow in the plasma. As can be seen in FIG. 3B,
where the oxygen flow during deposition has been significantly
increased to about 36 sccm, the film is smooth.
[0044] FIG. 3B shows an Atomic Force Microscopy (AFM) image of an
ITO film deposited using the process described in slot #19 of
Tables 1 and 2. In that process, the oxygen flow rate is increased
to 36 sccm. The film appears to be transparent and conductive and
the surface roughness is .about.6 .ANG. Ra and Rms of about 13
.ANG., which is acceptable for OLED requirements. As can be seen
from FIGS. 3A and 3B, variation in oxygen partial pressure (as
indicated by increased flow rate) has a large influence on the
characteristics of the resulting deposited film.
[0045] The resistivity of the film layer and the smoothness of the
film layer can be related. In general, the higher the resistivity
of the film layer, the smoother the film layer. FIG. 4 shows the
variation of bulk resistivity of the ITO as a function of the
oxygen flow rate used for two different target powers before and
after a 250.degree. C. anneal in vacuum. The bulk resistivity of
the film exhibits a sudden transition downward as the oxygen flow
rate is lowered. This transition occurs when the target surface
becomes metallic from being poisoned with oxygen. The data utilized
to form the graph shown in FIG. 4 has been taken from Tables 1 and
2.
[0046] FIG. 5 shows the variation of the sheet resistance of an ITO
film as function of the O.sub.2 flow used for two different target
powers before and after a 250 C anneal in vacuum. As shown in FIG.
5, the sheet resistance follows similar trends as the bulk
resistivity of the film.
[0047] FIG. 6 shows the target current and voltage (min and max) as
a function of the oxygen flow rate. The target voltage increases as
the oxygen flow rate is lowered. It could be seen here that at a 40
sccm oxygen flow rate through repeated depositions, the target
voltage is not constant. This illustrates the utility of a target
voltage feedback control system that adjusts the power supplied to
target 12 to hold the target voltage constant. Therefore, as shown
in FIG. 1A, PDC power 14 can include feedack loop to control the
voltage on target 12.
[0048] FIG. 7 shows the thickness change of a resulting film as a
function of oxygen flow rate in sccm. The thickness of the film
increases as the oxygen flow decreases but this could make opaque
metallic films and so choosing the correct oxygen flow and
utilizing an oxygen flow feedback control system to control
material characteristics such as, for example, transparency or
conductivity can be desirable.
[0049] In some embodiments, instead of oxygen flow rate, oxygen
partial pressure can be controlled with a feedback system 20 (see
FIG. 1A). Controlling the oxygen partial pressure can provide
better control over the oxygen content of the plasma, and therefore
the oxygen content of the resulting films, and allows better
control over the film characteristics. FIG. 8 illustrates the
relationship between the flow rate and partial pressure. As can be
seen from FIG. 8, in order to reach the saturated region (e.g.,
when target 12 is completely poisoned with oxygen), no increase in
flow rate is required. In some embodiments, reactor 10 can include
a partial pressure feedback loop controller 20 that controls the
oxygen flow in order to maintain a desired partial pressure of
oxygen in the plasma. Such a controller can be the IRESS system,
that can be purchased from Advanced Energy, Inc., Ft. Collins,
Colo. It has been found that film parameters such as resistivity,
smoothness, and transparency can be highly dependent on oxygen
partial pressures, and therefore these characteristics of the
resulting deposited layer can be controlled by adjusting the oxygen
partial pressures.
[0050] Some embodiments of the present invention can be deposited
with ceramic targets. An example target is an ITO (In/Sn 90/10)
ceramic target can be utilized. Table 3 illustrates some example
processes for deposition of ITO utilizing a ceramic target
according to the present invention. Bulk resistivity, sheet
resistance, resistance, thicknesses, deposition rates, and index of
refraction of the resulting films are shown along with the process
parameters utilized in the deposition. FIG. 9A shows an AFM
depiction of a transparent conductive oxide film corresponding to
run #10 in Table 3. FIG. 9B shows an AFM depiction of a transparent
conductive oxide film corresponding to run #14 in Table 3. FIG. 9C
shows an AFM depiction of a transparent conductive oxide film
corresponding to run #16 in Table 3. FIG. 9D shows an AFM depiction
of a transparent conductive oxide film layer corresponding to run
#6 in Table 3.
[0051] FIGS. 9A through 9D illustrate the roughnesses of selective
depositions of ITO deposited utilizing the ceramic target. In FIG.
9A, the roughest surface shown, the film was deposited using 3 kW
RF power, 100 W bias, 3 sccm O.sub.2 and 60 sccm Ar at a
temperature of 280.degree. C. The layer grew to a thickness of 1200
.ANG. in 100 seconds of deposition time and exhibited a sheet
resistance of 51 ohms/sq. The roughness illustrated in FIG. 9A is
characterized by an Ra=2.3 nm and R.sub.MS of 21 nm.
[0052] The ITO film shown in FIG. 9B was deposited using 3 kW RF
power, 300 W bias, 3 sccm O.sub.2 and 60 sccm Ar at a temperature
of 280.degree. C. The layer illustrated in FIG. 9B grew to a
thickness of 1199 .ANG. in 100 sec. The layer in FIG. 9B exhibited
a sheet resistance of 39 ohms/sq. The roughness illustrated in FIG.
9B is characterized by an Ra=1.1 nm and Rmax of 13 nm.
[0053] The ITO film shown in FIG. 9C was deposited using 3 kW RF
power, 300 W bias, 3 sccm O.sub.2, 30 sccm Ar at a temperature of
280.degree. C. The layer grew to a thickness of 1227 .ANG. in 100
seconds of deposition time and exhibited a sheet resistance of 57
ohms/sq. The roughness illustrated in FIG. 9C can be characterized
by an Ra=0.88 nm and a Rmax of 19.8 nm.
[0054] FIG. 9D was deposited using 1.5 kW RF power, 300 W bias, 0
sccm O.sub.2, 30 sccm Ar at a temperature of 280 C. The layer grew
to a thickness of 580 .ANG. in 100 seconds of deposition time and
exhibited a sheet resistance of 106 ohms/sq. The roughness
illustrated in FIG. 9C can be characterized by an Ra=0.45 nm and an
Rmax of 4.6 nm.
[0055] Utilizing the example depositions described herein, the
roughness and resistivity of a transparent oxide film can be tuned
to particular applications. In general, particularly high
resistivities can be obtained, which are useful for touch sensitive
devices. As shown in Table 3, the sheet resistance ranged from
about 39 .OMEGA./sq for trial #14 to a high of 12,284 .OMEGA./sq
for trial #1. Careful variation of the process parameters,
therefore, allow control of sheet resistance over an extremely
broad range. Low resistivities can be obtained by adjusting the
process parameters for uses in devices such as OLEDS and MEMS
display devices. As is illustrated in Table 3, the bulk resistivity
can be controlled to be between about 2E-4 micro-ohms-cm to about
0.1 micro-ohms-cm. Additionally, other parameters such as
refractive index and transparency of the film can be
controlled.
[0056] Further, deposition of transparent conductive oxide layers,
for example ITO, can be doped with rare-earth ions, for example
erbium or cerium, can be utilized to form color-conversion layers
and light-emission sources. In some embodiments, a rare-earth doped
target can be made in a single piece to insure uniformity of
doping. Co-doping can be accomplished in the target.
[0057] Similar processes for other metallic conductive oxides can
also be developed. For example, deposition of zinc oxide films.
Further, as can be seen in the examples shown in Table 3, low
temperature depositions can be performed. For example, transparent
conductive oxides according to the present invention can be
deposited at temperatures as low as about 100.degree. C. Such low
temperature depositions can be important for depositions on
temperature sensitive materials such as plastics.
[0058] Other thin film layers according to the present invention
include deposition of other metal oxides to form conducting and
semi-conducting films. Thin films formed according to the present
invention can be utilized in many devices, including, but not
limited to, displays, photovoltaics, photosensors, touchscreens,
and EMI shielding.
[0059] Embodiments of the invention disclosed here are examples
only and are not intended to be limiting. Further, one skilled in
the art will recognize variations in the embodiments of the
invention described herein which are intended to be included within
the scope and spirit of the present disclosure. As such, the
invention is limited only by the following claims.
TABLE-US-00001 TABLE I Target Target Voltage (V) Current (Amps)
Slot # Process Min Max Mix Max 14 1.5 kw/100 w/200 khz/2.2
.mu.s/300 s/20Ar/80O.sub.2 244 252 5.94 6.14 15 1.5 kw/100 w/200
khz/2.2 .mu.s/300 s/20Ar/40O.sub.2 254 263 5.7 5.9 17 1.5 kw/100
w/200 khz/2.2 .mu.s/300 s/20Ar/40O.sub.2 252 260 5.76 5.96 19 1.5
kw/100 w/200 khz/2.2 .mu.s/300 s/20Ar/36O.sub.2 254 263 5.72 5.92
21 1.5 kw/100 w/200 khz/2.2 .mu.s/300 s/20Ar/30O.sub.2 255 268 5.76
5.9 1 1 kw/100 w/200 khz/2.2 .mu.s/300 s/20Ar/80O.sub.2 224 233
4.32 4.5 2 1 kw/100 w/200 khz/2.2 .mu.s/300 s/20Ar/36O.sub.2 231
243 4.12 4.3 3 1 kw/100 w/200 khz/2.2 .mu.s/300 s/20Ar/32O.sub.2
232 242 4.12 4.28 4 1 kw/100 w/200 khz/2.2 .mu.s/300
s/20Ar/28O.sub.2 237 243 4.1 4.22 5 1 kw/100 w/200 khz/2.2
.mu.s/300 s/20Ar/24O.sub.2 233 243 4.1 4.34 6 1 kw/100 w/200
khz/2.2 .mu.s/300 s/20Ar/28O.sub.2 231 245 4.12 4.3
TABLE-US-00002 TABLE II Rs (Ohms/ Bulk Rho Slot # Process Sq) Rs
unif % Th (nm) Th std 1sig (.mu.Ohm-cm) R.I (@632 nm) R.I Unif (%)
Comments 14 1.5 kw/100 w/200 khz/2.2 .mu.s/ 38.59 0.16 1.980758
0.000005 transparent 300 s/20Ar/80O2 15 1.5 kw/100 w/200 khz/2.2
.mu.s/ 94112 2 57.28 0.51 539073.5 1.951452 0.029342 translucent
300 s/20Ar/40O2 17 1.5 kw/100 w/200 khz/2.2 .mu.s/ 33927 60.282
58.48 1.37 198405.1 1.936166 0.040957 translucent 300 s/20Ar/40O2
19 1.5 kw/100 w/200 khz/2.2 .mu.s/ 7335.32 72.49 67.75 1.03 49696.8
1.980746 0.000018 translucent 300 s/20Ar/36O2 21 1.5 kw/100 w/200
khz/2.2 .mu.s/ 22.3507 2.995 80 178.8 metallic 300 s/20Ar/30O2 1 1
kw/100 w/200 khz/2.2 .mu.s/ 26.69 0.32 1.980326 0.00096 transparent
300 s/20Ar/80O2 2 1 kw/100 w/200 khz/2.2 .mu.s/ 36.4 0.13 1.980756
0.000003 transparent 300 s/20Ar/36O2 3 1 kw/100 w/200 khz/2.2
.mu.s/ 39.3 0.15 1.980761 0 transparent 300 s/20Ar/32O2 4 1 kw/100
w/200 khz/2.2 .mu.s/ 44.02 0.24 1.98076 0.000001 transparent 300
s/20Ar/28O2 5 1 kw/100 w/200 khz/2.2 .mu.s/ 58.1031 7.467 50 290.5
metallic 300 s/20Ar/24O2 6 1 kw/100 w/200 khz/2.2 .mu.s/ 58.0992
10.566 45 261.4 metallic 300 s/20Ar/28O2
TABLE-US-00003 TABLE III Target Run Power T Rs Rs (non- Bulk Rho
Thickness DepRate Trial (sec) (kW) Bias/W O2 Ar (.degree. C.)
(Ohms/Sq) unif) (uOhmcm) (.ANG.) n (A/sec) Target/V Target/I 14 100
3 300 3 60 280 38.69 4.07% 4.64E-04 1200 1.864 12 16 100 3 300 3 30
280 56.90 7.94% 6.98E-04 1227 1.888 12.27 288-308 9.86-10.42 10 100
3 100 3 60 280 50.98 11.89% 6.25E-04 1225 1.933 12.25 265-275
10.92-11.36 4 100 1.5 100 3 30 280 383.62 21.72% 2.09E-03 543.9
2.016 5.439 238-251 5.98-6.32 8 100 1.5 300 3 30 280 504.02 7.23%
2.44E-03 483.5 2.082 4.835 239-250 5.98-6.33 2 100 1.5 100 3 30 280
402.52 26.80% 2.10E-03 520.7 2.056 5.207 225-239 6.46-6.68 6 100
1.5 300 0 30 280 106.21 6.12% 6.17E-04 580.5 1.945 5.805 237-250
5.98-6.38 12 100 3 100 4 30 280 374.34 19.43% 4.18E-03 1116 1.917
11.16 285-300 9.98-10.52 15 100 3 300 4 30 100 6264.69 58.18%
6.81E-02 1087 1.897 10.87 282-304 10.00-10.62 7 100 1.5 200 4 30
100 7509.45 44.14% 2.95E-02 392.3 2.149 3.923 237-250 6.02-632 1
100 1.5 100 4 30 100 12284.82 112.55% 4.78E-02 389.1 2.236 3.891
238-250 6.04-632 11 100 3 100 3 60 100 631.77 49.40% 7.30E-03 1155
1.958 11.55 266-273 10.96-11.38 9 100 3 100 0 30 100 43.78 7.47%
5.55E-04 1268 1.945 12.68 288-307 9.78-10.42 5 100 1.5 200 3 60 100
1293.53 14.82% 5.88E-03 454.8 2.149 4.548 225-235 6.46-6.68 3 100
1.5 100 4 60 100 4154.43 28.25% 1.78E-02 428.8 2.211 4.288 226-235
6.44-6.64 13 100 3 200 0 60 100 49.05 7.24% 6.16E-04 1256 1.913
12.56 264-275 10.96-11.38 18 100 2.25 100 3 30 100 1476.79 21.54%
1.10E-02 744.5 2.044 7.445 263-277 8.08-8.56 17 100 1.5 150 0 60
100 157.23 8.83% 9.91E-04 630.5 1.931 6.305 225-231 6.48-6.74 19
100 2.25 150 3 60 100 526.72 13.01% 4.29E-03 814.2 2.021 8.142
247-255 8.78-9.14
* * * * *