U.S. patent application number 11/564272 was filed with the patent office on 2007-05-24 for precursor material delivery system with staging volume for atomic layer deposition.
This patent application is currently assigned to Planar Systems, Inc.. Invention is credited to Bradley J. Aitchison, Kari Harkonen, Pekka Kuosmanen, Teemu Lang, Hannu Leskinen, Jarmo Maula, Martti Sonninen, Tommy Turkulainen.
Application Number | 20070117383 11/564272 |
Document ID | / |
Family ID | 31997597 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070117383 |
Kind Code |
A1 |
Aitchison; Bradley J. ; et
al. |
May 24, 2007 |
PRECURSOR MATERIAL DELIVERY SYSTEM WITH STAGING VOLUME FOR ATOMIC
LAYER DEPOSITION
Abstract
A precursor delivery system includes a flow path from a
precursor container to a reaction space of a thin film deposition
system, such as an atomic layer deposition (ALD) reactor. A staging
volume is preferably established between the precursor container
and the reaction space for receiving at least one dose of the
precursor material from the precursor container, and from which
pulses are released toward the reaction space. A pulse control
device is preferably interposed between the staging volume and the
reaction space. A sensor may sense a physical condition in the
staging volume for providing feedback to a controller of the
precursor delivery system, for performance monitoring and
control.
Inventors: |
Aitchison; Bradley J.;
(Eugene, OR) ; Maula; Jarmo; (Espoo, FI) ;
Leskinen; Hannu; (Espoo, FI) ; Lang; Teemu;
(Helsinki, FI) ; Kuosmanen; Pekka; (Espoo, FI)
; Harkonen; Kari; (Kauniainen, FI) ; Sonninen;
Martti; (Espoo, FI) ; Turkulainen; Tommy;
(Kirkkonummi, FI) |
Correspondence
Address: |
STOEL RIVES LLP
900 SW FIFTH AVENUE
SUITE 2600
PORTLAND
OR
97204-1268
US
|
Assignee: |
Planar Systems, Inc.
Beaverton
OR
|
Family ID: |
31997597 |
Appl. No.: |
11/564272 |
Filed: |
November 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10660365 |
Sep 10, 2003 |
7141095 |
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11564272 |
Nov 28, 2006 |
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10400054 |
Mar 25, 2003 |
6936086 |
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11564272 |
Nov 28, 2006 |
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60410067 |
Sep 11, 2002 |
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60410067 |
Sep 11, 2002 |
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Current U.S.
Class: |
438/680 ;
118/715 |
Current CPC
Class: |
C23C 16/4404 20130101;
C23C 16/4557 20130101; C30B 25/14 20130101; C23C 16/45544 20130101;
B01D 45/06 20130101; C23C 16/4402 20130101; C23C 16/45525 20130101;
C23C 16/4412 20130101; Y10S 55/14 20130101 |
Class at
Publication: |
438/680 ;
118/715 |
International
Class: |
H01L 21/44 20060101
H01L021/44; C23C 16/00 20060101 C23C016/00 |
Claims
1. A precursor delivery system for delivering pulses of a precursor
material to a reaction space in a thin film deposition system,
comprising: a precursor container for holding a supply of precursor
material; a flow path extending from the precursor container and
adapted to be coupled, in use, to the reaction space; and a staging
volume interposed in the flow path downstream from the precursor
container and upstream from the reaction space, in use, for
receiving at least one dose of the precursor material from the
precursor container, the staging volume being selectively
isolatable from the precursor container, and the staging volume
being selectively isolatable from the reaction space for releasing
a series of pulses of the precursor material from the staging
volume toward the reaction space; a pulse control device interposed
between the staging volume and the reaction space, in use, the
pulse control device adapted to selectively release pulses of the
precursor material from the staging volume toward the reaction
space via the flow path; and a sensor coupled to the staging volume
for sensing a physical condition in the staging volume.
2. The system of claim 1, further comprising a controller coupled
to the sensor and responsive to the sensor for controlling the
operation of the precursor delivery system.
3. The system of claim 1, further comprising a controller coupled
to the sensor for monitoring the precursor delivery system.
4. The system of claim 1, further comprising a controller coupled
the pulse control device for automatically controlling the
operation of the pulse control device, the controller being
responsive to an output of the sensor representative of the
physical condition in the staging volume.
5. The system of claim 1, in which the sensor includes a pressure
transducer.
6. The system of claim 1, in which the sensor includes a
temperature sensor.
7. The system of claim 1, in which the pulse control device
includes a pulse valve.
8. The system of claim 7, in which the pulse control device further
includes a diffusion barrier operably connected to the flow path
downstream from the pulse valve for preventing leakage from the
pulse valve from reaching the reaction space.
9. The system of claim 1, in which the pulse control device
includes an inert gas valve operably coupled to the flow path.
10. The system of claim 1, further comprising a particle filter
interposed between the precursor container and the staging volume
for filtering particles from the precursor material.
11. The system of claim 10, in which the particle filter includes a
high conductivity particle filter, the high conductivity particle
filter including at least one inertial trap adjacent the flow path
for filtering particles from the precursor material without
significantly restricting flow of the pulses through the flow
path.
12. The system of claim 1, further comprising an isolation valve
interposed in the flow path between the precursor container and the
staging volume for selectively isolating the staging volume from
the precursor container.
13. The system of claim 1, further comprising a heater thermally
associated with the precursor container for vaporizing at least a
portion of the precursor material.
14. The system of claim 1, further comprising a vacuum source
coupled to the precursor container via a vacuum flow path for
controlling a pressure within the precursor container.
15. The system of claim 14, further comprising a vacuum shut-off
valve operably interposed between the vacuum source and the
precursor container for selectively interrupting the vacuum flow
path.
16. The system of claim 15, further comprising a vacuum filter
interposed in the vacuum flow path between the precursor container
and the vacuum shut-off valve.
17. The system of claim 14, further comprising an isolation valve
interposed between the precursor container and the staging volume
for sealing the flow path downstream from the precursor container
to facilitate adjustment of the pressure in the precursor container
via the vacuum source.
18. The system of claim 1, further comprising a high conductivity
particle filter interposed in the flow path between the precursor
container and the reaction space, the high conductivity particle
filter including at least one inertial trap adjacent the flow path
for filtering particles from the precursor material without
significantly restricting flow of the pulses through the flow
path.
19. The system of claim 18, in which the high conductivity particle
filter further includes: an inlet coupled to an upstream portion of
the flow path; an outlet coupled to a downstream portion of the
flow path; a filter passage in communication with the inlet and the
outlet, the filter passage including multiple turns between the
inlet and the outlet; and in which the inertial trap communicates
with the filter passage and is positioned in proximity to one of
the turns so that the inertia of the particles causes the particles
to travel into the trap as the precursor material flows through the
filter passage through said turn, thereby preventing the particles
from passing into the reaction space.
20. The system of claim 19, in which at least some of the turns of
the filter passage form a spiral.
21. The system of claim 19, in which at least some of the turns of
the filter passage are defined by a series of baffles between the
inlet and the outlet.
22. The system of claim 18, in which the flow path and the filter
passage are bordered by surfaces that are passivated.
23. The system of claim 22, in which a passivation of the surfaces
is selected from the group consisting of oxides, nitrides,
carbides, and mixtures thereof.
24. The system of claim 1, further comprising a supply of inert
boost gas coupled to the staging volume.
25. The system of claim 1, in which the staging volume is
sufficiently large so that the release of a single pulse of the
precursor material from the staging volume causes a pressure inside
the staging volume to decrease no more than 50 percent.
26. The system of claim 1, in which the flow path is formed in one
or more solid blocks of thermally conductive material, said one or
more blocks together forming an elongate thermally conductive body
extending from the precursor container to the reaction space.
27. The system of claim 26, in which internal surfaces of the
thermally conductive body bordering the flow path are
passivated.
28. The system of claim 27, in which a passivation of the internal
surfaces is selected from the group consisting of oxides, nitrides,
carbides, and mixtures thereof.
29. The system of claim 26, further comprising at least one heater
in thermal association with the thermally conductive body for
maintaining a temperature gradient in the flow path that increases
toward the reaction space.
30. The system of claim 1, in which the flow path is bordered by
surfaces having a passivation selected from the group consisting of
Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, TiO.sub.2, Ta.sub.2O.sub.5,
Nb.sub.2O.sub.5, AlN, ZrN, HfN, TiN, TaN, NbN, AlC, ZrC, HfC, TiC,
TaC, NbC, and mixtures thereof.
31. The system of claim 1, in which the thin film deposition system
comprises an atomic layer deposition system.
32. A method of delivering pulses of a precursor vapor to a
reaction space in a thin film deposition system, comprising:
providing a supply of precursor material; establishing a flow path
from the supply of precursor material to the reaction space;
vaporizing at least a portion of the precursor material to form a
precursor vapor; accumulating at least one dose of the precursor
vapor in a staging volume located downstream in the flow path from
the supply of precursor material and upstream from the reaction
space; isolating the staging volume from the supply of precursor
material; sensing a physical condition in the staging volume; and
selectively releasing pulses of the precursor vapor from the
staging volume through the flow path and toward the reaction
space.
33. The method of claim 32, further comprising controlling the
release of the pulses based on the physical condition sensed.
34. The method of claim 32, further comprising triggering an alarm
in response to sensing a physical condition indicative of leakage
in the precursor delivery system.
35. The method of claim 32, in which the physical condition
includes a fluid pressure within the staging volume.
36. The method of claim 32, further comprising filtering parties
from the precursor vapor as it passes through the flow path.
37. The method of claim 36, in which the filtering of particles
includes directing the precursor vapor through a filter passage
having multiple turns, at least one of the turns being positioned
in proximity to an inertial trap in communication with the filter
passage so that inertia of particles carried into the filter
passage by the precursor vapor causes the particles to travel into
the trap as the precursor vapor flows through said turn.
38. The method of claim 32, in which the vaporizing of the
precursor material includes heating the supply of precursor
material.
39. The method of claim 32, further comprising storing the supply
of precursor material in a precursor container and drawing a vacuum
inside the precursor container.
40. The method of claim 39, in which the drawing of the vacuum
inside the precursor container is accomplished via a vacuum flow
path that bypasses the reaction space.
41. The method of claim 40, further comprising filtering particles
from the vacuum flow path.
42. The method of claim 32, further comprising accumulating
multiple doses of the precursor vapor in the staging volume before
commencing the release of the pulses.
43. The method of claim 32, further comprising injecting an inert
boost gas into the staging volume.
44. The method of claim 32, further comprising establishing a
positive temperature gradient in the flow path that increases
toward the reaction space.
45. The method of claim 32, in which the thin film deposition
system comprises an atomic layer deposition system.
Description
RELATED APPLICATIONS
[0001] This application is a divisional under 35 U.S.C. .sctn. 121
and claims priority under 35 U.S.C. .sctn. 120 from U.S.
application Ser. No. 10/660,365, filed Sep. 10, 2003, issued as
U.S. Pat. No. 7,141,095, which claims the benefit under 35 U.S.C.
.sctn. 119(e) of U.S. Provisional Patent Application No.
60/410,067, filed Sep. 11, 2002, and which is a
continuation-in-part of U.S. patent application Ser. No.
10/400,054, filed Mar. 25, 2003, now U.S. Pat. No. 6,936,086, all
of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The field of the present disclosure relates to methods and
devices for storing precursor materials in a thin film deposition
process, such as atomic layer deposition; conditioning such
precursor materials in preparation for deposition, e.g., by
adjusting their temperature and/or pressure; and introducing pulses
of vaporized precursor material into a reaction space of a thin
film deposition system.
BACKGROUND
[0003] Atomic layer deposition ("ALD"), formerly known as atomic
layer epitaxy ("ALE"), is a thin film deposition process that has
been used to manufacture electroluminescent ("EL") displays for
over 20 years. See, e.g., U.S. Pat. No. 4,058,430 of Suntola et
al., incorporated herein by reference. The films yielded by the ALD
technique have exceptional characteristics such as being pinhole
free and possessing almost perfect step coverage. Recently, ALD has
been proposed for use in the semiconductor processing industry for
depositing thin films on semiconductor substrates, to achieve
desired step coverage and physical properties needed for
next-generation integrated circuits. ALD offers several benefits
over other thin film deposition methods commonly used in
semiconductor processing, such as physical vapor deposition ("PVD")
(e.g., evaporation or sputtering) and chemical vapor deposition
("CVD"), as described in Atomic Layer Epitaxy (T. Suntola and M.
Simpson, eds., Blackie and Son Ltd., Glasgow, 1990).
[0004] In contrast to CVD, in which the flows of precursors are
static (i.e., flow rates are steady during processing), precursor
flows in ALD processing are dynamic. There are many precursor
delivery system components, such as mass flow controllers and
particle filters, that can be used in CVD processing in which flow
resistance and switching speed are not especially important.
However, the inventors have recognized that such delivery system
components have limited utility in ALD processes and equipment, due
to the dynamic precursor flows and fast switching needed in
ALD.
[0005] Successful ALD growth typically requires the sequential
introduction of two or more different precursor vapors into a
reaction space around a substrate. ALD is usually performed at
elevated temperatures and pressures. For example, the reaction
space may be heated to between 200.degree. C. and 600.degree. C.
and pumped down to a pressure of approximately 1 Torr. In a typical
ALD reactor, the reaction space is bounded by a reaction chamber
sized to accommodate one or more substrates. One or more precursor
material delivery systems (also known as "precursor sources") are
typically provided for feeding precursor materials into the
reaction chamber.
[0006] After the substrates are loaded into the reaction chamber
and heated to a desired processing temperature, a first precursor
vapor is directed over the substrates. Some of the precursor vapor
chemisorbs on the surface of the substrates to make a one monolayer
thick film. For true ALD, the molecules of precursor vapor will not
attach to other like molecules, and the process is therefore
self-limiting. Next the reaction space is purged to remove excess
of the first vapor and any volatile reaction products. Purging is
typically accomplished by introduction of an inert or non-reactive
purge gas into the reaction space. After purging, a second
precursor vapor is introduced. Molecules of the second precursor
vapor chemisorb or otherwise react with the chemisorbed first
precursor molecules to form a thin film product of the first and
second precursors. To complete the ALD cycle, the reaction space is
again purged to remove any excess of the second vapor as well as
any volatile reaction products. The steps of first precursor pulse,
purge, second precursor pulse, and purge are typically repeated
hundreds or thousands of times until the desired thickness of the
film is achieved.
[0007] A key to successful ALD growth is to have the first and
second precursor vapors pulsed into the reaction chamber
sequentially and without overlap. An ideal set of ALD precursor
pulses would be a pair of Delta functions, as illustrated in FIG.
1, which is a simplified timing diagram representing two cycles of
a simple ALD process. With reference to FIG. 1, alternating pulses
of a first precursor 12 and a second precursor 14 are separated by
intervals 16, which can be made small compared to the duration "d"
of each of the pulses 12 and 14. For simplicity of illustration,
the pulses 12 and 14 are shown in FIG. 1 as having equal duration,
but unequal pulse durations would also be feasible.
[0008] As noted above, FIG. 1 illustrates an ideal set of precursor
pulses. However, in practice, imperfections in the precursor
delivery system, precursor adsorption on the walls of the delivery
system and reaction chamber, and fluid flow dynamics cause the
concentration of precursor material in the ALD reaction space to
have a leading edge slope and an exponential decay during purge.
FIG. 2 is a simplified timing diagram illustrating respective first
and second pulses 22 and 24 in an ALD reactor, each with a leading
edge slope 26 and exponential decay 28. With reference to FIG. 2,
because the actual pulses 22 and 24 are not Delta functions, they
will overlap if the second precursor pulse 24 is started before the
first precursor pulse 22 is completely decayed, as illustrated by
overlap region 29. If substantial amounts of both of the first and
second precursor chemicals are present in the reaction space at the
same time, then non-ALD growth can occur, which can generate
particles, non-uniform film thickness, and other defects. To
prevent the problems caused by non-ALD growth, the pulses 22 and 24
are desirably separated by a purge interval that is long enough to
prevent overlap 29.
[0009] FIG. 3 illustrates a purge interval 32, between respective
first and second precursor pulses 34 and 36, that is sufficiently
long to prevent overlap. For simplicity, the purge interval 32 is
illustrated as having a duration similar to the duration of the
pulses 34 and 36. However, in practice, it is common for purge
times in an ALD process to be 10 times longer than the pulse times,
due to long exponential decays of precursor pulses caused by flow
restrictions and cold spots in the flow path. For example, a ALD
process including precursor vapor pulses having a duration of 50
milliseconds (ms) may require pulse intervals of 500 ms or longer
to prevent overlap and achieve good film thickness uniformity. Long
purge intervals increase processing time, which substantially
reduces the overall efficiency of the ALD reactor. The present
inventors have recognized that reducing the rise and decay times
also reduces the overall time required for each ALD process cycle
without causing non-ALD growth, thereby improving the throughput of
the ALD reactor.
[0010] Conventionally, precursors have been stored and vapors
delivered from glass tubes placed inside the reactor, as described
in U.S. Pat. No. 4,389,973 of Suntola et al., incorporated herein
by reference. The flow of each precursor vapor is controlled by
so-called "inert gas valving," which involves controlling the
direction of an inert gas flowing through the tube containing the
precursor chemical. Conventional inert gas valving has been
employed for about 20 years for the fabrication of EL displays,
including its use with certain solid precursors like ZnCl.sub.2 and
MnCl.sub.2. However, the present inventors have found that the
particle requirements for other applications, particularly
semiconductor processing, are far more stringent than those
required for EL display manufacturing. Conventional precursor
delivery methods and inert gas valving do not provide a barrier to
prevent particles present in powdered precursors from being carried
into the reaction space with the pulses of precursor vapor.
Further, the conventional methods cannot accommodate certain highly
reactive precursors useful for semiconductor processing, which
cannot be loaded in an open tube due to their reactivity with air
and/or moisture.
[0011] For most films grown by ALD, unwanted particles in or on the
film will reduce the manufacturing yield. It is therefore important
that the precursor delivery system does not emit particles.
Preventing particles is especially difficult when one or more of
the precursors exist in powdered form at room temperature and
pressure. CVD systems commonly include a high efficiency particle
filter that can block up to 99.99999% of particles smaller than
0.003 microns. However, the present inventors have found that
CVD-type high efficiency particle filters are unsuitable for use in
ALD processing because they are highly resistive to flow, which
leads to long precursor rise and/or decay times. High efficiency
particle filters also have a tendency to become blocked by coarse
particles emanating from a supply of precursor material, which can
cause system failures and yield losses in manufacturing. A new type
of ALD-oriented particle filtering is therefore needed.
[0012] The inventors have also recognized a need for improved
control of unwanted precursor migration between pulses (during
purging).
[0013] U.S. Patent Application Publication No. 2001/0042523 A1 of
Kesala discloses a reactant gas source contained in a vacuum shell.
Liquid or solid reactant matter is held in an ampoule having an
opening covered by a high efficiency particle filter. The ampoule
is enclosed within a gas-tight container that defines a gas space
around the ampoule. An outlet of the gas-tight container leads from
the gas space through a second high efficiency particle filter and
into the reaction chamber. Pulses of reactant gases are switched by
a backflow of inert gas in a line between the second high
efficiency particle filter and the reaction chamber.
[0014] U.S. Pat. No. 6,270,839 of Onoe at el. discloses a precursor
source for a CVD system that does not include a mechanism for
pulsing, as required in an ALD system.
[0015] Thus the inventors have recognized a need for improved
methods and devices for storing precursor materials in a thin film
deposition process, conditioning such precursor materials in
preparation for deposition, and introducing pulses of vaporized
precursor material into a reaction space of a thin film deposition
system.
SUMMARY
[0016] A precursor delivery system for delivering pulses of
precursor material to a reaction space in a thin film deposition
system includes a precursor container for holding a supply of
precursor material and a flow path from the precursor container to
the reaction space. In a preferred embodiment, a pulse control
device is interposed between the precursor container and the
reaction space for selectively permitting pulses of the precursor
material to flow from the precursor container to the reaction space
via the flow path. In some embodiments, a staging volume may be
established downstream from the precursor container and upstream
from the reaction space for receiving at least one dose of the
precursor material from the precursor container. The staging volume
is preferably selectively isolatable from the reaction space for
releasing a series of pulses of the precursor material from the
staging volume toward the reaction space. The staging volume may
also be selectively isolatable from the precursor container. One or
more sensors may be coupled to the staging volume for sensing a
physical condition of the staging volume or the precursor material
present in it, such as temperature or pressure, for monitoring
system performance and/or providing feedback to an automatic
controller of the precursor delivery system for closed-loop
control.
[0017] The precursor material is preferably vaporized after loading
it in the precursor container by heating the precursor material or
reducing pressure inside the precursor container. A vacuum line may
be coupled to the precursor container for reducing pressure inside
the precursor container. The vacuum line preferably bypasses a
reaction chamber of the thin film deposition system to prevent
particles from being drawn through the flow path and into the
reaction chamber. The vaporized precursor material (hereinafter
"precursor vapor") may be drawn into the staging volume, via a
pressure differential, upon opening an optional isolation valve
between the precursor container and the staging volume. A particle
filter may be interposed in the flow path between the precursor
container and the reaction space, and preferably between the
precursor container and a staging volume, for filtering particles
from the precursor vapor.
[0018] The particle filter may include a high conductivity particle
filter for preventing the particles from passing into the reaction
space without significantly restricting the flow of the pulses
through the flow path. In a preferred embodiment, the high
conductivity particle filter defines a filter passage having
multiple turns, at least one of which passes near a trap in
communication with the filter passage such that the inertia of the
particles causes them to travel into the trap as the precursor
material flows through said turn. The particle filter may also
comprise a compound filter including one or more high efficiency
filters downstream from a high conductivity particle filter. In the
compound filter arrangement, the high conductivity particle filter
operates to remove coarse particles before the precursor reaches
the high efficiency filters, thereby protecting the high efficiency
filters from clogging.
[0019] Methods and devices in accordance with the disclosed
embodiments may be useful in atomic layer deposition ("ALD"), as
well as for other pulsed thin film deposition techniques, such as
pulsed chemical vapor deposition ("Pulsed-CVD") and pulsed
metal-organic chemical vapor deposition ("Pulsed-MOCVD"), for
example.
[0020] Additional aspects and advantages will be apparent from the
following detailed description of preferred embodiments, which
proceeds with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Non-exhaustive embodiments are described with reference to
the figures, in which like reference numerals identify like
elements.
[0022] FIG. 1 is a simplified timing diagram representing two
cycles of an idealized thin film deposition process;
[0023] FIG. 2 is a timing diagram illustrating overlapping first
and second precursor pulses in a simplified prior art ALD process,
which may cause non-ALD film growth;
[0024] FIG. 3 is a timing diagram illustrating a simplified prior
art ALD process, in which a purge interval prevents overlapping of
sequential first and second precursor pulses;
[0025] FIG. 4 is a schematic representation of a precursor delivery
system in accordance with a preferred embodiment;
[0026] FIG. 5 is an isometric section view illustrating an
embodiment of the precursor delivery system of FIG. 4;
[0027] FIG. 6 is an enlarged isometric section view of a removable
precursor container module for use with the precursor delivery
system of FIG. 5, including detail of an optional high conductivity
particle filter positioned within the precursor container of the
precursor container module;
[0028] FIG. 7 is a schematic representation of the precursor
delivery system of FIGS. 4 and 5, illustrating a flow of purge gas
controlled by a diffusion barrier module of the precursor delivery
system during a purging step of an ALD process cycle;
[0029] FIG. 8 is a schematic representation of the precursor
delivery system of FIGS. 4 and 5, illustrating the flow of
precursor vapors and purge gas during a precursor pulse step of the
ALD process cycle; and
[0030] FIGS. 9-16 show various embodiments of a high conductivity
particle filter used in the precursor delivery system of FIGS. 4-6,
of which:
[0031] FIG. 9 is a cross-sectional view of one embodiment;
[0032] FIG. 10 is a cross-sectional view of an alternative
embodiment;
[0033] FIG. 11 is a cross-sectional view of a second alternative
embodiment;
[0034] FIG. 12 is a cross-sectional view of a third alternative
embodiment;
[0035] FIG. 13A is a plan view of a first plate for another
alternative embodiment;
[0036] FIG. 13B is a plan view of a second plate for use with the
plate of FIG. 13A;
[0037] FIG. 13C is a perspective view of plates of FIGS. 13A and
13B arranged sequentially;
[0038] FIG. 13D is a cross-sectional view of a filter incorporating
the plates of FIGS. 13A and 13B arranged sequentially as shown in
FIG. 13C;
[0039] FIG. 14 is a cross-sectional view of an alternative
embodiment;
[0040] FIG. 15 is a cross-sectional perspective view of yet another
alternative embodiment; and
[0041] FIG. 16 is a cross-sectional view of still another
alternative embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0042] Throughout the specification, reference to "one embodiment,"
or "an embodiment," or "some embodiments" means that a particular
described feature, structure, or characteristic is included in at
least one embodiment. Thus appearances of the phrases "in one
embodiment," "in an embodiment," or "in some embodiments" in
various places throughout this specification are not necessarily
all referring to the same embodiment.
[0043] Furthermore, the described features, structures, or
characteristics may be combined in any suitable manner in one or
more embodiments. Various embodiments can be practiced without one
or more of the specific details or with other methods, components,
materials, etc. In other instances, well-known structures,
materials, or operations are not shown or not described in detail
to avoid obscuring aspects of the embodiments.
[0044] As used herein, terminology referring to "communication" or
"fluid communication" between components is inclusive of both a
direct connection between components and an indirection connection
in which such communication is effected via one or more
intermediate components or pathways.
System Overview
[0045] FIG. 4 shows an schematic representation of a precursor
delivery system 100 in accordance with a preferred embodiment. FIG.
5 is an isometric cross section view illustrating an embodiment of
the precursor delivery system 100 of FIG. 4. With reference to
FIGS. 4 and 5, a supply of precursor material (not shown) is stored
in a precursor container (PC) 102, where it is preferably vaporized
before flowing through a flow path 104 of the system 100 and into a
reaction space inside a reaction chamber 110 of a thin film
deposition system. Precursor material may originate as a solid,
liquid, gas, or mixtures thereof, although it will most commonly be
in powdered or liquid form when initially loaded into precursor
container 102. When the precursor material originates in gaseous
form, it is typically unnecessary to take steps for vaporizing the
precursor material, such as heating or pressure reduction in
precursor container 102. Valves V1, V2, V3, and V4 are used to
regulate the pressure at different stages in precursor delivery
system 100 and to control the flow of precursor material, as
further described below. For clarity, the details of valves V1, V2,
V3, and V4 are omitted and, in FIGS. 5 and 6, the valve stems and
valve actuators of the valves are merely outlined in dashed lines.
Any of a variety of diaphragm valves, fast-switching shut-off
valves, or other flow shut-off mechanisms may be used. A preferred
diaphragm valve is described in U.S. patent application Ser. No.
10/609,134, filed Jun. 26, 2003, incorporated herein by
reference.
[0046] A staging volume (VOL) 114 is defined by the walls of a
volume module 116, which is interposed in flow path 104 downstream
from precursor container 102 and upstream from reaction chamber
110. Staging volume 114 is selectively isolatable from precursor
container 102 and reaction chamber 110 for receiving and holding at
least one dose of precursor material from which one or more pulses
of precursor vapor may be released through flow path 104 and into
reaction chamber 110. A particle filter module (PF2) 120 prevents
particles from being transported into staging volume 114 when it
receives a dose of the precursor from precursor container 102.
Particle filter module 120 may include a high conductivity particle
filter, as described below; a high efficiency filter; or a compound
filter including a high conductivity particle filter followed by a
series of one or more high efficiency filters. In the embodiment of
FIGS. 4 and 5, particle filter module 120 includes a series of four
filters 122a, 122b, 122c, and 122d arranged in flow path 104, of
which the first filter 122a is a high conductivity filter and the
second, third, and fourth filters 122b, 122c, 122d are high
efficiency filters. The high conductivity filter of the first
filter 122a may preferably be of the type described below with
reference to FIGS. 9-11, including a spiraling filter passage
flanked by a series of inertial traps. In some embodiments, filters
122a, 122b, 122c, and 122d comprise filters of progressively
increasing efficiency to prevent clogging. For example, the first
filter 122a may be the coarsest filter and the last filter may be
the finest. In other embodiments (not shown), particle filter
module 120 may include a greater or fewer number of filters in
series.
[0047] A fast switching pulse control device 124 includes a pulse
valve (V4) 126 for controlling the timing and duration of pulses of
precursor material released into reaction chamber 110. Pulse valve
126 may include a diaphragm valve for selectively interrupting flow
path 104. A suitable diaphragm valve is described in U.S. patent
application Ser. No. 10/609,134, filed Jun. 26, 2003, which is
incorporated herein by reference. In alternative embodiments (not
shown), pulse control device 124 includes other devices for
releasing pulses of precursor vapor, such as an inert gas valve.
Pulse control device 124 preferably includes a diffusion barrier
(DB) 130 positioned in the precursor flow path between pulse valve
126 and reaction chamber 110. One purpose of diffusion barrier 130
is to purge flow path 104 and reaction chamber 110 between pulses
by injecting an inert gas such as nitrogen (N.sub.2) into flow path
104 at a location upstream from reaction chamber 110 and downstream
from pulse valve 126. Diffusion barrier 130 also operates so that
any precursor material that might leak through pulse valve 126,
when closed, is prevented from diffusing into reaction chamber 110
and reacting with a different precursor material being delivered
into reaction chamber 110 by a second precursor delivery system
(not shown).
[0048] In one embodiment, a high conductivity particle filter
(HCPF) 140 is the last component in flow path 104 of precursor
delivery system 100 before reaction chamber 110 to prevent
particles from reaching reaction chamber 110. High conductivity
particle filters may also be placed at other locations along flow
path 104, to prevent particles from clogging or fouling valves,
high efficiency particle filters, and other components of precursor
delivery system 100.
[0049] An isolation valve (V2) 146 is positioned downstream from
particle filter module 120 and upstream from volume module 116 for
selectively isolating staging volume 114 from precursor container
102. Isolation valve 146 may include a diaphragm valve for
selectively interrupting flow path 104 between staging volume 114
and precursor container 102. A suitable diaphragm valve is
described in U.S. patent application Ser. No. 10/609,134. A pump
152 is coupled to precursor container 102 and can draw a vacuum
within precursor container 102 independently of vacuum drawn at
other locations in precursor delivery system 100 or the thin film
deposition reactor. A vacuum path 156 between precursor container
102 and pump 152 is selectively opened and closed by a vacuum valve
(V1) 158. Vacuum valve 158 may include a diaphragm valve for
selectively interrupting vacuum path 156, such as the diaphragm
valve described in U.S. patent application Ser. No. 10/609,134.
Pump 152 may be the same pumps used to reduce the pressure in the
reaction chamber 110 or independent pumps, but vacuum path 156
preferably bypasses reaction chamber 110 so that any particles
drawn into vacuum path 156 from precursor chamber 102 will not pass
through reaction chamber 110. By bypassing reaction chamber 110,
vacuum path 156 also facilitates the use of less expensive
precursor chemicals because it allows high vapor pressure
contaminants and byproducts, such as water, to be removed from the
supply of precursor material without contaminating the reaction
space 110. Isolation valve 146 preferably prevents the portion of
flow path 104 located downstream from isolation valve 146 from the
effects of pumps 152. Vacuum valve 158 and isolation valve 146 may
cooperate so that normally no more than one of them is open at a
time. A particle filter (PF1) 160 (FIG. 4) may be interposed
between precursor container 102 and vacuum valve 158 to prevent
particles from clogging or fouling vacuum valve 158. Particle
filter 160 preferably comprises a high conductivity particle filter
of the type described below with reference to FIGS. 9-16.
Alternatively, particle filter 160 may include a high efficiency
particle filter.
[0050] A boost valve (V3) 164 connects a source of inert boost gas
166 to staging volume 114 at a location downstream from isolation
valve 146. The diffusion barrier 130 includes a control valve (V5)
168 and a network of flow channels with flow restrictors R1, R2,
and R3. Diffusion barrier 130 includes an input channel 174 from a
purge gas source 176 supplying an inert gas, and an output channel
178 to a diffusion barrier pump 182. Purge gas source 176 and
diffusion barrier pump 182 may be shared or combined with the
source of boost gas 166 and the vacuum pump 152, respectively.
[0051] FIG. 6 is an enlarged sectional perspective view of a
removable precursor container module 190 of the system 100 of FIG.
5, including precursor container 102, vacuum valve 158, and
particle filter module 120. A valve 194 (not shown in FIGS. 4 and
5) is included at the end of module 190 opposite from vacuum valve
158 to allow precursor container 102 to be sealed before it is
disconnected from precursor delivery system 100, to thereby prevent
leakage of precursor material into the workspace when changing
precursor container module 190. When precursor container module 190
is removed, isolation valve 146 (FIGS. 4 and 5) is shut to prevent
leakage of precursor from staging volume 114 or loss of pressure in
reaction chamber 110.
[0052] A high conductivity particle filter 196 (not shown in FIGS.
4 and 5) is optionally disposed within precursor chamber 102 above
a reservoir 198 where a supply of precursor material is held (not
shown). Filter 196 may take the place of or be in addition to
particle filter 160 (FIG. 4). Also, if high conductivity particle
filter 196 is used, then first filter 122a of particle filter
module 120 may optionally be a high efficiency filter or may be
omitted. In yet another embodiment (not shown), filter module 120
may be entirely replaced by high conductivity particle filter
196.
[0053] Filter 196 includes a series of stacked plates 202 and
non-aligned apertures 204 creating a labyrinth filter passage
within the precursor container 102 that passes by a series of
inertial traps for filtering particles without significantly
impeding the flow of precursor vapor. The filter passage extends
between an inlet 203 communicating with flow path 104 at an
upstream part of filter 196, and an outlet 205 communicating with
flow path 104 at a downstream part of filter 196. (In the
embodiment of FIG. 6, the flow path 104 begins at the reservoir 198
and follows the labyrinth filter passage through the filter 196 to
outlet 205 and beyond.) Spacer pins (not shown, see FIG. 13) hold
plates 202 in spaced relation and keep plates 202 held together as
a unit that is easily replaceable and removable. The entire unit
preferably rests on a lip 208 circumscribing precursor container
102, but could also hang from a removable lid 210 of precursor
container 102 or stand on legs (not shown) extending to the bottom
212 of precursor container 102. Plates 202 may be closely fit to
the walls of precursor container 102, thereby eliminating the need
for a resilient seal or bushing therebetween. By preventing the
transmission of particles, filter 196 protects high efficiency
particle filters 122a-d from clogging and increases their life. A
high conductivity filter design similar to filter 196 is described
below in greater detail with reference to FIGS. 13A, 13B, 13C, and
13D. Various other embodiments of high conductivity particle
filters useful in precursor container module 190 are described
below with reference to FIGS. 9-16.
[0054] A pair of monitoring ports 206 and 207 are optionally
provided for facilitating fluid measurements immediately upstream
and immediately downstream of particle filter 120. Optional
pressure sensors may be inserted in ports 206 and 207 for measuring
a pressure drop across particle filter 120 to determine conductance
of the filter and to provide a signal or alarm when particle filter
120 is clogged and requires cleaning or replacement. Pressure
sensors may be coupled to controller 250 (FIG. 4) for monitoring
and control purposes. Alternatively, ports may be plugged if not
used.
Precursor Loading and Stabilization
[0055] A precursor such as ZrCl.sub.4 is loaded into the precursor
container 102 under possibly inert conditions such as a
nitrogen-filled glove box. Lid 210 is sealed with an o-ring 214 and
valves 158, 194 are leak tight. Precursor container module 190 is
connected to downstream components of precursor delivery system 100
via bolts extending through mounting holes 216 and flow path 104 is
sealed by an o-ring fitted in an annular groove 218 at the
connecting end of precursor container module 190. The pressure in
precursor container 102 is reduced by opening vacuum valve 158 to
the bypass path 156 (vacuum path). The precursor material is also
heated to operating temperature by a heater 222 positioned adjacent
precursor container module 190, which can lead to an increase in
pressure within precursor container 102 due to the expulsion of
crystalline or adsorbed water and reaction by products with the
precursor material. Pressure buildup in precursor container 102 may
be periodically released by again opening vacuum valve 158. Once
the precursor material has reached operating temperature, the
precursor source is stabilized and ready for use. A thermocouple
(not shown) may be used to monitor the temperature of the precursor
material and a pressure transducer (not shown) may be used to
monitor the pressure in precursor container 102, for closed loop
control of heater 222 and vacuum valve 158, via an automatic
controller 250 (FIG. 4).
[0056] The various components of the precursor delivery system 100
are preferably formed in or supported on one or more thermally
conductive blocks 230 or other solid bodies, preferably made of a
heat-resistant thermally conductive material, such as aluminum,
stainless steel, titanium, or another suitable metal. Precursor
delivery system 100 may be made modular through the use of more
than one block 230 removably joined and sealed, thereby
facilitating equipment modifications, repair, and replacement.
Blocks 230 together form an elongate thermally conductive body
extending from the precursor container 102 to the reaction chamber
110. In an alternative embodiment, precursor delivery system 100
may be formed in a single block of solid thermally conductive
material, to eliminate the possibility of leakage at seams between
the blocks 230 of FIG. 4. Because blocks 230 are each formed of a
solid block of thermally conductive material, they provide around
and along flow path 104 a thermal pathway having low thermal
resistance, which allows a positive temperature gradient to be
maintained along the flow path 104 (the temperature preferably
increases toward the reaction space) via heater 222 and a second
heater 234 (FIG. 5). A positive temperature gradient ensures that
precursor vapor flowing through flow path 104 will not encounter
cold spots downstream from precursor container 102 and condense in
flow path 104. In particular, heaters 222 and 234 ensure that the
temperature of staging volume 114 is maintained at a higher
temperature than precursor container 102, so that precursor
material will not condense when released from precursor container
102 into staging volume 114.
Operation and ALD Processing
[0057] Referring to the schematic of FIG. 4, the following is a
preferred sequence of steps for sending pulses of precursor vapor
to the reaction chamber 110:
[0058] 1) Isolation valve 146 is opened to allow precursor vapor to
flow into the staging volume 114 for filling of staging volume
114.
[0059] 2) A control circuit 250 monitors the pressure in staging
volume 114 via a pressure sensor 238.
[0060] 3) When the pressure reaches a preset or target level, the
control circuit 250 signals the isolation valve 146 to close.
[0061] 4) The control circuit 250 then signals the inert gas boost
valve 164 to open.
[0062] 5) A control circuit 250 monitors the pressure in staging
volume 114 via the pressure sensor 238.
[0063] 6) When the pressure reaches a preset operating level, the
control circuit 250 signals the inert gas boost valve 164 to
close.
[0064] 7) The diffusion barrier control valve 168 is opened to
change the direction of the diffusion barrier flow as shown in FIG.
8.
[0065] 8) The precursor pulse valve 126 is opened, which allows a
pulse of the precursor vapor to flow from staging volume 114
towards reaction chamber 110.
[0066] 9) The precursor vapor travels through high conductivity
particle filter (HCPF) 140 where it must make several high speed
changes of direction. This action separates any remaining particles
from the precursor vapor due to the higher inertia of the
particles.
[0067] 10) The precursor vapor enters the reaction chamber 110
where a single monolayer chemisorbs on the surface of the
substrate.
[0068] 11) Pulse valve 126 is then closed and the concentration
precursor material present in reaction chamber 110 decays through
the action of inert purge gas supplied by diffusion barrier 130 or
otherwise (i.e., the reaction chamber is purged of the precursor
material). Diffusion barrier control valve 168 is closed to change
the direction of the diffusion barrier flow as shown in FIG. 7, to
prevent any precursor material leaking through pulse valve 126 from
reaching reaction chamber 110.
[0069] 12) After a suitable purge time has elapsed, a pulse of
second precursor material is released into reaction chamber 110 via
a second precursor delivery system (not shown) acting in a similar
manner as described above.
[0070] 13) The pulsing sequence of the two (or more) precursors is
repeated until the desired thickness of the film is reached.
[0071] At the end of the process the integrity of the seals in
valves 126, 146, and 164 may be checked by filling staging volume
114 to a predetermined pressure and using pressure sensor 238 to
check for a pressure change in staging volume 114 over time. If the
pressure decreases then it is assumed that pulse valve 126 is
leaking; if the pressure increases it is assumed that either boost
valve 164 or isolation valve 146 is leaking. Either situation
suggests maintenance is needed.
[0072] The level of the precursor may be checked by filling staging
volume 114 to a predetermined pressure with inert gas (via boost
valve 164), then opening isolation valve 145. The pressure measured
by pressure sensor 238 will decrease as the inert gas expands into
the precursor container in the open space above the supply of
precursor material. The ideal gas equation PV=nRT can be used to
calculate the volume additional volume filled by the expanding gas,
which represents the open space above the supply of precursor
material in the bottom of precursor container 102. The volume can
then be compared to baseline information on the known volume of an
empty precursor container 102, to determine the amount of precursor
material remaining in precursor container 102.
[0073] Turning again to FIG. 4, the precursor material is loaded
into precursor container 102 at a pressure of about 1 bar. Many
precursors cause a large pressure increase in the container upon
first heating, which can lead to large amounts of particles in the
reaction chamber 110 if the pressure increase is released via the
flow path 104 toward the reaction chamber 110. To eliminate this
source of particles, vacuum valve 158 and vacuum path (bypass path)
156 allows excess pressure and agitated particles to be directed to
pumps 152 away from reaction chamber 110. To prevent vacuum valve
158 from becoming plugged, a particle filter 160 may be provided.
Particle filter 160 inhibits particles from powdered precursors
(and droplets, in the case of liquid precursors) from being carried
into staging volume 114. Particle filter 160 may include a high
efficiency particle filter having low flow conductivity, or a high
conductivity particle filter 196 (FIG. 6), or a combination of both
kinds of filters. Because filter 160 is not located between pulse
valve 126 and reaction chamber 110, a high flow resistance of
filter 160 will not increase the rise or decay time of precursor
pulses. If filter 160 has a high resistance (low conductivity), it
can also act as a flow dampener to reduce turbulence in precursor
container 102 during pump down of precursor container 102 (i.e.,
when reducing pressure in precursor container 102 via vacuum path
156 and pumps 152). Reducing turbulence in precursor container 102
further reduces the incidence of particle transmission into flow
path 104 and reaction chamber 110.
[0074] For improved process control it is advantageous to control
the dose of precursor in each pulse. A control system 250
("controller" in FIG. 4) typically includes a computer and drive
electronics (for solenoid valves) or a pneumatic control system
(for pneumatically driven valves) for driving the valves 126, 146,
158, 164, 168 between their open and closed states. Control system
250 coordinates the operation of the valves to direct the precursor
material to the reaction chamber, as described above, and, via
diffusion barrier 130, to prevent any leaked precursor from
reaching the reaction chamber 110. To improve the repeatability of
the dose of precursor material included in each pulse released by
pulse valve 126, pressure sensor 238 may be used to provide
closed-loop feedback to control system 250. In one embodiment, a
sensor may be coupled to the staging volume for sensing a physical
condition of the staging volume or the precursor material present
in it, such as temperature or pressure, for monitoring system
performance and/or providing feedback to an automatic controller of
the precursor delivery system for closed-loop control.
[0075] Another potential advantage of pressure sensor 238 is the
ability to do diagnostic tests on valves periodically or before
each process run, to monitor valve leakage or failure. Over time
all of the valves that come in contact with the precursor vapors
will begin to leak, which can lead to non-uniform films and non-ALD
growth. By setting the pressure of staging volume 114 to a certain
level and determining the rate of change of the pressure it may be
possible to determine if a valve is leaking significantly. It may
also be possible to determine if the precursor supply has been
exhausted, as described above.
[0076] It may also be possible to increase the pressure of staging
volume 114 before each pulse, by injecting N.sub.2 or another inert
gas via boost valve 164. Pressure increase provided by an inert gas
boost enhances the injection of precursor material vapor into the
reaction chamber 110, which is especially important for low vapor
pressure precursors. Alternatively, an inert gas boost may be
utilized to increase the pressure in staging volume 114 before the
precursor vapor is released into it from precursor container 102,
so that the pressure difference between the precursor container 102
and the staging volume 114 is reduced. A reduced pressure
differential between precursor container 102 and staging volume 114
during filling of staging volume 114 may help prevent turbulence
upon opening of isolation valve 146, which can otherwise cause
particles to be stirred and transmitted into staging volume 114,
especially when using high vapor pressure powder precursors.
[0077] Pulse valve 126 allows precursor vapor to travel from
staging volume 114 toward reaction chamber 110. Pulse valve 126 is
the principal barrier preventing the precursor material from
entering the reaction chamber 110 at undesired times. However,
diaphragm valves of the type used for pulse valve 126 will
eventually begin to leak after prolonged exposure to most precursor
vapors. To prevent leaked precursor vapor from reaching the
reaction chamber 110 and causing CVD growth, the so-called
"diffusion barrier" concept is employed. In this manifestation of
the "diffusion barrier" concept, any vapor leaked from pulse valve
126 will preferentially be carried towards the "P2 out" outlet
channel 178 by a backflow of inert gas, as shown in FIG. 7, in
which pumps 182 draw the leaked vapor away from the system 100,
bypassing reaction chamber 110. As shown in FIG. 8, when a pulse of
precursor vapor is released, the diffusion barrier control valve
168 is opened to release a forward flow of inert gas (such as
N.sub.2), to prevent the precursor vapor from being drawn into pump
182 and bypassing the reaction chamber 110. The gas flows during
the pulse time are illustrated in FIG. 8. The ability to switch
between a backflow of inert gas in flow path 104, as shown in FIG.
7, and a forward flow of inert gas, as shown in FIG. 8, merely
through opening and closing of a single control valve 168, is
achieved by adjusting flow restrictors R1, R2, and R3 to properly
balance the pressures at each intersection in diffusion barrier
130.
[0078] During the purge cycle (FIG. 7), pulse valve 126 is closed
to stop the flow of precursor material from the staging volume 114,
and any remaining precursor gases are purged by a flow of inert gas
from inlet channel 174 ("IG in") though the diffusion barrier 130
(as illustrated in FIG. 7 by black arrows). The inert gas also
flows through the high conductivity particle filter 140 and the
reaction chamber 110 to purge residual precursor material. The
backflow of inert gas is pumped through pumps 182 in diffusion
barrier 130 upstream from the inlet channel 174. This backflow of
inert gas carries out of the system through pump 182 any precursor
chemical that may leak through the pulse valve 126 (as indicated by
the white arrows).
[0079] One potential benefit of the diffusion barrier 130 is that
the flow of inert gas may tend to push the flow of the precursor
material during the purge stage, reducing the delay between the
time when the precursor material is released from staging volume
114 and when it enters the reaction chamber 110. An even greater
boost is provided by inert gas boost module 164, 166, coupled to
the flow path upstream from staging volume 114. When boost valve
164 is opened, inert gas is pumped into the staging volume 114 via
inlet IG1. If staging volume 114 holds only a single dose of
precursor material, boost valve 164 may be opened when pulse valve
126 is opened, to push precursor material from the staging volume
114 into the reaction chamber 110 more quickly. When the pulse
valve 126 is closed, the boost valve 164 may also be closed to
maintain the lowered working pressure of staging volume 114.
Isolation valve 146 may then be opened to recharge staging volume
114 with another dose of the precursor material.
[0080] Preferably, staging volume 114 holds more than one dose of
precursor material, in which case the use of an inert gas boost
during pulsing may be unnecessary. Further, when the staging volume
114 holds much more than a single pulse, a smaller pressure
differential need be applied between staging volume 114 and
reaction chamber 110 in order to release sufficient precursor vapor
for thin film deposition processing. A smaller pressure
differential further reduces turbulence and the transmission of
particles from staging volume 114 through flow path 104. For
example, staging volume 114 should desirably hold enough precursor
vapor so that upon release of a single pulse of precursor vapor
(and without inert gas boost or other inflow into staging volume
114), the pressure inside staging volume 114 decreases less than
50% of its pre-pulse pressure. More preferably the pressure
decreases no more than 30% of its pre-pulse pressure.
[0081] A high conductivity particle filter 140 is preferably the
last element in the flow path 104 before reaction chamber 110. It
is important that this filter is highly conductive, as any flow
resistance will lead to a lengthening of the precursor decay. To
separate particles from the precursor vapor without adding
significant resistance in the flow path 104, the high conductivity
particle filter 140 includes a labyrinth filter passage that
requires the precursor vapor to make many fast changes of
direction. The inertia of particles carried by the precursor vapor
causes them to be trapped in dead ends of the labyrinth (i.e.,
"inertial traps") while the precursor vapor can continue to flow
through the high conductivity particle filter 140. As described
below with reference to FIGS. 9-16, the labyrinth and inertial
traps may be formed of a variety of different structures and may
have a variety of different shapes and orientations.
High Conductivity Particle Filters
[0082] Referring to FIG. 9, a cross-sectional view of one
embodiment of a high conductivity particle filter 410 is shown. The
filter 410 provides a primarily two-dimensional flow that captures
unwanted particles. In order to separate particles from a vapor
stream, the higher inertia of particles is used to separate the
particles.
[0083] The filter 410 includes a filter passage (hereinafter "flow
path") 412 that may be formed in a block 414. The flow path 412 is
configured as a continuous spiral in communication with an input
416 and an output 418. The arrows indicate the direction of vapor
flow through the flow path 412. The output 418 may be oriented
perpendicular to the flow path 412. In application, the flow path
412 provides one-way directional flow of a vapor stream from the
input 416 to the output 418. Configured as shown, the flow path 412
is a plane curve that moves around the fixed point of the output
418 while constantly approaching the output 418.
[0084] The flow path 412 is in communication with a plurality of
tangential particle reservoirs or traps 420. As vapor travels
through the flow path 412 the particles have greater inertia than
the vapor. As the vapor travels through the curve, the inertia of
particles does not allow the particles to follow and the particles
are captured in the traps 420 while the vapor continues. Several
traps 420 disposed along the flow path 412 provide a highly
efficient filter 410 that does not constrain flow. The exact number
of traps 420 may vary and depends, in part, on system design
limitations.
[0085] The filter 410 may be formed from a block 414 of
heat-resistant material, such as metal. The material may be
aluminum, silicon, titanium, copper, stainless steel or other high
thermal conductivity material. In manufacturing, the flow path 412
may be drilled or otherwise machined from the block 414. A lid may
then be placed on the block 414 to seal the flow path 412. The
filter 410 may be interchangeable in a modular system to facilitate
equipment modifications, repair, and replacement. After forming the
filter 410, the filter 410 (including the walls of the flow path
412) may be coated with Al.sub.2O.sub.3 or other chemically
resistant material to protect the filter 410 from corrosive vapors
and/or abrasive particles.
[0086] Referring to FIG. 10, another embodiment of a high
conductivity particle filter 422 is shown that also relies on a
primarily two-dimensional flow path 424. The filter 422 may be
formed in a manner similar to the previous embodiment. The flow
path 424 is in communication with an input 426 and an output 428.
The flow path 424 is configured as a spiral, but not a curved
spiral as in FIG. 9. As defined herein, the term spiral refers to a
path that moves around and approaches a fixed point, such as an
output. Thus, the spiral need not be continuously curving, but does
move around and approaches a fixed point.
[0087] The movement around the fixed point may be achieved through
angled turns 430. The angled turns 430 of FIG. 10 are approximately
45 degrees relative to the flow path 424. Of course, turns having
other angles may also be used. The flow path 424 includes two
angled turns 430 in order to negotiate a 90-degree turn in the
block 414. One of skill in the art will appreciate that the
configuration of the spiral flow path 424 may vary and the
embodiments shown herein are for exemplary purposes only. For
example, the block 414 may not have a rectangular cross section in
which case, the flow path 424 may be adjusted accordingly. As such,
the angles and the number of turns may be varied as required.
[0088] A trap 432 is disposed before an angled turn 430 such that
the trap 432 continues along the direction of the flow path 424
before the angled turn 430. As the vapor stream approaches the
turn, the inertia of the particles is greater than that of the
vapor. As the vapor stream passes through an angled turn 430,
particles continue along the former path of the flow path 424 and
into a trap 432. The filter 422 includes several traps 432 to
provide high filtering efficiency. The traps 432 do not limit the
flow of a vapor stream, which allows for high conductivity.
[0089] The turns need not all have the same angle in order to
accommodate the flow path. For example, in the embodiment shown in
FIG. 10, two 90-degree angles are used for the first and last turns
434 in the flow path 424. Based on design considerations, the
angles of the turns 430, 434 may vary. Furthermore, not every turn
430, 434 needs to have a corresponding trap 432. Nevertheless, in
order to maximize efficiency it is desirable to include a greater
number of traps.
[0090] Referring to FIG. 11, a cross-sectional view of another
embodiment of a high conductivity particle filter 436 is shown. As
in the foregoing embodiments, the filter 436 may be formed from a
block 414 with a flow path 438 machined within. The flow path 438
is similar to the embodiments of FIGS. 9 and 10 in that it spirals
around and approaches an output 440. The flow path 438 is also in
communication with an input 442 for introducing a vapor stream into
the filter 436.
[0091] The spiral flow path 438 is comprised entirely of 90-degree
angled turns 444. In alternative implementations, the angle of the
turns 444 may vary. A trap 446 is disposed prior to an angled turn
444 such that the trap 446 continues along the direction of the
flow path 438 before the angled turn 444. As the vapor stream
passes through an angled turn 444, particles continue along the
former path of the flow path 438 and into a trap 446. Traps 446 may
be placed prior to each turn 444 to maximize the efficiency of the
filter 436.
[0092] The flow paths shown in FIGS. 9-11 may be altered into
various configurations and still provide a spiral that approaches a
central point. A flow path may include a combination of features
heretofore described. For example, a flow path may include
45-degree angled turns, 90-degree angle turns and turns of other
angles. A flow path may also include a combination of curves and
angled turns. In an alternative embodiment, the input and the
output may be reversed such that the flow path originates at a
center point and moves around the center point as it approaches the
output. In such an embodiment, the traps are disposed in an
alternative configuration to capture particles. Thus, high
conductivity particle filters are not necessarily limited to the
embodiments shown, which are for exemplary purposes only.
[0093] Referring to FIG. 12, a cross-sectional view of another
embodiment of a high conductivity particle filter 450 is shown. The
filter 450 may be formed from a block of heat resistant material as
in previous embodiments. The filter 450 includes a housing 451 that
surrounds elements of the filter 450, such as a flow path 452. The
flow path 452 is in communication with an input 454 and an output
456 and includes a series of 180-degree turns 457 to separate
particles from a vapor stream.
[0094] The filter 450 includes a series of baffles aligned to
define paths and traps. The filter 450 includes a major baffle 460
that defines a path 462 for a vapor stream. The housing 451
provides an opposing side and also defines the path 462. A minor
baffle 464, that is substantially in the same plane as a
corresponding major baffle 460, defines a trap 458 to capture
particles. The housing 451 also defines the trap 458. The trap 458
continues in the same direction as the path 462. The turns 457
require abrupt directional changes and particle inertia will cause
particles to enter traps. As in previous filters, the trap 458 is a
dead end to capture and retain particles. As the names indicate,
the major baffle 460 has a greater length than the minor baffle
464. Accordingly, the path 462 is longer than a corresponding trap
458.
[0095] An aperture 466 separates the major and minor baffles and is
nonaligned with a subsequent adjacent aperture. The aperture 466
may also be nonaligned with the input 454 and output 456. The
aperture 466 provides the only exit for a vapor stream from the
path 462 to a subsequent path. The aperture 466 may be referred to
as providing the only flow path exit from the path 462. The flow
path is defined as passing from the input 454 to the output 456 in
the direction indicated by the arrows. Thus, the vapor stream must
pass through the aperture 466 and be subject to a 180-degree angled
turn 457.
[0096] As the vapor stream enters the filter 450, the vapor stream
enters the path 462. The input 454 may be disposed perpendicular to
the major baffle 460. The vapor stream continues along the path
462, toward the trap 458, until encountering the aperture 466.
Since the vapor has less inertia than the particles, the path of
the vapor will tend to bend and travel through the aperture 466.
The particles, due to their greater inertia, will tend to continue
on their direction and enter the trap 458.
[0097] A second major baffle 470 is disposed parallel to the first
minor baffle 464, and together the first minor baffle 464 and the
second major baffle 470 defines a pocket 472 that serves as a
secondary trap to capture particles ejected from the flow path 462
after the flow path has passed through the aperture 466.
[0098] A vapor stream passing through the aperture 466 enters a
second path 468 that is defined by the second major baffle 470 and
the first major baffle 460. The second major baffle 470 is disposed
to create a 180-degree turn 457 for the vapor stream. The second
major baffle 470 is separated from a second minor baffle 474 by a
second aperture 476. The second minor baffle 474 is substantially
in the same plane as the second major baffle 470 and defines a
second trap 478. The second trap 478 continues in the same
direction as the second path 468 to capture particles. The second
major baffle 470 is longer than the second minor baffle 474 as the
second path 468 is longer than the second trap 478.
[0099] The second aperture 476 provides the only exit for a vapor
stream passing from the first path 462 to the second path 468. The
second aperture 476 is nonaligned with the aperture 466 or a
subsequent downstream aperture.
[0100] Additional major and minor baffles with separating apertures
may be similarly disposed to create a series of 180-degree turns
457 and corresponding traps. Some particles, especially smaller
particles, may be able to follow the vapor through one or more
apertures without being captured in a trap. Further, while the
traps are designed to retain particles, it remains possible for
particles collected in a trap to be drawn back into the vapor
stream. Accordingly, multiple stages of filtering are used to
increase the overall effectiveness of the filter 450.
[0101] To increase the chances that a particle will be captured,
the velocity of the stream should be as high as possible at the
turn 457. The inertia differences that separate particles from the
vapor are a function of the velocity of the flow and, in
particular, the velocity of the particles. Accordingly, the path
leading up to a trap should be as long as space allows, which will
allow sufficient room in which to accelerate the particles to a
substantial linear velocity before reaching the turn adjacent the
trap.
[0102] The output 456 may be disposed perpendicular to a final
major baffle 477 and is in communication with a final path 479. The
number of baffles and turns may vary based on design
considerations, but allows for high conductivity while maintaining
the efficiency of the filter 450.
[0103] The surface of each trap 458, 478 and pocket 472 may be
modified to help retain particles in the traps and pockets. For
example, one or more of the trap and pocket surfaces may be
roughened or have an adhesive coating applied, to cause particles
to adhere to the surfaces. The entire flow path may include a rough
surface or an adhesive coating as well. In this implementation,
particles traveling through the flow path would be collected and
retained by the flow path surface.
[0104] Referring to FIG. 13A, a plan view of a plate 480 for use in
another embodiment of a high conductivity particle filter is shown.
The plate 480 may be formed of a heat resistant material and in any
number of shapes including a circle, oval, ellipse, rectangle and
the like. The plate 480 includes an aperture 482 that provides an
exit for a vapor stream passing through a filter. The aperture 482
may be aligned off-center so as to be nonaligned with a filter
input and output. The aperture 482 is not disposed on the perimeter
or edge of the plate 480, rather the aperture 482 is disposed at an
intermediate location on the surface area of the plate 480. As
such, the surface area of the plate 480 surrounds the aperture 482,
and the aperture does not contact a perimeter of the plate 480. The
plate 480 serves as a retaining wall to capture and retain
particles.
[0105] Referring to FIG. 13B, a plan view of a second plate 484 is
shown for use in series with the plate 480 of FIG. 13A. The second
plate 484 may be formed of a similar shape and size as the first
plate 480. The second plate 484 also includes a second aperture 486
that provides an exit for vapor stream passing through a filter. As
with the first plate 480, the aperture 486 is disposed at an
intermediate location on the surface area of the plate 480. The
second plate 484 may, in fact, be identical to the first plate 480.
However, when disposed adjacent to the first plate 480, the second
plate 484 may be rotated 180 degrees such that the second aperture
486 is nonaligned with the first aperture 482.
[0106] Referring to FIG. 13C, a perspective view of a series of
plates 480, 484 is shown. The plates 480, 484 are aligned as they
may be disposed in a high conductivity particle filter. The number
of plates 480, 484 may vary based on design considerations and
desired filtering efficiency. Each plate 480, 484 is spaced apart
from one another to form a chamber therebetween. The plates 480,
484 are disposed such that the apertures 482, 486 are nonaligned
with sequential apertures. For good conductivity, the spacing
between the plates is preferably the same as the average diameter
of the aperture, which is preferably the same as the average
diameter of the input and output.
[0107] Referring to FIG. 13D, a cross-sectional view of a high
conductivity particle filter 488 is shown which includes plates
480, 484 within a housing 490. The housing 490 couples to each
plate 480, 484 and fixes the plates 480, 484 in spaced-apart
relation. The housing 490 may be cylindrical or other shape, and
has sealed first and second ends 492, 494 to define an interior
496. The housing 490 and the plates 480, 484 define multiple
sequential chambers 498 within the interior 496. The housing 490 is
secured to each plate 480, 484 so that the corresponding aperture
482, 486 provides the only exit from one chamber 498 to an adjacent
chamber.
[0108] An input 500 provides passage through the first end 492 and
is in communication with a first chamber 502. Similarly, an output
504 provides passage through the second end 494 and is in
communication with a final chamber 506. The input 500 and output
504 may be disposed perpendicular to the surface area of the plates
482, 484. The input 500 and output 504 may be nonaligned with the
sequential apertures 482, 486.
[0109] The filter 488 may be characterized as providing a
three-dimensional flow path, as vapor movement is not primarily
confined to two dimensions. A vapor stream must pass through the
provided aperture to exit each chamber and undergoes a series of
turns. Sequential apertures 482, 486 are preferably distanced from
each other as much as possible to lengthen the flow path and
increase the velocity of the vapor stream. As the vapor stream
passes through the apertures 482, 486, the particles, having a
greater inertia, will continue along their former path and collect
in traps of the chambers 498 adjacent the apertures. A series of
plates 480, 484 and chambers 498 provide a highly efficient filter
without unnecessary flow resistance. The interior surfaces of the
chambers 498 may be modified to encourage particle adhesion. For
example, the interior surfaces of a chamber 498 may be roughened or
coated with an adhesive to retain particles.
[0110] In one embodiment (not shown), the plates 480, 484 may be
spaced progressively closer to one another along a flow path to
sequentially decrease the volumes of the chambers. Accordingly, the
first chamber 502 would have a greater volume than the second
chamber 508, the subsequent chamber would have a volume less than
the second chamber 508, and so forth. The final chamber 506 may be
configured with the smallest volume of all the previous chambers.
Progressively decreasing the chamber volumes gradually decreases
the cross-section of the flow path through the filter 488 and
increases the velocity of a vapor stream. An increased vapor stream
velocity increases the likelihood of smaller particles being
retained in a trap 498. Apertures 482, 486 may also have
sequentially decreasing diameters to decrease the cross-section of
the flow path.
[0111] Referring to FIG. 14, a cross-section of another embodiment
of a high conductivity particle filter 510 is shown. The particle
filter 510 includes a housing 512 with sealed first and second ends
514, 516, which define an interior 518. The filter 510 includes an
input 520 and an output 521, which allows passage through the first
and second ends 514, 516 respectively.
[0112] The filter 510 includes tubes 522 that are disposed parallel
to one another. Each tube 522 has sealed first and second ends 524,
526 and a first (input) aperture 528 and a second (output) aperture
530 disposed along the length of the tube 522. The apertures 528,
530 allow for a flow path 536 through the tube 522 and define first
and second traps 532, 534 within each tube 522. The traps 532, 534
extend from corresponding apertures 528, 530 to the respective
second and first sealed ends 526 and 524. As such, each trap 532,
534 is a "dead end" in which particles are captured and retained in
a manner similar to previously described embodiments.
[0113] Each tube 522 includes a path 537 which may be generally
defined as the length of the tube 522 from the first aperture 528
to the second aperture 530. Vapor exiting the path 537 must turn
through the output aperture 530 and particles, having a higher
inertia than the vapor, continue in the same direction and enter a
trap 534.
[0114] The tubes 522 are in communication with one another to
provide a sinuous flow path that includes a series of paths 537 and
turns. Traps 532, 534 are disposed adjacent each aperture 528, 530
to capture particles unable to negotiate a turn. The number of
tubes 522 used for a flow path may vary based on system design
constraints and desired efficiency of the filter 510.
[0115] The first and second apertures 528, 530 provide
communication between the tubes 522 in the filter 510 as shown in
FIG. 14. Thus, whether an aperture may be characterized as an input
or output is relative to the tube since an output for one tube is
an input for an adjacent tube.
[0116] The last tube in the flow path is defined herein as the
output tube 538 and is in communication with or passes through the
output 521. The output tube 538 may have an open end 540 to provide
an exit for the vapor stream as shown in FIG. 14. Alternatively,
the output tube 538 may have one or more output apertures.
[0117] In the embodiment shown in FIG. 14, the filter 510 provides
split paths 536a and 536b. After passing through the input 520 into
the interior 518, the vapor stream is bifurcated into the two flow
paths 536a and 536b. Each flow path passes through a series of
parallel tubes 522 configured with paths 537 and apertures 528,
530. The flow paths 536a and 536b merge when reaching the output
tube 538 before exiting the filter 510. One of skill in the art
will appreciate that the tubes 522 may be arranged in series to
provide a single flow path, or two or more flow paths.
[0118] The filter 510 may further include one or more preliminary
traps 542 adjacent the input 520. The preliminary traps 542 may be
formed by the extending the walls of the tubes 522 beyond their
sealed first ends 524. The preliminary traps 542 may be disposed
such that incoming vapor stream must turn and pass over the traps
542 before entering into the tubes 522. As in previous embodiments,
the preliminary traps 542 and the previously discussed first and
second traps 532, 534 may have their interior surface roughened or
coated with an adhesive to retain particles. The entire interior
surface of the tubes 522 and the output tube 538 may include a
rough surface or an adhesive coating to capture and retain
particles.
[0119] A method of increasing velocity is to decrease the cross
section of paths 537. Thus, the tubes 522 may be configured with
progressively decreasing cross sectional areas in the direction of
a flow path. Decreasing the cross sectional area of a flow path
increases the velocity of a fluid as it travels along the flow
path.
[0120] FIG. 15 is a perspective cross-section view of an
alternative embodiment of a high conductivity particle filter 546
similar to the filter 510 of FIG. 14. With reference to FIG. 15,
the filter 546 is formed of concentric tubes 548 having
progressively smaller diameters as the flow path traverses from a
first tube 550 to subsequent tubes 552, 554, 556, and 558. The
decreasing diameters of the tubes 550, 552, 554, 556, and 558 form
progressively smaller cross-sectional flow areas as the flow path
(or paths) proceeds to the output tube 538. Apertures 530 may also
be configured with incrementally decreasing diameters along a
defined flow path.
[0121] The vapor stream proceeds from tube 550 to 552 to 554 to 556
to 558 and, since the cross section is decreasing, the vapor stream
velocity is increasing, thereby increasing the inertia of any
particles in the vapor. The decreasing diameters and increasing
particle inertia encourage separation of the increasingly smaller
particles from the vapor stream as the flow proceeds to the outlet
540.
[0122] Referring to FIG. 16 another alternative embodiment of a
filter 560 having high conductivity is shown. The traps 562 include
an orifice 564 that is in communication with a pump or a bypass
line (not shown). An orifice 564 may be effectively implemented
with traps of previously discussed embodiments.
[0123] An orifice 564 may have a cross-section that is
approximately 1 to 5 percent as large as the cross-sectional area
of the vapor flow channel 566. The orifices 564 communicating with
a pump improve the ability of the filter 560 to capture and retain
particles from a vapor stream 572. The orifices 564 also provide a
means for cleaning the traps in-situ, without disassembling the
filter 560, to thereby prevent the traps from becoming filled with
particles that might otherwise be drawn back into the vapor stream
572. The resistance of the orifices 564 should be high enough so
that the majority (e.g., preferably more than 90 percent) of the
vapor stream 572 flowing through the filter 560 does not go through
an orifice 564, but rather continues to the exit of the filter
560.
[0124] To direct the particles toward an orifice 564, a trap 568
may have sidewalls that are tapered toward the orifice 564 in a
funnel configuration. In this implementation, particles traveling
through the orifice 564 are directed away from the trap 568 down a
separate path 570. The particles are permanently removed from the
vapor stream 572. Some traps 568 may have tapering configurations
while other traps 562 do not. Furthermore, some traps 562 may have
orifices 564 while others do not.
[0125] The high conductivity particle filters described herein
provide a flow path with turns and traps to capture particles. The
number of turns and traps ensure filter efficiency. The turns
preferably involve abrupt high-speed changes of direction, which
separates particles from vapor due to higher inertia. The filter's
high conductivity offers little flow resistance, thereby speeding
up precursor vapor pulse decay. Faster switching times for
precursor vapor are possible due to the decreased resistance.
Although the filter is described for use in a precursor vapor
delivery system, the filter may also be used in a pumping line, a
reaction chamber, and other applications.
[0126] Depending upon the location of the filter, the preferred
dimensions and operating conditions will vary. When the filter is
in a precursor delivery system of an ALD system or other thin film
deposition system, it may typically operate at a temperature in the
range of 120.degree. C. to 250.degree. C. and at a pressure in the
range of 1 to 10 Torr with flows less than 1 standard liter per
minute (slm). If the filter is located near a reaction chamber, it
may typically operate at a temperature in the range of 200.degree.
C. to 500.degree. C. and at a pressure of 0.5 to 5 Torr at flows in
the range of 1 to 10 slm. If the filter is located in the pumping
line, it may operate near room temperature at pressures in the
range of 0.1 to 10 Torr and at flows in the range of 1 to 10
slm.
Passivation
[0127] In embodiments of the precursor delivery system 100, the
interior surfaces of the flow path 104 (including valves and high
conductivity particle filters) exposed to the vapor stream are
preferably coated or passivated to prevent chemical reactions.
Otherwise, the precursor vapor stream may react with the surface of
the material of which the filter is made. Reactions affect the
concentration of a vapor stream and destabilize precursor delivery
system 100. The coating or passivation may include, for example,
oxides such as Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, TiO.sub.2,
Ta.sub.2O.sub.5, and Nb.sub.2O.sub.5; nitrides such as AlN, ZrN,
HfN, TiN, TaN, and NbN; or carbides such as AlC, ZrC, HfC, TiC,
TaC, and NbC; and mixtures thereof.
Uses
[0128] Precursor material delivery systems 100 in accordance with
the embodiments described herein are preferred for precursors that
are solids at temperatures they are vaporized. Examples of such
precursors include metal halides, metal .beta.-diketonates, and
organometal compounds. In particular, such systems are preferred
for hafnium tetrachloride (HfCl.sub.4), zirconium tetrachloride
(ZrCl.sub.4), aluminum trichloride (AlCl.sub.3), tantalum
pentachloride (TaCl.sub.5), niobium pentachloride (NbCl.sub.5),
molybdenum pentachloride (MoCl.sub.5), tungsten hexachloride
(WCl.sub.6), platinum (II) acetylacetonate (Pt(acac).sub.2), and
tris(cyclopentadienyl)scandium (Sc(Cp).sub.3), among others. As
noted above, precursor material delivery systems in accordance with
the disclosed embodiments may be adapted for use in various types
of thin film deposition systems, including ALD systems, CVD
systems, MOCVD systems, PVD systems and others, especially when it
is desirable or necessary to deliver pulses of precursor vapor to
the reaction chamber in such systems. Furthermore, precursor
material delivery systems in accordance with various embodiments
may accept precursors originating in any of a number of different
forms, including solid, liquid, gas, fluid, slurry, powder, and
mixtures thereof.
[0129] It will be obvious to those having skill in the art that
many changes may be made to the details of the above-described
embodiments without departing from the underlying principles of the
invention. The scope of the present invention should, therefore, be
determined only by the following claims.
* * * * *