U.S. patent application number 10/414443 was filed with the patent office on 2003-12-11 for coating formation by reactive deposition.
Invention is credited to Bi, Xiangxin, Chiruvolu, Shivkumar, Gardner, James T., Kumar, Sujeet, Lim, Seung M., McGovern, William E., Mosso, Ronald J..
Application Number | 20030228415 10/414443 |
Document ID | / |
Family ID | 26934086 |
Filed Date | 2003-12-11 |
United States Patent
Application |
20030228415 |
Kind Code |
A1 |
Bi, Xiangxin ; et
al. |
December 11, 2003 |
Coating formation by reactive deposition
Abstract
Light reactive deposition uses an intense light beam to form
particles that are directly coated onto a substrate surface. In
some embodiments, a coating apparatus comprising a noncircular
reactant inlet, optical elements forming a light path, a first
substrate, and a motor connected to the apparatus. The reactant
inlet defines a reactant stream path. The light path intersects the
reactant stream path at a reaction zone with a product stream path
continuing from the reaction zone. The substrate intersects the
product stream path. Also, operation of the motor moves the first
substrate relative to the product stream. Various broad methods are
described for using light driven chemical reactions to produce
efficiently highly uniform coatings.
Inventors: |
Bi, Xiangxin; (San Ramon,
CA) ; Mosso, Ronald J.; (Fremont, CA) ;
Chiruvolu, Shivkumar; (Sunnyvale, CA) ; Kumar,
Sujeet; (Newark, CA) ; Gardner, James T.; (San
Jose, CA) ; Lim, Seung M.; (Livermore, CA) ;
McGovern, William E.; (LaFayette, CA) |
Correspondence
Address: |
PATTERSON, THUENTE, SKAAR & CHRISTENSEN, P.A.
4800 IDS CENTER
80 SOUTH 8TH STREET
MINNEAPOLIS
MN
55402-2100
US
|
Family ID: |
26934086 |
Appl. No.: |
10/414443 |
Filed: |
April 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10414443 |
Apr 15, 2003 |
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PCT/US01/32413 |
Oct 16, 2001 |
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10414443 |
Apr 15, 2003 |
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09715935 |
Nov 17, 2000 |
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60241200 |
Oct 17, 2000 |
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Current U.S.
Class: |
427/180 |
Current CPC
Class: |
B22F 1/054 20220101;
C23C 24/10 20130101; C23C 18/1266 20130101; B05C 9/14 20130101;
B05B 7/228 20130101; C23C 26/02 20130101; C23C 16/483 20130101;
C23C 16/482 20130101; C23C 16/402 20130101; B05D 3/06 20130101 |
Class at
Publication: |
427/180 |
International
Class: |
B05D 001/12 |
Claims
What is claimed is:
1. A method for coating a substrate comprising: reacting a flowing
reactant stream to form a stream of product particles; and
depositing at least a portion of the product particles onto a
substrate at a deposition rate of at least about 5 g/hr.
2. The method of claim 1 wherein the deposition rate is at least
about 10 g/hr.
3. The method of claim 1 wherein the deposition rate is from about
25 g/hr to about 5 kg/hr.
4. The method of claim 1 wherein the reactant stream has a cross
section perpendicular to the propagation direction characterized by
a major axis and a minor axis, the major axis being at least a
factor of two greater than the minor axis.
5. The method of claim 1 wherein the depositing at least a portion
of the product particles comprises moving the substrate relative to
the stream of product particles.
6. The method of claim 1 wherein the reacting of the flow is driven
by a light beam.
7. A method for coating a substrate comprising: reacting a flowing
reactant stream to form a stream of product particles; and
depositing a least a portion of the product particles onto a
substrate, wherein the deposition of the product particles
comprises moving the substrate relative to the stream of product
particles at a rate of at least about 0.1 centimeters per
second.
8. The method of claim 7 wherein the deposition of the product
particles comprises moving the substrate relative to the stream of
product particles at a rate of at least about 0.5 centimeters per
second.
9. The method of claim 7 wherein the deposition of the product
particles comprises moving the substrate relative to the stream of
product particles at a rate from about 1 centimeters per second to
about 30 centimeters per second.
10. The method of claim 7 wherein reacting the reactant stream is
driven by a radiation beam and wherein the reactant stream is
elongated in a direction along the propagation direction of the
radiation beam to produce a line of particles with the relative
motion of the substrate sweeping at least a portion of the line of
product particles across the substrate.
11. The method of claim 10 wherein the radiation beam is generated
by a light source.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International
Application PCT/US01/32413, designating the U.S. filed on Oct. 16,
2001 to Bi et al., entitled "Coating Formation By Reactive
Deposition," incorporated herein by reference, which claims
priority to U.S. Provisional Patent Application No. 60/241,200,
filed on Oct. 17, 2000 to Bi et al., entitled "Coating Formation By
Reactive Deposition," incorporated herein by reference, and which
is a continuation-in-part of U.S. patent application Ser. No.
09/715,935, filed Nov. 17, 2000 to Bi et al., entitled "Coating
Formation By Reactive Deposition," incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The invention relates to the formation of a coating on the
surface of a substrate, for example, for eventual formation of
optical devices or electrical devices. In particular, the invention
relates to highly uniform particle coatings on substrates and to
efficient ways of forming highly uniform particle coatings that can
be further processed to form glasses and other highly uniform
coatings on a substrate.
BACKGROUND OF THE INVENTION
[0003] The consolidation or integration of mechanical, electrical
and optical components into integral devices has created enormous
demands on material processing. Furthermore, the individual
components integrated in the devices are shrinking in size.
Therefore, there is considerable interest in the formation of
specific compositions applied to substrates. In order to form
optical devices with high quality optical coatings from these
materials, the coatings must be highly uniform. Interest in forming
highly uniform materials for these coatings has sparked the
development of processes.
[0004] Presently used optical communication light wavelengths are
from 1.3 to 1.6 microns. Optical waveguides generally have
dimensions many times the wavelength. Thus, optical structures can
have dimensions from a few microns to about 100 microns depending
on optical mode requirements and other factors.
[0005] An explosion of communication and information technologies
including internet-based systems has motivated a worldwide effort
to implement fiber optical communication networks to take advantage
of a very large bandwidth. The capacity of optical fiber technology
can be expanded further with implementation of Dense Wavelength
Division Multiplexing technology. With increasing demands more
channels are needed to fulfill the system functions. Integrated
components can be used to replace discrete optical components to
supply the desired capacity.
[0006] Optical components can be integrated onto a planar chip-type
base similar to an electronic integrated circuit. By placing the
optical components onto an integrated chip such as a silicon wafer,
many optical components can be squeezed into a very small
footprint. For the mass production of these integrated optical
chips, existing semiconductor technology, such as lithography and
dry etching, can be involved advantageously in appropriate steps of
the production process.
[0007] The production of integrated optical components requires the
deposition of high quality optical materials onto the substrate
surface. Furthermore, the optical materials must be fashioned into
specific devices. In particular, a promising technology for the
integration of optical components centers around the production of
planar waveguides. Semiconductor approaches have been used to form
the waveguides following the deposition of optical materials.
[0008] Basic characteristics of optical film coatings include
surface quality, film uniformity and optical quality. Optical
quality refers to small enough absorption and scattering loss to
achieve desired levels of transmission. Optical quality also
includes the uniformity of optical properties, such as index of
refraction and bi-refringence properties. In addition, optical
quality includes interface quality, such as the interface between
the core layers and cladding layers. Current benchmarks are
established, for example, by glass fibers, planar waveguide glass,
lithium niobate, and InP. For silica (SiO.sub.2) suitable forms
include a glass, while for other materials single crystal forms
have the highest quality optical transmission.
[0009] Several approaches have been used and/or suggested for the
deposition of the optical materials. These approaches include, for
example, flame hydrolysis deposition, chemical vapor deposition,
physical vapor deposition, sol-gel chemical deposition and ion
implantation. Flame hydrolysis deposition has become the leader for
commercial implementation of planar waveguides. Flame hydrolysis
and forms of chemical vapor deposition have also been successful in
the production of glass fibers for use as fiber optic elements.
Flame hydrolysis deposition involves the use of a hydrogen-oxygen
flame to react gaseous precursors to form particles of the optical
material as a coating on the surface of the substrate. Subsequent
heat treatment of the coating can result in the formation of a
uniform optical material, which generally is a glass material.
[0010] No clear approach has been established as the leading
contender for production of the next generation of integrated
optical components that will have stricter tolerances for
uniformity and purity. Flame hydrolysis deposition is efficient,
but cannot be easily adapted to obtain more uniform coatings.
Chemical vapor deposition involves the deposition of radicals,
molecules and/or atoms onto the substrate surface rather than
particles. Chemical vapor deposition can achieve very uniform
materials, but the process is extremely slow. If attempts are made
to increase the rates, the film quality is compromised, which
reduces any advantage of the chemical vapor deposition process.
[0011] At the same time, approaches have been developed for the
production of highly uniform submicron and nanoscale particles by
laser pyrolysis. Highly uniform particles are desirable for the
fabrication of a variety of devices including, for example,
batteries, polishing compositions, catalysts, and phosphors for
optical displays. Laser pyrolysis involves an intense light beam
that drives the chemical reaction of a reactant stream to form
highly uniform particles following the rapid quench of the stream
after leaving the laser beam.
SUMMARY OF THE INVENTION
[0012] In a first aspect, the invention pertains to a coating
apparatus comprising a noncircular reactant inlet, optical elements
forming a light path, a first substrate, and a motor connected to
the apparatus. The reactant inlet defines a reactant stream path.
The light path intersects the reactant stream path at a reaction
zone with a product stream path continuing from the reaction zone.
The substrate intersects the product stream path. Also, operation
of the motor moves the first substrate relative to the product
stream.
[0013] In another aspect, the invention pertains to a method of
coating a substrate, the method comprising reacting a reactant
stream, directing a product stream to a substrate, and moving the
substrate relative to the product stream to coat the substrate. The
reaction of the reactant stream is performed by directing a focused
radiation beam at the reactant stream to produce a product stream
comprising particles downstream from the radiation beam. In these
embodiments, the reaction is driven by energy from the radiation
beam. The coating method can be incorporated into a method of
forming a glass coating. The glass coating is formed by heating a
particle coating at a temperature and for a period of time
sufficient to fuse the particles into a glass. The method of
forming the glass coating can be used in a method of forming an
optical component on a substrate surface. The method for forming
the optical component further includes removing a portion of a
glass coating to form the optical component.
[0014] In a further aspect, the invention pertains to a method of
coating a substrate comprising generating a reactant stream,
reacting the reactant stream to form a product stream of particles,
and directing the stream of particles to a substrate, wherein flow
of the product stream is maintained other than by pumping on the
substrate. In some embodiments, the reactant stream has a cross
section perpendicular to the propagation direction characterized by
a major axis and a minor axis, the major axis being at least a
factor of two greater than the minor axis.
[0015] In addition, the invention pertains to a method of coating a
substrate having a diameter greater than about 5 cm, the method
comprising reacting a reactant stream to form a product stream
comprising product particles and depositing a stream of particles.
The particles are deposited simultaneously over the entire surface
of the substrate. In some embodiments, at least about 5 grams per
hour of particles are deposited onto the substrate.
[0016] Furthermore, the invention pertains to a method of coating a
substrate comprising simultaneously generating multiple product
streams by chemical reaction driven by a light beam. Then, the
multiple product streams are deposited simultaneously on a moving
substrate at sequential locations on the substrate.
[0017] Also, the invention pertains to a method of coating a
substrate comprising reacting a reactant stream to form a product
stream of particles at a high-throughput rate, and depositing this
product stream of particles onto a substrate. The invention further
pertains to a high-rate method of producing a coated substrate
comprising reacting a reactant stream to form a product stream of
particles, and depositing this product stream of particles onto a
substrate wherein the substrate and the particle flow move relative
to each other at a high rate (e.g., at a rate greater than about 1
substrate per minute).
[0018] In an additional aspect, the invention pertains to a method
for coating a substrate comprising reacting a flowing reactant
stream to form a stream of product particles and depositing at
least a portion of the product particles onto a substrate. The
deposition of the particles is performed at a deposition rate of at
least about 5 g/hr.
[0019] In further aspects, the invention pertains to a method for
coating a substrate comprising reacting a flowing reactant stream
to form a stream of product particles and depositing a least a
portion of the product particles onto a substrate. The deposition
of the product particles comprises moving the substrate relative to
the stream of product particles at a rate of at least about 0.1
centimeters per second.
[0020] Other systems, methods, features and advantages of the
invention will be or will become apparent to one with skill in the
art upon examination of the following figures and detailed
description. It is intended that all such additional systems,
methods, features and advantages be included within this
description, be within the scope of the invention, and be protected
by the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1A is a schematic illustration of a particle coating
formed with 1 micron diameter particles.
[0022] FIG. 1B is a schematic illustration of a continuous coating
formed by heat treating the particle coating in FIG. 1A.
[0023] FIG. 1C is a schematic illustration of a particle coating
formed with 20 nm diameter particles.
[0024] FIG. 1D is a schematic illustration of a continuous coating
formed by heat treating the particle coating of FIG. 1C.
[0025] FIG. 2 is a schematic diagram of a light reactive deposition
apparatus for performing the coating deposition under ambient
atmospheric conditions.
[0026] FIG. 3 is a schematic diagram of a light reactive deposition
apparatus formed with a particle production apparatus connected to
a separate coating chamber through a conduit.
[0027] FIG. 4 is a schematic diagram of a light reactive deposition
apparatus in which a particle coating is applied to a substrate
within the particle production chamber.
[0028] FIG. 5 is a schematic, sectional view of an embodiment of a
particle production apparatus, where the cross section is taken
through the middle of the light radiation path. The upper insert is
a bottom view of the exit nozzle, and the lower insert is a top
view of the injection nozzle.
[0029] FIG. 6 is a schematic, side view of a reactant delivery
apparatus for the delivery of vapor reactants to the particle
production apparatus of FIG. 5.
[0030] FIG. 7 is a schematic, side view of a reactant delivery
apparatus for the delivery of an aerosol reactant to the particle
production apparatus of FIG. 5. The insert is a top view of the
outer nozzle.
[0031] FIG. 8 is a perspective view of an alternative embodiment of
a particle production apparatus.
[0032] FIG. 9 is a sectional view of the inlet nozzle of the
alternative particle production apparatus of FIG. 8, the cross
section being taken along the length of the nozzle through its
center. The insert is a top view of the nozzle.
[0033] FIG. 10 is a sectional view of the inlet nozzle of the
alternative particle production apparatus of FIG. 8, the cross
section being taken along the width of the nozzle through its
center.
[0034] FIG. 11 is a perspective view of an embodiment of an
elongated reaction chamber for performing light reactive
deposition.
[0035] FIG. 12 is a perspective view of a coating chamber where the
walls of the chamber are transparent to permit viewing of the
internal components.
[0036] FIG. 13 is a sectional side view of an embodiment of a
reaction chamber and coating chamber wherein the coating chamber is
at a very different pressure from the reaction chamber.
[0037] FIG. 14 is a perspective view of a particle nozzle directed
at a substrate in which the particle nozzle moves to coat different
portions of the substrate.
[0038] FIG. 15 is perspective view of a particle nozzle directed at
a substrate mounted on a rotating stage.
[0039] FIG. 16 is a side view of a particle nozzle directed at a
substrate on a conveyor.
[0040] FIG. 17 is a perspective view of a particle nozzle directing
particles past transducers that defocus the particle stream.
[0041] FIG. 18 is a perspective view of a combination particle
production chamber and coating chamber.
[0042] FIG. 19 is a perspective view of a reactant nozzle
delivering reactants to a reaction zone positioned near a
substrate.
[0043] FIG. 20 is a sectional view of the apparatus of FIG. 19
taken along line 20-20.
[0044] FIG. 21A is a side view of an alternative embodiment of a
nozzle depositing reactants in a reaction zone near a substrate
surface.
[0045] FIG. 21B is a sectional view of another alternative
embodiment of a nozzle depositing reactants in a reaction zone near
a substrate surface.
[0046] FIG. 22 is a perspective view of an alternative embodiment
of a reactant nozzle depositing reactants at a reactant zone near a
substrate surface, in which the reaction zone is generated by light
from a filament.
[0047] FIG. 23 is a side view of the apparatus of FIG. 22.
[0048] FIG. 24 is a schematic side view of a particle coating
apparatus with a beam to control the deposition thickness.
[0049] FIG. 25 is a schematic top view of the apparatus of claim
24.
[0050] FIG. 26 is a schematic side view of an apparatus that uses a
conveyor to transport a substrate with a particle coating into a
furnace.
[0051] FIG. 27 is a schematic side view of a coating apparatus with
three particle conduits connected to three reaction chambers.
[0052] FIG. 28 is a schematic perspective view of three particle
streams generated within a reaction chamber that simultaneously
deposit particles on a single substrate.
[0053] FIG. 29 is a schematic side view of an optical device on a
substrate.
[0054] FIG. 30 is a schematic view of coupled optical waveguides on
a substrate.
[0055] FIG. 31 is a perspective view of a process chamber used for
wafer coating with silicon oxide with a panel removed to expose the
interior of the chamber.
[0056] FIG. 32 is an expanded view of the process chamber of FIG.
31.
[0057] FIG. 33 is an expanded view of the process nozzle and wafer
support of the process chamber of FIG. 32.
[0058] FIG. 34 is an alternative embodiment of the process chamber
of FIG. 31.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0059] An improved coating process is based on the use of radiation
to drive and mediate a chemical reaction to form highly uniform
particles that are deposited onto a substrate to form a coating.
The particle production feature of the invention can take advantage
of various compositions and processing improvements that have been
developed for radiation-based particle formation, especially using
laser pyrolysis. Light reactive deposition, as described herein, is
an adaptation of laser pyrolysis for the immediate deposition of
particles onto a surface. In particular, a wide range of reaction
precursors can be used in either gaseous and/or aerosol form, and a
wide range of highly uniform product particles can be efficiently
produced. Following deposition of the particle coating, the
substrate and coating can be heated to fuse the particles into a
highly uniform continuous coating. The resulting coating can be
further processed into components, especially optical components.
The heating process can be adjusted to yield a glass.
[0060] For the production of particles, laser pyrolysis apparatuses
have included a collector system to collect particles for
subsequent use. The present approaches for light reaction
deposition involve the direct coating onto a substrate without
separate collection of the particles. Furthermore, if the reaction
zone is positioned near the substrate surface, the particles can be
hot when they contact the surface. Thus, the particles are never
segregated as a particle collection prior to forming the coating on
a substrate.
[0061] The substrate can be porous or non-porous. Generally, the
substrate is flat, sturdy and has a high melting point. The
substrate can be heated during or prior to the deposition to reduce
thermal stress of to stimulate compaction of the particles during
the deposition prior to a subsequent melting process to consolidate
the particles into a uniform layer. Alternatively, the substrate
can be cooled or maintained at a temperature cooler than the
particle stream such that the hot particles are attracted to the
surface. The direct coating approach described herein is in
contrast with collection on a porous filter for subsequent
separation of the particles from the filter material. The particles
coated on the substrate can be further processed into a uniform
coating with desired characteristics.
[0062] In some embodiments, the reactant flow is directed through a
reaction zone to produce a product flow that is directed toward a
substrate open to the atmosphere. The reaction zone includes the
intersection of the reactant flow with a focused radiation beam.
The product stream acts as a flat particle spray. The reaction zone
can be enclosed in a chamber to form a spray nozzle. The pressure
of the reactant stream drives the flow of the product stream toward
the substrate. The reactant flow generally is at a pressure greater
than 760 torr if the deposition is performed at atmospheric
pressure.
[0063] In other embodiments, the coating is performed within a
coating chamber sealed from the ambient atmosphere. The coating
chamber can be separate from but connected to the reaction chamber,
or the coating chamber can be integral with the reaction chamber
such that the particles are produced in the same chamber in which
the coating is formed on the substrate. For embodiments with a
separate coating chamber, the coating chamber can be connected to
the reaction chamber through a conduit. A pump can be connected to
the coating chamber to maintain overall flow and an appropriate
pressure through the system. Alternatively, the flow of reactants
and diluents into the chamber can maintain the flow. To perform the
coating, the substrate is placed to contact the product particle
stream. Product particles stick to the surface while remaining
gases and any remaining particles are carried away by the flow.
[0064] If the coating is performed within the particle production
chamber, the radiation can intersect with reactants at a reaction
zone near the opening from the nozzle delivering the reactants. The
substrate surface to be coated is placed just beyond the reaction
zone. The distance between the reaction zone and the nozzle and
between the reaction zone and the substrate can be made adjustable.
The optimal distances can be evaluated empirically. Generally, in
these embodiments the particles are deposited shortly after they
are produced.
[0065] After the initial coating process, a layer of particles is
located on the coated surface. Having formed a particle coating on
the substrate, a binder or other additives can be applied to the
particles to stabilize the particle coating. A variety of organic
polymers can be used as a binder. Alternatively, the binder or
additives can be added during the particle deposition process. The
binder or additive can be used to enhance particle-substrate
adhesion, to enhance particle-particle adhesion, to lower the
sintering temperature, to form an etching barrier to assist with
subsequent etching, or to contribute other desired characteristics
to the coating. In some embodiments, the additives are removed
prior to or during a heat treatment step to consolidate the powders
into a solid layer.
[0066] In other alternative embodiments, the substrate with the
particle coating can be heated to melt and fuse the particles into
a continuous layer. Other elements such as titanium, boron,
phosphorous and geranium can be added to lower the melting point of
the materials to assist with consolidation of the powders into a
continuous layer. However, the use of nanoparticles can
significantly lower the melting point without the need for the use
of additives to lower the melting or flow temperature. Thus, the
deposition of nanoparticles has a significant potential advantage
over the deposition of larger particles.
[0067] Since the packing of particles results in a considerable
thickening even with submicron particles, the thickness of the
coating generally shrinks considerably due to the fusing of the
particles during the consolidation step. For example, the powders
can form a layer as thick as a few millimeters that generally
shrinks down to less than about 100 microns following the
consolidation into a solid layer. There is a corresponding increase
in the density. An amorphous, i.e., glass, coating or a crystalline
coating can result following cooling of the consolidated layer,
depending on the composition of the particles and the precise
heating and cooling conditions. It is typical to form a glass since
polycrystalline materials that can form may not have sufficiently
good optical properties due to scattering.
[0068] In particular, the quench rate should be controlled to
produce a consolidated material with desired properties. The quench
is typically not too fast since a fast quench can introduce
stresses in the glass that can result in cracking of the glass. If
the quench is too slow, crystallites can form that scatter light.
SiO.sub.2 forms a glass that transmits light with a 1.55 micron
wavelength. While a sufficient temperature to melt the particles
may be relatively high, the heating temperature generally is
selected to avoid melting the substrate.
[0069] In some embodiments, light reactive deposition is used to
produce submicron or nanoscale particles that are directed to a
non-porous surface to perform the coating. In light reactive
deposition, a reactant stream is pyrolyzed by an intense light
beam, such as a laser beam. While a laser beam is a convenient
energy source, other intense, focused light sources can be used in
light reactive deposition. The intense light source drives the
reaction, in contrast with combustion reactions driven by heat from
the chemical reaction itself. The energy from the light source
drives the reaction even if the reaction is exothermic since the
light energy results in completion of the reaction within a small
reaction zone. Light reactive deposition can provide for formation
of phases of materials that are difficult to form under
thermnodynamic equilibrium conditions. As the reactant stream
leaves the light beam, the product particles are rapidly
quenched.
[0070] A basic feature of successful application of light reactive
deposition for the production of particles is production of a
reactant stream containing appropriate chemical precursors and a
radiation absorber. The chemical precursors can be sufficient
radiation absorbers such that no separate radiation absorber is
needed. The chemical precursors supply the atomic constituents for
the product particles. The reaction conditions can be varied to
produce product particles with a desired stoichiometry and
structure. As described further below, laser pyrolysis has been
successfully applied for the production of a wide variety of
product particles. By analogy, these same particle compositions can
be generated using light reactive deposition.
[0071] In some embodiments, the light reactive deposition apparatus
includes an extended reactant inlet such that a stream of particles
is generated within a flowing sheet forming a reactant/product
stream. Using an extended reactant inlet, a line of particles can
be simultaneously deposited. Also, a higher particle production
rate can be maintained without sacrificing control of the product
particle properties or deposition uniformity. Thus, by depositing a
line of particles, the coating process can be performed more
rapidly.
[0072] Light reactive deposition has considerable advantage for the
production of particles for coating substrate surfaces. First,
light reactive deposition can be used in the production of a large
range of product particles. Thus, the composition of the coating
can be adjusted in a variety of ways. Furthermore, light reactive
deposition can produce very small particles with a high production
rate. When small particles are coated onto the surface of the
substrate, a smoother coating with a more uniform thickness
results.
[0073] In some embodiments, the non-porous substrate and the
product particle stream are moved relative to each other to
generate the coating on the surface. The rate of the relative
motion can be selected to provide a desired coating thickness.
Generally, this relative motion is accomplished by mounting the
non-porous substrate on a stage or conveyor. The stage or conveyor
can be motorized and programmed to move at a selected rate.
Movement of the stage or conveyor can sweep the product stream
across the surface of the substrate to deposit a uniform coating of
particles across the surface.
[0074] In some embodiments, the product particle stream is
defocused to produce a uniform cloud of product particles. The
distance between the particle nozzle and the substrate is far
enough that the particles lose the direct momentum to the
substrate. The particles can be sprayed into an open volume to form
a cloud of particles. External fields, such as, thermal gradients
and electric field gradients, can be used to pull the particles
toward the surface where the particles condense into a coating.
External fields can also be used to defocus the particle beam to
form the particle cloud. The particle cloud is directed at the
substrate surface to deposit the coating simultaneously across the
all or a desired portion of the surface of the substrate. Thus, a
large uniform coating can be applied without needing moving parts
to sweep the substrate.
[0075] In some embodiments, the system is configured for the
coating of multiple substrates without opening the internal
components of the apparatus to the ambient atmosphere. For example,
a plurality of substrates can be mounted on a stage. Following
completion of coating of one substrate, the stage advances the
coated substrate out of the way and positions another substrate to
be coated next. Particle production can be momentarily stopped
during the positioning of a subsequent substrate or particle
production can be continued with a modest amount of waste of the
particles that are generated when there is no substrate in position
for deposition.
[0076] Alternatively, the substrates can be mounted on a conveyor.
Similar to the stage embodiment, the conveyor moves the substrate
relative to the product particle stream to coat the substrate with
a uniform layer of particles. Once a substrate is coated, the
conveyor moves another substrate into position and moves the coated
substrate to another station for further processing of the coated
substrate within the chamber. In particular, a coated substrate can
be moved to a continuous flow furnace for heat processing.
[0077] There are at least two mechanisms that can lead to surface
roughness. First, since the glass melt is a viscous liquid at the
consolidation temperature, a long time may be required for the
melted glass to diffuse uniformly to other areas. Local density
variation due to non-uniform diffusion naturally causes surface
roughness as the melt is quenched into a solid. In addition,
non-uniform densities can result from process instability in the
particle deposition process that results in different particle
properties across the substrate surface. Variation in particle
formation can lead to surface roughness since the consolidation
process may not eliminate the non-uniformity reflected in the
deposited particles. Therefore, it is important to produce not only
small and uniform particles, but also to control process stability
to deposit these particles uniformly across the substrate
surface.
[0078] Coating formation with smaller and more uniform particles
can result in a more uniform continuous coating following further
processing. This is visually shown in a representation in FIG. 1.
Referring to FIG. 1A, a monolayer coating with 1 micron particles
is shown schematically. Upon melting and subsequent cooling, a
continuous layer is formed with corrugations along the top surface
with about 0.01 micron variations at a wavelength of about 1
micron, as shown in FIG. 1B.
[0079] While coatings generally are formed with thicknesses many
times the particle diameters, comparable results would be expected
with thicker coatings. The corrugations reflect some
characteristics of the particles, such as size and uniformity, and
may also reflect the uniformity of the deposition process with
respect to the evenness of the coating. In summary, the formation
of a continuous coating by the melting of solid powders has a
particle deposition step, a heating step and a quenching step. The
melt formed in the heating step has a high viscosity. The presence
of the substrate generally limits the heating temperature, such
that a high temperature melt cannot be formed that would flow
rapidly to form a smooth surface.
[0080] Referring to FIG. 1C, a hypothetical coating formed with 20
nm particles is shown schematically. Upon fusing or annealing to
form a uniform coating, the variations on the surface are less than
a nanometer (0.001 microns) with a period of about 20 nm. This
increased smoothness and uniformity generally is maintained through
further processing steps. In summary, light reactive deposition
provides a rapid and efficient approach for the production of a
wide variety of coating materials suitable for the production of
higher quality coatings. Of course, to achieve the advantages of
small, uniform particles, the deposition should be controlled to
uniformly deposit the particles onto the substrate.
[0081] As described in the examples below, silicon oxide glass
coatings following heating have been formed that have a root mean
square surface roughness, as measured by atomic force microscopy,
of about 0.25 to about 0.5 nm. Thus, the surfaces are smoother than
are thought to be obtained by flame hydrolysis deposition and
roughly comparable to smoothnesses obtainable by chemical vapor
deposition. These smooth glass coating applied by light reactive
deposition (LRD) were deposited at relatively high deposition rates
by moving the substrate through the product stream. Thus, LRD has
already demonstrated the ability to be an efficient and effective
approach for the formation of very high quality glass coatings.
[0082] For the production of discrete devices or structures on the
substrate surface formed by the coating, various patterning
approaches can be used. For example, conventional approaches from
integrated circuit manufacturing, such as photolithography and dry
etching, can be used to pattern the coating following
deposition.
[0083] Before or after patterning, the coating can be heat
processed to transform the coating from a layer of discrete
particles into a continuous layer. In some embodiments, particles
in the coating are heated to consolidate the particles into a
glass. Glass formation is particularly desirable for the production
of optical devices. Alternatively, a crystalline coating can be
formed from the particle coating by heating under conditions to
anneal the particles to form crystals. The heating and quenching
times can be adjusted to change the properties of the consolidated
coatings.
[0084] In addition to the formation of optical devices, particle
coatings applied by light reactive deposition are useful for a
variety of other applications. For example, iron oxide particles
and/or iron carbide particles can be formed into a coating with a
binder for electromagnetic shielding. These coatings are described
in U.S. Pat. No. 5,938,979 to Kambe et al., entitled
"Electromagnetic Shielding," incorporated herein by reference.
Photocatalytic coatings are described in copending and commonly
assigned U.S. Pat. No. 6,099,798 to Kambe et al., entitled
"Ultraviolet Light Block And Photocatalytic Materials,"
incorporated herein by reference. Prior applications of
nanoparticle coating have required the harvesting of the particles
prior to the production of the coating using the particles. The
present improvements couple the particle generation process with
the deposition process that provides for the production of desired
materials that are incorporated into high quality coatings.
[0085] In some applications, the particles are used to form optical
devices on the surface of the substrate. For example, high-silica
glass can be used to form optical waveguides, optical fiber guides
and optical device guides on a silicon surface. The optical
waveguides need to have a different index of refraction from the
materials surrounding them. Layers with different compositions and
corresponding indices of refraction can be deposited. Dopants can
be introduced to effect the changes in index of refraction.
[0086] To form the particular optical devices desired, one or more
layers of particles are deposited onto the surface. The layer
contacting the surface is an undercladding layer. A core layer is
placed onto the undercladding layer, and an over-cladding layer is
placed onto the core layer. In one embodiment, the undercladding
layer and the over-cladding layer are formed from SiO.sub.2 and the
core layer is formed from doped SiO.sub.2. The composite of the
layers can be referred to as a film.
[0087] The core layer can be etched to form the desired optical
devices. Photolithography and other appropriate patterning
approaches can be used to pattern the core layer for the etching
process. The processing to form integrated optical devices is
described further below. See also, U.S. Pat. No. 4,735,677 to
Kawachi et al., entitled "Method For Fabricating Hybrid Optical
Integrated Circuit," incorporated herein by reference.
[0088] A. Particle Production
[0089] As described above, light reactive deposition involves the
generation of particles using a radiation beam. The particles are
subsequently deposited onto a substrate. In some embodiments, the
particles remain very hot when they contact the surface since the
reaction zone is positioned near the substrate. Light reactive
deposition incorporates features of laser pyrolysis for the
production of submicron and nanoscale particles. The particles
generally can include crystalline particles and/or amorphous
particles that are suitable for subsequent processing into a
finished coating.
[0090] The coating can be performed onto a substrate exposed to the
ambient atmosphere or the coating can be performed within a coating
chamber isolated from the ambient atmosphere. If the coating is
performed exposed to the ambient atmosphere, the reactant stream
generally is generated at greater than atmospheric pressure. The
product particles can be directed directly to the substrate or
through a nozzle that isolates a reaction chamber at a pressure
greater than atmospheric. Referring to FIG. 2, a reactant nozzle 50
generates a reactant stream 52 that intersects a focused light beam
54 from a light source 56. Product particles 58 are generated that
are directed at a substrate 60. Substrate 60 is exposed to the
ambient atmosphere. An optional enclosure 62, shown in FIG. 2 with
phantom lines, can be used to enclose reactant nozzle 50 and the
reactant zone at the intersection of light beam 54 and reactant
stream 52.
[0091] In alternative embodiments, light reactive deposition can be
used to generate particles that are directed to a coating apparatus
to form a coating on a substrate. If a separate coating chamber is
used, the outflow from the reaction chamber leads to a conduit that
directs the particles to a coating chamber. Alternatively, the
coating deposition can be performed directly within the reaction
chamber.
[0092] If a separate coating chamber is used, conventional
constructions of the reaction chamber can be used. The collection
system is then replaced by the coating chamber. An appropriate
conduit can be used to connect the two chambers. Referring to FIG.
3, the coating apparatus 66 comprises a reaction apparatus 68, a
coating chamber 70, a conduit 72 connecting the reaction apparatus
with coating chamber 70, an exhaust conduit 74 leading from coating
chamber 70 and a pump 76 connected to exhaust conduit 74. A valve
78 can be used to control the flow to pump 76. Valve 78 can be, for
example, a manual needle valve or an automatic throttle valve.
Valve 78 can be used to control the pumping rate and the
corresponding chamber pressures. Pump 76 generally is vented to the
atmosphere either directly or through a scrubber, recycler or the
like.
[0093] If the coating is performed within the reaction chamber, the
structure of the reaction chamber generally is modified accordingly
to provide an appropriate flow through the chamber. In particular,
the chamber can be designed to account for potential relative
motion of the substrate and changing directions of flows within the
chamber, as described further below. Such an apparatus 84 is shown
schematically in FIG. 4. The reaction/coating chamber 86 is
connected to a reactant supply system 88, a radiation source 90 and
an exhaust 92. Exhaust 92 can be connected to a pump 94, although
the pressure from the reactants themselves can maintain flow
through the system.
[0094] In some embodiments, the momentum of the particles from the
reaction chamber is directed at the substrate to perform the
coating process. The substrate and the particle flow move relative
to each other to apply the coating across the substrate surface.
Additional substrates can be moved into and out from the flow to
process multiple substrates. In alternative embodiments, forces are
applied to disperse the particles into a uniform cloud such that
the entire surface or a significant portion of the substrate
surface can be simultaneously coated. This cloud based coating can
be performed open to the ambient atmosphere, within the reaction
chamber or within a separate coating chamber.
[0095] As described in detail below, laser pyrolysis apparatuses
have been designed for the production of commercial quantities of
nanoscale powders. These apparatuses can be adapted for coating
formation either in a separate coating chamber or within the
reaction chamber. Alternatively or in addition, the invention
provides that the rate of production and/or deposition of the
particles can be varied substantially, depending on a number of
factors (e.g., the starting materials being utilized, the desired
reaction product, the reaction conditions, the deposition
efficiency, and the like, and suitable combinations thereof). Thus,
in one embodiment, the rate of particle production can vary in the
range(s) from about 5 grams per hour of reaction product to about
10 kilograms per hour of desired reaction product. Specifically,
using apparatuses described herein, coating can be accomplished at
particle production rates of up to at least about 10 kilograms per
hour (kg/hr), in other embodiments at least about 1 kg/hr, in other
embodiments with lower production rates at least about 25 grams per
hour (g/hr) and in additional embodiments at least about 5 g/hr. A
person of ordinary skill in the art will recognize that production
rates intermediate between these explicit production rates are
contemplated and are within the present disclosure. Exemplary rates
of particle production (in units of grams produced per hour)
include not less than about 5, 10, 50, 100, 250, 500, 1000, 2500,
5000, or 10000.
[0096] Not all of the particles generated are deposited on the
substrate. In general the deposition efficiency depends on the
relative speed of the substrate through the product stream with the
particles, for embodiments based on moving the substrate through a
sheet of product particles. At moderate relative rates of substrate
motion, coating efficiencies of about 15 to about 20 percent have
been achieved, i.e. about 15 to about 20 percent of the produced
particles are deposited on the substrate surface. Routine
optimization can increase this deposition efficiency further. At
slower relative motion of the substrate through the product
particle stream, deposition efficiencies of at least about 40% have
been achieved. In some embodiments, the rates of particle
production are such that at least about 5 grams per hour, or
alternatively or in addition, at least about 25 grams per hour, of
reaction product are deposited on the substrate. In general, with
the achievable particle production rates and deposition
efficiencies, deposition rates can be obtained of at least about 5
g/hr, in other embodiments at least about 25 g/hr, in further
embodiments at least from about 100 g/hr to about 5 kg/hr and in
still other embodiment from about 250 g/hr to about 2.5 kg/hr. A
person of ordinary skill in the art will recognize that deposition
rates between these explicit rates are contemplated and are within
the present disclosure. Exemplary rates of particle deposition (in
units of grams deposited per hour) include not less than about 5,
10, 25, 50, 100, 250, 500, 1000, 2500, or 5000.
[0097] Alternatively or in addition, the invention provides that
the rate of the movement of the substrate and the particle flow
relative to each other can vary substantially, depending on the
desired specifications for the coated substrate. Thus, in one
embodiment, the rate can be measured on an absolute scale, and can
vary in the range(s) from about 0.001 inches per second to about 12
inches per second, or even more. Further, in another embodiment,
the rate can be measured on a scale relative to the substrate being
coated, and can vary in the range(s) from about 1 substrate per
minute to about 1 substrate per second.
[0098] For appropriate embodiments using a sheet of product
particles, the rate of substrate motion generally is a function of
the selected deposition rate and the desired coating thickness as
limited by the ability to move the substrate at the desired rate
while obtaining desired coating uniformity. Due to the high
deposition rates achievable with light reactive deposition,
extremely fast coating rates are easily achievable. These coating
rates by LRD are dramatically faster than rates that are achievable
by competing methods. In particular, at particle production rates
of about 10 kg/hr, an eight-inch wafer can be coated with a
thickness of about 10 microns of powder in approximately one second
even at a deposition efficiency of only about 2.5 percent, assuming
a powder density of about 10% of the bulk density. A person of
ordinary skill in the art can calculate with simple geometric
principles a particular coating rate based on the deposition rate,
the desired thickness and the density of powder on the
substrate.
[0099] In particular, apparatus designs based on an actuator arm
moving a substrate through the product particle stream within a
reaction chamber, as described herein, can straightforwardly move a
substrate at rates to coat an entire eight-inch wafer in about 1
second or less. Generally, in embodiments of particular interest
that take advantage of the rapid rates achievable, substrates are
coated at rates of at least about 0.1 centimeters per second
(cm/s), in additional embodiments at least about 0.5 cm/s, in other
embodiments at least about 1 cm/s, in further embodiments from
about 2 cm/s to about 30 cm/s, and in other embodiments from about
5 cm/s to about 30 cm/s. A person of ordinary skill in the art will
recognize that coating rates intermediate between these explicit
rates are contemplated and are within the present disclosure.
[0100] 1. Particle Generation Generally
[0101] As with laser pyrolysis, the reaction conditions determine
the qualities of the particles produced by light reactive
deposition. The reaction conditions for light reactive deposition
can be controlled relatively precisely in order to produce
particles with desired properties. The appropriate reaction
conditions to produce a certain type of particles generally depend
on the design of the particular apparatus. Furthermore, some
general observations on the relationship between reaction
conditions and the resulting particles can be made.
[0102] Increasing the light intensity or laser power results in
increased reaction temperatures in the reaction region as well as a
faster quenching rate. A rapid quenching rate tends to favor
production of high energy phases, which may not be obtained with
processes near thermal equilibrium. Similarly, increasing the
chamber pressure also tends to favor the production of higher
energy structures. Also, increasing the concentration of the
reactant serving as the oxygen source in the reactant stream favors
the production of particles with increased amounts of oxygen.
[0103] Reactant flow rate and velocity of the reactant gas stream
are inversely related to particle size so that increasing the
reactant gas flow rate or velocity tends to result in smaller
particle sizes. Light intensity also influences particle size with
increased light intensity favoring larger particle formation for
lower melting materials and smaller particle formation for higher
melting materials. Also, the growth dynamics of the particles have
a significant influence on the size of the resulting particles. In
other words, different forms of a product compound have a tendency
to form different size particles from other phases under relatively
similar conditions. Similarly, in multiphase regions at which
populations of particles with different compositions are formed,
each population of particles generally has its own characteristic
narrow distribution of particle sizes.
[0104] Laser pyrolysis has become the standard terminology of
reactions driven by an intense light radiation with rapid quenching
of product after leaving a narrow reaction region defined by the
light beam. The name, however, is a misnomer in the sense that a
strong, incoherent, but focused light beam can replace the laser
for certain chemical precursors with high reactivity under mild
heat conditions. Thus, for some chemical reactions, non-laser light
can drive the reaction. Also, the reaction is not a pyrolysis in
the sense of a thermal pyrolysis. The laser pyrolysis reaction is
not thermally driven by the exothermic combustion of the reactants.
In fact, the "laser pyrolysis" reaction can be conducted under
conditions where no visible flame is observed from the reaction.
Similarly, the particle formation process in light reactive
deposition is driven by the intense focused light source rather
than a thermal process.
[0105] Light reactive deposition can be performed with gas/vapor
phase reactants. Many metal/metalloid precursor compounds can be
delivered into the reaction chamber as a gas. Metalloids are
elements that exhibit chemical properties intermediate between or
inclusive of metals and nonmetals. Metalloid elements include
silicon, boron, arsenic, antimony, and tellurium. Appropriate
metal/metalloid precursor compounds for gaseous delivery generally
include metal compounds with reasonable vapor pressures, i.e.,
vapor pressures sufficient to get desired amounts of precursor
gas/vapor into the reactant stream. The vessel holding liquid or
solid precursor compounds can be heated to increase the vapor
pressure of the metal precursor, if desired. Solid precursors
generally are heated to produce a sufficient vapor pressure.
[0106] A carrier gas can be bubbled through a liquid precursor to
facilitate delivery of a desired amount of precursor vapor.
Similarly, a carrier gas can be passed over the solid precursor to
facilitate delivery of the precursor vapor. In other embodiments,
the carrier gas is mixed with the precursor vapor before delivery
into the reaction zone. Suitable silicon precursors for vapor
delivery include, for example, silicon tetrachloride (SiCl.sub.4),
trichlorosilane (Cl.sub.3HSi), trichloromethyl silane
CH.sub.3SiCl.sub.3, and tetraethoxysilane
(Si(OC.sub.2H.sub.5).sub.4, also known as ethyl silane and
tetraethyl silane). The chlorine in these representative precursor
compounds can be replaced with other halogens, e.g., Br, I and
F.
[0107] Suitable dopants for silicon materials include, for example,
boron, germanium, phosphorous, titanium, zinc and aluminum.
Suitable boron precursors include, for example, boron trichloride
(BCl.sub.3), diborane ((B.sub.2H.sub.6), and BH.sub.3. Suitable
phosphorous precursors include, for example, phosphine (PH.sub.3),
phosphorus trichloride (PCl.sub.3), phosphorus oxychloride
(POCl.sub.3) and P(OCH.sub.3).sub.3. Suitable germanium precursors
include, for example, GeCl.sub.4. Suitable titanium precursors
include, for example, titanium tetrachloride (TiCl.sub.4), and
titanium isopropoxide (Ti[OCH(CH.sub.3).sub.2].sub.4). Suitable
liquid zinc precursor compounds include, for example, diethyl zinc
(Zn(C.sub.2H.sub.5).sub.2) and dimethyl zinc (Zn(CH.sub.3).sub.2).
Suitable solid, zinc precursors with sufficient vapor pressure of
gaseous delivery include, for example, zinc chloride (ZnCl.sub.2).
Suitable liquid, aluminum precursors include, for example, aluminum
s-butoxide (Al(OC.sub.4H.sub.9).sub.3). A number of suitable solid,
aluminum precursor compounds are available including, for example,
aluminum chloride (AlCl.sub.3), aluminum ethoxide
(Al(OC.sub.2H.sub.5).sub.3), and aluminum isopropoxide
(Al[OCH(CH.sub.3).sub.2].sub.3).
[0108] The use of exclusively gas phase reactants is somewhat
limiting with respect to the types of precursor compounds that can
be used conveniently. Thus, techniques can be used to introduce
aerosols containing reactant precursors to the reaction zone.
Improved aerosol delivery apparatuses for laser pyrolysis reaction
systems are described further in commonly assigned and copending
U.S. patent application Ser. No. 09/188,670, now U.S. Pat. No.
6,193,936 to Gardner et al., entitled "Reactant Delivery
Apparatuses," filed Nov. 9, 1998, incorporated herein by reference.
These aerosol delivery apparatuses can be adapted for performing
light reactive deposition.
[0109] Using aerosol delivery apparatuses, solid precursor
compounds can be delivered by dissolving the compounds in a
solvent. Alternatively, powdered precursor compounds can be
dispersed in a liquid/dispersant for aerosol delivery. Liquid
precursor compounds can be delivered as an aerosol from a neat
liquid, a multiple liquid dispersion or a liquid solution. Aerosol
reactants can be used to obtain a significant reactant throughput.
A solvent/dispersant can be selected to achieve desired properties
of the resulting solution/dispersion. Suitable solvents/dispersants
include water, methanol, ethanol, isopropyl alcohol, other organic
solvents and mixtures thereof. The solvent should have a desired
level of purity such that the resulting particles have a desired
purity level. Some solvents, such as isopropyl alcohol, are
significant absorbers of infrared light from a CO.sub.2 laser such
that no additional laser-absorbing compound may be needed within
the reactant stream if a CO.sub.2 laser is used as a light
source.
[0110] If aerosol precursors are used, the liquid
solvent/dispersant can be rapidly evaporated by the light beam in
the reaction chamber such that a gas phase reaction can take place.
Thus, the fundamental features of the laser pyrolysis reaction are
unchanged by the presence of an aerosol. Nevertheless, the reaction
conditions are affected by the presence of the aerosol. Below in
the Examples, conditions are described for the production of
nanoscale silicon dioxide particles using aerosol precursors in a
particular reaction chamber. Thus, the parameters associated with
aerosol reactant delivery can be explored further based on the
description below.
[0111] While light reactive deposition is another route to the
production of planar glass, two challenges are associated with the
aerosol-based process. First, many solvents used for dissolving
solid precursors often contain, C, H, O and/or N atoms. These atoms
often form bonds with the materials of interest under most
synthesis conditions. Water and other byproducts may or may not be
removed by a subsequent consolidation heat process. Also, optical
glass formation requires high purity chemicals. SiCl.sub.4 often
needs to be purified through several distillation steps to drive
away the water.
[0112] A number of suitable solid, metal precursor compounds can be
delivered as an aerosol from solution. Suitable silicon precursors
for aerosol production include, for example, silicon tetrachloride
Si(Cl.sub.4), which is soluble in ether, and trichlorosilane
(Cl.sub.3HSi), which is soluble in carbon tetrachloride. Suitable
dopants can be delivered in an aerosol. For example, zinc chloride
(ZnCl.sub.2) and zinc nitrate (Zn(NO.sub.3).sub.2) are soluble in
water and some organic solvents, such as isopropyl alcohol.
Similarly, a boron dopant can be delivered as an aerosol using
ammonium borate ((NH.sub.4).sub.2B.sub.4O.sub.7), which is soluble
in water and various organic solvents.
[0113] The precursor compounds for aerosol delivery are dissolved
in a solution that, in some embodiments, can have a concentration
greater than about 0.1 molar. Generally, the greater the
concentration of precursor in the solution the greater the
throughput of reactant through the reaction chamber. As the
concentration increases, however, the solution can become more
viscous such that the aerosol may have droplets with larger sizes
than desired. Thus, selection of solution concentration can involve
a balance of factors in the selection of a suitable solution
concentration.
[0114] In some embodiments, secondary reactants serving as an
oxygen source include, for example, O.sub.2, CO, N.sub.2O,
H.sub.2O, CO.sub.2, O.sub.3 and mixtures thereof. Molecular oxygen
can be supplied as air. The secondary reactant compound should not
react significantly with the metal precursor prior to entering the
reaction zone since this generally would result in the formation of
large particles.
[0115] Light reactive deposition can be performed with a variety of
optical frequencies, using either a laser or other strong focused
radiation (e.g., light) source. In some embodiments, light sources
operate in the infrared portion of the electromagnetic spectrum.
CO.sub.2 lasers can be used as sources of light. Infrared absorbers
for inclusion in the reactant stream include, for example,
C.sub.2H.sub.4, isopropyl alcohol, NH.sub.3, SF.sub.6, SiH.sub.4
and O.sub.3. O.sub.3 can act as both an infrared absorber and as an
oxygen source. The radiation absorber, such as the infrared
absorber, absorbs energy from the radiation beam and distributes
the energy to the other reactants to drive the reaction.
[0116] In a typical embodiment, the energy absorbed from the light
beam increases the temperature at a tremendous rate, many times the
rate that heat generally would be produced by exothermic reactions
under controlled condition. While the process generally involves
nonequilibrium conditions, the temperature can be described
approximately based on the energy in the absorbing region. The
light reactive deposition reaction process is qualitatively
different from the process in a combustion reactor where an energy
source initiates a reaction, but the reaction is driven by energy
given off by an exothermic reaction. In a combustion reactor, there
is no well defined reaction zone with a boundary. The reaction zone
is large and the residence time of the reactants is long. Lower
thermal gradients are generally present in the combustion reactor.
In contrast, the laser/light driven reactions have extremely high
heating and quenching rates. The laser/light intensity is
controllable such that the reaction conditions are similarly
controllable.
[0117] An inert shielding gas can be used to reduce the amount of
reactant and product molecules contacting the reactant chamber
components. Inert gases can also be introduced into the reactant
stream as a carrier gas and/or as a reaction moderator. Appropriate
inert shielding gases include, for example, Ar, He and N.sub.2.
[0118] An appropriate light reactive deposition apparatus can
include a reaction chamber isolated from the ambient environment.
Alternatively, the reaction zone can be exposed to the ambient
atmosphere. If the reaction zone is exposed to the ambient
atmosphere, the configuration is similar except that no surrounding
walls are present. The discussion below focuses on embodiments in
which a reaction chamber is present, although the modification for
the case in which the reaction zone is exposed to the ambient
atmosphere is a straightforward modification. In addition, if the
pressure in the reaction chamber is higher than the ambient
pressure, the reaction chamber can be oriented to direct product
particles toward a substrate at ambient pressure. For example, in
embodiments with an elongated reactant inlet, a sheet of particles
can be directed at a substrate.
[0119] A reactant inlet connected to a reactant delivery apparatus
produces a reactant stream through the reaction chamber. A light
beam path intersects the reactant stream at a reaction zone.
Generally, the light source, such as a laser, is located external
to the reaction chamber, and the light beam enters the reaction
chamber through an appropriate window. In some embodiments, the
light source can be located within the reaction chamber.
[0120] 2. Separate Laser Pyrolysis Apparatuses
[0121] When the coating is performed in a separate chamber from the
particle production chamber, the laser pyrolysis chamber can be
based on known designs. The reactant/product stream continues after
the reaction zone to an outlet, where the reactant/product stream
exits the reaction chamber and passes into the coating chamber. A
conduit can be used to connect the reaction chamber and the coating
chamber.
[0122] Referring to FIG. 5, a particular embodiment 100 of a
particle production chamber for a light reactive deposition system
involves a reactant delivery apparatus 102, reaction chamber 104,
shielding gas delivery apparatus 106, exhaust conduit 108 and light
source 110. A first reaction delivery apparatus described below can
be used to deliver exclusively gaseous reactants. An alternative
reactant delivery apparatus is described for delivery of one or
more reactants as an aerosol.
[0123] Referring to FIG. 6, a first embodiment 112 of reactant
delivery apparatus 102 includes a source 120 of a precursor
compound. For liquid or solid reactants, a carrier gas from one or
more carrier gas sources 122 can be introduced into precursor
source 120 to facilitate delivery of the reactant. Precursor source
120 can be a liquid holding container, a solid precursor delivery
apparatus or other suitable container. The carrier gas from carrier
gas source 122 can be either an infrared absorber and/or an inert
gas.
[0124] The gases from precursor source 120 are mixed with gases
from infrared absorber source 124, inert gas source 126 and/or
secondary reactant source 128 by combining the gases in a single
portion of tubing 130. The gases are combined a sufficient distance
from reaction chamber 104 such that the gases become well mixed
prior to their entrance into reaction chamber 104. The combined gas
in tube 130 passes through a duct 132 into channel 134, which is in
fluid communication with reactant inlet 206.
[0125] A second reactant can be supplied from second reactant
source 138, which can be a liquid reactant delivery apparatus, a
solid reactant delivery apparatus, a gas cylinder or other suitable
container or containers. As shown in FIG. 6, second reactant source
138 delivers a second reactant to duct 132 by way of tube 130.
Alternatively, second reactant source can deliver the second
reactant into a second duct such that the two reactants are
delivered separately into the reaction chamber where the reactants
combine at or near the reaction zone. Mass flow controllers 146 can
be used to regulate the flow of gases within the reactant delivery
system of FIG. 6.
[0126] As noted above, the reactant stream can include one or more
aerosols. The aerosols can be formed within reaction chamber 104 or
outside of reaction chamber 104 prior to injection into reaction
chamber 104. If the aerosols are produced prior to injection into
reaction chamber 104, the aerosols can be introduced through
reactant inlets comparable to those used for gaseous reactants,
such as reactant inlet 134 in FIG. 6.
[0127] Referring to FIG. 7, embodiment 210 of the reactant supply
system 102 can be used to supply an aerosol to duct 132. Reactant
supply system 210 includes an outer nozzle 212 and an inner nozzle
214. Outer nozzle 212 has an upper channel 216 that leads to a
rectangular outlet 218 at the top of outer nozzle 212, as shown in
the insert in FIG. 7. Rectangular nozzle has selected dimensions to
produce a reactant stream of desired expanse within the reaction
chamber. Outer nozzle 212 includes a drain tube 220 in base plate
222. Drain tube 220 is used to remove condensed aerosol from outer
nozzle 212. Inner nozzle 214 is secured to outer nozzle 212 at
fitting 224.
[0128] The top of the nozzle can be a twin orifice internal mix
atomizer 226. Liquid is fed to the atomizer through tube 228, and
gases for introduction into the reaction chamber are fed to the
atomizer through tube 230. Interaction of the gas with the liquid
assists with droplet formation.
[0129] Referring to FIG. 5, reaction chamber 104 includes a main
chamber 250. Reactant supply system 102 connects to the main
chamber 250 at injection nozzle 252. Reaction chamber 104 can be
heated to a surface temperature above the dew point of the mixture
of reactants and inert components at the pressure in the
apparatus.
[0130] The end of injection nozzle 252 has an annular opening 254
for the passage of inert shielding gas, and a reactant inlet 256
(left lower insert) for the passage of reactants to form a reactant
stream in the reaction chamber. Reactant inlet 256 can be a slit,
as shown in the lower inserts of FIG. 5. Annular opening 254 has,
for example, a diameter of about 1.5 inches and a width along the
radial direction from about 1/8 in to about {fraction (1/16)} in.
The flow of shielding gas through annular opening 254 helps to
prevent the spread of the reactant gases and product particles
throughout reaction chamber 104.
[0131] Tubular sections 260, 262 are located on either side of
injection nozzle 252. Tubular sections 260, 262 include ZnSe
windows 264, 266, respectively. Windows 264, 266 are about 1 inch
in diameter. Windows 264, 266 can be cylindrical lenses with a
focal length equal to the distance between the center of the
chamber to the surface of the lens to focus the light beam to a
point just below the center of the nozzle opening. Windows 264, 266
can have an antireflective coating. Appropriate ZnSe lenses are
available from Laser Power Optics, San Diego, Calif. Tubular
sections 260, 262 provide for the displacement of windows 264, 266
away from main chamber 250 such that windows 264, 266 are less
likely to be contaminated by reactants and/or products. Window 264,
266 are displaced, for example, about 3 cm from the edge of the
main chamber 250.
[0132] Windows 264, 266 are sealed with a rubber o-ring to tubular
sections 260, 262 to prevent the flow of ambient air into reaction
chamber 104. Tubular inlets 268, 270 provide for the flow of
shielding gas into tubular sections 260, 262 to reduce the
contamination of windows 264, 266. Tubular inlets 268, 270 are
connected to shielding gas delivery apparatus 106.
[0133] Referring to FIG. 5, shielding gas delivery system 106
includes inert gas source 280 connected to an inert gas duct 282.
Inert gas duct 282 flows into annular channel 284 leading to
annular opening 254. A mass flow controller 286 regulates the flow
of inert gas into inert gas duct 282. If reactant delivery system
112 of FIG. 6 is used, inert gas source 126 can also function as
the inert gas source for duct 282, if desired. Referring to FIG. 5,
inert gas source 280 or a separate inert gas source can be used to
supply inert gas to tubes 268, 270. Flow to tubes 268, 270 can be
controlled by a mass flow controller 288.
[0134] Light source 110 is aligned to generate a light beam 300
that enters window 264 and exits window 266. Windows 264, 266
define a light path through main chamber 250 intersecting the flow
of reactants at reaction zone 302. After exiting window 266, light
beam 300 strikes power meter 304, which also acts as a beam dump.
An appropriate power meter is available from Coherent Inc., Santa
Clara, Calif. Light source 110 can be a laser or an intense
conventional light source such as an arc lamp. In some embodiments,
light source 110 is an infrared laser, especially a CW CO.sub.2
laser such as an 1800 watt maximum power output laser available
from PRC Corp., Landing, N.J.
[0135] Reactants passing through reactant inlet 256 in injection
nozzle 252 initiate a reactant stream. The reactant stream passes
through reaction zone 302, where reaction involving the metal
precursor compounds takes place. Heating of the gases in reaction
zone 302 is extremely rapid, roughly on the order of 105 degree
C./sec depending on the specific conditions. The reaction is
rapidly quenched upon leaving reaction zone 302, and particles 306
are formed in the reactant/ product stream. The nonequilibrium
nature of the process allows for the production of nanoparticles
with a highly uniform size distribution and structural
homogeneity.
[0136] The path of the reactant stream continues to exit nozzle
310. Exit nozzle 310 has a circular opening 312, as shown in the
upper insert of FIG. 5. Circular opening 312 feeds into exit
conduit 108.
[0137] The chamber pressure is monitored with a pressure gauge 320
attached to the main chamber. The chamber pressure for the
production of the desired oxides generally can be in the range(s)
from about 80 Torr to about 1000 Torr. Pressures above 760 Torr can
be used for coating onto a substrate at atmospheric pressures. In
addition, infrared emission from the reaction zone can be monitored
with a broadband infrared detector 322.
[0138] Exhaust conduit 108 leads to a coating chamber or to a
substrate at ambient pressure. The structure of appropriate coating
chambers is described further below.
[0139] The apparatus can be controlled by a computer 350.
Generally, the computer controls the light source and monitors the
pressure in the reaction chamber. The computer can be used to
control the flow of reactants and/or the shielding gas. Computer
350 can integrate control of the reaction chamber, the coating
chamber and pump.
[0140] An alternative embodiment of a particle production apparatus
is shown in FIG. 8. Particle production apparatus 400 includes a
reaction chamber 402. The reaction chamber 402 has a shape of a
rectangular parallelepiped. Reaction chamber 402 extends with its
longest dimension along the light beam. Reaction chamber 402 has a
viewing window 404 at its side, such that the reaction zone can be
observed during operation.
[0141] Reaction chamber 402 has tubular extensions 408, 410 that
define an optical path through the reaction chamber. Tubular
extension 408 is connected with a seal to a cylindrical lens 412.
Tube 414 connects laser 416 or other optical source with lens 412.
Similarly, tubular extension 410 is connected with a seal to tube
418, which further leads to beam dump/light meter 420. Thus, the
entire light path from laser 416 to beam dump 420 is enclosed.
[0142] Inlet nozzle 426 connects with reaction chamber 402 at its
lower surface 428. Inlet nozzle 426 includes a plate 430 that bolts
into lower surface 428 to secure inlet nozzle 426. Referring to
FIGS. 9 and 10, inlet nozzle 426 includes an inner nozzle 432 and
an outer nozzle 434. Inner nozzle 432 can have a twin orifice
internal mix atomizer 436 at the top of the nozzle. Suitable gas
atomizers are available from Spraying Systems, Wheaton, Ill. The
twin orifice internal mix atomizer 436 has a fan shape to produce a
thin sheet of aerosol and gaseous precursors. Liquid is fed to the
atomizer through tube 438, and gases for introduction into the
reaction chamber are fed to the atomizer through tube 440.
Interaction of the gas with the liquid assists with droplet
formation.
[0143] Outer nozzle 434 includes a chamber section 450, a funnel
section 452 and a delivery section 454. Chamber section 450 holds
the atomizer of inner nozzle 432. Funnel section 452 directs the
aerosol and gaseous precursors into delivery section 454. Delivery
section 450 leads to an about 3 inch by 0.5 inch rectangular outlet
456, shown in the insert of FIG. 9. Outer nozzle 434 includes a
drain 458 to remove any liquid that collects in the outer nozzle.
Outer nozzle 434 is covered by an outer wall 460 that forms an
shielding gas opening 462 surrounding outlet 456. Inert gas is
introduced through inlet 464.
[0144] Referring to FIG. 8, exit nozzle 470 connects to apparatus
400 at the top surface of reaction chamber 402. Exit nozzle 470
forms a conduit leading to a coating chamber or to a substrate at
ambient pressure.
[0145] Another alternative design of a particle production
apparatus has been described in U.S. Pat. No. 5,958,348 to Bi et
al., entitled "Efficient Production of Particles by Chemical
Reaction," incorporated herein by reference. This alternative
design is intended to facilitate production of commercial
quantities of particles by laser pyrolysis. Additional embodiments
and other appropriate features for commercial capacity laser
pyrolysis apparatuses are described in copending and commonly
assigned U.S. patent application Ser. No. 09/362,631 to Mosso et
al., entitled "Particle Production Apparatus," incorporated herein
by reference. Many features described in this copending application
can be incorporated into a particle production apparatus for light
reactive deposition.
[0146] In one embodiment of a high capacity particle production
apparatus, the reaction chamber and reactant inlet are elongated
significantly along the light beam to provide for an increase in
the throughput of reactants and products. The embodiments described
above for the delivery of gaseous reactants and aerosol reactants
can be adapted for the elongated reaction chamber design.
Additional embodiments for the introduction of an aerosol with one
or more aerosol generators into an elongated reaction chamber is
described in commonly assigned and copending U.S. patent
application Ser. No. 09/188,670, now U.S. Pat. No. 6,193,936 to
Gardner et al., entitled "Reactant Delivery Apparatuses,"
incorporated herein by reference.
[0147] In general, the particle production apparatus with the
elongated reaction chamber and reactant inlet is designed to reduce
contamination of the chamber walls, to increase the production
capacity and to make efficient use of resources. To accomplish
these objectives, the elongated reaction chamber provides for an
increased throughput of reactants and products without a
corresponding increase in the dead volume of the chamber. The dead
volume of the chamber can become contaminated with unreacted
compounds and/or reaction products. Furthermore, an appropriate
flow of shielding gas confines the reactants and products within a
flow stream through the reaction chamber. The high throughput of
reactants makes efficient use of the light energy.
[0148] The design of the improved reaction chamber 460 is shown
schematically in FIG. 11. A reactant inlet 462 leads to main
chamber 464. Reactant inlet 462 conforms generally to the shape of
main chamber 464. Main chamber 464 includes an outlet 466 along the
reactant/product stream for removal of particulate products, any
unreacted gases and inert gases. Shielding gas inlets 470 are
located on both sides of reactant inlet 462. Shielding gas inlets
are used to form a blanket of inert gases on the sides of the
reactant stream to inhibit contact between the chamber walls and
the reactants or products. The dimensions of elongated reaction
chamber 464 and reactant inlet 462 can be designed for high
efficiency particle production. Reasonable dimensions for reactant
inlet 462 for the production of ceramic nanoparticles, when used
with a 1800 watt CO2 laser, are from about 5 mm to about 1
meter.
[0149] Tubular sections 480, 482 extend from the main chamber 464.
Tubular sections 480, 482 hold windows 484, 486 to define a light
beam path 488 through the reaction chamber 460. Tubular sections
480, 482 can include inert gas inlets 490, 492 for the introduction
of inert gas into tubular sections 480, 482.
[0150] Outlet 466 leads to a conduit leading to a coating chamber.
There is not necessarily a change in dimension that demarcates a
transition from the reaction chamber to a conduit to the coating
chamber. The reaction zone is located within the reaction chamber,
and the conduit can but does not necessarily involve a change in
direction of the flow.
[0151] 3. Particle Coating Deposition External to the Particle
Production Chamber
[0152] If the coating process is not performed within the reaction
chamber where particles are produced, the product particles are
directed through a conduit to a separate coating chamber or to a
coating area with a substrate at ambient pressure. The conduit from
the particle production apparatus leads to a particle nozzle that
opens into the coating chamber. The coating chamber may or may not
be maintained under reduced pressure. The coating process can be
performed by moving the substrate and nozzle relative to each
other. Alternatively, external forces are applied to disperse the
particles into a cloud that is used to simultaneously coat the
entire substrate or a significant fraction thereof.
[0153] If the chamber is sealed from the ambient environment, one
or more substrates can be processed before the coated substrates
are harvested from the coating chamber. Alternatively, the coated
substrates can be passed through an airlock to a position for
further processing or for retrieval of the coated substrates. If
the chamber operates near atmospheric pressure, the coated
substrates and fresh uncoated substrates can be passed into and out
from the chamber at will. In either case, additional processing,
such as heat treatment, can be performed in an automated process
without intervention or the substrates with particle coatings can
be manually directed to specific locations for further
processing.
[0154] Referring to FIG. 12, conduit 500 from the particle
production apparatus leads to coating chamber 502. Conduit 500
terminates at opening 504 within chamber 502. In some embodiments,
opening 504 is located near the surface of substrate 506 such that
the momentum of the particle stream directs the particles directly
onto the surface. Substrate 506 can be mounted on a stage or other
platform 508 to position substrate 506 relative to opening 504.
Generally, coating chamber 502 is vented through a channel 510. If
coating chamber 502 is maintained at pressures less than
atmospheric, channel 510 generally leads to a pump 512. A
collection system, filter or scrubber 514 can be placed between the
coating chamber 502 and pump 512 to remove particles that did not
get coated onto the substrate surface. A manual or automatic valve
516 can be used to control the pumping rate.
[0155] The coating chamber can operate at a significantly different
pressure than the reaction chamber. One apparatus to accomplish
this is shown in FIG. 13. In apparatus 530, laser pyrolysis chamber
532 leads to conduit 534. Conduit 534 leads to a venturi tube 536.
Venturi tube 536 includes a nozzle 538 connected to an inert gas
supply 540. Nozzle 538 leads to a tapered tube 542. The pressure of
the inert gas from nozzle 538 creates negative pressure in conduit
534 and reaction chamber 532 and propels the product particles down
tapered tube 542.
[0156] Tapered tube 542 leads to coating chamber 544. As shown in
FIG. 13, substrate 546 is swept past the opening of tapered tube
542 by a moving stage 548. Motor 550 moves stage 548 along track
552. Coating chamber 544 is vented through an exhaust 554.
[0157] In general, if a focused particle stream is delivered to the
coating chamber, the substrate and the delivery nozzle move
relative to each other to sweep the particle stream across the
surface of the substrate forming a coating over the surface or
portion thereof. In some embodiments, the particle nozzle moves
relative to a fixed substrate. Referring to FIG. 14, substrate 570
is mounted onto a stage 572. Stage 572 can be fixed, or stage 572
can move to bring different substrate within the particle flow. In
some embodiments, stage 572 includes thermal control features, such
that the temperature of substrate 570 can be increased or decreased
to a desired value. Particle nozzle 574 moves relative to substrate
570 to direct particles across the substrate surface. As shown in
FIG. 14, particle nozzle 574 rotates relative to conduit 576 at
hinges 578. Motor 580 is used to control the movement of nozzle
574.
[0158] In alternative embodiments, the substrate is moved relative
to a fixed nozzle. Referring to FIG. 15, a particle nozzle 590
directs particles toward a stage 592. As shown in FIG. 15, four
substrates 594 are mounted on stage 592. More or less substrates
can be mounted on a moveable stage with corresponding modifications
to the stage and size of the chamber. Movement of stage 592 sweeps
the particle stream across a substrate surface and positions
particular substrate 594 within the path of nozzle 590. As shown in
FIG. 15, a motor is used to rotate stage 592. Stage 592 can include
thermal control features that provide for the separate or
simultaneous control of the temperature of the substrates on stage
592. Alternative designs involve the linear movement of a stage, as
shown in FIG. 13.
[0159] In an alternative embodiment, a conveyor is used to
transport substrates past a particle nozzle as well as to deliver
fresh uncoated substrates and remove coated substrate. Referring to
FIG. 16, particle nozzle 600 is directed toward conveyor 602.
Conveyor 602 includes motorized rollers 604 and a belt 606,
although variations in design can be used. Conveyor belt 606 sweeps
a substrate 608 past the opening of nozzle 600. As with the stages
described above, conveyor 602 can include thermal control features
to adjust the temperature of a substrate to desired values. Fresh
uncoated substrates 610 can be delivered from a hopper 612. Coated
substrates 614 can be stacked in a rack 616.
[0160] Referring to FIG. 17, particle nozzle 630 delivers the
particles to an applied field formed by transducers 632. For
example, transducers 632 can be plates connected to a power source
to supply an electrostatic field. Alternatively, an electromagnet
or a permanent magnet can be used to generate a magnetic field. The
electrical or magnetic field disperses the particles into a cloud
that can be relatively uniformly dispersed. A cloud of particles
then settles onto the surface of substrate 634. Substrate 634 does
not have to be moved relative to nozzle 630 to coat the surface.
However, substrate 634 can be mounted onto a stage to move
different substrate into position.
[0161] 4. Combination Laser Pyrolysis and Coating Chambers
[0162] In some embodiments, the coating is performed within the
same chamber in which the particles are produced. An appropriate
apparatus 650 for performing the coating within the particle
production chamber is shown schematically in FIG. 18. Apparatus 650
includes a chamber 652 and two tubes 654, 656 extending from
chamber 652. In this embodiment, tube 654 is connected to a laser
658, although other radiation sources can be used. Tube 656
terminates at a beam dump 660. Tubes 654, 656 extend optical
components such as lenses and the like from chamber 652 such that
contamination of the optical components by particles is reduced or
eliminated. In some embodiments, tubes 654, 656 include inert gas
inlets 662, 664 connected to inert gas sources, such that inert gas
can be directed into tubes 654, 656 to reduce the flow of
containments into tubes 654, 656.
[0163] Reactant conduit 670 joins chamber 652 with a reactant
delivery system. Suitable reactant delivery systems are described
above. In principle, chamber 652 can be vented to the atmosphere,
possibly through a scrubber. In these embodiments, flow through the
chamber is maintained by the reactant stream. However, in some
embodiments an exhaust conduit 672 connects with a pump 674. Pump
674 has an exhaust 676 that vents to the atmosphere directly or
through a scrubber. A collector, filter or the like 678 can be
placed into the flow to the pump to remove extra particles from the
flow. Similarly, valves can be included to control the pumping. In
some embodiments, the pressure within the chamber ranges from about
80 Torr to about 700 Torr.
[0164] The inside of the chamber is shown schematically in FIG. 19.
A substrate 680 moves relative to a reactant nozzle 682, as
indicated by the right directed arrow. Reactant nozzle 682 is
located just above substrate 680. An optical path 684 is defined by
suitable optical elements that direct a light beam along path 684.
Optical path 684 is located between nozzle 682 and substrate 680 to
define a reaction zone just above the surface of substrate 680. The
hot particles tend to stick to the cooler substrate surface. A
sectional view is shown in FIG. 20. A particle coating 686 is
formed as the substrate is scanned past the reaction zone.
[0165] In general, substrate 680 can be carried on a conveyor 688.
In some embodiments, the position of conveyor 688 can be adjusted
to alter the distance from substrate 686 to the reaction zone.
Changes in the distance from substrate to the reaction zone
correspondingly change the temperature of the particles striking
the substrate. The temperature of the particles striking the
substrate generally alters the properties of the resulting coating
and the requirements for subsequent processing, such as a
subsequent heat processing consolidation of the coating. The
distance between the substrate and the reaction zone can be
adjusted empirically to produce desired coating properties. In
addition, the stage/conveyor supporting the substrate can include
thermal control features such that the temperature of the substrate
can be adjusted to higher or lower temperatures, as desired.
[0166] One alternative embodiment of the nozzle is shown in FIG.
21A. Nozzle 690 includes a central reactant conduit 692 at a
pressure P.sub.1. An adjacent shielding/cooling gas conduit 694 is
located downstream relative to the motion of the substrate with
respect to the reaction zone. In alternative embodiments, the
substrate is moved in the opposite direction with some modification
of the deposition conditions. Inert gas at a pressure PS is
directed into the shielding gas/cooling gas conduit. A pump conduit
696 at pressure P.sub.2 is located along the other side of the
reactant conduit. The chamber pressure is P.sub.c. In some
embodiments, the order of the pressures is as follows:
P.sub.s.gtoreq.P.sub.1>P.sub.c>P.sub.2.
[0167] The reactants flow down the reactant conduit to the reaction
zone at or near where the reactants intersect with the light beam.
The shielding/cooling gas helps to prevent the flow of reactant
particles through the chamber, and the inert gas further helps to
cool the product particles on the surface of the substrate to help
the particles condense onto the substrate. The pump conduit is used
to remove unreacted gases, inert gases and any residual particles
as well as maintain the chamber pressure at desired values.
P.sub.1, P.sub.2 and P.sub.s can be independently set. P.sub.c is
determined by the other pressures as well as the chamber design. In
general, the pump pressure can be changed to obtain a desired value
for the chamber pressure.
[0168] Another alternative embodiment of the nozzle is shown in a
cross sectional view in FIG. 21B. Reactant delivery nozzle 671
delivers reactants through a central channel 673 and shielding gas
through side channels 675. Reactant delivery nozzle 671 is
connected to delivery system 677 including reactant sources.
Reactant delivery nozzle 671 delivers reactants through a laser
beam path 679 such that product particles flow to wafer 681. Wafer
681 is mounted on a movable stage 683 that sweeps wafer 681 though
the product stream. Vacuum channels 685, 687 are connected to a
suitable pump to maintain the chamber pressure at desired values.
Vacuum channels 685, 687 are mounted on either side of the reaction
zone where the reactant stream intersects laser beam path 679.
Inert buffer gas is directed through gaps 689, 691 between vacuum
channels 685, 687 and stage 683.
[0169] For coating within the reaction chamber, it may be desirable
to use an incoherent light source located within the chamber rather
than a laser. Referring to FIG. 22, reactant nozzle 700 directs
reactants toward substrate 702. Substrate 702 moves relative to
nozzle 700 as shown with the arrow using a stage, conveyor or the
like. As shown in FIGS. 22 and 23, light source 704 includes a
linear filament 706, a parabolic mirror 708 and a long cylindrical
lens 710. Filament 706 can be selected to emit high intensity
infrared light. Parabolic mirror 708 helps to collect light emitted
by filament 704 and direct the rays parallel to the axis of the
mirror. Cylindrical lens 710 focuses the light at a reaction zone
712 in the path of the reactant stream from nozzle 700.
Alternatively, light source 704 can be replaced with a diode laser
array or other light emitting diode array of corresponding
dimensions and orientation. Substrate 702 moves relative reaction
zone 712 as indicated by the arrow. A particle coating 714
results.
[0170] 5. Control of Particle Production and Coating Deposition
[0171] Since a major objective is the generation of substrate
coatings with improved uniformity, a significant aspect of
achieving this control involves monitoring and adjustment of the
processing conditions. Two aspects in particular can be monitored.
First, the conditions in the reaction zone can be monitored to
ensure uniform products being produced. In addition, the deposition
of the particles on the substrate can be monitored to improve the
uniformity and flatness of the resulting coating.
[0172] Product generation is sensitive to the pressure in the
reaction zone. In some embodiments, the pressure in the reaction
zone is monitored, for example using a pressure sensor, such as
pressure gauge 320, shown in FIG. 5 or comparable pressure sensor
in the particular reaction configuration. A processor controller,
such as computer 350, can use a feedback loop to maintain the
pressure within acceptable ranges. The pressure can be adjusted
under computer control by changing the degree of opening of a
valve, such as valve 78 of FIG. 3, connected to a pump, adjusting
the pumping rate or varying the flow of reactants and/or shielding
gas flowing in the vicinity of the reaction zone.
[0173] In addition, it may be desirable to control the thermal
properties in the reaction zone within a desired range. For
example, a thermal detector can be placed in a suitable position to
detect energy levels within the reaction zone. To avoid
interference with reactant/product flow, the sensor can be placed
on or near a wall away from the reactant flow. However, shielding
gas generally is used to confine the flow, such that the
temperature at a sensor away from the reactant/product flow may not
be able to detect the temperature at the reaction zone. However, in
one embodiment, a detector includes a broadband infrared detector,
such as detector 322 of FIG. 5, oriented to receive infrared
emissions from the reaction zone. Suitable detectors include, for
example, infrared photodiodes. Infrared emission generally provides
an accurate estimate of temperatures in the reaction zone without
needing to contact the flow. The temperature of the reaction zone
can be maintained within a desired range by a feedback loop
controlled by the control computer. For example, the laser power
can be adjusted up or down if the temperature reading drops or
rises, respectively, relative to the desired range.
[0174] While maintaining particle production uniformity is
important, the deposition uniformity is also important. The
maintenance of a consistent particle production rate may not be
sufficient since relatively small fluctuations in precursor
delivery may lead to undesirable levels of coating variation if
extremely flat coatings are desired. Thus, it is desirable to
monitor coating deposition directly to correlate substrate scanning
rate with coating deposition.
[0175] Referring to FIGS. 24 and 25, a deposition apparatus 720
includes a conveyor 722 that transports a substrate 724 across the
path of a product stream 726. A low power laser beam 728 is
directed just above the substrate surface. Laser beam 728 is
generated by a laser 730, which can be, for example, a helium/neon
laser, a diode laser or any other low power laser. The beam can be
focused to a narrow diameter, for example, a one millimeter
diameter. The beam is positioned such that the coating blocks a
significant portion of the beam when the coating reaches the
desired thickness. The beam is terminated by a detector 732, such
as a diode detector to measure the laser output that reaches the
detector. The measurement system can be mode-locked with a chopper
to improve signal-to-noise and to reduce variations from the
deposition stream.
[0176] Conveyor 722 includes a motor 734, such as a stepper motor
or other suitable motor. Conveyor 722 and detector 732 are
connected to a control process 736. In some embodiments, conveyor
722 remains at a particular location until the signal from detector
732 indicates that the coating thickness has reached a desired
value. Detector values can be calibrated by comparing detector
output with coating thicknesses made by visual inspection systems
that can make very accurate height measurements. For example, a
projected pattern of light can be used in a multiphased structured
light measurement system to image an object, as described in U.S.
Pat. No. 6,049,384 to Rudd et al., entitled "Method and Apparatus
For Three Dimensional Imaging Using Multi-Phased Structured Light,"
incorporated herein by reference.
[0177] When the detector value is reached indicating the desired
coating thickness, processor 736 can instruct conveyor 722 to
activate motor 734 to advance substrate 724. Substrate 724 is moved
to another position until the detector signal again indicates that
the desired coating thickness is reached. This process is repeated
until the selected portion of the substrate is covered. In
alternative embodiments, the substrate can be moved at a slow
continuous rate. Measurements from detector 732 can be used to
adjust the rate desired amounts to maintain coating thicknesses
within acceptable tolerances.
[0178] B. Particle Properties
[0179] A variety of chemical particles, generally solid particles,
can be produced by the methods described herein. Solid particles
generally are deposited as powders. Chemical powders of particular
interest include, for example, carbon particles, silicon particles,
metal particles, and metal/metalloid compounds, such as,
metal/metalloid oxides, metal/metalloid carbides, metal/metalloid
nitride, metal/metalloid sulfides. Generally, the powders include
fine or ultrafine particles with particle sizes in the micron or
smaller range.
[0180] For some applications, it is desirable to have very uniform
particles. Processes using focused radiation are particularly
suitable for the formation of highly uniform particles, especially
nanoscale particles. In particular, light reactive deposition can
produce a collection of particles of interest generally with an
average diameter for the primary particles of less than about 750
nm, alternatively from about 3 nm to about 100 nm, similarly from
about 3 nm to about 75 nm, and also from about 3 nm to about 50 nm.
Particle diameters are evaluated by transmission electron
microscopy. Diameter measurements on particles with asymmetries are
based on an average of length measurements along the principle axes
of the particle.
[0181] The agglomeration of nanoparticles is a factor that can
affect the coating quality. The flow dynamics of those agglomerates
are affected by their size and degree of agglomeration. In general,
non-agglomerated particles are more likely to form denser coatings.
It should be noted, however, that transmission electron micrographs
of particles collected on a filter may not represent the degree of
particle agglomeration property shortly after the particles are
produced and leave the reaction zone. In many of the light reactive
deposition processes, the particles are directly deposited without
agglomerating onto the substrate where they are quenched.
[0182] The primary particles can have a high degree of uniformity
in size. Light reactive deposition, as described above, generally
results in particles having a very narrow range of particle
diameters. With aerosol delivery of reactants for light reactive
deposition, the distribution of particle diameters is particularly
sensitive to the reaction conditions. Nevertheless, if the reaction
conditions are properly controlled, a very narrow distribution of
particle diameters can be obtained with an aerosol delivery system.
However, broad distributions of primary particles sizes can also be
obtained, if desired, by controlling the flow rates, reactant
densities and residence times in light reactive deposition or using
other fluid flow reaction systems.
[0183] In highly uniform powders, as determined from examination of
transmission electron micrographs, the primary particles generally
have a distribution in sizes such that at least about 95 percent,
and in another embodiment at least about 99 percent, of the primary
particles have a diameter in the range(s) greater than about 40
percent of the average diameter and less than about 160 percent of
the average diameter. Similarly, in even more highly uniform
powders, the primary particles can have a distribution of diameters
such that at least about 95 percent, and in another embodiment at
least about 99 percent, of the primary particles have a diameter in
the range(s) greater than about 60 percent of the average diameter
and less than about 140 percent of the average diameter.
[0184] Furthermore, in embodiments with highly uniform particles,
effectively no primary particles have an average diameter greater
than about 4 times the average diameter, with alternative
embodiments of greater than about 3 times the average diameter, and
greater than about 2 times the average diameter. In other words,
the particle size distribution effectively does not have a tail
indicative of a small number of particles with significantly larger
sizes. This is a result of the small reaction region and
corresponding rapid quench of the particles. An effective cut off
in the tail of the size distribution indicates that there are less
than about 1 particle in 106 have a diameter greater than a
specified cut off value above the average diameter. Narrow size
distributions, lack of a tail in the distributions and the roughly
spherical morphology can be advantageous for obtaining highly
uniform coatings.
[0185] Small particle size and particle uniformity do contribute
overall to the uniformity of the resulting coating. In particular,
the lack of particles significantly larger than the average, i.e.,
the lack of a tail in the particle size distribution, leads to a
more uniform coating.
[0186] In addition, the particles can have a very high purity
level. The nanoparticles produced by the above described methods
are expected to have a purity greater than the reactants because
the reactions and, when applicable, the crystal formation process
tends to exclude contaminants from the particle. Some impurities on
the surface of the particles may be removed by heating the
particles.
[0187] A plurality of types of nanoscale particles can be produced
by laser pyrolysis and, alternatively or in addition, by light
reactive deposition based on the description above.
[0188] Exemplary such nanoscale particles can generally be
characterized as comprising a composition including a number of
different elements and present in varying relative proportions,
where the number and the relative proportions vary as a function of
the application for the nanoscale particles. Typical numbers of
different elements include, for example, numbers in the range(s)
from about 2 elements to about 15 elements, with numbers of 1, 2,
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 being contemplated.
General numbers of relative proportions include, for example,
values in the range(s) from about 1 to about 1,000,000, with
numbers of about 1, 10, 100, 1000, 10000, 100000, 1000000, and
suitable sums thereof being contemplated.
[0189] Alternatively or in addition, such nanoscale particles can
be characterized as having the following formula:
A.sub.aB.sub.bC.sub.cD.sub.dE.sub.eF.sub.fG.sub.gH.sub.hI.sub.iJ.sub.jK.su-
b.kL.sub.lM.sub.mN.sub.nO.sub.o,
[0190] where each A, B, C, D, E, F, G, H, I, J, K, L, M, N, and O
is independently present or absent and at least one of A, B, C, D,
E, F, G, H, I, J, K, L, M, N, and O is present and is independently
selected from the group consisting of elements of the periodic
table of elements comprising Group 1A elements, Group 2A elements,
Group 3B elements (including the lanthanide family of elements and
the actinide family of elements), Group 4B elements, Group 5B
elements, Group 6B elements, Group 7B elements, Group 8B elements,
Group 1B elements, Group 2B elements, Group 3A elements, Group 4A
elements, Group 5A elements, Group 6A elements, and Group 7A
elements; and each a, b, c, d, e, f, g, h, i, j, k, l, m, n, and o
is independently selected from a value in the range(s) from about 1
to about 1,000,000, with numbers of about 1, 10, 100, 1000, 10000,
100000, 1000000, and suitable sums thereof being contemplated.
[0191] For example, the production of silicon oxide nanoparticles
is described in copending and commonly assigned U.S. patent
application Ser. No. 09/085,514 to Kumar et al., entitled "Silicon
Oxide Particles," incorporated herein by reference. This patent
application describes the production of amorphous SiO.sub.2. The
production of titanium oxide nanoparticles and crystalline silicon
dioxide nanoparticles is described in copending and commonly
assigned, U.S. patent application Ser. No. 09/123,255, now U.S.
Pat. No. 6,387,531 to Bi et al., entitled "Metal (Silicon)
Oxide/Carbon Composites," incorporated herein by reference. In
particular, this application describes the production of anatase
and rutile TiO.sub.2.
[0192] Amorphous nanoscale powders and glass layers with dopants,
such as rare earth dopants and/or other metal dopants, are
described in copending and commonly assigned U.S. Provisional
Patent Application serial No. 60/313,588 to Home et al., entitled
"Doped Glass Materials," incorporated herein by reference. Suitable
dopants include rare earth metals, which can impart desirable
modifications of properties, such as index-of-refraction. Powders
and glass layers can be formed with complex compositions including
a plurality of selected dopants in an amorphous material. The
powders can be used to form optical materials and the like. The
glass layers can be formed by directly depositing a uniform
particle coating using light reactive deposition and subsequently
annealing the powder into a uniform glass layer.
[0193] Amorphous submicron and nanoscale particles can be produced
with selected dopants, including rare earth metals, using laser
pyrolysis and other flowing reactor systems. Using these approaches
a variety of new materials can be produced. The dopants can be
introduced at desired stoichiometries by varying the composition of
the reactant stream. The dopants are introduced into an appropriate
host glass forming material. By appropriately selecting the
composition in the reactant stream and the processing conditions,
submicron particles incorporating one or more metal or metalloid
elements as glass-forming hosts with selected dopants can be
formed. Since the host amorphous materials generally are oxides, an
oxygen source should also be present in the reactant stream. The
conditions in the reactor should be sufficiently oxidizing to
produce the oxide materials. Similarly, light reactive deposition
can be used to form highly uniform coatings of glasses with dopants
including, for example, rare earth dopants and/or complex blends of
dopant compositions.
[0194] Some metal/metalloid oxides are particularly desirable for
optical applications and/or for their ability to anneal into
uniform glass layers. Suitable glass forming host oxides for doping
include, for example, TiO.sub.2, SiO.sub.2, GeO.sub.2,
Al.sub.2O.sub.3, P.sub.2O.sub.5, B.sub.2O.sub.3, TeO.sub.2, and
combinations and mixtures thereof. While phosphorous is located in
the periodic table near the metal elements, it is not generally
considered a metalloid element. However, phosphorous in the form of
P.sub.2O.sub.5 is a good glass former similar to some metalloid
oxides, and doped forms of P.sub.2O.sub.5 can have desirable
optical properties. For convenience, as used herein including in
the claims, phosphorous is also considered a metalloid element.
[0195] Dopants can be introduced to vary properties of the
amorphous particles and/or a resulting glass layer. For example,
dopants can be introduced to change the index-of-refraction of the
glass. For optical applications, the index-of-refraction can be
varied to form specific optical devices that operate with light of
a selected frequency range. Dopants can also be introduced to alter
the processing properties of the material. In particular, some
dopants change the flow temperature, i.e., the glass transition
temperature, such that the glass can be processed at lower
temperatures. Dopants can also interact within the materials. For
example, some dopants are introduced to increase the solubility of
other dopants. Rare earth dopants are desirable for their
modification of optical properties of the resulting doped material.
Rare earth doped glasses are useful in the production of optical
amplifiers.
[0196] Particles of particular interest include amorphous
compositions that form optical glasses with a plurality of dopants.
In some embodiments, the one or plurality of dopants are rare earth
metals. Rare earth metals are particularly desirable because of
their modification of optical properties of the materials. If the
particles are annealed into a glass layer, the resulting material
can have an index-of-refraction influenced by the rare earth
dopants as well as other dopants. In addition, the rare earth
dopants influence the optical absorption properties that can alter
the application of the materials for the production of optical
amplifiers and other optical devices. Rare earth metals include the
transition metals of the group IIIb of the periodic table.
Specifically, the rare earth elements include Sc, Y and the
Lanthanide series. Other suitable dopants include elements of the
actinide series. For optical glasses, the rare earth metals of
particular interest as dopants, include, for example, Er, Yb, Nd,
La, Y, Pr and Tm. Suitable non-rare earth metal dopants include,
for example, Bi, Sb, Zr, Pb, Li, Na, K, Ba, W and Ca.
[0197] To form a uniform glass layer, a layer of amorphous
particles can be annealed. To anneal the glass, the powders are
heated to a temperature above their flow temperature. At these
temperatures, the powders densify to form a uniform layer of glass
material. Incorporation of the dopants into the particles results
in a distribution of the dopants through the densified material
directly as a result of the powder deposition.
[0198] Material processing remains a significant consideration in
the design of desired optical devices. For example, the composition
and properties, such as density, of a material are adjusted to
obtain materials with a desired index-of-refraction. Similarly, the
thermal expansion and flow temperatures of a material have to be
consistent with a reasonable processing approach for forming the
materials into a monolithic, integrated structure. The consolidated
optical materials can have good optical properties such that light
transmission through the materials does not result in undesirable
amount of loss. In addition, the materials have to be processable
under reasonable conditions to form the integrated devices of the
integrated optical circuit or electro-optical circuit. Similar
material constraints can be problematic for the formation of
state-of-the-art integrated electronic devices.
[0199] Doped glasses are useful in the production of optical
devices. Using the techniques described herein, the doped glasses
can be formulated into planar optical devices. The dopant can
change the optical properties of the materials to be particularly
suitable for particular optical applications. Rare earth doped
glasses are particularly suitable for use in the formation of
optical amplifiers. The amplifier material is excited by a pump
light signal transversely coupled to the optical material. The pump
light excites the rare earth doped materials. An optical input
passing through the optical material at a lower frequency than the
pump signal is then amplified by stimulated emission. Thus, energy
from the pump light is used to amplify the input light signal.
[0200] In particular, nanoscale manganese oxide particles have been
formed. The production of these particles is described in copending
and commonly assigned U.S. patent application Ser. No. 09/188,770,
now U.S. Pat. No. 6,506,493 to Kumar et al., entitled "Metal Oxide
Particles," incorporated herein by reference. This application
describes the production of MnO, Mn.sub.2O.sub.3, Mn.sub.3O.sub.4
and Mn.sub.5O.sub.8.
[0201] Also, the production of vanadium oxide nanoparticles is
described in U.S. Pat. No. 6,106,798 to Bi et al., entitled
"Vanadium Oxide Nanoparticles," incorporated herein by reference.
Similarly, silver vanadium oxide nanoparticles have been produced,
as described in copending and commonly assigned U.S. patent
application Ser. Nos. 09/246,076 to Home et al., now U.S. Pat. Nos.
6,225,007, and 09/311,506, now U.S. Pat. No. 6,394,494 to Reitz et
al., both entitled "Metal Vanadium Oxide Particles," both of which
are incorporated herein by reference.
[0202] Furthermore, lithium manganese oxide nanoparticles have been
produced by laser pyrolysis along with or without subsequent heat
processing, as described in copending and commonly assigned U.S.
patent application Ser. Nos. 09/188,768 to Kumar et al., entitled
"Composite Metal Oxide Particles," and 09/334,203, now U.S. Pat.
No. 6,482,374 to Kumar et al., entitled "Reaction Methods for
Producing Ternary Particles," and U.S. Pat. No. 6,136,287 to Home
et al., entitled "Lithium Manganese Oxides and Batteries," all
three of which are incorporated herein by reference.
[0203] The production of aluminum oxide nanoparticles is described
in copending and commonly assigned, U.S. patent application Ser.
No. 09/136,483 to Kumar et al., entitled "Aluminum Oxide
Particles," incorporated herein by reference. In particular, this
application disclosed the production of .gamma.-Al.sub.2O.sub.3.
The formation of delta-Al.sub.2O.sub.3 and theta-Al.sub.2O.sub.3 by
laser pyrolysis/light reactive deposition along with
doped-crystalline and amorphous alumina is described in copending
and commonly assigned U.S. patent application Ser. No. 09/969,025
to Chiruvolu et al., entitled "Aluminum Oxide Powders,"
incorporated herein by reference. Amorphous aluminum oxide
materials can be combined with other glass formers, such as
SiO.sub.2 and/or P.sub.2O .sub.3. For example, suitable metal oxide
dopants for aluminum oxide for optical glass formation include
cesium oxide (Cs.sub.2O), rubidium oxide (Rb.sub.2O), thallium
oxide (Tl.sub.2O), lithium oxide (Li.sub.2O), sodium oxide
(Na.sub.2O), potassium oxide (K.sub.2O), beryllium oxide (BeO),
magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO)
and barium oxide (BaO). Glass dopants can affect, for example, the
index-of-refraction, sintering temperature and/or the porosity of
the glass. Suitable metal oxide dopants for infrared emitters
include, for example, cobalt oxide (CO.sub.3O .sub.4).
[0204] In addition, tin oxide nanoparticles have been produced by
laser pyrolysis, as described in copending and commonly assigned
U.S. patent application Ser. No. 09/042,227, now U.S. Pat. No.
6,200,674 to Kumar et al., entitled "Tin Oxide Particles,"
incorporated herein by reference. The production of zinc oxide
nanoparticles is described in copending and commonly assigned U.S.
patent application Ser. No. 09/266,202 to Reitz, entitled "Zinc
Oxide Particles," incorporated herein by reference. In particular,
the production of ZnO nanoparticles is described.
[0205] Submicron and nanoscale particles and corresponding coatings
of rare earth metal oxide particles, rare earth doped
metal/metalloid oxide particles, rare earth metal/metalloid
sulfides and rare earth doped metal/metalloid sulfides are
described in copending and commonly assigned U.S. patent
application Ser. No. 09/843,195 to Kumar et al, entitled "High
Luminescence Phosphor Particles," incorporated herein by reference.
Suitable host materials for the formation of phosphors include, for
example, ZnO, ZnS, Zn.sub.2SiO.sub.4, SrS, YBO.sub.3,
Y.sub.2O.sub.3, Al.sub.2O.sub.3, Y.sub.3Al.sub.5O.sub.12 and
BaMgAl.sub.14O.sub.23. Exemplary non-rare earth metals for
activating phosphor particles as dopants include, for example,
manganese, silver and lead. Exemplary rare earth metals for forming
metal oxide phosphors include, for example, europium, cerium,
terbium and erbium. Generally, heavy metal ions or rare earth ions
are used as activators in phosphors. For phosphor applications, the
particles are generally crystalline.
[0206] The production of iron, iron oxide and iron carbide is
described in a publication by Bi et al., entitled "Nanocrystalline
.alpha.-Fe, Fe.sub.3C, and Fe.sub.7C.sub.3 produced by CO.sub.2
laser pyrolysis," J. Mater. Res. Vol. 8, No. 7 1666-1674 (July
1993), incorporated herein by reference. The production of
nanoparticles of silver metal is described in copending and
commonly assigned U.S. patent application Ser. No. 09/311,506, now
U.S. Pat. No. 6,394,494 to Reitz et al., entitled "Metal Vanadium
Oxide Particles," incorporated herein by reference. Nanoscale
carbon particles produced by laser pyrolysis is described in a
reference by Bi et al., entitled "Nanoscale carbon blacks produced
by CO.sub.2 laser pyrolysis," J. Mater. Res. Vol. 10, No. 11,
2875-2884 (November 1995), incorporated herein by reference.
[0207] The production of iron sulfide (Fe.sub.1-xS) nanoparticles
by laser pyrolysis is described in Bi et al., Material Research
Society Symposium Proceedings, vol. 286, p. 161-166 (1993),
incorporated herein by reference. Precursors for laser pyrolysis
production of iron sulfide were iron pentacarbonyl (Fe(CO).sub.5)
and hydrogen sulfide (H.sub.2S).
[0208] Cerium oxide can be produced using the laser pyrolysis
apparatuses described above. Suitable precursors for aerosol
delivery include, for example, cerous nitrate (Ce(NO.sub.3).sub.3),
cerous chloride (CeCl.sub.3) and cerous oxalate
(Ce.sub.2(C.sub.2O.sub.4).sub.3). Similarly, zirconium oxide can be
produced using the laser pyrolysis apparatuses described above.
Suitable zirconium precursors for aerosol delivery include, for
example, zirconyl chloride (ZrOCl.sub.2) and zirconyl nitrate
(ZrO(NO.sub.3).sub.2).
[0209] The deposition of coatings of dielectric materials for chip
capacitors is described in copending and commonly assigned U.S.
Provisional Patent Application serial No. 60/312,234 to Bryan,
entitled "Reactive Deposition For The Formation Of Chip
Capacitors," incorporated herein by reference. Particularly
suitable dielectric materials include a majority of barium titanate
(BaTiO.sub.3), optionally mixed with other metal oxides. Other
dielectric oxides suitable for incorporation into ceramic chip
capacitors with appropriate dopants include, for example,
SrTiO.sub.3, CaTiO.sub.3, SrZrO.sub.3, CaZrO.sub.3,
Nd.sub.2O.sub.3--2TiO.sub.3 and La.sub.2O.sub.3--2TiO.sub.2.
[0210] The production of ternary nanoparticles of aluminum silicate
and aluminum titanate can be performed by laser pyrolysis following
procedures similar to the production of silver vanadium oxide
nanoparticles described in copending and commonly assigned U.S.
patent application Ser. No. 09/311,506, now U.S. Pat. No. 6,394,494
to Reitz et al., entitled "Metal Vanadium Oxide Particles,"
incorporated herein by reference. Suitable precursors for the
production of aluminum silicate include, for vapor delivery, a
mixture of aluminum chloride (AlCl.sub.3) and silicon tetrachloride
(SiCl.sub.4) and, for aerosol delivery, a mixture of
tetra(N-butoxy) silane and aluminum isopropoxide
(Al(OCH(CH.sub.3).sub.2).sub.3). Similarly, suitable precursors for
the production of aluminum titanate include, for aerosol delivery,
a mixture of aluminum nitrate (Al(NO.sub.3).sub.3) and titanium
dioxide (TiO.sub.2) powder dissolved in sulfuric acid or a mixture
of aluminum isopropoxide and titanium isopropoxide
(Ti(OCH(CH.sub.3).sub.2).sub.4).
[0211] The formation of submicron and nanoscale particles along
with coatings of metal/metalloid compounds with complex anions is
described in copending and commonly assigned U.S. patent
application Ser. No. 09/845,985 to Chaloner-Gill et al., entitled
"Phosphate Powder Compositions And Methods For Forming Particles
With Complex Anions," incorporated herein by reference. Suitable
complex anions include, for example, phosphates, silicates and
sulfates. The compositions can include multiple metal/metalloid
elements.
[0212] The synthesis by laser pyrolysis of silicon carbide and
silicon nitride is described in copending and commonly assigned
U.S. patent application Ser. No. 09/433,202 to Reitz et al.,
entitled "Particle Dispersions," incorporated herein by
reference.
[0213] In embodiments in which the coating is performed within the
same chamber as the particle production, the reaction zone may be
positioned close to the substrate surface. In these embodiments,
the particles may impact the surface while still significantly hot.
Due to the temperature of the particles, the particles may be
deformed and possibly fused upon contacting the surface. This
deformation and fusion can be increased by heating the substrate.
This deformation and fusion process can facilitate subsequent
consolidation of the coating into a uniform surface. Since the
heated particles may never cool significantly following their
formation, the may not be well characterized as solid particles.
The term "particles" is used generally to include melted droplets
at high temperature or softened particles that are not fully
quenched as well as fully quenched solid particles.
[0214] C. Particle Deposition Process and Processing of Particle
Coatings
[0215] The basic process for the deposition of particle coatings
has been described in detail above. The features of the coating can
be varied to obtain particular objectives. In particular, the
coating can be varied at different locations on the surface. In
addition, multiple layers of particles can be deposited in a
controlled fashion.
[0216] First, the particle coating can be applied over the entire
surface of the substrate or only a portion of the substrate, for
example, with the use of a mask. The procedures described above can
be adapted to apply the coating to desired sections, for example by
sweeping the substrate relative to the particle nozzle such that
only the desired portion of the substrate is swept past the
nozzle.
[0217] Similarly, the coating can be made a uniform thickness, or
different portions of the substrate can be coated with different
thicknesses of particles. Different coating thicknesses can be
applied by varying the sweep speed of the substrate relative to the
particle nozzle or by making multiple sweeps of portions of the
substrate that receive a thicker particle coating. The particle
composition can be similarly varied over different portions of the
substrate. This can be accomplished, for example, by changing the
reactant stream during the coating process, or by performing
multiple partial coating sweeps over different portions of the
substrates.
[0218] The temperature of the substrate during the deposition
process can be adjusted to achieve particular objectives. For
example, the substrate can be cooled during the deposition process
since a relatively cool substrate can attract the particles to its
surface. However, in some embodiments, the substrate is heated, for
example to about 500.degree. C., during the deposition process.
Particles stick better to a heated substrate. In addition, the
particles tend to compact and fuse on a heated substrate such that
a subsequent consolidation of the coating into a fused glass or
other material is facilitated if the coating were formed initially
on a heated substrate.
[0219] In general, the particle coating thickness can be made as
thin or as thick, as desired, within the practice limits of the
particle size and apparatus size. Of course, the minimum thickness
is a monolayer of particles. From a practice sense, it is difficult
to apply directly a monolayer of particles uniformly over the
substrate. Therefore, a uniform coating of greater than about five
times the average particle thickness can be applied in some
embodiments. On the other hand, coatings can be applied at
arbitrary thicknesses with the only limitation being that more time
is required for additional thicknesses. In some embodiments, the
thickness of the coating following heat treatment to consolidate
the material into a single layer is generally at least about 100
nm.
[0220] The particle coating is held together by relatively weak
forces. However, for some applications the coated surface may be
useful in that form. For most applications, the particle coating is
subjected to additional processing. In some embodiments, a binder
is directly added to the particle coating to stabilize the coating.
The binder can be, for example, an organic polymer material such as
polytetrafluoroethylene, polyvinylidene fluoride, polyethylene
oxide, polyethylene, polypropylene, polyurethanes, polyacrylates,
ethylene-(propylene-diene monomer) copolymer (EPDM) and mixtures
and copolymers thereof. The binders can be added, for example, as
polymer solutions in a solvent. Volatile solvents can be used that
evaporate after addition of the binder. Alternatively, polymer
binders can be applied as melts sprayed onto the coating with the
polymers solidifying upon cooling. Inorganic binders, such as
metals and metal compounds, can be deposited on the particle
coating by vapor deposition techniques.
[0221] In some embodiments, the particle coatings are heat treated.
Heat treatment can melt and fuse the particles and lead to
compaction, i.e., densification, of the coating material. This
fusing of the particles is generally referred to as consolidation.
Sufficient heating can lead to an essentially uniform material in a
coating. Generally, the heating is performed under conditions to
melt the particles into a viscous liquid. Because of the high
viscosity, the material does not flow significantly on the
substrate surface. Processing at higher temperatures to reduce the
viscosity of the melt can result in undesirable melting of the
substrate, migration of compositions between layers or in flow from
a selected area of the substrate. Under desired heating conditions,
some remnants of the particle characteristics can be found in the
surface of the resulting coating even though the material is
essentially uniform through the thickness of the coating.
[0222] Suitable processing temperatures and time generally depend
on the composition of the particles. Small particles on the
nanometer scale generally can be processed at lower temperatures
and/or for shorter times due to lower melting points for the
nanoparticles in comparison with bulk material. In addition, heat
treatment can remove undesirable impurities and/or change the
stoichiometry and crystal structure of the material. For example,
carbon impurities can be removed by heat treatment.
[0223] For silicon dioxide coatings formed by flame hydrolysis
deposition, it has been observed that heat treatment at
1050.degree. C. for 20 hours or more in a nitrogen atmosphere can
reduce undesirable hydrogen content in the form of OH groups in the
glass material. See U.S. Pat. No. 4,038,370 to Tokimoto et al. (the
'370 patent), entitled "Method of Producing High-Purity Transparent
Vitreous Silica," incorporated herein by reference. As described in
the '370 patent, the substrate is coated within the periphery of
the flame such that molten particles are deposited directly on the
substrate to form a continuous material rather than a particle
coating. If particles are deposited following formation by flame
hydrolysis, the particles can be heated in an oxygen atmosphere at
1500.degree. C. to sinter the particles. See, for example, U.S.
Pat. No. 3,934,061 to Keck et al., entitled "Method of Forming
Planar Optical Waveguides," incorporated herein by reference. It
has been suggested that sintering of silica particles involving a
heating step at lower temperatures of about 500.degree. C. followed
by gradual heating to higher temperatures of 1100.degree. C.
results in fewer OH groups. See U.S. Pat. No. 5,622,750 to Kilian
et al., entitled "Aerosol Process For The Manufacture of Planar
Waveguides," incorporated herein by reference. Generally, the
smaller particles produced by light reactive deposition can be
heated under lower temperatures to achieve the same results.
[0224] For the processing of silicon oxide nanoparticles, the
particle coatings can be heated to a temperature on the order of
1200.degree. C. However, it has been observed generally that
nanoscale powders have lower melting temperatures than the
corresponding bulk materials and larger particles. Therefore, lower
melting temperatures generally can be used with nanoscale
particles, although it may be desirable to use a comparable melting
temperature to obtain greater surface smoothness that results from
improved melting of the nanoparticles.
[0225] Heat treatments can be performed in a suitable oven. It may
be desirable to control the atmosphere in the oven with respect to
pressure and/or the composition of the gases. Suitable ovens
include, for example, an induction furnace or a tube furnace with
gas flowing through the tube. The heat treatment can be performed
following removal of the coated substrates from the coating
chamber. In alternative embodiments, the heat treatment is
integrated into the coating process such that the processing steps
can be performed sequentially in the apparatus in an automated
fashion.
[0226] For example, referring to FIG. 15 heating elements can be
built into the base of stage 592 such that substrates with particle
coatings can be heated from below while other substrates are being
coated with particles. The heat treatment can be performed using
the natural atmosphere in the coating chamber. Alternatively, it
may be possible to alter the local environment of the heated
substrate by directing a gas flow at the substrate if the pumping
capacity is sufficient to prevent significant flow of gas into the
coating chamber.
[0227] In other embodiments, the substrates with particle coatings
are moved to other portions of the apparatus where they can be
heated uniformly. This can be accomplished, for example, with a
conveyor, such as shown in FIG. 16. Referring to FIG. 26, coating
apparatus 740 includes conveyor 742 that transports a substrate
from a hopper 744 past a particle nozzle 746. Conveyor 742 can
include rollers 750 and a belt 752 or a other comparable
structures. A particle coating 754 is placed on substrate 756 at
particle nozzle 746.
[0228] Conveyor 742 carries a particle coated substrate into oven
758. Oven 758 can be open to the same atmosphere as coating chamber
760, or oven 758 can have separate environmental control. For
example, a coated substrate can pass through an air lock to reach
oven 758. Alternatively, if oven 758 is connected to a pump,
desired gases can be flowed into oven 758. In some embodiments, the
pump removes the gases directed into the oven at a sufficient rate
to prevent undesired amounts of flow into coating chamber 760
and/or the reaction chamber. Following heating in the oven, heat
processed substrates 762 can be collected in a manner consistent
with the design of oven 760.
[0229] For many applications, it is desirable to apply multiple
particle coatings with different compositions. These multiple
particle coatings can be arranged adjacent to each other across the
x-y plane of the substrate being coated (e.g., perpendicular to the
direction of motion of the substrate relative to the product
stream), or stacked one on top of the other across the z plane of
the substrate being coated, or in any suitable combination of
adjacent and stacked layers. Each coating can be applied to a
desired thickness. For example, in some embodiments, silicon oxide
and doped silicon oxide can be deposited in alternating layers.
Specifically, two layers with different compositions can be
deposited with one on top of the other, and or additionally or
alternatively, with one next to the other, such as layer A and
layer B formed as AB. In other embodiments, more than two layers
each with different compositions can be deposited, such as layer A,
layer B and layer C deposited as three sequential (e.g., stacked
one on top of the other, or adjacent to the other, or adjacent and
stacked) layers ABC. Similarly, alternating sequences of layers
with different compositions can be formed, such as ABABAB . . .
ABCABCABC . . .
[0230] For many applications, the desirability of applying multiple
particle coatings with different compositions (e.g., adjacent to
each other, or stacked one on top of the other) can be suggested by
functional requirement(s) for the coated substrate. Thus, for
example, in optical applications, it can be desirable to apply
multiple coatings with different compositions to achieve one, or
any suitable combination of two or more of, the following
functions: optical waveguide/conduit/fiber (e.g., Bragg grating),
optical attenuator, optical splitter/coupler, optical filter,
optical switch, optical amplifier, optical polarizer, optical
mirror/reflector, optical phase-retarder, and optical detector.
Suitable particle coating materials for each such optical function
can be selected from those particles discussed above.
[0231] The material with multiple particle coatings can be heat
treated after the deposition of each layer or following the
deposition of multiple layers or some combination of the two. The
optimal processing order generally would depend on the melting
point of the materials. Generally, however, heat treating and
consolidating the composite layers can occur simultaneously. If the
heating temperatures are picked at reasonable values, the melted
materials remain sufficiently viscous that the layers do not merge
undesirable amounts at their edges. Slight merging of the layers
generally does not effect performance unacceptable amounts,
especially if the layers are slightly thicker than minimum
requirements.
[0232] Light reactive deposition (LRD) is a particularly suitable
approach for the application of multiple particle layers for
simultaneous consolidation through heat treatments. Due to the
uniformity that is possible with the LRD approach, multiple layers
can be deposited without reaching unacceptable levels of surface
smoothness.
[0233] In addition, multiple materials with different compositions
can be simultaneously produced by laser pyrolysis and
simultaneously deposited in a sequential fashion on a substrate.
For example, referring to FIG. 27, three laser reaction chambers
770, 772, 774 direct particles along three conduits 776, 778, 780
to substrate 782. The reaction chambers can be configured to
produce particles with a different composition or the same
composition as the other reaction chambers. Thus, a substrate can
be coated with one, two or three different compositions with this
embodiment. If two different materials are produced, the different
material can be between or adjacent the two layers formed from the
same material. As substrate 782 moves along on conveyor 784,
particles from conduits 776, 778, 780 are sequentially deposited.
The particles can be simultaneously deposited such that all three
types of particles are deposited in one pass of the substrate past
the conduits.
[0234] In addition, multiple particle flows can be simultaneously
deposited within a single reaction chamber. Referring to FIG. 28, a
reaction chamber 790 includes three reactant flows 792, 794, 796
directed toward a substrate 798. In some embodiments, each reactant
flow includes a blanket of shielding gas such that the three
reactions are isolated from each other by the shielding gas. Three
laser beams 800, 802, 804 are directed at reactant flows 792, 794,
796, respectively, to drive the three separate reactions. As
substrate 798 moves on conveyor 806, substrate 798 is coated
sequentially by particles produced from reactant streams 792, 794,
796. The reactions can be performed simultaneously, such that one
pass of the substrate provides a coating with the three reaction
products. A reactant stream can have the same or different
compositions from the other reactant streams.
[0235] In FIGS. 27 and 28, two embodiments are described for the
simultaneous deposition of multiple particle layers. Based on the
description above, many variations of these embodiments can be
straightforwardly generated.
[0236] It may be desirable to etch or otherwise process one or more
heat treated layers before depositing additional particle layers,
as described further below for the formation of planar waveguides.
The processing order generally is influenced by the device to be
formed and the structure of the device.
[0237] D. Optical Device Formation
[0238] While the coatings described herein can have a variety of
applications, as noted above, optical devices formed on a substrate
surface are of particular interest. The control of light
propagation along the optical devices requires variation in the
index of refraction in adjacent materials. A device can be
distinguished by boundaries of a material with an index of
refraction that is different from adjacent materials that thereby
define the boundaries of the device. A basic feature of the optical
devices is that they are produced from a crystalline or amorphous
material that is transparent to the electromagnetic radiation to be
transmitted through the device. Devices of interest include, for
example, optical waveguides and optical couplers.
[0239] Waveguides placed on a substrate surface are referred to as
planar waveguides. Planar waveguides are useful in the production
of integrated optical circuits for optical communication and other
opto-electronics applications. Light propagates along a material
having a higher refractive index than the surroundings. In some
embodiments, the planar waveguides have a thickness approximately
equal to the wavelength of the light, i.e., electromagnetic
radiation, to be transmitted along the waveguide. In some
embodiments, waveguides do not significantly attenuate the light
transmitted through the material.
[0240] To produce a planar optical waveguide by particle coating
technology, generally three layers are deposited. A core layer
forms the optical component on an under-cladding layer, and a
over-cladding layer encloses the optical component. The
under-cladding layer generally is applied between the substrate and
the core layer since the substrate generally does not have an
appropriate index of refraction. In other words, the core layer may
be formed directly onto the substrate surface, however, one or more
strata generally are deposited between the core layer and the
substrate.
[0241] In one embodiment, the substrate is formed from silicon. An
under-cladding layer of silicon dioxide is deposited over the
substrate. A core layer is then deposited over the cladding layer.
The under-cladding layer generally is consolidated prior to the
addition of an additional layer, although both layers can be
consolidated simultaneously if the heat treatment is performed
under suitably mild conditions. If the particles forming the core
layer are added after consolidation of the of the under-cladding
layer, the core layer is consolidated following deposition of the
particles forming the core layer. The core layer should have an
index of refraction greater than the cladding layer. A convenient
approach to the production of a layer with a higher index of
refraction is to use a doped silicon oxide. Suitable dopants
include, for example, titanium oxide, tantalum oxide, tin oxide,
niobium oxide, zirconium oxide, aluminum oxide, lanthanum oxide,
germanium oxide, boron oxide, other suitable dopants identified
herein or combinations thereof.
[0242] As the index of refraction of the core material increases,
the desired thickness of the layer decreases because of changes in
the wavelength with index of refraction. Thus, the correlation
between these parameters should be controlled accordingly. The use
of excessive amounts of dopants should be avoided since excessive
dopants can result in the loss of transparency of the material with
respect to the light. The upper limit on the amount of dopant
depends on the dopant, although for all materials there would
generally be less than about 40% by weight dopant. The
undercladding layer and the core layer do not need to be deposited
by the same approach, although in some embodiments the layers are
sequentially deposited by light reactive deposition followed by a
suitable heat treatment.
[0243] The core layer can be deposited over selected portions of
the substrate to form specific structures. Alternatively, after
consolidation of the core layer, the material can be contoured to
produce desired devices. The contouring can be performed by
patterning with photolithography combined with etching and/or with
other techniques used in the formation of electronic integrated
circuits. After the formation of the desired structures from the
core material, an over-cladding layer generally is applied. The
over-cladding layer also has a lower index of refraction than the
core layer. The formation of planar waveguides by flame hydrolysis
deposition is described further in U.S. Pat. No. 3,934,061 to Keck
et al., entitled "Method of Forming Planar Optical Waveguides,"
incorporated herein by reference.
[0244] An exemplary structure is shown schematically in FIG. 29.
Optical component 810 is located on substrate 812. Under-cladding
layer 814 is located adjacent substrate 812. Core structure 816 is
located on top of cladding layer 814. Over-cladding layer 818 is
located on top of core layer 816. Such a structure can be formed by
patterning and etching a core layer to form the patterned core
structure 816.
[0245] In order to form integrated optical devices on the substrate
surface, it can be desirable to form various coupling devices to
connect with planar optical waveguides. A variety of devices can be
formed. Examples of an integrated structure 820 are shown in FIG.
30. Sections of planar waveguides 822 are connected by branches
824. A plurality of guides 826 is placed on substrate 828. Guides
826 can be used to align and secure components such a fiber optical
cables, solid state lasers, detectors and the like in contact with
ends of waveguides 822 to couple the different elements. Waveguides
822, branches 824 and guides 826 can be formed by etching the
deposited layers to have desired shapes. The formation of such
coupling elements is described further in U.S. Pat. No. 4,735,677
to Kawachi et al., entitled "Method For Fabricating Hybrid Optical
Integrated Circuit," incorporated herein by reference.
[0246] As utilized herein, the term "in the range(s)" or "between"
comprises the range defined by the values listed after the term "in
the range(s)" or "between", as well as any and all subranges
contained within such range, where each such subrange is defined as
having as a first endpoint any value in such range, and as a second
endpoint any value in such range that is greater than the first
endpoint and that is in such range.
EXAMPLES
[0247] This example describes the successful coating of a silicon
substrate with a silicon oxide glass using light reactive
deposition.
[0248] Particle coating was been performed using light reactive
deposition in which wafer coating was been performed within the
reaction chamber by sweeping the substrate through a product
particle stream. This example focuses on this embodiment, although
successful coating of a wafer within the reaction chamber has also
been performed in preliminary experiments with a fixed
substrate.
[0249] The apparatus used to coat a substrate/wafer moved through
the reaction stream is shown in FIGS. 31-33. Referring to FIG. 31,
process chamber 850 includes a light tube 852 connected to a
CO.sub.2 laser and a light tube 854 connected to a beam dump. An
inlet tube 856 connects with a precursor delivery system that
delivers vapor reactants and carrier gases. Inlet tube 856 leads to
process nozzle 858. A particle transport tube 860 connects to
process chamber 850 along the flow direction from process nozzle
858. Particle transport tube 860 leads to a particle filtration
chamber 862. Particle filtration chamber 862 connects to a pump at
pump connector 864.
[0250] An expanded view of process chamber 850 is shown in FIG. 32.
A wafer carrier 866 supports a wafer above process nozzle 858.
Wafer carrier 866 is connected with an arm 868, which translates
the wafer carrier to move the wafer through the particle stream
emanating from the reaction zone where the laser beam intersects
the precursor stream from process nozzle 858. Arm 868 includes a
linear translator that is shielded with a tube. A laser entry port
870 is used to direct a laser beam between process nozzle 858 and
the wafer. Unobstructed flow from process nozzle would proceed
directly to exhaust nozzle 872, which leads to particle transport
tube 860.
[0251] An expanded view of wafer carrier 866 and process nozzle 858
is shown in FIG. 33. The end of process nozzle 858 has an opening
for precursor delivery 874 and a shielding gas opening 876 around
precursor opening to confine the spread of precursor and product
particles. Wafer carrier 866 includes a support 878 that connects
to process nozzle 858 with a bracket 880. A circular wafer 882 is
held in a mount 884 such that wafer 882 slides within mount 884
along tracks 886 to move wafer 882 into the flow from the reaction
zone. Backside shield 888 prevents uncontrolled deposition of
particles on the back of wafer 882. Tracks 886 connect to arm 868.
An alternative embodiment, not used for the present examples is
shown in FIG. 34. In the embodiment of FIG. 34, wafer 890 is held
with a wafer carrier 892 at an angle relative to the flow from
process nozzle 858. Linear translator 894 is placed at a similar
angle to move wafer 890 through the flow at the selected angle.
[0252] SiO.sub.2 was coated onto a silicon wafer by light reactive
deposition. The reaction was carried out in a chamber comparable to
the chamber shown in FIGS. 30-33 with a precursor delivery system
similar the system shown schematically in FIG. 5. Silicon
tetrachloride (Strem Chemical, Inc., Newburyport, Mass.) precursor
vapor was carried into the reaction chamber by bubbling N.sub.2
carrier gas through SiCl.sub.4 liquid in a container at room
temperature. Dopants for the ultimate silica glass were also
introduced by bubbling N.sub.2 carrier gas through liquid
precursors. Dopant precursors were POCl.sub.3 and/or GeCl.sub.4.
Argon gas was mixed with the reactant stream as a diluent/inert gas
to moderate the reaction. C.sub.2H.sub.4 gas was used as a laser
absorbing gas. O.sub.2 was used as an oxygen source and was mixed
with the reactants. The reactant gas mixture containing SiCl.sub.4,
argon, nitrogen, dopant precursor (POCl.sub.3 and/or GeCl.sub.4)
and C.sub.2H.sub.4 was introduced into the reactant gas nozzle for
injection into the process chamber.
[0253] During a run, the wafer was moved through the product stream
twice at a rate of 0.5 to 1.0 cm/sec. A majority of the powder
produced was deposited on the wafer with a portion collected in the
pumping system. Representative reaction conditions for the
production of silicon oxide coatings are described in Table 1.
1 TABLE 1 Sample 1 2 Pressure (Torr) 500 350 Ar-Win (slm) 10 10
Ar-Sld. (slm) 2.8 2.8 Ethylene (slm) 0.75 0.75 Carrier Gas for 0.41
0.41 SiCl.sub.4-N.sub.2 (slm) Carrier Gas for POCl3 0.992 1.24
POCl.sub.3-N.sub.2 (slm) Carrier Gas for 0 0.2 GeCl.sub.4 (slm)
Oxygen (slm) 1.268 1.268 Argon Dilution Gas 5.88 5.88 (slm) Laser
Power - Input 1200 1200 (watts) Laser Power - Output 995 1000
(watts) Run Time (minutes) 10 10 slm = standard liters per minute
Argon - Win. = argon flow through inlets positions in tubes holding
the laser windows. Argon - Sld. = argon flow as shielding gas
surrounding the reactant flow.
[0254] Following completion of the coating run, the wafers appeared
to have a powdery white coating that appeared uniform across the
surface of the wafer. The coating had a thickness of roughly 5 to 6
microns, as measured by scanning electron microscopy (SEM).
[0255] The coated wafers were heated in an oven at 1300.degree. C.
for 2 hours. After being removed from the oven, the wafers had a
clear glass on their surface. The root mean square (RMS) surface
roughness s low as about 0.25 to about 0.5 nm was achieved on some
wafers. Surface roughness was measured using atomic force
microscopy with a 20 by 20 micron scan on a 3000 AFM Instrument
from Veeco Instruments, Inc.
[0256] The embodiments described above are intended to be
illustrative and not limiting. Additional embodiments are within
the claims below. Although the present invention has been described
with reference to specific embodiments, workers skilled in the art
will recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *