JPS6083902A - Formation of blazed grating - Google Patents

Abstract

PURPOSE:To obtain a high-performance grating by forming successively a photoresist film having the ion etching rate lower than the ion etching rate of a base plate, a metallic film and the 2nd photoresist film on the surface of the base plate to be worked and forming a relief type holographic diffraction grating on the 2nd photoresist film then etching successively the base plate and obtaining the high-performance grating. CONSTITUTION:The 1st photoresist film 2 is formed on a base plate 1 which is a base plate consisting of InP, GaAs, etc. having a high etching rate or an acrylic plate, by using the resist having the etching rate higher than the etching rate of the base plate. A thin metallic film 3 consisting of Au, Ni, etc. and the 2nd photoresist film 4 are formed on the same material as the film 2 on the film 2. A relief type holographic diffraction grating 4 is then formed on the film 4. The film 3 is etched to a rectangular section with the grating 4 as a mask and UV light 5 is exposed from the top surface of the grating to form the rectangular section of the 1st resist layer 2. After the film 3 is etched away, an ion beam 6 is projected from diagonally above with the layer 2 as a mask to form a blazed grating on the base plate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a blazed grating used as a wavelength dispersion element or a hologram element in a spectrometer, and more specifically to a method for manufacturing a blazed grating in which a holographic grating is blazed by ion etching. be.

Compared to 9-mechanical cut gratings and electron beam drawn gratings, Holgram diffraction gratings have advantages such as less generation of ghosts and stray light, and the ability to easily manufacture gratings with arbitrary grating pitches. Furthermore, the periodic distribution of the grating can be controlled by the phase of the two-beam interference light during manufacturing.

Elements with a wavefront conversion function have applications in hologram scanners, hologram lenses, holographic couplers, etc. However, the diffraction efficiency of the hologram grating is low and is a practical problem. the current.

The most effective method for increasing the diffraction efficiency of a hologram grating is the ion etching method, in which a pre-formed hop graphite relief grating is used as a shadow mask and etched with an ion beam from the diagonal direction of the top surface of the substrate to form a blazed grating. There is. A blazed grating can theoretically be applied to a specific diffraction order by controlling the blaze angle of the grating.
00% of light can be diffracted.

Apply a photoresist such as AZ-1350J on either side on which the PMMA (polymethmethylacrylate) layer is formed.
A photoresist relief grating mask is formed by recording interference fringes on this resist layer using two-beam interference of a He-Cd laser, and the substrate surface is etched with a parallel ion beam from an oblique upper surface in the grating periodic direction of this mask grating. However, the shape of the relief grating used as a shadow mask in ion etching in this case is a holographically formed semicircle or sinusoidal cross section. be.

Therefore, the shadow effect is insufficient and a blazed grid with good performance cannot be manufactured.

It is an object of the present invention to provide a method for forming high-quality blazed gratings by ion etching, which eliminates the above-mentioned drawbacks.

The method for forming a blazed grating of the present invention includes the steps of: applying a first photoresist having an ion etching rate lower than that of the material of the substrate to be processed on the surface of the substrate to be processed, and etching the metal film using the diffraction grating as a mask. a step of chemically etching the metal film to form a lattice pattern with a rectangular cross section;
exposing the first photoresist layer to ultraviolet light from the top surface of the mask using the grating pattern with the rectangular cross section as a shielding mask, and developing the first photoresist to form a diffraction grating with the rectangular cross section; After removing the membrane,
This method of forming a blazed grating is characterized in that it includes the step of performing ion etching in the periodic distribution direction of the grating and from the diagonal upper surface direction with respect to the substrate surface.

The present invention will be described in detail below with reference to the drawings.

1 to 9 are cross-sectional views for explaining an embodiment of the present invention in the order of steps. 3. FIG. FIG. 3 is a cross-sectional view showing a state in which a slow first photoresist 2 is applied. It is desirable that the substrate to be processed be made of a material that has a high ion etching rate, and examples of materials that have a high etching rate include InP, GaAs, Au+Ag, etc., and two of these materials were coated using a spinner. The film thickness of the photoresist layer 2 varies depending on the lattice pitch to be formed, and is 0.3 to 1.0 μm.
It was made into an edition. After baking this first photoresist layer 2,
As shown in FIG. 2, at 5, a metal film 3 such as Au, Cr,
Several thousand pieces of N i + Cu were formed. Furthermore, a second photoresist 4 was applied on the metal film 3 as shown in Figure g3. As the second photoresist 4, the same AZ-1350J as the first photoresist 2 was used, and the film thickness was 0.3.
It was applied with a ~1.0 μ drop spinner. Next, in order to form a holographic relief grating on the second photoresist film 4, interference fringes were exposed and developed on the photoresist film using a two-beam interferometer using a K, He--Cd laser as a light source.

FIG. 4 is a sectional view showing the state after development. In addition, instead of using a laser interferometer, the interference fringes recorded on a silver salt dry plate can be used as a density mask and contact printing with υ■ light can also be used to obtain the fourth image.
A holographic relief grating as shown in the figure can be formed.

A lattice having a nearly rectangular cross section can be formed on the metal layer 3 by using a chemical etching solution as shown in FIG. 4, for example, potassium iodide when the metal film 3 is Au. Next, as shown in FIG. 6, the top surface of the grid is exposed to ultraviolet light (UV light) 5.

The lattice pattern of the metal layer with a rectangular cross section serves as a mask for shielding ultraviolet light, and since the gamma of the photoresist is high, a lattice with a rectangular cross section can be formed in the first resist layer 2. FIG. 7 is a sectional view showing the state after development. The second photoresist grid 4 is exposed to ultraviolet light 5 and melts away during development. Next, as shown in Figure 8, a rectangular lattice with the metal layer 3 removed using the same chemical egging solution for the metal film as described above was used as a shadow mask, and an ion beam 6 (argon ion When the rectangular lattice mask 2 is etched with (or oxygen ions) until the rectangular lattice mask 2 disappears, a seven-seased lattice as shown in FIG. 9 is formed. The etching time is calculated from the ion beam etching angle to be set by examining the dependence of the etching rate 9 on the incident angle of the first photoresist material.

In this example, the case where the base substrate is an old material to be processed is explained, but this method can also be applied to the case where the substrate to be processed is made of tW II"A as the base substrate, for example, an organic material with a fast etching rate. .

As detailed above, by using method 1 of the present invention, -
In blazing, which involves etching a hologram grating,
A high-performance blazed grid is obtained.

[Brief explanation of drawings]

1 to 9 are cross-sectional views of the substrate state in each process 11 according to the present invention. As shown in the figure, the branched substrate 22 is a first photoresist film, 3 is a metal film, 4 is a second photoresist film, 5 is an ultraviolet light beam, and 6 is an ion beam.

Claims (1)

[Scope of Claims] A step of applying a first photoresist having a slower ion etching rate than the material of the substrate to be processed on the surface of the substrate to be processed, and a step of forming a metal film on the first photoresist film,
a step of applying a second photoresist film on the metal film, a step of forming a relief-type holographic diffraction grating on the applied second photoresist film, and a step of chemically etching the metal film using the diffraction grating as a mask. forming a metal film in a lattice pattern with a rectangular cross section, and using the lattice pattern with a rectangular cross section as a shielding mask, the first photoresist layer is illuminated with ultraviolet light from the upper surface of the mask; A process of developing to form a diffraction grating with a rectangular cross section, and after removing the metal film, the process is performed in the direction of the periodic distribution of the grating. 1. A method for forming a blazed grating, comprising the step of performing ion etching from an oblique upper surface direction with respect to a substrate surface.