U.S. patent application number 11/194695 was filed with the patent office on 2006-02-09 for microstructure and manufacturing process thereof.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Noriyuki Iguchi, Kazuhiro Iida, Masafumi Nakada.
Application Number | 20060027290 11/194695 |
Document ID | / |
Family ID | 35756255 |
Filed Date | 2006-02-09 |
United States Patent
Application |
20060027290 |
Kind Code |
A1 |
Iguchi; Noriyuki ; et
al. |
February 9, 2006 |
Microstructure and manufacturing process thereof
Abstract
It is an object of the present invention to attain a
microstructure having a miniature continuous structure which has
high throughput and has been processed with high accuracy. To
achieve this, provided is a microstructure having a column-shaped
structure and a slit-forming portion which extends in a side-face
direction from a side face of the column-shaped structure, wherein
the slit-forming portion has a plurality of slits aligned in
parallel at an interval from 20 to 1,000 nm in a direction along a
center axis of the column-shaped structure.
Inventors: |
Iguchi; Noriyuki;
(Minato-ku, JP) ; Nakada; Masafumi; (Minato-ku,
JP) ; Iida; Kazuhiro; (Minato-ku, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NEC CORPORATION
|
Family ID: |
35756255 |
Appl. No.: |
11/194695 |
Filed: |
August 2, 2005 |
Current U.S.
Class: |
148/241 |
Current CPC
Class: |
G02B 5/1847 20130101;
G02B 5/3058 20130101; G02B 5/1809 20130101 |
Class at
Publication: |
148/241 |
International
Class: |
C23C 8/04 20060101
C23C008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 2004 |
JP |
2004-226713 |
Claims
1. A microstructure comprising a column-shaped structure and a
slit-forming portion which extends in a side-face direction from a
side face of the column-shaped structure, wherein the slit-forming
portion has a plurality of slits aligned in parallel at intervals
from 20 to 1,000 nm in a direction along a center axis of the
column-shaped structure.
2. An optical element comprising the microstructure according to
claim 1.
3. The optical element according to claim 2, wherein a surface is
covered with a metal layer.
4. The optical element according to claim 2 or 3, wherein the
intervals of the slit in a direction along a center axis of the
column-shaped structure are constant.
5. An optical filter using the optical element according to any of
claims 2 or 3.
6. A branching filter comprising the optical filter according to
claim 5.
7. The optical element according to claim 2 or 3, wherein the
slit-forming portion comprises slits aligned in parallel at a first
interval and slits aligned in parallel at a second interval in a
direction along a center axis of the column-shaped structure.
8. The optical element according to claim 7, wherein a ratio of the
first interval to the second interval is from 1:5 to 1:20.
9. A polarized beam splitter using the optical element according to
claim 8.
10. A process for manufacturing a microstructure which comprises a
column-shaped structure and a slit-forming portion which extends in
a side-face direction from a side face of the column-shaped
structure, wherein the slit-forming portion has a plurality of
slits aligned in parallel in a direction along a center axis of the
column-shaped structure, the process comprising the steps of: (1)
preparing a substrate which has a thickness greater than a height
of the column-shaped structure; (2) providing a mask extending in a
prescribed direction of an upper face of the substrate which
comprises a narrow-width portion in a direction which intersects
with the extending direction for defining a portion to serve as the
slit-forming portion and a broad-width portion in a direction which
intersects with the extending direction for defining a portion to
serve as the column-shaped portion; (3) forming two facing grooves
by carrying out isotropic etching on an upper face of the substrate
by a reactive ion etching method using SF6 gas using the mask as a
etching mask, and excavating in a thickness direction at least a
portion of both sides opposing the extending direction of the mask
of the upper face of the substrate; (4) covering the upper face of
the substrate forming the grooves with a passivation film formed by
plasma reaction using C4F8 gas; (5) providing apertures for
connecting between grooves which are faced sandwiching the
narrow-width portion of the mask at least below the narrow-width
portion of the mask, by carrying out isotropic etching on the upper
face of the substrate covered with the passivation film by a
reactive ion etching method using SF6 gas; and (6) repeating the
steps (3) to (5) for aligning in parallel the apertures in a
thickness direction below the narrow-width portion of the mask, to
thereby attain the microstructure as well as extending the grooves
in a thickness direction of the substrate.
11. The process for manufacturing a microstructure according to
claim 10, wherein the mask comprises a portion extending from one
end to another end which is on an upper face of the substrate, and
the ends are the broad-width portions.
12. The process for manufacturing a microstructure according to
claim 11, wherein the mask further comprises the broad-width
portion on a portion other than on the end.
13. The process for manufacturing a microstructure according to any
of claims 10 to 12, wherein the mask extends in a branched manner
in a plurality of prescribed directions.
14. The process for manufacturing a microstructure according to any
of claims 10 to 12, wherein the substrate is an SOI substrate.
15. The process for manufacturing a microstructure according to any
of claims 10 to 12, wherein the steps (3) to (5) are finished prior
to the grooves penetrating as far as a lower face of the substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a microstructure, and
manufacturing process thereof, which is minute and has excellent
molding precision. The present invention particularly relates to a
process for manufacturing a microstructure which can be employed as
an optical element.
[0003] 2. Description of the Related Art
[0004] In recent years, microminiaturization, increasing precision
and increasing super-high-end performance for a variety of
structures has been progressing across a wide-range of technical
fields, wherein for example, a structure miniaturized to a
dimension in the order of nanometers (hereinafter referred to as a
"microstructure") has been sought after. Microstructures have been
manufactured using various processes in the past. Specific examples
include the following. [0005] (1) Utilization of a self-organized
structure [0006] (2) An optical shaping method using a laser or a
light confocus [0007] (3) A method for fabricating a
three-dimensional structure using an electron beam or ion beam.
[0008] (4) Utilizing a semiconductor process [0009] (5) A
nanoimprinting process
[0010] Here, (1) a self-organized structure, as disclosed in
Japanese Patent Laid-Open No. 2002-023356 is a method which places
a molecule capable of self-organization at a specific site of an
underlying layer, such as a substrate, to form a highly oriented
compound onto the substrate in an oriented manner through
interaction with a molecule having an associated functional group
which can react with the molecule capable of self-organization. (2)
the optical shaping method, as disclosed in Japanese Patent
Laid-Open No. 1995-329188, is a method for manufacturing a
microstructure by irradiating ultraviolet rays or similar laser
beam onto a liquid photosetting resin to thereby form a thin film,
and then successively laminating this thin film. (3) a method for
fabricating a three-dimensional structure using an electron beam or
ion beam, as disclosed in Japanese Patent Laid-Open No.
1989-261601, is a method for manufacturing a microstructure by
irradiating an intensity-modulated electron beam onto a resist film
coated onto a substrate. (4) a semiconductor process is a method
for forming a structure by repeatedly carrying out the steps of
forming a mask pattern by photolithography and removing an exposed
portion by etching. (5) nanoimprinting is a method for transcribing
a template pattern onto a substrate by pressing the substrate with
a template having a nano-size pattern.
[0011] However, in (1) a self-organized structure, the position of
the portion which undergoes shape-processing and self-organization
is restricted, thus making it difficult to attain a structure
having a desired shape or position. For (2) optical shaping method,
since light is employed for the resin curing, shape-processing of a
structure in the order of nanometers is difficult. Furthermore,
when performing complete curing by a full-cure step after molding
of the photosetting resin, the entire structure shrinks from one to
several percent, whereby molding of a structure with a high degree
of precision is difficult. For (3) a method for fabricating a
three-dimensional structure, the thickness that can be processed is
restricted, whereby the degree of freedom for the shape in a
thickness direction is small, and throughput is also small. For (4)
a semiconductor process and (5) nanoimprinting process, since a
three-dimensional structure is made by fabricating a planer
structure and then building these planar structures up, a long time
is required for structure fabrication. Furthermore, since these
techniques undergo a number of steps, a high precision processing
of structure is difficult.
[0012] Meanwhile, at pages 304 to 306 of Micromachine/MEMS
Technology Outlook, a Bosch process is disclosed. The Bosch process
is a type of processing method for silicon substrates, which etches
a silicon substrate layer in its thickness direction by alternating
between etching with SF.sub.6 gas and forming a passivation film
from C.sub.4F.sub.8 gas, whereby a minute and continuous structure
can be attained.
SUMMARY OF THE INVENTION
[0013] The present invention was created with the above-described
problems in mind, wherein it aims at obtaining a microstructure
comprising a minute structure which has a high throughput and in
which shape-processing is possible with high precision.
[0014] The invention also aims at providing an optical element
having excellent optical processing characteristics comprising a
microstructure.
[0015] To resolve the above-described problems, the present
invention is characterized by having the following structure. That
is, the present invention relates to a microstructure comprising a
column-shaped structure and a slit-forming portion which extends in
a side-face direction from a side face of the column-shaped
structure, wherein the slit-forming portion has a plurality of
slits aligned in parallel at intervals from 20 to 1,000 nm in a
direction along a center axis of the column-shaped structure.
[0016] The present invention also relates to a process for
manufacturing a microstructure which comprises a column-shaped
structure and a slit-forming portion which extends in a side-face
direction from a side face of the column-shaped structure, wherein
the slit-forming portion has a plurality of slits aligned in
parallel in a direction along a center axis of the column-shaped
structure, the process comprising the steps of: [0017] (1)
preparing a substrate which has a thickness greater than a height
of the column-shaped structure; [0018] (2) providing a mask
extending in a prescribed direction of an upper face of the
substrate which comprises a narrow-width portion in a direction
which intersects with the extending direction for defining a
portion to serve as the slit-forming portion and a broad-width
portion in a direction which intersects with the extending
direction for defining a portion to serve as the column-shaped
portion; [0019] (3) forming two facing grooves by carrying out
isotropic etching on an upper face of the substrate by a reactive
ion etching method using SF.sub.6 gas using the mask as a etching
mask, and excavating in a thickness direction at least a portion of
both sides opposing the extending direction of the mask of the
upper face of the substrate; [0020] (4) covering the upper face of
the substrate forming the grooves with a passivation film formed by
plasma reaction using C.sub.4F.sub.8 gas; [0021] (5) providing
apertures for connecting between grooves which are faced
sandwiching the narrow-width portion of the mask at least below the
narrow-width portion of the mask, by carrying out isotropic etching
on the upper face of the substrate covered with the passivation
film by a reactive ion etching method using SF.sub.6 gas; and
[0022] (6) repeating the steps (3) to (5) for aligning in parallel
the apertures in a thickness direction below the narrow-width
portion of the mask, to thereby attain the microstructure as well
as extending the grooves in a thickness direction of the
substrate.
[0023] According to the manufacturing process of the present
invention, a microstructure can be attained which has a high
throughput and in which the shape has been processed with high
precision. Furthermore, according to the manufacturing process of
the present invention, the shape, size and intervals, etc of the
connecting portions and the aperture can be controlled easily.
Therefore, a microstructure according to the present invention can
be used in a wide variety of applications by utilizing such
characteristic. The microstructure according to the present
invention can be, in particular, used as an excellent optical
element by utilizing its minuteness and the high precision of its
processed shape.
[0024] According to the manufacturing process of the present
invention, a microstructure can be manufactured which is minute,
has high throughput and which has a shape processed with high
precision. Furthermore, since control of the manufacturing
conditions is easy and the manufacturing steps are simple, a
microstructure can be manufactured in short time using a simple
apparatus. Furthermore, according to the manufacturing process of
the present invention, the mask formed on the manufacturing
substrate may comprise at least one or more width-varying portions,
and the mask having a variety of shapes can be employed. Therefore,
the manufacturing process of the present invention can have a high
degree of design freedom.
[0025] According to the manufacturing process of the present
invention, by forming a plurality of width-varying portions in the
mask, a structure of a slit-forming portion can be easily
controlled. In addition, a microstructure can be attained wherein
an intended characteristic varies depending on the position in the
microstructure. According to the manufacturing process of the
present invention, by forming a width-varying portion at both ends
of the mask, a structure can be formed wherein a slit-forming
portion is sandwiched between column-shaped structures, whereby the
slit-forming portion can be protected from damage during
manufacture.
[0026] Furthermore, if the microstructure according to the present
invention is employed as an optical element, the desired
characteristics which are required to be an optical element can be
exhibited by utilizing the minuteness and high precision of the
shape. In addition, a microstructure according to the present
invention can exhibit even more excellent desired optical element
characteristics by arranging the connecting portions and the
apertures (slits) in equal intervals in an axial direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic view illustrating one example of a
process for manufacturing a microstructure according to the present
invention;
[0028] FIG. 2 is a schematic view illustrating one example of a
process for manufacturing a microstructure according to the present
invention;
[0029] FIG. 3 is a schematic view illustrating one example of a
process for manufacturing a microstructure according to the present
invention;
[0030] FIG. 4 is a schematic view illustrating one example of a
microstructure according to the present invention;
[0031] FIG. 5 is an electron microscope photograph illustrating one
example of a microstructure according to the present invention;
[0032] FIG. 6 is a schematic view illustrating one example of a
microstructure according to the present invention;
[0033] FIG. 7 is an electron microscope photograph illustrating one
example of a microstructure according to the present invention;
[0034] FIG. 8 is a schematic view illustrating one example of a
microstructure according to the present invention;
[0035] FIG. 9 is a schematic view illustrating one example of a
microstructure according to the present invention;
[0036] FIG. 10 is a schematic view illustrating one example of a
microstructure according to the present invention;
[0037] FIG. 11 is a view illustrating one example of a mask pattern
used in the process for manufacturing a microstructure according to
the present invention;
[0038] FIG. 12 is a schematic view illustrating one example of a
branching filter according to the present invention;
[0039] FIG. 13 is a schematic view illustrating one example of a
wire grid according to the present invention;
[0040] FIG. 14 is a diagram illustrating a mask pattern used and a
microstructure manufactured in examples;
[0041] FIG. 15 is a view illustrating one example of a mask pattern
used in the process for manufacturing a microstructure according to
the present invention.
[0042] FIG. 16 is a schematic view illustrating one example of a
process for manufacturing a microstructure according to the present
invention;
[0043] FIG. 17 is a schematic view illustrating one example of a
process for manufacturing a microstructure according to the present
invention; and
[0044] FIG. 18 is a schematic view illustrating one example of a
process for manufacturing a microstructure according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
(Process for Manufacturing a Microstructure)
[0045] A microstructure according to the present invention can be
manufactured by alternating between isotropic etching and process
fabricating a protective film on the entire etching surface. For
example, when fabricating a microstructure by using a silicon
substrate, a Bosch process (also called ASE: Advanced Silicon
Etching) can be employed. A Bosch process is process silicon
etching which alternates between etching using SF.sub.6 and
fluorocarbon deposition using C.sub.4F.sub.8, thus enabling etching
with high selectivity and a high aspect ratio to be realized.
[0046] One example of a process for manufacturing a microstructure
according to the present invention will now be described in detail
with reference to FIG. 1. First, a substrate 11 having a thickness
greater than the height of the column-shaped structures is
prepared. As the substrate, a silicon substrate or an SOI substrate
is used, and a thermal oxidation film SiO.sub.2 is formed on a
surface of the substrate. Narrow-width portion 33 is connected with
broad-width portion 32 via width-varying portion 31 in this mask
12.
[0047] Then, substrate exposed portion 13 which is not covered by
the mask is formed on the substrate by photolithography. FIG. 1 (a)
and (b) are schematic views which illustrate this state, wherein
FIG. 1 (a) is a view showing the substrate from an upper face in a
thickness direction and FIG. 1 (b) is a cross-sectional view in the
A-A' direction of FIG. 1 (a). (In FIG. 1, as one example, a mask is
used having two width-varying portions 31.) Although the mask 12 is
not especially restricted, a resist mask or a SiO.sub.2 film, for
example, can be employed.
[0048] After this, a Bosch process is carried out. That is, using
the mask on the substrate as the etching mask, isotropic etching of
the substrate by a reactive ion etching process using SF.sub.6 gas,
deposition of a passivation film by a plasma reaction using
C.sub.4F.sub.8 gas and isotropic etching using SF.sub.6 gas in the
same manner as the initial isotropic etching are carried out a
number of times. This will now be explained in more detail.
[0049] First, in the initial isotopic etching, at least a mask-side
portion of exposed portion 13 of the substrate (an aperture formed
on a portion having both sides sandwiching the mask in direction
intersecting with direction 14 along which the mask extends) is
excavated in thickness direction of a substrate to form a pair of
grooves 16 (FIG. 1 (d)). Viewed along a cross-section parallel to
the substrate, these groves 16 are formed in a shape which
stretches over outline 13 of the mask. FIG. 1 (c) to (e) are
schematic views which illustrate this state, wherein FIG. 1 (c) is
a view showing the substrate from an upper face in a thickness
direction, FIG. 1 (d) is a cross-sectional view in the A-A'
direction of FIG. 1 (c) and FIG. 1 (e) is a cross-sectional view in
the B-B' direction of FIG. 1 (c).
[0050] As the isotropic etching proceeds, the pair of grooves 16
connect partially and abut onto a width-varying portion within the
mask, whereby aperture 17 connecting (connecting in direction 15
intersecting with extending direction 14 of the mask) the opposing
grooves and sandwiching the narrow-width portion 33 below
narrow-width portion 33, is formed. The portion where aperture 17
(slit) is formed is not limited to the portion below narrow-width
portion 33. Depending on the shape of the mask and etching
conditions, the aperture may be formed in a form stretching from
the lower part of narrow-width portion 33 to the lower part of
width-varying portion 31. Furthermore, since the isotropic etching
finishes before the pair of grooves 16 completely connect,
connecting portion 18 which is not removed by the isotropic etching
is formed directly below narrow-width portion 33.
[0051] Next, a fluorocarbon passivation film 19 using
C.sub.4F.sub.8 is formed on the substrate by a CVD chemical vapor
growth process. FIG. 2(a) to (c) are schematic views which
illustrate this state, wherein FIG. 2(a) is a view showing the
substrate from an upper face in a thickness direction, FIG. 2(b) is
a cross-sectional view in the A-A' direction of FIG. 2(a) and FIG.
2(c) is a cross-sectional view in the B-B' direction of FIG.
2(a).
[0052] Subsequently, in the same manner as the initial isotropic
etching, isotropic etching is conducted by a reactive ion etching
process. FIG. 3(a) to (c) are schematic views which illustrate this
state, wherein FIG. 3(a) is a view showing the substrate from an
upper face in a thickness direction, FIG. 3(b) is a cross-sectional
view in the A-A' direction of FIG. 3(a) and FIG. 3(c) is a
cross-sectional view in the B-B' direction of FIG. 3(a). During
this etching, since a voltage bias is being applied, passivation
film 21 of the side wall of the initial groove (side etching
portion) is not removed by the etching, wherein the passivation
film in the horizontal direction of substrate is preferentially
removed. Etching then further proceeds in a thickness direction
lower portion of the substrate to form grooves 20. These grooves 20
connect partially below aperture 17, whereby aperture (slit) 22
connecting the opposing grooves and sandwiching a narrow-width
portion of the mask, is formed. Because the isotropic etching
finishes before grooves 20 completely connect, connecting portion
23 which was not removed by the etching is formed in the space
between initially formed aperture 17 and aperture 22.
[0053] Next, the slit-forming portion can be fabricated by forming
in parallel a plurality of slits in a thickness direction (a
direction along a center axis of the column-shaped structure) of
the substrate by carrying out isotropic etching and the passivation
film deposition as illustrated in FIGS. 1 to 3. The number of times
that such isotropic etching and passivation film deposition are
carried out is preferably at least two times or more, but the
number of times is not especially restricted.
[0054] Furthermore, the other example of a process for
manufacturing a microstructure according to the present invention
will now be described in detail with reference to FIGS. 16 to 18.
First, mask 12 is formed on a substrate 11 in the same manner as
FIG. 1. Then, substrate exposed portion which is not covered by the
mask is formed on the substrate by photolithography. After this, a
Bosch process is carried out. First, in the initial isotopic
etching using SF.sub.6 gas, at least a mask-side portion of exposed
portion of the substrate is excavated in thickness direction of a
substrate (FIG. 16(c)). FIG. 16(a) to (c) are schematic views which
illustrate this state, wherein FIG. 16(a) is a view showing the
substrate from an upper face in a thickness direction, FIG. 16(b)
is a cross-sectional view in the A-A' direction of FIG. 16(a) and
FIG. 16(c) is a cross-sectional view in the B-B' direction of FIG.
16(a).
[0055] Next, a fluorocarbon passivation film 19 using
C.sub.4F.sub.8 gas is formed on the substrate by a CVD chemical
vapor growth process. FIG. 17(a) to (c) are schematic views which
illustrate this state, wherein FIG. 17(a) is a view showing the
substrate from an upper face in a thickness direction, FIG. 17(b)
is a cross-sectional view in the A-A' direction of FIG. 17(a) and
FIG. 17(c) is a cross-sectional view in the B-B' direction of FIG.
17(a).
[0056] Subsequently, isotropic etching is conducted by a reactive
ion etching process. As the isotropic etching proceeds, the pair of
grooves 16 connect partially and abut onto a width-varying portion
within the mask, whereby aperture 17 connecting (connecting in
direction 15 intersecting with extending direction 14 of the mask)
the opposing grooves and sandwiching the narrow-width portion 33
below the narrow-width portion 33, is formed. FIGS. 18(a) and (b)
are schematic views which illustrate this state, wherein FIG. 18(a)
corresponds to a cross-sectional view in the A-A' direction of
microstructure of FIG. 17(a) and FIG. 18(b) corresponds to a
cross-sectional view in the B-B' direction of microstructure of
FIG. 17(a). During this etching, since a voltage bias is being
applied, passivation film of the side wall of the groove (side
etching portion) is not removed by the etching, wherein the
passivation film in the horizontal direction of substrate is
preferentially removed to thereby form grooves. These grooves
connect partially, whereby aperture (slit) connecting the opposing
grooves and sandwiching a narrow-width portion of the mask, is
formed. The isotropic etching finishes before grooves completely
connect.
[0057] Thus, one aperture is formed by process of FIGS. 16 to 18.
Next, the slit-forming portion can be fabricated by repeating
process as illustrated in FIGS. 16 to 18.
[0058] The conditions for each isotropic etching and passivation
film deposition may be the same or different. If these conditions
are the same, each of the connecting portions and the apertures
(slits) have the same shape and size, thus enabling the intervals
in thickness direction of the substrate to be formed with high
precision at equal intervals. Therefore, by forming the aperture
intervals with high precision at equal intervals, a microstructure
having intended characteristics depending on the purpose can be
manufactured. On the other hand, if the conditions for each
isotropic etching and passivation film deposition are changed, each
of the connecting portions and the apertures (slits) have a
different shape and size, whereby these intervals in thickness
direction of the substrate are also different.
[0059] Next, once the isotropic etching is conducted to a desired
depth in the substrate, etching is finished. This etching may be
stopped before the grooves penetrate the substrate, or may be
conducted until penetrating through the substrate. If etching is
stopped before the grooves penetrate the substrate, a
microstructure formed on the substrate can be attained, while if
etching is conducted until the grooves penetrate through the
substrate, only a microstructure can be attained. The substrate
thickness is preferably from 5 to 100 .mu.m, and more preferably
from 10 to 50 .mu.m.
[0060] Subsequently, a microstructure according to the present
invention is formed by removing the remaining mask 12 and
passivation film 19. This microstructure is illustrated in FIG.
4(a). FIG. 4(b) is a perspective view illustrating only the
connecting portions of the microstructure of the FIG. 4(a).
[0061] FIG. 4(c) is a cross-sectional view in the A-A' direction of
the connecting portions of FIG. 4(b). The uppermost connecting
portion 59 (the connecting portion is uppermost in thickness
direction of the substrate; corresponding to uppermost connecting
portion 44 in FIG. 4(a)) is composed of face 53 and face 54.
Connecting portion 60 (corresponding to the connecting portion
second from the top among the connecting portions 45 in FIG. 4(a))
is composed of face 54 and face 55. Connecting portion 58
(corresponding to the connecting portion third from the top among
the connecting portions 45 in FIG. 4(a)) is composed of face 56 and
face 57. While in the microstructure of FIG. 4(a), two connecting
portions are formed below the connecting portion 58, the connecting
portions formed below connecting portion 58 of these connecting
portions have the same shape as connecting portion 58, and the
connecting portion formed at the lowermost part has the reverse
shape to the uppermost connecting portion 59. Therefore, the two
connecting portions formed below connecting portion 58 have been
omitted from FIGS. 4(b) and (c).
[0062] An electron microscope photograph of an actually fabricated
microstructure is illustrated in FIG. 5. FIG. 5(a) is a photograph
of the microstructure viewed from an oblique direction. FIG. 5(b)
is enlarged view of slit-forming portions of the microstructure of
FIG. 5(a). From the electron microscope photograph of FIG. 5, it
can be understood that a periodic structure is formed with
excellent precision.
[0063] In the manufacturing process according to the present
invention, the mask to be used is not restricted to the
above-described masks. By changing the extending direction of mask,
the shape and size of the width-varying portion, the position of
the width-varying portion is formed in the mask, or the width of
the narrow-width portion and the broad-width portion, or adjusting
the etching conditions, the shape, size and interval of connecting
portions and slits of the microstructure can be processed into a
desired shape with excellent precision. In addition, a minute
three-dimensional microstructure can be fabricated at a high
throughput with good reproducibility.
[0064] The mask can be formed so as to extend in a prescribed
direction, and may comprise a single closed curve or have both ends
open. The mask may also be a linear shape extending in a fixed
direction, or a curved shape in which the extending direction
changes. In addition, a plurality of linear masks, curved masks or
combination of these masks linked together are also preferable.
Still further, the mask may branch into a plurality of masks
midway, or the plurality of masks branched out midway may be linked
together. The branched mask and linked mask may each be closed or
open, and may also be linear or curved.
[0065] The width-varying portion is acceptable as long as its width
varies. In the present specification, regardless of whether the
width variation is continuous or discontinuous. If the width
variation is continuous, viewed from extending direction of the
mask, a portion where the width increases or decreases continuously
is taken to be a width-varying portion. Thus, if there are a
portion where the width increases continuously and a portion where
the width decreases continuously, each of these width-varying
portions independently compose the different width-varying
portions. For example, when the width changes in a discontinuous
step-like manner (e.g., FIG. 1 (a) 31), the width-varying portion
is linear in the direction perpendicular to the extending direction
of the mask, and without any length in the extending direction of
the mask (e.g. FIG. 1 (a) 14). The ratio by which the width of the
width-varying portion varies is not especially restricted, and
neither is such shape especially restricted. A side portion of a
width-varying portion where the width continuously varies is
constituted from a curve or a straight line. In such case, the
curve may be concave or convex or an uneven shape. The
width-varying portion may be constituted from a single straight
line having different slopes, or from a plurality of straight
lines. Furthermore, these shapes may be plural or a combined
shape.
[0066] The narrow-width portion and the broad-width portion are
connected via a width-varying portion. That is, a portion having a
narrow width is termed "narrow-width portion", and a portion having
a broad width is termed a "broad-width portion" of the mask formed
on both sides sandwiching a width-varying portion. Thus,
"narrow-width" and "broad-width" are relative terms, so that even
the same portion of a mask can be termed narrow-width or
broad-width. For example, FIG. 15 is a diagram viewed from an upper
part of a mask formed on a substrate in a step-like manner. The
mask in FIG. 15 has width-varying portions 1501 to 1503. Taking
width-varying portion 1503 as a reference, masks 1506 and 1507
exist on either side of the portion. Because mask 1506 is the
broader of the two masks 1506 and 1507, mask 1506 is the
"broad-width portion" and mask 1507 is the "narrow-width portion".
However, if width-varying portion 1502 is taken as the reference,
masks 1505 and 1506 exist on either side of the portion. Because
mask 1505 is the broader of the two masks 1505 and 1506, mask 1505
is the "broad-width portion" and mask 1506 is the "narrow-width
portion". That is, mask 1506 is a "broad-width portion" if it takes
width-varying portion 1503 as a reference, and is a "narrow-width
portion" if it takes width-varying portion 1502 as a reference.
Thus, "narrow-width portion" or "broad-width portion" are depends
on the width-varying portion taken as a reference, so that even the
same portion in a mask can be a "narrow-width portion" or a
"broad-width portion". Furthermore, the "narrow-width portion" and
"broad-width portion" may have no length in the extending direction
(e.g. FIG. 1(a) 14) and be a straight line in direction
intersecting with extending direction of mask (e.g. FIG. 9(a) 904,
FIG. 10(a) 1024), or may have a prescribed length in the extending
direction of the mask.
[0067] For example, FIG. 8(a) is a drawing which illustrates one
example of a mask used in the present invention. In FIG. 8(a),
reference numerals 81 to 84 denote width-varying portions, and
reference numerals 810, 820, 830 and 840 denote narrow-width
portions. Reference numerals 815, 825, 835, 845 and 855 denote
broad-width portions. When such mask is used, a microstructure
having a structure as shown in FIGS. 8(b) and (c) can be
manufactured. FIG. 8(b) is a cross-sectional view in the A-A'
direction of FIG. 8(a) and FIG. 8(c) is a perspective view
illustrating only the connecting portions of the microstructure of
FIG. 8(a). Uppermost connecting portion 811 and connecting portion
812 are formed below narrow-width portion 810, uppermost connecting
portion 821 and connecting portion 822 are formed below
narrow-width portion 820, uppermost connecting portion 831 and
connecting portion 832 are formed below narrow-width portion 830
and uppermost connecting portion 841 and connecting portion 842 are
formed below narrow-width portion 840.
[0068] As can be understood from FIG. 8, if the width ratio of the
narrow-width portion to the broad-width portion becomes increasing,
the groove formed in the region including the mask aperture portion
becomes bigger, and the height H and width W' of the uppermost
connecting portion and the connecting portions becomes smaller. If
the width ratio of the narrow-width portion to the broad-width
portion becomes decreasing, the groove formed in the region
including the mask aperture portion becomes smaller and the height
H and width W' of the uppermost connecting portion and the
connecting portions becomes larger. Furthermore, if the length L of
the narrow-width portion becomes longer, the length L' of the
uppermost connecting portion and the connecting portions also
becomes longer, and if the length L of the narrow-width portion
becomes shorter, the length L' of the uppermost connecting portion
and the connecting portions also becomes shorter. (Thus, by
adjusting the height H of the uppermost connecting portion and the
connecting portions, the intervals between the parallel slits can
also be adjusted.)
[0069] A mask as illustrated in FIG. 9 can also be used. FIG. 9(a)
is a drawing which illustrates one example of a mask used in the
present invention. FIG. 9(b) is a cross-sectional view in the A-A'
direction of the microstructure of FIG. 9(a) and FIG. 9(c) is a
perspective view illustrating only the connecting portions of the
microstructure of FIG. 9(a). In FIG. 9(a), reference numerals 91
and 94 to 96 denote width-varying portions. The sides of the
width-varying portions 91, 94 and 96 are constituted from a
straight line, and a side portion of width-varying portion 95 is
partially constituted from a curve. Furthermore, reference numerals
901 to 904 denote narrow-width portions and reference numerals 905
to 909 denote broad-width portions. Uppermost connecting portion 92
and connecting portions 93 are mainly formed below width-varying
portion 91, uppermost connecting portion 97 and connecting portions
98 are mainly formed below two width-varying portions 94, uppermost
connecting portion 99 and connecting portions 100 are mainly formed
below two width-varying portions 95 and structure 101 is mainly
formed below two width-varying portions 96.
[0070] When a microstructure is manufactured using the
width-varying portion 91 from FIG. 9, the height and width of
connecting portions 92 and 93 are at a minimum at one end 901.
Furthermore, when a microstructure is manufactured using
width-varying portions 94 and 95, the height and width of
connecting portions 97 to 100 are at a minimum at centers 902 and
903 in extending direction 14. When a width-varying portion 96 is
used, the height and width of connecting portion 101 is at a
minimum at center 904 in extending direction 14. (In the case of
reference numeral 101 in FIG. 9(c), a portion of the column-shaped
structure is also included in the drawing.)
[0071] Thus, height H and width W' of the connecting portions
corresponding to the broad-width portions of the mask become
larger, and the height H and width W' of the connecting portions
corresponding to the narrow-width portions of the mask become
smaller. Furthermore, if the width W of the width-varying portions
is dramatically varied, the portions corresponding to the
connecting portions also dramatically vary.
[0072] FIG. 10(a) is a drawing which illustrates the other example
of a mask used in the present invention. Reference numerals 1010 to
1013 denote width-varying portions, reference numerals 1021 to 1024
denote narrow-width portions, and reference numerals 1031 to 1035
denote broad-width portions. FIG. 10(b) is a cross-sectional view
in the A-A' direction of the microstructure of FIG. 10(a) and FIG.
10(c) is a perspective view illustrating only the connecting
portions of the microstructure of FIG. 10(a). The width-varying
portions of FIG. 10(a) differ from the width-varying portions of
FIG. 8(a) and FIG. 9(a) in that the broad-width portions and
narrow-width portions of the width-varying portions are aligned
along face 1014. Uppermost connecting portion 1001 and connecting
portions 1002 are formed below narrow-width portion 1021, uppermost
connecting portion 1003 and connecting portions 1004 are formed
below narrow-width portion 1022, uppermost connecting portion 1005
and connecting portions 1006 are mainly formed below width-varying
portion 1012 and uppermost connecting portion 1007 and connecting
portions 1008 are mainly formed below width-varying portion
1013.
[0073] Furthermore, a mask having the same shape as that shown in
FIG. 11 can be used as the mask. In the masks of FIG. 11 (a) and
(c), the mask is closed, while the mask of FIG. 11 (b) is open.
Furthermore, in the masks of FIG. 11 (a) and (b), a width-varying
portion is formed at their respective apex.
[0074] Thus, even if a microstructure is manufactured using masks
having a variety of shapes, a narrow-width portion is formed in at
least one location, so that a connecting portion and an aperture is
formed at least below this portion by isotropic etching.
[0075] While the number of width-varying portions, narrow-width
portions and broad-width portions formed in the mask is not
especially restricted, at least one or more need to be formed. In
addition, while the position of these width-varying portions,
narrow-width portions and broad-width portions in the mask is not
especially restricted, for an open mask, these portions are
preferably formed so that the broad-width portion is at both ends.
More preferably, the broad-width portion is formed at both ends of
the mask and at a portion sandwiched by both ends of the mask. By
forming a broad-width portion at both ends of the mask, the
slit-forming portion can be sandwiched by a column-shaped
structure, to thereby prevent damage to the slit-forming portion.
Furthermore, by also forming a broad-width portion at portions
other than both ends, a microstructure can be attained having
apertures with high precision and high surface area density in the
slit-forming portion.
[0076] When forming a plurality of width-varying portions,
narrow-width portions and broad-width portions, their length in
extending direction of the mask is not especially restricted, and
may be set freely. Preferably, all these portions are made to have
the same length. For example, FIG. 6(b) illustrates a
microstructure manufactured using a mask having a plurality of the
width-varying portions 31, narrow-width portions 33 and broad-width
portions 32 shown in FIG. 6(a). Using such a mask, by carrying out
isotropic etching and passivation film deposition by plasma
reaction using C.sub.4F.sub.8 gas in the same manner as that
described above, a microstructure is formed having four
column-shaped structures 61 aligned in a prescribed direction, and
slit-forming portions 62 in the space adjacent to column-shaped
structures 61. On each slit-forming structure 62 are formed an
uppermost bridge structure (an uppermost connecting portion) 64,
three apertures 63 and three bridge-shaped structures (connecting
portions) 65.
[0077] Furthermore, an electron microscope photograph of a
microstructure actually fabricated using such a mask is shown in
FIG. 7. (In FIG. 7, as one example, two microstructures are
illustrated, wherein the closer microstructure has been fabricated
as far as a middle portion in the photograph.) From FIG. 7 it can
be understood that the apertures and the connecting portions in the
slit-forming portion are aligned with uniform intervals.
[0078] The isotropic etching and passivation film deposition of
steps (3) and (5) can be carried out using conventionally-known
Bosch process operation conditions.
[0079] The substrate is not restricted to being a silicon substrate
or a SOI substrate. Substrates made from a variety of materials can
be employed. For example, when using a substrate made from
SiO.sub.2, as the isotropic etching conditions, it is preferable to
carry out isotropic etching using anhydrous HF vapor, and as the
passivation film deposition conditions, it is preferable to set
conditions in the same manner as those described above.
(Microstructure)
[0080] The microstructure according to the present invention has at
least one column-shaped structure and a slit-forming portion which
extends in a side face direction (direction intersecting with an
axis direction of the column-shaped structure) from a side face of
the column-shaped structure. The slit-forming portions has a
plurality of slits which are aligned in intervals from 20 to 1,000
nm in a direction along the center axis of the column-shaped
structure, and are minute and excellent in shape uniformity. By
utilizing these characteristics of being minute and excellent in
shape uniformity, the microstructure according to the present
invention can be used across a wide range of fields, and can be
used, for instance, as a filter for optical telecommunications. In
such a case, by setting the intervals between slits (slit period)
to be 20 nm or more, filtering in the visible light region becomes
possible. Furthermore, by setting to 1,000 nm or less, transmission
loss is lessened and filtering is possible as far as the
telecommunications waveband (wavelength of 2 .mu.m or less).
Although the interval between slits corresponds to the height H of
the connecting portions or the uppermost connecting portion in the
direction along the center axis of the column-shaped structure, if
the height H of the connecting portions or the uppermost connecting
portion is varied in the length direction of the connecting
portions or the uppermost connecting portion, the height of any
portion can be taken as the slit interval.
[0081] The slits may be aligned with a fixed interval, or with two
kinds of interval therebetween (The slits can have a first interval
and a second interval). In such case, the intervals between the
slits may be aligned so as to alternate between the first interval
and the second interval, or may be aligned with the first intervals
in a prescribed region, and with the second intervals in the other
prescribed region. The slits may also be aligned with three or more
different intervals. For example, a structure is also acceptable in
which the intervals between the slits gradually decrease in the
direction along the center axis of the column-shaped
structures.
[0082] The interval between slits is preferably from 120 to 750 nm.
In addition, slit thickness (width of a slit in the direction along
the center axis of the column-shaped structures) is also preferably
about the same width as the interval between slits.
[0083] FIG. 4 illustrates one example of a microstructure according
to the present invention. The microstructure comprises two
column-shaped structures 41 and a slit-forming portion 42 formed
between adjacent column-shaped structures. As seen from an axial
direction 43 of the column-shaped structures, slit-forming portions
42 alternately have connecting portions (44 and 45) and a slit 46
(wherein the slits are aligned at a prescribed interval).
[0084] Here, "column-shaped structure" is defined as a portion
which does not manifest any slits in its cross-section when viewed
from face parallel in an axial direction of the microstructure and
perpendicular to the aligned direction 14 of the column-shaped
structures. That is, in FIG. 4(a), the portions of cross-section 48
and 49 does not manifest any slits in its cross-section, and is
thus a column-shaped structure when viewed from face parallel in an
axial direction of the microstructure and perpendicular to the
aligned direction 14 of the column-shaped structures. A "connecting
portion" is defined as a structure which connects a portion of a
side face of adjacent column-shaped structures 41, a portion which
manifests any slits in its cross-section when viewed from face
parallel in an axial direction of the microstructure and
perpendicular to the aligned direction 14 of the column-shaped
structures. Seen from an axial direction, the connecting portion at
the uppermost location is termed the uppermost connecting portion.
The uppermost connecting portion connects the uppermost face of a
column-shaped structure (corresponding to the uppermost face of the
substrate) with a part of a side face of a column-shaped structure.
The shape of the cross-section intersecting with the axial
direction of the column-shaped structure is mainly prescribed by
the broad-width portion of the mask formed on an upper portion
thereof.
[0085] The column-shaped structures of the microstructure of FIG.
4(a) are constituted from a curved face. The shape of the pair of
column-shaped structures connected by a connecting portion may be
such that their height H in an axial direction is the same and
these structures is on the same plane, and their shape is not
especially restricted. For example, a column-shaped structure may
include a concave face, a convex face or an uneven face on at least
a part of the side face. For example, the height of the
column-shaped structure is preferably from 1 to 20 .mu.m, and more
preferably from 2 to 12 .mu.m. Maximum width of the column-shaped
structure is preferably from 150 nm to 3 .mu.m, and more preferably
from 200 nm to 1 .mu.m. Length of the column-shaped structure is
preferably no greater than twice the width, and more preferably is
about the same as the width. Due to the fact that the size of the
column-shaped structure (height, length, width) is within these
ranges, a microstructure can be manufactured having desired
characteristics depending on the intended use.
[0086] Uppermost connecting portion 59 in FIG. 4(b) is constituted
from uppermost face 50 viewed from axial direction 43 and two
curved faces 53. Looking towards the axial direction, the change in
surface area of the cross-section perpendicular to axial direction
43 of the uppermost connecting portion 59 reaches a maximum at
uppermost face 50, and continuously decreases towards the lower
side in the axial direction, becoming zero at passing bottommost
portion 501. Furthermore, looking towards length direction 51, the
change in surface area of the cross-section perpendicular to length
direction 51 of uppermost connecting portion 59 reaches a maximum
at one end 502 in the length direction, continuously decreases to
reach a minimum at center 503 in length direction, then
continuously increases to reach a maximum at other end 502 in the
length direction.
[0087] While the shape of the connecting portion is not especially
restricted, the uppermost connecting portion is constituted from an
uppermost face and at least two or more curved faces. How many
faces the faces other than the uppermost face are constituted from
is dependent on the size of width-varying portion of the mask
initially formed and the width and position etc. of the broad-width
portions and narrow-width portions. The curved face may be concave,
convex or uneven on its inner side.
[0088] In FIG. 4(b), connecting portion 60 is constituted from four
faces 54 and 55, and connecting portion 58 is constituted from four
faces 56 and 57.
[0089] Looking towards the axial direction 43, the change in
surface area of the cross-section perpendicular to axial direction
43 of these connecting portions 60 and 58 reaches zero at uppermost
portion 504, continuously increases towards the lower side in the
axial direction to reach a maximum, then continuously decreases to
reach zero at passing bottommost portion 505.
[0090] Furthermore, looking towards length direction 51, the change
in the surface area of cross-section perpendicular to length
direction 51 reaches a maximum at one end 506 in the length
direction, continuously decreases to reach a minimum at center of a
length direction, then continuously increases to reach a maximum at
other end 507 in the length direction.
[0091] While the shape of the connecting portion is not especially
restricted, such portion may be constituted from a plurality of
faces. How many faces the connection portion is constituted from is
dependent on the size of the width-varying portion of the mask
initially formed, and the width and position etc. of the
broad-width portions and narrow-width portions. This curved face
may be concave, convex or uneven on its inner side.
[0092] The faces other than the uppermost face of the uppermost
connecting portion and each face of the connecting portions may be
the same or different. Furthermore, it is also acceptable to make
only a part of the connecting portions the same, while a part can
be made different. Thus, to make the shape of each face the same,
the etching conditions for forming each face and the deposition
conditions of the passivation film should be made the same.
Furthermore, to make the shape of each face different, the etching
conditions for forming each face and the deposition conditions of
the passivation film should be made different.
[0093] The maximum height of the connecting portions is preferably
from 25 to 200 nm, and more preferably from 25 to 150 nm. Length is
preferably from 2 to 20 times the width, and more preferably from 5
to 10 times the width. Maximum width is preferably from 50 to 500
nm, and more preferably from 100 to 250 nm. Due to the fact that
the size of the uppermost connecting portion and the connecting
portions (maximum height, length, maximum width) is within these
ranges, a microstructure can be manufactured having desired
characteristics depending on the intended use.
[0094] The maximum height of the uppermost connecting portion is
preferably from 15 to 100 nm, and more preferably from 15 to 80
nm.
[0095] The slits are formed between the connecting portions in a
slit-forming portion. Here, looking from the axial direction, a
slit is constituted from faces of adjacent connecting portions
which face each other. For example, in the microstructure of FIG.
4, a slit is constituted from face 53 of uppermost connecting
portion 59 and face 54 of connecting portion 60. A slit is also
constituted from face 55 of connecting portion 60 and face 56 of
connecting portion 58.
[0096] The connecting portions and slits are preferably aligned in
equal intervals in an axial direction. In such case, the alignment
interval is preferably from 100 nm and 1 .mu.m, and more preferably
from 120 and 750 nm. Due to the fact that the alignment interval is
within these ranges, a microstructure can be manufactured in which
has the shape with high precision and a high surface area
density.
[0097] While FIG. 4 illustrates a microstructure in which two
column-shaped structures are formed on the ends, the number of
column-shaped structures included in the microstructure according
to the present invention is acceptable as long as it is at least
one, and the number of such structures is not especially
restricted. In the case of a plurality of column-shaped structures,
such structures may be aligned in a straight line in a prescribed
direction, or may be aligned at random. The slit-forming portions
are either formed on a side face of a single column-shaped
structure, or between two column-shaped structures. When a
plurality of column-shaped structures are formed, the slit-forming
portions may be formed between two column-shaped structures
adjacent to each other, or may be formed on a side face of a single
column-shaped structure among a plurality of column-shaped
structures. Furthermore, on a side face of a single column-shaped
structure, three or more slit-forming portions may be formed.
[0098] Even when three or more connecting portions are formed
between a pair of column-shaped structures, or even when a
connecting portion are formed between three or more column-shaped
structures, connecting portions can be formed having the same shape
and size as the above-described connecting portion. Furthermore,
even when forming a plurality of microstructures, the connecting
portions of these differing microstructures can be made the same
shape and size as the above-described connecting portions. Still
further, among these connecting portions, it is also acceptable to
make only a part of the connecting portions the same, while a part
can be made different.
[0099] The microstructure according to the present invention can be
used as an optical element because of its minuteness and due to the
fact that the microstructure can comprise connecting portions and
apertures in which the intervals and shape are controlled with high
precision. This will now be described in more detail.
(Optical Element)
[0100] The following four different mechanisms can be employed as
an application for an optical element of the microstructure
according to the present invention. They are: [0101] (1) Structural
birefringence [0102] (2) Guided-mode resonance [0103] (3) Wire grid
[0104] (4) Periodic structure
[0105] The principles behind each mechanism will be briefly
explained, and a device applying such principles will be
illustrated.
(1) Structural Birefringence
[0106] When the structure is sufficiently smaller than the
wavelength of the light to be used, the structure can be deemed to
be located in a uniform electromagnetic field. The refractive index
in such case greatly differs from that where light is incident in
the direction perpendicular to the slit-forming portion (e.g.
direction 1000 in FIG. 4(a)), depending on the incident
polarization direction. The dielectric constant for TE waves
(transverse electric waves) having an electric field intersecting
with the slit direction (e.g. direction 14 in FIG. 4(a)) is
expressed as: .epsilon.TE=f.epsilon..sub.1+(f-1).epsilon..sub.2
Here, f denotes the volume fraction of the slit structure material,
.epsilon..sub.1 denotes the dielectric constant of the slit
structure material and .epsilon..sub.2 denotes the refractive index
of the medium.
[0107] In contrast, the dielectric constant for TM waves
(transverse magnetic waves) having an electric field parallel to
the slit direction (e.g. direction 14 in FIG. 4(a)) is expressed
as: 1/.epsilon.TE=f/.epsilon..sub.1+(f-1)/.epsilon..sub.2
[0108] If slits are made from Si, and f is set to 0.5, the
refractive index of TE direction is n.sub.TE=2.56 and the
refractive index of TM is n.sub.TM=1.36, whereby birefringence can
be achieved that could not be achieved using conventional
materials.
Wave Plate
[0109] Providing the slit thickness (e.g. thickness of direction
1000 in FIG. 4(a)) in accordance with the wavelength to be used
allows 1/2 wave and 1/4 wave plates to be fabricated. Applying
birefringence of this magnitude enables the following self-standing
type optical element to be achieved.
Polarized Beam Splitter
[0110] By combining a slit having a period .lamda.1 which is
sufficiently smaller than the wavelength with a slit having a
period .lamda.2 which diffracts the light wavelength to be used, a
polarized beam splitter can be formed. That is, portions having a
large polarization dependency is formed by .lamda.1, and a grading
of .lamda.2 is formed by these portions. Although TE waves are
diffracted because of grading of .lamda.2, a polarized beam
splitter transmitting TM waves can be fabricated from a
self-standing type microstructure. The period is preferably no
greater than 1/10 of the intended wavelength.
High-Efficiency Diffraction Grating
[0111] Gradually varying the period .lamda.1 in the polarized beam
splitter enables the diffraction efficiency to be increased.
(2) Guided-Mode Resonance
[0112] When the slit period is about the same as the wavelength of
the light to be used, a guided-mode is formed in the slit. In the
microstructure according to the present invention, the interval
between slits (period) is from 20 to 1,000 nm. By setting the
interval between slits to be from 20 to 1,000 nm, filtering of a
broad waveband is possible from the waveband used in
telecommunications (wavelength of 2 .mu.m or less) through to
visible light, whereby a reflective type filter can be attained in
which transmission loss is small.
(3) Wire Grid
[0113] By coating a metal over the surface of a slit made from Si,
a wire grid structure can be attained. When forming a wire grid
structure, the wire grid can be formed by depositing a metal layer
by a well-known deposition method onto a microstructure
manufactured in accordance with the manufacturing process according
to the present invention. As a deposition method, for example, CVD
method and sputtering method can be employed.
[0114] When the slit period is sufficiently smaller than the
wavelength of the light to be used (generally P (period)/.lamda.
(wavelength)<0.1), TE waves are transmitted through and TM waves
are reflected. By employing such a structure, a polarized element
can be realized. Further, by selecting an appropriate period, a
low-pass filter of TM waves can be formed. For example, FIG. 13
illustrates one example of a wire grid according to the present
invention. Of the TE waves and TM waves that are incident from
direction 1301, in the microstructure according to the present
invention TM waves are reflected, and only TE waves are
transmitted. Therefore, by employing a microstructure according to
the present invention, specific linear polarization can be taken
Out.
(4) Periodic Structure
[0115] Since a connecting portion and an aperture have a periodic
structure toward a axial direction in the microstructure according
to the present invention, when light is incident parallel to a
slit-forming portion (e.g. direction 14 in FIG. 4(a)), a variety of
filters can be formed. The periodic structure can be designed using
the same design method as that for a thin-film dielectric filter.
The thickness of microstructure direction 14 is from 20 to 1000 nm,
when the microstructure is made from Si in combination with using
air for the void portion of the microstructure, such as the
slits.
[0116] As explained above, by using a microstructure according to
the present invention, most kinds of optical element can be
attained. The combination of such a microstructure with an optical
waveguide can realize the following optical device in a compact
form and at low cost.
(Dispersion Compensator)
[0117] The refractive index of all optical materials such as glass
changes according to wavelength, which is called wavelength
dispersion. In long distance optical multiplexing
telecommunication, transmission time varies depending on wavelength
as a consequence of this refractive index wavelength dispersion,
which becomes a problem. To prevent this, a technique called
dispersion compensation is used which connects in the transmission
path devices having dispersion characteristics opposite to those of
the wavelength dispersion Qf the optical fiber. A dispersion
compensator is realized to control wavelength dispersion having an
equivalent refractive index in accordance with a structure in a
dielectric multilayer film. The control of equivalent refractive
index is also possible in the microstructure according to the
present invention in accordance with its structure, whereby a
dispersion compensator can be formed.
(Branching Filter)
[0118] A branching filter can be formed by making a narrow-band
reflection filter utilizing guided-mode resonance align in one row
at an appropriate angle (preferably 45.degree.) toward the
waveguide and optimizing the filter structure in accordance with
the extracted wavelength. FIG. 12 illustrates one example of a
branching filter according to the present invention. Incident light
consisting of wavelengths .lamda.3 to .lamda.6 is branched by
filters 1201 to 1203 into light of respective wavelengths .lamda.3
to .lamda.6.
EXAMPLE 1
[0119] Thermal oxidation was performed on a p-type silicon
substrate having an orientation of (100) planes, to thereby form a
50 nm silicon oxide film on the substrate surface. Subsequently, a
negative-type EB resist, Calix (6) arena 3 weight % solution, was
coated onto the silicon oxide film at a substrate revolution speed
of 4,000 rpm using a spin coater. The coated film was baked at a
temperature of 100.degree. C. for 1 hour. Next, the pattern shown
in FIG. 14(a) was formed on the baked film using an electron beam
lithography system (JEOL-5FE; manufactured by JEOL). FIG. 14(b) is
an enlarged SEM photograph of a part of the resist mask pattern of
FIG. 14(a). A Rainbow 4500 (manufactured by Lam Research
Corporation) apparatus was then used to transcribe a resist mask
pattern onto the silicon oxide film under conditions of CF.sub.4:
CHF.sub.3: Ar=20:10:150 sccm, 150 mTorr, RF 200 W, 10.degree. C.
and 15 seconds. Next, using a MULTIPLEX-ICP (manufactured by
Sumitomo Precision Products Co., Ltd.), silicon etching and
passivation film formation as 1 cycle were carried out by a Bosch
process at 20.degree. C. for 20 cycles. The conditions at this time
are shown in Table 1. TABLE-US-00001 TABLE 1 C.sub.4F.sub.8 Gas
SF.sub.6 Gas Gas Substrate Time Pressure Concentration
Concentration Impressed Impressed Treatment (s) (Pa) (SCCM) (SCCM)
Power (W) Power (W) Etching 7 16 35 90 500 30 Passivation Film 5 16
190 0 350 0 Formation
[0120] The silicon oxide film and passivation film were
subsequently removed, to thereby manufacture a microstructure
according to the present invention. The microstructure showed a
shape as illustrated in FIG. 14(c) and had a connecting portion as
illustrated in FIG. 14(d). The connecting portion of the
microstructure was height 20 nm, width 70 nm and length 650 nm. The
aperture of the microstructure was height 100 nm, width 70 nm and
length 650 nm.
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