U.S. patent application number 13/802830 was filed with the patent office on 2013-08-01 for gas delivery system.
This patent application is currently assigned to LAOR CONSULTING LLC. The applicant listed for this patent is LAOR CONSULTING LLC. Invention is credited to Herzel Laor, Yuval Laor.
Application Number | 20130193594 13/802830 |
Document ID | / |
Family ID | 47828654 |
Filed Date | 2013-08-01 |
United States Patent
Application |
20130193594 |
Kind Code |
A1 |
Laor; Yuval ; et
al. |
August 1, 2013 |
GAS DELIVERY SYSTEM
Abstract
A gas flow bubbler system for delivering a precursor gas to a
production chamber, the bubbler system comprising: a bubbler for
containing precursor molecules in a liquid phase; a cyclone
separator for removing aerosol particles from the precursor gas;
and a tube through which precursor gas generated in the bubbler
flows to the cyclone separator.
Inventors: |
Laor; Yuval; (Boulder,
CO) ; Laor; Herzel; (Boulder, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LAOR CONSULTING LLC; |
Denver |
CO |
US |
|
|
Assignee: |
LAOR CONSULTING LLC
Denver
CO
|
Family ID: |
47828654 |
Appl. No.: |
13/802830 |
Filed: |
March 14, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13608259 |
Sep 10, 2012 |
|
|
|
13802830 |
|
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|
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61532115 |
Sep 8, 2011 |
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Current U.S.
Class: |
261/19 |
Current CPC
Class: |
F16L 53/38 20180101;
C23C 16/455 20130101; C23C 16/45561 20130101; B01F 3/04099
20130101; F16L 55/02736 20130101; F16L 55/02772 20130101 |
Class at
Publication: |
261/19 |
International
Class: |
B01F 3/04 20060101
B01F003/04 |
Claims
1. A gas flow bubbler system for delivering a precursor gas to a
production chamber, the bubbler system comprising: a bubbler for
containing precursor molecules in a liquid phase; a cyclone
separator for removing aerosol particles from the precursor gas;
and a tube through which precursor gas generated in the bubbler
flows to the cyclone separator.
2. A gas flow bubbler system according to claim 1 and comprising a
rotary flow unit through which gas from the bubbler flows on its
way to the cyclone separator.
3. A gas flow bubbler system according to claim 2 wherein the
rotary flow unit comprises cyclone fins that impart rotary flow to
the gas.
4. A gas flow bubbler system according to claim 2 wherein the
rotary flow unit is coupled to a heater that heats gas flowing
through the rotary flow unit.
5. A gas flow bubbler system according to claim 1 wherein the
cyclone separator has a central axis and the tube through which the
precursor gas flows to the cyclone separator is positioned so that
the precursor gas flows into the cyclone separator off center of
the central axis.
6. A gas flow bubbler system according to claim 1 wherein the
cyclone separator is coupled to the bubbler so that aerosol
particles removed from the precursor gas by the cyclone separator
are returned to the bubbler.
7. A gas flow bubbler system according to claim 6 and comprising a
pump which aspirates gas from the cyclone separator to the bubbler.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 13/608,259, which claims benefit under 35
U.S.C. 119(e) of U.S. Provisional Application 61/532,115 filed Sep.
8, 2011, the disclosure of which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] Embodiments of the invention relate to gas flow.
BACKGROUND
[0003] Various thin layer deposition processes such as atomic layer
deposition (ALD) and the many different epitaxial deposition
techniques, such as chemical vapor deposition (CVD), hydride vapor
phase epitaxial (HVPE) processes to name a few of the large family
of deposition techniques used in manufacturing semiconductor
devices are known. The processes are generally performed in device
referred to as a reactor. The reactor has a production chamber in
which a substrate having a surface on which a layer of a desired
material is to be formed is supported by a pedestal in a region of
the production chamber referred to as a "growth zone". A gas
delivery system in communication with the production chamber
delivers precursor gases to the growth zone where they react and/or
decompose under conditions of temperature and pressure that
facilitate deposition of the desired material on the substrate
surface. The reactor comprises various heating elements and pumps
that are controlled to maintain regions of the production chamber
and growth zone at desired temperatures and pressures.
[0004] The gas delivery system typically comprises a system of
delivery flow pipes, pumps, and valves that are controlled to
transport the precursor gases from their sources outside the
reactor to the production chamber at desired flow rates and partial
pressures. Excess quantities of precursor gases delivered to the
production chamber are removed from the production chamber after
delivery to the growth zone by an exhaust system. The exhaust
system may comprise an exhaust flow pipe that delivers the excess
precursor gases to an abatement unit, which removes toxic gas
components from the excess gases before the excess gases are
released to the atmosphere.
[0005] The various thin layer production processes may often be
complex processes in which the quality of a deposited layer of a
material is sensitively dependent on temperature, pressure and flow
rates of the precursor gases used to form the layer. Generally,
temperature of a precursor gas has to be maintained within an
operating range of temperatures limited by lower and upper bound
operating temperatures for the gas to function as required in a
given deposition process. The range may be relatively small and in
some instances the lower bound operating temperature may be a
temperature below which the precursor gas forms an aerosol of
liquid or solid particles and an upper bound operating temperature
may be a temperature above which the gas undergoes pyrolysis and
decomposes.
[0006] Change in gas temperature to above an advantageous upper
bound operating temperature or below an advantageous lower bound
operating temperature may be caused by Joule-Thomson cooling or
heating as the precursor gas undergoes pressure changes in flowing
through the flow pipes pumps and valves of the gas delivery system
from a source to the growth zone.
SUMMARY
[0007] An embodiment of the invention relates to providing a gas
flow system that maintains temperature of a gas flowing along a
flow path of the system to within a desired temperature range.
Optionally the gas flow system is a gas flow system that delivers a
precursor gas to a reactor.
[0008] In an embodiment of the invention, the gas flow system
comprises at least one flow pipe, in which the gas flows that has a
wall configured to provide enhanced contact with the gas so that
energy transfer between the wall and molecules of the gas that
collide with the wall contributes advantageously to maintaining
temperature of the gas within a desired operating temperature
range. Contact of a gas with a wall or feature of the gas flow
system refers to a frequency of collisions of molecules of the gas
with the wall or feature. A flow pipe configured in accordance with
an embodiment of the invention to provide desired contact with the
gas, that is a desired frequency of collisions between gas
molecules and the flow pipe wall, may be referred to as a "contact
flow pipe".
[0009] In an embodiment of the invention, the contact flow pipe may
have a cross section area that increases gradually along its length
to provide slow change in pressure of the gas, so that contact
between the gas and the wall maintains the gas within a desired
temperature range. Optionally, the contact flow pipe may be
serpentine to provide enhanced contact between aerosol particles
that may be carried by the precursor gas and the wall of the
contact flow pipe. The enhanced contact operates to increase a
probability that the aerosols will evaporate or be sublimated and
removed from the precursor gas. Additionally or alternatively, to
provide enhanced contact, the contact flow pipe may be configured
so that a cross section of the flow pipe has a circumference equal
to or greater than about five times that of a circle having a same
area as the cross section. Optionally, the contact flow pipe may
have a cross section area that increases gradually along the length
of the flow pipe to provide enhanced contact between the gas and
the wall
[0010] Optionally, a region of the wall of the flow pipe is
maintained at a temperature for which energy transfer between the
wall and molecules of the gas that collide with the wall is
advantageous for maintaining the temperature of the gas within the
desired temperature operating range. The wall temperature may be
determined to cause vaporization of aerosol particles of the gas
that collide with the wall.
[0011] The contact flow pipe may comprise protuberances that
contact the gas. In an embodiment of the invention, the
protuberances are maintained at a temperature for which energy
transfer between the protuberances and molecules of the gas that
collide with the protuberances is advantageous for maintaining the
temperature of the gas within the desired temperature operating
range and/or for vaporizing or sublimating aerosol particles of the
gas. Optionally, the protuberances are fin shaped, and may have an
orientation that imparts a desired flow direction to the flowing
gas. Optionally, the fin shaped protuberances impart a helical,
rotary, or turbulent flow to the gas. Hereinafter helical or rotary
flow may be referred to as rotary flow.
[0012] The gas flow system may comprise an energy source, such as
an electromagnetic or acoustic energy source, that is controllable
to add energy to the gas to maintain the gas at a desired
temperature. In an embodiment of the invention, the gas flow system
comprises a temperature sensor that acquires measurements of the
temperature of the gas and a controller that controls temperature
of the wall or the energy source responsive to the acquired
measurements.
[0013] In an embodiment of the invention, changes in pressure of a
first gas flowing in the flow system in a region of the flow path
are moderated to maintain temperature of the first gas within a
desired operating range by providing the region with a second gas
at a pressure that moderates a rate and magnitude of expansion of
the first gas.
[0014] In the discussion, unless otherwise stated, adjectives such
as "substantially" and "about" modifying a condition or
relationship characteristic of a feature or features of an
embodiment of the invention, are understood to mean that the
condition or characteristic is defined to within tolerances that
are acceptable for operation of the embodiment for an application
for which it is intended
[0015] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used to limit the scope of the claimed
subject matter.
BRIEF DESCRIPTION OF FIGURES
[0016] Non-limiting examples of embodiments of the invention are
described below with reference to figures attached hereto that are
listed following this paragraph. Identical features that appear in
more than one figure are generally labeled with a same label in all
the figures in which they appear. A label labeling an icon
representing a given feature of an embodiment of the invention in a
figure may be used to reference the given feature. Dimensions of
features shown in the figures are chosen for convenience and
clarity of presentation and are not necessarily shown to scale.
[0017] FIG. 1 schematically shows a gas flow system comprising a
serpentine contact flow pipe for transporting a gas that is
advantageous for maintaining a desired temperature of the gas in
accordance with an embodiment of the invention;
[0018] FIG. 2 schematically shows a production chamber of a reactor
that may be coupled to the gas flow system shown in FIG. 1 for
which gas passing through the production chamber has a flow pattern
characterized by a substantially constant cross section, in
accordance with an embodiment of the invention;
[0019] FIG. 3 schematically shows a production chamber of a reactor
that may be coupled to the gas flow system shown in FIG. 1 for
which flow of gas in the production chamber is controlled by gas
pressure, in accordance with an embodiment of the invention;
[0020] FIG. 4 schematically shows a coil contact flow pipe, for
transporting a gas that is advantageous for maintaining a desired
temperature of the gas in accordance with an embodiment of the
invention;
[0021] FIG. 5 schematically shows an enhanced surface area contact
flow pipe for transporting a gas that is advantageous for
maintaining a desired temperature of the gas in accordance with an
embodiment of the invention;
[0022] FIG. 6 schematically shows a contact flow pipe having active
elements for controlling temperature of a gas flowing in the
contact flow pipe in accordance with an embodiment of the
invention; and
[0023] FIG. 7 schematically shows a gas flow system comprising a
bubbler for transporting a precursor gas configured to reduce
aerosols in the precursor gas flow, in accordance with an
embodiment of the invention.
DETAILED DESCRIPTION
[0024] FIG. 1 schematically shows a gas flow system 20 comprising a
serpentine contact flow pipe 22 having a wall 24 for delivering a
gas, optionally to a production chamber 26 of a reactor (not shown
in FIG. 1), that is advantageous for maintaining a desired
temperature of the gas, in accordance with an embodiment of the
invention. An axis of contact flow pipe 22 along a midline of the
lumen defined by wall 24 of contact flow pipe 22 is represented by
a dashed line "S". Only a portion of the production chamber is
shown. The gas is assumed to be a precursor gas optionally mixed
with a suitable carrier gas that is to be delivered to the
production chamber so that it flows over a surface 51 of a
substrate 50 to form a layer (not shown) of a desired material on
surface 51. Substrate 50 is supported on a pedestal 27 located in
the production chamber. The production chamber 26 has a conical
flow disperser 28 into which the precursor gas enters upon exit
from contact flow pipe 22 via an inlet aperture 29 of flow
dispenser 28. Flow disperser 28 is configured to facilitate radial
flow of the precursor gas that enters production chamber 26 so that
it flows over substrate 50 in directions indicted by flow arrows
99. For convenience of presentation, unless indicated otherwise, a
mixture of a precursor gas and a carrier gas is referred to as a
precursor gas or a gas.
[0025] The precursor gas is provided by a source (not shown) of the
precursor gas so that it flows into contact flow pipe 22 at an
optionally relatively small inlet aperture 31 having dimensions
that match an outlet aperture of the source. Flow of precursor gas
into contact flow pipe 22 at inlet aperture 31 is schematically
indicated by a flow arrow 100. Contact flow pipe 22 functions as a
spatial adapter that transports the precursor gas from the
relatively small inlet aperture 31 to a relatively large outlet
aperture 32 that has dimensions adapted to dimensions and flow
requirements of production chamber 26.
[0026] For example, substrate 50 shown in FIG. 1 may be a 300 mm
diameter silicon semiconductor wafer, and whereas inlet aperture 31
may advantageously be 2 to 10 mm in diameter, outlet aperture 32
may advantageously be 10-50 mm in diameter to match inlet aperture
29 of flow disperser 28. Some reactor chambers are configured for
processing more than one substrate at a time and for such
multi-substrate production chamber outlet aperture 32 may
advantageously be larger than 50 mm. In flowing from aperture 31 to
aperture 32 volume of the precursor gas in general changes and
undergoes expansion.
[0027] Changes in gas volume are usually accompanied by
corresponding changes in temperature as a result of a Joule-Thomson
effect. Generally, with expansion a gas undergoes cooling as
kinetic energy of the gas is converted to potential energy in
overcoming van-der-Waals attractive forces. In some situations a
gas may be heated as it expands as a result of conversion of
internal energy of gas molecules to kinetic energy of the gas
molecules. Contact flow pipe 22 in accordance with an embodiment of
the invention is configured to moderate changes in temperature of
the precursor gas as it flows from relatively small inlet aperture
31 to relatively large outlet aperture 32 and undergoes increase in
volume.
[0028] In an embodiment of the invention a ratio "R.sub.OI" of area
of outlet aperture 32 divided by area of inlet aperture 31 is
greater than or equal to about 2. Optionally, R.sub.OI is greater
than or equal to about 5. In some embodiments of the invention
R.sub.OI is greater than or equal to about 10. To moderate
temperature change for a contact flow pipe 22 having a given
R.sub.OI, increase in cross section area of contact flow pipe 22
with distance along the flow pipe is constrained by an upper bound
constraint. If "A" is the cross sectional area of the flow pipe at
any given point along the contact flow pipe, the constraint may be
(1/A).differential.A/.differential.s.ltoreq.K, where
.differential.A/.differential.s is the first derivative of A with
respect to displacement "s" along axis S. In an embodiment of the
invention K is less than or equal to 0.25 Optionally K is less than
or equal to about 0.10. In an embodiment K is less than 0.05.
[0029] Constraining rate of increase in cross sectional area of
contact flow pipe 22 in accordance with an embodiment of the
invention may provide sufficient frequency of collisions of
molecules of precursor gas with wall 24 of contact flow pipe 22 so
that energy exchange between the wall and gas provides a desired
moderation of gas temperature due to volume expansion and pressure
decline.
[0030] Additionally or alternatively, in an embodiment, contact
flow pipe 22 may be configured sufficiently serpentine so that
aerosol particles that may be carried by the gas, because of their
relatively large inertia, collide with greater frequency with wall
24 of contact flow pipe 22. The greater frequency of collision
tends to evaporate or sublimate the aerosol particles and reduce
their possible deleterious effects on processes that take place in
production chamber 26 in forming the layer of desired material on
substrate 50.
[0031] Let a measure of a degree to which flow pipe 22 is
serpentine be referred to as a serpentine index (SI). SI may be
defined as an integral of an absolute value of changes in angle of
direction that an "imaginary" unit vector 60 tangent to axis S of
contact flow pipe 22 undergoes as an origin 61 of the vector moves
along the axis from the inlet aperture 31 to the outlet aperture
32.
[0032] Increasing SI tends to increase a number of times aerosol
particles carried by a precursor gas flowing in contact flow pipe
22 collides with and exchanges energy with wall 24 of the contact
flow pipe 22. The increased number of collisions enhances a
probability that the aerosol particles will evaporate or be
sublimated before they reach production chamber 26. In an
embodiment of the invention SI is greater than or about equal to
about 180.degree.. Optionally SI is greater than or about equal to
360.degree.. Optionally SI is greater than or equal to about
720.degree.. Inspection of FIG. 1 indicates that SI for contact
flow pipe 22 is equal to 630.degree..
[0033] In some embodiments of the invention, contact flow pipe 22
comprises mixing fins 80 that are optionally relatively thin, stave
shaped deflectors that protrude inward from the wall of contact
flow pipe 22 towards the axis S of the flow pipe. Mixing fins 80
tend to deflect flow of gas molecules and introduce turbulence into
flow of the precursor gas that homogenizes gas temperature. Mixing
fins 80 also aid in removing aerosol particles from the gas by
transferring energy to aerosol particles that collide with the fins
and increasing a probability that the aerosol particles evaporate
or are sublimated. Flow directions and turbulence introduced by
mixing fins 80 is indicated by arrows 101 representing flow of the
gas in the vicinity of the mixing fins.
[0034] In an embodiment, contact flow pipe 22 comprises "cyclone"
fins 81 located near exit aperture 32 of the contact flow pipe,
shown magnified in an inset 90. Cyclone fins 81 introduce
relatively smooth rotary flow into the precursor gas as it exits
contact flow pipe 22 and enters production chamber 26. The rotary
flow of the precursor gas is schematically indicated by curly flow
arrows 102 aids in generating radial flow, indicated by flow arrows
99 of the precursor gas over substrate 50 after it enters
production chamber 26
[0035] Production chamber 26 in an embodiment of the invention is a
uniform flow production chamber. A uniform flow production chamber
is configured so that precursor gas that enters the chamber from a
gas flow system, such as gas flow system 20, flows with a
substantially a same area cross section at all regions along its
flow path through the production chamber. As a result, a uniform
production chamber in accordance with an embodiment of the
invention tends to prevent the formation of aerosols in the
precursor gas as a result of a change in gas volume and concomitant
drop in gas temperature.
[0036] FIG. 2 schematically shows a uniform flow production chamber
200 of a reactor (not shown) in accordance with an embodiment of
the invention. Production chamber 200 is optionally substantially
rotationally symmetric about an axis of rotation 201 of the
production chamber. Precursor gas optionally mixed with an inert
carrier gas enters the production chamber through an inlet aperture
202 having an area, substantially equal to an outlet aperture of a
gas flow system, such as outlet aperture 32 of gas flow system 20
that delivers the precursor gas to the production chamber. From
inlet aperture 202, the precursor gas flows radially in a region
204 over a substrate 50 supported on a pedestal 27 towards a
perimeter 206 of the pedestal. Region 204 is bounded optionally by
a surface 208 of a conical flow disperser 210 and substantially a
surface 212 of pedestal 27. Radial flow of the precursor gas is
indicated by flow arrows 103. At the perimeter, after flowing over
substrate 50 excess precursor gas flows "downwards" in directions
indicated by flow arrows 104 into a region 212 from which the
excess gas exhausts via an exit aperture 214 optionally to an
abatement unit (not shown). Region 212 is optionally bounded by a
surface 216 that is substantially a mirror image surface of surface
208.
[0037] Let "A" represent area of inlet aperture 202, "R.sub.o"
represent radius of the aperture, "Rp" radius of the perimeter of
pedestal 27 and "R.sub.C" radius of production chamber 200. In
accordance with an embodiment, to provide constant cross section
flow over substrate 50 in directions indicated by flow arrows 103,
height H of surface 208 at radius R.gtoreq.R.sub.o substantially
satisfies an expression H=A/2.sigma.R. To match flow cross section
at perimeter 206 in direction of flow arrows 104 to flow cross
section of radial flow indicated by flow arrows 103 over substrate
50, R.sub.C and Rp may substantially satisfy an expression
A=.pi.(R.sub.C+Rp)(R.sub.C-Rp).
[0038] FIG. 3 schematically shows a cross section of a production
chamber 300 coupled to an exhaust system 302 that evacuates excess
precursor gas after the precursor gas has entered a region 304 of
production chamber 300 and passed over substrate 50, in accordance
with an embodiment of the invention. Substrate 50 is supported by a
pedestal 27 mounted on a pedestal stem 306 optionally journaled in
a stem socket 307. The pedestal and substrate may be raised and
lowered in production chamber 300 by raising and lowering the stem
pedestal relative to stem socket 307 to enable insertion and
removal of substrate 50 via a slit valve 317. Production chamber
300 is substantially rotationally symmetric about an axis 301.
[0039] Exhaust system 302 comprises an exhaust manifold 310,
optionally rotationally symmetric with respect to axis 301 that
communicates with a region 312 of production chamber 300 via a slit
or plurality of holes 314 in a wall 315 of the production chamber.
Precursor gas after passing over substrate 50 exits from region 304
of production chamber 300 and into region 312 and from region 312
into manifold 310 via the holes or slit. The precursor gas is
evacuated from the manifold to an abatement unit 318 comprised in
the exhaust system by a vacuum pump 320 that maintains region 312
at a pressure less than pressure in region 304 and pressure in a
region 314 below pedestal 27. Flow barriers 322 operate to limit a
rate at which precursor gas flows from region 304 into, and expands
in region 312 and exhaust manifold 310. Flow barriers 324 operate
to limit flow of gas between regions 312 of production chamber 300
and region 314 below pedestal 27.
[0040] In an embodiment of the invention a gas, referred to as an
inert gas, that does not participate or affect reactions involving
the precursor gas in region 304 of production chamber 300, is
introduced via an inlet 324 into region 314 of the production
chamber. Pressure of the inert gas functions to limit leakage of
precursor gas into region 314 and to control and moderate a
pressure differential between regions 304 and 312. Moderating the
pressure differential between regions 304 and 312 moderates a rate
at which precursor gas exits region 304 and flows and expands into
region 312 and manifold 310 and as a result temperature changes in
the gas that may be generated by a Joule-Thomson effect.
[0041] FIG. 4 schematically shows another serpentine gas contact
flow pipe 400 in accordance with an embodiment of the invention.
Contact gas flow pipe 400 has an inlet aperture 401, at least one
pipe coil 402, and an outlet aperture 403 having a diameter
suitable for matching to an inlet aperture of a production chamber
of a reactor such as production chamber 26 (FIG. 1). Contact flow
pipe 400 has a pipe axis indicted by a dashed line "S" that passes
through centers of cross sections of the contact flow pipe. Whereas
contact flow pipe 400 is shown as having a circular cross section,
practice of embodiments of the invention is not limited to a coil
contact flow pipe having a circular cross section. A coil contact
flow pipe, as well as other contact flow pipes, in accordance with
an embodiment of the invention may for example, have an elliptical,
rectangular, triangular, or irregular cross section. A coil contact
flow pipe in accordance with an embodiment of the invention, may
also have a shape of a spiral curve, such as by way of example a
logarithmic or equiangular spiral, for which the coils of the
spiral lie substantially in a plane.
[0042] By way of example, in FIG. 4 contact flow pipe 400 comprises
five pipe coils 402 but is not limited to five pipe coils and may
have less or more than five coils. A distance L between inlet
aperture 401 and outlet aperture 403 is shown in FIG. 4. For
convenience of visualization, contact flow pipe 400 is shown
relative to a Cartesian coordinate system having x, y and z
axes.
[0043] In an embodiment of the invention contact flow pipe 400 has
a percent rate of change in cross section area A with distance "s"
along S that satisfies the constraint discussed above,
(1/A).differential.A/.differential.s.ltoreq.K. For the exemplary
five pipe coils 402 comprised in contact flow pipe 400, the contact
flow pipe has a serpentine index SI substantially equal to
1,800.degree..
[0044] FIG. 5 schematically shows another contact flow pipe 500 in
accordance with an embodiment of the invention. Contact flow pipe
500 has an axis S, and comprises a relatively small area circular
inlet aperture 501 and a relatively large area circular outlet
aperture 502. Contact flow pipe 500 may have regions 512, 513, . .
. , 516. In region 512, the cross section of contact flow pipe 500
morphs from having a substantially circular shape near inlet
aperture 501 to a noncircular shape cross section 520 in regions
513, . . . , 516. By way of example, the noncircular cross sections
520 are rectangular. Optionally, the area of cross sections 520
increases with proximity of the cross sections to outlet 502 in
regions 513 and 514 and remains substantially constant in region
515. In region 516 contact flow pipe 500 may morph to a pipe shape
having a relatively large circular cross section substantially
equal to that of outlet aperture 502.
[0045] In accordance with an embodiment of the invention, a
circumference of each cross section 520 is substantially larger
than a circumference of a circle having a same area as the cross
section 520. Let "C.sub.R" represent a ratio of the circumference
of a cross section 520 to a circumference of a circle having a same
area as the cross section. In an embodiment of the invention
C.sub.R is greater than or about equal to 5. Optionally, C.sub.R is
greater than or about equal to 10. In some embodiments of the
invention C.sub.R is greater than or about equal to 25.
[0046] For a given cross section area of a gas flow pipe, molecules
of a gas flowing in a pipe having a cross section with a greater
circumference collide more frequently with the pipe wall than gas
flowing in a pipe having a cross section of smaller circumference.
By providing contact flow pipe 500 with cross sections 520 having a
relatively large C.sub.R a precursor gas flowing in contact flow
pipe 500 may experience an enhanced frequency of collisions with
the wall of the contact flow pipe sufficient to moderate changes in
temperature of the gas due to changes in volume of the gas.
[0047] A graph 550 shows a curve 551 that illustrates, in
accordance with an embodiment of the invention, a hypothetical
dependence of temperature T of a gas flowing from inlet aperture
501 to outlet aperture 502 of contact flow pipe 500 as a function
of s along axis S of the contact flow pipe. By way of example, it
is assumed that it is advantageous that the gas remain in a range
of temperatures between a temperature lower bound T.sub.LB and a
temperature upper bound T.sub.UB and that the walls of contact flow
pipe 500 are maintained at a suitable temperature between T.sub.LB
and T.sub.UB, and optionally near T.sub.UB.
[0048] Following entry into contact flow pipe 500 at inlet aperture
501, the volume of the gas expands in regions 512-514 and
temperature of the gas decreases as indicated by curve 551.
However, because of the relatively large value of C.sub.R for cross
sections 520 in regions 512-514 in accordance with an embodiment of
the invention, it is expected that the decrease in temperature is
smaller than might obtain for a conventional gas flow pipe. In
region 515, the volume of the gas is substantially constant and by
way of example is assumed to remain substantially constant in
region 516. However, because of the increased interaction of the
gas with the walls of contact flow pipe 500 resulting from a
relatively large value C.sub.R for cross section 520 in regions 515
and 516, temperature of the gas increases relatively quickly to the
temperature of the wall of contact flow pipe 500.
[0049] FIG. 6 schematically shows a gas contact flow pipe 600
having a wall 602 and active elements for controlling temperature
of a precursor gas flowing in the contact flow pipe, in accordance
with an embodiment of the invention. Contact flow pipe 600 is
optionally coupled to a gas disperser 603 through which a precursor
gas exits the contact flow pipe to flow over a substrate 50.
[0050] Contact flow pipe 600 is optionally serpentine and comprises
temperature control elements 604 coupled to wall 602 that are
controllable by a controller (not shown) to maintain a desired
temperature of the wall. Optionally, contact flow pipe 600
comprises temperature sensors 608 configured to acquire
measurements of temperature of a precursor gas flowing in the
contact flow pipe. In an embodiment, the controller controlling
elements 604 controls the elements responsive to temperature
measurements acquired by sensors 608. Temperature control elements
may be controllable to heat and/or cool wall 602 and may for
example comprise a Peltier device.
[0051] Optionally, contact flow pipe 600 comprises temperature
control fins 610 that may be heated and/or cooled to control
temperature of gas flowing in the contact flow pipe. Heating or
cooling of a fin may be accomplished by a suitable heating and/or
cooing element or device, such as by way of example, temperature
control elements 604, thermally coupled to the fin or housed inside
the fin. In an embodiment of the invention contact flow pipe 600
comprises cyclone fins 612 that introduce rotary flow to a gas
flowing in the contact flow pipe. Optionally, cyclone fins 612 may
be heated and/or cooled to control temperature of a gas flowing in
the contact flow pipe.
[0052] In an embodiment of the invention, contact flow pipe
comprises an energy transmission window 614 thru which a source of
electromagnetic or acoustic energy may be transmitted from outside
the contact flow pipe to a gas flowing in the contact flow pipe.
For example, energy transfer window 614 may comprise a thin
dielectric window through which electromagnetic energy may be
transmitted into contact flow pipe 600. Optionally, the window
comprises a microwave antenna on a side of the window facing the
lumen of contact flow pipe 600 and a conductive contacts for
connecting a microwave power source to the antenna on a side of the
window facing away from the lumen.
[0053] FIG. 7 schematically shows a gas flow bubbler system 700
comprising a bubbler 702 for delivering a precursor gas contained
in bubbler 702 as a liquid 704 to a production chamber (not shown)
and a cyclone separator 720 for removing aerosols in the precursor
gas, in accordance with an embodiment of the invention.
[0054] Bubbler system 700 optionally comprises a heater (not shown)
that heats liquid 704 to generate precursor gas and a bubbler inlet
pipe 705. An inert carrier gas is introduced via inlet pipe 705 to
flow through liquid precursor 704 and form bubbles 706 in the
liquid precursor that acquire precursor gas generated in the liquid
precursor by the heater. Bubbles 706 of carrier gas and precursor
flow leave liquid 704 to flow as a gas in a direction indicated by
flow arrows 107 that leaves the bubbler via an exit pipe 707 and
optionally a rotary flow unit 708 comprising cyclone fins 709.
Optionally exit pipe 707 and rotary flow unit 708 are coupled to
heaters 710. Heaters 710 heat the gas leaving bubbler 702 to remove
aerosol particles in the gas. Cyclone fins 709 in rotary flow unit
708 impart rotary flow to the gas that operates to spin aerosol
particles in the gas to the walls of the rotary gas flow unit and
flow pipes downstream of the rotary gas flow unit. In collisions of
the aerosol particles with the walls and cyclone fins 709 the
aerosol particles tend to pick up energy that evaporates and/or
sublimates the aerosol particles.
[0055] After passing through exit pipe 707 and rotary flow unit 708
the gas of carrier and precursor molecules flows through a bridging
pipe 712 coupled to cyclone separator 720. Cyclone separator 720 is
substantially rotationally symmetric about an axis 721 and
comprises a funnel 722. Bridging pipe 712 is positioned so that gas
flowing though bridging pipe 712 enters and flows off center from
axis 721 to generate rotational flow of the entering gas relative
to the axis. Centrifugal forces generated by the rotational flow of
the gas causes aerosol particles carried by the gas to impact the
wall of funnel 722 and drip back to precursor liquid 704 in bubbler
702 via a drip pipe 714. Carrier and precursor molecules in the gas
are reflected upwards to exit the cyclone separator via a delivery
pipe through which the gas, relatively free of aerosol particles
flows towards the production chamber. Flow of carrier and precursor
gas in cyclone separator 720 is schematically indicated by a curled
flow arrow 110. Dripping of aerosol particles to liquid 704 is
indicated by an arrow 111 and is facilitated optionally by a pump
724 which aspirates gas from cyclone separator 720 to bubbler
702.
[0056] It is noted whereas in the above, a bubbler is used to
provide a precursor in a gas phase a sublimation precursor gas
generator can be used in place of a bubbler to generate a precursor
in a gas phase.
[0057] In the description and claims of the present application,
each of the verbs, "comprise" "include" and "have", and conjugates
thereof, are used to indicate that the object or objects of the
verb are not necessarily a complete listing of components, elements
or parts of the subject or subjects of the verb.
[0058] Descriptions of embodiments of the invention in the present
application are provided by way of example and are not intended to
limit the scope of the invention. The described embodiments
comprise different features, not all of which are required in all
embodiments of the invention. Some embodiments utilize only some of
the features or possible combinations of the features. Variations
of embodiments of the invention that are described, and embodiments
of the invention comprising different combinations of features
noted in the described embodiments, will occur to persons of the
art. The scope of the invention is limited only by the claims.
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