JPS61189503A - Manufacture of diffraction grating - Google Patents

Abstract

PURPOSE:To improve the controllability of etching by forming a resist diffraction grating on a substrate surface by using a metallic mask which has the same period with the resist diffraction grating and then etching the substrate surface by using the resist diffraction grating as a mask. CONSTITUTION:A thin metallic film 7 which is thick enough not to transmit light is formed on a photoresist film 6 on the surface of the substrate 1 and a photoresist film 2 with film thickness corresponding to the period of the diffraction grating is formed by rotating coating. The resist film 2 is exposed by an interference exposing means which uses laser light beams 3 and 3' and developed to form the resist diffraction grating of the resist film 2 on the film 7. The resist 6 is etched through the metallic mask which is formed by etching the film 7 and has the same period with interference fringes, and exposure and development are carried out to form the diffraction grating of the resist on the surface of the substrate 1 with good reproducibility. Consequently, the controllability of the chemical etching is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a diffraction grating on a substrate surface with good reproducibility and controllability.

Conventional technology Recently, diffraction gratings have become promising for optical integrated circuits.

It is attracting attention as an optical resonant mirror for DBR lasers, etc., or as a wavelength demultiplexing element for wavelength multiplexing communications.

When diffraction gratings are used in optical integrated circuits, the spacing between the diffraction gratings is usually small to several thousand, and highly accurate processing techniques are required.

FIG. 2 shows a manufacturing process for a conventionally used diffraction grating, in which 1 is a substrate on which a diffraction grating is to be formed, 2 is a photoresist film, and 3 is a laser beam. First, board 1
After coating the photoresist film 2 with a spinner,
The photoresist film is exposed by an interference exposure method using laser beams 3 and 3' (A). Next, when development is performed, the photoresist is removed at a period equal to the period of the interference fringes, and a resist diffraction grating is formed (B). When the substrate 1 is chemically etched using a chemical etching solution using this as a mask, grooves are formed with a period equal to the period of the resist diffraction grating (C). Thereafter, the resist 2 is removed and the diffraction grating 4 is produced (D).

FIG. 3 shows the manufacturing process of another conventional diffraction grating. First, a photoresist film 2 is spin-coated onto a substrate 1 using a spinner in the same manner as the process shown in FIG. .

Next, this resist mask is subjected to plasma treatment 6 to etch and shape it to a state suitable for the next chemical etching (C). Thereafter, using this as a mask, chemical etching is performed (d), and the photoresist is further removed to produce the diffraction grating 4 (g)).

Problems to be Solved by the Invention The manufacturing method shown in FIG. 2 has the following drawbacks.

First, when chemical etching is performed, it is basically necessary that no photoresist remains in the grooves 2' of the resist mask. However, in the interference exposure method, the groove 2'
The closer the resist is to the bottom, the more difficult it is to expose and develop, making it difficult to produce a resist mask that is effective for chemical etching.

Second, various conditions such as exposure, development, and resist film thickness in the photorin process are intricately involved in the process of forming a resist diffraction grating. It is difficult to optimally control the

Next, in the case of the manufacturing method shown in FIG. 3, damage occurs to the substrate due to the use of plasma treatment, making it difficult to obtain stable characteristics in an element using the diffraction grating obtained by this manufacturing method.

Means for Solving the Problems In order to solve the above problems, the present invention first spin-coats a photoresist film on the substrate surface, forms a metal thin film on the film, and then coats the photoresist film again on the metal thin film. After spin-coating the film, a resist diffraction grating is formed on the metal thin film,
Next, using this as a mask, the metal thin film is etched to produce a metal mask having a period equal to the period of the resist diffraction grating, and then a resist diffraction grating is formed on the substrate surface using this metal mask. Provided is a method for manufacturing a diffraction grating, characterized in that the diffraction grating is manufactured on a substrate by etching using a resist diffraction grating as a mask.

action The effect of this technical means is as follows.

First, the resist grating to be formed on the substrate surface as a mask for chemical etching is obtained through a metal mask having a desired pattern, so that the remaining photoresist, which is unique to interference exposure, is removed from the grooves of the resist grating. In addition, there is no need for complicated condition settings required for interference exposure method.

Second, during etching by plasma processing, the photoresist film between the substrate and the metal thin film acts as a buffer layer, so the substrate is not damaged.

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

FIG. 1 shows an example in which InP is used for the substrate.

In the figure, 1 is an InP substrate, 2 is a photoresist film, and 3 is a laser beam. First, a photoresist film 6 is spin-coated on the surface of an InP substrate 1 using a spinner, and a thin metal film such as aluminum having a thickness that does not allow light to pass is formed on the photoresist film 6 by vacuum evaporation. Furthermore, a photoresist film 2 having an appropriate thickness according to the period of the diffraction grating is spin-coated on the metal thin film T. After proper pre-baking, laser light 3. The photoresist film 2 is exposed by an interference exposure method using a photoresist (m).

Then, by developing the resist film 2 on the metal thin film T.
Q3) to form a resist diffraction grating consisting of: After performing appropriate post-baking, the metal thin film 2 is etched by plasma treatment 6 using a gas such as CCE4 or by chemical treatment.

As a result, a metal mask having a pattern having a period equal to that of the interference fringes is formed (C). Next, the photoresist 6 is etched with a chemical solvent through this metal mask, or the substrate 1 is exposed to ultraviolet light 3'' having an appropriate wavelength without the influence of diffraction, and then developed.
(Φ) to fabricate a diffraction grating made of resistors on a surface with good reproducibility. Furthermore, saturated bromine water is applied using this resist grating as a mask.

The substrate 1 is etched with a mixed solution of phosphoric acid and water (2:1:16) (K). When the resist mask is removed, InP
A diffraction grating 4 is obtained (F). Note that in this embodiment, the substrate 1
Although InP is used for the substrate material, G
2LA! ! , Si, etc. can also be used.

Effects of the Invention As described above, according to the present invention, a resist mask that is effective for chemical etching can be formed with good reproducibility and a high aspect ratio.As a result, the controllability of chemical etching is improved, and the resist mask is uniform and reproducible. It becomes possible to fabricate a diffraction grating rich in .

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining a method of manufacturing a diffraction grating according to an embodiment of the present invention, and FIGS. 2 and 3 are cross-sectional views for explaining a conventional method of manufacturing a diffraction grating. 1...Substrate, 2,6...Photoresist, 3...Laser light, 4...Diffraction grating, 6...Plasma treatment , 7...metal film. Name of agent: Patent attorney Toshio Nakao and 1 other person3,
J'-... Laser light 12 diagram! , 5. Substrate 2...Photoresist 3.3'',...Reply. Galaz ° Manushi 浬

Claims (1)

[Claims] A metal thin film is formed on the substrate surface coated with a first photoresist in advance, and a second photoresist is further coated, and then a second resist diffraction grating having a desired period is formed on the metal thin film. etching the metal thin film using the second resist diffraction grating as a mask to form a metal mask having the period; then, forming the first resist diffraction grating with the metal mask; 1. A method of manufacturing a diffraction grating, comprising etching the substrate using a resist diffraction grating of No. 1 as a mask to form a diffraction grating on the surface of the substrate.