U.S. patent application number 11/253560 was filed with the patent office on 2006-02-23 for micro-shape transcription method, micro-shape transcription apparatus, and optical-component manufacture method.
Invention is credited to Hiroyuki Asakura, Tsuguhiro Korenaga, Makoto Umetani.
Application Number | 20060038309 11/253560 |
Document ID | / |
Family ID | 16410827 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060038309 |
Kind Code |
A1 |
Korenaga; Tsuguhiro ; et
al. |
February 23, 2006 |
Micro-shape transcription method, micro-shape transcription
apparatus, and optical-component manufacture method
Abstract
A micro-shape transcription method has preparing a mold having a
transcription face on which a concavo-convex pattern is formed,
pressing the transcription face against a base material softened by
heating, then forcibly separating the mold from the base material
to transcribe a reverse pattern of the concavo-convex pattern to
the surface of the base material, wherein when assuming a
temperature for pressing the mold against the base material as
T.sub.1 (.degree. C.), a temperature for separating the mold from
the base materials T.sub.2 (.degree. C.), thermal expansion
coefficients of the mold and the base material as .alpha..sub.a and
.alpha..sub.b, and the maximum distance between the transcription
center of the transcription face and the concavo-convex pattern as
d (mm), the following relations (1) and (2): T.sub.1.gtoreq.T.sub.2
(1)
|.alpha..sub.a-.alpha..sub.b|(T.sub.1-T.sub.2)d.ltoreq.4.times.10.sup.-2
(2) are simultaneously satisfied.
Inventors: |
Korenaga; Tsuguhiro; (Osaka,
JP) ; Umetani; Makoto; (Osaka, JP) ; Asakura;
Hiroyuki; (Osaka, JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
1850 M STREET, N.W., SUITE 800
WASHINGTON
DC
20036
US
|
Family ID: |
16410827 |
Appl. No.: |
11/253560 |
Filed: |
October 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09609250 |
Jun 30, 2000 |
|
|
|
11253560 |
Oct 20, 2005 |
|
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Current U.S.
Class: |
264/2.7 ;
264/322; 425/406 |
Current CPC
Class: |
B29D 11/00 20130101;
B29D 11/00769 20130101; B29K 2995/0034 20130101; B29L 2011/0075
20130101; B29L 2011/00 20130101; B29C 43/021 20130101; B29C
2043/025 20130101; B29C 2059/023 20130101; B29C 59/022
20130101 |
Class at
Publication: |
264/002.7 ;
264/322; 425/406 |
International
Class: |
B29D 11/00 20060101
B29D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 1999 |
JP |
HEI 11-199,616 |
Claims
1-11. (canceled)
12. A micro-shape transcription apparatus comprising: a first mold
means provided with a transcription face having a micro-shape; a
second mold means facing the first mold means and holding a base
material thereon; a mechanism for driving at least one of the first
and second molds means to press the transcription face into the
base material and to separate the first mold means from the base
material; and a vacuum chuck for attracting and fixing the base
material to the second mold means; wherein the mechanism presses at
a temperature up to 180.degree. C. and separates at a temperature
ranging from 120 to 150.degree. C., said separating temperature
being less than said pressing temperature.
13. The micro-shape transcription apparatus according to claim 12,
wherein the micro shape is rectangular in cross-section.
14. The micro-shape transcription apparatus according to claim 12,
wherein the micro shape has a depth of approximately 5 .mu.m and a
width of approximately 8 .mu.m.
15. The micro-shape transcription apparatus according to claim 12,
wherein the first mold means has a protective coating.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for
micro-fabricating a surface of a base material and a method for
manufacturing an optical component whose surface is
micro-fabricated such as an optical waveguide, diffraction grating,
or polarizer.
[0003] 2. Related Art of the Invention
[0004] Because optical-unit related markets such as those of
optical communication, optical disk, display, and optical sensor
have been progressed, coexistence of high performance and low cost
is requested for an optical component. Particularly, price
reduction is requested for a passive optical component that itself
does not operate.
[0005] Particularly, optical waveguides and diffraction gratings
require a very fine and accurate pattern for their surfaces. Dry
etching frequently used for a semiconductor process is generally
used to form the above pattern. As an example of micro-fabrication
by dry etching, a process for manufacturing a single-mode optical
waveguide for optical communication is described below by referring
to the accompanying drawings.
[0006] FIG. 7(a) is a top view of a general quartz-based
single-mode optical waveguide and FIG. 7(b) is a sectional view of
the waveguide in FIG. 7(a), taken along the line A-A in FIG. 7(a).
Because a core 71 has a refractive index higher than that of a clad
72, the light meeting a specific condition is transmitted by being
confined in a core pattern. By patterning the core 71 as shown in
FIG. 7(a), it is possible to constitute an optical circuit. In a
wavelength band of 1.3 to 1.55 .mu.m, the core 71 generally has a
square cross section one side of which is approx. 8 .mu.m. A core
shape and a core-surface roughness greatly influence a light
propagation performance.
[0007] FIGS. 8(a) to 8(c) are process charts showing a general
manufacture method for a conventional quartz-based optical
waveguide (refer to Kawauchi, OPTRONICS No. 8,851, 1988). In the
illustrated steps, a core film 81 is formed on a quartz substrate
82 also serving as a lower clad layer in accordance with the flame
deposition method (FIG. 8(a)). However, when using a substrate
other than a quartz substrate, a lower clad layer is previously
formed in accordance with the flame deposition method. Then, a core
film is formed into a predetermined pattern through
photolithography and dry etching (FIG. 8(b)). An upper clad layer
83 is then formed in accordance with the flame deposition method
(FIG. 8(c)). An optical waveguide having a small loss has been
manufactured so far in accordance with the above method.
[0008] In recent years, however, not only quartz but also resin
have been studied as an optical-waveguide material. At present,
resin is inferior to quartz in transparency and reliability. Resin
is easily molded and superior in transparency at a wavelength of
approx. 650 to 850 nm, however. Therefore, it is a very prospective
optical-waveguide material. Polymethyl methacrylate (PMMA) superior
in transparency is known as a specific resin. Recently, it is also
studied to realize low absorption in a wavelength area of 1.3 to
1.55 .mu.m by performing deuteration or fluorination on the basis
of PMMA.
[0009] To manufacture an optical waveguide by using resin, a method
is generally used in which a core layer and a clad layer are formed
mainly by spin coating and the core layer is patterned by dry
etching. Resin has a high productivity because it has a short film
deposition time and a low annealing temperature of 200 to
300.degree. C. compared to quartz.
[0010] As described above, dry etching is used to pattern a core of
quartz or resin in the case of conventional optical-waveguide
manufacturing.
[0011] However, dry etching is a complex process and requires a lot
of equipment. Therefore, when considering cost, it cannot be said
that dry etching is suitable for manufacturing a passive optical
component, setting aside a semiconductor device. Therefore, various
methods are proposed for manufacturing an optical component.
Particularly, pressing-molding and injection-molding methods are
prospective.
[0012] Proposed examples of press-molding are exclusively directed
to glass materials and include a method disclosed in the
specification of Japanese Patent Laid-Open No. 8-320420. The method
is an optical-waveguide manufacturing method of simultaneously
forming groove portions serving as core patterns by pressing a mold
91 on which a predetermined core pattern 92 is formed against a
base material 93 also serving as a lower clad at a high temperature
as shown in FIG. 9. The method makes it possible to efficiently
form an optical waveguide by omitting the photolithography and
dry-etching steps which have been used so far.
[0013] A method is also proposed in which a diffraction grating is
manufactured by transcripting a pattern on a metal reflection film
using pressing-molding (the specification of Japanese Patent
Laid-Open No. 10-96808).
[0014] A micro-pattern transcription method using pressing-molding
disclosed in the specification of Japanese Patent Laid-Open No.
8-320420 is briefly described below. First, a base material
(workpiece) is heated and softened and brought into contact with a
mold. While keeping the above state, the base material is cooled
and separated from the mold when the shape of the base material is
fixed. In this case, as shown in FIG. 10, a convex portion 103
formed on a mold 101 is provided correspondingly to a required
waveguide pattern and pressed against a resin substrate 102, and a
reverse pattern is formed on the resin substrate 102.
[0015] However, when using the above transcription method, a high
pattern accuracy may not be obtained. Deterioration of the pattern
accuracy seems to be caused by a difference between thermal
expansion coefficients. That is, when bringing the base material
softened by heating into contact with the mold and cooling the base
material and the mold, a thermal stress is generated due to a
difference between thermal expansion coefficients of the base
material and mold. As a result, the accuracy of a pattern
transcribed to the base material is lowered and the mold is broken
if the mold is weak in strength. This problem becomes remarkable
when using resin because resin has a thermal expansion coefficient
1 to 2 digits larger than that of quartz used as the material of a
mold.
[0016] According to specific study by the present inventor, the
width of a groove is increased at a micron-order level and the
shape of the groove is deformed by transcribing a pattern to a
resin substrate by using a mold. It is estimated that this
phenomenon results from the fact that the resin substrate contracts
toward the center of transcription because the substrate contracts
more than the mold. This phenomenon remarkably occurs when a
transcription face is a plane. Moreover, when the cross section of
a micro shape is rectangular, a pattern is further deformed.
[0017] Thus, resin can be molded at a low temperature and it is
advantageous in the manufacturing cost. However, it has a problem
that a micro pattern cannot be accurately transcribed when
transcribing a pattern by pressing-molding.
SUMMARY OF THE INVENTION
[0018] The present invention is made to solve the conventional
problems and its object is to provide a method for efficiently
transcribing a high-accuracy micro shape.
[0019] It is another object of the present invention to provide a
method for fabricating an optical component such as an optical
waveguide by using the above transcription method.
[0020] To achieve the above objects, a micro-shape transcription
method of the present invention is a micro-shape transcription
method comprising preparing a mold with a transcription face and
including a concavo-convex pattern formed on the transcription
face, pressing the transcription face against a base material
softened by heating and then forcibly separating the mold from the
base material, to transcribe a reverse pattern of the
concavo-convex pattern to the surface of the base material, wherein
when assuming a temperature for pressing the mold against the base
material as T.sub.1 (.degree. C.), a temperature for separating the
mold from the base material as T.sub.2 (.degree. C.), thermal
expansion coefficients of the mold and the base material as
.alpha..sub.a and .alpha..sub.b, and the maximum distance between
the transcription center of the transcription face and the
concavo-convex pattern as d (mm), the following relations (1) and
(2) are simultaneously satisfied. T.sub.1.gtoreq.T.sub.2 (1)
|.alpha..sub.a-.alpha..sub.b|(T.sub.1-T.sub.2)d.ltoreq.4.times.10.sup.-2
(2).
[0021] The present invention is particularly preferable when the
transcription face of a mold is a plane or a stepped plane.
[0022] Moreover, the present invention is particularly preferable
when the sectional form of a concavo-convex pattern is
rectangular.
[0023] Furthermore, the present invention is particularly
preferable when |.alpha..sub.a-.alpha..sub.b| is equal to or higher
than 50.times.10.sup.-7/.degree. C.
[0024] Furthermore, the present invention is particularly
preferable when the line width of a concavo-convex pattern is equal
to or less than 100 .mu.m.
[0025] Furthermore, the present invention is particularly
preferable when the depth of a concavo-convex pattern is equal to
or more than 1 .mu.m.
[0026] Furthermore, in the above described method of the present
invention, a base material is preferably an optically transparent
thermoplastic resin or glass. It is preferable to use any one of
polyolefin, polymethyl methacrylate, polycarbonate, norbornane, and
acrylic resins as the thermoplastic resin.
[0027] A micro-shape transcription apparatus of the present
invention comprises a first mold provided with a transcription face
having a micro-shape, a second mold facing the first mold, a
mechanism for driving either of the first and second molds, a
heating source for controlling the temperatures of the first and
second molds, and a vacuum chuck for attracting and fixing a base
material to the second mold.
[0028] An optical-component manufacturing method of the present
invention forms a pattern for controlling light in accordance with
the above-described micro-shape transcription method. An optical
component of the present invention includes an optical waveguide,
diffraction grating, polarizer, or lens. When the optical component
is an optical waveguide, a pattern corresponding to a core is
formed in accordance with a micro-shape transcription method of the
present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a sectional view showing a configuration of a
pressing machine used for an embodiment of a micro-shape
transcription method of the present invention;
[0030] FIGS. 2(a) and 2(b) are illustrations showing a pattern
formed on a transcription face of a mold used for an embodiment of
a micro-shape transcription method of the present invention;
[0031] FIG. 3 is a sectional perspective view showing an example of
an optical waveguide formed by the machine shown in FIG. 1;
[0032] FIG. 4 is an SEM photograph of a cross section of a resin
substrate obtaining a preferable transcription quality from an
embodiment of the present invention;
[0033] FIG. 5 is an SEM photograph of a cross section of a resin
substrate obtaining a bad transcription quality from an embodiment
of the present invention;
[0034] FIG. 6 is a photograph showing a result of measuring the
surface shape of a resin substrate obtaining a preferable
transcription quality by an embodiment of the present
invention;
[0035] FIG. 7(a) is a top view of a general quartz-based
single-mode optical waveguide and FIG. 7(b) is a sectional view of
the waveguide in FIG. 7(a);
[0036] FIGS. 8(a) to 8(c) are process charts showing a method for
manufacturing a conventional general optical waveguide;
[0037] FIG. 9 is a sectional view showing a conventional method for
manufacturing an optical waveguide through pressing; and
[0038] FIG. 10 is a conventional pattern used for a method for
manufacturing an optical waveguide through pressing..
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] Embodiments of the present invention are described below by
referring to the accompanying drawings.
[0040] FIG. 1 shows a pressing machine used for a micro-shape
transcription method of the present invention. The machine is
provided with a pair of upper and lower heater blocks 11 and 12.
The upper heater block 11 is vertically movable and the lower
heater block 12 is fixed. A cope 13 is fixed to the upper heater
block 11 with the transcription face turning downward. The cope 13
is made of quarts having a size of 20.times.20 mm and has a micro
shape formed through dry etching on the flat transcription face.
FIGS. 2(a) and 2(b) show a pattern formed on the transcription face
of a cope 21. FIG. 2(a) is a top view of the pattern and FIG. 2(b)
is a sectional view of the pattern in FIG. 2(a), taken along the
line A-A in FIG. 2(a). In this case, the pattern is convex. The
convex pattern 22 has a depth of approx. 5 .mu.m and a width of
approx. 8 .mu.m.
[0041] In this case, a polyolefin-based thermoplastic resin is used
as a base material 14 to be formed. This resin is optically
transparent and has a glass-transition temperature of 140.degree.
C. and a load deflection temperature of 123.degree. C. The base
material has a size of 8.times.8 mm and is set on a planar drag 15
fixed on the lower heater block 12. The base material 14 is fixed
to the drag 15 by a vacuum chuck.
[0042] A micro-shape transcription method is described below by
referring to FIG. 1.
[0043] The quartz mold 13 serving as a cope and the resin substrate
14 serving as a workpiece are overlapped at the molding machine so
that the transcription face of the quartz mold 13 contacts with the
resin substrate 14. In this case, the center of the quartz mold 13
is almost adjusted to the center of the resin substrate 14. Under
the above state, the upper and lower heater blocks 11 and 12 are
electrified, the resin substrate 14 is heated up to 180.degree. C.
to be softened, and the upper heater block 11 to which the quartz
mold 13 is fixed is moved downward and pressed. While a convex
pattern of the quartz mold 13 bites into the resin substrate 14,
heater temperature is lowered to 150.degree. C. by controlling
electrification of upper and lower heaters and the upper heater
block 11 is raised to forcibly separate the cope 13 from the resin
substrate 14. In this case, the resin substrate 14 is fixed to the
drag 15 by a vacuum chuck and smoothly separated from the cope 13
without being distorted or deformed. Thereafter, the resin
substrate 14 is cooled up to approx. room temperature and taken out
of the molding machine.
[0044] As a result of observing the surface and cross section of
the taken-out resin substrate by an optical microscope and an
electron microscope, the groove of a micro-pattern to which the
convex pattern of the quartz mold is accurately transcribed is
confirmed over the entire surface of a resin substrate having a
diameter of approx. 20 mm.
[0045] Then, epoxy resin having a refractive index approx. 0.3%
higher than that of the resin substrate is embedded in the groove
of the resin substrate and a flat resin substrate made of the same
material as the above resin substrate is bonded onto the above
resin substrate. Thus, the optical waveguide shown in FIG. 3 is
fabricated.
[0046] The optical waveguide is provided with epoxy resin as a core
32 and polyolefin resin substrates as clads 31, 33. The optical
waveguide has a sufficient serviceability.
[0047] Moreover, molding is studied by using a molding temperature
which is a temperature for pressing a mold against a resin
substrate and a mold releasing temperature which is a temperature
for releasing the mold from the resin substrate as parameters and
the resin substrate is observed after molding. Table 1 shows an
example of observation results. TABLE-US-00001 TABLE 11 Mold
Transcription Molding releasing quality temperature temperature
evaluation 160 80 x 160 90 x 160 100 .smallcircle. 160 120
.smallcircle. 160 140 .smallcircle. 180 80 x 180 100 x 180 120
.smallcircle. 180 150 .smallcircle.
[0048] In the case of Table 1, the quality of a transcription shape
is observed at a position 1 cm separate from the transcription
center of a transcription face. In this case, an object transcribed
at a submicron accuracy is judged as .largecircle. and an object
not transcribed at a submicron accuracy is judged as x.
[0049] FIGS. 4 and 5 show electron micrographs of the cross
sections of a groove transcribed onto a resin substrate.
[0050] In the case of FIGS. 4 and 5, cross sections are obtained by
coating the formed resin substrate with a metallic film, embedding
it in epoxy resin, and polishing it, and lower portions show the
formed substrate. A while boundary line shows the metallic film.
FIG. 4 is obtained at a molding temperature of 180.degree. C. and a
mold releasing temperature of 150.degree. C. at which the
transcription quality is judged to be good, and FIG. 5 is obtained
at a molding temperature of 180.degree. C. and a mold releasing
temperature of 80.degree. C. at which the transcription quality is
judged to be bad.
[0051] FIG. 6 shows the result of measurement of the surface
roughness of a groove pattern, which was obtained at a molding
temperature of 180.degree. C. and a mold releasing temperature of
150.degree. C. at which the transcription quality is judged to be
good, by a non-contact roughness meter.
[0052] The photograph is overlapped with a photograph when viewing
a groove from the surface, the sectional form is shown by leader
lines L1 to L5, and the groove has a width of 7.8 .mu.m and a depth
of 4.68 .mu.m. The irregularity of the surface of the molded resin
substrate is originally present on a quartz mold.
[0053] Thereby, it is confirmed that the groove is vertical and
transcribed at a roughness of a submicron level or lower. That is,
it is found that transcription is smoothly performed even if
measuring methods are changed.
[0054] The following Equation 1 is calculated on the above
result.
[Equation 1] M=|.alpha..sub.a-.alpha..sub.b|(T.sub.1-T.sub.2)d
Equation 1
[0055] In the above Equation, .alpha..sub.a denotes a thermal
expansion coefficient of quartz serving as a mold and b denotes a
thermal expansion coefficient of polyolefin-based resin serving as
a workpiece, in which .alpha..sub.a is equal to
5.times.10.sup.-7/.degree. C. and .alpha..sub.b is equal to
600.times.10.sup.-7/.degree. C. Moreover, T.sub.1 denotes a molding
temperature and T.sub.2 denotes a mold releasing temperature.
Symbol d (mm) denotes the distance between the position at which
transcription quality is evaluated and the transcription
center.
[0056] As a result of calculating the Equation 1 on each molding
condition in Table 1, it is found that a preferable transcription
quality is obtained in the case of M.ltoreq.4.times.10.sup.-2. As
for the above relation, it is found that the same result is
obtained even if using one of polymethyl-methacrylate-,
polycarbonate-, acrylic-, and norbornane-based thermoplastic resins
or glass for a substrate to be molded, using one of various metals
including nickel, various ceramics including zirconium, WC-based
cemented carbide, diamond film, and DLC for a mold base material,
combining various mold materials with a material to be molded, and
changing molding conditions. That is, it is clarified that a micro
shape can be transcribed as long as a molding condition meets the
condition of Expression 1.
[0057] In this embodiment, manufacturing of an optical waveguide is
described. However, a method of the present invention is not
restricted to the above case but it is suitable for manufacturing
all components requiring a micro pattern including an optical
component, mechanical component, and micromechanics-related
component. It is particularly suitable for manufacturing a
high-accuracy optical component including an optical waveguide,
diffraction grating, polarizer and lenz.
[0058] Moreover, for this embodiment, a mold provided with a convex
pattern is used. However, the same advantage can be obtained by
using a concave pattern or a concavo-convex pattern. A pattern
sectional form is not restricted. For example, the mold is
effective for a trapezoidal shape, triangular shape, or wave shape.
The mold is particularly effective for a micro shape having a
rectangular cross section on a flat transcription face that is
easily influenced by thermal expansion and on which a pattern
easily collapses.
[0059] Moreover, for this embodiment, the flat pattern shape shown
in FIG. 2 is described. However, a pattern shape is not restricted
to the flat pattern shape.
[0060] Furthermore, as a result of studying various materials, it
is found that a method of the present invention is particularly
effective when a difference between thermal expansion coefficients
of a mold and a base material is 50.times.10.sup.-7/.degree. C. or
more, a pattern has a width of 100 .mu.m or less, and a
concavo-convex pattern has a depth of 1 .mu.m or more. That is,
under the above conditions, separation cannot be made by a
conventional method but separation can be realized by the present
invention.
[0061] Moreover, though a material of a mold or a material to be
molded is not restricted, the mold is particularly effective for a
thermoplastic resin having a comparatively large thermal expansion
coefficient. By applying protective coating to a mold and
performing molding in an inert-gas atmosphere, it is possible to
transcribe a micro pattern to glass.
[0062] As described above, the present invention makes it possible
to efficiently transcribe a high-accuracy micro pattern.
[0063] Moreover, the present invention makes it possible to
efficiently manufacture an optical component such as an optical
waveguide.
[0064] Particularly, the present invention makes it possible to
accurately transcribe a micro pattern to a wide area of resin
having a large thermal expansion coefficient that is a problem as a
material of an optical component.
[0065] Thus, according to the present invention, it is possible to
efficiently manufacture various optical components including an
optical waveguide and a diffraction grating.
* * * * *