JPS5850323B2 - Method of manufacturing optical phase plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a phase plate used to impart an optical phase difference to a display pattern in the production of a Fourier transform hologram.

Fourier transform holograms are attracting attention as large-capacity memories because of their high-density recording and redundancy.

A Fourier transform hologram with a pattern displayed in binary form in a matrix includes a spatial modulator that displays the matrix pattern and a phase plate that provides a random optical phase difference to the displayed pattern in order to suppress the steep intensity peak of the Fourier transform pattern. It is manufactured using.

Although various spatial modulators for displaying matrix patterns have been devised, the liquid crystal spatial modulator has sufficient S/N, writing speed, and size.

When an independent phase plate is stacked on a liquid crystal spatial modulator, the pattern display part and the phase plate are separated by the thickness of the glass substrate that makes up the liquid crystal cell, so if light is incident obliquely, the phase plate pattern and spatial modulation will be different. Since the pattern of the device is shifted, the effect of the phase plate is reduced.

To solve this problem, a phase plate must be installed inside the liquid crystal cell.

The phase plate has an optically flat surface in order not to disturb the uniformity of the electric field applied to the liquid crystal, and to prevent contribution to the optical retardation of the liquid crystal and provide the designed precise optical retardation. There must be.

As mentioned above, a phase plate that has an optically flat surface and provides partially different optical retardations is manufactured by depositing two kinds of transparent thin films with different refractive indexes on a transparent substrate and patterning them. is easy.

Generally, the materials for the transparent substrate and thin film are limited to those with similar chemical properties, such as glass and oxides.

Therefore, when patterning a thin film, the usual method of chemically corroding using a resist as a mask is difficult to use because it may corrode the transparent substrate.

A lift-off method is known as a method for avoiding such obstacles.

In this method, a resist mask having a desired pattern is first formed on the surface of a transparent substrate, a thin film material is deposited on top of the mask, and then the resist is peeled off along with the unnecessary thin film using the above-mentioned resist stripping agent. be.

This method is a simple method when the thin film is thin and the pattern is relatively fine; however, when the thin film is thick and the pattern is rough, it has the disadvantage that the resist underneath the thin film cannot be removed.

Retarder plates require fairly thick deposits of thin film material to provide sufficient optical retardation, and generally use rough, wide-area patterns.

Therefore, the lift-off method described above cannot be used.

In a new lift-off method that has recently become known, a first metal film is deposited on a transparent substrate, and a second metal film of limited types such as chromium (Cr), titanium (Ti), platinum (Pt), etc. A desired pattern is formed by a conventional lift-off method, and using this as a mask, the first metal film is chemically etched excessively, so that the first and second metal films have a rough cross section. A laminated mask is formed.

A desired thin film pattern is produced by depositing a desired thin film material thereon and peeling off the thin film material deposited on the laminated mask together with the laminated mask.

However, with this new lift-off method, it is difficult to remove a thickly deposited thin film material over a large area because the laminated mask must be made considerably thick or a removal agent with a very high corrosion rate must be selected.

An object of the present invention is to provide a method for manufacturing an optical phase plate that is easier than the conventional method by using a new coarsely aligned laminated mask.

According to the present invention (f), zinc oxide (ZnO
), a process (a
), step (b) of producing a metal thin film on this auxiliary thin film,
A step of forming a resist mask having a desired pattern on this metal thin film (cl) a step of corroding only the metal thin film (a) a step of corroding only the auxiliary thin film (e), a step of attaching the first transparent thin film ( f), step (g) of corroding and removing the metal thin film and the auxiliary thin film, leaving only the first transparent thin film, is carried out sequentially to shape the pattern of the first transparent thin film, and then the step (g) is continued. a), step (b), and step (C)' of forming a resist mask having a pattern opposite to the resist pattern of step (c) on the metal thin film.
, the step (d), the step (e), the step (f)' of depositing a second transparent thin film having a different refractive index and approximately the same thickness as the first transparent thin film; A method for manufacturing an optical phase plate is obtained in which step (g)' of etching and removing the auxiliary thin film and the metal thin film, leaving only the second transparent thin film, is carried out in sequence.

Next, the present invention will be explained in detail using the drawings.

1 to 8 are process schematic diagrams of an embodiment of the present invention.

In FIG. 1, a zinc oxide thin film 2 and a gold thin film 3 are continuously provided on the surface of an optically polished glass substrate 1 by high frequency sputtering, and a photoresist film 4 of AZ-1350 is further applied thereon.

The thickness of the zinc oxide thin film 2 and the gold thin film 3 is approximately 8000 mm each.
There are 2,000 people.

Next, the photoresist film 4 is formed by normal exposure and phenomenon processing.
A photoresist mask 21 with a desired pattern is formed.

FIG. 2 shows this state.

The width of the pattern is a minimum of a few nanometers and a maximum of a few centimeters.

Subsequently, the gold thin film 3 is etched with a mixed solution of potassium iodide (KI), potassium iodide (KI), and water to form a gold thin film pattern 22 having the same shape as the photoresist mask 21, as shown in FIG.

Next, the zinc oxide thin film 2 is corroded with a 10% concentration phosphoric acid solution to obtain a zinc oxide thin film pattern 23 having substantially the same shape as the gold thin film pattern 22.

At this time, the end portion 31 of the zinc oxide thin film pattern 23 is corroded excessively to the inside of the gold thin film pattern 22 by several microns.

Photoresist mask 21 is removed in this step.

FIG. 4 shows this state.

Silicon oxide (S i02 ), which is a transparent thin film material, is deposited by vacuum evaporation onto the laminated patterns 22 and 23 obtained as described above.

Through this step, as shown in FIG.
A silicon oxide thin film 24 is deposited on the stacked patterns 22 and 23, and a silicon oxide thin film 25 is also deposited on the laminated patterns 22 and 23, but these are not interconnected.

Next, the zinc oxide thin film 2 was immersed in a phosphoric acid solution with a concentration of 50%.
3 is completely corroded and the gold thin film 22 and silicon oxide thin film 25 adhering thereto are also removed from the glass substrate 1 at the same time, as shown in FIG. Only 24 patterns remain.

Two types of metal thin films can be used as the laminated pattern described above, but if the silicon oxide thin film 25 is thick and has a pattern covering a wide area, corrosion from the end faces of the laminated pattern can be prevented in the process shown in FIG. The slow speed makes it difficult to completely remove the unnecessary silicon oxide thin film 25 from the substrate.

In the above example, a case was explained in which zinc oxide was used, but thin films of zinc sulfide, cadmium oxide, cadmium sulfide, etc. can also withstand corrosive liquids of specific metals.
It can be used in the present invention because it dissolves very quickly in low concentrations of phosphoric acid.

FIG. 7 shows a layered pattern consisting of a zinc oxide thin film pattern 23' and a gold thin film pattern 22' having the same shape as the silicon oxide thin film pattern 24 of FIG.
This figure shows a state formed by the same steps as those shown in FIG. 4.

Next, zirconium oxide (Zr02), which is a transparent thin film material, is vacuum-deposited onto the laminated patterns 22' and 23' obtained in FIG.
After three people adhered 6, unnecessary thin films were removed along with the zinc oxide thin film 23' using 50% phosphoric acid, and a silicon oxide thin film 24 and a zircon oxide thin film 2 were formed as shown in FIG.
An optical phase plate consisting of 6 is obtained.

The refractive index of silicon oxide and zircon oxide is wavelength 6328
For human light, they are 1.46 and 2.05, respectively, so light with a wavelength of 6328λ passing through each thin film produces a phase difference of π/2.

As explained above, according to the manufacturing method of the present invention, a thin film having an optically flat surface and giving partially different optical retardations can be easily obtained.

[Brief explanation of drawings]

1 to 8 are diagrams schematically showing the manufacturing process in the present invention. In the figure, 1 is a glass substrate, 2 is a zinc oxide thin film, 3 is a gold thin film, 4 is a photoresist, 24 is a silicon oxide thin film, and 26 is a zircon oxide thin film.

Claims (1)

[Scope of Claims] 1. Step (a) of manually depositing an auxiliary thin film of any one of zinc oxide, zinc sulfide, cadmium oxide, and cadmium sulfide on the surface of a transparent substrate; step (b) of depositing a metal thin film on the auxiliary thin film; Step (c) of forming a resist mask having a desired pattern on this metal thin film; Step (d) of corroding only the metal thin film; (d) Step of excessively corroding only the auxiliary thin film and removing the resist mask; (e), step (f) of attaching a first transparent thin film, leaving only a portion of the first transparent thin film attached to the surface of the transparent substrate, and corroding the other pre-auxiliary thin film and metal thin film; By sequentially performing the removing step (g), a first transparent thin film pattern is formed on the surface of the transparent substrate, and then the step (a'1), the step (b), and the step (c)
step (c)' of forming a resist mask having a pattern opposite to the resist pattern in step (c)' on the metal thin film; and step (d). step (e), step (f) of depositing a second transparent thin film having a different refractive index and approximately the same thickness as the first transparent thin film, leaving the first and second transparent thin films; Step (g) of corroding and removing other auxiliary thin films and metal thin films
1. A method for manufacturing an optical phase plate, characterized by sequentially performing steps . 2. The method for manufacturing an optical phase plate according to claim 1, wherein the first transparent thin film is a silicon oxide thin film. 3. The method for manufacturing an optical phase plate according to claim 1 or 2, wherein the second transparent thin film is a zircon oxide thin film.