JPS60146282A - Manufacture of hologram - Google Patents

Abstract

PURPOSE:To manufacture a lattice having a deep groove by applying the first photoresist film, a metallic film, and the second photoresist film onto the surface of a substrate, and repeating an exposure and an etching. CONSTITUTION:The first photoresist film 2 is applied to a substrate 1, and thereafter, a metallic film 3 is coated, and also the second photoresist film 4 is applied on said film. Subsequently, a laser light interference fringe is exposed to the second resist film 4, and developed by a developer. Next, the metallic film 3 is etched by a chemical etching liquid, and a lattice having a roughly rectangular section is formed on the metallic layer 3. Subsequently, a deep groove is formed on the first resist layer by irradiating a far-ultraviolet ray from the upper face of the lattice. The metallic layer mask 3 is melted and removed by a chemical etching liquid, and therefore, etching is executed to the substrate surface by an argon ion beam from the vertical direction, by which a corner of the lattice becomes round.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a hologram.

In particular, it relates to a method for producing a hologram of this type used for scanning a light beam.

Holograms have applications in which they are placed on optical elements, such as holographic lenses, holographic lenses, and duplexers. Among these, holographic scanners are already commercially available as barcode reading devices, but in order to use them as optical scanners such as laser beam printers, the scanning line needs to be able to scan in a straight line without curves. . It is known that the most promising method for this purpose is to use simple grating holograms with a grating period on the order of the wavelength and arranging them around the circumference of the disk, whereby a straight scanning line can be obtained with a specific optical arrangement. What is advantageous for this linear scanning hologram is that high diffraction efficiency is theoretically predicted. In other words, similar to a holographic grating, a grating with X cross-sections of a force sinusoidal grating has a grating period of about the wavelength, and 1 of the grating period.
This is because it is known that a Bragg grating can have a diffraction efficiency of 90% or more if the grooves have a depth of about 5 to 2 times.

For example, for a grating whose grating period is equal to the wavelength, the maximum diffraction efficiency of 96 is obtained when the groove depth is 175 times the grating period. Although gratings with such high diffraction efficiency could not be obtained in the past,
For holographic gratings with a grating period comparable to the wavelength, it is difficult to form a grating with a depth that exceeds the grating period by recording interference fringes on photoresist, and it is difficult to form a grating with a depth that exceeds the grating period. This is because it could not be manufactured.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming gratings with deep grooves that cannot be formed using holographic techniques alone.

The method for manufacturing a hologram of the present invention includes the steps of applying a first photoresist on the substrate surface, forming a metal film on the 'r' photoresist film, and forming a second photoresist on the metal film.
a step of applying a photoresist film, and a step of applying a second photoresist film;
forming a relief-type holographic grating on a photoresist layer; forming the metal film into a grating pattern with a rectangular cross section by chemical etching using the holographic grating as an etching mask; and shielding the grating pattern with a rectangular cross section. Mask and [7 force in direction of mask top surface]
A process of exposing the first photoresist layer to light and developing the first photoresist to form a grating 7, and after removing the metal film, exposing the first photoresist layer to light from a direction perpendicular to the substrate. 1. A method for manufacturing a porogram, characterized in that it includes a step of ion etching.

Hereinafter, the present invention will be described in detail with reference to the drawings.

I will clarify. FIG. 1 to FIG. 7 are diagrams for explaining one embodiment of the present invention in the order of steps.

Figure 1 shows the substrate IK first photoresist filter τf=, cloth 1
．． 2 is a cross-sectional view showing a state in which a metal film 3i)L and a second photoresist 4 are further coated on the top surface of the button. As the substrate, a glass plate and an acrylic plate with good optical transmittance were used to form a transmission type grating.

The first photoresist film 2 may be either a deep UV resist or a UV resist, but a deep IJV resist was used because it can easily form a fine pattern with a large aspect ratio. 1
) eepUV resist has negative type and positive type,
The negative resist has the advantages and disadvantages of high sensitivity, and the positive resist has high resolution.6 In this embodiment, a negative resist 8BL-NFA (manufactured by Somar Kogyo Co., Ltd.), which has a relatively high resolution, is used.

This was applied using a spinner. 5EL-NFA has 2 epoxy groups of glycyl methacrylate as functional groups.
．． 4, substituted with dichlorobenzoic acid. The film thickness is approximately 15 μm. After baking this first photoresist layer 1 in a nitrogen oven, a metal film 3 such as Au, Ni, etc.
Cu was formed in a thickness of several tens of thousands by either plating or vapor deposition. Furthermore, a second photoresist film 4 was applied on the metal film 3. As the second photoresist 4, Az-135 is used.
0J (manufactured by Shisopray Co., Ltd.) was spin-coated using a spinner, and then baked in the same manner as the first photoresist.

The coating thickness varies depending on the lattice pitch to be formed, and is 0.3 μm.
m to 05 μm. Next, the second photoresist film 4 was exposed to light 1 and developed with a developer. FIG. 2 is a sectional view showing the state after development. In addition, when using a laser interference needle, the interference fringes recorded on a silver salt dry plate are used as a density mask.
A relief grating as shown in FIG. 2 can also be formed by contact printing with V light.

The shape of the relief grating is a semicircular cross section of half a sine wave in order to serve as an etching mask for the underlying metal film 3. Second
By etching the sample as shown in the figure with a chemical etching solution, for example, when the metal film 3 is made of Au, a saturated solution of potassium iodide and iodine, the metal layer 3 is etched using the relief grating 4 as a mask, as shown in Figure 3. A grid of approximately rectangular cross section can be formed.

Next, as shown in Figure 4, far ultraviolet light 5
irradiate. Since the rectangular cross-sectional lattice pattern 3 of the metal layer serves as a mask for shielding far ultraviolet light, deep grooves can be formed in the first resist layer 2.

FIG. 5 is a sectional view showing the state after development. In wet development, when forming grooves as deep as about 1.8 with respect to the grating pitch, the grooves are not cut completely to the bottom, resulting in a rounded shape. Next, as shown in FIG. 6, after dissolving and removing the metal layer mask 3 with a saturated solution of potassium iodide and iodine, which is the same as the chemical etching solution for the metal film described above, argon ions are etched in a direction almost perpendicular to the substrate surface. Esochinxult on beam 6,
Since the incidence angle dependence of the ion etching rate in argon etching reaches its maximum around 60°, the angle of the lattice decreases and progresses to form a plane with the maximum etching angle. Therefore, a sinusoidal grating with rounded corners and a cross-sectional shape as shown in FIG. 7 can be obtained. Argon ion etching conditions were gas pressure 1.5×10 Torr%.
The acceleration voltage was set to 500v. The etching time is determined by the etching rate of the first photoresist material.

In this example, the first photoresist film is
Although a V resist was used, a UV resist can also be used.

In this case, it is necessary to form the metal film 3 on the first photoresist film 2 by a method that does not expose the UV resist to light, such as electroless plating.

As detailed above, by using the method of the present invention, a high-quality hologram with deep r-grooves can be manufactured and high diffraction efficiency can be obtained.

[Brief explanation of drawings]

1 to 7 are cross-sectional views showing the present invention in the order of steps. In Figure D, 1 is a substrate, 2 is a first photoresist film, and 3 is a substrate.
4 is a metal film, 4 is a second photoresist film, 5 is an ultraviolet light film, 6 is a metal film, and 4 is a second photoresist film.
is an ion beam.

Claims (1)

[Claims] A step of applying a first photoresist on the substrate surface, a step of forming a relief-type holographic grating on the applied second photoresist film, and a step of etching the metal film using the holographic grating as an etching mask. forming a lattice pattern with a rectangular cross section by chemical etching, and developing the first photoresist layer by exposing the first photoresist layer to light from above the mask using the lattice pattern with a rectangular cross section as a shielding mask. 1. A method for manufacturing a hologram, comprising the steps of: forming a lattice using a metal film; and, after removing the metal film, performing ion etching from a direction approximately perpendicular to the substrate #1.