JPH06281805A - Production of refractive index modulating pattern - Google Patents

Abstract

PURPOSE:To provide the process for stable production of patterns modulated in refractive index by a simple equipment and process. CONSTITUTION:A substrate having a photopolymeriable mixture layer consisting of a mixture composed of methyl methacrylate and phenyl methacrylate, etc., is irradiated with linearly polarized coherent light (for example, excimer laser beam), by which the compd. is polymerzed and thereafter, the unreacted monomers remaining in the photopolymerizable mixture layer is polymerized by irradiating the entire surface of the photopolymerizable mixture layer with the incoherent light or heating, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a refractive index modulation pattern in which a region having a high refractive index and a region having a low refractive index are repeated at a period of 1 μm or less. INDUSTRIAL APPLICABILITY The present invention can be used for producing optical parts such as a diffraction grating, a polarizing filter, an optical rotator, various filters having a light control function, and various decorative / advertising articles such as holographic displays.

[0002]

2. Description of the Related Art The following is a conventional method for producing a very fine pattern having a pitch of 1 μm or less by using the action of light. (1) A mask on which a fine pattern has been drawn is placed on a photosensitive resin film, and after irradiating light from the mask, a reaction part (positive type) or unreacted portion of the photosensitive resin is used by using a solvent or the like. A method (mask exposure method) of forming a fine pattern on a photosensitive resin film by dissolving and removing a portion (negative type). The mask is manufactured by using an electron beam drawing method, a laser beam drawing method, an interference exposure method, or the like. (2) The photosensitive resin at the position where the lights intensify each other is caused to react by the interference fringes generated by irradiating the photosensitive resin film with two lights capable of interfering with each other, and a reaction portion or an unreacted portion is caused by using a solvent or the like. Method (interference exposure method).

[0003]

In the mask exposure method of (1) above, a high level of technique is required to manufacture a mask, and its manufacturing cost is high. Further, in the interference exposure method of (2) above,
Precise positioning, sufficient vibration countermeasures, etc. are required, and a manufacturing facility capable of precise control is required for a stable manufacturing process, which causes an increase in cost. As described above, in the conventional method, a high technique is required in ancillary parts such as a mask and manufacturing equipment, and it is difficult to form a fine pattern having a pitch of 1 μm or less with a simple equipment / process.

In view of the above points, an object of the present invention is to provide a method for stably producing a fine pattern in which the refractive index is modulated by a simple facility / process.

[0005]

The above-mentioned object is to irradiate a substrate provided with a photopolymerizable mixture layer composed of two or more photopolymerizable compounds having different refractive indices with coherent light containing a linearly polarized component. By photopolymerizing the compound,
Then, the unreacted monomer remaining in the photopolymerizable mixture layer is polymerized to achieve the method for producing a refractive index modulation pattern of the present invention.

As the above-mentioned photopolymerizable compound, a compound having one or more carbon-carbon double bonds in the molecule, for example, an acryloyl group, a methacryloyl group, a vinyl group, an allyl group or the like which can be polymerized Monomers or oligomers containing one or more groups can be used. Preferred examples of the photopolymerizable compound include methyl acrylate,
Ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, butenyl acrylate, phenyl acrylate, tribromophenyl acrylate, phenoxyethyl acrylate, tribromophenoxyethyl acrylate, benzyl acrylate, p-bromobenzyl acrylate, isobornyl acrylate, 2- Ethylhexyl acrylate, lauryl acrylate, 2,2,3,3-tetrafluoropropyl acrylate and methacrylates corresponding to these monofunctional acrylates, or polyester acrylate, polyol polyacrylate, modified polyol polyacrylate, polyisocyanuric acid skeleton Acrylate, melamine acrylate, polyacryle with hydantoin skeleton Door, polybutadiene acrylate,
Epoxy acrylates, urethane acrylates, polyfunctional acrylates such as bisphenol A diacrylate, 2,2-bis (4-methacryloxyethoxy-3,5-dibromophenyl) propane, and methacrylates corresponding to these acrylates, and , Vinyl compounds such as styrene, p-chlorostyrene, p-bromostyrene, divinylbenzene, vinyl acetate, acrylonitonyl, N-vinylpyrrolidone, vinylnaphthalene, vinylanthracene, etc., or diethylene glycol bisallyl carbonate, triallyl isocyanurate, diarylidene Examples include allyl compounds such as pentaerythritol, diallyl phthalate, diallyl isophthalate and the like. The photopolymerizable mixture layer in the present invention is composed of a mixture of two or more compounds selected from the above-mentioned photopolymerizable compounds and having different refractive indexes. From the viewpoint that the optical parts and the like utilizing the pattern obtained in the present invention have a high function, it is preferable that the difference in the refractive index of each of the two or more photopolymerizable compounds is 0.01 or more,
It is more preferably 0.05 or more. The mixing ratio of the two compounds is preferably 5:95 to 95: 5 (weight ratio). Further, if necessary, a photopolymerization initiator can be added.

In the present invention, as a method for providing a photopolymerizable mixture layer on a substrate, a mixture of two or more photopolymerizable compounds is coated on a clean substrate such as glass or plastic by a spin coating method or the like. In addition to the method, a method of adsorbing or impregnating the above mixture on the surface of the substrate is adopted. The degree of vacuum when adsorbing the photopolymerizable mixture on the substrate surface is 10 ⁻⁵ mmHg to 76.
The range of 0 mmHg (normal pressure) is preferable. If the degree of vacuum is too high, the monomer may evaporate before light irradiation. The substrate temperature during adsorption is preferably below the melting point of the photopolymerizable mixture. If the substrate temperature is too high, the photopolymerizable mixture may not be sufficiently adsorbed on the substrate. When the surface of the substrate is impregnated with the photopolymerizable mixture, the surface of the substrate such as a plastic may be contacted with the surface of the photopolymerizable mixture for, for example, 10 to 600 minutes and allowed to penetrate.
In this case, it can be heated to 40 to 150 ° C. if necessary. Of the photopolymerizable mixture provided on the substrate by the above-mentioned method, the component having a high photopolymerization rate is preferentially photopolymerized with coherent light, and then the whole surface of the photopolymerizable mixture layer is irradiated with incoherent light, By heating the photopolymerizable mixture layer under a temperature condition in which the unreacted monomer is not evaporated, the unreacted monomer remaining in the photopolymerizable mixture layer is polymerized.

In the present invention, the linearly polarized coherent light with which the substrate is irradiated for photopolymerization has a wavelength of 190 to 36.
The range of 0 nm and the intensity of linearly polarized coherent light are preferably in the range of 10 mW to 1 W per square centimeter because high reaction efficiency can be obtained. As the light source used in the present invention, a laser device such as an excimer laser is preferable in terms of efficiency, but a device that also emits light other than linearly polarized coherent light may be used. When irradiating with incoherent light for polymerizing unreacted monomers, it is preferable to use a high pressure mercury lamp or the like, and when heating, it is preferable to use an oven.

[0009]

When a material surface is irradiated with linearly polarized coherent light, the material surface is etched and a fine periodic structure appears, for example, IEEE, Journal of Quantum Electronics, Volume QE22, 138.
Reported on page 4 (1986). It is believed that this is because the scattering efficiency of light linearly polarized due to fine irregularities on the surface of the substance increases in a specific direction, propagates to the surface, and interferes with incident light. In the present invention, the coherent light scattered on the surface of the substrate having the photopolymerizable mixture layer and the coherent light incident on the substrate interfere with each other to form an interference pattern. In the interference pattern, the photopolymerization reaction of the compound proceeds in the part where the lights intensify each other, and the photopolymerization reaction does not proceed in the part where the lights interfere with each other due to the interference. Here, of the two types of monomers,
Since the components that are more easily photopolymerized undergo photopolymerization faster, a concentration distribution is generated in the photopolymerizable mixture layer, and a pattern in which the refractive index is modulated is formed. Therefore, a pattern having a periodicity in the direction perpendicular to the electric field vector direction of the coherent light or in the horizontal direction is formed on the substrate at the same period as the interference fringes. Then, the refractive index distribution is maintained by polymerizing the unreacted monomer. According to the present invention, interference fringes are generated by one light flux, and the interfering light passes through almost the same optical path, so that it is not necessary to take measures against vibrations or adjust the optical system with high accuracy.
The angle of incidence on the substrate does not have to be vertical. The period g of the refractive index modulation pattern formed by the present invention is generally expressed by the following equation. g = λ / (cos θ) where λ is the wavelength of the incident coherent light and θ is the incident angle (radian). Therefore, by changing the wavelength of the coherent light or the incident angle of the coherent light, a pattern with an arbitrary period can be produced.

[0010]

【Example】

Example 1 An excimer laser having a wavelength of 248 nm was used as a coherent light source, and methyl methacrylate (refractive index after polymerization: 1.4 was used as a material for forming the photopolymerizable mixture layer).
9) A mixture of 50 parts by weight and phenyl methacrylate (refractive index after polymerization: 1.55) parts by weight was used. Under a reduced pressure of 10 ⁻³ mmHg in a vacuum chamber, 0.1 mg of the mixture was adsorbed on the surface of a glass substrate at a liquid nitrogen temperature (film thickness: about 1 μm), and pulse energy of 40 was applied to the substrate.
A laser beam of mJ / cm ² was irradiated for 10 minutes under the conditions of an incident angle of 30 degrees and a repetition frequency (pulse) of 10 Hz.
After that, ultraviolet rays (1
It was irradiated with 0 mW / cm ² ) for 30 minutes. As a result, a pattern in which the refractive index was modulated was formed on the substrate, and its period was 0.2 to 0.3 μm.

Examples 2 to 4 Excimer lasers were used in the same manner as in Example 1 to fabricate refractive index modulation patterns using the materials shown in Table 1. Table 1 also shows the excimer laser irradiation conditions and the unreacted monomer removal conditions in Examples 2 to 4.

[Table 1] In each of the examples, a refractive index modulation pattern was formed and its period was 0.2 to 0.3 μm.

Example 5 An excimer laser having a wavelength of 248 nm was used as a coherent light source, and a mixture of 30 parts by weight of methyl methacrylate and 70 parts by weight of phenyl methacrylate was used as a material constituting the photopolymerizable mixture layer. The surface of the PMMA substrate was impregnated with the mixture so that the thickness of the photopolymerizable mixture layer was about 1 μm, and the pulse energy of 4 was applied to the substrate.
A laser beam of 0 mJ / cm ² was irradiated for 10 minutes under the conditions of an incident angle of 30 degrees and a repetition frequency (pulse) of 10 Hz. Then, the entire surface of the substrate was irradiated with ultraviolet rays (10 mW / cm ² ) for 30 minutes using a mercury lamp. As a result,
A refractive index modulation pattern was formed on the substrate, and its period was 0.2 to 0.3 μm.

Example 6 A refractive index modulation pattern was prepared in the same manner as in Example 5, except that a mixture of 50 parts by weight of chlorostyrene and 50 parts by weight of styrene was used. A pattern of ˜0.3 μm was formed.

[0014]

According to the present invention, it is not necessary to use an expensive mask and it is not necessary to take measures against vibrations.
A fine pattern in which the refractive index is modulated can be stably manufactured with simple equipment and processes.

Claims (3)

[Claims] 1. A substrate provided with a photopolymerizable mixture layer comprising two or more photopolymerizable compounds having different refractive indices is irradiated with coherent light containing a linearly polarized component to photopolymerize the compound, and A method for producing a refractive index modulation pattern, which comprises polymerizing unreacted monomers remaining in a photopolymerizable mixture layer. 2. The compound is photopolymerized by the action of interference light generated between coherent light scattered on the surface of a substrate having a photopolymerizable mixture layer and coherent light incident on the substrate. The method for producing a refractive index modulation pattern according to claim 1. 3. The difference in refractive index between two or more photopolymerizable compounds constituting the photopolymerizable mixture layer is 0.01.
It is above, The manufacturing method of the refractive index modulation pattern of Claim 1 or 2 characterized by the above-mentioned.