U.S. patent application number 10/594154 was filed with the patent office on 2007-06-28 for production method of curved-surface metal mold having fine uneven structure and production method of optical element using this metal mold.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Masahiro Higuchi, Shinji Kobayashi, Yoshiaki Maeno, Satoshi Sumi, Atsushi Yamaguchi.
Application Number | 20070144700 10/594154 |
Document ID | / |
Family ID | 35056056 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070144700 |
Kind Code |
A1 |
Kobayashi; Shinji ; et
al. |
June 28, 2007 |
Production method of curved-surface metal mold having fine uneven
structure and production method of optical element using this metal
mold
Abstract
A method of easily manufacturing a metal mold able to add an
antireflection structure to a lens or the like having a complicated
surface shape such as an aspherical lens. The method comprises the
steps of forming a silicon dioxide film (SiO.sub.2) film (2) on a
curved-surface base substrate (1) formed in a specified shape,
etching the silicon dioxide film (SiO.sub.2) film (2) using a
resist mask (3) to form a specified shaped antireflection structure
pattern, bonding a metal used for the metal mold (4) onto a silicon
dioxide film (SiO.sub.2) film (21) on which this antireflection
film pattern is formed to transfer the antireflection film pattern
onto the metal used for the metal mold (4), and then re-moving the
silicon dioxide film (SiO.sub.2) film to form a metal mold (4a)
having an antireflection structure on the curved surface.
Inventors: |
Kobayashi; Shinji; (Gifu,
JP) ; Yamaguchi; Atsushi; (Gifu, JP) ; Sumi;
Satoshi; (Gifu, JP) ; Higuchi; Masahiro;
(Gifu, JP) ; Maeno; Yoshiaki; (Gifu, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
SANYO ELECTRIC CO., LTD.
5-5 KEIHANHONDORI 2-CHOME
MORIGUCHI-SHI
JP
570-8677
|
Family ID: |
35056056 |
Appl. No.: |
10/594154 |
Filed: |
March 18, 2005 |
PCT Filed: |
March 18, 2005 |
PCT NO: |
PCT/JP05/05012 |
371 Date: |
September 25, 2006 |
Current U.S.
Class: |
164/14 |
Current CPC
Class: |
B29C 45/263 20130101;
B29L 2011/0016 20130101; B22D 17/2245 20130101; B22C 9/061
20130101; B29C 33/3878 20130101 |
Class at
Publication: |
164/014 |
International
Class: |
B22C 3/00 20060101
B22C003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2004 |
JP |
2004-089859 |
Claims
1. A production method of a curved-surface metal mold having a fine
uneven structure characterized by comprising: forming a
silicon-base film on a curved-surface base substrate formed in a
specified shape; etching the silicon-base film with a mask to form
a specified shaped fine uneven structure pattern; bonding a metal
used for the metal mold on the silicon-base film with the fine
uneven structure pattern formed thereon; and removing the
silicon-base film after the fine uneven structure pattern is
transferred to the metal used for the metal mold to form the metal
mold having the fine uneven structure on the curved surface
thereof.
2. The production method of the curved-surface metal mold having
the fine uneven structure according to claim 1 characterized in
that said fine uneven structure pattern is an antireflection
pattern.
3. The production method of the curved-surface metal mold having
the fine uneven structure according to claim 1 or 2 characterized
in that said mask is made from a photoresist, and an antireflective
film is formed between said curved-surface base substrate and
silicon-base film.
4. The production method of the curved-surface metal mold having
the fine uneven structure according to claim 1 or 2 characterized
in that a mold release material film is formed between said
curved-surface base substrate and silicon-base film.
5. The production method of the curved-surface metal mold having
the fine uneven structure according to claim 1 or 2 characterized
in that said silicon-base film is a silicon dioxide film formed by
a sputtering method.
6. A production method of a metal mold having a fine uneven
structure characterized by comprising: forming a silicon-base film
on a curved-surface base substrate formed in a specified shape;
providing a mask on the silicon-base film, the mask having a
specified shaped fine uneven pattern on an effective area part of
the mask, and the uneven pattern changing its volume percent toward
the outside of the mask; etching the silicon-base film using the
mask to form a fine pattern composed of fine unevenness gradually
becoming deeper from the outer region to the inner region and
having a predetermined depth and shape on the effective area;
bonding metal used for the metal mold to the substrate with the
uneven pattern formed thereon; and releasing the metal used for the
metal mold from the substrate to form a metal mold after the uneven
pattern is transferred to the metal used for the metal mold.
7. A production method of an optical element characterized by:
forming a silicon-base film on a curved-surface base substrate
formed in a specified shape; etching the silicon-base film using a
mask to form a pattern of a specified shaped fine uneven structure;
bonding metal used for the metal mold to the silicon-base film with
the pattern of fine uneven structure formed thereon; removing the
silicon-base film after the pattern of the fine uneven structure is
transferred to the metal used for the metal mold to form a metal
mold having the fine uneven structure on the curved surface of the
metal mold; attaching the metal mold to at least either of a
stationary mold or moving mold; and performing an injection molding
with the stationary mold and moving mold to manufacture the optical
element having the fine uneven structure on at least one of
surfaces thereof.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method for manufacturing
curved-surface metal molds having a fine uneven structure serving
as an antireflection structure or the like, a method for
manufacturing the curved-surface metal molds having the fine uneven
structure by using easily workable materials to form a curved
surface, and a method for manufacturing optical elements with the
metal mold.
BACKGROUND ART
[0002] Conventionally, optical elements such as optical pickups and
aspherical lenses made of glass, plastic or other
light-transmitting materials are subjected to a surface treatment
to prevent light reflection on the light incident surface of a
substrate. This surface treatment includes a method in which a
multilayer film composed of laminated thin dielectric films is
formed on a surface of a light-transmitting substrate by vacuum
deposition or the like and a method in which fine, dense unevenness
are provided on a surface of an optical element.
[0003] An antireflection structure of fine, dense uneven shape
formed on the surface of the optical element is known to be formed
by molding plastic with a metal mold (e.g. Japanese unexamined
patent publication No. 62-96902).
[0004] The metal mold for forming the optical element having the
antireflection structure of fine, dense uneven shape is formed with
a substrate made from quartz or silicon. The substrate is subjected
to an etching process to form a specified antireflection structure
thereon and plated to form the metal mold.
[0005] By the way, in order to provide the above-mentioned
antireflection structure on a lens, such as a lens for optical
pickups, having a specified curvature, a predetermined treatment is
required to form a curved surface on the quartz or silicon which
will be a substrate.
BRIEF SUMMARY OF THE INVENTION
Problems to be Solved
[0006] In the case of a lens having a complex surface shape like an
aspherical lens, it is difficult to work on the substrate to form
the metal mold. In other words, the quartz or silicon used as a
substrate is unworkable and often subjected to fractures and chips
in the course of manufacture of the substrate. Therefore, the
manufacture of the metal mold is time consuming and expensive.
[0007] This invention is made to solve the above-discussed
conventional problems and has an object to provide a method for
readily manufacturing metal molds to add the fine, dense uneven
shape to a lens having complex surface shapes such as an aspherical
lens.
[0008] In addition, this invention has an object to provide a
method for readily manufacturing optical elements, including the
lens having complex surface shapes such as an aspherical lens, with
the fine, dense uneven shape provided on the surface of the optical
elements.
MEANS TO SOLVE THE PROBLEM
[0009] A production method of the metal mold having the fine uneven
structure according to the invention is characterized by: forming a
silicon-base film on a curved-surface base substrate formed in a
specified shape; etching the silicon-base film with a mask to form
a specified shape of a fine uneven pattern; bonding metal used for
the metal mold on the silicon-base film with the pattern of the
fine uneven structure formed thereon; and removing the silicon-base
film after the pattern of the fine uneven structure is transferred
to the metal used for the metal mold to form the metal mold with
the fine uneven structure on a surface thereof.
[0010] The pattern of the fine uneven structure is characterized by
being an antireflection pattern.
[0011] The mask is made of a photoresist and an antireflective film
may be formed between the curved-surface base substrate and
silicon-base film.
[0012] A mold release material film may be formed between the
curved-surface base substrate and silicon-base film.
[0013] In addition, the silicon-base film can be a silicon dioxide
film formed by a sputtering method.
[0014] In addition, a production method of the metal mold having
the fine uneven structure according to this invention is
characterized by: forming a silicon-base film on a curved-surface
base substrate formed in a specified shape; providing a mask on
this silicon-base film, the mask having a specified shaped fine
uneven pattern on an effective area part of the mask and the uneven
pattern changing its volume percent toward the outside; etching the
silicon-base film using this mask to form a fine pattern composed
of fine unevenness gradually becoming deeper from the outer region
to the inner region and having a predetermined depth and shape on
the effective area; bonding metal used for the metal mold to the
substrate with the uneven pattern formed thereon; and releasing the
metal used for the metal mold from the substrate to form a metal
mold after the uneven pattern is transferred to the metal used for
the metal mold.
[0015] In addition, a production method of an optical element,
according to this invention, is characterized by: forming a
silicon-base film on a curved-surface base substrate formed in a
specified shape; etching the silicon-base film using a mask to form
a pattern of a specified shaped fine uneven structure; bonding
metal used for the metal mold to the silicon-base film with the
pattern of fine uneven structure formed thereon; removing the
silicon-base film after the pattern of the fine uneven structure is
transferred to the metal used for the metal mold to form a metal
mold having the fine uneven structure on the curved surface;
attaching the metal mold to at least either of a stationary mold or
moving mold; and performing an injection molding with the
stationary mold and moving mold to manufacture the optical element
having the fine uneven structure on at least one of surfaces
thereof.
EFFECTS OF THE INVENTION
[0016] As discussed above, according to this invention, a
curved-surface base substrate having a specified curved surface
shape can be readily formed even if it has a complex shape such as
a spherical surface and axisymmetric aspherical surface. Based on
the curved surface of this curved-surface base substrate, a metal
mold having a specified curved-surface with a fine, dense uneven
structure can be formed even if it has a complex shape such as a
spherical surface and axisymmetric aspherical surface.
[0017] In addition, the provision of the antireflective film allows
the resist to be pattered more densely, thereby being able to form
the curved-surface metal mold having the antireflection structure
of further fine, dense uneven shape.
[0018] The use of the mold release material film facilitates the
separation between the metal mold side and substrate side.
[0019] In addition, the use of the curved-surface metal mold having
the antireflection function gradually becoming deeper from the
outer region to the inner region and the antireflection structure
with the unevenness of conical shape formed at a predetermined
pitch on the effective area allows the filled resin to be readily
peeled off from the outer region, thereby eliminating the possible
breakage of the metal mold (stamper) and molded articles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A-1H are cross-sectional views illustrating a
step-by-step manufacturing process of a curved-surface metal mold
having an antireflection structure according to the first
embodiment of this invention.
[0021] FIGS. 2A-2I are cross-sectional views illustrating a
step-by-step manufacturing process of a curved-surface metal mold
having an antireflection structure according to the second
embodiment of this invention.
[0022] FIGS. 3A-3J are cross-sectional views illustrating a
step-by-step manufacturing process of a curved-surface metal mold
having an antireflection structure according to the third
embodiment of this invention.
[0023] FIGS. 4A-4H are cross-sectional views illustrating a
step-by-step manufacturing process of a curved-surface metal mold
having an antireflection structure according to the fourth
embodiment of this invention.
[0024] FIG. 5 is a plan view illustrating an exposure process to
gradually deepen the antireflection function of the optical element
from the outer region toward inner region.
[0025] FIG. 6 illustrates the relation of adherability between the
metal mold and molded article in each area of the optical elements
manufactured according to this invention.
[0026] FIG. 7 is a cross-sectional side view illustrating
configuration and structure of a molding tool used for the
manufacturing method of the optical element according to this
invention.
EXPLANATION OF REFERENCE NUMBER
[0027] 1 curved-surface base substrate [0028] 2 a silicon dioxide
film (SiO.sub.2) film [0029] 3 resist film [0030] 4 metal layer
[0031] 4a,4b metal mold (stamper)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The following is a description of embodiments of this
invention with reference to drawings. FIGS. 1A-1H are
cross-sectional views illustrating a step-by-step manufacturing
process of a curved-surface metal mold having an antireflection
structure composed of dense, fine unevenness according to the first
embodiment of this invention.
[0033] As shown in FIG. 1A, a curved-surface base substrate 1 with
a specified curved surface, such as a spherical surface and
axisymmetric aspherical surface used in an objective lens for
optical pickups, collimating lens and other lenses, is prepared.
This curved-surface base substrate 1 is made of a metal substrate
which can be easily curved, a resin substrate formed by the metal
mold or a glass substrate. In this embodiment, good cuttable
aluminum alloy or carbon free copper are polished with a rotating
diamond tool of an ultra precision microfabrication equipment to
have a mirror-finished specified curved-surface like a spherical
surface or axisymmetric aspherical surface.
[0034] Subsequently, as shown in FIG. 1B, a silicon dioxide film
(SiO.sub.2) film 2 with a thickness of approximately 500 nm to 1
.mu.m is formed as a silicon-base film on the specified curved
surface of the curved-surface base substrate 1 by a sputtering
method. In this embodiment, a silicon dioxide film (SiO.sub.2) film
2 with a thickness of 900 nm is formed by an RF magnetron sputter
using a SiO.sub.2 target. The film is formed under the conditions:
with the SiO.sub.2 target; a substrate temperature of 200 degrees
C.; an argon (Ar) gas flow rate of 20 sccm; and a pressure of 1.36
Pa.
[0035] As shown in FIG. 1C, a resist is then applied on the silicon
dioxide film (SiO.sub.2) film 2. This resist application is
performed by spin-coating a resist, for example, the trade name
"TDUR-P009" manufactured by TOKYO OHKA KOGYO CO., LTD., at 4000 rpm
to consequently form a resist film 3 having a thickness of 600
nm.
[0036] Subsequently, as shown in FIG. 1D, the applied resist film 3
is exposed to light and developed to form a resist pattern 30. In
this embodiment, a two-beam interference exposure system
(wavelength .lamda.=266 nm) is used as an exposure system. The
first exposure is made with an exposure power of 750 mJ, and then a
multi-exposure is made with an exposure power of 750 mJ after the
substrate is turned at 90 degrees. Then, development is made with
the trade name "NMD-W" manufactured by TOKYO OHKA KOGYO CO., LTD.
to form a resist pattern 30 with a multitude of conical projections
at a pitch of 250 nm.
[0037] Next, as shown in FIG. 1E, the silicon dioxide film
(SiO.sub.2) film 2 is patterned using the above-discussed resist
pattern 30 as a mask by reactive ion etching (RIE). In this
embodiment, the trade name "NLD-800" manufactured by ULVAC, Inc. is
used as an RIE etching system. Conical grooves 21 with a processed
depth of 500 nm are formed using a mixed gas of C.sub.4Fs and
CH.sub.2F.sub.2 as an etching gas, an antenna power source of 1500
W and a bias power source of 400 W, at an etching rate of the
silicon dioxide film (SiO.sub.2) of 12 nm/sec.
[0038] After that, as shown in FIG. 1F, removal of the resist film
making up the resist pattern 30 by oxygen plasma ashing brings a
specified curved-surface antireflection structure 2a made of
silicon dioxide film (SiO.sub.2) and provided with fine, dense
conical unevenness thereon.
[0039] Then, as shown in FIG. 1G, a metal layer 4 to be a metal
mold (stamper) is formed on the antireflection structure 2a made of
the silicon dioxide film (SiO.sub.2). The metal layer 4 is formed
as follows: a nickel (Ni) seed layer is formed by sputtering; a
nickel layer is formed on the nickel seed layer by electrolytic
plating; and the rear surface is polished. The metal layer 4 having
a predetermined thickness is thus formed to be a mold
(stamper).
[0040] At last, as shown in FIG. 1H, by mechanically releasing the
mold (stamper) 4a from the boundary of the silicon dioxide film
(SiO.sub.2) and metal layer 4, the curved-surface metal mold 4a
according to the embodiment is obtained having the antireflection
structure with the fine, dense conical unevenness formed at a pitch
of 250 nm.
[0041] According to the above-described embodiment, the
curved-surface base substrate 1 having a specified curved surface,
even if the specified curved surface is complicated in shape like a
spherical surface and axisymmetric aspherical surface, can be
readily formed by the ultra precision microfabrication equipment.
By undergoing the above steps B-H along the curved surface of the
curved-surface base substrate 1, the curved-surface metal mold 4a
having a specified curved surface and an antireflection structure
of fine, dense uneven shape can be formed even if the curved
surface is complicated in shape like a spherical surface and
axisymmetric aspherical surface.
[0042] Next description will be made on the second embodiment of
this invention with reference to FIGS. 2A-2I. FIGS. 2A-2I are
cross-sectional views illustrating a step-by-step manufacturing
process of a curved-surface metal mold having an antireflection
structure according to the second embodiment of this invention. The
same components as those in the first embodiment are denoted with
the same reference numbers and their detailed descriptions are
omitted to avoid repetition.
[0043] Just as with the first embodiment, as shown in FIG. 2A, a
curved-surface base substrate 1, having a specified curved surface
shape such as a spherical surface and axisymmetric aspherical
surface used in an objective lens for optical pickups, collimating
lens and other lenses, is prepared.
[0044] Subsequently, as shown in FIG. 2B, an antireflective
material 11 is provided on the specified curved surface of the
curved-surface base substrate 1. In the second embodiment, a
chromium (Cr) film with a thickness of 100 nm is formed first, and
a chrome-oxide (CrO) film with a thickness of 100 nm is formed on
the chromium film as the antireflective material 11 by a sputtering
method. In addition to the above materials, the antireflective
material 11 can be Al.sub.2O.sub.3, CeO.sub.2, LaF.sub.3,
MgF.sub.3, TiO.sub.2, TiN, ZnS, ZrO.sub.2 or the like.
[0045] After that, as shown in FIG. 2C, a silicon dioxide film
(SiO.sub.2) film 2 having a thickness from approximately 500 nm to
1 .mu.m is formed on the antireflective material 11 formed on the
curved-surface base substrate 1 by the sputtering method. The
silicon dioxide film (SiO.sub.2) film 2 formed in this embodiment
has a thickness of 900 nm. This silicon dioxide film (SiO.sub.2)
film 2 is formed under the same conditions as the first
embodiment.
[0046] Then, as shown in FIG. 2D, a resist film 3 with a thickness
of 600 nm is formed on the silicon dioxide film (SiO.sub.2) film 2.
This resist film 3 is also the same resist film used in the first
embodiment.
[0047] Subsequently, as shown in FIG. 2E, the applied resist film 3
is exposed to light and developed, in the same manner as the first
embodiment, to form a resist pattern 30 with a multitude of conical
projections formed at a pitch of 250 nm.
[0048] Next, as shown in FIG. 2F, the silicon dioxide film
(SiO.sub.2) film 2 is patterned, in the same manner as the first
embodiment, using the above resist pattern 30 as a mask by reactive
ion etching (RIE). This patterning forms conical grooves 21 each
having a processed depth of 500 nm. This patterning is also
performed under the same conditions as the first embodiment.
[0049] After that, as shown in FIG. 2G, removal of the resist 30 by
oxygen plasma ashing brings a specified curved-surface
antireflection structure 2a made of silicon dioxide film
(SiO.sub.2) and provided with fine, dense conical unevenness on the
surface.
[0050] Then, as shown in FIG. 2H, a metal layer 4 to be a mold
(stamper) is formed on the antireflection structure 2a made of the
silicon dioxide film (SiO.sub.2).
[0051] At last, as shown in FIG. 2I, by mechanically releasing a
mold (stamper) 4a from a boundary of the silicon dioxide film
(SiO.sub.2) and metal layer 4, the curved-surface metal mold 4a
according to the embodiment is obtained having an antireflection
structure with conical unevenness formed at a pitch of 250 nm.
[0052] In the above-described second embodiment, in addition to the
effect of the first embodiment, the antireflective material 11
allows the resist to be patterned more densely, thereby being able
to form the curved-surface metal mold 4a having the antireflection
structure of finer, denser uneven shape.
[0053] Next description will be made on the third embodiment of
this invention with reference to FIGS. 3A-3J. FIGS. 3A-3J are
cross-sectional views illustrating a step-by-step manufacturing
process of a curved-surface metal mold having an antireflection
structure according to the third embodiment of this invention. The
same components as those in the first and second embodiments are
denoted with the same reference numbers and their detailed
descriptions are omitted to avoid repetition.
[0054] As shown in FIG. 3A, a curved-surface base substrate 1,
having a specified curved surface shape such as a spherical surface
and axisymmetric aspherical surface used in an objective lens for
optical pickups, collimating lens and other lenses, is prepared
just as with the first embodiment.
[0055] Subsequently, as shown in FIG. 3B, a mold release material
12 having an antireflection function is provided on the specified
curved surface of the curved-surface base substrate 1. In the third
embodiment, a resist having an antireflection function against
ultraviolet rays is applied and hard-baked to be used as the mold
release material 12. In this embodiment, the trade name
"SWK-248DTr" manufactured by TOKYO OHKA KOGYO CO., LTD. is used as
the resist and hard-baked at 180 degrees C.
[0056] After that, as shown in FIG. 3C, a silicon dioxide film
(SiO.sub.2) film 2 having a thickness of approximately from 500 nm
to 1 .mu.m is formed on the mold release material 12 formed on the
curved-surface base substrate 1 by the sputtering method. The
silicon dioxide film (SiO.sub.2) film 2 formed in this embodiment
has a thickness of 900 nm. This silicon dioxide film (SiO.sub.2)
film 2 is formed under the same conditions as the first
embodiment.
[0057] Then, as shown in FIG. 3D, a resist film 3 with a thickness
of 600 nm is formed on the silicon dioxide film (SiO.sub.2) film 2.
This resist film 3 is the same used in the first embodiment.
[0058] Subsequently, as shown in FIG. 3E, the applied resist film 3
is exposed to light and developed in the same manner as the first
embodiment, to form a resist pattern 30 with a multitude of conical
projections formed at a pitch of 250 nm.
[0059] Next, as shown in FIG. 3F, the silicon dioxide film
(SiO.sub.2) film 2 is patterned, in the same manner as the first
embodiment, using the above-described resist pattern 30 as a mask
by reactive ion etching (RIE). This patterning forms conical
grooves 21 each having a processed depth of 500 nm. This patterning
is performed under the same conditions as the first embodiment.
[0060] After that, as shown in FIG. 3G, removal of the resist 30 by
oxygen plasma ashing brings a specified curved-surface
antireflection structure 2a made of silicon dioxide film
(SiO.sub.2) and provided with fine, dense conical unevenness on the
surface.
[0061] Then, as shown in FIG. 3H, a metal layer 4 to be a mold
(stamper) is formed on the antireflection structure 2a of the
silicon dioxide film (SiO.sub.2).
[0062] After that, as shown in FIG. 3I, the mold (stamper) 4a is
mechanically released together with the silicon dioxide film
(SiO.sub.2) from the boundary of the mold release material 12 and
silicon dioxide film (SiO.sub.2).
[0063] Subsequently, as shown in FIG. 3J, the resist for releasing
the mold, which adheres to the mold (stamper) side is removed by
oxygen plasma, and only the silicon dioxide film (SiO.sub.2) 2a is
then removed by reactive ion etching (RIE). Etching gas used is
CHF.sub.3. Thus, a curved-surface metal mold 4a having the
antireflection structure with conical unevenness formed at a pitch
of 250 nm according to this embodiment is obtained.
[0064] In the above-described third embodiment, the separation
between the mold (stamper) side and base substrate 1 side can be
readily achieved.
[0065] By the way, when optical elements are formed by filling
resin into the above-described metal mold with the antireflection
structure of the fine unevenness formed, the resin is filled into
the fine pattern having a high aspect. This increases a load upon
release of the metal mold from the resin. Especially, adherability
significantly increases at the boundary between the non-patterned
area and patterned area, and therefore causes breakage of the
stamper and molded article. Hence, this fourth embodiment is made
for decreasing the load upon the release. For this purpose, the
unevenness of the antireflection function are gradually deepened
from the outer region of the optical element toward the inner
region to gradually increase the load upon the release, thereby
readily releasing the filled resin from the outer region. The
following description is on the fourth embodiment with reference to
FIGS. 4A-4H and 5.
[0066] FIG. 4A-4H are cross-sectional views illustrating a
step-by-step manufacturing process of a curved-surface metal mold
having an antireflection structure according to the fourth
embodiment of this invention, while FIG. 5 is a plan view
illustrating an exposing process for gradually deepening the
unevenness of the antireflection function of the optical element
from the outer region of the optical element toward the inner
region. The same components as those in the first, second and third
embodiments are denoted with the same reference numbers and their
detailed descriptions are omitted to avoid repetition.
[0067] As shown in FIG. 4A, a curved-surface base substrate 1,
having a specified curved surface shape such as a spherical
surface, axisymmetric aspherical surface used in an objective lens
for optical pickups, collimating lens or other lenses, is
prepared.
[0068] Subsequently, as shown in FIG. 4B, a silicon dioxide film
(SiO.sub.2) film 2 with a thickness of 900 nm is formed on the
specified curved surface formed on the curved-surface base
substrate 1 by an RF magnetron sputter. This silicon dioxide film
(SiO.sub.2) film 2 is formed under the same conditions as the first
embodiment.
[0069] Then, as shown in FIG. 4C, a resist is applied on the
silicon dioxide film (SiO.sub.2) film 2. This resist application is
performed by spin-coating a negative resist used with electron
beams at 3000 rpm. The negative resist is, for example, the trade
name "NEB22" manufactured by Sumitomo Chemical Co., Ltd. Thus a
resist film 3a with a thickness of 600 nm is formed.
[0070] Subsequently, as shown in FIG. 4D and FIG. 5, an electron
beam is irradiated to the applied resist film 3a using an electron
beam (EB) lithography system. The irradiation energy is increased
toward the outer region. For example, as shown in FIG. 5, the
electron beam is irradiated by one-hundred micro meter square for
printing. An effective area 30a is irradiated with the electron
beam at energy of 10 .mu.C/cm.sup.2; an area 30b1 outside the
effective area 30a is irradiated with the electron beam at energy
of 12 .mu.C/cm.sup.2; an area 30b2 outside the area 30b1 is
irradiated with the electron beam at energy of 14 .mu.C/cm.sup.2;
and the outermost area 30b3 is irradiated with the electron beam at
energy of 16 .mu.C/cm.sup.2. After being printed by the EB, the
resist film 3a is post-exposure baked (PEB) at 110 degrees C. by a
hot plate for two minutes, and then developed for two minutes with
developer No. "MF CD-26" manufactured by Shipley Far East, Ltd. As
a result, a resist pattern 31 is formed having a multitude of
conical projections formed at a pitch of 250 nm on the effective
area 30a and formed on the areas 30b so as to be wider toward the
outside. This resist pattern 31 is a mask with a volume ratio of
the uneven pattern changing from the effective area toward the
outside.
[0071] Next, as shown in FIG. 4E, the silicon dioxide film
(SiO.sub.2) film 2 is patterned using the above-described resist
pattern 31 as a mask by reactive ion etching (RIE). In this
embodiment, the trade name "NLD-800" manufactured by ULVAC, Inc. is
used for the RIE etcher; a mixed gas of C.sub.4F.sub.8 and
CH.sub.2F.sub.2 is used as etching gas; the antenna power source is
1500 W; the bias power source is 400 W; and the etching rate of the
silicon dioxide film (SiO.sub.2) is 12 nm/sec to form grooves 21
with a processed depth of 500 nm on the effective area. As a
result, a pattern is formed so that the antireflection-functional
grooves are gradually deepened from the outer region toward the
inner region in the areas outside the effective area 30a.
[0072] After that, as shown in FIG. 4F, removal of the resist 30 by
oxygen plasma ashing brings a specified curved-surface
antireflection structure 2b of the silicon dioxide film (SiO.sub.2)
having the antireflective function gradually deepening from the
outer region toward the inner region in the areas outside the
effective area 30a and the specified fine, dense unevenness in the
effective area 30a.
[0073] Then, as shown in FIG. 4G, a metal layer 4 to be a mold
(stamper) is formed on the antireflection structure 2b made of the
silicon dioxide film (SiO.sub.2). The metal layer 4 is formed as
follows: a nickel (Ni) seed layer is formed by sputtering; a nickel
layer is formed on the seed layer by electrolytic plating; and the
rear surface is polished. The metal layer 4 having a predetermined
thickness is thus formed to be a mold (stamper).
[0074] At last, as shown in FIG. 4F, by mechanically releasing a
mold (stamper) 4a from the boundary of the silicon dioxide film
(SiO.sub.2) and metal layer 4, the curved-surface metal mold 4b
according to this embodiment is obtained having the antireflection
structure with the conical unevenness formed at a pitch of 250 nm
on the effective area 30a and the antireflective grooves gradually
deepening from the outer region toward the inner region in the
areas outside the effective area 30a.
[0075] As discussed above, the curved-surface metal mold 4b, having
the antireflection structure with the antireflective function
gradually deepening from the outer region toward the inner region
in the areas outside the effective area 30a and the conical
unevenness formed at a predetermined pitch in the effective area
30a, allows the filled resin to be easily peeled off from the outer
region, thereby eliminating the possible breakage of the stamper
and molded articles.
[0076] A molded article is formed using the metal mold with the
antireflection structure formed at a uniform depth as shown in FIG.
1. In addition, a molded article is formed using the metal mold as
shown in FIG. 4. Comparison was made in respect to adherability of
the molded articles to the metal mold shown in FIG. 1 and the metal
mold shown in FIG. 4. As a result, as shown in FIG. 6, according to
this invention, the adherability diminishes in an area 11b
positioned from the outer region to the outer edge. Consequently,
according to the fourth embodiment of this invention, when the
resin is filled in the mold, the resin can be readily peeled off
from the outer region of the mold, thereby eliminating the possible
breakage of the stamper and molded articles.
[0077] The structure of this fourth embodiment can provide the same
effect even if the structure is applied to the above-discussed
second and third embodiments.
[0078] Although the silicon dioxide film (SiO.sub.2) film is used
as a silicon-base film in the above embodiments, a silicon (Si)
film, silicon nitride (SiN) film and other films are also
available. Further, an SOG film formed by spin-coating organic
silane or the like is also available as the silicon-base film.
[0079] Next, the manufacture of optical elements using the metal
mold according to this invention will be described with reference
to FIG. 7. FIG. 7 is a cross-sectional side view illustrating
configuration and structure of a molding tool used for
manufacturing the optical elements according to this invention.
This molding tool comprises a stationary mold 60 and a moving mold
70. When the moving mold 70 is pushed against the stationary mold
60, a cavity 80 is created between the molds 60 and 70. At a part
of the periphery of the cavity 80, a gate 81 linking to the cavity
80 is formed. Molten plastic resin is supplied to this cavity 80
through the gate 81 to fill up the inside of the cavity 80.
[0080] The stationary mold 60 includes a first member 61 in the
middle and a second member 62 on the periphery side, and both are
made from steel and fixed in a mutually integrated manner. The
first member 61 includes a smooth concave molding surface 61a
facing the moving mold 70, while the second member 61 includes a
molding surface 61b, which is a ring-shaped groove, arranged on the
periphery of the molding surface 61a. The molding surface 61a of
the first member 61 corresponds to one surface of a lens (not
shown) which is a molded article, while the molding surface 62a of
the second member 62 corresponds to a flange provided on the
periphery of the lens.
[0081] The moving mold 70 includes a pushing part 71 which is a
molding member in the middle and a main body 72 supporting the
pushing part 71 at its periphery. On the end of the pushing part
71, the mold (stamper) 4a manufactured by any one of the
above-discussed methods according to the first to fourth
embodiments of this invention is attached. The metal mold 4a is
formed to have a concave surface corresponding to the other surface
of the lens and includes the antireflection structure 40a made of
the fine, dense uneven surface on the concave surface. The
peripheral molding surface 72a defined by the main body 72
corresponds to the flange on the periphery.
[0082] The pushing part 71 is fitted in a hole 72b provided in the
main body 72 so as to slide in the axial (X) direction. After mold
opening, which means both molds 60 and 70 are disengaged from each
other, this pushing part 71 is moved toward the stationary mold 60
with respect to the main body 72, thereby releasing the lens laid
on the moving mold 70 side.
[0083] Next, lens molding using the molding tool shown in FIG. 7
will be described in brief. First, the moving mold 70 is engaged
with the stationary mold 60 to close the molding tool. At this
time, the stationary mold 60 and moving mold 70 are aligned using
an alignment mechanism such as a fitting pin (not shown) and then
secured. Such mold closing creates the cavity 80, in the shape made
by closing and joining the molding surfaces 61a, 61b of the
stationary mold 60 and the molding surface 40a, 72a of the moving
mold 70, between the molds 60 and 70.
[0084] Next, molten plastic resin is injected into the cavity 80
created between the molds 60 and 70. The molten plastic resin is
introduced through the gate 81 to the cavity 80 between molds 60
and 70 to fill up the cavity 80.
[0085] Subsequently, the molten plastic resin filled in the cavity
80 dissipates heat and is cooled down. The molten plastic resin
injected into the cavity 80 usually has a temperature of 200 to 300
degrees C. and therefore is cooled and cured upon contact with the
molding surfaces 40a, 72a, 61a, 61b of the molds 60, 70 which are
maintained at generally 100 to 180 degrees C. At this time, the
molten plastic resin almost completely penetrates into the fine
uneven pattern formed on the molding surface 40a of the pushing
part 71.
[0086] Next, the molten plastic resin filled in the cavity 80 waits
to be completely cured. After all, a lens corresponding to the
shape of the cavity 80 is obtained. One surface of the lens is a
smooth convex surface corresponding to the molding surface 61a,
while the other surface of the lens is a convex surface having the
antireflection structure corresponding to the molding surface 40a.
In addition, a flange is formed on the periphery of the lens,
corresponding to the molding surfaces 61b and 72a.
[0087] After that, the mold opening is performed to disengage the
moving mold 70 from the stationary mold 60. As a result, the molded
article stays on the side of the moving mold 70, but is separated
from the stationary mold 60.
[0088] Then, the pushing part 71 accommodated in the main body 72
is driven toward the stationary mold 60 by a driving device (not
shown). This driving process completely demolds, in other words,
separates the lens from the moving mold 71.
[0089] Thus obtained lens is applicable to an optical pickup device
and so forth. Although the metal mold with the fine uneven pattern
is attached to the moving mold 70 in the above embodiment, the
metal mold can be attached to the stationary mold 60 and moving
mold 70 as appropriate based on the design of the optical element
to be manufactured, for example, either of the stationary mold 60
or moving mold 70, or both.
[0090] Although the antireflection structure is cited as an example
use of the fine, dense uneven shape in the above embodiment, the
present invention can be applied to any cases to manufacture the
optical-element pattern structure having the other functions as
long as the optical elements require the fine, dense uneven shape.
For example, the present invention is applicable to manufacture
fine patterns included in wave plates and diffraction gratings.
[0091] It should be understood that the embodiments disclosed
herein are to be taken as examples and are not limited. The scope
of the present invention is defined not by the above described
embodiments but by the following claims. All changes that fall
within meets and bounds of the claims, or equivalence of such meets
and bounds are intended to be embraced by the claims.
INDUSTRIAL APPLICABILITY
[0092] This invention is applicable to the method for manufacturing
diffraction gratings for optical pickup, wave plates for optical
pickups, lenses for optical pickups, display covers for cellular
phones and other optical elements to provide the antireflection
structure on surfaces of these elements.
* * * * *