JPH01252902A - Low reflection diffraction grating and its fabrication method - Google Patents

Abstract

PURPOSE:To obtain the low reflection diffraction grating which is inexpensive and is highly reliable by providing a rugged structure having the periods smaller than the wavelengths of visible rays on the surface of the diffraction grating. CONSTITUTION:A copolymer consisting of an equal mole of methyl methacrylate and chloromethyl methacrylate, etc., is synthesized. Benzophenone is added to this copolymer at the mol equal to the mol of the chloromethyl methacrylate to prepare a 4wt.% benzene soln. and this soln. is applied on a glass substrate 21 to form a transparent photosensitive film 22. The film is exposed via. for example, a photomask 23 for the diffraction grating and is then subjected to two-beam interference exposing to bond the benzophenone to the chloromethyl methacrylate. Finally, the substrate is heated under a reduced pressure to sublimate the unreacted benzophenone, by which the diffraction grating 20 having the rugged surface is obtd. The low-reflection diffraction grating which is inexpensive and is highly reliable is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a diffraction grating used in optoelectronic products such as CD players and color imaging devices.

[Prior Art] In a diffraction grating used as an optical low-pass filter of an imaging device, it is necessary to prevent the image from being changed due to reflection on the grating surface.

Is it necessary to use a reflective diffraction grating with reduced reflectance on the grating surface?

The structure of a conventional low reflection diffraction grating will be explained with reference to FIG. Conventionally, Mg was deposited on the surface of the diffraction grating by vacuum evaporation method etc.
A low reflection diffraction grating is fabricated by coating multiple layers of inorganic dielectric films 51, 52 such as F2,5iOz, Sin, A1201, etc.

[Problem to be Solved by the Invention] However, the low reflection diffraction grating shown in FIG. 5 has the problem that it is inevitably expensive because it is coated with multiple layers of inorganic dielectric films 51 and 52 by vacuum evaporation. There was. Furthermore, when plastic is used as the material for the grid substrate 50, there is a problem in that the adhesion between the plastic and the inorganic dielectric film is poor and reliability is low.

The present invention has been made in view of these points, and an object of the present invention is to provide a low-reflection diffraction grating that is inexpensive and highly reliable.

[Means for Solving the Problems] In order to achieve the above object, the low-reflection diffraction grating according to the present invention is characterized in that the surface of the diffraction grating is provided with an uneven structure whose period is equal to or less than the wavelength of visible light. .

FIG. 1 shows a cross-sectional view of a low reflection diffraction grating according to the present invention. In this invention, as a method for making the surface of the diffraction grating l low reflective, an uneven structure 2 with a period less than the wavelength of visible light is provided on the surface of the diffraction grating l. As a result,
Due to the effect of the uneven structure 2, the refractive index of the surface of the diffraction grating 1 changes continuously from the refractive index nO of air to the refractive index n of the grating material 3, so that the surface substantially becomes a low reflection surface. Moreover, the uneven structure 2 was produced using an interference exposure method.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Example 1 The procedure for manufacturing a low reflection diffraction grating according to the first example is shown in FIG. As shown in FIG. 2(A), glass with a thickness of 1 mm (diameter 3 cm) was used as the substrate 21. Figure 2 (
As shown in B), a photosensitive transparent film 2 is formed on a glass substrate 21.
form 2. As the photosensitive resin of this photosensitive transparent film 22, an equimolar copolymer of methyl methacrylate and cromethyl methacrylate is synthesized, and benzophenone is added in an equimolar amount to the components of crotyl methacrylate-1 in this copolymer. A 41% benzene solution was prepared. This solution was applied to a glass substrate 21 by a spin code method to form a photosensitive transparent film 22. Next, as shown in FIG. 2(C), this photosensitive transparent film 22 was heated at 2000 mJ using an ultra-high pressure mercury lamp through a photomask 23 for a diffraction grating with a period of 30 gm.
/crm", and then, as shown in the second rJ (D), a He-Cd laser with a wavelength of 325 nm was applied to θ=54
．． Two-beam interference exposure was performed diagonally upward on the left and right at an angle of 3°, and exposure was performed at approximately 1000 mJ/c+s2 to bond benzophenone to the crotyl methacrylate component. Finally, the sample was heated under reduced pressure at a pressure of 0.2 mmHg and a temperature of 100° C. to sublimate unreacted benzophenone, thereby producing a low-reflection diffraction grating 20 as shown in FIG. 2(E). The period of the concavo-convex structure 24 was 0.2 lm, the step height of the concavo-convex structure 24 was 0.2 lm, and a low reflection diffraction grating 20 with a reflectance of 1% or less in the entire visible range was obtained.

Example 2 The procedure for manufacturing a low reflection diffraction grating according to the second example is shown in FIG. As shown in FIG. 3(A), a glass substrate 21 having a thickness of 1 mm (diameter 3 cm) was used. Figure 3 (
As shown in B), photosensitive transparent ll! is deposited on the glass substrate 31 by the same method as in the first embodiment. I32 was applied. This photosensitive transparent film 32 is coated with He-C with a wavelength of 422 nm.
By direct laser writing using a lens 34 using a d laser beam 33, exposure was carried out in the form of a diffraction grating with a period of 1 to 2 pm.

Next, as shown in FIG. 3(D), three-beam interference exposure was performed in the same manner as in the first embodiment, and finally, the sample was developed by heating under reduced pressure under the same conditions. A low reflection diffraction grating 30 shown in E) was manufactured. The period of the uneven structure 35 is 0.
2 μm, the height difference of the uneven structure 35 was 0.2 gm, and a low reflection diffraction grating with a reflectance of 1% or less in the entire visible range was obtained.

Example 3 The procedure for manufacturing a low reflection diffraction grating according to the third example is shown in FIG. First, on the low reflection diffraction grating 41 obtained by the first or second embodiment shown in FIG. 4(A), an Ag film 42 was deposited by the vacuum evaporation method shown in FIG. 4(B), Next, as shown in FIG. 4(C), a Ni film 43 having a thickness of 300 m was formed by electroforming to produce a Ni stub bar 44 shown in FIG. 4(CD). Next, as shown in FIG. 4(E), 2P UV resin 45 is applied to the Ni stand bar 44, and then, as shown in FIG. 4(F), a glass substrate 46 is placed on it. , the glass substrate 46
The low reflection diffraction grating 40 shown in FIG. 4(G) was exposed from the side to light of about 10,100 O/cm2 from an ultra-high pressure mercury lamp.
was duplicated. Although the level difference of the replicated concavo-convex structure 40 was slightly smaller than that of the original, the reflectance was less than 1% in the entire visible range.

[Effects of the Invention] As explained above, according to the present invention, an inexpensive and highly reliable low-reflection diffraction grating is provided by forming an uneven structure with a period or less than the wavelength of visible light on the surface of a single diffraction grating. I have something to do.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of a portion of a low-reflection diffraction grating according to the present invention, and FIGS. 2 (A) to (E) are enlarged cross-sectional views showing a method for manufacturing a low-reflection diffraction grating according to the first embodiment. Figure 3 (A) - (
E) is an enlarged cross-sectional view showing a method for manufacturing a low-reflection diffraction grating according to the second embodiment, and FIGS. 4(A) to (G) are enlarged cross-sectional views showing a method for manufacturing a low-reflection diffraction grating according to the third example. FIG. 5 is an enlarged cross-sectional view of a conventional low reflection diffraction grating. 1.20, 30.40... Diffraction grating 2.24, 35
．． 47...Concave and convex structure with a period less than the wavelength of visible light Patent applicant: Rira Shi Co., Ltd.

Claims (1)

[Scope of Claims] 1. A low-reflection diffraction grating, characterized in that, in order to reduce the surface reflectance of the diffraction grating, the surface of the diffraction grating is provided with a concavo-convex structure with a period less than the wavelength of visible light. 2. In order to reduce surface reflectance in a diffraction grating used as an optical low-pass filter for an imaging device,
A low reflection diffraction grating characterized in that the surface of the diffraction grating is provided with an uneven structure having a period less than the wavelength of visible light. 3. After applying a photosensitive resin to the surface of the substrate, and then performing photomask exposure to create the diffraction grating and interference exposure to create the uneven structure, the diffraction grating and the uneven structure are 3. The method for producing a low reflection diffraction grating according to claim 1, further comprising developing the pattern. 4. After applying a photosensitive resin to the surface of the substrate, and then performing laser beam direct writing to create the diffraction grating and interference exposure to create the uneven structure, the diffraction grating and the uneven structure are formed. 3. The method for producing a low-reflection diffraction grating according to claim 1 or 2, wherein a pattern of the following is developed. 5. In order to reduce the surface reflectance of the diffraction grating, the surface of the diffraction grating is reproduced using a matrix for molding the diffraction grating, which has an uneven structure with a period less than the wavelength of visible light. How to make a reflection diffraction grating. 6. A molding mold is prepared from the low-reflection diffraction grating produced by the method according to claim 3 or claim 4, and replication is performed using the molding mold. 2. The method for producing a low reflection diffraction grating according to 2. 7. After applying a photosensitive resin to the surface of the molding mold on which the above-mentioned diffraction grating is formed and then performing interference exposure to create the above-mentioned uneven structure, developing the above-mentioned photosensitive resin and applying the above-mentioned molding method. 3. The method of manufacturing a low-reflection diffraction grating according to claim 1, wherein a mold for molding the low-reflection grating is produced by etching the mold, and the low-reflection diffraction grating is replicated using the mold.