U.S. patent application number 15/881872 was filed with the patent office on 2018-05-31 for deposition system and method using a delivery head separated from a substrate by gas pressure.
The applicant listed for this patent is Eastman Kodak Company. Invention is credited to David H. Levy.
Application Number | 20180148839 15/881872 |
Document ID | / |
Family ID | 39272914 |
Filed Date | 2018-05-31 |
United States Patent
Application |
20180148839 |
Kind Code |
A1 |
Levy; David H. |
May 31, 2018 |
DEPOSITION SYSTEM AND METHOD USING A DELIVERY HEAD SEPARATED FROM A
SUBSTRATE BY GAS PRESSURE
Abstract
A process for depositing a thin film material on a substrate is
disclosed, comprising simultaneously directing a series of gas
flows from the output face of a delivery head of a thin film
deposition system toward the surface of a substrate, and wherein
the series of gas flows comprises at least a first reactive gaseous
material, an inert purge gas, and a second reactive gaseous
material, wherein the first reactive gaseous material is capable of
reacting with a substrate surface treated with the second reactive
gaseous material, wherein one or more of the gas flows provides a
pressure that at least contributes to the separation of the surface
of the substrate from the face of the delivery head. A system
capable of carrying out such a process is also disclosed.
Inventors: |
Levy; David H.; (Rochester,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Eastman Kodak Company |
Rochester |
NY |
US |
|
|
Family ID: |
39272914 |
Appl. No.: |
15/881872 |
Filed: |
January 29, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11620744 |
Jan 8, 2007 |
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15881872 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/02178 20130101;
C23C 16/45553 20130101; H01L 21/02186 20130101; C23C 16/4408
20130101; H01L 21/02164 20130101; H01L 21/02183 20130101; C23C
16/45574 20130101; H01L 21/02189 20130101; H01L 21/0262 20130101;
C23C 16/403 20130101; C23C 16/45563 20130101; H01L 21/02192
20130101; C23C 16/45519 20130101; C23C 16/45551 20130101; H01L
21/0228 20130101; H01L 21/02557 20130101; C23C 16/45525 20130101;
C23C 16/545 20130101; H01L 21/02181 20130101; C23C 16/45527
20130101 |
International
Class: |
C23C 16/455 20060101
C23C016/455; H01L 21/02 20060101 H01L021/02; C23C 16/40 20060101
C23C016/40; C23C 16/54 20060101 C23C016/54; C23C 16/44 20060101
C23C016/44 |
Claims
1. An atomic layer deposition system for depositing a thin film
onto a substrate comprising: a delivery head having an output face
with a means for providing a series of gas flows and a means for
moving the substrate relative to the series of gas flows, wherein:
at least a portion of the output face provides the series of gas
flows in the order of a gas flow of a first reactant gas, a gas
flow of a purge gas, a gas flow of a second reactant gas; wherein
each of the gas flows flow from an associated output opening in the
output face to one or more associated exhaust openings in the
output face and is located between the output face and a surface of
the substrate, and wherein the distance between of the substrate
and the output face is at least in part controlled by one or more
of the gas flows during thin film deposition.
2. The atomic layer deposition system of claim 1 wherein the gas
flows are parallel to the direction of the relative motion of the
substrate.
3. The atomic layer deposition system of claim 2 wherein the output
face has alternating output openings and exhaust openings.
4. The atomic layer deposition system of claim 2 wherein each of
the gas flows shares an exhaust opening with an adjacent gas
flow.
5. The atomic layer deposition system of claim 2 wherein the gas
flow has a portion which is in the direction of substrate travel
and a portion that is 180 degrees to the direction of the relative
motion of the substrate.
6. The atomic layer deposition system of claim 1 wherein in the
series of gas flows in the portion of the output face, a portion of
the purge gas flow is exhausted with the first reactant gas flow in
a first common exhaust opening and a portion of the purge gas flow
is exhausted with the second reactant gas flow in a second common
exhaust opening.
7. The atomic layer deposition system of claim 1 wherein the gas
flows are transverse to the direction of the relative motion of the
substrate.
8. The atomic layer deposition system of claim 7 wherein there are
exhaust openings at the edge of the output face.
9. The atomic layer deposition system of claim 7 wherein the gas
flow has a portion which flows toward an edge of the substrate and
a portion that flows toward an opposite edge of the substrate.
10. The atomic layer deposition system of claim 7 wherein the gas
flows are perpendicular to the direction of the relative motion of
the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of prior U.S. patent
application Ser. No. 11/620,744, filed Jan. 8, 2007, which is
hereby incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention generally relates to the deposition of
thin-film materials and, more particularly, to apparatus for atomic
layer deposition onto a substrate using a distribution head
directing simultaneous gas flows onto a substrate.
BACKGROUND OF THE INVENTION
[0003] Among the techniques widely used for thin-film deposition is
Chemical Vapor Deposition (CVD) that uses chemically reactive
molecules that react in a reaction chamber to deposit a desired
film on a substrate. Molecular precursors useful for CVD
applications comprise elemental (atomic) constituents of the film
to be deposited and typically also include additional elements. CVD
precursors are volatile molecules that are delivered, in a gaseous
phase, to a chamber in order to react at the substrate, forming the
thin film thereon. The chemical reaction deposits a thin film with
a desired film thickness.
[0004] Common to most CVD techniques is the need for application of
a well-controlled flux of one or more molecular precursors into the
CVD reactor. A substrate is kept at a well-controlled temperature
under controlled pressure conditions to promote chemical reaction
between these molecular precursors, concurrent with efficient
removal of byproducts. Obtaining optimum CVD performance requires
the ability to achieve and sustain steady-state conditions of gas
flow, temperature, and pressure throughout the process, and the
ability to minimize or eliminate transients.
[0005] Especially in the field of semiconductor, integrated
circuit, and other electronic devices, there is a demand for thin
films, especially higher quality, denser films, with superior
conformal coating properties, beyond the achievable limits of
conventional CVD techniques, especially thin films that can be
manufactured at lower temperatures.
[0006] Atomic layer deposition ("ALD") is an alternative film
deposition technology that can provide improved thickness
resolution and conformal capabilities, compared to its CVD
predecessor. The ALD process segments the conventional thin-film
deposition process of conventional CVD into single atomic-layer
deposition steps. Advantageously, ALD steps are self-terminating
and can deposit one atomic layer when conducted up to or beyond
self-termination exposure times. An atomic layer typically ranges
from about 0.1 to about 0.5 molecular monolayers, with typical
dimensions on the order of no more than a few Angstroms. In ALD,
deposition of an atomic layer is the outcome of a chemical reaction
between a reactive molecular precursor and the substrate. In each
separate ALD reaction-deposition step, the net reaction deposits
the desired atomic layer and substantially eliminates "extra" atoms
originally included in the molecular precursor. In its most pure
form, ALD involves the adsorption and reaction of each of the
precursors in the absence of the other precursor or precursors of
the reaction. In practice, in any system it is difficult to avoid
some direct reaction of the different precursors leading to a small
amount of chemical vapor deposition reaction. The goal of any
system claiming to perform ALD is to obtain device performance and
attributes commensurate with an ALD system while recognizing that a
small amount of CVD reaction can be tolerated.
[0007] In ALD applications, typically two molecular precursors are
introduced into the ALD reactor in separate stages. For example, a
metal precursor molecule, ML.sub.x, comprises a metal element, M
that is bonded to an atomic or molecular ligand, L. For example, M
could be, but would not be restricted to, Al, W, Ta, Si, Zn, etc.
The metal precursor reacts with the substrate when the substrate
surface is prepared to react directly with the molecular precursor.
For example, the substrate surface typically is prepared to include
hydrogen-containing ligands, AH or the like, that are reactive with
the metal precursor. Sulfur (S), oxygen (O), and Nitrogen (N) are
some typical A species. The gaseous metal precursor molecule
effectively reacts with all of the ligands on the substrate
surface, resulting in deposition of a single atomic layer of the
metal:
substrate-AH+ML.sub.x.fwdarw.substrate-AML.sub.x-1+HL (1)
where HL is a reaction by-product. During the reaction, the initial
surface ligands, AH, are consumed, and the surface becomes covered
with L ligands, which cannot further react with metal precursor
ML.sub.x. Therefore, the reaction self-terminates when all of the
initial AH ligands on the surface are replaced with AML.sub.x-1
species. The reaction stage is typically followed by an inert-gas
purge stage that eliminates the excess metal precursor from the
chamber prior to the separate introduction of a second reactant
gaseous precursor material.
[0008] The second molecular precursor then is used to restore the
surface reactivity of the substrate towards the metal precursor.
This is done, for example, by removing the L ligands and
redepositing AH ligands. In this case, the second precursor
typically comprises the desired (usually nonmetallic) element A
(i.e., O, N, S), and hydrogen (i.e., H.sub.2O, NH.sub.3, H.sub.2S).
The next reaction is as follows:
substrate-A-ML+AH.sub.Y.fwdarw.substrate-A-M-AH+HL (2)
This converts the surface back to its AH-covered state. (Here, for
the sake of simplicity, the chemical reactions are not balanced.)
The desired additional element, A, is incorporated into the film
and the undesired ligands, L, are eliminated as volatile
by-products. Once again, the reaction consumes the reactive sites
(this time, the L terminated sites) and self-terminates when the
reactive sites on the substrate are entirely depleted. The second
molecular precursor then is removed from the deposition chamber by
flowing inert purge-gas in a second purge stage.
[0009] In summary, then, the basic ALD process requires
alternating, in sequence, the flux of chemicals to the substrate.
The representative ALD process, as discussed above, is a cycle
having four different operational stages:
[0010] 1. MLX reaction;
[0011] 2. MLX purge;
[0012] 3. AH.sub.y reaction; and
[0013] 4. AH.sub.y purge, and then back to stage 1.
[0014] This repeated sequence of alternating surface reactions and
precursor-removal that restores the substrate surface to its
initial reactive state, with intervening purge operations, is a
typical ALD deposition cycle. A key feature of ALD operation is the
restoration of the substrate to its initial surface chemistry
condition. Using this repeated set of steps, a film can be layered
onto the substrate in equal metered layers that are all alike in
chemical kinetics, deposition per cycle, composition, and
thickness.
[0015] ALD can be used as a fabrication step for forming a number
of types of thin-film electronic devices, including semiconductor
devices and supporting electronic components such as resistors and
capacitors, insulators, bus lines and other conductive structures.
ALD is particularly suited for forming thin layers of metal oxides
in the components of electronic devices. General classes of
functional materials that can be deposited with ALD include
conductors, dielectrics or insulators, and semiconductors.
[0016] Conductors can be any useful conductive material. For
example, the conductors may comprise transparent materials such as
indium-tin oxide (ITO), doped zinc oxide ZnO, SnO.sub.2, or
In.sub.2O.sub.3. The thickness of the conductor may vary, and
according to particular examples it can range from about 50 to
about 1000 nm.
[0017] Examples of useful semiconducting materials are compound
semiconductors such as gallium arsenide, gallium nitride, cadmium
sulfide, intrinsic zinc oxide, and zinc sulfide.
[0018] A dielectric material electrically insulates various
portions of a patterned circuit. A dielectric layer may also be
referred to as an insulator or insulating layer. Specific examples
of materials useful as dielectrics include strontiates, tantalates,
titanates, zirconates, aluminum oxides, silicon oxides, tantalum
oxides, hafnium oxides, titanium oxides, zinc selenide, and zinc
sulfide. In addition, alloys, combinations, and multilayers of
these examples can be used as dielectrics. Of these materials,
aluminum oxides are preferred.
[0019] A dielectric structure layer may comprise two or more layers
having different dielectric constants. Such insulators are
discussed in U.S. Pat. No. 5,981,970 hereby incorporated by
reference and copending U.S. application Ser. No. 11/088,645,
hereby incorporated by reference. Dielectric materials typically
exhibit a band-gap of greater than about 5 eV. The thickness of a
useful dielectric layer may vary, and according to particular
examples it can range from about 10 to about 300 nm. A number of
device structures can be made with the functional layers described
above. A resistor can be fabricated by selecting a conducting
material with moderate to poor conductivity. A capacitor can be
made by placing a dielectric between two conductors. A diode can be
made by placing two semiconductors of complementary carrier type
between two conducting electrodes. There may also be disposed
between the semiconductors of complementary carrier type a
semiconductor region that is intrinsic, indicating that that region
has low numbers of free charge carriers. A diode may also be
constructed by placing a single semiconductor between two
conductors, where one of the conductor/semiconductors interfaces
produces a Schottky barrier that impedes current flow strongly in
one direction. A transistor may be made by placing upon a conductor
(the gate) an insulating layer followed by a semiconducting layer.
If two or more additional conductor electrodes (source and drain)
are placed spaced apart in contact with the top semiconductor
layer, a transistor can be formed. Any of the above devices can be
created in various configurations as long as the necessary
interfaces are created.
[0020] In typical applications of a thin film transistor, the need
is for a switch that can control the flow of current through the
device. As such, it is desired that when the switch is turned on a
high current can flow through the device. The extent of current
flow is related to the semiconductor charge carrier mobility. When
the device is turned off, it is desirable that the current flow be
very small. This is related to the charge carrier concentration.
Furthermore, it is generally preferable that visible light have
little or no influence on thin-film transistor response. In order
for this to be true, the semiconductor band gap must be
sufficiently large (>3 eV) so that exposure to visible light
does not cause an inter-band transition. A material that is capable
of yielding a high mobility, low carrier concentration, and high
band gap is ZnO. Furthermore, for high-volume manufacture onto a
moving web, it is highly desirable that chemistries used in the
process be both inexpensive and of low toxicity, which can be
satisfied by the use of ZnO and the majority of its precursors.
[0021] Self-saturating surface reactions make ALD relatively
insensitive to transport non-uniformities, which might otherwise
impair surface uniformity, due to engineering tolerances and the
limitations of the flow system or related to surface topography
(that is, deposition into three dimensional, high aspect ratio
structures). As a general rule, a non-uniform flux of chemicals in
a reactive process generally results in different completion times
over different portions of the surface area. However, with ALD,
each of the reactions is allowed to complete on the entire
substrate surface. Thus, differences in completion kinetics impose
no penalty on uniformity. This is because the areas that are first
to complete the reaction self-terminate the reaction; other areas
are able to continue until the full treated surface undergoes the
intended reaction. Typically, an ALD process deposits about 0.1-0.2
nm of a film in a single ALD cycle (with one cycle having numbered
steps 1 through 4 as listed earlier). A useful and economically
feasible cycle time must be achieved in order to provide a uniform
film thickness in a range of about from 3 nm to 30 nm for many or
most semiconductor applications, and even thicker films for other
applications. According to industry throughput standards,
substrates are preferably processed within 2 minutes to 3 minutes,
which means that ALD cycle times must be in a range from about 0.6
seconds to about 6 seconds.
[0022] ALD offers considerable promise for providing a controlled
level of highly uniform thin film deposition. However, in spite of
its inherent technical capabilities and advantages, a number of
technical hurdles still remain. One important consideration relates
to the number of cycles needed. Because of its repeated reactant
and purge cycles, effective use of ALD has required an apparatus
that is capable of abruptly changing the flux of chemicals from
ML.sub.x to AH.sub.y, along with quickly performing purge cycles.
Conventional ALD systems are designed to rapidly cycle the
different gaseous substances onto the substrate in the needed
sequence. However, it is difficult to obtain a reliable scheme for
introducing the needed series of gaseous formulations into a
chamber at the needed speeds and without some unwanted mixing.
Furthermore, an ALD apparatus must be able to execute this rapid
sequencing efficiently and reliably for many cycles in order to
allow cost-effective coating of many substrates.
[0023] In an effort to minimize the time that an ALD reaction needs
to reach self-termination, at any given reaction temperature, one
approach has been to maximize the flux of chemicals flowing into
the ALD reactor, using so-called "pulsing" systems. In order to
maximize the flux of chemicals into the ALD reactor, it is
advantageous to introduce the molecular precursors into the ALD
reactor with minimum dilution of inert gas and at high pressures.
However, these measures work against the need to achieve short
cycle times and the rapid removal of these molecular precursors
from the ALD reactor. Rapid removal in turn dictates that gas
residence time in the ALD reactor be minimized. Gas residence
times, .tau., are proportional to the volume of the reactor, V, the
pressure, P, in the ALD reactor, and the inverse of the flow, Q,
that is:
.tau.=VP/Q (3)
[0024] In a typical ALD chamber the volume (V) and pressure (P) are
dictated independently by the mechanical and pumping constraints,
leading to difficulty in precisely controlling the residence time
to low values. Accordingly, lowering pressure (P) in the ALD
reactor facilitates low gas residence times and increases the speed
of removal (purge) of chemical precursor from the ALD reactor. In
contrast, minimizing the ALD reaction time requires maximizing the
flux of chemical precursors into the ALD reactor through the use of
a high pressure within the ALD reactor. In addition, both gas
residence time and chemical usage efficiency are inversely
proportional to the flow. Thus, while lowering flow can increase
efficiency, it also increases gas residence time.
[0025] Existing ALD approaches have been compromised with the
trade-off between the need to shorten reaction times with improved
chemical utilization efficiency, and, on the other hand, the need
to minimize purge-gas residence and chemical removal times. One
approach to overcome the inherent limitations of "pulsed" delivery
of gaseous material is to provide each reactant gas continuously
and to move the substrate through each gas in succession. For
example, U.S. Pat. No. 6,821,563 entitled "GAS DISTRIBUTION SYSTEM
FOR CYCLICAL LAYER DEPOSITION" to Yudovsky describes a processing
chamber, under vacuum, having separate gas ports for precursor and
purge gases, alternating with vacuum pump ports between each gas
port. Each gas port directs its stream of gas vertically downward
toward a substrate. The separate gas flows are separated by walls
or partitions, with vacuum pumps for evacuating gas on both sides
of each gas stream. A lower portion of each partition extends close
to the substrate, for example, about 0.5 mm or greater from the
substrate surface. In this manner, the lower portions of the
partitions are separated from the substrate surface by a distance
sufficient to allow the gas streams to flow around the lower
portions toward the vacuum ports after the gas streams react with
the substrate surface.
[0026] A rotary turntable or other transport device is provided for
holding one or more substrate wafers. With this arrangement, the
substrate is shuttled beneath the different gas streams, effecting
ALD deposition thereby. In one embodiment, the substrate is moved
in a linear path through a chamber, in which the substrate is
passed back and forth a number of times.
[0027] Another approach using continuous gas flow is shown in U.S.
Pat. No. 4,413,022 entitled "METHOD FOR PERFORMING GROWTH OF
COMPOUND THIN FILMS" to Suntola et al. A gas flow array is provided
with alternating source gas openings, carrier gas openings, and
vacuum exhaust openings. Reciprocating motion of the substrate over
the array effects ALD deposition, again, without the need for
pulsed operation. In the embodiment of FIGS. 13 and 14, in
particular, sequential interactions between a substrate surface and
reactive vapors are made by a reciprocating motion of the substrate
over a fixed array of source openings. Diffusion barriers are
formed by having a carrier gas opening between exhaust openings.
Suntola et al. state that operation with such an embodiment is
possible even at atmospheric pressure, although little or no
details of the process, or examples, are provided.
[0028] While systems such as those described in the '563 Yudovsky
and '022 Suntola et al. disclosures may avoid some of the
difficulties inherent to pulsed gas approaches, these systems have
other drawbacks. Neither the gas flow delivery unit of the '563
Yudovsky disclosure nor the gas flow array of the '022 Suntola et
al. disclosure can be used in closer proximity to the substrate
than about 0.5 mm. Neither of the gas flow delivery apparatus
disclosed in the '563 Yudovsky and '022 Suntola et al. patents are
arranged for possible use with a moving web surface, such as could
be used as a flexible substrate for forming electronic circuits,
light sensors, or displays, for example. The complex arrangements
of both the gas flow delivery unit of the '563 Yudovsky disclosure
and the gas flow array of the '022 Suntola et al. disclosure, each
providing both gas flow and vacuum, make these solutions difficult
to implement and costly to scale and limit their potential
usability to deposition applications onto a moving substrate of
limited dimensions. Moreover, it would be very difficult to
maintain a uniform vacuum at different points in an array and to
maintain synchronous gas flow and vacuum at complementary
pressures, thus compromising the uniformity of gas flux that is
provided to the substrate surface.
[0029] US Patent Pub. No. 2005/0084610 to Selitser discloses an
atmospheric pressure atomic layer chemical vapor deposition
process. Selitser et al. state that extraordinary increases in
reaction rates are obtained by changing the operating pressure to
atmospheric pressure, which will involve orders of magnitude
increase in the concentration of reactants, with consequent
enhancement of surface reactant rates. The embodiments of Selitser
et al. involve separate chambers for each stage of the process,
although FIG. 10 in Selitser '4610 shows an embodiment in which
chamber walls are removed. A series of separated injectors are
spaced around a rotating circular substrate holder track. Each
injector incorporates independently operated reactant, purging, and
exhaust gas manifolds and controls and acts as one complete
mono-layer deposition and reactant purge cycle for each substrate
as is passes there under in the process. Little or no specific
details of the gas injectors or manifolds are described by Selitser
et al., although they state that spacing of the injectors is
selected so that cross-contamination from adjacent injectors is
prevented by purging gas flows and exhaust manifolds incorporate in
each injector.
[0030] One aspect of ALD processing that has been of special
interest relates to temperature control of the silicon wafer
substrate. Among the solutions proposed for accurate temperature
control during materials deposition are those described in US
Patent Application Publication No. 2004/0142558 by Granneman. In
the Granneman '2558 disclosure, platens positioned above and below
the wafer act as both gas sources and heating components. In pulsed
deposition embodiments described in U.S. Pat. No. 6,183,565
entitled "METHOD AND APPARATUS FOR SUPPORTING A SEMICONDUCTOR WAFER
DURING PROCESSING" to Granneman et al., the semiconductor wafer
substrate is supported by heated gas streams during deposition,
thus providing control of temperature using conductive heating,
rather than radiated heat transfer, during this process. Similarly,
for CVD applications, Japanese Publication Nos. 62-021237 entitled
"TABLE FOR WAFER POSITIONING" to Sugimoto, 04-078130 entitled
"SEMICONDUCTOR VAPOR GROWTH EQUIPMENT" to Hashimoto et al., and
61-294812 entitled "GAS PHASE FLOATING EPITAXIAL GROWTH" to Tokisue
et al. describe "levitation" of a semiconductor wafer by streams of
gas jets during deposition processing. It has thus been recognized
that heating and transport of the semiconductor wafer during
chemical deposition can be effected using gas jets. At least one
commercial product used in semiconductor fabrication, the LEVITOR
RTP (Rapid Thermal Processing) Reactor manufactured by ASM
International N.V., Bilthoven, Netherlands, employs this "gas fluid
bearing" method for its thermal transfer and wafer-handling
advantages. However, this and similar devices do not provide
spatial separation of gases from each other during deposition, but
are based on the pulsed delivery model described earlier in this
background material.
[0031] It can be appreciated that the use of air-bearing principles
or, more generally, gas fluid-bearing principles, can yield a
number of advantages for improved wafer transport during vapor
deposition and ALD processes. However, existing solutions have been
directed to pulsed deposition systems, necessitating the design of
fairly complex mechanical and gas-routing systems and components.
Air-bearing levitation of the wafer in such systems requires that a
chamber be provided, having a base block on one side of the wafer
that continuously provides an inert gas for levitating the wafer
and a deposition block on the other side of the wafer for providing
the repeated, rapid sequencing of reactant and purge gas cycles
necessary for efficient materials deposition. Thus, it can be seen
that there is a need for ALD deposition method and apparatus that
can be used with a continuous process and that can provide improved
gas mobility and gas flow separation over earlier solutions.
SUMMARY OF THE INVENTION
[0032] The present invention provides a process for depositing a
thin film material on a substrate, comprising simultaneously
directing a series of gas flows from the output face of a delivery
head of a thin film deposition system toward the surface of a
substrate, wherein the series of gas flows comprises at least a
first reactive gaseous material, an inert purge gas, and a second
reactive gaseous material. The first reactive gaseous material is
capable of reacting with a substrate surface treated with the
second reactive gaseous material. One or more of the gas flows
provides a pressure that at least contributes to the separation of
the surface of the substrate from the face of the delivery
head.
[0033] Another aspect of the present invention provides a
deposition system for thin film deposition of a solid material onto
a substrate comprising:
[0034] a) a plurality of sources for, respectively, a plurality of
gaseous materials comprising at least a first, a second, and a
third source for a first, a second, and a third gaseous material,
respectively;
[0035] b) a delivery head for delivering the gaseous materials to a
substrate receiving thin film deposition and comprising: [0036] (i)
a plurality of inlet ports comprising at least a first, a second,
and a third inlet port for receiving the first, the second, and the
third gaseous material, respectively; and [0037] (ii) an output
face comprising a plurality of output openings and facing the
substrate a distance from the surface of the substrate, wherein the
first, second, and third gaseous materials are simultaneously
exhausted from the output openings in the output face;
[0038] c) an optional substrate support for supporting the
substrate; and
[0039] d) maintaining a substantially uniform distance between the
output face of the delivery head and the substrate surface during
thin film deposition, wherein pressure generated due to flow of one
or more of the gaseous materials from the delivery head to the
substrate surface for thin film deposition provides at least part
of the force separating the output face of the delivery head from
the surface of the substrate.
[0040] In one embodiment, the system provides a relative
oscillating motion between the distribution head and the substrate.
In a preferred embodiment, the system can be operated with
continuous movement of a substrate being subjected to thin film
deposition, wherein the system is capable of conveying the support
on or as a web past the distribution head, preferably in an
unsealed environment to ambient at substantially atmospheric
pressure.
[0041] It is an advantage of the present invention that it can
provide a compact apparatus for atomic layer deposition onto a
substrate that is well suited to a number of different types of
substrates and deposition environments.
[0042] It is a further advantage of the present invention that it
allows operation, in preferred embodiments, under atmospheric
pressure conditions.
[0043] It is yet a further advantage of the present invention that
it is adaptable for deposition on a web or other moving substrate,
including deposition onto a large area substrate.
[0044] It is still a further advantage of the present invention
that it can be employed in low temperature processes at atmospheric
pressures, which process may be practiced in an unsealed
environment, open to ambient atmosphere. The method of the present
invention allows control of the gas residence time ti in the
relationship shown earlier in equation (3), allowing residence time
ti to be reduced, with system pressure and volume controlled by a
single variable, the gas flow.
[0045] These and other objects, features, and advantages of the
present invention will become apparent to those skilled in the art
upon a reading of the following detailed description when taken in
conjunction with the drawings wherein there is shown and described
an illustrative embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter of the
present invention, it is believed that the invention will be better
understood from the following description when taken in conjunction
with the accompanying drawings, wherein:
[0047] FIG. 1 is a cross-sectional side view of one embodiment of a
delivery head for atomic layer deposition according to the present
invention;
[0048] FIG. 2 is a cross-sectional side view of one embodiment of a
delivery head showing one exemplary arrangement of gaseous
materials provided to a substrate that is subject to thin film
deposition;
[0049] FIGS. 3A and 3B are cross-sectional side views of one
embodiment of a delivery head, schematically showing the
accompanying deposition operation;
[0050] FIG. 4 is a perspective exploded view of a delivery head in
a deposition system according to one embodiment;
[0051] FIG. 5A is a perspective view of a connection plate for the
delivery head of FIG. 4;
[0052] FIG. 5B is a plan view of a gas chamber plate for the
delivery head of FIG. 4;
[0053] FIG. 5C is a plan view of a gas direction plate for the
delivery head of FIG. 4;
[0054] FIG. 5D is a plan view of a base plate for the delivery head
of FIG. 4;
[0055] FIG. 6 is a perspective view showing a base plate on a
delivery head in one embodiment;
[0056] FIG. 7 is an exploded view of a gas diffuser unit according
to one embodiment;
[0057] FIG. 8A is a plan view of a nozzle plate of the gas diffuser
unit of FIG. 7;
[0058] FIG. 8B is a plan view of a gas diffuser plate of the gas
diffuser unit of FIG. 7;
[0059] FIG. 8C is a plan view of a face plate of the gas diffuser
unit of FIG. 7;
[0060] FIG. 8D is a perspective view of gas mixing within the gas
diffuser unit of FIG. 7;
[0061] FIG. 8E is a perspective view of the gas ventilation path
using the gas diffuser unit of FIG. 7;
[0062] FIG. 9A is a perspective view of a portion of the delivery
head in an embodiment using vertically stacked plates;
[0063] FIG. 9B is an exploded view of the components of the
delivery head shown in FIG. 9A;
[0064] FIG. 9C is a plan view showing a delivery assembly formed
using stacked plates;
[0065] FIGS. 10A and 10B are plan and perspective views,
respectively, of a separator plate used in the vertical plate
embodiment of FIG. 9A;
[0066] FIGS. 11A and 11B are plan and perspective views,
respectively, of a purge plate used in the vertical plate
embodiment of FIG. 9A;
[0067] FIGS. 12A and 12B are plan and perspective views,
respectively, of an exhaust plate used in the vertical plate
embodiment of FIG. 9A;
[0068] FIGS. 13A and 13B are plan and perspective views,
respectively, of a reactant plate used in the vertical plate
embodiment of FIG. 9A;
[0069] FIG. 13C is a plan view of a reactant plate in an alternate
orientation;
[0070] FIG. 14 is a side view of a delivery head showing relevant
distance dimensions and force directions;
[0071] FIG. 15 is a perspective view showing a distribution head
used with a substrate transport system;
[0072] FIG. 16 is a perspective view showing a deposition system
using the delivery head of the present invention;
[0073] FIG. 17 is a perspective view showing one embodiment of a
deposition system applied to a moving web;
[0074] FIG. 18 is a perspective view showing another embodiment of
deposition system applied to a moving web;
[0075] FIG. 19 is a cross-sectional side view of one embodiment of
a delivery head with an output face having curvature;
[0076] FIG. 20 is a perspective view of an embodiment using a gas
cushion to separate the delivery head from the substrate; and
[0077] FIG. 21 is a side view showing an embodiment for a
deposition system comprising a gas fluid bearing for use with a
moving substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0078] The present description is directed in particular to
elements forming part of, or cooperating more directly with,
apparatus in accordance with the invention. It is to be understood
that elements not specifically shown or described may take various
forms well known to those skilled in the art.
[0079] For the description that follows, the term "gas" or "gaseous
material" is used in a broad sense to encompass any of a range of
vaporized or gaseous elements, compounds, or materials. Other terms
used herein, such as: reactant, precursor, vacuum, and inert gas,
for example, all have their conventional meanings as would be well
understood by those skilled in the materials deposition art. The
figures provided are not drawn to scale but are intended to show
overall function and the structural arrangement of some embodiments
of the present invention.
[0080] For the description that follows, superposition has its
conventional meaning, wherein elements are laid atop or against one
another in such manner that parts of one element align with
corresponding parts of another and that their perimeters generally
coincide.
[0081] Terms "upstream" and "downstream" have their conventional
meanings as relates to the direction of gas flow.
[0082] The apparatus of the present invention offers a significant
departure from conventional approaches to ALD, employing an
improved distribution device for delivery of gaseous materials to a
substrate surface, adaptable to deposition on larger and web-based
or web-supported substrates and capable of achieving a highly
uniform thin-film deposition at improved throughput speeds. The
apparatus and method of the present invention employs a continuous
(as opposed to pulsed) gaseous material distribution. The apparatus
of the present invention allows operation at atmospheric or
near-atmospheric pressures as well as under vacuum and is capable
of operating in an unsealed or open-air environment.
[0083] Referring to FIG. 1, there is shown a cross-sectional side
view of one embodiment of a delivery head 10 for atomic layer
deposition onto a substrate 20 according to the present invention.
Delivery head 10 has a gas inlet conduit 14 that serves as an inlet
port for accepting a first gaseous material, a gas inlet conduit 16
for an inlet port that accepts a second gaseous material, and a gas
inlet conduit 18 for an inlet port that accepts a third gaseous
material. These gases are emitted at an output face 36 via output
channels 12, having a structural arrangement that may include a
diffuser, as described subsequently. The dashed line arrows in FIG.
1 and subsequent FIGS. 2-3B refer to the delivery of gases to
substrate 20 from delivery head 10. In FIG. 1, dotted line arrows X
also indicate paths for gas exhaust (shown directed upwards in this
figure) and exhaust channels 22, in communication with an exhaust
conduit 24 that provides an exhaust port. For simplicity of
description, gas exhaust is not indicated in FIGS. 2-3B. Because
the exhaust gases still may contain quantities of unreacted
precursors, it may be undesirable to allow an exhaust flow
predominantly containing one reactive species to mix with one
predominantly containing another species. As such, it is recognized
that the delivery head 10 may contain several independent exhaust
ports.
[0084] In one embodiment, gas inlet conduits 14 and 16 are adapted
to accept first and second gases that react sequentially on the
substrate surface to effect ALD deposition, and gas inlet conduit
18 receives a purge gas that is inert with respect to the first and
second gases. Delivery head 10 is spaced a distance D from
substrate 20, which may be provided on a substrate support, as
described in more detail subsequently. Reciprocating motion can be
provided between substrate 20 and delivery head 10, either by
movement of substrate 20, by movement of delivery head 10, or by
movement of both substrate 20 and delivery head 10. In the
particular embodiment shown in FIG. 1, substrate 20 is moved by a
substrate support 96 across output face 36 in reciprocating
fashion, as indicated by the arrow A and by phantom outlines to the
right and left of substrate 20 in FIG. 1. It should be noted that
reciprocating motion is not always required for thin-film
deposition using delivery head 10. Other types of relative motion
between substrate 20 and delivery head 10 could also be provided,
such as movement of either substrate 20 or delivery head 10 in one
or more directions, as described in more detail subsequently.
[0085] The cross-sectional view of FIG. 2 shows gas flows emitted
over a portion of output face 36 of delivery head 10 (with the
exhaust path omitted as noted earlier). In this particular
arrangement, each output channel 12 is in gaseous flow
communication with one of gas inlet conduits 14, 16 or 18 seen in
FIG. 1. Each output channel 12 delivers typically a first reactant
gaseous material O, or a second reactant gaseous material M, or a
third inert gaseous material I.
[0086] FIG. 2 shows a relatively basic or simple arrangement of
gases. It is envisioned that a plurality of non-metal deposition
precursors (like material O) or a plurality of metal-containing
precursor materials (like material M) may be delivered sequentially
at various ports in a thin-film single deposition. Alternately, a
mixture of reactant gases, for example, a mixture of metal
precursor materials or a mixture of metal and non-metal precursors
may be applied at a single output channel when making complex thin
film materials, for example, having alternate layers of metals or
having lesser amounts of dopants admixed in a metal oxide material.
Significantly, an inter-stream labeled I for an inert gas, also
termed a purge gas, separates any reactant channels in which the
gases are likely to react with each other. First and second
reactant gaseous materials O and M react with each other to effect
ALD deposition, but neither reactant gaseous material O nor M
reacts with inert gaseous material I. The nomenclature used in FIG.
2 and following suggests some typical types of reactant gases. For
example, first reactant gaseous material O could be an oxidizing
gaseous material; second reactant gaseous material M would be a
metal-containing compound, such as a material containing zinc.
Inert gaseous material I could be nitrogen, argon, helium, or other
gases commonly used as purge gases in ALD systems. Inert gaseous
material I is inert with respect to first or second reactant
gaseous materials O and M. Reaction between first and second
reactant gaseous materials would form a metal oxide or other binary
compound, such as zinc oxide ZnO or ZnS, used in semiconductors, in
one embodiment. Reactions between more than two reactant gaseous
materials could form a ternary compound, for example, ZnAlO.
[0087] The cross-sectional views of FIGS. 3A and 3B show, in
simplified schematic form, the ALD coating operation performed as
substrate 20 passes along output face 36 of delivery head 10 when
delivering reactant gaseous materials O and M. In FIG. 3A, the
surface of substrate 20 first receives an oxidizing material
continuously emitted from output channels 12 designated as
delivering first reactant gaseous material O. The surface of the
substrate now contains a partially reacted form of material O,
which is susceptible to reaction with material M. Then, as
substrate 20 passes into the path of the metal compound of second
reactant gaseous material M, the reaction with M takes place,
forming a metallic oxide or some other thin film material that can
be formed from two reactant gaseous materials. Unlike conventional
solutions, the deposition sequence shown in FIGS. 3A and 3B is
continuous during deposition for a given substrate or specified
area thereof, rather than pulsed. That is, materials O and M are
continuously emitted as substrate 20 passes across the surface of
delivery head 10 or, conversely, as delivery head 10 passes along
the surface of substrate 20.
[0088] As FIGS. 3A and 3B show, inert gaseous material I is
provided in alternate output channels 12, between the flows of
first and second reactant gaseous materials O and M. Notably, as
was shown in FIG. 1, there are exhaust channels 22, but preferably
no vacuum channels interspersed between the output channels 12.
Only exhaust channels 22, providing a small amount of draw, are
needed to vent spent gases emitted from delivery head 10 and used
in processing.
[0089] One aspect of operation for delivery head 10 relates to its
providing gas pressure against substrate 20, such that separation
distance D is maintained, at least in part, by the force of
pressure that is exerted. By maintaining some amount of gas
pressure between output face 36 and the surface of substrate 20,
the apparatus of the present invention provides at least some
portion of an air bearing, or more properly a gas fluid bearing,
for delivery head 10 itself or, alternately, for substrate 20. This
arrangement helps to simplify the transport requirements for
delivery head 10, as described subsequently. Importantly, the
effect of allowing the delivery head to approach the substrate such
that it is supported by gas pressure, helps to provide isolation
between the gas streams. By allowing the head to float on these
streams, pressure fields are set up in the reactive and purge flow
areas that cause the gases to be directed from inlet to exhaust
with little or no intermixing of other gas streams.
[0090] In one embodiment, since the separation distance D is
relatively small, even a small change in distance D (for example,
even 100 micrometers) would require a significant change in flow
rates and consequently gas pressure providing the separation
distance D. For example, in one embodiment, doubling the separation
distance D, involving a change less than 1 mm, would necessitate
more than doubling, preferably more than quadrupling, the flow rate
of the gases providing the separation distance D. As a general
principle, it is considered more advantageous in practice to
minimize separation distance D and, consequently, to operate at
reduced flow rates.
[0091] The exploded view of FIG. 4 shows, for a small portion of
the overall assembly in one embodiment, how delivery head 10 can be
constructed from a set of apertured plates and shows an exemplary
gas flow path for just one portion of one of the gases. A
connection plate 100 for the delivery head 10 has a series of input
ports 104 for connection to gas supplies that are upstream of
delivery head 10 and not shown in FIG. 4. Each input port 104 is in
communication with a directing chamber 102 that directs the
received gas downstream to a gas chamber plate 110. Gas chamber
plate 110 has a supply chamber 112 that is in gas flow
communication with an individual directing channel 122 on a gas
direction plate 120. From directing channel 122, the gas flow
proceeds to a particular elongated exhaust channel 134 on a base
plate 130. A gas diffuser unit 140 provides diffusion and final
delivery of the input gas at its output face 36. An exemplary gas
flow F1 is traced through each of the component assemblies of
delivery head 10. The x-y-z axis orientation shown in FIG. 4 also
applies for FIGS. 5A and 7 in the present application.
[0092] As shown in the example of FIG. 4, delivery assembly 150 of
delivery head 10 is formed as an arrangement of superposed
apertured plates: connection plate 100, gas chamber plate 110, gas
direction plate 120, and base plate 130. These plates are disposed
substantially in parallel to output face 36 in this "horizontal"
embodiment. Gas diffuser unit 140 can also be formed from
superposed apertured plates, as is described subsequently. It can
be appreciated that any of the plates shown in FIG. 4 could itself
be fabrication from a stack of superposed plates. For example, it
may be advantageous to form connection plate 100 from four or five
stacked apertured plates that are suitably coupled together. This
type of arrangement can be less complex than machining or molding
methods for forming directing chambers 102 and input ports 104.
[0093] Gas diffuser unit 140 can be used to equalize the flow
through the output channel providing the gaseous materials to the
substrate. Copending, co-assigned USSN (docket 93328), entitled
"DELIVERY HEAD COMPRISING GAS DIFFUSER DEVICE FOR THIN FILM
DEPOSITION," hereby incorporated by reference, discloses various
diffuser systems that optionally can be employed.
[0094] Alternatively, the output channel can be used to provide the
gaseous materials without a diffuser, as in U.S. Pat. No. 4,413,022
to Suntola et al., hereby incorporated by reference. By providing
undiffused flows, higher throughputs may be obtained, possibly at
the expense of less homogenous deposition. On the other hand, a
diffuser system is especially advantageous for a floating head
system described above, since it can provide a back pressure within
the delivery device that facilitates the floating of the head.
[0095] FIGS. 5A through 5D show each of the major components that
are combined together to form delivery head 10 in the embodiment of
FIG. 4. FIG. 5A is a perspective view of connection plate 100,
showing multiple directing chambers 102. FIG. 5B is a plan view of
gas chamber plate 110. A supply chamber 113 is used for purge or
inert gas for delivery head 10 in one embodiment. A supply chamber
115 provides mixing for a precursor gas (O) in one embodiment; an
exhaust chamber 116 provides an exhaust path for this reactive gas.
Similarly, a supply chamber 112 provides the other needed reactive
gas, metallic precursor gas (M); an exhaust chamber 114 provides an
exhaust path for this gas.
[0096] FIG. 5C is a plan view of gas direction plate 120 for
delivery head 10 in this embodiment. Multiple directing channels
122, providing a metallic precursor material (M), are arranged in a
pattern for connecting the appropriate supply chamber 112 (not
shown in this view) with base plate 130. Corresponding exhaust
directing channels 123 are positioned near directing channels 122.
Directing channels 90 provide the other precursor material (O) and
have corresponding exhaust directing channels 91. Directing
channels 92 provide purge gas (I). Again, it must be emphasized
that FIGS. 4 and 5A-5D show one illustrative embodiment; numerous
other embodiments are also possible.
[0097] FIG. 5D is a plan view of base plate 130 for delivery head
10. Base plate 130 has multiple elongated emissive channels 132
interleaved with exhaust channels 134.
[0098] FIG. 6 is a perspective view showing base plate 130 formed
from horizontal plates and showing input ports 104. The perspective
view of FIG. 6 shows the external surface of base plate 130 as
viewed from the output side and having elongated emissive channels
132 and elongated exhaust channels 134. With reference to FIG. 4,
the view of FIG. 6 is taken from the side that faces gas diffuser
unit 140.
[0099] The exploded view of FIG. 7 shows the basic arrangement of
components used to form one embodiment of an optional gas diffuser
unit 140, as used in the embodiment of FIG. 4 and in other
embodiments as described subsequently. These include a nozzle plate
142, shown in the plan view of FIG. 8A. As shown in the views of
FIGS. 6, 7, and 8A, nozzle plate 142 mounts against base plate 130
and obtains its gas flows from elongated emissive channels 132. In
the embodiment shown, output passages 143 provide the needed
gaseous materials. Sequential first exhaust slots 180 are provided
in the exhaust path, as described subsequently.
[0100] A gas diffuser plate 146, which diffuses in cooperation with
plates 142 and 148, shown in FIG. 8B, is mounted against nozzle
plate 142. The arrangement of the various passages on nozzle plate
142, gas diffuser plate 146, and face plate 148 are optimized to
provide the needed amount of diffusion for the gas flow and, at the
same time, to efficiently direct exhaust gases away from the
surface area of substrate 20. Slots 182 provide exhaust ports. In
the embodiment shown, gas supply slots forming second diffuser
output passages 147 and exhaust slots 182 alternate in gas diffuser
plate 146.
[0101] A face plate 148, as shown in FIG. 8C, then faces substrate
20. Third diffuser output passages 149 for providing gases and
exhaust slots 184 again alternate with this embodiment.
[0102] FIG. 8D focuses on the gas delivery path through gas
diffuser unit 140; FIG. 8E then shows the gas exhaust path in a
corresponding manner. Referring to FIG. 8D there is shown, for a
representative set of gas ports, the overall arrangement used for
thorough diffusion of the reactant gas for an output flow F2 in one
embodiment. The gas from base plate 130 (FIG. 4) is provided
through first output passage 143 on nozzle plate 142. The gas goes
downstream to a second diffuser output passage 147 on gas diffuser
plate 146. As shown in FIG. 8D, there can be a vertical offset
(that is, using the horizontal plate arrangement shown in FIG. 7,
vertical being normal with respect to the plane of the horizontal
plates) between passages 143 and 147 in one embodiment, helping to
generate backpressure and thus facilitate a more uniform flow. The
gas then goes further downstream to a third diffuser output passage
149 on face plate 148 to provide output channel 12. The different
output passages 143, 147 and 149 may not only be spatially offset,
but may also have different geometries to optimize mixing.
[0103] In the absence of the optional diffuser unit, the elongated
emissive channels 132 in the base plate can serve as the output
channels 12 for delivery head 10 instead of the third diffuser
output passages 149.
[0104] FIG. 8E symbolically traces the exhaust path provided for
venting gases in a similar embodiment, where the downstream
direction is opposite that for supplied gases. A flow F3 indicates
the path of vented gases through sequential third, second and first
exhaust slots 184, 182, and 180, respectively. Unlike the more
circuitous mixing path of flow F2 for gas supply, the venting
arrangement shown in FIG. 8E is intended for the rapid movement of
spent gases from the surface. Thus, flow F3 is relatively direct,
venting gases away from the substrate surface.
[0105] Referring back to FIG. 4, the combination of components
shown as connection plate 100, gas chamber plate 110, gas direction
plate 120, and base plate 130 can be grouped to provide a delivery
assembly 150. Alternate embodiments are possible for delivery
assembly 150, including one formed from vertical, rather than
horizontal, apertured plates, using the coordinate arrangement and
view of FIG. 4.
[0106] Referring to FIG. 9A, there is shown, from a bottom view
(that is, viewed from the gas emission side) an alternate
arrangement that can be used for delivery assembly 150 using a
stack of superposed apertured plates that are disposed
perpendicularly with respect to output face 36. For simplicity of
explanation, the portion of delivery assembly 150 shown in the
"vertical embodiment" of FIG. 9A has two elongated emissive
channels 152 and two elongated exhaust channels 154. The vertical
plates arrangement of FIGS. 9A through 13C can be readily expanded
to provide a number of emissive and exhaust channels. With
apertured plates disposed perpendicularly with respect to the plane
of output face 36, as in FIGS. 9A and 9B, each elongated emissive
channel 152 is formed by having side walls defined by separator
plates, shown subsequently in more detail, with a reactant plate
centered between them. Proper alignment of apertures then provides
fluid communication with the supply of gaseous material.
[0107] The exploded view of FIG. 9B shows the arrangement of
apertured plates used to form the small section of delivery
assembly 150 that is shown in FIG. 9A. FIG. 9C is a plan view
showing a delivery assembly 150 having five elongated channels for
emitted gases and formed using stacked, apertured plates. FIGS. 10A
through 13B then show the various apertured plates in both plan and
perspective views. For simplicity, letter designations are given to
each type of apertured plate: Separator S, Purge P, Reactant R, and
Exhaust E. From left to right in FIG. 9B are separator plates 160
(S), also shown in FIGS. 10A and 10B, alternating between plates
used for directing gas toward or away from the substrate. A purge
plate 162 (P) is shown in FIGS. 11A and 11B. An exhaust plate 164
(E) is shown in FIGS. 12A and 12B. A reactant plate 166 (R) is
shown in FIGS. 13A and 13B. FIG. 13C shows a reactant plate 166'
obtained by flipping the reactant plate 166 of FIG. 12A
horizontally; this alternate orientation can also be used with
exhaust plate 164, as required. Apertures 168 in each of the
apertured plates align when the plates are superposed, thus forming
ducts to enable gas to be passed through delivery assembly 150 into
elongated emissive output channels 152 and exhaust channels 154, as
were described with reference to FIG. 1.
[0108] Returning to FIG. 9B, only a portion of a delivery assembly
150 is shown. The plate structure of this portion can be
represented using the letter abbreviations assigned earlier, that
is:
[0109] S-P-S-E-S-R-S-E-(S)
[0110] (With the last separator plate in this sequence not shown in
FIGS. 9A or 9B.) As this sequence shows, separator plates 160 (S)
define each channel by forming side walls. A minimal delivery
assembly 150 for providing two reactive gases along with the
necessary purge gases and exhaust channels for typical ALD
deposition would be represented using the full abbreviation
sequence:
[0111]
S-P-S-E1-S-R1-S-E1-S-P-S-E2-S-R2-S-E2-S-P-S-E1-S-R1-S-E1-S-P-S
-E2-S-R2-S-E2-S-P-S-E1-S-R1-S-E1-S-P-S
[0112] where R1 and R2 represent reactant plates 166 in different
orientations, for the two different reactant gases used, and E1 and
E2 correspondingly represent exhaust plates 164 in different
orientations.
[0113] Exhaust channel 154 need not be a vacuum port, in the
conventional sense, but may simply be provided to draw off the flow
from its corresponding output channel 12, thus facilitating a
uniform flow pattern within the channel. A negative draw, just
slightly less than the opposite of the gas pressure at neighboring
elongated emissive channels 152, can help to facilitate an orderly
flow. The negative draw can, for example, operate with draw
pressure at the source (for example, a vacuum pump) of between 0.2
and 1.0 atmosphere, whereas a typical vacuum is, for example, below
0.1 atmosphere.
[0114] Use of the flow pattern provided by delivery head 10
provides a number of advantages over conventional approaches, such
as those noted earlier in the background section, that pulse gases
individually to a deposition chamber. Mobility of the deposition
apparatus improves, and the device of the present invention is
suited to high-volume deposition applications in which the
substrate dimensions exceed the size of the deposition head. Flow
dynamics are also improved over earlier approaches.
[0115] The flow arrangement used in the present invention allows a
very small distance D between delivery head 10 and substrate 20, as
was shown in FIG. 1, preferably under 1 mm. Output face 36 can be
positioned very closely, to within about 1 mil (approximately 0.025
mm) of the substrate surface. The close positioning is facilitated
by the gas pressure generated by the reactant gas flows. By
comparison, CVD apparatus require significantly larger separation
distances. Earlier approaches such as the cyclical deposition
described in the U.S. Pat. No. 6,821,563 to Yudovsky, cited
earlier, were limited to 0.5 mm or greater distance to the
substrate surface, whereas embodiments of the present invention can
be practiced at less than 0.5 mm, for example, less than 0.450 mm.
In fact, positioning the delivery head 10 closer to the substrate
surface is preferred in the present invention. In a particularly
preferred embodiment, distance D from the surface of the substrate
can be 0.20 mm or less, preferably less than 100 .mu.m.
[0116] It is desirable that when a large number of plates are
assembled in a stacked-plate embodiment, the gas flow delivered to
the substrate is uniform across all of the channels delivering a
gas flow (I, M, or O channels). This can be accomplished by proper
design of the apertured plates, such as having restrictions in some
part of the flow pattern for each plate which are accurately
machined to provide a reproducible pressure drop for each emissive
output or exhaust channel. In one embodiment, output channels 12
exhibit substantially equivalent pressure along the length of the
openings, to within no more than about 10% deviation. Even higher
tolerances could be provided, such as allowing no more than about
5% or even as little as 2% deviation.
[0117] Although the method using stacked apertured plates is a
particularly useful way of constructing the article of this
invention, there are a number of other methods for building such
structures that may be useful in alternate embodiments. For
example, the apparatus may be constructed by direct machining of a
metal block, or of several metal blocks adhered together.
Furthermore, molding techniques involving internal mold features
can be employed, as will be understood by the skilled artisan. The
apparatus can also be constructed using any of a number of
stereolithography techniques.
[0118] One advantage offered by delivery head 10 of the present
invention relates to maintaining a suitable separation distance D
(FIG. 1) between its output face 36 and the surface of substrate
20. FIG. 14 shows some key considerations for maintaining distance
D using the pressure of gas flows emitted from delivery head
10.
[0119] In FIG. 14, a representative number of output channels 12
and exhaust channels 22 are shown. The pressure of emitted gas from
one or more of output channels 12 generates a force, as indicated
by the downward arrow in this figure. In order for this force to
provide a useful cushioning or "air" bearing (gas fluid bearing)
effect for delivery head 10, there must be sufficient landing area,
that is, solid surface area along output face 36 that can be
brought into close contact with the substrate. The percentage of
landing area corresponds to the relative amount of solid area of
output face 36 that allows build-up of gas pressure beneath it. In
simplest terms, the landing area can be computed as the total area
of output face 36 minus the total surface area of output channels
12 and exhaust channels 22. This means that total surface area,
excluding the gas flow areas of output channels 12, having a width
w1, or of exhaust channels 22, having a width w2, must be maximized
as much as possible. A landing area of 95% is provided in one
embodiment. Other embodiments may use smaller landing area values,
such as 85% or 75%, for example. Adjustment of gas flow rate could
also be used in order to alter the separation or cushioning force
and thus change distance D accordingly.
[0120] It can be appreciated that there would be advantages to
providing a gas fluid bearing, so that delivery head 10 is
substantially maintained at a distance D above substrate 20. This
would allow essentially frictionless motion of delivery head 10
using any suitable type of transport mechanism. Delivery head 10
could then be caused to "hover" above the surface of substrate 20
as it is channeled back and forth, sweeping across the surface of
substrate 20 during materials deposition.
[0121] As shown in FIG. 14, delivery head 10 may be too heavy, so
that the downward gas force is not sufficient for maintaining the
needed separation. In such a case, auxiliary lifting components,
such as a spring 170, magnet, or other device, could be used to
supplement the lifting force. In other cases, gas flow may be high
enough to cause the opposite problem, so that delivery head 10
would be forced apart from the surface of substrate 20 by too great
a distance, unless additional force is exerted. In such a case,
spring 170 may be a compression spring, to provide the additional
needed force to maintain distance D (downward with respect to the
arrangement of FIG. 14). Alternately, spring 170 may be a magnet,
elastomeric spring, or some other device that supplements the
downward force.
[0122] Alternately, delivery head 10 may be positioned in some
other orientation with respect to substrate 20. For example,
substrate 20 could be supported by the air bearing effect, opposing
gravity, so that substrate 20 can be moved along delivery head 10
during deposition. One embodiment using the air bearing effect for
deposition onto substrate 20, with substrate 20 cushioned above
delivery head 10 is shown in FIG. 20. Movement of substrate 20
across output face 36 of delivery head 10 is in a direction along
the double arrow as shown.
[0123] The alternate embodiment of FIG. 21 shows substrate 20 on a
substrate support 74, such as a web support or rollers, moving in
direction K between delivery head 10 and a gas fluid bearing 98. In
this embodiment, delivery head 10 has an air-bearing or, more
appropriately, a gas fluid-bearing effect and cooperates with gas
fluid bearing 98 in order to maintain the desired distance D
between output face 36 and substrate 20. Gas fluid bearing 98 may
direct pressure using a flow F4 of inert gas, or air, or some other
gaseous material. It is noted that, in the present deposition
system, a substrate support or holder can be in contact with the
substrate during deposition, which substrate support can be a means
for conveying the substrate, for example a roller. Thus, thermal
isolation of the substrate being treated is not a requirement of
the present system.
[0124] As was particularly described with reference to FIGS. 3A and
3B, delivery head 10 requires movement relative to the surface of
substrate 20 in order to perform its deposition function. This
relative movement can be obtained in a number of ways, including
movement of either or both delivery head 10 and substrate 20, such
as by movement of an apparatus that provides a substrate support.
Movement can be oscillating or reciprocating or could be continuous
movement, depending on how many deposition cycles are needed.
Rotation of a substrate can also be used, particularly in a batch
process, although continuous processes are preferred. An actuator
may be coupled to the body of the delivery head, such as
mechanically connected. An alternating force, such as a changing
magnetic force field, could alternately be used.
[0125] Typically, ALD requires multiple deposition cycles, building
up a controlled film depth with each cycle. Using the nomenclature
for types of gaseous materials given earlier, a single cycle can,
for example in a simple design, provide one application of first
reactant gaseous material O and one application of second reactant
gaseous material M.
[0126] The distance between output channels for O and M reactant
gaseous materials determines the needed distance for reciprocating
movement to complete each cycle. For the example delivery head 10
of FIG. 4 may have a nominal channel width of 0.1 inches (2.54 mm)
in width between a reactant gas channel outlet and the adjacent
purge channel outlet. Therefore, for the reciprocating motion
(along the y axis as used herein) to allow all areas of the same
surface to see a full ALD cycle, a stroke of at least 0.4 inches
(10.2 mm) would be required. For this example, an area of substrate
20 would be exposed to both first reactant gaseous material O and
second reactant gaseous material M with movement over this
distance. Alternatively, a delivery head can move much larger
distances for its stroke, even moving from one end of a substrate
to another. In this case the growing film may be exposed to ambient
conditions during periods of its growth, causing no ill effects in
many circumstances of use. In some cases, consideration for
uniformity may require a measure of randomness to the amount of
reciprocating motion in each cycle, such as to reduce edge effects
or build-up along the extremes of reciprocation travel.
[0127] A delivery head 10 may have only enough output channels 12
to provide a single cycle. Alternately, delivery head 10 may have
an arrangement of multiple cycles, enabling it to cover a larger
deposition area or enabling its reciprocating motion over a
distance that allows two or more deposition cycles in one traversal
of the reciprocating motion distance.
[0128] For example, in one particular application, it was found
that each O-M cycle formed a layer of one atomic diameter over
about 1/4 of the treated surface. Thus, four cycles, in this case,
are needed to form a uniform layer of 1 atomic diameter over the
treated surface. Similarly, to form a uniform layer of 10 atomic
diameters in this case, then, 40 cycles would be required.
[0129] An advantage of the reciprocating motion used for a delivery
head 10 of the present invention is that it allows deposition onto
a substrate 20 whose area exceeds the area of output face 36. FIG.
15 shows schematically how this broader area coverage can be
effected, using reciprocating motion along the y axis as shown by
arrow A and also movement orthogonal or transverse to the
reciprocating motion, relative to the x axis. Again, it must be
emphasized that motion in either the x or y direction, as shown in
FIG. 15, can be effected either by movement of delivery head 10, or
by movement of substrate 20 provided with a substrate support 74
that provides movement, or by movement of both delivery head 10 and
substrate 20.
[0130] In FIG. 15 the relative motion directions of the delivery
head and the substrate are perpendicular to each other. It is also
possible to have this relative motion in parallel. In this case,
the relative motion needs to have a nonzero frequency component
that represents the oscillation and a zero frequency component that
represents the displacement of the substrate. This combination can
be achieved by: an oscillation combined with displacement of the
delivery head over a fixed substrate; an oscillation combined with
displacement of the substrate relative to a fixed substrate
delivery head; or any combinations wherein the oscillation and
fixed motion are provided by movements of both the delivery head
and the substrate.
[0131] Advantageously, delivery head 10 can be fabricated at a
smaller size than is possible for many types of deposition heads.
For example, in one embodiment, output channel 12 has width w1 of
about 0.005 inches (0.127 mm) and is extended in length to about 3
inches (75 mm).
[0132] In a preferred embodiment, ALD can be performed at or near
atmospheric pressure and over a broad range of ambient and
substrate temperatures, preferably at a temperature of under
300.degree. C. Preferably, a relatively clean environment is needed
to minimize the likelihood of contamination; however, full "clean
room" conditions or an inert gas-filled enclosure would not be
required for obtaining good performance when using preferred
embodiments of the apparatus of the present invention.
[0133] FIG. 16 shows an Atomic Layer Deposition (ALD) system 60
having a chamber 50 for providing a relatively well-controlled and
contaminant-free environment. Gas supplies 28a, 28b, and 28c
provide the first, second, and third gaseous materials to delivery
head 10 through supply lines 32. The optional use of flexible
supply lines 32 facilitates ease of movement of delivery head 10.
For simplicity, optional vacuum vapor recovery apparatus and other
support components are not shown in FIG. 16, but could also be
used. A transport subsystem 54 provides a substrate support that
conveys substrate 20 along output face 36 of delivery head 10,
providing movement in the x direction, using the coordinate axis
system employed in the present disclosure. Motion control, as well
as overall control of valves and other supporting components, can
be provided by a control logic processor 56, such as a computer or
dedicated microprocessor assembly, for example. In the arrangement
of FIG. 16, control logic processor 56 controls an actuator 30 for
providing reciprocating motion to delivery head 10 and also
controls a transport motor 52 of transport subsystem 54. Actuator
30 can be any of a number of devices suitable for causing
back-and-forth motion of delivery head 10 along a moving substrate
20 (or, alternately, along a stationary substrate 20).
[0134] FIG. 17 shows an alternate embodiment of an Atomic Layer
Deposition (ALD) system 70 for thin film deposition onto a web
substrate 66 that is conveyed past delivery head 10 along a web
conveyor 62 that acts as a substrate support. The web itself may be
the substrate or may provide support for an additional substrate. A
delivery head transport 64 conveys delivery head 10 across the
surface of web substrate 66 in a direction transverse to the web
travel direction. In one embodiment, delivery head 10 is impelled
back and forth across the surface of web substrate 66, with the
full separation force provided by gas pressure. In another
embodiment, delivery head transport 64 uses a lead screw or similar
mechanism that traverses the width of web substrate 66. In another
embodiment, multiple delivery heads 10 are used, at suitable
positions along web 62.
[0135] FIG. 18 shows another Atomic Layer Deposition (ALD) system
70 in a web arrangement, using a stationary delivery head 10 in
which the flow patterns are oriented orthogonally to the
configuration of FIG. 17. In this arrangement, motion of web
conveyor 62 itself provides the movement needed for ALD deposition.
Reciprocating motion could also be used in this environment.
[0136] Referring to FIG. 19, an embodiment of a portion of delivery
head 10 is shown in which output face 36 has an amount of
curvature, which might be advantageous for some web coating
applications. Convex or concave curvature could be provided.
[0137] In another embodiment that can be particularly useful for
web fabrication, ALD system 70 can have multiple delivery heads 10,
or dual delivery heads 10, with one disposed on each side of
substrate 66. A flexible delivery head 10 could alternately be
provided. This would provide a deposition apparatus that exhibits
at least some conformance to the deposition surface.
[0138] In another embodiment, one or more output channels 12 of
delivery head 10 may use the transverse gas flow arrangement that
was disclosed in U.S. application Ser. No. 11/392,006, filed Mar.
29, 2006 by Levy et al. and entitled "APPARATUS FOR ATOMIC LAYER
DEPOSITION," cited earlier and incorporated herein by reference. In
such an embodiment, gas pressure that supports separation between
delivery head 10 and substrate 20 can be maintained by some number
of output channels 12, such as by those channels that emit purge
gas (channels labeled I in FIGS. 2-3B), for example. Transverse
flow would then be used for one or more output channels 12 that
emit the reactant gases (channels labeled O or M in FIGS.
2-3B).
[0139] The apparatus of the present invention is advantaged in its
capability to perform deposition onto a substrate over a broad
range of temperatures, including room or near-room temperature in
some embodiments. The apparatus of the present invention can
operate in a vacuum environment, but is particularly well suited
for operation at or near atmospheric pressure.
[0140] Thin film transistors having a semiconductor film made
according to the present method can exhibit a field effect electron
mobility that is greater than 0.01 cm.sup.2/Vs, preferably at least
0.1 cm.sup.2/Vs, more preferably greater than 0.2 cm.sup.2/Vs. In
addition, n-channel thin film transistors having semiconductor
films made according to the present invention are capable of
providing on/off ratios of at least 10.sup.4, advantageously at
least 10.sup.5. The on/off ratio is measured as the maximum/minimum
of the drain current as the gate voltage is swept from one value to
another that are representative of relevant voltages which might be
used on the gate line of a display. A typical set of values would
be -10V to 40V with the drain voltage maintained at 30V.
[0141] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the scope of the invention as described above, and as noted in the
appended claims, by a person of ordinary skill in the art without
departing from the scope of the invention. For example, while air
bearing effects may be used to at least partially separate delivery
head 10 from the surface of substrate 20, the apparatus of the
present invention may alternately be used to lift or levitate
substrate 20 from output surface 36 of delivery head 10. Other
types of substrate holder could alternately be used, including a
platen for example.
EXAMPLES
Comparative Example C1
[0142] For comparison to the present invention, a film of
Al.sub.2O.sub.3 was grown on a silicon wafer using a control APALD
(Atmospheric Pressure Atomic Layer deposition) as disclosed in U.S.
application Ser. No. 11/392,006, filed Mar. 29, 2006 by Levy et al.
and entitled "APPARATUS FOR ATOMIC LAYER DEPOSITION". The APALD
device was configured to have 11 output channels in a configuration
as follows:
[0143] Channel 1: Purge Gas
[0144] Channel 2: Oxidizer containing gas
[0145] Channel 3: Purge Gas
[0146] Channel 4: Metal precursor containing gas
[0147] Channel 5: Purge Gas
[0148] Channel 6: Oxidizer containing gas
[0149] Channel 7: Purge Gas
[0150] Channel 8: Metal precursor containing gas
[0151] Channel 9: Purge Gas
[0152] Channel 10: Oxidizer containing gas
[0153] Channel 11: Purge Gas
[0154] The film was grown at a substrate temperature of 150.degree.
C. Gas flows delivered to the APALD coating head were as
follows:
[0155] (i) A nitrogen inert purge gas was supplied to channels
1,3,5,7,9,11 at a total flow rate of 2000 sccm (standard cubic
centimeters per minute).
[0156] (ii) A nitrogen based gas stream containing
trimethylaluminum (TMA) was supplied to channels 4 and 8. This gas
stream was produced by mixing a flow of 300 sccm of pure nitrogen
with a flow of 7 sccm of nitrogen saturated with TMA at room
temperature.
[0157] (iii) A nitrogen based gas stream containing water vapor was
supplied to channels 2, 6, and 10. This gas stream was produced by
mixing a flow of 300 sccm of pure nitrogen with a flow of 25 sccm
of nitrogen saturated with water vapor at room temperature.
[0158] The coating head with the above gas supply streams was
brought to a fixed position of approximately 30 micrometers above
the substrate, using a micrometer adjustment mechanism. At this
point, the coating head was oscillated for 175 cycles across the
substrate to yield an Al.sub.2O.sub.3 film of approximately 900A
thickness.
[0159] A current leakage test structure was formed by coating
aluminum contacts on top of the Al.sub.2O.sub.3 layer using a
shadow mask during an aluminum evaporation. This process resulted
in aluminum contact pads on top of the Al.sub.2O.sub.3 that were
approximately 500A thick with an area of 500 microns.times.200
microns.
[0160] The leakage current from the silicon wafer to the Al
contacts was measured by applying a 20V potential between a given
aluminum contact pad to the silicon wafer and measuring the amount
the current flow with an HP-4155C.RTM. parameter analyzer.
[0161] For this sample at a 20 V potential, the leakage current was
8.2.times.10.sup.-8 A.
Example E1
[0162] A film of Al.sub.2O.sub.3 was grown on a silicon wafer using
the APALD device of the present invention. The APALD device was
configured analogously to the device of comparative example C1. The
film was grown at a substrate temperature of 150.degree. C. Gas
flows delivered to the APALD coating head were as follows:
[0163] (i) A nitrogen inert purge gas was supplied to channels 1,
3, 5, 7, 9, and 11 at a total flow rate of 3000 sccm.
[0164] (ii) A nitrogen based gas stream containing
trimethylaluminum was supplied to channels 4 and 8. This gas stream
was produced by mixing a flow of -400 sccm of pure nitrogen with a
flow of 3.5 sccm of nitrogen saturated with TMA at room
temperature.
[0165] (iii) A nitrogen based gas stream containing water vapor was
supplied to channels 2, 6, and 10. This gas stream was produced by
mixing a flow of -350 sccm of pure nitrogen with a flow of 20 sccm
of nitrogen saturated with water vapor at room temperature.
[0166] The coating head with the above gas supply streams was
brought into proximity with the substrate and then released, so
that it floated above the substrate based upon the gas flows as
described earlier. At this point, the coating head was oscillated
for 300 cycles across the substrate to yield an Al.sub.2O.sub.3
film of approximately 900 .ANG. thickness.
[0167] A current leakage test structure was formed by coating
aluminum contact pads on top of the Al.sub.2O.sub.3 layer with the
same procedure and contact pad size as in example C1.
[0168] At a 20 V potential, the leakage through the Al.sub.2O.sub.3
dielectric was 1.3.times.10.sup.-11 A. As can be seen from this
test data, the gas elevation coating head of this example produces
a film with significantly lower current leakage, which is desired
for the production of useful dielectric films.
PARTS LIST
[0169] 10 delivery head
[0170] 12 output channel
[0171] 14, 16, 18 gas inlet conduit
[0172] 20 substrate
[0173] 22 exhaust channel
[0174] 24 exhaust conduit
[0175] 28a, 28b, 28c gas supply
[0176] 30 actuator
[0177] 32 supply line
[0178] 36 output face
[0179] 50 chamber
[0180] 52 transport motor
[0181] 54 transport subsystem
[0182] 56 control logic processor
[0183] 60 Atomic Layer Deposition (ALD) system
[0184] 62 web conveyor
[0185] 64 delivery head transport
[0186] 66 web substrate
[0187] 70 Atomic Layer Deposition (ALD) system
[0188] 74 substrate support
[0189] 90 directing channel for precursor material
[0190] 91 exhaust directing channel
[0191] 92 directing channel for purge gas
[0192] 96 substrate support
[0193] 98 gas fluid bearing
[0194] 100 connection plate
[0195] 102 directing chamber
[0196] 104 input port
[0197] 110 gas chamber plate
[0198] 112, 113, 115 supply chamber
[0199] 114, 116 exhaust chamber
[0200] 120 gas direction plate
[0201] 122 directing channel for precursor material
[0202] 123 exhaust directing channel
[0203] 130 base plate
[0204] 132 elongated emissive channel
[0205] 134 elongated exhaust channel
[0206] 140 gas diffuser unit
[0207] 142 nozzle plate
[0208] 143, 147, 149 first, second, third diffuser output
passage
[0209] 146 gas diffuser plate
[0210] 148 face plate
[0211] 150 delivery assembly
[0212] 152 elongated emissive channel
[0213] 154 elongated exhaust channel
[0214] 160 separator plate
[0215] 162 purge plate
[0216] 164 exhaust plate
[0217] 166, 166' reactant plate
[0218] 168 aperture
[0219] 170 spring
[0220] 180 sequential first exhaust slot
[0221] 182 sequential second exhaust slot
[0222] 184 sequential third exhaust slot
[0223] A arrow
[0224] D distance
[0225] E exhaust plate
[0226] F1, F2, F3, F4 gas flow
[0227] H height
[0228] I third inert gaseous material
[0229] K direction
[0230] M second reactant gaseous material
[0231] O first reactant gaseous material
[0232] P purge plate
[0233] R reactant plate
[0234] S separator plate
[0235] w1, w2 channel width
[0236] X arrow
* * * * *