JPH01234881A - Method of developing phase type hologram - Google Patents

Abstract

PURPOSE:To obtain a uniform hologram which is free from unequal development with good reproducibility by setting a pulling up speed and immersing speed at the speeds set within the range of the adequate pulling up speed from a swellable solvent and the adequate immersing speed in a bad solvent. CONSTITUTION:An exposed hologram dry plate 1 is immersed in the solvent A and is pulled up from the solvent and is immersed into the solvent B in a developing device P. The degree of swelling of the polymer is small and the development weakens if the amt. the deposition of the solvent A is small. Conversely, the rapid elution of the solvent A in the carrier into the solvent B is retarded by the shielding effect of the excess solvent A and the development weakens if the deposition is too large. The specified deposition is maintained by the principle similar to the principle of dip coating by controlling the pulling up speed of the immersed dry plate. The immersing speed is set at this value by empirically determining the speed at which the unequalness is least. The uniform development with the good reproducibility is thereby executed without the unequal development over a wide area.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a method for developing a phase-type hologram, and in order to solve the problem of dripping patterns and streaks that occur after development due to a decrease in diffraction efficiency, etc., a swelling solvent is used. The device is configured to control the rate of lifting from the tank and the rate of immersion in the poor solvent.

(Industrial Application Field) The present invention relates to a method for developing a photopolymer when producing a hologram, which is one form of use of photography.

[Prior Art and Problems to be Solved by the Invention] Photopolymers are used in a wide range of fields such as photoresists, printing plates, and photography. In any field, a photosensitive polymer is subjected to a development treatment after being exposed to light to form a desired image.

Photopolymers have recently been used as hologram recording materials. There are two types of homodulum: amplitude holograms and phase holograms. This phase-type hologram consists of materials that diffract light due to their surface irregularities, such as thermoplastics and photoresists, and dichromate gelatin (
DG) and polyvinylcarbazole (PVCz) materials n
(Unexamined Japanese Patent Publication No. 53-15153.5 PIC Proceedi
ng Vol, 60Q (03)), which causes diffraction to occur due to the refractive index distribution of the carrier material. In the former case, a large number of copies can be made by transferring the surface irregularities to the mold, but if the hologram is thick or the irregularities are not perpendicular to the substrate but are inclined, the mold cannot be pulled out. Therefore, although it is suitable for mass production, its range of applications is limited. On the other hand, the latter can be applied to thick films and reflective holograms (Lippmann type) in which interference fringes are almost parallel to the substrate, and has a wide range of applications, but requires exposure and development one by one. However, the hologram development process is generally very delicate and the manufacturing yield is low. Regarding yield, the situation is similar for photoresists, but with photoresist, if one mask hologram is produced, many copies can be made, so the yield of the resist hologram, which is a mask, is not so much of an issue. On the other hand, in the latter refractive index distribution type, each sheet is developed, so it is extremely important to improve the yield in the development process.

The development process for refractive index gradient phase holograms (hereinafter simply referred to as holograms) is performed using DC and PVC, which are typical materials.
This will be explained below using z as an example.

(2) After interference exposure, the carrier is immersed in a solvent A that has swelling properties for the polymer that will become the recording carrier. In DC, water at 35℃ (
Applied Optics Vol.7. No1O
P2102) and PVCz use xylene at 40°C (Japanese Patent Application Laid-Open No. 53-15153). Although there are no detailed reports on the state of the carrier at this time, it is presumed that there is a difference in the swelling rate between the exposed areas (areas where the light strengthens each other) and the unexposed areas (areas where the light weakens each other). .

- After immersion in solvent A, solvent A contained in the carrier polymer is removed with another solvent B that acts as a poor solvent □ for the carrier polymer and is compatible with solvent A.

At this time, a refractive index distribution corresponding to the interference pattern is developed. As the solvent B, isopropyl alcohol is used in DG, and n-hexane is used in PVCz. Note that the reason why the refractive index distribution is formed by the treatment (2) is not clear for any of the materials.

A hologram with high diffraction efficiency can be formed by the above-described precess. However, it is extremely difficult to consistently obtain a predetermined diffraction efficiency and Bragg angle over a wide area, and depending on the location, a decrease in efficiency, a shift in the Bragg angle, or a dripping pattern may occur. This tendency is more pronounced in P than in DG.
This is noticeable at VCz, and becomes more noticeable as the film thickness increases.

Therefore, for refractive index distribution type holograms, it has been strongly desired to establish a development process that can obtain uniform holograms with good reproducibility without development unevenness.

[Means for solving the problem, action and effects of the invention]

The present invention has been made in order to solve the above problems, and after immersing a recording carrier on which a latent image of interference fringes has been formed in a solvent that has swelling properties on the recording carrier, the swollen carrier acts as a poor solvent on the carrier. In a method for developing a phase-type hologram in which a hologram is developed by immersing the hologram in a solvent, the pulling speed is set within a range of an appropriate lifting speed from the swelling solvent and an appropriate immersion speed into the poor solvent. It is characterized by setting the dipping speed.

That is, in the present invention, by pulling the recording carrier from the swelling solvent A while controlling the pulling speed and immersing it in the solvent B at a predetermined speed, uniform development over a wide area and with good reproducibility can be achieved. becomes.

In other words, development unevenness refers to differences in development strength depending on location. Although it is difficult to quantify the development strength, qualitatively speaking, development becomes stronger when the temperature of solvent A is increased or the solvent is changed to increase the solubility of the polymer. Under the same exposure conditions, the stronger the development, the larger the refractive index modulation width Δn in the carrier.

In the above-mentioned known example, the type of solvent AB, liquid temperature, and immersion time are described as development conditions, but since these conditions are almost uniform within the surface, the existence of development unevenness is not explained above. This means that there are other parameters that affect development strength.

Therefore, as a result of examining the factors that affect development, we found that the amount of solvent A attached to the carrier surface immediately before immersion in solvent B and the speed at which solvent A in the carrier dissolves into solvent B have a large effect on development strength. It turned out to be dependent.

This will be further explained below.

The hologram dry plate 1 exposed in the developing device P shown in FIG. FIG. 2(a) conceptually shows the relationship between the amount of A adhering to the surface of the carrier polymer film of the pulled-up dry plate and the development strength. If the amount of attached solvent A is small, the degree of swelling of the polymer will be small and the development will be weak.On the other hand, if the amount is too large, the blocking effect of excess solvent A will cause the solvent A in the carrier to
Rapid elution into solvent B is inhibited, and development becomes weak.

Next, when the dry plate taken out from A is immersed in solvent B,
The friction between the dry plate and the solvent B causes the solvent B to be dragged by the dry plate, causing a flow, but unevenness in the flow occurs due to slight irregularities on the edge of the substrate, small dust on the film surface, waves on the liquid surface, etc. Non-uniformity in flow rate results in a difference in the elution rate of solvent A into solvent B, and a thin striped pattern parallel to the immersion direction appears as a difference in development strength.

This tendency is more pronounced as the dipping speed is faster and the viscosity of B is higher. On the other hand, if the dipping speed is slow, the vapor of solvent B near the liquid surface is absorbed by A on the film surface and becomes a poor solvent, so that development progresses. At this time, it is sufficient if the development is carried out in a similar manner, but the solvent is drawn out from the carrier film.

The liquid drips in the form of "drops", creating a dripping pattern. The dripping pattern is noticeable when the boiling point of the solvent B is low or when the swelling property for the polymer is extremely low. The appearance of the above development unevenness is shown in FIG. 2(b).

It has been shown above that unevenness in the amount of attached solvent A and inappropriate immersion speed in solvent B cause uneven development.

Therefore, by appropriately controlling these conditions, uneven development can be reduced or eliminated.

For this reason, the method specified above is adopted in the method of the present invention.

This will be further explained below.

First, the amount of attached solvent A can be fixed by controlling the lifting speed of the immersed dry plate (indicated by X in Figure 2 (d)) using the same principle as deep coating. be able to. The immersion speed is experimentally determined to be the most uniform speed (Y in Figure 2 (b)).
).

Note that when the size of the hologram is large, the time taken from the time it is taken out from A to the time it is immersed in solvent B is significantly different between the top and bottom of the hologram surface, so that solvent A dries in the upper part, making development weaker. This is different from the development unevenness shown in FIG. 2(b). In such a case, the difference in development strength can be reduced by setting the pulling speed from solvent A to be slightly faster in the upper part and slower in the lower part.

Incidentally, the degree of development unevenness varies greatly depending on the material and process, and the allowable range varies depending on the purpose of use. In general, unevenness is noticeable in thick films or in films where the interference fringes are tilted with respect to the substrate. Further, the larger the difference in solubility in the carrier polymer between solvent A and solvent B, the more remarkable it is. For example, in the case of DC, it is swollen with water and dehydrated with isopropyl alcohol (IPA), but the moment it is immersed in IPA,
The rPA near the DC membrane is mixed with the water attached to the membrane and D
The dehydration ability from the C membrane decreases. For this reason, dehydration progresses relatively slowly, so the strength of development varies depending on the location.
In other words, there is little development unevenness. On the other hand, when hexane is used as the solvent B in PVCz, xylene, which is the solvent A, is immediately converted into a poor solvent when mixed with hexane, so that elution of xylene from the PVCz film proceeds in an extremely short time. Therefore, the difference Δt in elution time depending on location,
The ratio Δ1/1 to the average elution time becomes relatively large, and uneven development tends to occur.

〔Example〕

Hereinafter, the present invention will be explained in detail using an example of developing a thick PVCz hologram that is likely to exhibit development unevenness.

(1) Photosensitive material: P with an average molecular weight (πW) of 750,000
70 g of VCz was dissolved in 920 g of an equal weight mixture of tetrahydrofuran and monochlorobenzene, and 7.0 g of tri(tert-butylperoxycarbonyl)benzene as a photosensitizer and 1.4 g of thiopyrylium salt were added and dissolved.
．． The coating solution was passed through a 0μ filter. Next, the above coating liquid was applied onto a 178 x 168 x 1, 1 mm glass substrate by a spin code method to form a photoresist film with a thickness of 6 tones, which was then used as a dry plate.

(2) Ar laser (488 nm) light is applied to the entire dry plate area.
Luminous interference exposure was performed. The spatial frequency of interference fringes is 1400
Line/1m, exposure amount is 350-250m-J/ct
I gave it an A.

(3) The exposed dry plate of (2) was developed using the developing device shown in FIG. Solvent A was a mixture of 30-t% toluene and 70 wt% xylene, and the temperature was adjusted to 21°C. Solvent B
The temperature was set to 23°C with pentane. The lifting and dipping speeds are controlled by a step motor connected to a computer.
500 steps corresponds to the distance traveled by one dragon. After immersing the dry plate in solvent A for 1 minute, v = 18-0.015
It was pulled up at x x - (mm/s). Here, X is the distance (1 m) from the top of the dry plate to the liquid level, and is adjusted so that the pulling speed becomes slower at the bottom of the dry plate. The immersion speed was 40 mm/s.

Through the above process, a diffraction efficiency of 70% or more was obtained over the entire hologram area. Further, uneven development as shown in FIG. 2 was not observed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the method of the present invention, and FIG. 2(a)
FIG. 2(b) is a graph showing the relationship between the development strength and the amount of attached solvent A, and the relationship between the frequency of uneven development and the immersion speed of solvent B, respectively. P... Hologram developing device, 1... Hologram dry plate, 2... Creation hologram.

Claims (1)

[Claims] 1. A phase type in which a record carrier with a latent image of interference fringes formed thereon is immersed in a solvent that has swelling properties on the record carrier, and then a hologram is developed by immersing the swollen carrier in a solvent that acts as a poor solvent for the carrier. In the method for developing a hologram, the pulling speed and the dipping speed are set within a range of an appropriate speed of lifting from the swelling solvent and an appropriate dipping speed in the poor solvent. How to develop a hologram.