U.S. patent application number 17/182473 was filed with the patent office on 2021-07-01 for fluid-assisted thermal management of evaporation sources.
This patent application is currently assigned to First Solar, Inc.. The applicant listed for this patent is First Solar, Inc.. Invention is credited to Markus Eberhard Beck, Ulrich Alexander Bonne, Robert G. Wendt.
Application Number | 20210198783 17/182473 |
Document ID | / |
Family ID | 1000005451087 |
Filed Date | 2021-07-01 |
United States Patent
Application |
20210198783 |
Kind Code |
A1 |
Beck; Markus Eberhard ; et
al. |
July 1, 2021 |
FLUID-ASSISTED THERMAL MANAGEMENT OF EVAPORATION SOURCES
Abstract
In various embodiments, evaporation sources for deposition
systems are heated and/or cooled via a fluid-based thermal
management system.
Inventors: |
Beck; Markus Eberhard;
(Scotts Valley, CA) ; Bonne; Ulrich Alexander;
(Sunnyvale, CA) ; Wendt; Robert G.; (Gilroy,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
First Solar, Inc. |
Tempe |
AZ |
US |
|
|
Assignee: |
First Solar, Inc.
Tempe
AZ
|
Family ID: |
1000005451087 |
Appl. No.: |
17/182473 |
Filed: |
February 23, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15904647 |
Feb 26, 2018 |
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17182473 |
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15082290 |
Mar 28, 2016 |
9932666 |
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15904647 |
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62140083 |
Mar 30, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 31/18 20130101;
C23C 14/542 20130101; H01L 51/001 20130101; C23C 16/0209 20130101;
C23C 16/4485 20130101; Y02E 10/541 20130101; C23C 16/52 20130101;
C23C 16/28 20130101; H01L 21/02568 20130101; H01L 31/046 20141201;
F25D 17/02 20130101; F25B 39/02 20130101; H01L 21/02631 20130101;
C23C 14/26 20130101; F25B 39/00 20130101; F28D 15/00 20130101; C23C
14/24 20130101; C23C 14/243 20130101; H01L 31/0322 20130101; H01L
51/56 20130101; H01L 31/0326 20130101; C23C 16/448 20130101 |
International
Class: |
C23C 14/26 20060101
C23C014/26; C23C 14/24 20060101 C23C014/24; C23C 14/54 20060101
C23C014/54; F28D 15/00 20060101 F28D015/00; H01L 31/046 20060101
H01L031/046; C23C 16/448 20060101 C23C016/448; F25B 39/00 20060101
F25B039/00; H01L 31/032 20060101 H01L031/032; H01L 31/18 20060101
H01L031/18; H01L 51/00 20060101 H01L051/00; H01L 51/56 20060101
H01L051/56; C23C 16/02 20060101 C23C016/02; C23C 16/28 20060101
C23C016/28; C23C 16/52 20060101 C23C016/52; F25D 17/02 20060101
F25D017/02 |
Claims
1. A deposition system comprising: a deposition chamber having an
interior enclosed by one or more chamber walls; an evaporation
source comprising (i) a vacuum shell defining a hollow source body
having a first reservoir therein for containing a feedstock
material for evaporation thereof, and (ii) an evaporation port for
fluidly coupling the source body with the interior of the
deposition chamber, (iii) a plurality of fluid inlets, and (iv) a
plurality of fluid outlets, wherein the evaporation source is
configured to establish and monitor a vacuum within the first
reservoir and the deposition chamber; a feedstock material disposed
within the source body; and a thermal management system comprising:
a second reservoir for containing heat-transfer fluid, a conduit
for thermally coupling the second reservoir with the evaporation
source, wherein a first portion of the conduit extends between the
second reservoir and one of the plurality of fluid inlets of the
evaporation source, wherein the conduit includes a plurality of
second portions disposed within the source body so as to directly
contact the feedstock material disposed therein, wherein one of the
second portions extends between the fluid inlet to which the first
portion of the conduit is attached and one of the fluid outlets,
wherein at least one of the plurality of second portions extends
between two fluid outlets, wherein the conduit includes a plurality
of third portions disposed outside of the source body, and wherein
each third portion extends between fluid outlets to which second
portions of the conduit are attached, such that the third portions
fluidly connect adjacent ones of the second portions, a fluid pump
fluidly connected within the first portion of the conduit, a
temperature-regulation mechanism for heating and/or cooling
heat-transfer fluid within the second reservoir, and a controller
for controlling flow of heated and/or cooled heat-transfer fluid
through the conduit between the evaporation source and the second
reservoir to thereby control a temperature of the evaporation
source, whereby heating of the evaporation source at least in part
via flow of heated heat-transfer fluid through the conduit results
in vaporization of feedstock material in the source body and flow
of vaporized the feedstock material into the deposition chamber via
the evaporation port.
2. The deposition system of claim 1, wherein the
temperature-regulation mechanism comprises at least one of a
heater, a heat exchanger, or a resistive heater.
3. The deposition system of claim 1, wherein the feedstock material
comprises at least one of phosphorous, sulfur, arsenic, tellurium,
or selenium.
4. The deposition system of claim 1, wherein the thermal management
system comprises a second heater for heating the evaporation source
in tandem with flow of heated heat-transfer fluid through the
conduit.
5. The deposition system of claim 4, wherein the second heater
comprises at least one of a resistive heater, an electron beam
source, a laser source, a thermoelectric heater, or a heat
exchanger.
6. The deposition system of claim 1, wherein the thermal management
system comprises a cooler for cooling the evaporation source in
tandem with flow of cooled heat-transfer fluid through the
conduit.
7. The deposition system of claim 6, wherein the cooler comprises a
source of gas, a heat exchanger, or a thermoelectric cooler.
8. The deposition system of claim 1, wherein the controller is
configured to control the temperature of the evaporation source via
flow of heated and/or cooled heat-transfer fluid through the
conduit over only a portion of an operating temperature range of
the evaporation source.
9. The deposition system of claim 1, further comprising
heat-transfer fluid disposed within the reservoir.
10. The deposition system of claim 9, wherein the heat-transfer
fluid comprises at least one of water, a glycol, a silicone, a
dielectric fluid, a fluorocarbon, polyalphaolefin, or a hydrocarbon
oil.
11. The deposition system of claim 1, wherein the source body
comprises at least one of a refractory metal, a ceramic material,
or a nickel-containing alloy.
12. The deposition system of claim 1, wherein one or more surfaces
of the source body are lined and/or coated with a lining
material.
13. The deposition system of claim 12, wherein the lining material
comprises a ceramic material.
14. The deposition system of claim 1, wherein the evaporation
source comprises one or more fill ports for introduction of
feedstock material therethrough into the source body.
15. The deposition system of claim 14, further comprising a
removable cover for covering at least one of the fill ports.
16. A deposition system comprising: a deposition chamber having an
interior enclosed by one or more chamber walls; an evaporation
source comprising (i) a vacuum shell defining a hollow source body
having a first reservoir therein for containing a feedstock
material for evaporation thereof, and (ii) an evaporation port for
fluidly coupling the source body with the interior of the
deposition chamber, (iii) a plurality of fluid inlets, and (iv) a
plurality of fluid outlets, wherein the evaporation source is
configured to establish and monitor a vacuum within the first
reservoir and the deposition chamber; a feedstock material disposed
within the source body; and a thermal management system comprising:
a second reservoir having heat-transfer fluid disposed therein, a
conduit for thermally coupling the second reservoir with the
evaporation source, wherein a first portion of the conduit extends
between the second reservoir and one of the plurality of fluid
inlets of the evaporation source, wherein the conduit includes a
plurality of second portions disposed within the source body so as
to directly contact the feedstock material disposed therein,
wherein one of the second portions extends between the fluid inlet
to which the first portion of the conduit is attached and one of
the fluid outlets, wherein at least one of the plurality of second
portions extends between two fluid outlets, wherein the conduit
includes a plurality of third portions disposed outside of the
source body, and wherein each third portion extends between fluid
outlets to which second portions of the conduit are attached, such
that the third portions fluidly connect adjacent ones of the second
portions, a fluid pump fluidly connected within the first portion
of the conduit, a temperature-regulation mechanism for heating
and/or cooling heat-transfer fluid within the second reservoir, a
cooler, and a controller for controlling flow of heated and/or
cooled heat-transfer fluid through the conduit between the
evaporation source and the second reservoir to thereby control a
temperature of the evaporation source, whereby heating of the
evaporation source at least in part via flow of heated
heat-transfer fluid through the conduit results in vaporization of
feedstock material in the source body and flow of vaporized the
feedstock material into the deposition chamber via the evaporation
port, wherein the cooler cools the evaporation source in tandem
with flow of cooled heat-transfer fluid through the conduit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/904,647, filed Feb. 26, 2018, which is a
continuation of U.S. patent application Ser. No. 15/082,290, filed
Mar. 28, 2016, which claims the benefit of and priority to U.S.
Provisional Patent Application No. 62/140,083, filed Mar. 30, 2015,
the entire disclosure of each of which is hereby incorporated
herein by reference.
TECHNICAL FIELD
[0002] In various embodiments, the present invention relates to
thermal evaporation, in particular to thermal management of
evaporation sources.
BACKGROUND OF THE INVENTION
[0003] Thermal evaporation is a well-known approach to forming a
number of materials such as III-V solid-state semiconductors via
molecular beam epitaxial (MBE) growth. Another commercial
application of this technique is the evaporation of aluminum (Al)
onto polymer foils for the packaging industry or other metals onto
polymer foils for capacitor manufacturing. In these applications,
the sources are typically point sources either of the Knudsen cell
design or the open boat design. Point sources are also used in
manufacturing of thin-film photovoltaic (PV) devices, in particular
copper indium gallium selenide (CuIn.sub.xGa.sub.1-xSe.sub.2or
CIGS) devices. In addition, large area organic light-emitting diode
(OLED) devices are often fabricated using thermal evaporation
sources. Due to their large-area substrates and required uniformity
of the deposited layers, thermal evaporation sources utilized for
OLEDs are typically of the linear type.
[0004] Some materials commonly deposited via thermal evaporation
are difficult to heat up or cool down due to their poor heat
capacity and poor thermal conductivity. Prime examples of such
materials are phosphorous (P), sulfur (S), and selenium (Se). All
of these elements have low heat capacities common for most solid
elements coupled with rather poor thermal conductivities. Other
group V elements, in particular arsenic (As) and antimony (Sb),
also common in thermal evaporation, exhibit two orders of magnitude
higher thermal conductivities. Tellurium (Te) is also of importance
in various applications and has a moderate thermal conductivity one
order of magnitude lower than As and P and one order of magnitude
higher than P, S, and Se. Table 1 below provides exemplary values
of heat capacities and thermal conductivities for these materials.
In comparison, copper (Cu) has a molar heat capacity of 24.44 J
mol.sup.-1K.sup.-1 (0.385 J g.sup.-1 K.sup.-1) and a thermal
conductivity of 401 W m.sup.-1K.sup.-1 at room temperature.
TABLE-US-00001 TABLE 1 Molar Heat Specific Heat Thermal capacity
capacity Conductivity Element [J mol.sup.-1 K.sup.-1] [J g.sup.-1
K.sup.-1] [W m.sup.-1 K.sup.-1] P 23.82 0.769 0.236 S 22.75 0.705
0.205 As 24.57 0.328 50 Se 25.35 0.321 0.519 Sb 25.20 0.207 24 Te
25.65 0.201 3
[0005] Furthermore, the temperature/vapor pressure relationship for
P, S, As, Se, and Te is significant when compared to metals such as
Sb, Cu, or refractory metals such as molybdenum (Mo). As FIG. 1
shows, the vapor pressures of P, S, As, Se, and Te increase very
rapidly with increasing temperature. In summary, thermal energy
couples poorly into P, S, and Se (and Te), but when it does the
vapor pressure of the material increases rapidly. These thermal
properties for P, S, and Se complicate control of the evaporation
rate in a thermal-evaporation process for these elements. In
addition, the heat-up and cool-down times for large amounts of
feedstock of these materials are long. Given the cost sensitivity
of commercial products--in particular for PV--manufacturing
requires long system run times and short system turnaround
("green-to-green") times. Thus, evaporation sources typically hold
significant volumes of feedstock to enable long-run campaigns.
Coupled with the desire to increase throughput, high deposition
rates and large-area substrates are essential to enabling lower
manufacturing costs. Therefore, conventional high-throughput
thermal evaporation sources have significant thermal mass and/or
utilize continuous feed of the source material. For some materials
continuous feed is a possibility (e.g., Al wire feed), while for
many others it is not.
[0006] Conventional systems with high thermal mass have the added
advantage that control of the thermal evaporation process is
simplified as temperature fluctuations based on power fluctuations
to the heaters are typically negligible. Highly effective thermal
insulation further reduces sensitivity to incoming power
fluctuations. Such thermal insulation also reduces heat losses to
the surroundings, i.e., it increases thermal coupling efficiency of
the electrical heater power to the material to be evaporated,
leading to lower operating costs. In summary, high thermal mass and
highly effective thermal insulation are important aspects of
conventional industrial thermal evaporation processes.
[0007] In addition, turnaround times typically need to be short for
industrial deposition processes. However, if the thermal
evaporation source has a high thermal mass and highly effective
insulation, the cool-down of the source between deposition runs
will necessarily be slow. The impact is most severe if an
unscheduled maintenance event necessitates shutdown of the
equipment with the large-volume sources still holding significant
amounts of feedstock. But even if the feedstock has been depleted,
the bodies of the evaporation sources themselves still have
significant thermal mass.
[0008] In view of the foregoing, there is a need for improved
thermal-management systems and techniques for thermal evaporation
that maintain high-quality insulation (and concomitant
insensitivity to power fluctuations) during deposition cycles and
that provide faster cooling and higher turnaround times between
deposition cycles.
SUMMARY OF THE INVENTION
[0009] Embodiments of the present invention utilize a heat-transfer
fluid to supplement (or replace) other means of heating and/or
cooling thermal evaporation sources, such as electric resistive
heating and radiative cooling. In various embodiments, fluid-based
thermal management is utilized only for heating (or additional
heating), while in other embodiments, heat-transfer fluid is
utilized only for cooling (or additional cooling). In various
embodiments, the heat-transfer fluid is utilized as the primary or
as a supplemental means of both heating and cooling of the thermal
evaporation source.
[0010] In some embodiments, fluid-based heating and/or cooling is
only utilized over a portion of the operating temperature range of
the thermal evaporation source. The temperature range over which a
heat-transfer fluid is utilized for thermal management of the
evaporation source may be related to the temperature/vapor pressure
relationship of the particular fluid. For example, if the fluid has
a steep rise in vapor pressure at a temperature of 260.degree. C.,
it may be utilized for heating only up to approximately that
temperature or slightly below that temperature (e.g., approximately
250.degree. C.). Beyond that temperature, pressurized gas (e.g.,
nitrogen gas) may be utilized to flush the fluid from the
heating/cooling lines and/or the heated source so that the fluid is
not subjected to higher temperatures. In various embodiments of the
invention, regardless of the temperature-vapor pressure
relationship of a heat-transfer fluid, the fluid may be utilized as
the means for cooling (or a supplemental means for cooling) of the
evaporation source. For example, the flow rate of the fluid may be
sufficiently high to keep the heat-transfer fluid at a temperature
below its critical temperature where decomposition occurs and/or
below the temperature at which the vapor pressure increases
dramatically.
[0011] In various embodiments of the present invention,
heat-transfer fluid flows through the thermal evaporation source
via two separate loops, one heated and one cooled. In other
embodiments, a single fluid loop is utilized, and the fluid in the
loop is heated (via, e.g., a heater) for heating of the source and
cooled for cooling of the source. The heat-transfer fluid may be
cooled utilizing, e.g., a heat exchanger. The heat exchanger may
utilize any of several different techniques to cool the
heat-transfer fluid, including thermal radiation from
large-surface-area surfaces (e.g., fins or other projections)
and/or air convection, or via heat exchange with a chilled water
loop. Thermal management systems in accordance with embodiments of
the invention also utilize control circuits to regulate the
temperature and/or flow rate of the heat-transfer fluid based on
the current and/or desired temperature of the thermal evaporation
source.
[0012] Thermal evaporation processes typically are performed in
vacuum ambients having very little background gas. This is
necessary to reduce scattering of the material being evaporated so
as to assure effective material transport from the evaporation
source to the substrate upon which the evaporated material is to
condense. As such, the primary loss of thermal energy in vacuum is
via radiation, i.e., long-wavelength electromagnetic radiation.
However, this process starts to lose effectiveness the lower the
temperature of the body to be cooled and the smaller the
temperature difference between the body cooling down and the system
absorbing the thermal energy. Thus, in a vacuum environment,
cooling via radiation is typically most effective above
approximately 300.degree. C. Similarly, coupling heat into
evaporation sources operating at low temperatures (e.g.,
<400.degree. C.) via radiation is also less effective, in
particular if the material is one with poor thermal conductivity
(e.g., P, S, or Se). The surface area of the reservoir wall to be
exposed to radiation typically must be very large to efficiently
couple radiative heat into these elements. Such concerns complicate
both the reservoir and resistive heater design, as well as thermal
evaporation rate control of these high-vapor-pressure elements.
[0013] Gas convection is another cooling technique. In gas
convection processes, a gas passes over or through the body to be
cooled and is able to transfer the thermal energy to a colder
surface nearby. Given that thermal evaporation processes are
typically performed under vacuum, hardly any heat is lost via
conduction. However, at the end of the process it is possible to
cool the deposition equipment with a gas--an operation which may be
repeated in fill/purge sequences where small amounts of gas are
introduced for short periods of times and then pumped out of the
system again as they have heated up and become less effective in
transferring heat away from the hot body. While this process has
been utilized in existing systems, it has limitations based on the
types of gases that are applicable. Air, the lowest cost gas
mixture available, is not suitable as components in the vacuum
system will oxidize. Nitrogen, another economical gas, has limited
use as well; it may only be utilized below temperatures at which
system component materials react with nitrogen. Moreover, both
oxygen and nitrogen, like most gases, have relatively low heat
capacities and are therefore less effective in convective cooling
compared to, e.g., liquids. Noble or other inert gases may not
react with any of the materials inside the deposition system, but
are typically more expensive or have even lower heat capacities
than nitrogen. For example, argon has a heat capacity only one-half
that of nitrogen. On the other hand, at five times the heat
capacity of nitrogen, helium (He) has the highest heat capacity of
gases--apart from hydrogen (H)--and is extremely inert. But its
cost is significantly higher than that of nitrogen.
[0014] In addition, since for low power consumption and stable
processes the evaporation source relies on highly effective thermal
insulation, it is often difficult to accomplish convection cooling
with gases. The details largely depend on the type of insulation
scheme. For example, if insulation is via shielding, a gas may
penetrate the gap between the various layers of shielding, but if
solid insulation is employed, the effect of convection cooling is
limited by the rate of heat transfer (thermal conductivity) through
the solid insulation.
[0015] However, liquid convection cooling as well as heating are
especially well-matched to the thermal evaporation of many elements
commonly utilized in thermal evaporation processes. Examples
include P, S, and Se--elements with the above-described
complexities of their thermal properties and temperature/vapor
pressure dependence. Embodiments of the present invention utilize,
in conjunction with the thermal evaporation source, a reservoir
with high direct contact area of the evaporant (i.e., the feedstock
or material to be evaporated) to the conduits (e.g., pipes)
carrying the heat-transfer fluid. Such embodiments enable highly
effective heat transfer from the heat-transfer fluid to the
evaporant under heating and/or cooling conditions.
[0016] Various embodiments of the invention utilize a circulation
system for heat-transfer fluid with two reservoirs (one heated, or
"hot," and one cooled, or "cold") to enable rapid switching between
heating and cooling of the thermal evaporation source. For example,
a pipe system with heat exchanger internal to the reservoir of the
thermal evaporation source may be connected to both the hot and
cold reservoirs. Control mechanisms (e.g., solenoid valves) enable
one to switch flow of heat-transfer fluid through either the heated
or cooled reservoir.
[0017] Thus, embodiments of the present invention solve a
manufacturing cost problem for processes employing thermal
evaporation of materials with poor thermal conductivity and/or high
vapor pressure/temperature dependence and/or operating temperatures
at .ltoreq.400.degree. C. Many heat-transfer fluids may be utilized
at temperatures up to approximately 400.degree. C., and thus,
embodiments of the invention address heating and/or cooling (or
supplemental heating and/or cooling) of a thermal evaporation
source up to approximately that temperature. However, as mentioned
above, heat-transfer fluid-assisted cooling may also be employed at
temperatures significantly above 400.degree. C. as long as the flow
rates of the liquid coolant are sufficiently high to keep the fluid
below its critical temperature. In addition, embodiments of the
invention incorporating heat-transfer fluid-based heating and/or
cooling beneficially reduce the response time of the source if
perturbations of the source temperature are intentional and enable
fast response to desired elevation or reduction of the source
temperature. Such embodiments may be helpful during process
development and optimization.
[0018] Thermal management for evaporation sources using
heat-transfer fluids in accordance with embodiments of the
invention may be utilized in various processes, such as MBE of
III-V materials, deposition of OLED materials, and materials for
thin-film photovoltaics such as CIGS or copper zinc tin sulfide
(CZTS). As detailed herein, embodiments of the present invention
reduce cost of ownership in manufacturing. As utilized herein, the
term "fluid" may refer to a liquid and/or a gas unless otherwise
specified. Embodiments of the invention may utilize heat-transfer
fluids such as, e.g., water (e.g., deionized water), mixtures of
water and glycol, silicones, dielectric fluids such as
fluorocarbons or polyalphaolefin, and/or hydrocarbon oils.
[0019] In an aspect, embodiments of the invention feature a
deposition system that includes or consists essentially of a
deposition chamber, an evaporation source, and a thermal management
system. The deposition chamber has an interior enclosed by one or
more chamber walls. The evaporation source includes, consists
essentially of, or consists of a hollow source body for containing
a feedstock material for evaporation thereof and an evaporation
port for fluidly coupling the source body with the interior of the
deposition chamber. The thermal management system includes or
consists essentially of a first reservoir, a first conduit, a
heater, a second reservoir, a second conduit, a cooler, and a
controller. The first reservoir contains heat-transfer fluid. The
first conduit fluidly and/or thermally couples the first reservoir
with the evaporation source. The heater heats heat-transfer fluid
within the first reservoir. The second reservoir is different from
the first reservoir and contains heat-transfer fluid. The second
conduit fluidly and/or thermally couples the second reservoir with
the evaporation source. At least a portion of the first conduit may
be different from at least a portion of the second conduit. The
cooler cools heat-transfer fluid within the second reservoir. The
controller controls flow of heated and cooled heat-transfer fluid
between the evaporation source and the first and second reservoirs
to thereby control a temperature of the evaporation source.
[0020] Embodiments of the invention may include one or more of the
following in any of a variety of combinations. The heater may
include, consist essentially of, or consist of a heat exchanger, a
laser source (and/or laser beam), an electron beam source (and/or
electron beam), a thermoelectric heater, and/or a resistive heater.
The cooler may include, consist essentially of, or consist of a
heat exchanger, a thermoelectric cooler, and/or a source of chilled
liquid (e.g., water). A feedstock material may be disposed within
the source body. The feedstock material may include, consist
essentially of, or consist of phosphorous, sulfur, arsenic,
tellurium, and/or selenium.
[0021] In another aspect, embodiments of the invention feature a
thermal evaporation source that includes, consists essentially of,
or consists of a hollow source body for containing a feedstock
material for evaporation thereof, an evaporation port for fluidly
coupling the source body with an interior of a deposition chamber,
a first conduit thermally coupled to an interior of the source
body, a first reservoir for containing heat-transfer fluid, and a
first mechanism for heating and/or cooling heat-transfer fluid
within the first reservoir. The first reservoir is fluidly coupled
to the first conduit.
[0022] Embodiments of the invention may include one or more of the
following in any of a variety of combinations. The first mechanism
for heating and/or cooling heat-transfer fluid may include, consist
essentially of, or consist of a heater, a resistive heater, an
electron beam (and/or a source thereof), a laser beam (and/or a
source thereof), a thermoelectric heater, and/or a heat exchanger.
A feedstock material may be disposed within the source body. The
feedstock material may include, consist essentially of, or consist
of phosphorous, sulfur, arsenic, tellurium, and/or selenium. The
thermal evaporation source may include a second conduit thermally
coupled to an interior of the source body, a second reservoir (for
containing heat-transfer fluid) fluidly coupled to the second
conduit, and a second mechanism for heating and/or cooling
heat-transfer fluid within the second reservoir. The second
mechanism for heating and/or cooling heat-transfer fluid may
include, consist essentially of, or consist of a heater, a
resistive heater, an electron beam (and/or a source thereof), a
laser beam (and/or a source thereof), a thermoelectric heater, a
thermoelectric cooler, and/or a heat exchanger. The thermal
evaporation source may include a second reservoir (for containing
heat-transfer fluid) fluidly coupled to the first conduit, as well
as a second mechanism for heating and/or cooling heat-transfer
fluid within the second reservoir. The second mechanism for heating
and/or cooling heat-transfer fluid may include, consist essentially
of, or consist of a heater, a resistive heater, an electron beam
(and/or a source thereof), a laser beam (and/or a source thereof),
a thermoelectric heater, a thermoelectric cooler, and/or a heat
exchanger.
[0023] In yet another aspect, embodiments of the invention feature
a method of thin-film deposition. An evaporation source is provided
within a deposition system (e.g., an evaporation system). The
evaporation source includes, consists essentially of, or consists
of a source body containing a feedstock material and an evaporation
port fluidly coupling the source body with an interior of the
deposition chamber. A first reservoir of heat-transfer fluid is
provided. The first reservoir is thermally coupled to the source
body and/or the feedstock material. A processing ambient is
established within the deposition chamber by (i) evacuating at
least a portion of gas disposed within the deposition chamber,
thereby establishing a vacuum ambient therein, and/or (ii)
introducing a process gas within the deposition chamber.
Heat-transfer fluid within the first reservoir is heated. The
evaporation source is heated at least in part by flowing heated
heat-transfer fluid (e.g., to and/or along and/or across the
evaporation source and/or the source body), whereby at least a
portion of the feedstock material vaporizes and exits the source
body through the evaporation port.
[0024] Embodiments of the invention may include one or more of the
following in any of a variety of combinations. The evaporation port
may include, consist essentially of, or consist of one or more
openings defined by the source body. The evaporation port may
include an elongated portion extending away from the source body.
An insulation material may be disposed around the evaporation
source to reduce heat loss therefrom. The process gas may be
introduced within the deposition chamber. The process may react
with the vaporized feedstock material. The insulation material may
include, consist essentially of, or consist of carbon and/or a
ceramic material. The insulation material may include, consist
essentially of, or consist of graphite, carbon fiber, mullite,
alumina, silica, and/or zirconia. The insulation material may
include, consist essentially of, or consist of tantalum, niobium,
and/or molybdenum. The insulation material may include, consist
essentially of, or consist of a felt, a foam, a sol gel material,
or a plurality of spaced-apart solid shields.
[0025] The first reservoir may be thermally coupled to the source
body and/or the feedstock material via a first conduit extending
from the first reservoir. Flowing heated heat-transfer fluid to
heat the evaporation source may include, consist essentially of, or
consist of flowing heated heat-transfer fluid through the first
conduit. Heat-transfer fluid within the first reservoir may be
cooled, and the evaporation source may be cooled at least in part
by flowing cooled heat-transfer fluid through the first conduit.
The evaporation source may be heated in part with a heat source
other than heated heat-transfer fluid. The heat source may include,
consist essentially of, or consist of a heater, a resistive heater,
an electron beam (and/or a source thereof), a laser beam (and/or a
source thereof), a thermoelectric heater, and/or a heat exchanger.
Heat-transfer fluid within the first reservoir may be cooled, and
the evaporation source may be cooled at least in part by flowing
cooled heat-transfer fluid (e.g., to and/or along and/or across the
evaporation source and/or the source body). The evaporation source
may be cooled in part with a cooling source other than cooled
heat-transfer fluid. The cooling source may include, consist
essentially of, or consist of a gas flowed through and/or around at
least a portion of the evaporation source, a heat exchanger, and/or
a thermoelectric cooler.
[0026] A second reservoir of heat-transfer fluid may be provided.
The second reservoir may be thermally coupled to the source body
and/or the feedstock material. Heat-transfer fluid within the
second reservoir may be cooled, and the evaporation source may be
cooled at least in part by flowing cooled heat-transfer fluid
(e.g., to and/or along and/or across the evaporation source and/or
the source body). The second reservoir may be thermally coupled to
the source body and/or the feedstock material via a second conduit
extending from the second reservoir. Flowing cooled heat-transfer
fluid to cool the evaporation source may include, consist
essentially of, or consist of flowing cooled heat-transfer fluid
through the second conduit. The evaporation source may be cooled in
part with a cooling source other than cooled heat-transfer fluid.
The cooling source may include, consist essentially of, or consist
of a gas flowed through and/or around at least a portion of the
evaporation source, a heat exchanger, and/or a thermoelectric
cooler. The feedstock material may include, consist essentially of,
or consist of phosphorous, sulfur, arsenic, tellurium, and/or
selenium.
[0027] In another aspect, embodiments of the invention feature a
method of thin-film deposition. An evaporation source is provided
within a deposition system (e.g., an evaporation system). The
evaporation source includes, consists essentially of, or consists
of a source body containing a feedstock material and an evaporation
port fluidly coupling the source body with an interior of the
deposition chamber. A first reservoir of heat-transfer fluid is
provided. The first reservoir is thermally coupled to the source
body and/or the feedstock material. A processing ambient is
established within the deposition chamber by (i) evacuating at
least a portion of gas disposed within the deposition chamber,
thereby establishing a vacuum ambient therein, and/or (ii)
introducing a process gas within the deposition chamber. A
heat-transfer fluid within the first reservoir is cooled. The
evaporation source is heated, whereby at least a portion of the
feedstock material vaporizes and exits the source body through the
evaporation port. After the evaporation source is heated (e.g.,
after the at least a portion of the feedstock material vaporizes
and exits the source body through the evaporation port), the
evaporation source is cooled at least in part by flowing cooled
heat-transfer fluid (e.g., to and/or along and/or across the
evaporation source and/or the source body).
[0028] Embodiments of the invention may include one or more of the
following in any of a variety of combinations. The evaporation port
may include, consist essentially of, or consist of one or more
openings defined by the source body. The evaporation port may
include an elongated portion extending away from the source body.
An insulation material may be disposed around the evaporation
source to reduce heat loss therefrom. The process gas may be
introduced within the deposition chamber. The process may react
with the vaporized feedstock material. The insulation material may
include, consist essentially of, or consist of carbon and/or a
ceramic material. The insulation material may include, consist
essentially of, or consist of graphite, carbon fiber, mullite,
alumina, silica, and/or zirconia. The insulation material may
include, consist essentially of, or consist of tantalum, niobium,
and/or molybdenum. The insulation material may include, consist
essentially of, or consist of a felt, a foam, a sol gel material,
or a plurality of spaced-apart solid shields.
[0029] The first reservoir may be thermally coupled to the source
body and/or the feedstock material via a first conduit extending
from the first reservoir. Flowing cooled heat-transfer fluid to
cool the evaporation source may include, consist essentially of, or
consist of flowing cooled heat-transfer fluid through the first
conduit. The evaporation source may be cooled in part with a
cooling source other than cooled heat-transfer fluid. The cooling
source may include, consist essentially of, or consist of a gas
flowed through and/or around at least a portion of the evaporation
source, a heat exchanger, and/or a thermoelectric cooler. The
feedstock material may include, consist essentially of, or consist
of phosphorous, sulfur, arsenic, tellurium, and/or selenium. The
evaporation source may be heated, at least in part, with a heat
source other than heated heat-transfer fluid. The heat source may
include, consist essentially of, or consist of a heater, a
resistive heater, an electron beam (and/or a source thereof), a
laser beam (and/or a source thereof), a thermoelectric heater,
and/or a heat exchanger.
[0030] These and other objects, along with advantages and features
of the present invention herein disclosed, will become more
apparent through reference to the following description, the
accompanying drawings, and the claims. Furthermore, it is to be
understood that the features of the various embodiments described
herein are not mutually exclusive and may exist in various
combinations and permutations. As used herein, the terms
"approximately" and "substantially" mean .+-.10%, and in some
embodiments, .+-.5%. The term "consists essentially of" means
excluding other materials that contribute to function, unless
otherwise defined herein. Nonetheless, such other materials may be
present, collectively or individually, in trace amounts. As used
herein, the term "conduit" refers to one or more pipes, channels,
ducts, tubes or other means for conveying a fluid (e.g.,
heat-transfer fluid).
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, emphasis instead generally
being placed upon illustrating the principles of the invention. In
the following description, various embodiments of the present
invention are described with reference to the following drawings,
in which:
[0032] FIG. 1 is a graph of vapor pressure as a function of
temperature for several different elements;
[0033] FIG. 2 is a schematic diagram of a deposition system in
accordance with various embodiments of the invention;
[0034] FIG. 3A is a schematic diagram of an evaporation source
utilizing a fluid-based thermal management system in accordance
with various embodiments of the invention;
[0035] FIG. 3B is a schematic diagram of an evaporation source
utilizing a fluid-based thermal management system in accordance
with various embodiments of the invention;
[0036] FIG. 4A is a perspective view of an evaporation source in
accordance with various embodiments of the invention;
[0037] FIG. 4B is a top view of the evaporation source of FIG. 4A;
and
[0038] FIG. 4C is a side view of the evaporation source of FIG.
4A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0039] FIG. 2 is a schematic diagram of an exemplary deposition
system 200 in accordance with embodiments of the present invention.
As shown, the system 200 features a thermal evaporation source 205
incorporating a reservoir 210 for feedstock material to be
evaporated. The reservoir 210 is at least partially surrounded by a
vacuum shell 215 that enables the establishment and maintenance of
very low pressures (i.e., very high vacuums) in the deposition
system 200. The source reservoir 210 has an evaporation port 220
through which the evaporant leaves the source 205 and enters a
deposition chamber 225 for, e.g., deposition on one or more
substrates. While only one evaporation source 205 is depicted in
FIG. 2 for simplicity, embodiments of the present invention utilize
two or more evaporation sources (e.g., for evaporation of different
materials). Multiple evaporation sources may share a single
fluid-based thermal management system, or each evaporation source
may utilize its own dedicated fluid-based thermal management
system. In various embodiments, the source 205 may be positioned
partially or entirely inside the deposition chamber 225 rather than
primarily outside of the deposition chamber as depicted in FIG.
2.
[0040] The source reservoir 210 is typically a hollow container for
containing the feedstock material during evaporation thereof. The
source reservoir 210 may include, consist essentially of, or
consist of, for example, one or more refractory metals (e.g.,
tantalum, tungsten, and/or molybdenum) and/or one or more ceramic
materials such as alumina and/or boron nitride and/or one or more
corrosion-resistant metal alloys such as nickel-based alloys
containing one or more alloying elements (e.g., molybdenum,
chromium, cobalt, iron, copper, manganese, titanium, zirconium,
aluminum, carbon, and/or tungsten), for example, one or more
Hastelloy alloys available from Haynes International Inc. of
Kokomo, Ind. In various embodiments, one or more surfaces of the
source body (e.g., the surfaces facing and/or in contact with the
feedstock material) may be coated or lined with a lining material,
e.g., a ceramic material such as alumina and/or boron nitride. The
source reservoir 210 and any insulation material therearound may be
heated by one or more heaters disposed proximate or around the
evaporation source. The one or more heaters may include or consist
essentially of, for example, a furnace in which the source is
disposed or one or more resistive heaters disposed around the
source. Exemplary feedstock materials used in various embodiments
of the present invention include P, S, As, Se, and/or Te.
[0041] FIG. 2 depicts the evaporation source 205 having its
evaporation port 220 facing sideways toward deposition chamber 225,
but other orientations of the port 220 are possible. For example,
the port 220 may be oriented to allow evaporant release upward or
even downward. Moreover, insulation may be disposed around one or
more sides of the source reservoir 210. In addition, while the
evaporation port 220 is depicted in FIG. 2 as being a substantially
straight regular cylinder, in various embodiments the evaporation
port 220 has a width or diameter that tapers (wider or narrower) as
a function of distance from the source reservoir 210. In various
embodiments, the evaporation port 220 may include or consist
essentially of a manifold port or a shower-head port, variants
known to those of skill in the art.
[0042] As shown in FIG. 2, a fluid-based thermal management system
230 is connected by one or more conduits 235 (e.g., pipes) to the
source 205 via, for example, one or more vacuum feedthroughs 240
that seal around the conduit(s) 235 to maintain vacuum within the
deposition system 200. The fluid-based thermal management system
230 may be fluidly connected to a source 245 of process chilled
water (PCW) for, e.g., cooling of the heat-transfer fluid heated by
exposure to the evaporation source. The fluid-based thermal
management system 230 may be fluidly connected to the source 245
via one or more conduits 250 (e.g., pipes). The source 245 may
include or consist essentially of, e.g., a reservoir of water or
other fluid. Electric or combustion fuel or heat exchange heating
of the heat-transfer fluid may also be present as part of the
fluid-based thermal management system. Additional means of heating
the evaporant--e.g., resistive electrical heating elements coupled
to and/or disposed around and/or in the source reservoir 210--may
be present simultaneously to the heat-transfer fluid-based
loop.
[0043] FIG. 3A is a schematic diagram of an exemplary fluid-based
thermal management system 230 in accordance with embodiments of the
present invention. As shown, the thermal management system 230
features two different reservoirs for heat-transfer fluid. A
reservoir 300 contains heat-transfer fluid and heats the fluid by,
e.g., resistive heaters 305 thermally coupled to the reservoir 300.
The heated heat-transfer fluid is channeled to the evaporation
source 205 by one or more pumps 308 via a series of conduits 310
(e.g., pipes) and valves 315, as shown. A reservoir 320 also
contains heat-transfer fluid (which may be the same or different
from the fluid within the heated reservoir 300) and cools the fluid
by, e.g., a heat exchanger 325 and recirculation of chilled water
from PCW source 245 for thermal exchange. The cooled heat-transfer
fluid is also channeled to and from the evaporation source 205 by
one or more pumps 308 via a series of conduits 310 and valves 315,
as shown.
[0044] While two different reservoirs 300, 320 are depicted in FIG.
3, embodiments of the invention utilize a single reservoir of
heat-transfer fluid that is heated or cooled on demand, depending
on the desired temperature regulation of the evaporation source
205. For example, FIG. 3B is a schematic diagram of another
exemplary fluid-based thermal management system 230 in accordance
with embodiments of the present invention. As shown, the thermal
management system 230 features a single reservoir 360 for
heat-transfer fluid, which is heated by, e.g., resistive heaters
305, and/or cooled by, e.g., heat exchanger 325 and recirculation
of chilled water from PCW source 245 for thermal exchange.
[0045] The conduits 310 connecting the reservoirs 300, 320, 360 to
the evaporation source 205 typically form a closed loop, and extend
within the source 205 (e.g., on a sinuous path) to maximize thermal
contact between the heat-transfer fluid and the feedstock in the
evaporation source 205. As shown in FIGS. 3A and 3B, recirculation
pumps 330 may be utilized to recirculate the heat-transfer fluid
within the reservoirs, via conduits 335, to thereby maintain the
heat-transfer fluid within each reservoir 300, 320, 360 at a
substantially constant temperature.
[0046] The operation of reservoirs 300, 320, 360 and the resulting
flow of heat-transfer fluid to and from the evaporation source 205
may be responsive to a computer-based control system so that the
temperature of the source 205 may be controlled before, during,
and/or after deposition processes that take place at elevated
temperatures. For example, as shown in FIGS. 3A and 3B, in various
embodiments of the present invention, a control system 340 may be
electrically connected and/or mechanically connected to the
reservoirs 300, 320, 360, valves 315, 330, and/or pumps 308 and
thus control various operations of the fluid-based thermal
management system 230.
[0047] The computer-based control system (or "controller") 340 in
accordance with embodiments of the present invention may include or
consist essentially of a general-purpose computing device in the
form of a computer including a processing unit (or "computer
processor") 345, a system memory 350, and a system bus 355 that
couples various system components including the system memory 350
to the processing unit 345. Computers typically include a variety
of computer-readable media that can form part of the system memory
350 and be read by the processing unit 345. By way of example, and
not limitation, computer readable media may include computer
storage media and/or communication media. The system memory 350 may
include computer storage media in the form of volatile and/or
nonvolatile memory such as read only memory (ROM) and random access
memory (RAM). A basic input/output system (BIOS), containing the
basic routines that help to transfer information between elements,
such as during start-up, is typically stored in ROM. RAM typically
contains data and/or program modules that are immediately
accessible to and/or presently being operated on by processing unit
345. The data or program modules may include an operating system,
application programs, other program modules, and program data. The
operating system may be or include a variety of operating systems
such as Microsoft WINDOWS operating system, the Unix operating
system, the Linux operating system, the Xenix operating system, the
IBM AIX operating system, the Hewlett Packard UX operating system,
the Novell NETWARE operating system, the Sun Microsystems SOLARIS
operating system, the OS/2 operating system, the BeOS operating
system, the MACINTOSH operating system, the APACHE operating
system, an OPENSTEP operating system or another operating system of
platform. In various embodiments, the controller 340 and/or one or
more components thereof may include or consist essentially of a
programmable logic controller operating in accordance with, e.g., a
set of pre-compiled instructions and/or programs.
[0048] Any suitable programming language may be used to implement
without undue experimentation the functions described herein.
Illustratively, the programming language used may include assembly
language, Ada, APL, Basic, C, C++, C*, COBOL, dBase, Forth,
FORTRAN, Java, Modula-2, Pascal, Prolog, Python, REXX, and/or
JavaScript for example. Further, it is not necessary that a single
type of instruction or programming language be utilized in
conjunction with the operation of systems and techniques of the
invention. Rather, any number of different programming languages
may be utilized as is necessary or desirable.
[0049] The computing environment may also include other
removable/nonremovable, volatile/nonvolatile computer storage
media. For example, a hard disk drive may read or write to
nonremovable, nonvolatile magnetic media. A magnetic disk drive may
read from or writes to a removable, nonvolatile magnetic disk, and
an optical disk drive may read from or write to a removable,
nonvolatile optical disk such as a CD-ROM or other optical media.
Other removable/nonremovable, volatile/nonvolatile computer storage
media that can be used in the exemplary operating environment
include, but are not limited to, magnetic tape cassettes, flash
memory cards, digital versatile disks, digital video tape, solid
state RAM, solid state ROM, and the like. The storage media are
typically connected to the system bus through a removable or
non-removable memory interface.
[0050] The processing unit 345 that executes commands and
instructions may be a general-purpose computer processor, but may
utilize any of a wide variety of other technologies including
special-purpose hardware, a microcomputer, mini-computer, mainframe
computer, programmed micro-processor, micro-controller, peripheral
integrated circuit element, a CSIC (Customer Specific Integrated
Circuit), ASIC (Application Specific Integrated Circuit), a logic
circuit, a digital signal processor, a programmable logic device
such as an FPGA (Field Programmable Gate Array), PLD (Programmable
Logic Device), PLA (Programmable Logic Array), RFID processor,
smart chip, or any other device or arrangement of devices that is
capable of implementing the steps of the processes of embodiments
of the invention. For example, the memory 350 may store therewithin
one or deposition (e.g., thermal-evaporation) recipes including
instructions (e.g., desired thermal profiles, heating times, etc.)
utilized by the controller 340 to control the various components
and systems of the deposition system, e.g., valves, interlocks,
pumps, heating systems, reservoirs 300, 320, etc. The recipes may
include indications before, during, and/or after evaporation
processes for the controller 340 to cool and/or heat evaporation
source 205 and the feedstock therewithin in order to, e.g., improve
throughput. The controller 340 may include one or more user
interfaces and/or input/output devices (e.g., keyboard, display,
mouse or other pointing device, etc.) for accepting user commands
and/or for the inputting of recipe information.
[0051] FIGS. 4A-4C depict an exemplary thermal evaporation source
205 usable in accordance with embodiments of the present invention.
The exemplary source 205 may have one or more fill ports 400
through which the feedstock material to be evaporated may be
introduced into the source 205. As shown, the fill ports 400 may
each be occluded by a cover after filling and during evaporation.
The source 205 may be evacuated and/or vented before and/or after
operation via a valve 405. The heated feedstock exits the source
205 via the evaporation port 220, as detailed herein. Heat-transfer
fluid for heating and/or cooling the feedstock material within the
source 205 is introduced via one or more fluid inlets 410, flows
through one or more conduits 415 fluidically coupled to the inlets
410 (and fluidically isolated from but thermally coupled to the
feedstock material itself), and exits the source via one or more
fluid outlets 420. Additional means of heating the feedstock
material--e.g., resistive electrical heating elements thermally
coupled to the reservoir 210 of the source 205--may be present
simultaneously to this heat-transfer fluid-based loop. For example,
resistive heaters and/or other auxiliary heaters or coolers may be
inserted into source 205 via one or more channels 425 for thermal
coupling to the feedstock material within source 205.
[0052] The terms and expressions employed herein are used as terms
and expressions of description and not of limitation, and there is
no intention, in the use of such terms and expressions, of
excluding any equivalents of the features shown and described or
portions thereof. In addition, having described certain embodiments
of the invention, it will be apparent to those of ordinary skill in
the art that other embodiments incorporating the concepts disclosed
herein may be used without departing from the spirit and scope of
the invention. Accordingly, the described embodiments are to be
considered in all respects as only illustrative and not
restrictive.
* * * * *