JPS634205A - Production of grating of phase diffraction grating type optical modulating element - Google Patents

Abstract

PURPOSE:To obtain a fine grating with a simple stage by providing a resist layer on a transparent substrate, then etching said layer to form a grating negative pattern, coating a heat resistant thermosetting resin thereon, subjecting the coating to a heating treatment to cure the coating, and removing the generated org. components and residues of ashing. CONSTITUTION:The resist 12 consisting of cyclized rubber, polycinnamic acid, novolak resin, etc., is uniformly coated onto the transparent resin 14 while the film thickness is adjusted to about 1-2mum. The resist is exposed over the entire surface through a mask 11 to form the latent image of the negative pattern in the resist 12. The resist is then subjected to post baking at 50-200 deg.C after development to form the negative pattern 13 consisting of the resist on the substrate 14. The heat resistant thermosetting resin 15 such as silicone org. polymer is coated over the entire surface while the recesses formed between the patterns are filled by the resin. The resin is then subjected to a heat treatment at 450-500 deg.C for 30min-2hr to evaporate the org. components of the residue. The residues 13' of ashing are removed. The fine grating having 1-3mum pitch and 1-2mum grating height is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention is applicable to optical display, optical recording, optical coupling, optical communication,
The present invention relates to a method of manufacturing a fine grating of a phase diffraction grating type light modulation element (hereinafter referred to as a light modulation element) suitable for various devices such as optical calculations.

[Prior Art] Conventionally, a light modulation element is composed of a plurality of gratings arranged in the direction of propagation of incident light, and the plurality of gratings are composed of a transparent optical member and a substance having a predetermined optical axis,
In addition, the optical axis direction of the substance differs depending on each of the plurality of gratings, and it is known as a light modulation device that modulates light having arbitrary polarization characteristics by controlling the optical axis direction of the substance.

FIG. 2 shows an example of the configuration of a light modulation element using a combination of a plurality of gratings and a material having a predetermined optical axis.

1 is a transparent spacer, 2 and 2' are transparent electrodes, 3 is a grating-shaped transparent optical member, 4 is a nematic liquid crystal having positive dielectricity as an example of a substance having a predetermined optical axis, and 5 is a substrate.

The substrate 5 and the transparent spacer 1 are generally formed of a glass plate, or a plastic plate, an acrylic plate, etc. are also used. The thickness of the transparent spacer 1 is desirably 0.3 mm or less in consideration of image deviation, etc., and the upper and lower gratings are configured to be perpendicular to each other.

FIG. 3 is a diagram explaining the principle of the light modulation element shown in FIG. 2. In FIG. 3, 26 is the incident light, 27° and 27' are the mutually orthogonal polarization components of the incident light 26, and the liquid crystal 2
4.24' indicates the direction of the optical axis of the liquid crystals 4, 4'.

In FIG. 3, the optical axes of the liquid crystals 24, 24' are oriented in the groove direction of the grating, and the optical axes of the liquid crystals of the first and second layers are perpendicular to each other. Further, the refractive index of the liquid crystals 24 and 24' is controlled by an electric field.

In a static state where no electric field is applied, in the first layer, the polarized light component 27' of the incident light 26 senses the extraordinary refractive index n@ of the liquid crystal 24, and the polarized light component 27 senses the ordinary refractive index n of the liquid crystal 24. I feel it. In addition, in the second layer, the polarized light component 27' is connected to the liquid crystal 24.
′ is the ordinary refractive index n′. , the polarized light component 27 is displayed on the liquid crystal 24'
extraordinary refractive index n'. I feel it. Here, the refractive index of the transparent optical member 23 forming the first layer grating is n,
If the refractive index of the transparent optical member 23 forming the second layer grating is n'8, the wavelength of the incident light is input, and the thicknesses of the 15th and second layer gratings are T and T', respectively, then the thickness of each layer is Diffraction efficiency η of zero-order transmitted diffracted light in grating
. and η′. can be expressed by the following equations (1) and (1)'.

From the above equation, when Δn=0 or Δn'=0, η. =1 or η
'. = 1, ΔnT=a+in, or Δn″T′=1
It can be seen that when the condition for a person (1"l + 2 + 3 + "") is satisfied, η.=0 or η'o=O.

If no=n, or n,=n, is satisfied in the first layer, one of the polarized light components 27 and 27' will pass through, and the other will be modulated according to equation (1).

Also in the second layer, n'. ;n'8 or t,=
nr.

If the equation (1) is satisfied, one of the polarized light components 27 and 27' will pass through, and the other will be modulated according to equation (1)'.

Next, when an electric field is applied to the liquid crystals 24 and 24', the direction of the optical axis of the liquid crystals 24 and 24' changes, and the refractive index felt by the polarized light components 27 and 27' changes accordingly. , modulation according to equations (1) and (1)' is performed in the second layer.

For example, if the same liquid crystal is used for the liquid crystals 24 and 24', n,=n', , no=n'. and the initial condition is Q,=n',;n6. T=T', l
If ne n, I a 7=mλ, the equations expressing the diffraction efficiency of the zero-order transmitted diffracted light in the first layer and the second layer both become equation (1).

It is assumed that the refractive index of the transparent spacer 21 is approximately equal to n. At this time, in a static state, the polarization component 27 of the incident light 26
' passes through the first layer, and the polarized light component 27' is η from equation (1). = 0, and zero-order transmitted light is not emitted and all becomes high-order diffracted light. Also, in the second layer, the polarization component 27 is η from equation (1). −〇, the zero-order transmitted light is not emitted and all becomes higher-order diffracted light.

Note that the polarized light component 27' passes through the second layer as high-order diffracted light. Therefore, there is no light emitted in the zero-order direction. Next, when a predetermined electric field is applied and the optical axes (orientation directions) of the liquid crystals 24 and 24' are directed perpendicular to the grating surface, that is, in the direction of incidence of the luminous flux, the polarization components 27 and 27' are 1
In the first and second layers, the ordinary refractive index n0 of the liquid crystal is sensed, and the light passes through the layer and becomes zero-order transmitted light. Therefore, by applying an electric field, it is possible to control the transmittance of zero-order transmitted diffracted light of light having arbitrary polarization properties. In the above description, zero-order diffracted light was considered as the modulated light, but it goes without saying that higher-order diffracted light can also be used.

As for the manufacturing method of the grating part of the light modulation element mentioned above, there are methods such as a lift-off method using a resist, a replica method, a cutting method using a ruling engine, an embossing method, a pitch method, etc., which have relatively simple processes. It is difficult to manufacture fine gratings that require microfabrication of 1.0 to 3.0 μι and grating height of 1 to 2 JLl.

On the other hand, a transparent inorganic film such as SiO□ is formed by a method such as vacuum evaporation or coating heating and baking, a resist positive pattern is formed by photolithography, a grating shape is formed by dry etching such as plasma etching, and finally a grating shape is formed by dry etching such as plasma etching. There is a method of peeling off the resist. However, this method requires complicated and expensive processes, and production costs are particularly high due to the high cost of dry etching equipment, the limited number of sheets processed per batch, and the time required for vacuuming. This has become an obstacle to the practical application of optical modulation elements.

[Problems to be Solved by the Invention] The present invention eliminates the drawbacks of the above-mentioned prior art, and uses a relatively simple process to solve the problem.
A fine grating of ~2.0μ■ can be formed,
It is an object of the present invention to provide a method for manufacturing a grating of an optical modulation element that can be obtained at a practical price with significantly lower manufacturing costs.

[Means for Solving the Problems] and [Operations] The present invention is a method for manufacturing a fine grating for a light modulation element, in which a resist layer is provided on a transparent substrate, and then etching is performed to form a grating negative pattern of the resist. Then, a heat-resistant thermosetting resin is applied thereon, heat-treated to harden the heat-resistant thermosetting resin, and the organic components in the resist are oxidized and decomposed and evaporated. The present invention is a method for manufacturing a grating for a light modulation element, characterized in that a transparent grating is formed by removing chemical residues.

The present invention will be explained in detail below.

FIGS. 1(a) to 1(e) are process diagrams showing an example of a method for manufacturing a grating of an optical modulation element of the present invention. Below, they will be explained in order.

First, in FIG. 1(a), a resist 12 is coated on a transparent substrate 14 to a thickness of about 1 to 2 .mu.m by a spin code method, a dip method, a spray method, or the like.

This resist 12 is generally made of cyclized rubber, polycinnamic acid,
Novolak resin or polymethyl methacrylate (
PMMA), polymethyl isopropenyl ketone (PMI
Depending on the type of photosensitive group, these organic substances can be exposed to UV light (ultraviolet light), Dee.
Classified for various types of lithography such as p-UV light, electron beam, and X-ray.

Etching of the resist 12 is performed by photolithography, electron beam, X&I lithography, or the like.

In particular, for the grating size of the light modulation element of the present invention (pitch 1 to 54 m, grating height 1 to 3 H),
Lithography using UV light or deep-UV light is desirable for mass production.

Next, the entire surface is exposed through the mask 11 to form a negative latent image in the resist.

Next, in FIG. 1(b), after development, post-bake (5
0 to 200°C) to form a negative pattern 13 of resist on the substrate 14.

Furthermore, in FIG. 1(c), the Dip method (Dip method)
Alternatively, the spaces in the lattice of the negative pattern 13 made of resist are filled with heat-resistant thermosetting resin 15 by a spin code method or the like. The heat-resistant thermosetting resin 15 is made of, for example, Owens-111inois.
(USA), Glass Resin (Glass Resin)
), MOF manufactured by Tokyo Ohka Co., Ltd., etc., and silicon-based organic polymers or oligomers [5i(OH)n.

5i(OCOCTo)4.3i(OCH3)n, 5x(
The main component is Sin or SiO□ and metal oxide (
This is a type of thermosetting resin that forms a mixed film with M, Oy).

The transparent substrate 14 is usually a glass plate and has a heat resistance comparable to that of SOO'C.

Next, in FIG. 1(d), when the negative resist pattern and the silicon-based polymer (oligomer) resin filled in the space thereof are heated to about 450 to soo"c for about 30 minutes to 2 hours, In the resist part, the organic components undergo thermal oxidative decomposition and evaporate, leaving only the ashing residue 13'. When decomposed by oxidation, the organic components evaporate and become inorganic, forming SiO□ or Si
Calcined product 15' of a mixture of O□ and metal oxide (M, 0)
is formed.

No pinholes, cracks, etc. were observed in the fired %j Is', and a good transparent state was observed.

Finally, in FIG. 1(e), the residue of the organic resist that has been ashed by the heating process in the above step is removed by ultrasonic cleaning with an appropriate solvent or high-pressure water cleaning to obtain the desired transparent grid. be able to.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example: Approximately 1.5p of Tokyo Ohka type Deep-IV resist 0DUR1013 (main component PMIPK) was applied on a glass plate of 37++s, width 2611mm, thickness 0.7mm.
The film was formed with a film thickness of m by a spin code method.

Next, a striped mask with a pitch of 1.5 = layers is coated on top of the resist, and 2-5 m1 from the top of the mask is coated.
After irradiating with 11cm2 of far ultraviolet light for a few seconds, develop with a special developer (main components M!: K, xylene) at 100°C.
A negative pattern was formed by post-baking.

Next, a silicon-based organic polymer (manufactured by Tokyo Ohka Co., Ltd., MOF) was deposited on the formed striped negative pattern.
When applied using the IP method and heated at 450°C for 60 minutes, the silicon-based organic polymer sintered and became a fired product.
, the resist produced ashing residue, so high-sonic cleaning was performed with MEK solvent, and the pitch was 1.5 gm and the grating height was 1.5 gm.
A fine grating of 51 zm was obtained.

Two pieces of the obtained fine gratings were combined so that the diffraction gratings were perpendicular to each other, and a light modulation element having the configuration shown in FIG. 2 was fabricated using TN403 (manufactured by ROCHE) as the liquid crystal.

When we measured the white light transmittance of this light modulation element when the electric field was ON and OFF, we found that it was 15% (when OFF) → 90% (when OFF)
The change in transmittance was obtained (at N time).

[Effects of the Invention] As explained above, according to the manufacturing method of the present invention, a 5in2
By simultaneously forming a transparent grating and removing the resist during heat treatment, it is possible to obtain a fine grating at a low manufacturing cost.

Furthermore, by using a fine grating manufactured by the method of the present invention, a light modulation element that requires fine processing of a transparent member can be provided at a practical price.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an example of a method for manufacturing a grating of a light modulation element of the present invention, FIG. 2 is a configuration diagram of the light modulation element, and FIG. 3 is an explanatory diagram showing the light modulation principle of the light modulation element. . 1.21-...Transparent spacer 2.2', 22.22'...Transparent electrode 3.23-.
・Transparent optical members 4.4', 24.24'...Liquid crystal 5...Substrate 11...Mask 12...Resist 13...Negative pattern 1:l' -...Iodide residue 14 ...Transparent substrate 15...Heat-resistant thermosetting resin 15'...Sintered product 26-...Incoming light 27.27'...Polarized light component

Claims (2)

[Claims] (1) In a method for manufacturing a fine grating for a phase diffraction grating type light modulation element, a resist layer is provided on a transparent substrate, etching is performed to form a grating negative pattern of the resist, and then a heat-resistant thermosetting layer is formed on the resist layer. A mold resin is applied and heated to harden the heat-resistant thermosetting resin, and the organic components in the resist are oxidized and decomposed and evaporated, and the ashing residue is removed to form a transparent grating. A method for manufacturing a grating for a phase grating type optical modulator, characterized in that: (2) The manufacturing method according to claim 1, wherein the heat-resistant thermosetting resin contains a silicone polymer or oligomer as a main component.