U.S. patent application number 11/936929 was filed with the patent office on 2008-03-13 for conformal coatings for micro-optical elements.
This patent application is currently assigned to Planar Systems, Inc.. Invention is credited to Jarmo Ilmari Maula, Runar Olof Ivar Tornqvist.
Application Number | 20080063802 11/936929 |
Document ID | / |
Family ID | 33096999 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080063802 |
Kind Code |
A1 |
Maula; Jarmo Ilmari ; et
al. |
March 13, 2008 |
CONFORMAL COATINGS FOR MICRO-OPTICAL ELEMENTS
Abstract
A micro-optical element is produced through vapor deposition
techniques, such as atomic layer deposition. An optical structure
having a surface with uneven structures is exposed to one or more
precursor vapors to create a self-limiting film growth on the
surface of the optical structure. The film thickness may be
increased and controlled by subsequent exposures. The resulting
film conforms to surface structures having varying complex
dimensions.
Inventors: |
Maula; Jarmo Ilmari; (Espoo,
FI) ; Tornqvist; Runar Olof Ivar; (Kauniainen,
FI) |
Correspondence
Address: |
STOEL RIVES LLP
900 SW FIFTH AVENUE
SUITE 2600
PORTLAND
OR
97204-1268
US
|
Assignee: |
Planar Systems, Inc.
Beaverton
OR
|
Family ID: |
33096999 |
Appl. No.: |
11/936929 |
Filed: |
November 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10404928 |
Mar 31, 2003 |
7294360 |
|
|
11936929 |
Nov 8, 2007 |
|
|
|
Current U.S.
Class: |
427/301 |
Current CPC
Class: |
G02B 1/113 20130101;
Y10T 428/24612 20150115; H01S 5/028 20130101; G02B 1/10 20130101;
C23C 16/45525 20130101; C23C 16/45555 20130101 |
Class at
Publication: |
427/301 |
International
Class: |
B05D 3/10 20060101
B05D003/10 |
Claims
1. A method for fabricating a micro-optical element, comprising:
providing an optical structure, the optical structure comprising a
trench having vertical and horizontal dimensions less than the
wavelength of the entire range of infrared light; placing the
optical structure into a reaction space; forming a self-limiting
film of uniform thickness comprising first and second film layers,
the self-limiting film conforming to the trench of the optical
structure, and defining a filmed trench, wherein forming the
self-limiting film includes, introducing a first chemical into the
reaction space such that a portion of the first chemical adsorbs
onto the trench of the optical structure and forms a first film
layer, after introducing the first chemical, purging the reaction
space, introducing a second chemical into the reaction space such
that a portion of the second chemical reacts with the adsorbed
first chemical to form a second film layer, and after introducing
the second chemical, purging the reaction space.
2. The method of claim 1 wherein the optical structure is a
diffractive optical structure.
3. The method of claim 1 wherein the optical structure is a
refractive optical structure.
4. The method of claim 1 wherein the optical structure is selected
from the group consisting of a beam shaper, beam splitter,
microlens, microlens array, diffuser, laser diode corrector,
pattern generator, collimator, grating device, DNA chip, biochip,
optical filter, waveguide, optical attenuator, gain flattening
filter, gray shade filter, image sensor and anti-reflective coating
structures.
5. The method of claim 1 wherein the optical structure is disposed
on a light detecting device.
6. The method of claim 5 wherein the light detecting device is
selected from the group consisting of: light diode, solar cell, CCD
device, CMOS device and an integrated circuit.
7. The method of claim 1 wherein the self-limiting film is selected
from the group consisting of: antireflection coating, optical low
pass filter, optical high pass filter, optical bandpass filter,
optical bandreject filter, waveguide, optical attenuator, gain
flattening filter, gray scale filter or a passivation layer.
8. The method of claim 1 wherein the optical structure includes a
material selected from the group consisting of acrylic, epoxy,
fuoro polymer, polyamide, polyimide, polystyrene, polyethylene,
polyethylene terephthalate, polyurethane, PTFE, polyolefins,
polycarbonate, polymethyl methacrylate (PMMA), EPON SU-8 epoxy
resin, organically modified silicates (Ormosils), nanomers,
plastics, and plexi-glass.
9. The method of claim 1 wherein the self-limiting film includes a
material selected from the group of TiO.sub.2, Al.sub.2O.sub.3,
HfO.sub.2, ZnO, SiO.sub.2, Ta.sub.2O.sub.5, and
Nb.sub.2O.sub.5.
10. The method of claim 1 wherein the self-limiting film includes a
layered structure of TiO.sub.2 and Al.sub.2O.sub.3.
11. The method of claim 1 wherein the trench has an aspect ratio of
approximately 1 to 10.
12. The method of claim 1 wherein introducing the first and second
chemicals into the reaction space includes using an inert carrier
gas selected from the group consisting of nitrogen, helium, neon,
argon, and carbon dioxide.
13. The method of claim 1 further comprising flowing an inert gas
through the reaction space.
14. A method for fabricating a micro-optical element, comprising:
providing an optical structure, the optical structure comprising an
optic including a trench having vertical and horizontal dimensions
less than the wavelength of the entire range of infrared light;
placing the optical structure into a reaction space; forming a
self-limiting film of uniform thickness comprising first and second
film layers, the self-limiting film conforming to the trench of the
optic, and defining a filmed trench, wherein forming the
self-limiting film includes, introducing a first chemical into the
reaction space such that a portion of the first chemical adsorbs
onto the trench of the optic and forms a first film layer, after
introducing the first chemical, purging the reaction space,
introducing a second chemical into the reaction space such that a
portion of the second chemical reacts with the adsorbed first
chemical to form a second film layer, and after introducing the
second chemical, purging the reaction space.
15. The method of claim 14 wherein the optical structure is a
diffractive optical structure.
16. The method of claim 14 wherein the optical structure is a
refractive optical structure.
17. The method of claim 14 wherein the optical structure is
selected from the group consisting of a beam shaper, beam splitter,
microlens, microlens array, diffuser, laser diode corrector,
pattern generator, collimator, grating device, DNA chip, biochip,
optical filter, waveguide, optical attenuator, gain flattening
filter, gray shade filter, image sensor and anti-reflective coating
structures.
18. The method of claim 14 wherein the optical structure is
disposed on a light detecting device.
19. The method of claim 18 wherein the light detecting device is
selected from the group consisting of: light diode, solar cell, CCD
device, CMOS device and an integrated circuit.
20. The method of claim 14 wherein the self-limiting film is
selected from the group consisting of: antireflection coating,
optical low pass filter, optical high pass filter, optical bandpass
filter, optical bandreject filter, waveguide, optical attenuator,
gain flattening filter, gray scale filter or a passivation
layer.
21. The method of claim 14 wherein the optical structure includes a
material selected from the group consisting of acrylic, epoxy,
fuoro polymer, polyamide, polyimide, polystyrene, polyethylene,
polyethylene terephthalate, polyurethane, PTFE, polyolefins,
polycarbonate, polymethyl methacrylate (PMMA), EPON SU-8 epoxy
resin, organically modified silicates (Ormosils), nanomers,
plastics, and plexi-glass.
22. The method of claim 14 wherein the self-limiting film includes
a material selected from the group of TiO.sub.2, Al.sub.2O.sub.3,
HfO.sub.2, ZnO, SiO.sub.2, Ta.sub.2O.sub.5, and
Nb.sub.2O.sub.5.
23. The method of claim 14 wherein the self-limiting film includes
a layered structure of TiO.sub.2 and Al.sub.2O.sub.3.
24. The method of claim 14 wherein the trench has an aspect ratio
of approximately 1 to 10.
25. The method of claim 14 wherein introducing the first and second
chemicals into the reaction space includes using an inert carrier
gas selected from the group consisting of nitrogen, helium, neon,
argon, and carbon dioxide.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. patent application
Ser. No. 10/404,928 filed on Mar. 31, 2003, and entitled "Conformal
Coatings for Micro-Optical Elements," which is hereby incorporated
by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to techniques for fabricating
optical elements and, more specifically, to techniques for
depositing thin films on optical elements having a surface with
uneven structures.
BACKGROUND OF THE INVENTION
[0003] Micron-scale fabrication has enabled the development of
micro-optical elements that are used in a variety of
optical-electronic applications. A micro-optical element (MOE)
offers compact, light-weight optics that can be mass-produced using
low cost replication techniques. With the given trend towards
miniaturization, these features are highly attractive. MOEs may be
refractive, such as microlenses and microlens arrays, and bend or
focus light according to geometric optics. MOEs may be diffractive,
such as phase plates, diffraction gratings, diffractive lenses, and
so forth, and alter light based on Fourier optics. MOEs may also be
mixed refractive/diffractive lenses which typically involves the
refractive lenses having a surface textured with diffracting
patterns.
[0004] MOEs include three-dimensional surface structures that are
typically based on complex mathematical modeling. Dimensional
accuracy and fabrication cost are important factors in production.
MOEs can be divided into two basic families: continuous relief and
binary, or multi-level, micro-optics. Continuous relief
microstructures have a smoothly varying surface profile between
multiple steps. Fabrication methods for continuous-relief
micro-optics include direct writing, such as by laser beam or
e-beam, direct machining, photoresist reflow, and gray tone
lithography. Binary optical elements have phase levels with a
number of steps and a flat surface of a constant height between the
steps. A common fabrication method for binary MOEs is a
high-resolution mask lithography and etching process.
[0005] MOEs are still an emerging technology that has not yet
developed a uniformly accepted nomenclature. The following
components are subgroups of micro-optical elements and include,
Diffractive Optical Element (DOE), Binary Optical Element (BOE),
Binary Optic, Microstructured Optic, grating, blazed grating,
fresnel element, micro-relief element, nanoperiodic surface
structures, refractive micro optics, subwavelength structure, and
subwavelength structured surface. As can be expected, each subgroup
has certain features specific to that group. As used herein, the
term MOE indicates all of the above-listed components. It is also
expected that there will be applications where MOEs will be
integrated on top of light detecting and light emitting devices and
integrated circuits.
[0006] DOEs are a broad class of optical components. Unlike
conventional optical components utilizing refraction and/or
reflection, DOEs utilize the wave nature of light and rely on
amplitude, phase, and the polarization state of light. With
diffractive optics, all these properties can be modified using
nano/micro structures. Diffraction structures on a surface can be
of several principles including binary, multi-level, continuous
profile, index modulated, and holographica.
[0007] All MOEs, either refractive or diffractive, have in common
that the wave nature of light is applied for their design and their
performance and tolerance modeling. Furthermore, all MOEs used
herein have three-dimensional surface structures with a dimension
of about 0.01 microns to about 10 micron.
[0008] A MOE may employ a film or coating disposed on its surface
structures for a variety of purposes. The film or coating may be a
semiconductor layer, insulator, metal contact, passivation layer,
anti-reflective coating, optical filter, waveguide or other
coating. The film or coating preferably follows a surface pattern
of the MOE. Otherwise, the functionality may be severely degraded,
or the element may be out of a specification range. In particular,
MOEs with structures having dimensions smaller than the wavelength
of light are difficult structures on which to apply conformal
coatings of uniform thickness. Such a structure is commonly
referred to herein as a subwavelength structure. Fabrication is
further complicated where such structures have high aspect
ratios.
[0009] A number of techniques exist to provide thin films and
coatings. These techniques include sputtering, evaporation, pulsed
laser ablation, oxidation, chemical vapor deposition,
electroplating, and other techniques commonly known in the art.
However, these conventional techniques are not able to provide
conformal coatings with uniform thickness for a subwavelength
structure.
[0010] Referring to FIG. 1, a cross-section view of a substrate 10
is shown wherein a thin film 12 is deposited by physical vapor
deposition (PVD). The PVD technique removes coating material from a
source using high temperature (evaporation) and/or bombards the
surface with highly energetic particles (sputtering). Removed
material particles have kinetic energy, and this kinetic energy is
used to transfer coating material onto the substrate 10. On an
atomic scale, sputtered atoms tend to travel in straight lines
without in-flight collisions from a cathode to the sample.
[0011] When coating material arrives on a substrate, its energy
does not allow extended movement on the substrate surface. As
shown, the thin film 12 does extend to a shadowed region 14 and
does not provide step coverage. This problem is pronounced where a
subwavelength structure is involved. The shadowed region 14 may be
caused by the shadow of the substrate 10 or even by the growing
thin film 12.
[0012] Methods to improve conformity involve rotating the substrate
10 or heating the substrate 10 to increase atom mobility. However,
the shadowed region will not be fully eliminated. Furthermore,
because PVD is based on flying material, there is always a "line of
sight" problem so that sides of walls are difficult to coat. In
case of high aspect ratio, good step coverage is impossible.
[0013] Referring to FIG. 2, a cross-sectional view is shown of a
structure 20 is shown having a trench 22. A thin film 24 is
deposited by chemical vapor deposition (CVD). CVD techniques use
continuous precursor flow to mix precursors in a reaction chamber
where a structure is placed. Energy is applied to the structure and
the precursor vapor to form a layer of a desired composition.
[0014] CVD methods have difficulties in applying very thin films
because the film does not always conform. As shown in FIG. 2, the
growth of the thin film 24 is not always uniform and does not
exactly follow the underlying surface. Voids 26 are created
underneath the film 26 as the trench 22 is filled. Thus, the
reliability of the CVD method for thin films is often in
question.
[0015] Referring to FIG. 3, a similar problem is shown wherein a
structure 30 includes a narrow trench 32. A thin film 34 is
deposited by a technique, such as by CVD, in order to completely
fill the trench 32. The thin film 34 pinches off at the opening 36
of the trench 32 before the trench 32 is completely filled. This
creates a void 38 within the trench 32 which destroys functionality
of the structure 30.
[0016] Referring to FIG. 4, another structure 40 is shown having
multiple step levels. A thin film 42 is deposited by sputtering.
Directionality of the sputtering is indicated by the arrows 44.
Directionality may be achieved by long distance origination and
mask and/or with ion beam sputtering. No side wall coating exists
where the film 42 is less than a step height.
[0017] Referring to FIG. 5, a structure 50 is shown similar to that
of FIG. 4. The sidewalls 52 are completely covered by increasing
the thickness of the film 54. This is, however, practical only in
applications having shallow steps and low aspect ratios.
[0018] Referring to FIG. 6, a structure 60 is shown with a trench
62 having a relatively high aspect ratio. Difficulties arise with
conventional techniques, such as CVD, in having a film 64 conform
to the deep trench 62. As shown, a void 66 occurs when the film 64
fails to fully conform to the trench 62.
[0019] Referring to FIG. 7, a structure 70 is shown with a thin
film 72 that is deposited by CVD or sputtering. The film 72
conforms poorly to the structure 70 and provides poor structural
dimensions.
[0020] The present inventors have recognized that the problems with
thin film depositions illustrated in FIGS. 1 to 7 often become even
more pronounced with subwavelength structures. Techniques for
overcoming void formations and providing controlled conformal
coatings would greatly improve the performance of micro-optical
elements. Such techniques would have particular application
beneficial for light transmissive optics that include
anti-reflective coatings.
SUMMARY OF THE INVENTION
[0021] The present invention utilizes vapor deposition techniques
to provide conformal film growth for a micro-optical element. The
film is deposited on an optical structure that is suitable for use
in a variety of applications, such as a beam shaper, beam splitter,
microlens, microlens array, diffuser, laser diode corrector,
pattern generator, collimator, grating device, DNA chip, biochip,
optical filter, waveguide, optical attenuator, gain flattening
filter, gray shade filter and anti-reflective coating structures.
The optical structure may be formed through any number of
conventional processing techniques.
[0022] In fabrication, an optical structure is placed in a reaction
chamber and exposed to a precursor vapor. The exposure creates a
chemical adsorption of a portion of a first chemical on the surface
of the optical structure. In one implementation, a purging gas is
introduced into the chamber to remove excess of the first chemical
and byproduct. A second chemical, different from the first
chemical, is introduced into the reaction chamber where it reacts
with the adsorbed first chemical to form a film conforming with the
surface of the optical structure.
[0023] The final film thickness is controlled by the number of
deposition cycles. Self-limiting growth provides excellent surface
conformance and allows coatings on high aspect ratio structures and
subwavelength structures. The present invention provides films that
are sufficiently thin and precise for practical applications for
MOEs. Furthermore, the resulting films are pinhole free, which is
necessary for functionality in certain applications.
[0024] Additional aspects and advantages of this invention will be
apparent from the following detailed description of preferred
embodiments, which proceeds with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Non-exhaustive embodiments of the invention are described
with reference to the figures in which:
[0026] FIG. 1 is a cross-sectional diagram of a MOE;
[0027] FIG. 2 is a cross-sectional diagram of a MOE;
[0028] FIG. 3 is a cross-sectional diagram of a MOE;
[0029] FIG. 4 is a cross-sectional diagram of a MOE;
[0030] FIG. 5 is a cross-sectional diagram of a MOE;
[0031] FIG. 6 is a cross-sectional diagram of a MOE;
[0032] FIG. 7 is a cross-sectional diagram of a MOE;
[0033] FIG. 8 is a cross-sectional view of a substrate reaction
chamber configured for deposition in accordance with the present
invention;
[0034] FIG. 9 is a cross-sectional diagram of a micro-optical
element;
[0035] FIG. 10 is a cross-sectional diagram of a micro-optical
element;
[0036] FIG. 11 is a graph illustrating the transmission spectrum of
a thin film produced by the techniques of the present
invention;
[0037] FIG. 12 is a graph illustrating the transmission spectrum of
another thin film produced by the techniques of the present
invention;
[0038] FIG. 13 is a graph illustrating the transmission spectrum of
another thin film produced by the techniques of the present
invention; and
[0039] FIG. 14 is a graph illustrating the transmission spectrum of
another thin film produced by the technique of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0040] Reference is now made to the figures in which like reference
numerals refer to like elements. For clarity, the first digit or
digits of a reference numeral indicates the figure number in which
the corresponding element is first used.
[0041] Throughout the specification, reference to "one embodiment"
or "an embodiment" means that a particular described feature,
structure, or characteristic is included in at least one embodiment
of the present invention. Thus, appearances of the phrases "in one
embodiment" or "in an embodiment" in various places throughout this
specification are not necessarily all referring to the same
embodiment.
[0042] Furthermore, the described features, structures, or
characteristics may be combined in any suitable manner in one or
more embodiments. Those skilled in the art will recognize that the
invention can be practiced without one or more of the specific
details, or with other methods, components, materials, etc. In
other instances, well-known structures, materials, or operations
are not shown or not described in detail to avoid obscuring aspects
of the invention.
[0043] Sequential vapor deposition (SVD) is a term used herein to
include various techniques of exposing a surface to sequentially
pulsed chemical vapors to form a film on the surface. A feature of
SVD is that the process is self-limiting in that each applied
reaction terminates without intervention. With SVD, a substrate or
other structure is placed in a reaction chamber where a first
chemical, which may be in the form of a vapor, reacts with the
surface and at least a portion of the first chemical is adsorbed
onto the surface. Excess first chemical and any reaction byproducts
are then purged from the chamber, and a second chemical, which may
also be in the form of a vapor, is introduced. The second chemical
reacts with the adsorbed first chemical and forms additional
material on the surface. The amount of material deposited is
limited by the reaction. Accordingly, the number of exposures
determines the thickness of the material. This process may be
continued until the desired layer thickness and uniformity is
achieved. SVD is particularly advantageous when using thin film
layers with subwavelength structures, especially those with narrow
openings and/or with high aspect ratios.
[0044] Although SVD is similar to CVD, it is significantly
different in that SVD is self-limiting and relies on sequential
pulses of exposure to create films of desired thickness. CVD also
includes a variety of more specific processes, including, but not
limited to, metalorganic CVD, plasma enhanced CVD and others. CVD
is commonly used to form non-selectively a complete, deposited
material on a substrate. CVD uses the simultaneous presence of
multiple species in a reaction chamber to react and form the
deposited material.
[0045] With CVD, the growth of thin films is primarily adjusted by
controlling the inflow rates of starting materials impinging on the
substrate. This differs from SVD wherein a substrate is contacted
with a single deposition species that chemisorbs to a substrate or
previously deposited species, thus allowing the substrate qualities
rather than the starting material concentrations or flow variables
to control the deposition rate and film quality.
[0046] Atomic layer deposition (ALD) is a form of SVD and has been
used to manufacture electroluminescent displays for over 20 years.
ALD has been referred to as Atomic Layer Epitaxy, but this
reference is more appropriately used for epitaxial films only.
Various techniques for ALD are disclosed in U.S. Pat. Nos.
4,058,430,4,413,022, 5,711,811, and 6,015,590, all of which are
incorporated herein by reference. Recently, ALD has gained
significant interest in the semiconductor and data storage
industries. The films that this technique yields have exceptional
characteristics, such as being pinhole free and possessing
excellent uniformity and step coverage even on very high aspect
ratio structures. ALD technique is also well suited for precise
tailoring of material compositions.
[0047] In performing ALD, process conditions, including
temperatures, pressures, gas flows and cycle timing, are adjusted
to meet the requirements of the process chemistry and substrate
materials. The temperature and pressure are controlled within a
reaction chamber. Typical temperatures are approximately 20 to 600
C, and pressure ranges from about 10 to 10,000 Pascal. Once the
reaction space reaches a stable temperature and pressure, a first
precursor vapor is directed over the substrate. In some cases, also
extra heating time or in-situ cleaning may be needed to remove any
harmful contaminants from the substrate.
[0048] For true ALD, the first precursor vapor reacts only with a
surface, and does not react to itself, and the process is therefore
self-limiting. In actual practice, the first precursor vapor may
attach to a limited amount of the same type of molecules, but the
growth is still self-limiting. Extended exposure of the precursor
vapor does not increase the amount of the film that attaches to the
surface.
[0049] An inert purge gas is introduced to remove any excess of the
first vapor and any volatile reaction products. The embodiments of
the deposition process are described herein as involving purging
with an inert gas. The terms "purging" and "purge" are intended to
be construed broadly, to include not only flushing of the reaction
space by introduction of a flow of an inert gas or other material,
but also more generally to include the removal or cleansing of
excess chemicals and reaction byproducts from the reaction space.
For example, excess chemicals and reaction byproducts may be
removed from the reaction space by pumping the reaction space
and/or by lowering the pressure within the reaction space.
Consistent with the broad definition of the term "purge," the
removal of excess chemicals from the reaction space need not be
perfectly effective, but will typically involve leaving surface
bound chemicals and possibly some insignificant amount of
non-surface bound chemicals or residual matter within the reaction
space.
[0050] Moreover, when a purge gas is used to remove chemicals from
the reaction space, various inert and non-inert purge gases may be
used. Preferred purge gases include nitrogen (N.sub.2), helium
(He), neon (Ne), argon (Ar), carbon dioxide (CO.sub.2), and
mixtures thereof. A constant or pulsed flow of one or more of these
purge gases may also be used to transport the first chemical and
the second chemical into the reaction space and/or to adjust the
pressure within the reaction space.
[0051] A second precursor vapor is introduced into the reaction
chamber and reacts with the adsorbed first precursor vapor and
creates a film conforming to the optical structure. As with the
first precursor vapor, the second precursor vapor does not react to
itself or attaches only to a limited amount of itself. Accordingly,
extended exposure of the second precursor vapor does not increase
the thickness of the film. The film may serve any number of
applications including an antireflection coating, optical low pass
filter, optical high pass filter, optical bandpass filter, optical
bandreject filter, waveguide, optical attenuator, gain flattening
filter, gray scale filter or a passivation layer.
[0052] The growth experienced for each introduced precursor vapor
is typically one monolayer or less. However, in some techniques, it
is possible to increase the growth to an amount slightly above a
monolayer.
[0053] The second precursor vapor is purged to remove excess
precursor vapor as well as any volatile reaction products. This
completes one cycle. This procedure is repeated until the desired
thickness of the film is achieved.
[0054] Successful ALD growth requires that the precursor vapors be
alternately pulsed into the reaction chamber without overlap. The
ALD process also requires that each starting material be available
in sufficient concentration for thin film formation over the
substrate area. Sufficient material also ensures that no extensive
precursor decomposition takes place in the thin film formation.
[0055] Another form of SVD is a technique referenced herein as
rapid vapor deposition. ALD is limited to its relatively slow
deposition rates because of its deposition of one monolayer for
each cycle. Rapid vapor deposition offers highly uniform and
conformal coatings with faster deposition rates. With rapid vapor
deposition, two different types of precursor vapor are
alternatively exposed to a substrate to form an increased growth
rate in a single cycle.
[0056] The first precursor vapor reacts with a surface to provide
self-limiting growth of a film conforming to the surface. Extended
exposure of the first precursor vapor does not increase the film
thickness. The first precursor vapor and byproduct are purged from
the reaction chamber, such as by introducing an inert purging
gas.
[0057] A second precursor vapor is introduced into the chamber and
uses the first precursor film as an activator. Film growth depends
on the amount of available second precursor vapor molecules. The
film growth by the second precursor vapor is self-limiting in that
the growth ultimately saturates and requires another activation
pulse of the first precursor vapor. A distinction between rapid
vapor deposition and CVD is that only one pulse of precursor vapor
is required after the activator pulse. Rapid vapor deposition
further differs from CVD in that film growth by both the first and
second precursor vapors is self-limiting.
[0058] In one implementation, disclosed in Dennis Hausmann et al.,
Rapid Vapor Deposition of Highly Conformal Silica Nanolaminates,
SCIENCE MAGAZINE, Oct. 11, 2002, at 402 which is incorporated
herein by reference, the two different precursor vapors are
trimethyaluminum (Me.sub.3Al) and tris(tert-butoxy)silanol
(BuO).sub.3SiOH. The two precursor vapors are supplied in
alternating pulses to heated substrates to form a layer of silica
nanolaminates. The layer thickness per cycle depends on the size of
the vapor doses and the heat of the substrate. The surface
reactions of the two different precursor vapors are self-limiting,
as evidenced by the saturation of the growth rate at high doses of
each reactant. The final result is a uniform, conformal coating
similar to that provided by ALD.
[0059] In the referenced implementation, a single cycle of rapid
vapor deposition produces more than 32 monolayers per cycle rather
than a single monolayer as experienced with ALD. In other
implementations, growth rate may range from 2 to 10 to 20
monolayers per cycle. Thus, although rapid vapor deposition
provides self-limiting reactions, the growth substantially exceeds
one monolayer per cycle.
[0060] SVD techniques provide excellent film depositions for MOEs.
In accordance with the present invention, MOEs are fabricated for
numerous applications including non-active elements, such as beam
shapers, beam splitters, microlenses, microlens arrays, diffusers,
laser diode correctors, pattern generators, collimators, grating
devices, DNA chips, biochips, anti-reflective coating structures,
optical filters, waveguides, optical attenuators, gain flattening
filters, gray shade filters and other applications.
[0061] MOEs are also used for active, light-emitting elements, such
as lasers, VCSEL lasers, LEDs, RC-LEDs and the like. Typically
MOEs, and conforming films on top of MOEs, are formed on wafers for
active elements like LEDs. The wafers are then cut to a final size.
In addition, MOEs can be used for active, light-detecting elements,
such as light diodes, solar cells, CCD devices, CMOS devices and
integrated circuits.
[0062] SVD techniques are able to reliably provide uniform,
conformal coatings for optical structures having a surface with
uneven structure having dimensions less than the 100 times the
wavelength of applied light, including subwavelength micro-optical
elements. A subwavelength micro-optical element has one or more
uneven structures with dimensions that are less than the wavelength
of applied light. Subwavelength structures may have dimensions that
are the smallest manipulating dimensions possible for applied
light. Subwavelength structures and structures with high aspect
ratios create difficulties in achieving thin film conformity. The
present invention overcomes the limitations previously experienced
with coating micro-optical elements.
[0063] The MOEs of the present invention may be used for
ultraviolet light, visible light, and infrared light. As defined
herein, applied light includes ultraviolet, visible, and infrared
light. The dimensions of subwavelength structures are relative to
the applied light.
[0064] Referring to FIG. 8, representation of a reaction chamber 80
for SVD techniques is shown. The reaction chamber 80 is a generic
representation and is used for exemplary purposes only. The
techniques disclosed herein may be practiced in any number of
reaction chambers, such as a Pulsar.TM. 2000 ALCVD.RTM. reactor
manufactured by ASM International. Process parameters, such as
temperatures, pressures, gas flows and cycle timing, may be
adjusted by one of skill in the art in accordance with the
substrate materials, precursor gases, and desired film thickness.
Such parameters are well known to the skilled technician of ALD and
rapid vapor deposition techniques.
[0065] The reaction chamber 80 may be maintained at temperatures
between about 150.degree. C. and about 600.degree. C. It is
expected that some embodiments of the deposition process may be
performed at temperatures below about 150.degree. C. and above
about 600.degree. C. Some operating temperatures may not be
preferable depending on the material of the thin film to be
deposited. Lower temperatures are believed to help avoid
decomposition during the deposition of the organometallic chemical.
For certain films, such as TiO.sub.2, Al.sub.2O.sub.3, ZnO,
SiO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5 and combinations
thereof, the operating temperature may range from less than 150
degrees to approximately room temperature.
[0066] Gases flow into the reaction chamber 80 through one or more
gas inlets 82. Gases introduced into the reaction chamber 80
include those commonly used for ALD and rapid vapor deposition
techniques, such as reactant precursor gases, oxidizing gases, and
carrier/purging gases. Reactant precursor gases can be any type
suitable for self-terminating chemisorption, such as halides,
metal, Si, or Ge containing organic compounds and many others known
in the art that are suitable for the desired coating and processing
parameters, including substrate temperature.
[0067] A large number of coatings are suitable for MOE production
depending on the intended use. In some applications, the coating
may be used as an antireflection coating, optical low pass filter,
optical high pass filter, optical bandpass filter, optical
bandreject filter, waveguide, optical attenuator, gain flattening
filter, gray shade filter or a passivation layer.
[0068] The coatings include elements, Al, Ti, Si, Ge, Ta, Nb, Zr,
Hf, Mo, W, V, Cr, Cu, Mo, Pt, Pd and Ir. The coatings also include
nitrides, such as AlN, TiN, TaN, Ta.sub.3N.sub.5, NbN, MoN, Si
nitrides, Ge nitrides, Zr nitrides, Hf nitrides, W nitrides, V
nitrides, Cr nitrides, Y nitrides, Ce nitrides, Mg nitrides, and Ba
nitrides. The coatings further include carbides, such as TiC, SiC,
TaC, HfC, Al carbides, Ge carbides, Nb carbides, Zr carbides, Mo
carbides, W carbides, V carbides, Cr carbides, Y carbides, Ce
carbides, Mg carbides, and Ba carbides. The coatings include
sulfides, such as ZnS, CaS, SrS, BaS, CdS, PbS. The coatings
include fluorides, such as CaF.sub.2, SrF.sub.2, and ZnF.sub.2. The
coatings include transparent conductors, such as In.sub.2O.sub.3,
InSnO, ZnO, ZnO:Al, and Sn-oxide. The coatings include oxides, such
as Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, HfO.sub.2,
Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, Y.sub.2O.sub.3, MgO, CeO.sub.2,
SiO.sub.2, La.sub.2O.sub.3, SrTiO.sub.3, BaTiO.sub.3, Ge oxides, Mo
oxides, W oxides, V oxides, and Cr oxides.
[0069] In one application, such as an anti-reflective coating, the
coating is a layered structure of TiO.sub.2 and Al.sub.2O.sub.3.
The listed coating materials are for illustrative purposes only and
should not be considered exhaustive. One of skill in the art will
appreciate that numerous ways exist to improve current MOE
components with coatings not previously considered.
[0070] For optical purposes, transparent oxides may be used for
antireflective coatings, waveguides and optical filter coatings.
Gray shade filters may be created using light absorbing coatings
like nitrides and carbides.
[0071] The carrier gas can be any inactive gas, such as nitrogen,
helium, or argon, suitable for conveying vapor-phase reactant gases
through the chamber 80 and can also be employed to purge the
chamber 80 between reactant gas pulses.
[0072] The inlet 82 is configured to keep reactant gases separate
until introduced into the chamber 80 to thereby avoid undesirable
CVD-type reactions and consequent particle formation or thickness
non-uniformity. The reactant gasses pass over an optical structure
84 where SVD occurs. The optical structure 84 represents a single
structure or a batch of structures.
[0073] The optical structure 84 is the basic component of a MOE and
may be any one of a number of optical structures. As such, the
optical structure 84 may be configured for diffraction, refraction,
reflection, grating, waveguiding or other light shaping or light
conducting function. The optical structure may be disposed on a
light detecting device, such as a light diode, solar cell, CCD
device, CMOS device, or integrated circuit. The optical structure
84 may also be an active element that generates light, such as a
laser, LED, and the like. The optical structure may be disposed on
a light emitting device, such as a laser device, VCSEL laser
device, light emitting diode, RC-LED, or an integrated circuit.
[0074] The optical structure 84 includes a substrate upon which
other elements of the optical structure 84 are disposed. In certain
implementations, additional elements of the optical structure 84
may be integrated with the substrate. The optical structure 84 may
include a variety of materials including glass, fused silica,
silicon, SiO.sub.2, SiON, Si.sub.3N.sub.4, metals, germanium,
germanium arsenide, III-V compound, zinc selenide, zinc sulphide,
II-VI compound, acrylic, epoxy, fluoro polymer, polyamide,
polyimide, polystyrene, polyethylene, polyethylene terephthalate,
polyurethane, PTFE, polyolefins, polycarbonate, polymethyl
methacrylate (PMMA), styrene acrylonitrile, Ormocer.TM., an
organically modified ceramics hybrid polymer manufactured by
Fraunhofer-Institute for Silicate Research (Fhh-ISC), EPON SU-8
Negative which is a photodefinable epoxy resin, ormosils
(organically modified silicates), nanomers (nanoparticle and
organic component containing polymer type materials), plastics, and
plexi-glass.
[0075] The optical structure 84 may be configured with uneven
structures that are subwavelength structures. Subwavelength
structures have a dimension less than the wavelength of applied
light, such as ultraviolet, visible, or infrared light.
Alternatively, the uneven structure have a dimension that is less
than 100 times or ten times the wavelength of applied light. A
dimension may be characterized as a horizontal length of a surface,
vertical height of a step, depth of a trench, profile, width of a
trench, and other dimensions well known in the art. The optical
structure 84 may be a structure, such as a trench or well, with
varying aspect ratios, such as greater than 1:1 and even greater
than 10:1.
[0076] The optical structure 84 may be prepared by plastics
processing technologies, such as compression molding, injection
molding or high pressure molding. Other processing methods include
embossing, replication by ultraviolet cured embossing, casting,
coining/stamping, single point diamond turning for continuous
profile, and direct write lithography. Lithographic processes
common to semiconductor manufacturing may also be used to form the
optical structure 84. A lithographic process forms the optical
structure 84 by exposing and developing the desired surface relief
structure into a photosensitive material coated onto a supporting
substrate and then transferring the surface relief structure into
the substrate by plasma reactive ion etching or chemical etching. A
surface pattern may be made directly on substrate material.
[0077] A particular application of the optical structure 84 is as
non-active component that passively receives, conducts, or passes
light. As defined herein, a non-active component does not generate
or emit light. As a non-active component, the optical structure 84
may be a reflective structure or a DOE. The optical structure 84
may form part of a non-active MOE suitable for use as a beam
shaper, beam splitter, microlens, microlens array, diffuser, laser
diode corrector, pattern generator, collimator, grating device,
optical filter, waveguide, optical attenuator, gain flattening
filter, gray shade filter, anti-reflective coating structures,
image sensor, camera lens and other numerous applications.
Microlens and microlens array have particular application for use
as optical readers, interfaces between laser diodes and optical
fibers, diffuser screens, integral photography, and cameras. All
applications referred to herein have particular needs for thin film
coatings based on their intended application.
[0078] The optical structure 84 may also form part of a non-active
MOE that is attached to an active component. A non-active MOE may
be attached to an active component surface, such as a semiconductor
device that generates light. As such, the non-active MOE may serve
to diffract emitted light but does not generate the light itself.
Diffractive structures attached to light path of light emitting
components, such as lasers and light emitting diodes (LEDs), are
common applications in the art.
[0079] Another common application in the art for non-active MOEs is
for receiving and detecting light. Such applications include light
diodes, solar cells, CCD devices, CMOS devices, and a variety of
light and image sensors. Components that passively receive light
are considered herein to be non-active as well.
[0080] Heaters 86, although not required in all applications, may
apply heat to the optical structure 84 and process gases in
accordance with process parameters. Unused gases, reaction
products, and carrier gases leave the chamber 80 through a gas
outlet 88.
[0081] Referring to FIG. 9, an optical structure 90 with steps is
shown with a thin film 92 deposited by SVD. The SVD technique
provides a highly conformal thin film 92 with excellent step
coverage. The SVD technique is reliable and highly repeatable.
[0082] Referring to FIG. 10, an optical structure 100 with an
isolated trench 102 having a high aspect ratio is shown. The
structure 100 may be a subwavelength structure with the trench 102
dimension having a length less than the wavelength of applied
light. Once again, the SVD technique provides excellent thin film
coverage thereby eliminating voids. Although SVD can coat high
aspect ratio structures, SVD cannot replicate the underlying
structure. SVD growth is isotropic, and SVD film growth occurs on
the entire surface. Accordingly, the SVD growth will eventually
planarize a structure. SVD provides excellent conformity and step
coverage and realizes subnanometre level accuracy in controlling
film thicknesses in addition to providing low production cost due
to batch processing.
[0083] SVD applications for MOEs provide numerous advantages over
conventional techniques. SVD provides self-limiting growth through
either ALD or rapid vapor deposition techniques. Film thickness is
controlled by the number of deposition cycles. Feedback from
real-time monitoring system, e.g. optical monitoring system, can
also be used for fine-tuning the number of depositions cycles in
very demanding applications. Self-limiting growth provides
excellent surface conformance and allows coatings on high aspect
ratio structures and subwavelength structures. Self-limiting growth
enables void free trench filling and controls layer thickness, as
thickness is directly related to number of cycles performed.
[0084] SVD techniques allow large-area coating of larger substrates
than available with other methods. This allows the use of batch
equipment that provides a production cost benefit. SVD techniques
further provide good reproducibility for high yields and thereby
provide another production cost benefit.
[0085] SVD techniques allow for atomic level control of material
composition. This enables production of coatings and thin films
with sharp interfaces and lattices. SVD techniques further allow
for surface modification, such as thin films that are used for
hydrofobic, biocompatible, or to improve hardness. SVD is suitable
for planarization of three-dimensional MOEs by filling trenches
without voids.
[0086] SVD relies on separate exposures of reactants such that
chemical exposures are spatially and temporally separated. As such,
there are no gas phase reactions with SVD and no gas phase
particulate generation as with CVD. SVD allows the use of
precursors that are highly reactive towards each other enabling
effective material utilization. SVD provides sufficient time to
complete each reaction step thereby allowing high-quality materials
at low processing temperatures.
[0087] SVD techniques accommodate wide processing temperature
windows. This allows preparation of multilayer structures in a
continuous process. Examples of low temperature coatings include
TiO.sub.2 that can be coated at room temperature and
Al.sub.2O.sub.3 which grows at 50C or even below. Organic materials
are especially preferred for point-of-care and personalized medical
applications since glass is not accepted in certain
environments.
[0088] ALD has accurate but slow growth rate. To compensate for the
slow growth, batch processing may be used to increase production
volume. ALD is well adapted for production of a large uniform area.
Thus, ALD provides low cost MOE coating due to the conformality and
large-area uniformity of batch processing. ALD can be used to coat
large area substrates having dimensions from 300 mm to several
meters. Furthermore, rapid vapor deposition allows for
significantly faster growth rates.
[0089] SVD allows all surfaces of a substrate or surface to be
coated at the same time. Coating all sides of a substrate in a
single application is useful in certain instances. For example,
antireflective and passivation coatings on all sides of a component
are needed in certain applications. Double or multi-sided coating
is very difficult with some conventional methods.
[0090] Films produced by SVD are pinhole free, which is vital in
applications using electrical field (no breakdowns) or in
protective applications against atoms/ions/molecules, biological
substances or radiation energy. In these protective applications,
thin film layers (<20nm) are often desired, and SVD enables
production of very thin film layers without pinholes.
[0091] SVD may produce thin films of common low cost materials,
such as Al.sub.2O.sub.3, SiO.sub.2, and TiO.sub.2. For
Al.sub.2O.sub.3, SVD can be used to produce thin films for MOEs
having an index of refraction less than 1.7. For SiO.sub.2
coatings, SVD can produce thin films having an index of refraction
less than 1.5. For TiO.sub.2, SVD can produce thin films having
index of refraction greater than 2 and 2.5. The high and low
refractive indexes enable the coatings for applications, such as
antireflective coatings, optical filter coatings, such as high
pass, low pass or band pass filters and band rejecting filters,
waveguides, optical attenuators, gain flattening filters, gray
shade filters and other optical coatings requiring a large
difference of refractive index.
[0092] SVD provides an easy way to tune film structure on a MOE
because every pulsed material combination can be different. SVD can
provide gradient refractive index layer coatings for optical
elements. Tailoring of thin film structures also allows creating
refractive indices, which do not naturally exist, and enables
flexible design of multilayer optical filters.
[0093] The SVD technique is able to make layers that are thin
enough to not inhibit the functionality of the MOE. Thin films may
be applied to MOEs as environmental protection barrier coatings,
such as TiO.sub.2 and Ta.sub.2O.sub.5, against chemical substances.
Thin films may also provide biocompatible surface coatings, such as
TiO.sub.2 and Ta.sub.2O.sub.5. Thin films can also be used as gray
shade filters by using nitrides or carbides, such as TiN, AlN, and
TiC.
[0094] Although thin films created by SVD are not hard compared to
other methods, they are harder than most other organic coatings.
Thus, SVD can provide coatings for MOE protection against
mechanical energy (scratch resistance) by using oxides, nitrides or
carbides, such as TiO.sub.2, TiN, AlN, TiC.
[0095] Deposited thin films may have varying indexes of refractions
depending on the intended application. An index of refraction may
range from between 1.2 to greater than 3.
[0096] It is very difficult to make direct optical measurements of
a MOE structure for process control purposes. Thus, a SVD process
batch typically includes additional monitor glass substrates for
indirect process control.
[0097] In operation, the SVD techniques of the present invention
have proven superior to conventional methods in providing conformal
thin films. In a first example, an optically low loss, high
refractive, index coating was applied to a MOE at room temperature.
A 155 mm.times.265 mm glass process monitor substrate (borosilicate
glass OA-2 (NEG)) and substrates with MOE structures were loaded
into the reaction space of a flow-type ALD batch reactor. The
substrate was disposed on a planar substrate holder plane in order
to expose only one side of the glass substrate surface to gas
flow.
[0098] After loading the substrate into the reactor, the reactor
was purged with N.sub.2 gas (99.99% purity, AGA). The flow rate was
2.75 SLM, and pumping speed was adjusted in order to maintain a
pressure of approximately 120 Pa inside the reaction space. The
reaction space was allowed to stabilize for eight hours without
heating, during which time the glass substrate reached a
temperature of about 22.degree. C.
[0099] Pulses of chemicals were sequentially introduced into the
reaction space to contact the surface of the substrate. The first
chemical was TiCl.sub.4 (99.9% purity, Sigma-Aldrich), the
transition metal chemical and metal source. The second chemical was
de-ionized water H.sub.2O, the oxygen source. Both first and second
chemicals were vaporized from external source vessels. TiCl.sub.4
source material was at room temperature, approximately 21.degree.
C., and H.sub.2O source material was at 14.degree. C. Between
pulses, the reaction space is purged with N.sub.2 gas.
[0100] The pulsing cycle was as follows: a TiCl.sub.4 pulse,
followed by an N.sub.2 purge, followed by a H.sub.2O pulse, and
followed by an N.sub.2-purge. The pulse lengths were as follows:
TABLE-US-00001 Pulse Sources Length of Pulse (seconds) TiCl.sub.4
0.2 N.sub.2-purge 10.0 H.sub.2O 0.6 N.sub.2-purge 10.0
The pulsing cycle was repeated 6000 times. Tape testing determined
that adhesion of the TiO.sub.2 film to the substrate is excellent.
Referring to FIG. 11, a graph is shown illustrating the
transmission spectrum of the TiO.sub.2 film.
[0101] The transmission data provides the following refractive
index values: TABLE-US-00002 Approximate Refractive index (using
fixed n of Wavelength [nm] Transmission substrate = 1.54 @ 589.3
nm) 1385 80.37% 2.12 846 79.85% 2.13 617 78.36% 2.17 497 76.10%
2.23 424 73.03% 2.33 379 67.20% 2.50
[0102] Average thickness of the TiO.sub.2 film was 507 nm, and
average growth rate was 0.0845 nm/cycle. The transmission data
shows that optical losses above 500 nm are below 0.3%, and above
1000 nm are below 0.1%. Without any specific optimization of the
process, the values were relatively uniform, showing a thickness
non-uniformity of less than 5% over the substrate area.
[0103] In a second example, an 840 nm, two-layer, antireflective
coating is applied to an optical structure at a relatively low
temperature. A two-layer, thin film, antireflective design requires
a high and low refractive index thin film. In this example,
TiO.sub.2 is the high index, and Al.sub.2O.sub.3 is the low index
film. The monitor substrate is borosilicate glass OA-2 (NEG).
[0104] Two pieces of 195 mm.times.265 mm glass process monitor
substrates were loaded into the reaction space of a flow-type ALD
batch reactor also having substrates with MOE structures in same
process batch run. One of the substrates was lying on the planar
substrate holder frame in order to expose both sides of the glass
substrate surfaces to the gas flow. This allows antireflective
coating on both sides of the substrate. Another substrate was lying
against the planar surface to prevent backside growth and, thus,
has antireflective coating on only one side of the glass
substrate.
[0105] After loading the substrate into the reactor, the reactor
was purged with N.sub.2 gas (99.99% purity, AGA). The flow rate was
2.75 SLM, and pumping speed was adjusted in order to maintain a
pressure of about 120 Pa inside the reaction space. The reaction
space was allowed to stabilize for eight hours, during which time
the glass substrate reached a temperature of about 82.degree.
C.
[0106] Pulses of chemicals were sequentially introduced into the
reaction space to contact the surface of the substrate. The first
chemical was TiCl.sub.4 (99.9% purity, Sigma-Aldrich), the
transition metal chemical and metal source. The second chemical was
de-ionized water H.sub.2O, the oxygen source. Both first and second
chemicals were vaporized from external source vessels. TiCl.sub.4
source material was at room temperature, approximately 21.degree.
C., and H.sub.2O source material was at 14.degree. C. Between
pulses, the reaction space is purged with N.sub.2 gas. Thus, the
pulsing cycle was as follows: a TiCl.sub.4 pulse, followed by an
N.sub.2-purge, followed by a H.sub.2O pulse, and followed by an
N.sub.2-purge. The pulse lengths were as follows: TABLE-US-00003
Pulse Sources Length of Pulse (seconds) TiCl.sub.4 0.4
N.sub.2-purge 10.0 H.sub.2O 0.6 N.sub.2-purge 10.0
This cycle gave growth rates of about 0.056 nm/cycle. The cycle was
repeated 700 times. The refractive index of the resulting film was
approximately 2.28.
[0107] The second antireflective coating included pulses of TMA
(99.9% purity, Crompton), the organometallic chemical and aluminum
source having temperature of 21.degree. C. The second coating also
included pulses of de-ionized water H.sub.2O, the oxygen source
having temperature of 14.degree. C. Both chemicals were vaporized
from external source vessels and introduced into the reaction space
such that they sequentially contacted the surface of the
substrates. Between pulses, the reaction space was purged with
N.sub.2 gas. Thus, the pulsing cycle was as follows: a TMA pulse
followed, by an N.sub.2-purge, followed by a H.sub.2O pulse, and
followed by an N.sub.2-purge. The pulse lengths were as follows:
TABLE-US-00004 Pulse Sources Length of Pulse (seconds) TMA 0.4
N.sub.2-purge 7.0 H.sub.2O 0.6 N.sub.2-purge 10.0
This cycle provides a growth rate of approximately 0.081 nm/cycle.
The cycle was repeated 2130 times. The refractive index was about
1.60.
[0108] After the second layer cycles were complete, an
antireflective film was present on the glass substrate. The
antireflective film completely covered the exposed surface of the
glass substrate. The resulting glass substrate was removed from the
reaction space. Tape testing was performed to determine adhesion of
the antireflective film to the substrate, which was found to be
excellent.
[0109] Referring to FIG. 12, a graph is shown illustrating the
transmission spectrum of the resulting antireflective thin film.
The antireflective thin film was analyzed with a spectrophotometer
to provide the plotted relative transmissions.
[0110] Without any specific optimization of the process, the peak
wavelength values were relatively uniform. Over the substrate area,
the substrate having a single side coating had an average peak
wavelength of 838 nm with a standard deviation of 2.6 nm. The
substrate having a double side coating had an average peak
wavelength of 837 nm with a standard deviation of 2.6 nm. Tuning of
the filter may be easily changed by altering the number of
cycles.
[0111] In a third example, a SiO.sub.2:Al.sub.2O.sub.3 coating is
applied to a substrate using the RVD technique. A 155 mm.times.265
mm glass process monitor substrate (borosilicate glass OA-2 (NEG))
and substrates with MOE structures, were loaded into the reaction
space of a flow-type ALD batch reactor. The substrate was lying on
the planar substrate holder plane in order to expose only one side
of the glass substrate surface to the gas flow.
[0112] After loading the substrate into the reactor, the reactor
was purged with N.sub.2 gas (99.99% purity, AGA). The flow rate was
3 SLM, and pumping speed was adjusted in order to maintain a
pressure of about 90 Pa inside the reaction space. The reaction
space was allowed to stabilize for five hours, during which time
the glass substrate reached a temperature of about 300.degree.
C.
[0113] Alternating pulses of first and second chemicals were then
introduced into the reaction space. The first chemical was a
chemical compound containing silicon and TMA (Trimethylaluminium
Al(CH.sub.3).sub.3, 99.9% purity, Crompton), the organometallic
chemical and aluminum source. The second chemical was "Tris
(Tert-Butoxy) Silanol" (99.999% purity) manufactured by the Aldrich
Chemical Company, Inc. The chemicals were vaporized from external
source vessels and introduced into the reaction space such that
they sequentially contacted the surface of the substrates. The TMA
source material was at room temperature (about 21.degree. C.) and
"Tris (Tert-Butoxy) Silanol" source material was at 85.degree. C.
Between pulses, the reaction space was purged with N.sub.2 gas.
Thus, the pulsing cycle was as follows: a TMA pulse, followed by an
N.sub.2-purge, followed by a "Tris (Tert-Butoxy) Silanol" pulse,
and followed by an N.sub.2-purge. The pulse lengths were as
follows: TABLE-US-00005 Pulse Sources Length of Pulse (seconds) TMA
0.6 N.sub.2-purge 2.0 "Tris (Tert - Butoxy) Silanol" 10.0
N.sub.2-purge 4.0
This cycle was repeated 200 times. One cycle results in a low index
film having approximately one layer of Al.sub.2O.sub.3 and 3 layers
of SiO.sub.2.
[0114] Tape testing was performed to determine the adhesion of the
SiO.sub.2 film to the substrate, which was found to be excellent.
Average thickness of the SiO.sub.2 film was 223 nm, and average
growth rate was 1.12 nm / cycle. The refractive index was
approximately 1.474. Without any specific optimization of the
process, the values were relatively uniform, showing a thickness
non-uniformity of less than 2% over the substrate area.
[0115] In a fourth example, an optically low loss, high refractive,
index Ta.sub.2O.sub.5 coating was applied to a substrate at a
relatively moderate temperature. A 195 mm.times.265 mm glass
process monitor substrate (borosilicate glass OA-2 (NEG)) and
substrates with MOE structures were loaded into the reaction space
of a flow-type ALD batch reactor. The substrate was lying on the
planar substrate holder plane in order to expose only one side of
the glass substrate surface to the gas flow.
[0116] After loading the substrate into the reactor, the reactor
was purged with a N.sub.2 gas (99.99% purity, AGA). The flow rate
was 2.75 SLM, and pumping speed was adjusted in order to maintain a
pressure of about 120 Pa inside the reaction space. The reaction
space was allowed to stabilize for three hours, during which time
the glass substrate reached a temperature of about 250.degree.
C.
[0117] Alternating pulses of chemicals were sequentially introduced
into the reaction space. A first chemical was Tantalum (V)
pentakis-ethoxide [Ta(OEt).sub.5].sub.2 (99.99% Inorgtech), the
organometallic chemical and tantalum metal source. The second
chemical was de-ionized water H.sub.2O, the oxygen source. The
first and second chemicals were vaporized from external source
vessels and introduced into the reaction space such that they
sequentially contacted the surface of the substrates. The
[Ta(Oet).sub.5].sub.2 source material was at temperature
140.degree. C., and H.sub.2O source material was at 20.degree. C.
Between pulses, the reaction space was purged with N.sub.2 gas.
Thus, the pulsing cycle was as follows: a TiCl.sub.4 pulse,
followed by an N.sub.2-purge, followed by a H.sub.2O pulse, and
followed by an N.sub.2-purge. The pulse lengths were as follows:
TABLE-US-00006 Pulse Sources Length of Pulse (seconds)
[Ta(Oet).sub.5].sub.2 0.6 N.sub.2-purge 0.6 H.sub.2O 0.5
N.sub.2-purge 1.7
This cycle was repeated 11605 times. Tape testing was performed to
determine the adhesion of the Ta.sub.2O.sub.5 film to the glass
substrate, which was found to be excellent.
[0118] Referring to FIG. 13, a graph is shown illustrating the
transmission spectrum of the resulting thin film. The thin film was
analyzed with a spectrophotometer to provide the plotted relative
transmissions.
[0119] Average thickness of the Ta.sub.2O.sub.5 film was 470 nm,
and average growth rate was 0.0405 nm/cycle. Typically, absorption
of Ta.sub.2O.sub.5 was less than 0.1%. Without any specific
optimization of the process, the values were relatively uniform,
showing a thickness non-uniformity of less than 3% over the
substrate area.
[0120] In a fifth example, a relatively thick thin film having low
optical loss and low index of refraction is formed at a moderate
temperature. A 195 mm.times.265 mm glass process monitor substrate
(glass 1737F, Corning) was loaded into the reaction space of a
flow-type ALD batch reactor. The substrate was lying on the planar
substrate holder plane in order to expose only one side of the
glass substrate surface to the gas flow.
[0121] After loading the substrate into the reactor, the reactor
was purged with N.sub.2 gas (99.99% purity, AGA). The flow rate was
3 SLM, and pumping speed was adjusted in order to maintain a
pressure of about 120 Pa inside the reaction space. The reaction
space was allowed to stabilize for five hours without heating,
during which time the glass substrate reached a temperature of
about 280.degree. C.
[0122] Alternating pulses of first and second chemicals were then
introduced into the reaction space. The first chemical was TMA
(99.9% purity, Crompton), the organometallic chemical and aluminum
source, having a temperature of 21.degree. C. The second chemical
was deionized water H.sub.2O, the oxygen source, having a
temperature of 14.degree. C. The precursors were vaporized from
external source vessels and introduced into the reaction space with
N.sub.2 gas such that they sequentially contacted the substrate
surface. Between pulses, the reaction space was purged with N.sub.2
gas. Thus, the pulsing cycle was as follows: a TMA pulse, followed
by an N.sub.2-purge, followed by a H.sub.2O pulse, and followed by
an N.sub.2-purge. The pulse lengths were as follows: TABLE-US-00007
Pulse Sources Length of Pulse (seconds) TMA 1.0 N.sub.2-purge 1.0
H.sub.2O 0.4 N.sub.2-purge 1.0
[0123] Testing was performed to determine the adhesion of the
Al.sub.2O.sub.3 film to the glass, which was found to be excellent.
This cycle gives a growth rate of approximately 0.10 nm/cycle. This
cycle was repeated 9927 times. The refractive index of the
resulting film is approximately 1.6.
[0124] Referring to FIG. 14, a graph is shown illustrating the
transmission spectrum of the resulting thin film. The thin film was
analyzed with a spectrophotometer to provide the plotted relative
transmissions.
[0125] It will be obvious to those having skill in the art that
many changes may be made to the details of the above-described
embodiments without departing from the underlying principles of the
invention. The scope of the present invention should, therefore, be
determined only by the following claims.
* * * * *