U.S. patent application number 16/918554 was filed with the patent office on 2020-10-22 for uniform chemical vapor deposition coating on a 3-dimensional array of uniformly shaped articles.
This patent application is currently assigned to 3M Innovative Properties Company. The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Bill H. Dodge, Nicholas T. Gabriel, Arokiaraj Jesudoss, Robert R. Kieschke, Erin A. McDowell, Andrew J. Ouderkirk, Max Powers.
Application Number | 20200333523 16/918554 |
Document ID | / |
Family ID | 1000004931144 |
Filed Date | 2020-10-22 |
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United States Patent
Application |
20200333523 |
Kind Code |
A1 |
Ouderkirk; Andrew J. ; et
al. |
October 22, 2020 |
UNIFORM CHEMICAL VAPOR DEPOSITION COATING ON A 3-DIMENSIONAL ARRAY
OF UNIFORMLY SHAPED ARTICLES
Abstract
A coated optical element has at least six contact points not all
in a same plane. Each contact point is an optical point of contact.
Adjacent contact points subtend an angle between about 25 to about
35 degrees at a center of the coated optical element.
Inventors: |
Ouderkirk; Andrew J.;
(Kirkland, WA) ; Powers; Max; (Minneapolis,
MN) ; Gabriel; Nicholas T.; (Woodbury, MN) ;
Dodge; Bill H.; (Finlayson, MN) ; McDowell; Erin
A.; (Afton, MN) ; Kieschke; Robert R.;
(Woodbury, MN) ; Jesudoss; Arokiaraj; (Singapore,
SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
1000004931144 |
Appl. No.: |
16/918554 |
Filed: |
July 1, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15105949 |
Jun 17, 2016 |
10739503 |
|
|
PCT/US2014/070507 |
Dec 16, 2014 |
|
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16918554 |
|
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61921238 |
Dec 27, 2013 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 27/283 20130101;
C23C 16/458 20130101; C23C 16/45546 20130101; C23C 16/442 20130101;
G02B 1/08 20130101; H01L 2933/0025 20130101; G02B 5/3083 20130101;
C23C 16/45502 20130101; G02B 27/14 20130101 |
International
Class: |
G02B 5/30 20060101
G02B005/30; C23C 16/455 20060101 C23C016/455; C23C 16/458 20060101
C23C016/458; C23C 16/442 20060101 C23C016/442; G02B 1/08 20060101
G02B001/08; G02B 27/14 20060101 G02B027/14; G02B 27/28 20060101
G02B027/28 |
Claims
1. A coated optical element having at least six contact points not
all in a same plane, each contact point being an optical point of
contact, wherein adjacent contact points subtend an angle between
about 25 to about 35 degrees at a center of the coated optical
element.
2. The coated optical element of claim 1, wherein the coated
optical element has at least twelve contact points.
3. The coated optical element of claim 1, wherein adjacent contact
points subtend an angle of about 30 degrees at the center of the
coated optical element.
4. The coated optical element of claim 3, wherein for each contact
point, the contact point and a closest adjacent contact point
subtend an angle of about 30 degrees at the center of the coated
optical element.
5. A three-dimensional array of optical elements, each optical
element being a coated optical element according to claim 1.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional patent application Ser. No.
15/105,949, filed Jun. 17, 2016, now allowed, which is a national
stage filing under 35 U.S.C. 371 of PCT/US2014/070507, filed Dec.
16, 2014, which claims the benefit of Provisional Patent
Application No. 61/921,238, filed Dec. 27, 2013, expired, the
disclosures of which are incorporated by reference in their
entirety herein.
TECHNICAL FIELD
[0002] The present invention is related generally to methods of
coating. In particular, the present invention is a method of
applying a coating onto uniformly shaped and sized articles.
BACKGROUND
[0003] In a remotely illuminated phosphor package, light from one
or more ultraviolet or blue pump LEDs is imaged by a hemispherical
lens onto a phosphor-containing layer that is approximately
adjacent and coplanar to the LEDs. Excellent color uniformity for a
single LED, and within a lot of LEDs can be achieved by using
precise and accurate optical coatings over the surface of the
hemispherical surface that reflect a large percentage of blue light
and transmit a high percentage of red and green light.
[0004] Two methods of making optical coatings have proved to
provide the necessary coating precision and accuracy required with
remotely illuminated phosphor packages; low pressure chemical vapor
deposition (LPCVD) and atomic layer deposition (ALD). LPCVD uses
reactive gases at about 1 Torr of pressure to deposit typically
inorganic oxide coatings on a refractory surface. LPCVD provides
high deposition speeds and excellent coating uniformity over a
single optical element. LPCVD deposition is determined by reaction
kinetics at solid surfaces, so gas velocity and history affect
coating speed. The effect of the flow history has a significant
effect on coating precision. ALD uses saturated physisorption or
chemisorption, or a combination of both, to limit coating thickness
in any one coating step. Very accurate and precise coatings can be
produced using ALD, assuming that all surfaces have enough exposure
to the reactant to develop a saturated adsorbed layer of reactant
or reactant-modified surface, and that the purge time is sufficient
to remove excess reactant and reaction products.
[0005] Both coating processes can be relatively time consuming,
with LPCVD taking 1 or more hours to develop a micron thick
coating, and ALD taking 10 hrs or more for the same coating
thickness. Therefore, in order to produce low cost coatings, a
significant number of optical elements must be coated at the same
time. However, loading a number of optical elements into a reactor
can create non-uniform gas flows. For LPCVD, this can cause some
optical elements to have too thick a coating, and some elements too
thin a coating. While ALD is less affected by the non-uniform gas
flow, the coating time can be substantially lengthened due to the
fact that the optical element surface receiving the least amount of
gas flow limits the coating speed.
[0006] The way that the optical elements fill the reactor can also
have a significant effect on coating cost and quality. For example,
a regular array with spaces can give high quality coatings, but at
the cost of lower packing density. Reducing packing density reduces
the potential throughput of the system, and assuming that the
substrates or optical elements take up volume, can increase mixing
within the reactor. Mixing can increase reactant and purge cycle
times in ALD systems. Reduced packing density also reduces
throughput of both ALD and LPCVD systems.
[0007] Another approach to filling reactors is to create a randomly
packed volume of elements. This approach is used for coating
powders. One advantage of random packing is that the reactor is
inexpensive to build and can be quickly filled and emptied. A
disadvantage is that random packing has a lower packing density
than when the elements are packed in a regular array. Regular
arrangements can include face-centered cubic (FCC) or hexagonal
close pack (HCP) arrays. While the lower packing density can have
the advantage of lowering flow resistance, this benefit comes at a
significant cost of increased reactant volume, commensurately lower
flow rates, and non-uniformity of flow. FIGS. 1A and 1B show a
simulation of the flow profile through an ALD reactor 10. FIG. 1A
shows the reactor filled with a HCP array of spheres 12. FIG. 1B
shows a top, cross-sectional view of the spheres in FIG. 1A.
Throughout the specification, the shading indicates velocity, with
lighter shading (blue) indicating low velocity and darker shading
(red) indicating high velocity. Thus, in FIGS. 1A and 1B, the
lighter shading (blue) between the spheres indicates low velocity,
the medium shading (green) around the perimeter of the cluster of
spheres indicates medium velocity, and the darker shading (red) at
the very outer perimeter of the reactor indicates high velocity.
The flow conditions are an outlet pressure of 1 Torr, 20 sccm
(standard cubic centimeters per minute) of nitrogen, and the
reactor temperature is 200.degree. C. The simulation was made with
Solidworks 2012 flow simulator sold by Dassault Systemes Corp,
Velizy, France.
SUMMARY
[0008] In one embodiment, the present invention is a method of
coating uniformly shaped and sized articles. The method includes
providing a reactor having an arrayed inner surface, positioning
the articles within the reactor, and coating the articles.
[0009] In another embodiment, the present invention is a reactor
for coating uniformly shaped and sized articles. The reactor
includes an inner arrayed surface, wherein the inner arrayed
surfaces matches a profile of adjacent articles.
[0010] In yet another embodiment, the present invention is an
article having a plurality of contact points. Adjacent contact
points are spaced between about 25 to about 35 degrees from each
other.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A shows a perspective view of a simulated flow profile
through a prior art ALD reactor.
[0012] FIG. 1B shows a top view of the simulated flow profile
through the prior art reactor of FIG. 1A.
[0013] FIG. 2A shows a perspective view of a simulated flow profile
through a first embodiment of a reactor of the present
invention.
[0014] FIG. 2B shows a top view of the simulated flow profile
through the first embodiment of the reactor of FIG. 2A.
[0015] FIG. 3A shows a perspective view of a simulated flow profile
through a second embodiment of a reactor of the present
invention.
[0016] FIG. 3B shows a top view of the simulated flow profile
through the second embodiment of the reactor of FIG. 3A.
[0017] FIG. 4 shows a top view of a first layer of optical elements
in an exemplary full transition boundary reactor.
[0018] FIG. 5A shows a cross-sectional view of the impact of
eliminating a single optical element from a packed array.
[0019] FIG. 5B shows an enlarged cross-sectional view of the impact
of eliminating a single optical element from the packed array of
FIG. 5B.
[0020] FIG. 6 shows a cross-section of the impact of eliminating a
single optical element from a packed array of FIGS. 5A and 5B.
[0021] FIG. 7 shows a top view of a randomly packed volume within a
reactor.
[0022] FIG. 8 shows a first step of packing a reactor of the
present invention using a first method.
[0023] FIG. 9 shows a second step of packing a reactor of the
present invention using a first method.
[0024] FIG. 10 shows a third step of packing a reactor of the
present invention using a first method.
[0025] FIG. 11 shows a second method of packing a reactor of the
present invention.
[0026] FIG. 12 shows a cross-sectional view of an exemplary
simulated flow profile of a full transition boundary reactor.
[0027] FIG. 13 shows a cross-sectional view of an exemplary
simulated flow profile of a full transition boundary reactor.
[0028] FIG. 14 shows a cross-sectional view of the exemplary
simulated fully developed velocity profile of the full transition
boundary reactor of FIG. 13 at 0.2 seconds.
[0029] FIG. 15 shows a cross-sectional view of the exemplary
simulated volume fraction of reactant of the full transition
boundary reactor of FIG. 13 at 0.2 seconds.
[0030] FIG. 16 shows a cross-sectional view of the exemplary
simulated volume fraction of reactant of the full transition
boundary reactor of FIG. 13 at 1 second.
[0031] FIG. 17 shows a cross-sectional view of the exemplary
simulated volume fraction of reactant of the full transition
boundary reactor of FIG. 13 at 2 seconds.
[0032] These figures are not drawn to scale and are intended merely
for illustrative purposes.
DETAILED DESCRIPTION
[0033] The reactor and method of the present invention allow a
plurality of articles, such as optical elements, to be uniformly
and efficiently coated. The reactor also allows simultaneous
coating of a plurality of optical elements in part by allowing a
uniform reaction between two reactants. Reactors that have very
uniform and reproducible flow conditions have the advantages of
higher coated optical element yields and rates and reduced
inspection requirements. For example, very uniform and reproducible
flow conditions allow shorter purge times for atomic layer
deposition (ALD) cycles, resulting in shorter overall coating time
and lower cost. It should be noted that while the figures and
specification depict and refer to the optical elements as hexagonal
glass spheres, the optical elements may be of any shape and made of
any material without departing from the intended scope of the
present invention. For example, the optical elements may be
spheres, lenses, or other shapes. In addition, although the
specification refers to the articles as optical elements, the
articles may be any element to be uniformly coated.
[0034] FIGS. 2A and 2B show a schematic perspective view and a top
view, respectively, of one embodiment of a reactor 20 of the
present invention and the flow profiles created by the reactor. The
side walls 22 and top wall 24 of the reactor 20 are designed to be
adjacent to the outermost optical elements 26 in the reactor 20. As
can be seen by the shading in FIGS. 2A and 2B, when the walls 22,
24 of the reactor 20 are adjacent to the optical elements 26, the
reactant is effectively directed through the array of the optical
elements 26, creating a more uniform flow. In the construction of
the reactor 20 shown in FIGS. 2A and 2B, excess volume is
eliminated, creating a semi-infinite boundary condition. In a
semi-infinite boundary condition, there are higher flow rates along
the sides of the reactor due to increased spacing between the
outermost optical elements 26 and the reactor walls 22, 24.
[0035] While the reactor design shown in FIGS. 2A and 2B show
improved flow design over the prior art design shown in FIGS. 1A
and 1B, there is still some non-uniformity of flow with a
semi-infinite boundary condition. For example, in a low pressure
chemical vapor deposition (LPCVD) system, the optical elements 26
near the reactor walls 22, 24 are adjacent to high-velocity gas
flows and may develop a relatively thick optical coating.
Alternatively, in an ALD system, the optical elements near
lower-velocity gas flows will have lower exposure to reactants and
purge gas, increasing the amount of time required to deposit the
desired coating.
[0036] The reactor design can be further improved by using a more
symmetrical array of optical elements and by extending the
repeating boundary conditions from the sides of the reactor to at
least one of the entrance or the exit of the reactor. FIGS. 3A and
3BA show a schematic perspective view and a top view, respectively,
of a second embodiment of a reactor 30 and the flow profiles
created by the reactor 30 in which the repeating boundary
conditions are extended from the sides walls 32 of the reactor 30
to at least one of the entrance 34 or the exit 36 of the reactor
30. The flow profiles of the reactor shown in FIGS. 3A and 3B show
that creating an infinite boundary condition on the four walls that
are perpendicular to the average flow direction can substantially
improve the flow velocity around the optical elements. The flow
between the spheres is at high velocity and substantially
uniform.
[0037] FIG. 4 shows a perspective, top view of a first layer of
optical elements 26 in an exemplary full transition boundary
reactor 40. The full transition boundary reactor 40 has side 42,
bottom 44 (not shown) and top walls 46 (not shown) that are arrayed
and correspond and conform to the shape of the outermost optical
articles 26, creating an infinite boundary condition. Arrayed
surfaces are surfaces that extend the structure of the optical
elements 26. The arrayed surfaces provide a transition from the
reactor walls 42, 44, 46 to the arrayed optical elements 26, where
reactant flow adjacent to the optical elements 26 next to the
reactor walls 42, 44, 46 is similar to the flow for optical
elements 26 that are surrounded by other optical elements 26. This
infinite boundary condition is present in a full transition
boundary reactor. Thus, the full transition boundary reactor 40 has
bottom 44 and side walls 42 with arrayed surface structures of
partial spheres. An infinite boundary condition can be
accomplished, for example, by machining the surface areas of the
reactor and then loading the reactor with the optical elements.
[0038] In an infinite boundary condition, the minimum gas flow
velocity for a given optical element is similar to the average gas
flow velocity for all optical elements. This provides a benefit for
both ALD and LPCVD processes. With ALD, the coating rate is
partially determined by reactant-purge cycle time, which is
determined by the lowest reactant exposure and slowest purge time,
so reducing the difference between the minimum and average gas flow
velocities reduces the overall ALD coating time. This small
difference will also improve LPCVD coating variations. In addition,
the maximum gas flow velocity for a given optical element is
similar to the average gas flow velocity for all optical elements.
This improves LPCVD coating variability, increases the utilization
of reactants in either process, and improves purging between
coating cycles in ALD. The infinite boundary condition also
produces nearly plug flow conditions which allows a uniform
reaction between reactants in ALD. This allows the reactor to be
used in a hybrid mode between ALD and LPCVD, where a reactant is
not fully purged before the next reactant flow begins. Another
advantage of the infinite boundary condition is that the uniformity
of coating between optical elements allows the possibility of doing
quality assurance through audits rather than 100% inspections,
particularly if the entrance and exit rows are separated from the
rest of the optical elements.
[0039] As an example, a conservative ALD half cycle for a small
reactor may be 0.2 seconds of reactant flow (A or B) followed by 20
seconds of purge (P). The purpose of the purge is to remove excess
reactant and reaction products from the surfaces of the optical
elements and from the reactor between reactant half cycles.
Reducing purge time is an effective way to reduce cost. As the
purge time is reduced for a given reactor, the reactants A and B
will begin reactions outside the pure ALD mode where saturated
sub-monolayers form during each half cycle. In other words, the
reactants A and B will begin to react through a combination of
reactants in the gas phase, or react to multiple adsorbed layers on
the optical elements. These reactions can be acceptable, or even
desirable if they are uniform in the reactor.
[0040] The manner in which the optical elements are packed in the
reactor is critical. FIGS. 5A and 5B show the impact of eliminating
a single optical element 50 in a packed array. FIG. 6 shows a
cross-sectional view of the reactor conditions of FIGS. 5A and 5B.
As can be seen in the figures, even a single defect can have a
substantial effect on flow. As shown in the figures, there is a
region of high velocity at the location of the missing optical
element and a region of lower velocity to the right. This
difference in velocity can result in longer cycle times and/or
non-uniform deposition. A series of defects can further aggravate
the issue. In addition, as the size of the optical elements
decreases and a larger number of optical elements exist within a
given volume, defects may become even more prominent.
[0041] In addition to defects, the fixed reactor diameter requires
that the packed optical elements fit within the dimensions of the
boundary wall such that the packed optical elements have a diameter
that substantially fits within a diameter of the reactor. For
example, if the diameter (or other suitable characteristic length)
of the optical elements on average is slightly larger than the
specified parameter, it would not be possible to fit the entire
array layer of optical elements within the boundaries. In such a
case, it may be necessary to replace one or more optical elements
with properly sized optical elements. Another option would be to
heat the reactor assembly to allow for thermal expansion of the
reactor. Heating can be continued up to the intended temperature at
which coating will take place. This assumes that the coefficient of
thermal expansion (CTE) of the reactor material is greater than
that of the optical elements being placed inside. In such a case,
extraction of the optical elements must also be done at the same
temperature. Allowing the system to cool may generate enormous
stress on the reactor and article array.
[0042] The reactor of the present invention allows for a coating to
be uniformly applied to uniformly shaped and sized optical
elements. In one embodiment, the coating is applied to the optical
elements in a chemical vapor deposition system where the reactor
forms a semi-infinite boundary condition for managing uniform
reactant flow for all optical elements in the three-dimensional
array. This is accomplished by having at least one wall surface of
the reactor being arrayed and in contact with the outermost layers
of the optical elements, causing reactant flow that is similar to
flow between optical elements.
[0043] FIG. 7 shows an example of a randomly packed volume within a
reactor 60. The optical elements 26, in this case spheres, are
packed in a combination of amorphous regions and crystalline
regions. As previously mentioned, randomly packing the reactor may
allow for either poor coating uniformity in a batch of spheres, or
slow coating time, or both. One way to increase reactor throughput
is to fill the reactor with a bimodal distribution of sizes of
optical elements. For example, 10 mm spheres can be combined with 4
mm spheres to increase packing density. In a first method of the
present invention of packing a reactor 70, the reactor is filled
using layer by layer packing and assembly. Utilizing a reactor with
a stackable modular design, the desired packing can be achieved by
first stacking the base and a single side wall boundary 72 as shown
in FIG. 8.
[0044] The optical elements 26 can be dispensed, for example, from
a reservoir of optical elements existing in a randomly packed
state, into a first layer of the reactor at a controlled rate. The
optical elements 26 can be dispensed by any means known in the art,
for example, via a funnel, manually, or an automated dispensing
process. In one embodiment, the optical elements 26 fill the
reactor one-by-one from some height above the plane of the base
component 74, within the perimeter of the side wall 72, as shown in
FIG. 9. In one embodiment, as optical elements 26 are being
dispensed into the reactor 70, vibrations of suitable magnitude and
frequency may be imposed on the reactor 70 via mechanical means or
sound. The vibrations serve to offset any optical elements 26 that
may have started to stack more than one layer high and have them
fall into a lower gravitational state. These vibrations may be
axial and/or radial in nature. As an alternative to reactor
vibration, manual manipulation of the dispensed optical elements
can also be performed.
[0045] Dispensing and vibration continues until the exact number of
optical elements which can fit within the first layer of the
reactor have been dispensed and the first layer of optical elements
is free from defects. After the defect free packing of the first
layer has been completed, a second reactor wall section can be
added as shown in FIG. 10. The process of dispensing and stacking
can be repeated until the desired array size has been reached.
[0046] In a second method for packing a reactor 80, the reactor 80
is filled using layer by layer packing. Starting with a reactor
that has the base 84 and all side wall 82 boundaries in place, as
shown in FIG. 11, the specific number of optical elements 26 which
are to fit in the first layer of the crystalline array are
dispensed into the top of the reactor 80. In one embodiment, the
optical elements are dispensed from a randomly packed reservoir.
The optical elements can be poured from a container into the
reactor, or dispensed one by one via a funnel or other means. As
described in the first method, a vibration input may be applied in
order to assist the proper formation of a crystalline layer without
defects. Once the first layer has been built, a second round of
optical elements is dispensed on top of the first layer. The
process is repeated layer by layer until the reactor is filled to
the top layer. In one embodiment, each layer may be coated with a
material that can reduce the probability of scratching during each
layer stacking process.
[0047] In a third method for packing a reactor, the reactor is
filled using continuous filling. Starting with the same reactor
setup as shown in FIG. 11, optical elements can be dispensed into
the reactor at a constant rate until the entire reactor is filled.
Unlike the first and second methods which dispense only a single
layer of optical elements at a time, the dispense rate would be
higher with this third method. Once again, as the optical elements
are being dispensed, a vibration input may be simultaneously
supplied to allow the optical elements to fall into proper
alignment. In one embodiment, the dispensing rate may be slowed as
the reactor approaches capacity in order to allow remaining defects
or voids to fill and to allow more optical elements to be
dispensed.
[0048] In a fourth method for packing the reactor, the reactor is
filled using fully automated placement. A robotic dispensing
apparatus which has a xyz programmable movement, in conjunction
with an optical elements feeding mechanism, can place individual
optical elements in precise locations one at a time. The automated
process would dispense optical elements in a radial or linear
fashion one layer at a time. This may be accomplished using a
reactor layout that is built layer by layer as well, or using an
assembled reactor layout as shown in FIG. 11 if the feed/dispenser
head has an additional control axis.
[0049] The optical elements coated by the reactor and method of the
present invention result in observable markings due to the geometry
of how they are packed into the reactor. An optical point of
contact of an optical element is defined as a point in which the
coating is significantly different than the average coating
structure. A regular point of contact of an optical element is
defined as a point which is spaced between about 25 to about 35
degrees from the closest adjacent optical point of contact. In one
embodiment, each optical point of contact is spaced about 30
degrees from the closest adjacent optical point of contact.
Adjacent contact points are therefore spaced about 25 to about 35
degrees from each other, and particularly about 30 degrees from
each other. The optical elements coated by the reactor and methods
of the present invention have at least three regular points of
contact in a 3-dimensional array. In some embodiments, the optical
elements have at least six regular points of contact. In another
embodiment, the optical elements have at least twelve regular point
of contact. In one embodiment, at least 80% of the optical elements
coated in a reactor by a method of the present invention have at
least six regular points of contact.
[0050] The regular points of contact may be visible in some
applications and thus, it may be desirable to position them on the
optical elements in a way that minimizes impact. For example, the
regular points of contact may be arranged such that the light
transmitted by the regular points of contact are positioned where
there will be minimal impact. Because the optical elements are not
randomly arranged in the reactor, they can be appropriately
positioned.
[0051] Optical elements with a dichroic coating have regular and
repeated observable fiducials on the coating. In one embodiment,
the dichroic coating on the optical elements covers at least 90% of
the area of a sphere, a hemisphere, or a hemisphere truncated such
that it has at least 40% of the thickness of a corresponding
sphere, where the band edge varies by less than 5 nm over the
surface and from spherical surface to spherical surface within the
lot.
Examples
[0052] The present invention is more particularly described in the
following examples that are intended as illustrations only, since
numerous modifications and variations within the scope of the
present invention will be apparent to those skilled in the art.
Unless otherwise noted, all parts, percentages, and ratios reported
in the following example are on a weight basis.
[0053] FIG. 12 shows a first embodiment of a full transition
boundary reactor 90. The atomic layer deposition (ALD) reactor flow
was simulated using Solidworks Flow simulation version 2012
(available from Dassault Systemes Solidworks Corp, Waltham, Mass.,
USA). As can be seen by the flow simulations of the reactor under
typical ALD conditions (1 Torr pressure, 200.degree. C., 20 sccm of
N2 carrier gas), the volume of the diffuser section at the top 92
of the reactor mixes the reactant with the purge gas--reducing the
desired plug-flow conditions. The volume of the reactor may be
increased to reduce the per-optical element coating cost.
[0054] FIG. 13 shows a second embodiment of a full transition
boundary reactor with improved flow (i.e lower volume and mixing)
and improved manufacturability. In the second embodiment, the gas
flow occurs from the left and goes to the top 102 of the reactor
and flows out the bottom 104. The reactor 100 works most
efficiently in medium to low vacuum to just above atmospheric
pressure. For example, the reactor 100 can operate at between about
0.1 Torr to above about 1 atmospheric pressure. In the simulation
shown in FIG. 13, the ALD reactor flow was simulated with the
boundary conditions being 20 sccm of a mixture of 21% oxygen and
79% nitrogen (air) for 0.20 seconds, followed with a 3 second purge
of 100% nitrogen at the same flow rate. The bottom exhaust boundary
condition was set for 1 Torr pressure. The reactor, the glass
spheres, and the incoming gas were all set to 200.degree. C.
[0055] FIG. 14 shows the fully developed gas velocity profile of
the reactor 100 of FIG. 13 at 0.2 seconds after starting the
simulation. As can be seen in FIG. 14, the gas velocity is highly
uniform across the cross-section of the reactor 100. The first row
of spheres shown in FIGS. 13 and 14 is a permanent part of the
reactor 100, serving both as a flow diffuser and to establish flow
profiles similar to that of the rest of the reactor 100.
[0056] FIGS. 15, 16, and 17 show that the "simulated reactant"
(simulated as air, relative to the background flow of pure nitrogen
gas) flows through the reactor 100 with a uniform profile, i.e.
plug flow. FIG. 17 shows a fraction of simulated reactant (air) at
0.2 seconds. The darker (red) shading is 1.0 or 100% reactant and
the lighter (blue) shading is 0 or 0% reactant, indicating that the
reactant just reached the initial optical elements. FIG. 18 shows a
fraction of simulated reactant at 1 second. The darker (red)
shading is 0.0544 or 5.44% reactant concentration and the lighter
(blue) shading is 0 or 0%, indicating that the inlet line of the
reactor has been fully purged. FIG. 19 shows a fraction of
simulated reactant at 2 seconds. The darker shading is 0.0544 or
5.44% reactant concentration and the lighter shading is 0 or 0%,
indicating that the inlet line of the reactor has been fully purged
and has much of the inlet port of the mixing manifold. As can be
seen in the figures, while the low pressure and high temperature
lead to a great deal of diffusion, the exposure of the optical
elements is uniform from the beginning (top) to the end (bottom) of
the reactor.
[0057] Although the present invention has been described with
reference to preferred 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.
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