U.S. patent application number 11/875787 was filed with the patent office on 2008-02-14 for systems and methods utilizing an aperture with a reactive atom plasma torch.
This patent application is currently assigned to RAPT INDUSTRIES, INC.. Invention is credited to Jeffrey W. Carr, Andrew Chang, Peter S. Fiske, Jude Kelley.
Application Number | 20080035612 11/875787 |
Document ID | / |
Family ID | 34221377 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080035612 |
Kind Code |
A1 |
Chang; Andrew ; et
al. |
February 14, 2008 |
Systems and Methods Utilizing an Aperture with a Reactive Atom
Plasma Torch
Abstract
A method for reducing heat applied to a workpiece by a plasma
discharge of a reactive plasma torch comprises determining a
footprint of the plasma discharge on a surface of the workpiece
based on a distance of the reactive atom plasma torch from the
surface, determining a maximum heat absorbable by the workpiece,
and determining an adjusted footprint of the reactive atom plasma
torch on the surface based on the maximum heat absorbable by the
workpiece. An aperture of an aperture device is selected based on
the adjusted footprint of the reactive atom plasma torch. The
aperture device is then positioned so that a portion of the plasma
is one or both of deflected and absorbed by the aperture device,
thereby reducing the heat absorbed by the workpiece.
Inventors: |
Chang; Andrew; (Oakland,
CA) ; Carr; Jeffrey W.; (Livermore, CA) ;
Kelley; Jude; (Belmont, CA) ; Fiske; Peter S.;
(Oakland, CA) |
Correspondence
Address: |
FLIESLER MEYER LLP
650 CALIFORNIA STREET
14TH FLOOR
SAN FRANCISCO
CA
94108
US
|
Assignee: |
RAPT INDUSTRIES, INC.
46535 Fremont Blvd.
Fremont
CA
94538
|
Family ID: |
34221377 |
Appl. No.: |
11/875787 |
Filed: |
October 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10911821 |
Aug 5, 2004 |
7304263 |
|
|
11875787 |
Oct 19, 2007 |
|
|
|
60495176 |
Aug 14, 2003 |
|
|
|
Current U.S.
Class: |
219/121.44 |
Current CPC
Class: |
H05H 1/30 20130101 |
Class at
Publication: |
219/121.44 |
International
Class: |
B23K 10/00 20060101
B23K010/00 |
Claims
1. A method for reducing heat applied to a workpiece by a plasma
discharge of a reactive atom plasma torch, comprising: determining
a footprint of the plasma discharge on a surface of the workpiece
based on a distance of the reactive atom plasma torch from the
surface; determining a maximum heat absorbable by the workpiece;
determining an adjusted footprint of the reactive atom plasma torch
on the surface based on the maximum heat absorbable by the
workpiece; selecting an aperture of an aperture device based on the
adjusted footprint of the reactive atom plasma torch; positioning
the aperture device so that a portion of the plasma is one or both
of deflected and absorbed by the aperture device, thereby reducing
the heat absorbed by the workpiece.
2. A method according to claim 1, wherein: the footprint of the
plasma discharge is approximately circular; and the adjusted
footprint of the plasma discharge has a smaller diameter than the
footprint.
3. A method according to claim 1, further comprising: using the
portion of the plasma passing through the aperture to modify the
surface of the workpiece, the surface of the workpiece containing a
material that can chemically combine with a reactive species
generated from the reactive precursor and leave the surface of the
workpiece.
4. A method according to claim 1, further comprising: altering a
shape of the portion of the plasma passing through the
aperture.
5. A method according to claim 1, further comprising: maintaining
the plasma at about atmospheric pressure.
6. A method according to claim 2, further comprising: varying a
diameter of the aperture of the aperture device based on the
adjusted footprint.
7. A method according to claim 1, further comprising: using a
temperature-reducing device to reduce the temperature of the
aperture device.
8. A method according to claim 7, wherein: the temperature-reducing
device includes an electrically-isolated water chiller capable of
circulating cooled liquid about the aperture.
9. A method according to claim 1, wherein: the aperture is selected
from the group consisting of single holes, single slits, multiple
holes, non-circular openings, irregular shapes, and regular
shapes.
10. A method according to claim 1, wherein selecting the aperture
further comprises: selecting the aperture from a plurality of
apertures rotatably arranged in the aperture device, the plurality
of apertures having one or both of different shapes and different
sizes.
11. A method according to claim 1, further comprising: selecting a
reactive atom plasma torch from the group consisting of inductively
coupled plasma (ICP) torch, microwave-induced plasma (MIP) torch,
and flame torch.
12. A tool for modifying a surface of a workpiece, comprising: a
reactive atom plasma torch including a plasma discharge having a
footprint; an aperture device positionable between the reactive
atom plasma torch and the surface of the workpiece so that a
portion of the plasma discharge is one or both of deflected and
absorbed by the aperture device; and a controller adapted to
determine one or both of an aperture size and a position of the
aperture device based on a maximum absorbable heat of the
workpiece.
13. The tool of claim 12, wherein the aperture device is made of a
material selected from the group consisting of high-temperature
metals and high-temperature ceramics.
14. The tool of claim 12, further comprising: an insulated rod
capable of supporting the aperture device in order to electrically
isolate the aperture device.
15. The tool of claim 12, further comprising: a
temperature-reducing device capable of reducing the temperature of
the aperture device.
16. The tool of claim 15, wherein: the temperature-reducing device
includes an electrically-isolated water chiller capable of
circulating cooled liquid about the aperture.
17. The tool of claim 12, further comprising: at least one channel
positioned about the aperture in the aperture device, the channel
capable of carrying at least one of a liquid and a gas capable of
removing heat from the aperture device.
18. The tool of claim 12, wherein the aperture device includes a
plurality of apertures differing by one or both of size and shape,
an aperture being selectable for use with the reactive atom plasma
torch from the plurality of apertures.
19. A method for modifying the active footprint of a reactive atom
plasma torch applied to a workpiece, comprising: determining a
modified footprint based on a maximum absorbable heat of the
workpiece; selecting one or both of an aperture size and a target
distance of the aperture from one or both of the reactive atom
plasma torch and a surface of the workpiece based on the modified
footprint; using a plasma torch to inject a reactive precursor into
the plasma to generate a reactive species; and positioning the
aperture and the plasma torch so that a portion of the plasma
having the modified footprint passes through the aperture and
affects a surface of a workpiece.
20. The method of claim 19, further comprising one or more of:
shaping the surface of the workpiece with the portion of the plasma
having the modified footprint; polishing the surface of the
workpiece with the portion of the plasma having the modified
footprint; planarizing the surface of the workpiece with the
portion of the plasma having the modified footprint; and cleaning
the surface of the workpiece with the portion of the plasma having
the modified footprint.
Description
CLAIM OF PRIORITY
[0001] This application is a Continuation of U.S. patent
application Ser. No. 10/911,821, entitled "Systems and Methods
Utilizing an Aperture with a Reactive Atom Plasma Torch," by Andrew
Chang, et al., filed Aug. 5, 2004, which claims priority to U.S.
Provisional patent application No. 60/495,176, entitled "Systems
and Methods Utilizing an Aperture with a Reactive Atom Plasma
Torch," by Andrew Chang, et al., filed Aug. 14, 2003.
CROSS-REFERENCED CASES
[0002] The following patent and applications are cross-referenced
and incorporated herein by reference:
[0003] U.S. patent application Ser. No. 10/008,236 entitled
"Apparatus and Method for Reactive Atom Processing for Material
Deposition," by Jeffrey W. Carr, filed Nov. 7, 2001, now U.S. Pat.
No. 6,660,177 B2, issued Dec. 9, 2003.
[0004] U.S. patent application Ser. No. 10/384,506 entitled
"Apparatus and Method for Non-Contact Cleaning of a Surface," by
Jeffrey W. Carr, filed Mar. 7, 2003; PCT Application No.
PCT/US2004/006773, filed Mar. 5, 2004, now published as WO
2004/081258 A2 on Sep. 23, 2004.
[0005] U.S. patent application Ser. No. 10/754,326, entitled
"Apparatus for Non-Contact Cleaning of a Surface," by Jeffrey W.
Carr, filed Jan. 9, 2004.
FIELD OF THE INVENTION
[0006] The field of the invention relates to the selective
modification or removal of material from a surface.
BACKGROUND
[0007] Modern materials present a number of formidable challenges
to the fabricators of a wide range of optical, semiconductor, and
electronic components, many of which require precision shaping,
smoothing, and polishing. The use of plasmas to etch materials has
become an important technique in the optical component and
semiconductor industries. Recent advances have introduced
sub-aperture plasma processes, such as reactive atom processing
(RAP), which act more like traditional machining tools by etching
only specific areas of a workpiece.
[0008] A plasma etching process differs from its mechanical
counterpart by the mechanism in which material is removed.
Traditional machine tools use mechanical parts to physically cut
away material from a workpiece. Plasma etching processes, on the
other hand, rely upon chemical reactions to transform the solid
material of the workpiece into a volatile or otherwise labile
byproduct. Plasmas offer advantages such as the contact-free
removal of material, in which little to no force is extered on the
workpiece. Reliance upon a chemical means of material removal
introduces a whole new set of factors to consider when treating a
material.
[0009] A RAP torch can be used to deterministically shape and
polish surfaces using a plasma or a flame. The discharge emitted
from the RAP torch can remove material for the surface of a
workpiece, somewhat analogous to the end mill used in traditional
machining. The footprint of a typical RAP torch tool is roughly
Gaussian in shape, and has a size that can be determined by the
inside diameter of the outer tube that contains and directs the
plasma host gas or non-reactive species.
[0010] In traditional machining, a variety of tool shapes and sizes
are required. For maximum utility, machine tools have been designed
to allow rapid interchange of bits and cutters. This approach is
also possible with a RAP tool, but the presence of induction coils
tends to complicate the changeover. Before any shift occurs, the
unit must cool down and the enclosure must be purged of any
dangerous fumes. The gas lines to the torch must be disconnected to
remove the torch assembly and then purged before a new unit is
installed. Depending on the size and type of the new torch, it may
be necessary to replace coils used to generate the inductively
coupled plasma (ICP). Once the torch assembly and coils have been
swapped, the entire setup must be meticulously realigned and tested
in order to assure proper function.
BRIEF DESCRIPTION OF THE FIGURES
[0011] FIG. 1 is a diagram of an ICP RAP torch system that can be
used in accordance with one embodiment of the present
invention.
[0012] FIG. 2 is a diagram showing the shape and footprint of a
plasma discharge from a RAP torch such as that shown in FIG. 1.
[0013] FIG. 3 is a diagram showing the shape and footprint of the
plasma discharge of FIG. 2 while passing the discharge through an
aperture in accordance with one embodiment of the present
invention.
[0014] FIG. 4 is a top view of a liquid-cooled aperture device that
can be used with the torch of FIG. 1.
[0015] FIG. 5 is a perspective view of a trench that can be formed
in a substrate using the torch of FIG. 2.
[0016] FIG. 6 is a perspective view of a trench that can be formed
in a substrate by the torch and aperture combination of FIG. 3.
[0017] FIG. 7 is a top view showing a multi-aperture device that
can be used with the torch of FIG. 1.
[0018] FIGS. 8(a) and 8(b) are diagrams of a plasma torch that can
be used in place of the ICP RAP torch of FIG. 1.
[0019] FIG. 9 is a diagram of an MIP torch system that can be used
in accordance with another embodiment of the present invention.
[0020] FIG. 10 is a flowchart showing a process that can be used
with the system of FIG. 2.
DETAILED DESCRIPTION
[0021] Systems and methods in accordance with embodiments of the
present invention can utilize a footprint-modification device, such
as a mechanical aperture, to control the size and/or shape of the
active footprint of an atmospheric pressure reactive atom plasma
(RAP) torch. For example, FIG. 2 shows the shape of a plasma
discharge 200 from a RAP torch 202, without the discharge passing
through an aperture 204 of an aperture device 206. FIG. 3 shows the
same plasma discharge 200 being passed through the aperture 204.
The portion 208 of the plasma passing through the aperture has a
smaller effective diameter, measured horizontally in the Figure,
resulting in a smaller active footprint. The aperture device can be
any appropriate device, such as a high temperature metal or ceramic
device having an opening that can allow passage of at least a
portion of an impinging RAP plasma or RAP flame.
[0022] The size of the aperture can vary, and different apertures
can be used with the same RAP torch to produce different
footprints. The differing apertures can be in the same aperture
device, necessitating only a shift or rotation in the aperture
device relative to the RAP torch in order to switch apertures. The
differing apertures can also be in separate aperture devices,
requiring that the devices be switched out in order to change
apertures. Alternatively, a number of torches can be used, with
each torch having an aperture device with a differently-sized
aperture. Any appropriate device can be used to position the
aperture device(s), such as a pneumatic, solenoid or stepper motor
driven actuator in combination with a control mechanism.
Alternatively, variable-diameter apertures can be used. The use of
a variable aperture can allow for "on-the-fly" adjustment of the
torch footprint size and shape, as well as reduction of the heat
load on the workpiece.
[0023] An exemplary process that can take advantage of differently
sized apertures is shown in the flowchart of FIG. 10. In the
process, an annular plasma is struck on a RAP torch, 900. A flow of
reactive species is injected into the center of the annular plasma
902, the reactive species being selected as being capable of
chemically reacting with the surface material of the workpiece
being processed. The appropriate footprint size to be used in
processing the workpiece can be determined 904, such as by using a
footprint calculation program or algorithm. An aperture of
appropriate size can be selected, in an aperture device of an
appropriate material 906. The material of the aperture device can
be selected based on, for example, the heat capacity and reactive
nature of the material. The aperture device can be positioned such
that the aperture is between the plasma and the workpiece, with the
aperture being positioned such that the impinging plasma has the
appropriate footprint 908. The footprint can be determined, for
example, at the point along the primary axis of the plasma
(vertical in FIG. 1) at which the proper amount of heat will be
applied to the workpiece, such that the torch can be moved an
appropriate distance from the workpiece. Once the aperture and
torch are in position relative to the workpiece, reactive atom
plasma processing can be used to modify the surface of the
workpiece 910, such as to etch, smooth, polish, clean, and/or
deposit material onto the workpiece. The torch and/or workpiece can
be moved relative to each other in order to process the necessary
portion(s) of the workpiece. The movement can be any appropriate
movement, such as along a predetermined path, along a raster or
"fixed" pattern, or can be determined dynamically be measuring the
surface to be modified.
[0024] The use of an aperture can help to circumvent inconveniences
associated with replacing the torch, while enabling smaller tool
footprints than previously obtainable. In order to prevent arcing
to ground, an aperture device can be electrically isolated. The
electric isolation can occur in one embodiment by suspending the
aperture device from an insulating rod, such as a ceramic rod,
having a high melting point. In order to withstand thermal shock as
well as the high temperatures of the plasma, an aperture device can
be constructed of an appropriate material, such as stainless steel,
platinum, or a high-temperature ceramic. For extended exposure to
the plasma, a temperature-reducing device such as an
electrically-isolated water chiller can be used to liquid cool the
aperture. Such a device is shown in FIG. 4. In the Figure, a
channel 304 in the aperture device 300 allows a flow of liquid or
gas to circulate about the aperture 302 in order to remove heat
from the area about the aperture. If liquid is circulated through
the channel 304, for example, the liquid can be cooled in order to
further reduce or remove heat from the aperture device 300.
[0025] As a plasma flame impinges on an aperture device, the flame
can be physically confined while passing through the aperture,
depending upon the shape and size of the aperture compared to that
portion of the flame passing through the aperture. In some
embodiments, the only lower limit on the size of the resulting tool
footprint is the size at which a hole or opening can be created,
such as by drilling, in the chosen aperture material. A variety of
different tool shapes can also be obtained through the use of
differently shaped apertures. An aperture itself can take on a
variety of shapes and sizes, such as multiple holes, non-circular
openings, irregular shapes, and slits tailored to the specific
application at hand.
[0026] Plasma torches typically have Gaussian discharges, such that
a trench formed in a workpiece using such a torch will have a
Gaussian cross-section regardless of the size of the footprint. For
example, FIG. 5 shows a trench 402 that could be formed in a
workpiece 400 using a standard RAP torch such as that shown in FIG.
2. Using the same torch passed through an aperture, such as shown
in FIG. 3, FIG. 6 shows another trench 502 that could be formed in
a workpiece 500. The trenches in FIGS. 5 and 6 have different
widths in cross-section, due to the use of an aperture in one
instance, but still retain the basic Gaussian shape.
[0027] One potential drawback to using an ICP plasma torch is the
possibility of applying too much heat to a workpiece. Excessive
heating can introduce strain into many types of materials, and
should be avoided where possible. An added benefit of using an
aperture with such a system is the reduction of the overall heat
flux into the work piece. An aperture can absorb some of the heat,
and can also act to deflect some of the incident plasma/heat away
from the workpiece. The ability of an aperture to deflect heat
allows a RAP process to be applied to heat sensitive materials.
Typically, the central part of a plasma can contain the highest
concentration of reactive species, but a lower heat concentration.
In the case of annular plasmas, the largest amount of heat can be
in the outermost region of the discharge. For such a configuration,
a centrally positioned aperture of the proper diameter can allow
for a desirable combination of high etch rate and low heat
load.
[0028] The need to fragment a non-reactive precursor for use as a
reactive atom, for example, can cause a certain amount of energy to
be supplied to the plasma, typically in the form of heat. In the
region where material removal is greatest, the bulk of the heat can
be contained in the outer sheath of argon gas. The use of an
aperture effectively deflects a substantial portion of the gas and
its concomitant energy away from the workpiece. With the correct
range of aperture sizes, a suitable amount of argon remains to act
as a protective sheath, blanketing the part and keeping the native
atmosphere from the reactive species. The separation of these two
zones improves the process by limiting the amount of reactive
species lost through recombination and by reducing the post-process
interaction of the reaction products with the residual gas in the
work chamber.
[0029] An aperture should typically be constructed of a material
that is capable of handling the high temperatures generated by the
plasma or flame with which the aperture is to be used. Simple
apertures in materials such as stainless steel, platinum, and
ceramics can be sufficient for short exposure times. For longer
exposure times, it can be necessary to apply active cooling to
material surrounding the aperture. As discussed above, liquid
cooling can be used wherein channels are fashioned in the material
surrounding the aperture in order to allow rapid flow of water or
another desired coolant.
[0030] Another embodiment in accordance with the invention utilizes
a configuration in which several apertures are situated in a
circular arrangement on a rotary turret, such as that shown in FIG.
7. In the Figure, seven apertures 602, 604, 606, 608, 610, 612, and
614 are included in the rotary turret, with each fixed aperture
having a different diameter. A variable aperture 616 is also shown
in the turret 600. The variable aperture can be sized such that the
effective diameter of the aperture varies from a completely closed
configuration to a completely open configuration that allows the
plasma to pass without contacting the aperture. Having a completely
closed configuration provides a position on the turret where no
heat or plasma will be applied to the workpiece. Having a
completely open configuration allows the full footprint of the
plasma to be applied to a workpiece. The variable aperture can be
of any appropriate design known to vary the size of an aperture,
such as those used in camera applications. The turret itself can be
made of any appropriate material, such as those mentioned above
with respect to aperture devices. Such a turret allows individual
apertures to be rotated into the plasma flame and quickly replaced.
While apertures of different sizes allow for rapid changing of the
tool footprint size, the use of identical apertures on a turret can
circumvent problems arising from excessive heating of a single
aperture. Active cooling of each aperture, such as that described
with respect to FIG. 4, can be utilized to further lengthen the
service time of a single aperture in a multiple aperture system.
Plasma temperatures are relatively high, but the heat capacity is
not necessarily high, such that a number of materials can be used
without a problem of sputter.
RAP Processing
[0031] RAP processes that can be used in accordance with
embodiments of the present invention include those described in
pending U.S. patent application Ser. Nos. 10/008,236, 10/383,478,
and 10/384,506, which are incorporated herein by reference
above.
[0032] FIG. 1 shows a reactive atom plasma (RAP) system that can be
used in accordance with embodiments of the present invention. FIG.
1 shows a plasma torch in a plasma box 106. The torch consists of
an inner tube 134, an outer tube 138, and an intermediate tube 136.
The inner tube 134 has a gas inlet 100 for receiving a stream of
reactive precursor gas 142 from a mass flow controller 118. The
torch can utilize different precursor gases during different
processing steps. For instance, the torch might utilize a precursor
adapted to clean a particular contaminant off a surface in a first
step, while utilizing a precursor for redistributing material on
the surface of the workpiece during a second step.
[0033] The intermediate tube 136 has a gas inlet 102 that can be
used to, for example, receive an auxiliary gas from the flow
controller 118. The outer tube 138 has a gas inlet 104 that can be
used to receive plasma gas from the mass flow controller 118. The
mass flow controller 118 can receive the necessary gases from a
number of gas supplies 120, 122, 124, 126, and can control the
amount and rate of gases passed to the respective tube of the
torch. The torch assembly can generate and sustain plasma discharge
108, which can be used to clean then shape or polish a workpiece
110 located on a chuck 112, which can be located in a workpiece box
114. A workpiece box 114 can have an exhaust 132 for carrying away
any process gases or products resulting from, for example, the
interaction of the plasma discharge 108 and the workpiece 110.
[0034] The chuck 112 in this embodiment is in communication with a
translation stage 116, which is adapted to translate and/or rotate
a workpiece 110 on the chuck 112 with respect to the plasma
discharge 108. The translation stage 116 is in communication with a
computer control system 130, such as may be programmed to provide
the necessary information or control to the translation stage 116
to allow the workpiece 110 to be moved along a proper path to
achieve a desired cleaning, shaping, and/or polishing of the
workpiece. The computer control system 130 is in communication with
an RF power supply 128, which supplies power to the torch. The
computer control system 130 also provides the necessary information
to the mass flow controller 118. An induction coil 140 surrounds
the outer tube 138 of the torch near the plasma discharge 108.
Current from the RF power supply 128 flows through the coil 140
around the end of the torch. This energy is coupled into the
plasma.
Other RAP Systems
[0035] Another RAP system that can be used in accordance with
embodiments of the present invention can utilize a simple flame,
such as a hydrogen-oxygen (H.sub.2/O.sub.2) flame that is adjusted
to burn with an excess of oxygen. A device using such a simple
flame can be cheaper, easier to develop and maintain, and
significantly more flexible than an ICP device. Existing
H.sub.2/O.sub.2 torches are principally used for quartz glass
blowing and by jewelers for melting platinum. Such torches can also
have significantly smaller footprints than ICP devices.
[0036] A flame torch 700 can be designed in several ways. In the
relatively simple exemplary design of FIG. 8(a), a reactive
precursor gas can be mixed with either the fuel or the oxidizer gas
before being injected into the torch through the fuel input 702 or
the oxidizer input 704. Using this approach, a standard torch could
be used to inject the precursor into the flame 706. Depending on
the reactive precursor, the torch head might have to be made with
specific materials. For example, mixing chlorine or
chlorine-containing molecules into an H.sub.2/O.sub.2 torch can
produce reactive chlorine radicals.
[0037] The slightly more complex exemplary design of FIG. 8(b) can
introduce the reactive precursor gas into the flame 706 using a
small tube 708 in the center of the torch 700 orifice. The flame
706 in this case is usually chemically balanced and is neither a
reducing nor oxidizing flame. In this design a variety of gases,
liquids, or solids can be introduced coaxially into the flame to
produce reactive components. The torch in this embodiment can
produce, for example, O, Cl, and F radicals from solid, liquid, and
gaseous precursors.
[0038] In any of the above cases, a stream of hot, reactive species
can be produced that can chemically combine with the surface of a
part or workpiece. When the reactive atoms combine with the
contaminants, a gas is produced that can leave the surface.
[0039] A RAP system can operate over a wide range of pressures. Its
most useful implementation can involve operation at or near
atmospheric pressure, facilitating the treatment of large
workpieces that cannot easily be placed in a vacuum chamber. The
ability to work without a vacuum chamber can greatly increase
throughput and reduce the cost of the tool that embodies the
process.
[0040] The flame system can easily be used with a multi-nozzle
burner or multi-head torch to quickly cover large areas of the
surface. For other applications, a small flame can be produced that
affects an area on the surface as small as about 0.2 mm full
width-half maximum (FWHM) for a Gaussian- or nearly Gaussian-shaped
tool. Another advantage of the flame system is that it does not
require an expensive RF power generator nor shielding from RF
radiation. In fact, it can be a hand-held device, provided that
adequate exhaust handing equipment and user safety devices are
utilized. Further, a flame torch is not limited to a
H.sub.2-O.sub.2 flame torch. Any flame torch that is capable of
accepting a source of reactive species, and fragmenting the
reactive species into atomic radicals that can react with the
surface, can be appropriate.
[0041] As shown in FIG. 9, another RAP system that can be used in
accordance with the present invention utilizes a microwave-induced
plasma (MIP) source. A MIP source has proven to have a number of
attributes that complement, or even surpass in some applications,
the use of an ICP tool or a flame as an atomization source. The
plasma can be contained in a quartz torch 800, which is
distinguished from a standard ICP by the use of two concentric
tubes instead of three. With a large enough bore, a toroidal plasma
can be generated and the precursor injected into the center of the
torch in a manner analogous to the ICP.
[0042] A helical insert 808 can be placed between the outer tube
802 and the inner tube 804 of the torch 800 to control tube
concentricity, as well as to increase the tangential velocity of
gas. The vortex flow can help stabilize the system, and the high
velocity can aid in cooling the quartz tubes 802, 804.
[0043] The main portion of the microwave cavity 812 can be any
appropriate shape, such as a circular or cylindrical chamber, and
can be machined from a highly conductive material, such as copper.
The energy from a 2.45 GHz (or other appropriate) power supply 830
can be coupled into the cavity 812 through a connector 814 on one
edge of the cavity. The cavity 812 can be tuned in one embodiment
by moving a hollow cylindrical plunger 806, or tuning device, into
or out of the cavity 812. The quartz torch 800 is contained in the
center of the tuning device 806 but does not move while the system
is being tuned.
[0044] An external gas sheath 820 can be used to shield the plasma
820 from the atmosphere. The sheath 820 confines and can contribute
to the longevity of the reactive species in the plasma, and can
keep the atmospheric recombination products as low as practically
possible. In one embodiment, the end of the sheath 820 is
approximately coplanar with the open end, or tip, of the torch 800.
The sheath 820 can be extended beyond the tip of the torch 800 by
installing an extension tube 822 using a threaded flange at the
outlet of the sheath 820. The sheath itself can be threadably
attached 818 to the main cavity 812, which can allow a fine
adjustment on height to be made by screwing the sheath either
toward or away from the cavity 812. Alternatively, the sheath 820
or the extension tube 822 can include an aperture in order to
control the tool footprint. Apertures could then be changed simply
by replacing the extension tube or sheath with an extension tube or
sheath having a different size aperture, for example.
[0045] A supply of process gas 828 can provide process gas to both
tubes 802, 804 of the torch 800. In one embodiment this process gas
is primarily composed of argon or helium, but can also include
carbon dioxide, oxygen or nitrogen, as well as other gases, if the
chemistry of the situation permits. Gas flows in this embodiment
can be between about one and about ten liters per minute. Again,
the gases introduced to the torch can vary on the application.
Reactive precursor gas(es) can be introduced to clean a surface,
followed by a different precursor gas(es) to shape or otherwise
modify the surface of the workpiece. This allows a workpiece to be
cleaned and processed in a single chamber without a need to
transfer the workpiece to different devices to accomplish each
objective.
Chemistry
[0046] A reactive atom plasma process in accordance with
embodiments of the present invention is based, at least in part, on
the reactive chemistry of atomic radicals and reactive fragments
formed by the interaction of a non-reactive precursor chemical with
a plasma. In one such process, the atomic radicals formed by the
decomposition of a non-reactive precursor interact with material of
the surface of the part being modified. The surface material is
transformed to a gaseous reaction product and leaves the surface. A
variety of materials can be processed using different chemical
precursors and different plasma compositions. The products of the
surface reaction in this process must be a gas under the conditions
of the plasma exposure. If not, a surface reaction residue can
build up on the surface which will impede further etching.
[0047] In the above examples, the reactive precursor chemical can
be introduced as a gas. Such a reactive precursor could also be
introduced to the plasma in either liquid or solid form. Liquids
can be aspirated into the plasma and fine powders can be nebulized
by mixing with a gas before introduction to the plasma. RAP
processing can be used at atmospheric pressure. RAP can be used as
a sub-aperture tool to precisely clean and shape surfaces.
[0048] A standard, commercially-available two- or three-tube torch
can be used. The outer tube can handle the bulk of the plasma gas,
while the inner tube can be used to inject the reactive precursor.
Energy can be coupled into the discharge in an annular region
inside the torch. As a result of this coupling zone and the ensuing
temperature gradient, a simple way to introduce the reactive gas,
or a material to be deposited, is through the center. The reactive
gas can also be mixed directly with the plasma gas, although the
quartz tube can erode under this configuration and the system loses
the benefit of the inert outer gas sheath.
[0049] Injecting the reactive precursor into the center of the
excitation zone has several important advantages over other
techniques. Some atmospheric plasma jet systems, such as ADP, mix
the precursor gas in with the plasma gas, creating a uniform plume
of reactive species. This exposes the electrodes or plasma tubes to
the reactive species, leading to erosion and contamination of the
plasma. In some configurations of PACE, the reactive precursor is
introduced around the edge of the excitation zone, which also leads
to direct exposure of the electrodes and plasma contamination. In
contrast, the reactive species in the RAP system are enveloped by a
sheath of argon, which not only reduces the plasma torch erosion
but also reduces interactions between the reactive species and the
atmosphere.
[0050] The inner diameter of the outer tube can be used to control
the size of the discharge. On a standard torch, this can be on the
order of about 18 to about 24 mm. The size can be somewhat
frequency-dependent, with larger sizes being required by lower
frequencies. In an attempt to shrink such a system, torches of a
two tube design can be constructed that have an inner diameter of,
for example, about 14 mm. Smaller inner diameters may be used with
microwave excitation, or higher frequency, sources.
[0051] The foregoing description of preferred embodiments of the
present invention has been provided for the purposes of
illustration and description. It is not intended to be exhaustive
or to limit the invention to the precise forms disclosed. Many
modifications and variations will be apparent to one of ordinary
skill in the art. The embodiments were chosen and described in
order to best explain the principles of the invention and its
practical application, thereby enabling others skilled in the art
to understand the invention for various embodiments and with
various modifications that are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the following claims and their equivalence.
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