U.S. patent application number 09/736090 was filed with the patent office on 2001-05-31 for low pressure vapor phase deposition of organic thin films.
Invention is credited to Ban, Vladimir S., Burrows, Paul E., Forrest, Stephen R..
Application Number | 20010002279 09/736090 |
Document ID | / |
Family ID | 25519260 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010002279 |
Kind Code |
A1 |
Forrest, Stephen R. ; et
al. |
May 31, 2001 |
Low pressure vapor phase deposition of organic thin films
Abstract
Methods for preparing organic thin films on substrates, the
method comprising the steps of providing a plurality of organic
precursors in the vapor phase, and reacting the plurality or
organic precursors at a sub-atmospheric pressure. Also included are
thin films made by such a method and apparatuses used to conduct
such a method. The method is well-suited to the formation of
organic light emitting devices and other display-related
technologies.
Inventors: |
Forrest, Stephen R.;
(Princeton, NJ) ; Burrows, Paul E.; (Princeton
Junction, NJ) ; Ban, Vladimir S.; (Princeton,
NJ) |
Correspondence
Address: |
KENYON & KENYON
One Broadway
New York
NY
10004
US
|
Family ID: |
25519260 |
Appl. No.: |
09/736090 |
Filed: |
December 13, 2000 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09736090 |
Dec 13, 2000 |
|
|
|
08972156 |
Nov 17, 1997 |
|
|
|
Current U.S.
Class: |
427/255.26 ;
118/724; 427/255.6 |
Current CPC
Class: |
C23C 14/568 20130101;
H01L 51/0059 20130101; C23C 16/45561 20130101; H01L 51/0081
20130101; H01L 51/56 20130101; H01L 51/001 20130101; C23C 14/12
20130101; C23C 14/50 20130101; C23C 16/30 20130101; H01L 51/0002
20130101; C23C 14/54 20130101 |
Class at
Publication: |
427/255.26 ;
427/255.6; 118/724 |
International
Class: |
C23C 016/00 |
Goverment Interests
[0001] This invention was made with Government support under
Contract No. F49620-92-J-05 24 (Princeton University), awarded by
the U.S. Air Force OSR (Office of Scientific Research). The
Government has certain rights in this invention.
Claims
What is claimed is:
1. A method for preparing an organic thin film on a substrate, said
method comprising the steps of: providing a plurality of organic
precursors, said organic precursors being in the vapor phase; and
reacting said plurality of organic precursors at a sub-atmospheric
pressure in the presence of said substrate to form said thin film
on said substrate.
2. The method of claim 1, wherein said substrate is located in a
reaction chamber.
3. The method of claim 2, further comprising the step of
transporting one of said plurality of organic precursors into said
reaction chamber prior to said step of reacting.
4. The method of claim 3, wherein said step of transporting
includes the step of using an inert gas to carry said transported
organic precursor into said reaction chamber.
5. The method of claim 4, wherein said inert gas is selected from
the group consisting of nitrogen, argon, helium, neon, krypton and
xenon.
6. The method of claim 1, wherein at least one of said plurality of
organic precursors is selected from the group consisting of MT,
DASI, MM, M.sub.fM, DASTh, MeOSI, DAS(Et)I, DAS(Et)OH, acetyl
toluenesulfonate, MA.sub.f, TTF, TCNQ, DCM, Alq.sub.3, TPP, TPD,
.alpha.-NPD, MTDATA, and (Alq.sub.2)'-OPh.
7. The method of claim 3, further comprising the step of
volatilizing said transported organic precursor prior to said step
of transporting.
8. The method of claim 7, wherein: said step of volatilizing
includes the step of loading said transported organic precursor
into a bubbler; and said step of transporting includes the step of
passing an inert gas through said bubbler for carrying said
transported organic precursor into said reaction chamber.
9. The method of claim 7, wherein: said step of volatilizing
includes the steps of placing said transported organic precursor
into an open container and heating said open container; and said
step of transporting includes the step of passing an inert gas over
said open container for carrying said transported organic precursor
into said reaction chamber.
10. The method of claim 7, wherein said step of volatilizing
includes the steps of: loading said transported organic precursor
into a Knudsen cell, said Knudsen cell extending into said reaction
chamber; and heating said Knudsen cell.
11. The method of claim 1, wherein the substrate is mounted to a
rotating sample holder.
12. The method of claim 1, wherein said sub-atmospheric pressure is
within the range of about 10.sup.-11-10.sup.2 torr.
13. An organic film produced by the method of claim 1.
14. The organic film of claim 13, wherein said film comprises a
light emitting material.
15. The organic film of claim 13, wherein said film comprises an
optically non-linear material.
16. An apparatus for preparing an organic thin film on a substrate,
said apparatus comprising: a reaction chamber; a heater
substantially surrounding said reaction chamber; tubing extending
into said reaction chamber; and a vacuum pump attached to said
reaction chamber.
17. The apparatus of claim 16, wherein said reaction chamber
comprises a reactor tube.
18. The apparatus of claim 16, wherein said heater is a multi-zone
heater/cooler.
19. The apparatus of claim 16, wherein said tubing comprises: a
tube having a first end and a second end, the second end of said
tube extending into said reaction chamber; and a gas source
connected to the first end of said tube.
20. The apparatus of claim 19, further comprising an open container
located inside of said tube, said open container for holding
organic precursor material.
21. The apparatus of claim 20, wherein said tube includes a
pressure regulator and a valve.
22. The apparatus of claim 16, wherein said tubing comprises: a
first tube having a first end and a second end, said second end of
said first tube extending into said reaction chamber; a bubbler
connected to the first end of said first tube, said bubbler for
containing organic precursor material; a second tube having a first
end and a second end, said second end of said second tube connected
to said bubbler; and a gas source connected to the first end of
said second tube.
23. The apparatus of claim 22, wherein said second tube includes a
pressure regulator and a valve.
24. The apparatus of claim 16, further comprising a
temperature-control block in contact with the substrate, said
temperature-control block having a channel therein.
25. The apparatus of claim 16, further comprising a trap attached
to said reaction chamber.
26. The apparatus of claim 16, further comprising a first roll and
a second roll in said reaction chamber for passing the substrate
between said first and second rolls.
27. An apparatus for preparing an organic thin film on a substrate,
said apparatus comprising: a reaction chamber; a Knudsen cell
extending into said reaction chamber; a sample holder connected to
the substrate; said sample holder being rotatable; and a vacuum
pump attached to said reaction chamber.
28. The apparatus of claim 27, further comprising tubing extending
into said reaction chamber, said tubing comprising: a first tube
having a first end and a second end, said second end of said first
tube extending into said reaction chamber; a bubbler connected to
the first end of said first tube, said bubbler for containing
organic precursor material; a second tube having a first end and a
second end, said second end of said second tube connected to said
bubbler; and a gas source connected to the first end of said second
tube.
29. The apparatus of claim 27, wherein said first tube is
heated.
30. The apparatus of claim 27, further comprising a cooled shroud
in said reaction chamber.
31. The apparatus of claim 27, further comprising a sensor for
detecting the thickness of the thin firm.
32. The apparatus of claim 31, wherein said sensor is a quartz
crystal.
33. The apparatus of claim 27, further comprising a load-lock
connected to said reaction chamber.
34. The apparatus of claim 27, wherein said vacuum pump is a
turbomolecular pump.
35. The apparatus of claim 27, further comprising a first roll and
a second roll in said reaction chamber for passing the substrate
between said first and second rolls.
36. An apparatus for preparing an organic thin film on a substrate,
said apparatus comprising: a plurality of vacuum chambers, said
plurality of vacuum chambers including a loading chamber and an
organic layer deposition chamber; and a conveyor belt passing
through said plurality of vacuum chambers, said conveyor belt
having a substrate thereon.
37. The apparatus of claim 36, wherein said organic layer
deposition chamber includes a reactant gas distributor.
38. The apparatus of claim 36, wherein said organic layer
deposition chamber includes a heater.
39. The apparatus of claim 36, further comprising a contact
deposition chamber.
40. An apparatus for preparing an organic thin film on a substrate,
said apparatus comprising: a reaction chamber; means for heating
said reaction chamber; means for introducing vapors of organic
precursor materials into said reaction chamber; and means for
reducing the pressure in said reaction chamber to below atmospheric
pressure.
41. A method for preparing an OLED, said method comprising the
steps of: providing a plurality of organic precursors, said organic
precursors being in the vapor phase; and reacting said plurality of
organic precursors at a sub-atmospheric pressure.
42. The method of claim 41, wherein said organic precursors are
light emitting materials.
43. The method of claim 41, wherein said step of reacting results
in the formation of a light emitting material.
Description
FIELD OF THE INVENTION
[0002] The present invention relates to the fabrication of optical
quality thin films, and more particularly to the low pressure
fabrication of such thin films for application in non-linear
optical devices and organic light emitting devices.
BACKGROUND OF THE INVENTION
[0003] The field of organic electroluminescence is a rapidly
growing technology. Spurred by potential application to displays,
organic light emitting devices (OLEDs) are capable of achieving
external quantum efficiencies of over 3%, and operational lifetimes
on the order of 10,000 hours at video brightness. Both small
molecule and polymer-based OLEDs are known, but polymer-based
devices have a general advantage of simple and inexpensive
fabrication by spin-on deposition techniques. In contrast, small
molecule devices are usually fabricated by thermal evaporation in
vacuum, which is usually a more expensive process than spin-on
deposition. Examples of OLED structures and processing techniques
are provided in published PCT application WO 96/19792, incorporated
herein by reference.
[0004] The use of organic vapor phase deposition (OVPD) has made
progress towards the low cost, large scale deposition of small
molecular weight organic layers with numerous potential photonic
device applications such as displays. The OVPD process is described
in U.S. Pat. No. 5,554,220 to Forrest et al.; S. R. Forrest et al.,
"Intense Second Harmonic Generation and Long-Range Structural
Ordering in Thin Films of an Organic Salt Grown by Organic Vapor
Phase Deposition," 68 Appl. Phys. Lett. 1326 (1996); and P. E.
Burrows et al., "Organic Vapor Phase Deposition: a New Method for
the Growth of Organic Thin Films with Large Optical
Non-linearities," 156 J. of Crystal Growth 91 (1995), each of which
is incorporated herein by reference.
[0005] The OVPD process uses carrier gases to transport source
materials to a substrate, where the gases condense to form a
desired thin film. The OVPD technique has been used, for example,
to deposit films of the optically non-linear organic (NLO) salt,
4'-dimethylamino-N-methyl-4-stil- bazolium tosylate (DAST), from
volatile precursors 4'-dimethylamino-N-meth- yl-4-stilbazolium
iodide (DASI) and methyl p-toluensulfonate (methyltosylate, MT),
which are transported by carrier gases to a heated substrate. In
this process, DASI thermally decomposes to form
4-dimethylamino-4-stilbazole (DAS), which subsequently reacts with
MT to form DAST on the substrate.
[0006] Because of its capability for controlled co-deposition of
materials with radically different vapor pressures, OVPD is
believed to be the only method for the precise stoichiometric
growth of multi-component thin films. However, the OPVD process is
conducted at atmospheric pressure, and films grown at or near
atmospheric pressure are often rough and have non-uniform surface
morphologies due to gas phase nucleation and a diffusion-limited
growth process.
SUMMARY OF THE INVENTION
[0007] The present invention makes use of low pressure deposition
techniques to produce organic thin films having superior surface
properties. In one aspect, the present invention comprises a method
for preparing an organic thin film on a substrate, the method
comprising the steps of providing a plurality of organic
precursors, the organic precursors being in the vapor phase; and
reacting the plurality of organic precursors at a sub-atmospheric
pressure in the presence of the substrate to form a thin film on
the substrate. In another aspect, the present invention includes
organic films made by such a method. In yet another aspect, the
present invention includes an apparatus designed to facilitate the
reaction of organic precursors at sub-atmospheric pressures to form
an organic film on a substrate.
[0008] One advantage of the present invention is that it provides
multi-component organic thin films wherein the amount of each
component in such films can be controlled accurately and
precisely.
[0009] Another advantage of the present invention is that it
provides uniform organic thin films having smooth surfaces.
[0010] Another advantage of the invention is that it provides a low
pressure organic vapor phase deposition method and apparatus for
the growth of thin films of organic light emitting materials and
optically non-linear organic salts.
[0011] Another advantage of the invention is that it provides a low
pressure organic molecular beam deposition method and apparatus for
the formation of thin films of organic light emitting materials and
optically non-linear organic salts.
[0012] Yet another advantage of the invention is that it provides a
method and apparatus for the uniform deposition of organic
materials over large substrate areas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 shows a LPOVPD reactor, in accordance with an
embodiment of the present invention.
[0014] FIG. 2 shows an OMVD reactor, in accordance with an
embodiment of the present invention.
[0015] FIG. 3 shows an apparatus for the continuous low pressure
deposition of organic materials onto substrates, in accordance with
an embodiment of the present invention.
[0016] FIGS. 4A and 4B are planar and cross-sectional views,
respectively, of a reactant gas distributor, in accordance with an
embodiment of the present invention.
[0017] FIG. 5 is a side view of a roll-to-roll substrate delivery
mechanism, in accordance with an embodiment of the present
invention.
DETAILED DESCRIPTION
[0018] The present invention provides a method and apparatus for
the growth of organic thin films on substrates while under
sub-atmospheric pressures. The method of the invention is herein
identified as low pressure organic vapor deposition (LPOVPD). The
LPOVPD method of the present invention allows for the accurate and
precise control of the deposition of multi-component organic thin
films. In addition, the thin films of the present invention are
characterized by superior surface properties such as low surface
roughnesses.
[0019] A LPOVPD reactor 10 in accordance with an embodiment of the
present invention is schematically shown in FIG. 1. Reactor 10
includes a reaction chamber, such as a reactor tube 12, and tubing
extending into the reaction chamber. Reactor tube 12 is a cylinder
having a suitable dimension such as, for example, a diameter of 10
cm and an approximate length of 45 cm in an experimental apparatus.
Reactor tube 12 is made of any suitable material such as glass or
quartz. An open container such as crucible 14 contains a first
organic precursor material and is placed within tube 36 near one
end 20 of the reactor tube 12. Alternatively, crucible 14 is placed
directly on the reactor tube 12 or on shelves or tubes therein.
Crucible 14 is heated or cooled by means of a multi-zone
heater/cooler 18, which substantially surrounds reactor tube 12.
The temperature control of crucible 14 results in the thermal
decomposition or volatilization of the first organic precursor
material within crucible 14. A regulated stream 30 of inert carrier
gas is passed through tube 36 and into the reaction chamber, thus
causing vapor of the first organic precursor to flow along the
reactor tube 12 toward its exhaust end 22. The inert carrier gas is
an inert gas such as nitrogen, helium, argon, krypton, xenon, neon
and the like. Gases with a reducing character, such as hydrogen,
ammonia and methane, are also inert for many organic materials. Use
of these reducing gases often has the additional benefit of
assisting in the burning of undesired excess reactants.
[0020] Inert gas is delivered from tank 24 through a regulator
valve 26 and into tubing 28 for delivery through at least two flow
paths, 30 and 38, and into reactor tube 12. One flow path 30
includes a series connected pressure regulator 32, flow meter 34
and quick switching valve 35 from which the carrier gas is
delivered into end 20 of reactor tube 12. The second flow path 38
includes a series connected pressure regulator 40, flow meter 42
and quick switching valve 39 from which the carrier gas flows into
a bubbler 46, which contains a second organic precursor material
48. To facilitate the temperature control of second organic
precursor material 48, bubbler 46 is partially immersed in bath 50
within container 52. Inert gas from tank 24 bubbles through the
second organic precursor 48 and through tubing 54 to carry vapor of
the second organic precursor 48 into reactor tube 12. During this
process, tube 54 must be maintained at a sufficiently high
temperature to avoid recondensation of the volatilized second
organic precursor 48 as it travels from the bubbler to the
reactor.
[0021] The amount of any precursor entering reactor tube 12 is
controlled by processing parameters such as the temperature and
flow rate of the carrier gas and the temperature of the reactants.
The LPOVPD method provides precise metering of the precursors or
reactants independently of their vapor pressure or chemical nature
using pressure mass flow controllers. The present method thus
permits the combination of materials with widely different
characteristics in ratios necessary for the production of desired
films.
[0022] The precursor streams are capable of being turned on and off
almost instantly by employing quick switching valves 35 and 39.
These valves direct the precursor streams into reactor 12 or into a
by-pass line (not shown) so that at any given time, different
precursor streams may be entering the reactor 12 for the deposition
of films of different compositions and characteristics. Valve 39
also regulates the admittance of carrier gas into bubbler 46.
Valves 35 and 39 thus allow the rapid change of reactant streams
entering the reactor 12, for changing the nature and the
composition of the grown films. It is thus possible, for example,
to grow ABAB, ABCABC, ABABCAB, and ABCDABCD-type films, where each
letter denotes a different molecular layer or composition.
[0023] A vacuum pump 66 and control throttle valve 68 are attached
to reactor 10 at the exhaust 62. Most of the organic vapors not
deposited onto substrate 58 are condensed in a trap 64 placed
upstream from pump 66. Trap 64 contains liquid nitrogen or a
neutral, fluorocarbon oil, for example. Throttle valve 68 regulates
the pressure in reactor 10. An appropriate pressure gauge is
connected to the reactor (not shown) with electronic feedback to
the control throttle valve 68 to maintain a desired pressure in the
reactor.
[0024] Vacuum pump 66 provides a pressure of about 0.001-100 Torr
in reactor tube 12. The actual pressure for any combination of
acceptor, donor, and single component layers is experimentally
determined with reference to the temperatures required to
volatilize the precursor materials, the wall temperature to prevent
condensation of the precursor materials, and the reaction zone
temperature gradient. The optimal choice of pressure is unique to
the requirements of each deposited organic layer. For example,
optimal pressures for the deposition of single component layers
such as tris-(8-hydroxyquinoline) aluminum (Alq.sub.3) or
N-N'-diphenyl-N,N-bis(3-methylphenyl) 1,1'-biphenyl-4,4'diamine
(TPD) are about 0.1-10 Torr.
[0025] The substrates on which the thin films of the present
invention are deposited are typically selected from those materials
that are commonly encountered in semiconductor and optics
manufacturing. Such materials include, for example, glass, quartz,
silicon, gallium arsenide and other III-V semiconductors, aluminum,
gold and other precious and non-precious metals, polymer films,
silicon dioxide and silicon nitride, indium-tin-oxide and the like.
For high quality optical thin films, it is preferable to use
substrates that provide crystalline interactions with the deposited
organic film to induce epitaxial growth. To achieve such epitaxial
growth, it is often necessary to coat substrates with non-polar
organics having crystalline structures similar to the film to be
deposited.
[0026] In addition, as an organic thin film is deposited onto
substrate 58, it is often desirable to control the temperature of
the substrate. Independent control of substrate temperature is
accomplished, for example, by contacting substrate 58 with
temperature-control block 60, which has channels therein for the
circulation of materials such as water, gas, freon glycerin, liquid
nitrogen, and the like. It can also be heated by the use of
resistance or radiant heaters positioned on or near the block
60.
[0027] Reactor 20 of FIG. 1 is expandable to include multiple
bubblers 46N to feed additional precursors into reactor 20.
Similarly, multiple carrier gas flow paths 30N are used to deliver
yet additional precursors from crucibles 14N. As an alternative,
crucibles 14, 14N are vertically stackable on shelves or in tubes
within reactor tube 12 for processing the additional precursors.
Depending on the organic film to be deposited, one or more flow
paths 30, 38 are used alone or in any combination to provide the
necessary precursor materials.
[0028] The method of the present invention is used to deposit a
wide variety of organic thin films from the reaction of vapor
precursors. As used herein, "reaction" refers to a chemical
reaction in which precursor reactants form a distinct reaction
product, or alternatively, it merely refers to a combination or
mixture of precursor materials, or where precursor materials form a
donor-acceptor or quest-host relationship. For example, in
accordance with the present invention, the following NLO materials
are formed as thin films by the reaction of the listed
precursors:
1 Film Material First Precursor Second Precursor
4'-dimethylamino-N- 4'-dimethylamino-4- methyl tosylate (MT)
methyl-4-stilbazolium stilbazole (DAS) tosylate (DAST)
4'-dimethylamino-4- methyl 4'-dimethylamino-4- methylstilbazolium
methanesulfonate stilbazole (DAS) methanesulfonate (MM) (DASM)
4'-dimethylamino-4- methyl 4'-dimethylamino-4- methyistilbazolium
trifluoromethane- stilbazole (DAS) trifluoromethanesulfonate
sulfonate (M.sub.fM) (DASM.sub.f) 4'-dimethylamino-N- methyl
tosylate 4'-dimethylamino-4- methyl-4-stilbazolium (MT)
methylstilbazolium tosylate (DAST) thiophenoxide (DASTh)
4'-methoxy-4- methyl tosylate 4'-methoxy-4- methylstilbazolium (MT)
methylstilbazole tosylate (MeOST) (MeOS) 4'-dimethylamino-N- methyl
tosylate 4'-dimethylamino-4- methyl-4-stilbazolium (MT)
ethylstilbazolium tosylate (DAST) iodide (DAS(Et)I)
4'-dimethylamino-N- methyl tosylate 4'-dimethylamino-4-
methyl-4-stilbazolium (MT) ethylstilbazolium tosylate (DAST)
hydroxide (DAS(Et)OH) 4'-dimethylamino-4- acetyl
4'-dimethylamino-4- acetylstilbazolium toluenesulfonate stilbazole
(DAS) tosylate (DAAST) (AT) 4'dimethylamino-4- methyl
4'-dimethylamino-4- methylstilbazolium trifluoroacetate stilbazole
(DAS) trifluoroacetate (MA.sub.f) (DASA.sub.f)
[0029] In another example relating more specifically to light
emitting materials used to make OLEDs, the precursors consist of,
for example, tetrathisferlvalene (TFF) and
7,7,8,8-tetracyanoquinodimethane (TCNQ). The mixing step results in
the charge transfer complex TTF-TCNQ which deposits onto a
substrate. In another example relating to OLEDs,
4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran
(DCM) is added into a high flow rate carrier gas stream while
Alq.sub.3 is added into a lower flow rate carrier gas stream. These
streams are then mixed in a central reactor tube, thus providing
the desired dilution of the guest molecule in the host matrix film
to form a single luminescent layer. Other guest molecule examples
in Alq.sub.3 hosts are 5,10,15,20-tetraphenyl-21H,23H-porphine
(TPP), Rubrene, DCM2, Coumarin, etc. As a variation, multiple
dopants can be added into a single host to achieve efficient broad
color conversion.
[0030] In another example, a bilayer light emitting device
consisting of a hole transporting layer ("HTL") such as TPD;
.alpha.-4,4'-bis[N-(1-naphth- yl)-N-Phenyl-amino]biphenyl
(.alpha.-NPD); or MTDATA, layered onto the surface of a light
emitting layer ("EL") such as Alq.sub.3, bis-
(8-hydroxyquinoline)aluminum oxyphenyl ((Alq.sub.2)'-OPh) or doped
combinations of these layers, is grown by sequentially growing the
HTL and EL to desired thicknesses. This is followed by growing
additional layers onto the organics, or by growth on metallic
contact layers using organometallic sources such as
trimethyl-indium, trimethyl-gallium, and the like.
[0031] In addition to the apparatus and method described with
reference to FIG. 1, the present invention includes a low pressure
reactor 70 and method as shown in FIG. 2. Reactor 70 includes a
modified ultra-high vacuum chamber 71 and a vacuum pump such as a
turbomolecular pump (not shown) connected to valve 72. Typical
chamber base pressures in chamber 71 are 10.sup.-8-10.sup.-11 Torr.
The process of depositing organic layers with the use of reactor 70
is called organic molecular beam vapor deposition (OMVD). Although
both LPOVPD and OMVD make use of sub-atmospheric pressures for the
deposition of organic layers, the principle difference between
these processes is that in the latter, the molecular mean free path
is comparable to or larger than the dimensions of the chamber 70.
In comparison, the mean free path in LPOVPD is significantly
shorter than the gas reactor dimensions. OMVD thus allows for the
formation of highly directed molecular "beams" from the injectors
to the substrate, allowing for precise kinetic control of the grown
film thickness, purity and morphology.
[0032] Bubbler 74 is included for containing a first precursor
material 75. The bubbler 74 is placed into container 76 and
immersed in a temperature controlled bath 80. A high purity inert
carrier gas 78 bubbles through first precursor 75, and carries
respective vapors through heated tubing 79 and into vacuum chamber
71 by way of injector 82. Once inside chamber 71, the precursor
vapors form a molecular beam 83 that impinges on substrate 85.
Substrate 85 is provided with a means for providing temperature
control such as coolant port 81, for example.
[0033] Vacuum chamber 71 optionally is provided with at least one
Knudsen or K-cell 86, which contains a second precursor material
88. K-cell 86 is a uniformly heated and controlled oven for the
effusion of evaporants under vacuum. For example, K-cell 86 is
heated to crack DASI or other precursor and sublime the resulting
DAS, such that it is injected into reactor 70 as a molecular beam
89. Alternatively, K-cell 86 simply sublimes a single component
substance such as Alq.sub.3. Alternatively, K-cell 86 is fitted
with a carrier gas inlet used to dilute the concentration of the
molecular species being sublimed or evaporated into the gas stream
by thermalization. This dilution process is particularly useful in
achieving precise doping levels of guest-host systems such as
DCM-Alq.sub.3 by controlling the temperatures of bath 80 and
Knudsen cell 86 as well as the flow of carrier gas 78 to bubbler
74.
[0034] Molecular beams 83 and 89 impinge on substrate 85 to deposit
an organic thin film, the thickness of which is monitored by quartz
crystal 93. Sample holder 90 rotates to ensure a uniform deposition
and reaction of precursor materials. The deposition of precursor
materials is further controlled by shutters 87, which are used to
interrupt molecular beams 83 and 89.
[0035] Reactor 70 also optionally includes a cooled shroud 91 to
help keep the pressure of vacuum chamber 71 to a minimum for
re-evaporated precursor materials. Also preferably included is a
partition 92 to keep precursor materials from migrating and thus
contaminating each other.
[0036] Reactor 70 is embellished with many of the same attributes
of the LPOVPD reactor shown in FIG. 1, such as quick switching
valves, bypass lines and the like. Reactor 70 is able to be fitted
with multiple Knudsen cells and bubblers for the deposition of
multiple precursor materials onto substrate 85. Reactor 70 also
preferably includes a "load-lock" 94 for sample introduction.
Load-lock 94 includes door 95 and vacuum pump 96, and provides for
the exchange of samples without compromising the pressure of
chamber 71.
[0037] The apparatus of FIG. 1 is optionally modified for the
continuous deposition of organic layers on large area substrates,
as shown by the example illustrated in FIG. 3. The apparatus of
FIG. 3 includes a plurality of vacuum chambers such as loading
chamber 146, organic layer deposition chambers 150 and 152, contact
deposition chamber 154, and unload chamber 156. As an example, each
deposition chamber is a LPOVPD reactor 10 of FIG. 1. The substrates
137 are transported on a conveyor belt 148 through each of chambers
150, 152, 154 and 156. In the embodiment shown in FIG. 3, chambers
150, 152 and 154 include sources 158, 160 and 162, respectively, of
radiant heat to prevent the condensation of organic vapors.
Although only two organic layer deposition chambers 150 and 152 are
shown in FIG. 3, additional chambers are included as desired. In
passing from the loading chamber 146 to the organic layer
deposition chambers 150 and 152, and from the contact deposition
chamber 154 to the unload chamber 156, the substrate 137 passes
through air locks (not shown) so as not to compromise the vacuum in
the chambers 150, 152, and 154. As an example relating to OLEDs,
chambers 150 and 152 are used for the deposition of TPD and
Alq.sub.3, respectively, and chamber 154 is used for the deposition
of an Mg:Ag contact layer.
[0038] Each of the chambers 150, 152, and 154 in the example of
FIG. 3 includes a reactant gas distributor (RGD) 108 for the
deposition of organic precursor materials, as shown in detail in
FIGS. 4A and 4B. RGD's 108 are used as an alternative to the
organic precursor delivery mechanisms of FIGS. 1 and 2, and are
used to provide gas curtains, 120, 120', 120" and 120"'. RGD 108
ensures that where multiple organic precursors are deposited, the
precursors remain separated until deposited on a substrate,
whereupon reaction of the precursors is permitted to take place.
RGD 108 includes heater 122, second carrier gas inlet 112 and gas
manifold 132. Heater 122 prevents the premature condensation of
organic precursor materials. Over RGD 108 is a first carrier gas
inlet 114 and distributor plate 110. First carrier gas inlet 114
supplies gas which usually carries a first organic precursor of
generally low volatility such as, for example, MT. The first
carrier gas enters a reaction chamber though distributor plate 110,
which is a wire mesh, a glass filter material, or a porous
stainless steel plate, for example. The column of carrier gas
flowing through distributor plate 110 is shadowed by the RGD 108.
RGD 108 provides a planar gas curtain 120 of a second organic
precursor of generally low vapor pressure such as, for example,
DAS. A second carrier gas containing a second organic precursor
enters at inlet 112 and is directed into gas manifold 132. Manifold
132 is a hollow tube having a line of holes 134 for feeding the
second carrier has into an annular cavity 126, which surrounds
manifold 132. Second carrier gas exits RGD 108 through slit 136,
thus giving it the shape of a planar curtain.
[0039] As an example, curtain 120 is comprised of TPD vapors,
curtain 120' is comprised of Alq.sub.3 vapors and curtain 120" is
comprised of vapors such as a polypyrole or metallorganic compounds
that produce a conductive surface. If desired, control or tuning of
the color of light emitted by an OLED can be effected by suitable
doping of the Alq.sub.3 layer with an additional RGD device 108 in
the chamber 152 that produces a curtain 120"' of dopant vapor.
[0040] The apparatus of FIG. 1, FIG. 2 or FIG. 3 is optionally
modified by using a "roll-to-roll" substrate delivery system, as
shown in FIG. 5. The delivery system shown in FIG. 5 is suitable
for the deposition of organic thin films onto large area, flexible
substrates. Substrate 180 is made of a polymer sheet or metal foil,
for example, and is delivered from roll 181 to roll 182. The
deposition of organic precursors onto substrate 180 occurs when
substrate 180 is unrolled from roll 181 and is therefore exposed to
the reaction chamber of FIG. 1, or when exposed to the molecular
beam or curtains of FIGS. 2 and 3, respectively. Rolls 181 and 182
are driven by any suitable means, such as a variable speed motor.
The speed at which substrate 180 is passed from roll 181 to roll
182 dictates the thickness of the organic film that forms on
substrate 180.
[0041] The present invention is further described with reference to
the following non-limiting examples.
EXAMPLE 1
[0042] Using the apparatus of FIG. 1, layers of organic light
emitting materials were grown using glass and flexible polyester
substrates precoated with transparent layers of indium tin oxide
(ITO). The ITO forms the anode of the device with a thickness of
1700 .ANG. and 1200 .ANG. for the glass and polyester substrates,
respectively, yielding anode resistances of 10 .OMEGA. and 60
.OMEGA., respectively. Glass substrates were cleaned by rinsing in
a solution of detergent and deionized water in an ultrasonic bath,
and then boiling in 1,1,1-trichloroethane, rinsing in acetone and
finally rinsing in 2-propanol. To avoid damage due to exposure to
organic solvents, the flexible substrates were cleaned by rinsing
only in the detergent and 2-propanol solutions.
[0043] Glass substrates were placed within the reactor tube 12 at a
location where the temperature was approximately 220.degree. C. The
first layer deposited on the ITO surface was TPD, a hole
transporting material. Specifically, TPD vapor was carried from
crucible 14 to substrate 28 via nitrogen carrier gas. The TPD
growth conditions included a source temperature of 200.+-.5.degree.
C., a nitrogen carrier gas flow rate of 100 sccm, a reactor
pressure of 0.50 Torr and a growth time of 20 minutes. At a
nitrogen flow rate of 100 sccm, the Reynolds number of the system
was .about.500, indicating operation well within the laminar flow
regime. The TPD layer was grown to a thickness of between 100-300
.ANG..
[0044] After deposition, the temperature near the TPD crucible was
reduced, and the corresponding nitrogen flow was shut off. Next, an
electron transporting layer of Alq.sub.3 was grown by turning on a
separate nitrogen line to carry Alq.sub.3 vapor from crucible 14N
into chamber 12. The Alq.sub.3 growth conditions included a source
temperature of 247.+-.8.degree. C., a nitrogen flow rate of 50
sccm, a pressure of 0.65 Torr and a growth time of 10 minutes.
During the deposition of both the TDP and Alq.sub.3, the substrate
was maintained at 15.degree. C. using a water cooled stainless
steel substrate holder. The TPD layer was grown to a thickness of
between 700-1100 .ANG..
[0045] After deposition of the Alq.sub.3 layer, the substrate was
removed from the reactor and a Mg:Ag top contact was applied by
thermal evaporation. The contact was completed with the evaporation
of a 1000 .ANG. thick protective Ag layer.
[0046] The use of low pressures during deposition resulted in
organic layers having smooth and uniform surfaces. For example, the
TPD and Alq.sub.3 layers were measured via atomic force microscopy
to have RMS roughnesses of 6-8 .ANG. and 9-11 .ANG., respectively.
The resulting OLED devices exhibited current-voltage
characteristics wherein I.alpha.V at low voltages and
I.alpha.V.sup.9 at higher voltages. The turn-on voltage, V.sub.T,
at which the power law dependence of I on V changed, was about
6V.
EXAMPLE 2
[0047] An NLO film was prepared using the apparatus shown in FIG.
1. MT 48 was loaded into a 30 cm.sup.3 bubbler 46, the temperature
of which was maintained at approximately 80.degree.-100.degree. C.
by silicone oil bath 50. Nitrogen gas was used to bubble through
the MT 48, thereby carrying MT vapor through glass tube 54 and into
reactor tube 12 at a location approximately 5 cm beyond crucible
14, which contained was placed on the floor of reactor tube 12 and
DASI. The pressure within reactor tube 12 was maintained at about
10.sup.-2 torr. DAS vapor reacted with the MT vapor to form a solid
film of DAST on substrates 58, which were supported on substrate
block 60. Excess unreacted MT vapor and any volatile side-reaction
products were exhausted from exhaust tube 62. DAST films thus
formed are useful as optical switches, for example.
[0048] The present invention makes use of low pressure deposition
techniques to produce organic thin films having superior surface
properties and accurate and precise compositions. Although various
embodiments of the invention are shown and described herein, they
are not meant to be limiting. For example, those of skill in the
art may recognize certain modifications to these embodiments, which
modifications are meant to be covered by the spirit and scope of
the appended claims.
[0049] The subject invention as disclosed herein may be used in
conjunction with co-pending applications: "High Reliability, High
Efficiency, Integratable Organic Light Emitting Devices and Methods
of Producing Same", Ser. No. 08/774,119 (filed Dec. 23, 1996);
"Novel Materials for Multicolor LED's", Ser. No. 08/850,264 (filed
May 2, 1997); "Electron Transporting and Light Emitting Layers
Based on Organic Free Radicals", Ser. No. 08/774,120 (filed Dec.
23, 1996); "Multicolor Display Devices", Ser. No. 08/772,333 (filed
Dec. 23, 1996); "Red-Emitting Organic Light Emitting Devices
(LED's)", Ser. No. 08/774,087 (filed Dec. 23, 1996); "Driving
Circuit For Stacked Organic Light Emitting Devices", Ser. No.
08/792,050 (filed Feb. 3, 1997); "High Efficiency Organic Light
Emitting Device Structures", Ser. No. 08/772,332 (filed Dec. 23,
1996); "Vacuum Deposited, Non-Polymeric Flexible Organic Light
Emitting Devices", Ser. No. 08/789,319 (filed Jan. 23, 1997);
"Displays Having Mesa Pixel Configuration", Ser. No. 08/794,595
(filed Feb. 3, 1997); "Stacked Organic Light Emitting Devices",
Ser. No. 08/792,046 (filed Feb. 3, 1997); "High Contrast
Transparent Organic Light Emitting Device Display", Ser. No.
08/821,380 (filed Mar. 20, 1997); "Organic Light Emitting Devices
Containing A Metal Complex of 5-Hydroxy-Quinoxaline as A Host
Material", Ser. No. 08/838,099 (filed Apr. 15, 1997); "Light
Emitting Devices Having High Brightness", Ser. No. 08/844,353
(filed Apr. 18, 1997); "Organic Semiconductor Laser", Ser. No.
60/046,061 (filed May 9, 1997); "Organic Semiconductor Laser", Ser.
No. 08/859,468 (filed May 19, 1997); "Saturated Full Color Stacked
Organic Light Emitting Devices", Ser. No. 08/858,994 (filed May 20,
1997); "An Organic Light Emitting Device Containing a Hole
Injection Enhancement Layer", Ser. No. 08/865,491 (filed May 29,
1997); "Plasma Treatment of Conductive Layers", Ser. No.
PCT/US97/10252; (filed Jun. 12, 1997; Patterning of Thin Films for
the Fabrication of Organic Multi-Color Displays", Ser. No.
PCT/US97/10289 (filed Jun. 12, 1997); "Double Heterostructure
Infrared and Vertical Cavity Surface Emitting Organic Lasers", Ser.
No. 60/053,176 (filed July 18, 1997); "Oleds Containing Thermally
Stable Asymmetric Charge Carrier Materials", Ser. No. 08/929,029
filed (Sep. 8, 1997), "Light Emitting Device with Stack of Oleds
and Phosphor Downconverter", Ser. No. 08/925,403 (filed Sep. 9,
1997), "An Improved Method for Depositing Indium Tin Oxide Layers
in Organic Light Emitting Devices", Ser. No. 08/928,800 (filed Sep.
12, 1997), "Azlactone-Related Dopants in the Emissive Layer of an
Oled" (filed Oct. 9, 1997), Ser. No. 08/948,130, "A Highly
Transparent Organic Light Emitting Device Employing A Non-Metallic
Cathode", (filed Nov. 3, 1997), Attorney Docket No. 10020/40
(Provisional), and "A Highly Transparent Organic Light Emitting
Device Employing a Non-Metallic Cathode", (filed Nov. 5, 1997),
Attorney Docket No. 10020/44, each co-pending application being
incorporated herein by reference in its entirety. The subject
invention may also be used in conjunction with the subject matter
of each of co-pending U.S. patent application Ser. Nos. 08/354,674,
08/613,207, 08/632,322 and 08/693,359 and provisional patent
application Ser. Nos. 60/010,013, 60/024,001 and 60/025,501, each
of which is also incorporated herein by reference in its
entirety.
* * * * *