U.S. patent application number 13/727033 was filed with the patent office on 2013-06-06 for compositions and methods to fabricate a photoactive substrate suitable for shaped glass structures.
This patent application is currently assigned to LIFE BIOSCIENCE, INC.. The applicant listed for this patent is Life Bioscience, Inc.. Invention is credited to Colin T. Buckley, Jeb H. Flemming, Carrie F. Schmidt.
Application Number | 20130142998 13/727033 |
Document ID | / |
Family ID | 39789068 |
Filed Date | 2013-06-06 |
United States Patent
Application |
20130142998 |
Kind Code |
A1 |
Flemming; Jeb H. ; et
al. |
June 6, 2013 |
COMPOSITIONS AND METHODS TO FABRICATE A PHOTOACTIVE SUBSTRATE
SUITABLE FOR SHAPED GLASS STRUCTURES
Abstract
A shaped photosensitive glass composition comprising silica,
K.sub.2O, Na.sub.2O, Ag.sub.2O, B.sub.2O.sub.3, Al.sub.2O.sub.3,
Li.sub.2O, and CeO.sub.2 with a high anisotropic-etch ratio formed
by a novel construction method. Furthermore, such shaped glass
structures can be used to form a negative mold for casting the
shape in other materials. Structures of the photosensitive glass
composition may include micro-channels, micro-optics, microposts,
or arrays of hollow micro-needles.
Inventors: |
Flemming; Jeb H.;
(Albuquerque, NM) ; Buckley; Colin T.;
(Albuquerque, NM) ; Schmidt; Carrie F.; (Las
Lunas, NM) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Life Bioscience, Inc.; |
Albuquerque |
NM |
US |
|
|
Assignee: |
LIFE BIOSCIENCE, INC.
Albuquerque
NM
|
Family ID: |
39789068 |
Appl. No.: |
13/727033 |
Filed: |
December 26, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12058588 |
Mar 28, 2008 |
8361333 |
|
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13727033 |
|
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60908631 |
Mar 28, 2007 |
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60910257 |
Apr 5, 2007 |
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Current U.S.
Class: |
428/156 |
Current CPC
Class: |
C03C 23/002 20130101;
B32B 3/10 20130101; C03C 3/095 20130101; C03C 25/62 20130101; Y10T
428/24479 20150115; C03C 15/00 20130101; C03C 2218/34 20130101;
C03C 4/04 20130101; C03C 3/108 20130101; C03C 23/007 20130101 |
Class at
Publication: |
428/156 |
International
Class: |
C03C 4/04 20060101
C03C004/04; C03C 3/108 20060101 C03C003/108; C03C 15/00 20060101
C03C015/00; C03C 3/095 20060101 C03C003/095 |
Claims
1. A shaped glass structure with a high anisotropic-etch ratio
comprising: a photosensitive glass substrate with a glass
transformation temperature, wherein the photosensitive glass
substrate comprises: a glass composition comprising 60-76 weight %
silica, 6 weight %-16 weight % of a combination of K.sub.2O and
Na.sub.2O with at least 3 weight % K.sub.2O, 0.001-1 weight %
Ag.sub.2O, 0.75 weight %-7 weight % B.sub.2O.sub.3, and 5-8 weight
% Al.sub.2O.sub.3, with the combination of B.sub.2O.sub.3, and
Al.sub.2O.sub.3 not exceeding 13 weight %, 8-15 weight % Li.sub.2O,
and 0.04-0.1 weight % CeO.sub.2, and one or more patterned
structure.
2. The shaped glass structure of claim 1, wherein the patterned
structure comprises at least one portion exposed to an activating
energy source, such as ultraviolet light, while leaving at least a
second portion of the glass substrate unexposed, wherein at least a
part of the exposed portion is a crystalline material formed by
heating the glass substrate to a temperature near the glass
transformation temperature, wherein when etching the glass
substrate in an etchant, the anisotropic-etch ratio of the exposed
portion to the unexposed portion is at least 30:1 when the glass is
exposed to a broad spectrum mid-ultraviolet flood lamp, to provide
a shaped glass structure with an aspect ratio of at least 30:1, and
to provide shaped glass structures with an aspect ratio much
greater than 30:1 when the glass is exposed using a high powered
energy source, such as a laser.
3. The shaped glass structure of claim 1, wherein the glass
composition is essentially germanium-free.
4. The shaped glass structure of claim 1, wherein the glass
composition comprises at least 0.5 weight % B.sub.2O.sub.3.
5. The shaped glass structure of claim 1, wherein the glass
composition comprises at least 1.25 weight % B.sub.2O.sub.3.
6. The shaped glass structure of claim 1, wherein the glass
composition comprises at least 0.3 weight % Sb.sub.2O.sub.3 or
As.sub.2O.sub.3.
7. The shaped glass structure of claim 1, wherein the glass
composition comprises 0.003-1 weight % Au.sub.2O.
8. The shaped glass structure claim 1, wherein the glass
composition contains 1-18 weight % of an oxide selected from the
group consisting of CaO, ZnO, PbO, MgO and BaO.
9. The shaped glass structure of claim 1, wherein the glass
composition contains 0-5 weight %, iron (Fe.sub.2O.sub.3) to make
the composition paramagnetic and/or to use iron (II) and iron (III)
to quench intrinsic autofluorescence.
10. The shaped glass structure of claim 1, wherein the glass
composition comprises up to 2 weight % Copper Oxide.
11. The shaped glass structure of claim 1, wherein the
anisotropic-etch ratio of exposed portion to the unexposed portion
is 30-45:1.
12. The shaped glass structure of claim 22, wherein the
anisotropic-etch ratio of exposed portion to said unexposed portion
is at least one of 10-20:1; 21-29:1; 30-45:1; 20-40:1; 41-45:1; and
30-50:1.
13. The shaped glass structure of claim 1, wherein the etchant
comprises hydrofluoric acid.
14. The shaped glass structure of claim 1, wherein the wavelength
of the ultraviolet light is about 308-312 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No.
12/058,588, filed Mar. 28, 2008, entitled "Compositions and Methods
to Fabricate a Photoactive Substrate Suitable for Shaped Glass
Structures", currently pending, which claims priority to U.S.
Provisional Application Ser. No. 60/908,631, filed Mar. 28, 2007,
and U.S. Provisional Application Ser. No. 60/910,257, filed on Apr.
5, 2007, the contents of each of which are incorporated by
reference herein in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a method to fabricate a
shaped glass structure with a high-anisotropic-etch ratio and, in
particular, a method to fabricate a shaped glass structure with a
high-anisotropic-etch ratio using a novel photosensitive glass
composition.
BACKGROUND OF THE INVENTION
[0003] Photosensitive glass structures have been suggested for a
number of micromachining and microfabrication processes such as
hollow microneedle arrays being developed for transdermal drug
delivery and the withdrawal of body fluids for biomedical and other
applications. Unfortunately, silicon microfabrication processes are
long, difficult, and expensive. These microfabrication processes
rely on expensive capital equipment; X-ray lithography and deep
reactive ion etching machines which generally cost in excess of one
million dollars each and require an ultra-clean, high-production
silicon fabrication facility costing millions more.
[0004] Anisotropic-etch ratios for FOTURAN.RTM. have generally been
reported to be about 20:1 when exposed using high-powered
(non-laser based) broad spectrum mid-ultraviolet flood lamp, but
one paper notes an increased aspect ratio obtained when the
photostructurable glass is patterned with a laser: "Effect of Laser
Parameters on the Exposure and Selective Etch Rate in
Photostructurable Glass" by Frank E. Livingston, et al., published
in the Proceedings of the SPIE Vol 4637, pp. 404-12 notes at the
top of page 410 that "In this high power regime, the measured etch
rate ratio remained constant at .about.30:1." (See also FIG. 7 on
the same page 410, labeled "Etch rate ratio versus incident laser
power for FOTURAN.RTM."). The prior art glass microfabrication
processes have had etch ratios of 30:1 when patterned with a laser
and 20:1 when patterned with a flood lamp, resulting in a
microstructure with a large wall slopes. Photostructured
microneedles and other micromachined structures such as
micro-lenses suffer precision due to excessive wall slope.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a method to do glass
micromachining with etch ratios of 30:1 or more using a
mid-ultraviolet flood exposure system and potentially 40:1 or more
(preferably 50:1 or more) using a laser-based exposure system, to
produce high-precision structures. Thus, for example, with nearly
vertical wall slopes on both the inside and outside diameters of
hollow photostructured microneedles only minor wall-thickness
variation from tip to base would occur. In addition, microposts,
which are non-hollow microneedles, may be micromachined to possess
a low wall slope, enabling a decrease in the overall micropost
diameter. Likewise, micro-lenses can be shaped with precisely
controlled horizontal variations and have only minor vertical
variation.
[0006] Furthermore, the precision shape of a glass structure with
an anisotropic-etch ratio of 40:1 or more can be used to determine
the shape of a non-glass material in the negative mold. A mold
material can be: (1) deposited onto a shaped glass structure with a
high-anisotropic-etch ratio to provide a negative mold; (2) the
negative mold removed from the glass device; (3) a non-glass
material cast into the negative mold; (4) the material in the
negative mold is solidified; (5) the solidified non-glass material
removed from the negative mold to provide a precision (e.g.
anisotropic-etch ratio of 40:1 to 50:1) casting of a non-glass
material. Furthermore, unlike expensive dry-etching processes used
in silicon-semiconductor-type processes, this process can produce
very high anisotropic-etch ratios with relatively inexpensive wet
etching.
[0007] The present invention includes a method for fabricating a
shaped glass structure with a high-anisotropic-etch ratio, using a
photosensitive glass substrate having a composition of: 60-76
weight % silica; at least 3 weight % K.sub.2O with 6 weight %-16
weight % of a combination of K.sub.2O and Na.sub.2O; 0.003-1 weight
% of at least one oxide selected from the group consisting of
Ag.sub.2O and Au.sub.2O; 0.003-2 weight % Cu.sub.2O; 0.75 weight
%-7 weight % B.sub.2O.sub.3, and 6-7 weight % Al.sub.2O.sub.3; with
the combination of B.sub.2O.sub.3; and Al.sub.2O.sub.3 not
exceeding 13 weight %; 8-15 weight % Li.sub.2O; and 0.001-0.1
weight % CeO.sub.2. This varied composition is generally referred
to as the APEX. At least one portion of the photosensitive glass
substrate is exposed to ultraviolet light, while leaving at least a
second portion of said glass substrate unexposed; the glass
substrate is heated to a temperature near the glass transformation
temperature to transform at least part of the exposed glass to a
crystalline material; and the glass substrate is etched in an
etchant, wherein the etch ratio of exposed portion to that of the
unexposed portion is at least 30:1 when exposed with a broad
spectrum mid-ultraviolet flood light, and greater than 30:1 when
exposed with a laser, to provide a shaped glass structure with an
anisotropic-etch ratio of at least 30:1. Percentages herein are in
weight percent of the constituents.
[0008] This photosensitive, shaped glass structure with a
high-anisotropic-etch ratio, can be composed of: 35-76 weight %
silica, 3-16 weight % K.sub.2O, 0.003-1 weight % Ag.sub.2O, 0.75-13
weight % B.sub.2O.sub.3, 8-15 weight % Li.sub.2O, and 0.001-0.1
weight % CeO.sub.2. This photosensitive glass is processed using at
least on of the following steps: At least one portion of the
photosensitive glass substrate is exposed to ultraviolet light,
while leaving at least a second portion of said glass substrate
unexposed; the glass substrate is heated to a temperature near the
glass transformation temperature to transform at least part of the
exposed glass to a crystalline material; and the glass substrate is
etched in an etchant, wherein the etch ratio of exposed portion to
that of the unexposed portion is at least 30:1 when exposed with a
broad spectrum mid-ultraviolet flood light, and greater than 30:1
when exposed with a laser, to provide a shaped glass structure with
an anisotropic-etch ratio of at least 30:1.
[0009] This can also be a method to fabricate a shaped glass
structure with a high-anisotropic-etch ratio, using a
photosensitive glass substrate having a composition of: 46-76
weight % silica, 3-16 weight % K.sub.2O, 0.003-1 weight %
Ag.sub.2O, 0.75-13 weight % B.sub.2O.sub.3, 6-7 weight %
Al.sub.2O.sub.3, 11-15 weight % Li.sub.2O, and 0.001-0.1 weight %
CeO.sub.2. The photosensitive glass is processed using at least one
of the following steps: At least one portion of the photosensitive
glass substrate is exposed to ultraviolet light, while leaving at
least a second portion of said glass substrate unexposed; the glass
substrate is heated to a temperature near the glass transformation
temperature to transform at least part of the exposed glass to a
crystalline material; and the glass substrate is etched in an
etchant, wherein the etch ratio of exposed portion to that of the
unexposed portion is at least 30:1 when exposed with a broad
spectrum mid-ultraviolet flood light, and greater than 30:1 when
exposed with a laser, to provide a shaped glass structure with an
anisotropic-etch ratio of at least 30:1. Our analysis indicates
that the formation of smaller crystalline LiAlSi.sub.2O.sub.6
during the processing may be an important factor in the observed
sensitivity to ultraviolet light exposure and etch rate.
[0010] All embodiments are essentially germanium-free. In some
embodiments, Sb.sub.2O.sub.3 or As.sub.2O.sub.3 is added (e.g. at
least 0.3 weight % Sb.sub.2O.sub.3 or As.sub.2O.sub.3) to help
control the oxidation state of the composition. In some preferred
embodiments, at least 0.75 weight % B.sub.2O.sub.3 is included, and
in others at least 1.25 weight % B.sub.2O.sub.3 is included. In
some preferred embodiments, at least 0.003% Au.sub.2O is included
in addition to at least 0.003 weight % Ag.sub.2O. In some
embodiments, a combination of CaO and/or ZnO is added up to 18
weight %. In some embodiments, up to 10 weight % MgO is added. In
some embodiments, up to 18 weight % lead oxide is added. Up to 5
weight %, Fe.sub.2O.sub.3, may be added to make the material
paramagnetic and iron (II) and iron (III) may be added as a
quenching agent to reduce autofluorescence of the glass.
[0011] Preferably, the glass substrate is heated to a temperature
of 420-520 C for between 10 minutes and 2 hours and then heated to
a temperature range heated to 520-620 C for between 10 minutes and
2 hours.
[0012] In some embodiments, the etchant is HF, in some embodiments
the etchant is a combination of HF and additional ingredients, such
as hydrochloric acid or nitric acid. The preferred wavelength of
the ultraviolet light used for exposure is approximately 308-312
nm.
[0013] In one embodiment, the present invention is a shaped glass
structure with a high anisotropic-etch ratio having a
photosensitive glass substrate with a glass transformation
temperature. The photosensitive glass substrate may have one or
more patterned structure and a glass composition of about 60-76
weight % silica, 6 weight %-16 weight % of a combination of
K.sub.2O and Na.sub.2O with at least 3 weight % K.sub.2O, 0.001-1
weight % Ag.sub.2O, 0.75 weight %-7 weight % B.sub.2O.sub.3, and
5-8 weight % Al.sub.2O.sub.3, with the combination of
B.sub.2O.sub.3, and Al.sub.2O.sub.3 not exceeding 13 weight %, 8-15
weight % Li.sub.2O, and 0.04-0.1 weight % CeO.sub.2.
[0014] The patterned structure may have at least one portion
exposed to an activating energy source such as ultraviolet light
and at least a second portion of the glass substrate not exposed to
the ultraviolet light. Part of this exposed portion may be
transformed into a crystalline material by heating the glass
substrate to a temperature near the glass transformation
temperature. When etching the glass substrate in an etchant such as
hydrofluoric acid, the anisotropic-etch ratio of the exposed
portion to the unexposed portion is at least 30:1 when the glass is
exposed to a broad spectrum mid-ultraviolet (about 308-312 nm)
flood lamp to provide a shaped glass structure with an aspect ratio
of at least 30:1, and to provide shaped glass structures with an
aspect ratio much greater than 30:1 when the glass is exposed using
a high powered energy source, such as a laser.
[0015] Preferably, the shaped glass structure contains at least one
of; a micro-optic lens, a micro-optic micro-post, a micro-channel,
or micro-ridge micro-optic waveguide. The micro-ridge, optical
waveguide may be formed by etching away exposed glass to leave a
glass micro-ridge such that light is guided by the micro-ridge. The
micro-ridge may be formed using a layer of photosensitive glass
overlying a layer of non-photosensitive glass of lower index of
refraction than the photosensitive glass, to substantially prevent
micro-ridge-guided light from leaving the bottom of the micro-ridge
in at least one portion of the micro-ridge (e.g. bottom vias may be
etched in the non-photosensitive glass to allow light coupling to a
light guide on a lower level).
[0016] In this embodiment, the composition of the shaped glass
structure may essentially be germanium-free, contain at least 0.5
weight % B.sub.2O.sub.3 or contain at least 1.25 weight %
B.sub.2O.sub.3, contain at least 0.3 weight % Sb.sub.2O.sub.3 or
As.sub.2O.sub.3, contain 0.003-1 weight % of at least one of
Au.sub.2O and Ag.sub.2O, contains 1-18 weight % of an oxide such as
of CaO, ZnO, PbO, MgO and BaO, contain 0-5 weight %, iron
(Fe.sub.2O.sub.3) to make the composition paramagnetic and/or to
use iron (II) and iron (III) to quench intrinsic autofluorescence,
and contain up to 2 weight % Copper Oxide. The shaped glass
structure may also have an anisotropic-etch ratio of about
30-45:1.
[0017] In another embodiment, the present invention is a shaped
glass structure with a high anisotropic-etch ratio having a
photosensitive glass substrate with a glass transformation
temperature. The photosensitive glass substrate may have one or
more patterned structure, and a glass composition of about 35-76
weight % silica, 3-16 weight % K.sub.2O, 0.001-1 weight % of at
least one oxide such as Ag.sub.2O and Au.sub.2O, 0.75-13 weight %
B.sub.2O.sub.3, 8-15 weight % Li.sub.2O, and 0.0014-0.1 weight %
CeO.sub.2.
[0018] In this embodiment, the patterned structure may have at
least one portion exposed to an activating energy source such as
ultraviolet light and at least a second portion of the glass
substrate not exposed to the ultraviolet light. Part of this
exposed portion may be transformed into a crystalline material by
heating the glass substrate to a temperature near the glass
transformation temperature. When etching the glass substrate in an
etchant such as hydrofluoric acid, the anisotropic-etch ratio of
the exposed portion to the unexposed portion is at least 30:1 when
the glass is exposed to a broad spectrum mid-ultraviolet (about
308-312 nm) flood lamp to provide a shaped glass structure with an
aspect ratio of at least 30:1, and to provide shaped glass
structures with an aspect ratio much greater than 30:1 when the
glass is exposed using a high powered energy source, such as a
laser. In addition, the composition of the shaped glass structure
may essentially be germanium-free, contain at least 0.5 weight %
B.sub.2O.sub.3 or at least 1.25 weight % B.sub.2O.sub.3.
[0019] In another embodiment, the present invention is a shaped
glass structure with a high anisotropic-etch ratio having a
photosensitive glass substrate with a glass transformation
temperature. The photosensitive glass substrate may have one or
more patterned structure, and a glass composition of about 46-76
weight % silica, 3-16 weight % K.sub.2O, 0.001-1 weight %
Ag.sub.2O, 0.5-13 weight % B.sub.2O.sub.3, 8-15 weight % Li.sub.2O,
and 0.001-0.1% CeO.sub.2. For example, the photosensitive glass
substrate may have one or more patterned structure, and a glass
composition of about 45, 50, 55, 60, 70, 75 or 76 weight % silica;
3, 5, 7, 8, 10, 12 or 16 weight % K.sub.2O; 0.001, 0.01, 0.1, 0.25,
0.5, 0.75 or 1 weight % Ag.sub.2O; 0.5, 1, 2.5, 5, 7.5, 10, 12.5 or
13 weight % B.sub.2O.sub.3; 8, 7, 9, 10, 12.5 or 15 weight %
Li.sub.2O; and 0.001, 0.01, 0.05 or 0.1% CeO.sub.2.
[0020] In this embodiment, the patterned structure may have at
least one portion exposed to an activating energy source such as
ultraviolet light and at least a second portion of the glass
substrate not exposed to the ultraviolet light. Part of this
exposed portion may be transformed into a crystalline material by
heating the glass substrate to a temperature near the glass
transformation temperature. When etching the glass substrate in an
etchant such as hydrofluoric acid, the anisotropic-etch ratio of
the exposed portion to the unexposed portion is at least 30:1 when
the glass is exposed to a broad spectrum mid-ultraviolet (about
308-312 nm) flood lamp to provide a shaped glass structure with an
aspect ratio of at least 30:1, and to provide shaped glass
structures with an aspect ratio much greater than 30:1 when the
glass is exposed using a high powered energy source, such as a
laser.
[0021] The glass structure may be patterned to create exposed
regions of higher index of refraction surrounded by areas of lower
index of refraction, such that light is substantially contained
within the higher index of refraction material. Conversely, the
patterned glass structure may be patterned to create exposed
regions of higher index of refraction surrounding areas of lower
index of refraction, such that light is substantially contained
within the lower index of refraction material. Either way, exposing
our glass with such ultraviolet light can raise index of refraction
of the glass and the changed index of refraction may used to
direct, manipulate, or process photons. Thus in some cases, etching
of the glass is not necessary to direct light within such a
patterned glass structure.
[0022] In some embodiments, the patterned glass structure is heated
to above its glass transition temperature for between 10 minutes
and 2 hours to allow the noble metal to coalesce and act as nuclei
for devitrification in the exposed portion of the photosensitive
glass substrate, and then the glass substrate is heated above its
glass-ceramic transition temperature (at least 25 C above its glass
transition temperature) for between 10 minutes and 2 hours. This
provides for transformation of the exposed portion of the
photosensitive glass substrate into a glass-ceramic during a
subsequent cooling of the glass substrate. The glass substrate can
then be etched in an HF-containing etchant solution, to give an
etch ratio of exposed-portion to unexposed-portion of at least 30:1
in a shaped glass structure.
[0023] In some embodiments, a surface-smoothing acid containing at
least one of nitric acid is used to dissolve surface metallic
silver and/or hydrochloric acid is used to dissolve surface cerium
metal is used during or after the HF etch, to reduce surface
roughness of at least one micro-optic device in the shaped glass
structure, such that light transmission through surfaces of a
micro-optic device is increased. The final patterned glass
structure may also be annealed near its glass transition
temperature to smooth out etched side walls.
[0024] Patterned glass structures that may be formed include
micro-optic lenses, micro-optic micro-posts, and micro-optic
waveguides such as micro-channels, micro-ridges (exposed glass is
etched away to leave a glass micro-ridge), and index of refraction
guides formed by patterned exposure of the glass.
[0025] In some embodiments, the patterned glass structure is
processed by flood exposing to 300-320 nm light and heated to a
temperature near its glass transformation temperature to allow at
least part of the reduced noble metal to coalesce to provide a
patterned glass structure is used to form larger clusters for at
least one plasmon analytical technique, e.g. surface enhanced
fluorescence, surface enhanced Raman spectroscopy, and surface
plasmon resonance.
[0026] In some embodiments, the patterned glass structure forms at
least part of a multilayer optical printed circuit board. This may
also be a method to make a micro-optical interconnection apparatus,
comprising: preparing a first photosensitive glass layer having a
first glass transformation temperature and having a composition
comprising: less than 76% silica, at least 0.0008% of at least one
of a noble metal oxide and/or a copper oxide, at least 11%
Li.sub.2O, and at least 0.0014% CeO.sub.2; exposing a first set of
paths in the first photosensitive glass layer with ultraviolet
light 240 to 360 nm light or a directed source of protons, while
leaving at least a second portion of the first glass layer
unexposed; depositing an ultraviolet-light reflecting-or-absorbing
layer on the first layer; depositing a layer of non-photosensitive
glass on the ultraviolet-light reflecting-or-absorbing layer;
patterning and etching vias in the ultraviolet-light
reflecting-or-absorbing layer and the non-photosensitive glass
layer to provide light-coupling vias; depositing a second
photosensitive glass layer on the patterned and etched
non-photosensitive glass, the second photosensitive glass layer
having a second glass transformation temperature and having a
composition comprising, less than 72% silica, at least 0.008% of at
least one of a noble metal oxide and a copper oxide, at least 11%
Li.sub.2O, at least 0.75% B.sub.2O.sub.3, and at least 0.0014%
CeO.sub.2, wherein the second photosensitive glass layer has a
higher index of refraction than the non-photosensitive glass;
exposing a second set of paths in the second photosensitive glass
layer with ultraviolet light 300 to 320 nm light or a directed
source of protons, while leaving at least a second portion of the
second photosensitive glass layer unexposed; and heating the
photosensitive glass layers to above their glass transformation
temperatures to raise the index of refraction of the first and
second sets of paths to render the sets of paths light-guiding.
[0027] This may also be a method to make a micro-optical
interconnection apparatus, comprising: preparing a first
photosensitive glass layer having a first glass transformation
temperature; exposing a first set of paths in the first
photosensitive glass layer with ultraviolet light 240 to 360 nm
light or a directed source of protons, while leaving at least a
second portion of the first glass layer unexposed; depositing an
ultraviolet-light reflecting-or-absorbing layer on the first layer;
depositing a layer of non-photosensitive glass on the
ultraviolet-light reflecting-or-absorbing layer; patterning and
etching vias in the ultraviolet-light reflecting-or-absorbing layer
and the non-photosensitive glass layer to provide light-coupling
vias; depositing a second photosensitive glass layer on the
patterned and etched non-photosensitive glass, the second
photosensitive glass layer having a second glass transformation
temperature and having a composition comprising, less than 72%
silica, at least 0.008% of at least one of a noble metal oxide and
a copper oxide, at least 11% Li.sub.2O, at least 0.75%
B.sub.2O.sub.3, and at least 0.0014% CeO.sub.2, wherein the second
photosensitive glass layer has a higher index of refraction than
the non-photosensitive glass; exposing a second set of paths in the
second photosensitive glass layer with ultraviolet light 300 to 320
nm light or a directed source of protons, while leaving at least a
second portion of the second photosensitive glass layer unexposed;
and heating the photosensitive glass layers to above their glass
transformation temperatures to raise the index of refraction of the
first and second sets of paths to render the sets of paths
light-guiding.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] For a more complete understanding of the features and
advantages of the present invention, reference is now made to the
detailed description of the invention along with the accompanying
figures and in which:
[0029] FIG. 1A is a first schematic of the processing of making
high-precision glass micromachined structures of the present
invention;
[0030] FIG. 1B is a second schematic of the processing of making
high-precision glass micromachined structures of the present
invention;
[0031] FIG. 1C is a third schematic of the processing of making
high-precision glass micromachined structures of the present
invention;
[0032] FIG. 1D is a fourth schematic of the processing of making
high-precision glass micromachined structures of the present
invention;
[0033] FIGS. 2A-2B are Field Emission Microscopy (FEM) images of
the high-precision glass micromachined structures of the present
invention;
[0034] FIG. 3A is a first FEM image of the high-precision glass
micromachined structures of the present invention;
[0035] FIG. 3B is a second FEM image of the high-precision glass
micromachined structures of the present invention;
[0036] FIG. 3C is a third FEM image of the high-precision glass
micromachined structures of the present invention;
[0037] FIG. 3D is a fourth FEM image of the high-precision glass
micromachined structures of the present invention;
[0038] FIGS. 4A-4B are FEM images of the high-precision glass
micromachined structures of the present invention;
[0039] FIG. 5A is a first FEM image of a high-precision glass
micromachined flower of the present invention;
[0040] FIG. 5B is a second FEM image of a high-precision glass
micromachined flower of the present invention;
[0041] FIG. 5C is a third FEM image of a high-precision glass
micromachined flower of the present invention;
[0042] FIGS. 6A-6B are FEM images of a high-precision glass
micromachined structures of the present invention;
[0043] FIG. 7 is a FEM image of a high-precision glass
micromachined structures of the present invention;
[0044] FIG. 8 is a FEM image of a high-precision glass
micromachined structures of the present invention;
[0045] FIGS. 9A and 9B are FEM images giving a side view of a
throughetched microchannel; and
[0046] FIGS. 10A and 10B are FEM images giving a side view of a
throughetched microchannel.
DETAILED DESCRIPTION OF THE INVENTION
[0047] While the making and using of various embodiments of the
present invention are discussed in detail below, it should be
appreciated that the present invention provides many applicable
inventive concepts that can be embodied in a wide variety of
specific contexts. The specific embodiments discussed herein are
merely illustrative of specific ways to make and use the invention
and do not restrict the scope of the invention.
[0048] To facilitate the understanding of this invention, a number
of terms are defined below. Terms defined herein have meanings as
commonly understood by a person of ordinary skill in the areas
relevant to the present invention. Terms such as "a", "an" and
"the" are not intended to refer to only a singular entity, but
include the general class of which a specific example may be used
for illustration. The terminology herein is used to describe
specific embodiments of the invention, but their usage does not
delimit the invention, except as outlined in the claims.
[0049] Photoetchable glasses have several advantages for the
fabrication of a wide variety of microsystems components.
Microstructures have been produced relatively inexpensively with
these glasses using conventional semiconductor processing
equipment. In general, glasses have high temperature stability,
good mechanical properties, are electrically insulating, and have
better chemical resistance than plastics and many metals. To our
knowledge, the only commercially available photoetchable glass is
FOTURAN.RTM., made by Schott Corporation and imported into the U.S.
only by Invenios Inc. FOTURAN.RTM. comprises a
lithium-aluminum-silicate glass containing traces of silver ions.
When exposed to UV-light within the absorption band of cerium oxide
the cerium oxide acts as sensitizers, absorbing a photon and
loosing an electron that reduces neighboring silver oxide to form
silver atoms (Please see the chemical equation below).
Ce.sup.3++Ag.sup.+.fwdarw.Ce.sup.4++Ag.sup.0
[0050] The silver atoms coalesce into silver nanoclusters during
the baking process and induces nucleation sites for crystallization
of the surrounding glass. If exposed to UV light through a mask,
only the exposed regions of the glass will crystallize during
subsequent heat treatment. This heat treatment must be performed at
a temperature near the glass transformation temperature (e.g.,
greater than 465.degree. C. in air for FOTURAN.RTM.). The
crystalline phase is more soluble in etchants, such as hydrofluoric
acid (HF), than the unexposed vitreous, amorphous regions. In
particular, the crystalline regions of FOTURAN.RTM. are etched
about 20 times faster than the amorphous regions in 10% HF,
enabling microstructures with wall slopes ratios of about 20:1 when
the exposed regions are removed. See T. R. Dietrich et al.,
"Fabrication technologies for microsystems utilizing photoetchable
glass," Microelectronic Engineering 30, 497 (1996), which is
incorporated herein by reference.
[0051] Preferably, the shaped glass structure contains at least one
of a micro-optic lens, a micro-optic micro-post, and a
micro-channel or micro-ridge micro-optic waveguide. The
micro-ridge, optical waveguide may be formed by etching away
exposed glass to leave a glass micro-ridge such that light is
guided by the micro-ridge. The micro-ridge may be formed with a
layer of photosensitive glass overlying a layer of
non-photosensitive glass of lower index of refraction than the
photosensitive glass, to substantially prevent light being guided
by the micro-ridge from leaving the bottom of the micro-ridge in at
least one portion of the micro-ridge. In some embodiments, a
surface-smoothing acid containing at least one of nitric acid to
dissolve surface metallic silver and hydrochloric acid to dissolve
surface cerium metal is used during or after the HF etch, whereby
surface roughness of at least one micro-optic device in the shaped
glass structure is reduced and whereby light transmission through
surfaces of a micro-optic device is increased.
[0052] FOTURAN.RTM. is described in information supplied by
Invenios (the sole source U.S. supplier for FOTURAN.RTM.) is
composed of silicon oxide (SiO.sub.2) of 75-85% by weight, lithium
oxide (Li.sub.2O) of 7-11% by weight, aluminum oxide
(Al.sub.2O.sub.3) of 3-6% by weight, sodium oxide (Na.sub.2O) of
1-2% by weight, 0.2-0.5% by weight antimonium trioxide
(Sb.sub.2O.sub.3) or arsenic oxide (As.sub.2O.sub.3), silver oxide
(Ag.sub.2O) of 0.05-0.15% by weight, and cerium oxide (CeO.sub.2)
of 0.01-0.04% by weight.
[0053] As used herein the term "APEX glass" or simply "APEX" is
used to denote one embodiment of the composition of the present
invention. Surprisingly, it was found that the compositions of the
present invention may appear to be similar to FOTURAN.RTM.,
however, the compositions of the present invention demonstrated a
surprising sensitivity to ultraviolet light exposure of over three
times that of the commercially available photosensitive glass, and
yielded up to six times the etch rate more compared to FOTURAN.RTM.
when both compositions were processed in the way recommended for
FOTURAN.RTM. (with the exception of the reduced exposure and bake
temperature used for APEX due to its greater sensitivity and lower
glass transformation temperature). Further, APEX glass had an etch
ratio of exposed portion to that of the unexposed portion of at
least 30:1 to 40:1, while the best reported etch ratio of the
commercially available FOTURAN.RTM. photosensitive glass exposed
with a broad spectrum mid-ultraviolet flood lamp is about 20:1.
[0054] The reason for the dramatically improved result is not well
understood. Not wanting to be bound by theory, it is believed that
changes in the APEX composition provides three main mechanisms for
its enhanced performance: (1) The higher amount of silver leads to
the formation of smaller ceramic crystals which are etched faster
at the grain boundaries, (2) the decrease in silica content (the
main constituent etched by the HF acid) decreases the undesired
etching of unexposed material, and (3) the higher total weight
percent of the alkali metals and boron oxide produces a much more
homogeneous glass during manufacturing. This facilitates more
consistent performance across the substrate over large
distances--but in any case, the results are surprising.
[0055] Kravitz et al. (U.S. Pat. No. 7,132,054), suggests that an
even less expensive method of fabricating the microneedles is to
replicate them using a negative mold made from the original glass
hollow microneedle array structure, as follows: "A negative mold
can be made by depositing a mold material onto the glass hollow
microneedle array. For example, a negative mold of FOTURAN.RTM..
Microneedles can be made by electroplating a metal (e.g., nickel,
copper, or gold) onto a sputtered seed layer deposited on the
FOTURAN.RTM. microneedles. After the negative plated mold is
created and released from the glass array, a liquid polymer, such
as Zeonor 1020R, can be cast into the mold. After the Zeonor 1020R
is cooled and solidified, the polymeric hollow microneedle array
can be easily peeled off the plated negative mold and the mold can
be re-used. Other plastics that can be hot embossed or injection
molded, such as polycarbonate, can also be used." Such an approach
can be improved by using APEX.
[0056] Alternatively, a negative mold can be made directly of the
photoetchable glass, as shown in their FIGS. 7A and 7E of Kravitz,
et al.'s U.S. Pat. No. 7,132,054. A similar process can be used
with our glass composition, and Kravitz, et al.'s U.S. Pat. No.
7,132,054 is hereby incorporated by reference. The composition of
the present invention is a glass composition referred to herein as
"APEX glass" or simply "APEX".
[0057] FIGS. 1A-D are schematics of the processing of making
high-precision glass micromachined structures with etch ratios of
30:1 to 50:1 of the present invention. FIG. 1A is an illustration
of the substrate 10 that is partially covered by the mask 12 and
treated with an emissions radiation 14. The emissions radiation 14
may be of a variety of types including mid-ultraviolet radiation
from a mid-ultraviolet flood exposure system or laser emission from
a laser-based exposure system. For example, the emission may be
approximately 308 to 312 nm; but the skilled artisan will recognize
that other wavelengths (50-100, 100-150, 150-200, 200-250, 250-300,
300-400, 400-500, 500-600, 600-700, 700-800, 800 nm or above) may
be used.
[0058] FIG. 1B is an illustration of the substrate 10 that has been
partially covered by the mask (not shown) and treated with an
emissions radiation (not shown) to produce exposed areas 16A and
16B and unexposed areas 18. The substrate 10 is then heated to a
temperature near the glass transformation temperature to transform
at least part of the exposed glass to a crystalline material.
[0059] FIG. 1C is an illustration of the substrate 10 treated with
an etching solution. The substrate 10 includes crystalline material
regions 16A and 16B and unexposed regions 18. The substrate 10 is
treated with an etchant 20 to etch the crystalline material regions
16A and 16B. The etching process results in etch ratio of exposed
portion to that of the unexposed portion is at least 30:1 when
exposed with a broad spectrum mid-ultraviolet flood light, and
greater than 30:1 when exposed with a laser, to provide a shaped
glass structure with an anisotropic-etch ratio of at least 30:1. In
some embodiments, the etchant 20 is HF, in some embodiments the
etchant 20 is a combination of HF and additional ingredients, such
as hydrochloric acid or nitric acid.
[0060] FIG. 1D is an illustration of the substrate 10 treated with
an etching solution to remove the crystalline material regions (not
shown) to leave the etched areas 22A and 22B in the unexposed
regions 18.
[0061] FIGS. 2A-2B are FEM images of the high-precision glass
micromachined structures of the present invention. FIGS. 3A-3D are
FEM images of the high-precision glass micromachined structures of
the present invention. FIGS. 3A and 3B are FEM images that
illustrate 4 different examples of types of micromachined
structures 18a-18d. The micromachined structures 18a-18d are
evident from the etched areas 22. FIG. 3C is an FEM image that
micromachined structures 18e-18f which is evident from the etched
areas 22. FIG. 3D is a FEM image that micromachined structures 18g
which is evident from the etched areas 22.
[0062] FIGS. 4A-4B are FEM images of the high-precision glass
micromachined structures of the present invention. FIG. 4A is an
FEM image that illustrates micromachined structures 18 having
etched areas 22 that produce a gap 24 between the unexposed regions
that form the micromachined structures 18. In FIG. 4A the gap 24 is
10 microns wide between adjacent micromachined structures 18 and
about 50 microns deep. FIG. 4B is a FEM image of the high-precision
glass micromachined structures of the present invention.
[0063] FIGS. 5A-5C are FEM images of a high-precision glass
micromachined flower that illustrate some of the capability of the
present invention. FIGS. 5A and 5B are FEM images that illustrates
micromachined flower 18 having etched areas 22 between the
unexposed regions that form the micromachined flower 18. FIG. 5C is
a higher magnification FEM image of a high-precision glass
micromachined flower 18 of the present invention. It is clear from
the extremely smooth top surface that the non-exposed surfaces 18
etches extremely slowly compared to the exposed area of the gap
24.
[0064] FIGS. 6A-6B are FEM images of a high-precision glass
micromachined structures of the present invention. FIG. 6A is an
FEM image that illustrates micromachined bricks 18a and 18b having
etched areas 22 between the unexposed regions that form the
micromachined bricks 18a and 18b. The analysis area 26 is magnified
in FIG. 6B. The aspect ratio of the micromachined brick 18a can be
calculated by comparing the vertical line height to the horizontal
line height; and result in this example to have an aspect ratio of
about 27:1.
[0065] FIG. 7 is a FEM image of a high-precision glass
micromachined structures of the present invention. FIG. 7 is an FEM
image that illustrates micromachined bricks 18a and 18b having
etched areas 22 between the unexposed regions that form the
micromachined bricks 18a and 18b. The analysis area 26 shows that
the aspect ratio of the micromachined brick 18a can be calculated
by comparing the vertical line height to the horizontal line height
to have an aspect ratio of about 27.66:1.
[0066] FIG. 8 is a FEM image of a high-precision glass
micromachined structures of the present invention. FIG. 8 is an FEM
image that illustrates micromachined structures 18a, 18b, 18c, 18d
and 18e having etched areas 22a-22d between the unexposed regions
18a, 18b, 18c, 18d and 18e. The profile of the walls formed by the
etched areas 22a-22d and the unexposed regions 18a, 18b, 18c, 18d
and 18e can be seen.
[0067] FIGS. 9A and 9B are FEM images giving a side view of a
through-etched 100 .mu.m wide microchannel (one half of walls
removed for FEM analysis). FIG. 9B is an image that shows the
smooth sidewall and top surfaces with very crisp edges.
[0068] FIGS. 10A and 10B are FEM images giving a side view of a
through-etched 100 .mu.m wide microchannel (one half of walls
removed for FEM analysis). FIG. 10B is an image of a cross section
of etched vias, 100 .mu.ms in diameter and 1 mm tall.
[0069] The glass structure may be patterned to create exposed
regions of higher index of refraction surrounded by areas of lower
index of refraction, such that light is substantially contained
within the higher index of refraction material. Conversely, the
patterned glass structure may be patterned to create exposed
regions of higher index of refraction surrounding areas of lower
index of refraction, such that light is substantially contained
within the lower index of refraction material. Either way, exposing
our glass with such ultraviolet light can raise index of refraction
of the glass such and the changed index of refraction may used to
direct, manipulate, or process photons. Thus in some cases, etching
of the glass is not necessary to direct light within such a
patterned glass structure. The degree to which the index of
refraction is changed can be varied through a simple bake process
where the glass structure is heated near its glass transition
temperature for between 10 minutes and 18 hours allowing the atomic
silver to coalesce into larger silver clusters.
[0070] In some embodiments, a surface-smoothing acid containing at
least one of nitric acid is used to dissolve surface metallic
silver and/or hydrochloric acid is used to dissolve surface cerium
metal is used during or after the HF etch, to reduce surface
roughness of at least one micro-optic device in the shaped glass
structure, such that light transmission through surfaces of a
micro-optic device is increased. The final patterned glass
structure may also be annealed past its glass transition
temperature to smooth out etched side walls.
[0071] Patterned glass structures that may be formed include
micro-optic lenses, micro-optic micro-posts, and micro-optic
waveguides such as micro-channels, micro-ridges (exposed glass is
etched away to leave a glass micro-ridge), and index of refraction
guides formed by patterned exposure of the glass (with or without
baking).
[0072] The glass substrate may also be heated to a temperature in
excess of the glass transformation temperature to allow at least
part of the reduced noble metal to coalesce to provide a patterned
glass structure is used to form larger clusters for at least one
plasmon analytical technique, e.g. surface enhanced fluorescence,
surface enhanced Raman spectroscopy, and surface plasmon
resonance.
[0073] In some embodiments, the patterned glass structure forms at
least part of a two or more layer optical printed circuit board.
This may also be a method to make a micro-optical interconnection
apparatus, comprising: preparing a first photosensitive glass layer
having a first glass transformation temperature and having a
composition comprising: less than 72% silica, at least 0.0008% of
at least one of a noble metal oxide and/or a copper oxide, at least
11% Li2O, and at least 0.0014% CeO2; exposing a first set of paths
in the first photosensitive glass layer with an activating energy
source, such as an ultraviolet light (240 to 360 nm) or a directed
source of protons, while leaving at least a second portion of the
first glass layer unexposed; depositing an ultraviolet-light
reflecting-or-absorbing layer on the first layer; depositing a
layer of non-photosensitive glass on the ultraviolet-light
reflecting-or-absorbing layer; patterning and etching vias in the
ultraviolet-light reflecting-or-absorbing layer and the
non-photosensitive glass layer to provide light-coupling vias;
depositing a second photosensitive glass layer on the patterned and
etched non-photosensitive glass, the second photosensitive glass
layer having a second glass transformation temperature and having a
composition comprising, less than 76% silica, at least 0.008% of at
least one of a noble metal oxide and a copper oxide, at least 11%
Li2O, at least 0.75% B2O3, and at least 0.0014% CeO2, wherein the
second photosensitive glass layer has a higher index of refraction
than the non-photosensitive glass; exposing a second set of paths
in the second photosensitive glass layer with an activating energy
source, such as ultraviolet light (300 to 320 nm) or a directed
source of protons, while leaving at least a second portion of the
second photosensitive glass layer unexposed; and heating the
photosensitive glass layers to above their glass transformation
temperatures to raise the index of refraction of the first and
second sets of paths to render the sets of paths light-guiding.
[0074] While light can go from layer to layer vertically through
vias, in some preferred embodiments light goes from layer to layer
at a non-vertical angle. Light may be transferred through an
elongated via using the same index of refraction in touching upper
and lower light-guiding paths that overlap for some distance. Light
may also be transferred through a less elongated via using a
slightly higher index of refraction (higher than the touching upper
and lower light-guiding paths) using 3-D patterning. The higher
index of refraction can be produced by higher 3-D exposure using
orthogonal laser beams focused on a series of points to create a
pattern of higher index of refraction points leading between upper
and lower light-guiding paths. The 3-D exposure can also create
other structures, including corners of reduced radius (as compared
to corners of constant index of refraction), polarizers, and
diffraction gratings.
[0075] General Photoactive Glass Manufacturing Design Rules:
[0076] Boron Oxide and Aluminum oxide basically conduct the same
task within the glass melt. Boron oxide may also be in the form of
anhydride boric acid (H.sub.3BO.sub.3), Borax Frits, Gerstley
Borate/Colemanite, Boric Acid, Borax, and Ulexite. A 13 weight %
represents the high end of B.sub.2O.sub.3 in borosilicate glasses.
Boron Oxide concentration range: Up to 13 weight %. Aluminum oxide
may be in the form of Alkali containing feldspars (such as Albite,
NaAlSi.sub.3O.sub.8) or alumina hydrate. Al.sub.2O.sub.3 may be
added by using kaolin or nepheline syenite (which contains
feldspar). Up to 8 weight %. This represents the high end of
Al.sub.2O.sub.3 in borosilicate glasses.crystallization Aluminum
Oxide concentration range: up to 7 weight %. Or more appropriately,
the combination of Boron Oxide and Aluminum Oxide should not exceed
13 weight %.
[0077] Potassium Oxide and Sodium Oxide basically conduct the same
task within the glass melt. Potassium oxide: Helps lower melting
point. Sometimes used to replace sodium in soda lime glasses. Range
up to 16 weight % as well. May also be Potash (K.sub.2CO.sub.3). If
used to replace Na.sub.2O, typically makes the glass more
chemically resistant.
[0078] Potassium Oxide concentration range: up to 16 weight %.
Sodium oxide helps lower melting point. Range up to 16 weight %
(common high end for soda lime glass). May also be soda ash
(Na.sub.2CO.sub.3) or Glauber's Salt (Na.sub.2SO.sub.4). Sodium
oxide concentration range: up to 16 weight %. Or more
appropriately, the combination of these two should not exceed 16
weight %. Silica: concentration range: 60-85 weight %.
[0079] Zinc oxide: Improves chemical resistance, lowers thermal
expansion, adds elasticity. Works similarly with CaO. Up to 18
weight % in E-Glass. Zinc Oxide concentration range: up to 18
weight %. Lithium Oxide: Aids in nucleation. Can be lithium
carbonate. Lithium Oxide concentration range: 8-15 weight %.
[0080] Cerium Oxide: Electron Donor. Cerium oxide concentration
range: up to 0.1 weight %. Antimonium trioxide: Oxygen donor.
Antimonium trioxide (Sb.sub.2O.sub.3) concentration range: up to
0.5 weight %. Arsenic Oxide: Oxygen donor. Arsenic oxide
(As.sub.2O.sub.3): Electron Donor. Arsenic Oxide concentration
range: up to 0.1 weight.
[0081] Silver Oxide concentration range: up to 1 weight %. Gold
Oxide concentration range: up to 1 weight %. Copper Oxide
concentration range: up to 2 weight %.
[0082] The above ingredients might be at least partially replaced
with the following compounds:
[0083] Calcium Oxide: Improves chemical resistance, lowers thermal
expansion, adds elasticity. Works similarly with ZnO. Up to 18
weight % in E-Glass. Calcium Oxide concentration range: up to 18
weight %. Magnesium Oxide: This is the upper end in E-glass. May be
in the form of MgCO.sub.3. Magnesium oxide concentrate range: up to
10 weight %. Barium Oxide Improves refractive index of the material
without increasing the dispersive power. Used as a replacement for
lead or lime. May also come in the form of BaCO.sub.3. Barium Oxide
concentration range: up to 18 weight %. Lead Oxide: Improves
refractive index of the material with out increasing the dispersive
power. Lead Oxide concentration range: up to 18 weight %.
[0084] Iron may be added to the melt to make the material
paramagnetic (e.g. Fe.sub.2O.sub.3). Iron oxide may additionally be
used to quench intrinsic autofluorescence of other compounds within
the glass. Iron Oxide Concentration range: up to 5 weight %.
[0085] Processing parameters. Patterning of the selected area(s) by
at least one process step selected from the group consisting
of:
[0086] Exposure-Exposing the glass substrate to an activating
energy source, such as 310 nm light or a directed source of
protons.
[0087] High anisotropic-etch ratios may be obtained using the
photoactive glass of the present invention using a total activation
energy between 0.4 J/cm.sup.2 and 4 J/cm.sup.2 of 310 nm light. In
contrast, FOTURAN.RTM. sometimes requires up to 54 J/cm.sup.2
activation energy to create a uniform exposure across large
distances (i.e., inches).
[0088] Baking-Baking typically occurs in a two step process.
Temperature 1 allows for the coalescing of silver ions into silver
nanoparticles and temperature 2 allows for the lithium oxide to
form around the silver nanoparticles. However, we have been
successful in doing a single ramp step.
[0089] Etching-Etching is done in an HF solution, typically 5-10%
by volume. However, we can also add other fluids to the etch
solution. For example, we can add hydrochloric or nitric acid to
the etch solution. We've had good success in using this solution to
obtain a smoother etch because it dissolves the silver
nanoparticles. This etch is especially useful in the fabrication of
structures and devices that require a smooth surfaces, such as
micro-lenses and micro-channels (e.g. to guide fluids).
[0090] In the fabrication of the micro-channels and many MEM's
devices many times it is important to have the ability to
hermetically seal more than one layer together. In the case of the
micro-channel these layers may consist of a top and/or bottom lid
with at least one section containing the actual micro-channel. The
hermetic seal is important for fluid or gas retention. APEX has
been shown to bonds to itself between temperatures of 450 C and 565
C creating a hermetic seal and bonding in such a way that two
individual pieces of glass become one piece of glass, making a
solid device. The temperatures used to bond APEX to itself are low
enough that many metallization procedures done prior to the bonding
step will not be affected by the elevated temperature.
[0091] The photoactive glass of the present invention can be used
to make micro-posts (.mu.Posts), electroposts, micro-optics,
micro-lenses, micro-waveguides for the directed moving of light,
and micro-channels for the directed moving of fluids.
[0092] The .mu.Posts can be optically transparent micron-scaled
posts that painlessly penetrate into the epidermal or dermal layers
of skin allowing for optical interrogation of the surrounding
tissue.
[0093] .mu.Post usages include: (1) In vivo optical
preconcentration/detection of low abundant compounds; used for a
feedback control loop for medicines; uses the heart for continued
blood turnover. (2) Detection of large molecular weight compounds
using FTIR, SERS, in vivo ELISAs, etc.
[0094] ElectroPosts can be electrically conductive micron-scaled
posts that painlessly penetrate into the epidermal or dermal layers
of skin allowing for the electrochemical interrogation of the
surrounding tissue. The conductive posts can be cast using an APEX
mold or a mold made using an APEX pattern, or with metal-plated
APEX. ElectroPosts can be made via micro-wire EDM.
[0095] .mu.Post usages include: (1) In vivo
preconcentration/detection of low abundant compounds; used for a
feedback control loop for medicines; uses the heart for continued
blood turnover. (2) Use conducting .mu.Posts to measure
conductivity. This allows the doctor to identify where
(epidermal/dermal) the tip of the analytical .mu.Post is. (3) Use
conducting posts (e.g. one or more metal plated .mu.Posts to
measure conductivity) included with .mu.Posts. This allows the
doctor to identify where (epidermal/dermal) the tip of the
analytical .mu.Post.
[0096] In the Kravitz et al. patent .mu.Posts were fabricated out
of FOTURAN.RTM., a photo-definable glass, in a three-step process
of expose, bake, and etch. Areas of exposed glass are more soluble
in dilute hydrofluoric acid. There are four main reasons why
FOTURAN.RTM. micro-structures provide added benefit over other
emerging technologies for non-invasive diagnostics (i.e.
microneedles, transdermal spectroscopy). First, FOTURAN.RTM. is
capable of making high anisotropic-etch ratio features. .mu.Posts
with anisotropic-etch ratios greater than 8:1 are easily obtained.
With these high anisotropic-etch ratios, the .mu.Posts are able to
easily penetrate into the skin without significant use of
force.
[0097] Additionally, because FOTURAN.RTM. is a glass it has greater
structural integrity than traditional materials, such as silicon or
plastic. In further attempts to decrease the likelihood of post
shearing inside a patient, the present inventors have been
successful in creating metal reinforced .mu.Posts capable of
withstanding more then 50 mN/post of shear force. Another advantage
FOTURAN.RTM. .mu.Posts have over other emerging technologies is
that diagnostics are performed within the patient. By coating the
tips of the .mu.Posts with capture proteins and placing the
analytical patch into a patient, the capture proteins are placed in
intimate contact with the sensing region of interest. With this
approach the present inventors avoid the complicated extraction of
fluids to secondary analysis systems, such as with microneedles.
FOTURAN.RTM. is glass-based, it is transparent in portions of the
electromagnetic spectrum important in spectroscopy (e.g. 400
nm-1100 nm). These optically transparent .mu.Posts will provide the
basis of a robust platform for the first minimally invasive in-vivo
diagnostic platform capable of recording events deep in the dermal
layers of a patient's skin. Again, similar use with our APEX glass
the photoactive glass of the present invention can be used to make
micro-posts can give an even better device.
TABLE-US-00001 TABLE 1 Comparison of performance metrics
Commercially Descrip- Available tion Photoactive Number Processing
Metrics APEX Glass 1 Aspect ratio +++* 2 Etch rate +++ 3 Pattern
resolution + + 4 Energy required for adequate +++ formation of
atomic silver 5 Forgiveness to overexposure + 6 Minimum feature
pitch + 7 Adjacent large and small features + + 8 Etch consistency
across substrate ++++ 9 Etch rate of non-exposed regions +++ 10 Max
etch depth + 11 Transparency of non-exposed ++ regions after etch
12 Ability to thermally bond to itself ++ 13 Total processing time
++ *The greater the "+", the higher the degree of differentiation
in favor of the noted glass.
[0098] Below is an elaboration of Table 1 above and the processing
metrics presented. This table is meant to represent qualitative
advantages or disadvantages of the photoactive glass of the present
invention versus a commercially available photoactive glass and the
skilled artisan will recognize that it is not meant to convey
absolute values.
[0099] Aspect ratio: Aspect ratios greater than 30:1 have been
produced using a broad spectrum mid-ultraviolet flood lamp. This
is, for example, 50% more than reported and observed values for the
commercially available photoactive glass.
[0100] Etch rate: Etch rates of ceramic regions range between
10-150 .mu.m/minute for the photoactive glass of the present
invention, compared to 1-20 .mu.m/min for the commercially
available photoactive glass. This faster etch rate aids in creating
high aspect ratios and preservation of crisp features and
transparency of non-exposed glass regions.
[0101] Pattern resolution: Both glasses present similar ability to
create large (i.e. millimeter regime) and small features (i.e.
double digit micrometer regime).
[0102] Energy required for adequate formation of atomic silver:
This is very important for laser-based exposure systems. Since APEX
has a higher sensitivity, smaller energy levels are required to
facilitate the formation of atomic silver formation--without
sacrificing feature formation.
[0103] Forgiveness to overexposure: The commercially available
photoactive glass has a greater ability to accept a larger amount
of delivered light energy without pattern bleed-over.
[0104] Minimum feature pitch: This is defined as how close features
can be placed together. Our studies have shown the photoactive
glass of the present invention has a slight advantage in placing
very small features adjacent to one another.
[0105] Adjacent large and small features: This is defined as
placing small (i.e. micron sized features) next to large (i.e.,
millimeter sized features). Both glasses present similar
results.
[0106] Etch consistency across substrate: This may be defined as
pattern yield. The photoactive glass of the present invention has
been demonstrated to provide very similar structures across large
distances (i.e. 4 inches). This is extremely important in product
manufacturing since high yields translate to lower overall costs.
Not wanting to be bound by theory, it is believed that the
increased concentration of alkali metals and boron oxide aid in
creating a more homogeneous glass mixture, which leads to more
consistent results across relatively large distances (inches vs.
microns) on the substrate.
[0107] Etch rate of non-exposed regions: This processing metric
helps in the creation of high aspect-ratio features, as unexposed
material (present in the glass state) are not preferentially
etched. Not wanting to be bound by theory, it is believed that the
lower silica content in the glass decreases its susceptibility to
etching (e.g. via acids, such as HF).
[0108] Max Etch Depth: This is defined as how deep into the
substrate patterns can be created. The photoactive glass of the
present invention has the ability to create deeper features, for
example greater than 2 mm etch depth.
[0109] Transparency of non-exposed regions after etch: Due to the
observed decrease etch rate of non-exposed regions, the glass
remains more transparent.
[0110] Ability to thermally bond to itself: This is important when
creating multi-layered substrates, like that used in more complex
devices (e.g. Microelectromechanical Systems (MEMs)/Biological
MEMs/semiconductor packaging, etc.) The photoactive glass of the
present invention provides a more consistent thermal bond at a
lower temperature than commercially available photoactive
glass.
[0111] Decreased processing time: This becomes important in
production environments where reduced processing usually translates
into lower unit costs. Due to several of the features described
above, the photoactive glass of the present invention can be
processed in a more rapid and efficient manner compared to other
commercially available photoactive substrates.
[0112] Table 2, below summarizes modern photosensitive glass
compositions and various compositions of the present invention.
While photosensitive glasses have been known for some time (e.g.
patents S. D. Stookey: "Photosensitively Opacifiable Glass" U.S.
Pat. No. 2,684,911 (1954), and also U.S. Pat. No. 2,628,160 and
U.S. Pat. No. 2,971,853 covering products sold as Fotoform and
Fotoceram, and sometimes described with broad composition ratios,
e.g., Speit and U.S. Pat. No. 5,078,771 by Wu), etch ratios
apparently have only been evaluated for FOTURAN.RTM., see Dietrich
et al. and Livingston, et al., above. Note that for practical
purposes anisotropic-etch ratios are easily and accurately
measurable. Note also that wall slope angles are difficult to
measure directly. E.g. Dietrich et al. give a relatively broad
range of 2-4 degrees for their wall slope angle corresponding to a
20:1 etch ratio. Aspect ratios may be calculated using the
following approach: The sine of wall slope angle is equal to the
unexposed etch rate divided by the exposed etch rate. Dietrich et
al.'s wall slope angle was calculated at 1:20 (or 0.05) unexposed
to exposed etch ratio, and thus is about 3 degrees (Sine of 3
degrees=0.052).
TABLE-US-00002 TABLE 2 Corning Dietrich 8603 (commercially Test 1
Fotoform Schott-Speiton available as Pat. No. Photosenitive Formula
Fotoceram PEG3 FOTURAN .RTM. FOTURAN .RTM.) 5,374,291 Glass #1
B.sub.2O.sub.3 0.75 K.sub.2O 4.10% 4.00% 3-6% trace** 6 SiO.sub.2
79.60% 78.00% 60-85% 75-85% 70-84% 71.66 Al.sub.2O.sub.3 4.00%
6.00% 2-25%* 3-6% 3-10% 6 Na.sub.2O 1.60% 1.00% 1-2% trace** 2 ZnO
1.00% 0-2% trace** 2 Li.sub.2O 9.30% 10.00% 5.5-15%* 7-11% 5-20% 11
CeO.sub.2 0.014% 0.080% 0.001-0.01 0.01-0.04% 0.01-0.1% 0.04
Sb.sub.2O.sub.3 0.400% 0.2-0.4% 0.4 Ag.sub.2O 0.11% 0.080% 0.0008
to 0.05 to 0.05 to 0.15 ~0.24* 0.15% 0.30% Au.sub.2O 0.001% 0.003%
SnO.sub.2 0.003% trace** As.sub.2O.sub.3 0.1-0.3% Cu.sub.2O
0.001-1% other trace** oxides Al.sub.20.sub.3:Li.sub.20 <1.7
Formula APG APG APG APG APG APG APG APG APG APG APG APG APG #2 #3
#4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14 Boron 1 0.75 1.25 2 0.5 0.5
0.75 0.75 1 0.5 0.5 0.5 0.75 Oxide Potassium 6 5.5 6 5 4 5 6 5.5
6.1 5 4 5 5 Oxide Silica 71.4 71.8 69.1 72.0 73.4 70.6 71.6 71.7
71.5 72.5 72.2 72.9 72.21 Aluminum 6 6 6 6.25 5.5 6.25 6 5.8 6.2
5.25 5.5 5.5 5.5 Oxide Sodium 2.5 2 2 1 2.25 2.5 2 2 1.75 2.5 2.25
2.5 2.5 Oxide Zinc Oxide 2.5 1.5 2 2 1.5 1.25 2 0.5 1.8 1.25 1.45 1
1 Lithium 10 11 11 10.2 11.2 11.5 11 11.5 10.5 11.5 11.5 11.5 11.5
Oxide Cerium 0.04 0.02 0.04 0.02 0.03 0.03 0.04 0.35 0.39 0.03 0.03
0.04 0.04 Oxide Antimonium 0.4 0.3 0.4 0.3 0.4 0.4 0.4 0.4 0.03 0.3
0.4 0.35 0.35 Trioxide Gold Oxide 0.08 0.04 0.15 0.15 Silver 0.05
0.15 0.12 0.14 0.06 0.1 0.15 0.15 0.15 Oxide Copper 0.1 0.5 1 Oxide
Iron Oxide 1 1 0.5 Calcium 1 1 1 Oxide Barium 1 1.75 0.5 1 2 Oxide
*0.001 to ~0.3 as AgCl **in some experiments in 5,374,291
[0113] This can also be a method to fabricate a shaped glass
structure with a high-aspect ratio, comprising: preparing a
photosensitive glass substrate having a glass transformation
temperature and having a composition of: less than 76 weight %
silica, at least 6 weight % K.sub.2O, at least 0.15 weight %
Ag.sub.2O, at least 0.75 weight % B.sub.2O.sub.3, and at least 6
weight % Al.sub.2O.sub.3, at least 11 weight % Li.sub.2O, and at
least 0.04 weight % CeO.sub.2. Patterning of the selected area(s)
by at least one process step selected from the group consisting of:
exposing at least one portion of the photosensitive glass substrate
to ultraviolet light, while leaving at least a second portion of
said glass substrate unexposed; heating the glass substrate to a
temperature near the glass transformation temperature to transform
at least part of the exposed glass to a crystalline material;
etching the glass substrate in an etchant, wherein the etch ratio
of exposed portion to said unexposed portion is at least 30:1 when
the glass is exposed to a broad spectrum mid-ultraviolet flood
lamp, to provide a shaped glass structure with an aspect ratio of
at least 30:1, and to provide shaped glass structures with an
aspect ratio much greater than 30:1 when the glass is exposed using
a high powered energy source, such as a laser.
[0114] The present invention can also be used to fabricate a shaped
glass structure with a high-aspect ratio, that includes: preparing
a photosensitive glass substrate having a glass transformation
temperature and having a composition of: less than 76 weight %
silica, at least 0.15 weight % Ag.sub.2O, at least 0.75 weight %
B.sub.2O.sub.3, at least 11 weight % Li.sub.2O, and at least 0.04
weight % CeO.sub.2 with preferably at least 0.85 weight %
B.sub.2O.sub.3 is used. Patterning of the selected area(s) by at
least one process step selected from the group consisting of:
Exposing at least one portion of the photosensitive glass substrate
to ultraviolet light, while leaving at least a second portion of
said glass substrate unexposed; heating the glass substrate to a
temperature near glass transformation temperature to transform at
least part of the exposed glass to a crystalline material; etching
the glass substrate in an etchant, wherein the etch ratio of
exposed portion to said unexposed portion is at least 30:1 when the
glass is exposed to a broad spectrum mid-ultraviolet flood lamp, to
provide a shaped glass structure with an aspect ratio of at least
30:1, and to provide shaped glass structures with an aspect ratio
much greater than 30:1 when the glass is exposed using a high
powered energy source, such as a laser.
[0115] It is contemplated that any embodiment discussed in this
specification can be implemented with respect to any method, kit,
reagent, or composition of the invention, and vice versa.
Furthermore, compositions of the invention can be used to achieve
methods of the invention.
[0116] It will be understood that particular embodiments described
herein are shown by way of illustration and not as limitations of
the invention. The principal features of this invention can be
employed in various embodiments without departing from the scope of
the invention. Those skilled in the art will recognize, or be able
to ascertain using no more than routine experimentation, numerous
equivalents to the specific procedures described herein. Such
equivalents are considered to be within the scope of this invention
and are covered by the claims.
[0117] All publications and patent applications mentioned in the
specification are indicative of the level of skill of those skilled
in the art to which this invention pertains. All publications and
patent applications are herein incorporated by reference to the
same extent as if each individual publication or patent application
was specifically and individually indicated to be incorporated by
reference.
[0118] The use of the word "a" or "an" when used in conjunction
with the term "comprising" in the claims and/or the specification
may mean "one," but it is also consistent with the meaning of "one
or more," "at least one," and "one or more than one." The use of
the term "or" in the claims is used to mean "and/or" unless
explicitly indicated to refer to alternatives only or the
alternatives are mutually exclusive, although the disclosure
supports a definition that refers to only alternatives and
"and/or." Throughout this application, the term "about" is used to
indicate that a value includes the inherent variation of error for
the device, the method being employed to determine the value, or
the variation that exists among the study subjects.
[0119] As used in this specification and claim(s), the words
"comprising" (and any form of comprising, such as "comprise" and
"comprises"), "having" (and any form of having, such as "have" and
"has"), "including" (and any form of including, such as "includes"
and "include") or "containing" (and any form of containing, such as
"contains" and "contain") are inclusive or open-ended and do not
exclude additional, unrecited elements or method steps.
[0120] The term "or combinations thereof" as used herein refers to
all permutations and combinations of the listed items preceding the
term. For example, "A, B, C, or combinations thereof" is intended
to include at least one of: A, B, C, AB, AC, BC, or ABC, and if
order is important in a particular context, also BA, CA, CB, CBA,
BCA, ACB, BAC, or CAB. Continuing with this example, expressly
included are combinations that contain repeats of one or more item
or term, such as BB, AAA, MB, BBC, AAABCCCC, CBBAAA, CABABB, and so
forth. The skilled artisan will understand that typically there is
no limit on the number of items or terms in any combination, unless
otherwise apparent from the context.
[0121] All of the compositions and/or methods disclosed and claimed
herein can be made and executed without undue experimentation in
light of the present disclosure. While the compositions and methods
of this invention have been described in terms of preferred
embodiments, it will be apparent to those of skill in the art that
variations may be applied to the compositions and/or methods and in
the steps or in the sequence of steps of the method described
herein without departing from the concept, spirit and scope of the
invention. All such similar substitutes and modifications apparent
to those skilled in the art are deemed to be within the spirit,
scope and concept of the invention as defined by the appended
claims.
* * * * *