JPH0465764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a resin thin film for protecting a photomask in lithography.

[Conventional technology and problems]

Photoresists that use ultraviolet rays as a light source in lithography for manufacturing integrated circuits are characterized by high resolution and high productivity, and are particularly useful for manufacturing highly integrated wafers or chips.
In this case, deep UV light is generally used because the shorter the wavelength of the light source, the higher the resolution.

Although this method has high resolution, small dust adhering to the image surface of the photomask reduces the accuracy of the etched image and causes defective products, and the photomask itself is easily damaged during the dust removal process. reduce its lifespan.

As a countermeasure against the above problem, a method has been used in which a thin resin film is inserted into the optical path on the image side of the photomask to protect the photomask image from adhesion of dust in the air. In this case, the dust will adhere to the surface of the resin thin film instead of adhering to the image surface of the photomask. At this time, if the thickness of the thin film itself and the distance between the photomask image and the thin film are constant over the entire surface, it is possible to outfocus the effect of the presence of foreign matter, that is, dust, on the thin film on the resist surface. , a pattern faithful to the photomask image can be obtained by exposure.

The above-mentioned thin film is used in the lithography process by adhesively supporting its outer periphery on a support frame having a predetermined thickness, and the thickness of the thin film is usually about 0.9 μm or about
Since it is extremely thin at 2.9 μm, special care is required in its preparation and handling.

The present inventors first proposed a method for producing a thin film for protecting photomasks by casting cellulose ester dissolved in an organic solvent onto a smooth glass plate, removing the solvent, and forming a thin film with a uniform thickness on the glass plate. After forming the thin film, wait for the thin film to separate from the glass plate in water and peel off naturally, collect it, and then adhesively support it on a support frame while it is in a wet state (Japanese Patent Laid-Open No. 1982-
219023) was proposed.

However, this method takes time to collect the thin film,
There was a problem that production efficiency was poor because the product had to be handled with great care and supported on a support frame.

Alternatively, a release agent is placed on the casting substrate, and after the thin film is formed, a frame coated with adhesive is directly adhered to the top surface of the thin film, and then the frame with the thin film attached is separated from the substrate surface. is disclosed in Japanese Patent Application Laid-Open No. 196501/1983. However, with this method, the presence of a release agent impairs the uniformity of the film thickness during casting;
Even with the aid of a release agent when separating the film from the substrate, the film is easily torn, and part of the release agent may be transferred or migrated to the thin film, resulting in poor light transmittance and appearance of the thin film. There were problems such as damage to the

Furthermore, Japanese Patent Application Laid-Open No. 60-35733 discloses that after forming a thin film on a casting substrate, a frame coated with adhesive is adhered to the top surface of the thin film, and the frame and casting substrate are immersed in water. A method for separating a substrate and a thin film in water is shown. In this method, the thin film is immersed with a load applied to it, so if you wait for it to peel off naturally, there is a risk that the film will be damaged.
Although it is necessary to forcibly peel it off, there is a risk of film damage due to the force applied during this process. Furthermore, since the adhesive and support frame are immersed in water, the immersion water is likely to become dirty, resulting in membrane surface contamination.

[Means for solving problems]

As a result of intensive research to solve the above-mentioned problems, the present inventors used cellulose ester as a thin film forming material, cast a polymer solution mainly composed of cellulose ester on a smooth substrate, removed the solvent, and then After forming a thin film of uniform thickness on top, a thin film support frame coated with adhesive or double-sided adhesive tape is adhered to the thin film surface, and the thin film is cut along the outer periphery of the support frame to remove the support. When water vapor or water droplets are brought into contact with the thin film surface to which the frame is attached and moistened,
The present invention was achieved by recognizing that it is surprisingly easy to separate a thin film adhered to a wet support frame from a substrate, and that a thin film suitable for protecting a photomask can be obtained by drying.

That is, the present invention involves the steps of: casting a solution of cellulose ester dissolved in an organic solvent onto a smooth substrate; removing the solvent to form a thin film with a uniform thickness on the smooth substrate; and adhering the thin film to a support frame. This invention relates to a method for producing a resin thin film for protecting a photomask, which comprises the steps of: moistening the thin film by contacting it with saturated water vapor or water droplets; and separating the thin film from a smooth substrate in a wet state. be.

Cellulose esters used in the present invention include cellulose nitrate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, and the like.

Since these cellulose esters are insoluble in water, they are generally considered to be hydrophobic substances, but their surfaces are easily compatible with water and are water vapor permeable, so they can be present on the top surface of thin films. The resulting moisture reaches the interface between the thin film and the substrate within a few minutes, facilitating separation at the interface.

It is also possible to mix acrylic copolymers, vinyl chloride copolymers, vinylidene chloride resins, and vinyl acetate copolymers with these cellulose esters, as long as they do not reduce their ultraviolet transmittance. .

In manufacturing the resin thin film, a so-called casting method is used to obtain a film without orientation. Cellulose esters are easily dissolved in relatively low boiling point solvents such as ketones and lower fatty acid esters, and a thin film with a predetermined finished thickness can be produced by regulating the solution concentration and casting thickness. For photomask protective thin film, for example, 2.8±0.3μm, 4.5±0.3μm
A film with a certain thickness such as 0.865±0.015 μm is used as a reticle protective thin film.

Note that a substrate made of glass is preferably used.

A support frame is attached to the upper surface of the thin film produced as described above, that is, the side opposite to the surface of the casting substrate.

Methods for adhering the thin film to the support frame include: a) applying an adhesive to the surface of the support frame that supports the thin film;
b) It is possible to apply double-sided adhesive tape, etc.

Adhesives and double-sided adhesive tapes are both water resistant and should be selected appropriately. For example, a rubber-based adhesive, an epoxy-based adhesive, or the like can be used.

After adhering the thin film and support frame using the above method, the thin film is cut along the outer periphery of the support frame, and water vapor or water droplets are applied to the support frame and thin film. After 2 to 10 minutes, the thin film is removed from the substrate together with the support frame. Can be easily separated.

Here, a simple and easy method is to place the substrate on top of the container with the side with the thin film to which the support frame is glued down, by pouring warm water of 35-98℃ into the container and putting the lid on. It's a method.

Further, as a method of contacting with water droplets, it is possible to use a sprayer or the like that is used in general households. There is no particular limit to the size of the fog droplets. It is also possible to extract water droplets from a washing bottle commonly used in chemical laboratories.

In the case of foggy water, the substrate is preferably carried out with the side with the thin film on top, to which the support frame is glued. Further, the water vapor may be mixed with a solvent vapor that does not dissolve cellulose ester, such as toluene, xylene, or fluorocarbon solvent vapor.

It is also possible to obtain a thin film supported by a support frame smaller than the inner diameter of the support frame from the thin film supported by the support frame obtained by this method. In this case, it is obtained by applying an adhesive or pasting a double-sided adhesive tape to the support frame, placing it on a thin film, adhering it, and then cutting the thin film along the outer periphery of the support frame.

Although the stress applied to separate the wet film from the substrate is very small, the film still develops slight elongation in some areas. However, when this extension dries, it contracts again, and a uniform and sagging support state is obtained.

〔Effect of the invention〕

The manufacturing method of the present invention skillfully utilizes the behavior of the cellulose ester thin film toward water, and as a result, there is no risk of the thin film itself being contaminated with dust, oil, mold release agent, etc., and the state of support to the support frame is improved. It provides an extremely uniform and good thin film with good production efficiency.

The thin film obtained by the manufacturing method of the present invention has a uniform thickness and is supported under uniform tension, so it can be used not only for protecting photomasks but also as a material for polarizing beam splitters (half mirrors). I can do it.

〔Example〕

The present invention will be further explained below with reference to Examples.

Example 1 64 g of nitrified cotton RS-5 (manufactured by Daicel Chemical Industries, Ltd., isopropanol wet cotton, solid content 70%), 146 g of methyl ethyl ketone, 120 g of butyl acetate, and toluene
Clearance of nitrified cotton dope consisting of 120g
It was applied onto a smooth and clean glass plate using a 50 μm percoater, left to dry at room temperature (20°C) for 24 hours, and further dried at 60°C for 1 hour.

Then outer diameter: 107mm, inner diameter: 103mm, thickness: 3.4
After applying epoxy adhesive (Hi-Super, manufactured by Cemedine Co., Ltd.) to the top surface of the round hard aluminum support frame of mm size, and attaching the surface to the surface of the nitrified cotton thin film dried on a glass plate, the hard aluminum The thin film was cut along the outer periphery of the support frame using a cutter.

The film was then wetted as shown in FIG. That is, a glass plate 2 is placed in the upper opening of a stainless steel container 5, which has a diameter of 15 cm and a capacity of 2 and contains about 500 ml of hot water 6 at 90°C, with the thin film 1 side on which the hard aluminum support frame 4 is glued facing down. and left for 5 minutes. No spontaneous peeling occurred during this time.

Thereafter, it was separated from the container, and the thin film was separated from the glass plate by applying a slight force with the hand holding the hard aluminum support frame to obtain a thin film fixed to the support frame. Separating the thin film from the glass was extremely easy and took about 15 seconds.

After washing the obtained thin film with water and drying it at 50° C. for 2 hours, a cellulose nitrate thin film with a thickness of 2.87 μm supported by a hard aluminum support frame with uniform tension was obtained.

The obtained cellulose nitrate thin film had a good appearance without scratches, and had a light transmittance of 93.2% in the wavelength range of 350 to 450 nm.

Therefore, the cellulose nitrate thin film was extremely useful as a dustproof thin film for photomasks used in the manufacture of LS1 (large scale integrated circuits).

Example 2 After creating a dried nitrified cotton thin film on a glass plate in the same manner as in Example 1, a double-sided adhesive tape (manufactured by 3M, ST-416 ), and the surface was adhered to the surface of the nitrified cotton thin film on a glass plate, and then the thin film was cut using a cutter along the outer periphery of the hard aluminum support frame in the same manner as in Example 1.

Thereafter, the thickness was supported by a hard aluminum support frame with a uniform tension in the same manner as in Example 1.
A cellulose nitrate thin film of 2.86μ was obtained.

The obtained cellulose nitrate thin film had a good appearance and a light transmittance of 93.5% in the wavelength range of 350 to 450 nm.

Example 3 57 g of nitrified cotton RS-5 (manufactured by Daicel Chemical Industries, Ltd., isopropanol wet cotton, solid content 70%) and a butyl acetate solution of isobutyl methacrylate polymer (solid content: 33.8% by weight, viscosity: 20 A dope prepared by mixing 19 g of Poise (23°C), glass transition temperature: 45-46°C) in a mixed solvent of 146 g of methyl ethyl ketone, 120 g of butyl acetate, and 120 g of toluene was set on a spin coater to coat a smooth, clean sheet with a diameter of 20 mm. Drop onto a glass plate and rotate at 100 rpm for 5 seconds, then at 330 rpm.
Rotate the glass plate for 20 seconds, apply it on the glass plate, leave it to dry at room temperature (20℃) for 18 hours, and then apply it to 60℃.
and dried for 30 minutes.

Thereafter, the thickness was supported by a hard aluminum support frame with a uniform tension in the same manner as in Example 1.
A 2.85 μm cellulose nitrate-isobutyl methacrylate polymer mixed thin film was obtained.

The obtained mixed thin film has good appearance and wavelength
The light transmittance from 350 to 450 nm was 94.2%.

Reference example After applying epoxy adhesive (High Super, manufactured by Cemedine Co., Ltd.) to the top surface of a circular hard aluminum support frame with an outer diameter of 60 mm, an inner diameter of 50.8 mm, and a thickness of 3.5 mm, the sample obtained in Example 2 was After placing and adhering the central part of the cellulose nitrate thin film supported by the aluminum support frame, the thin film was cut using a cutter along the outer periphery of the support frame, and was supported by the hard aluminum support frame with a uniform tension. A cellulose nitrate thin film was obtained.

When this thin film was used as a half mirror by vapor-depositing metals such as nickel and aluminum, it was found to have good performance, with no distortion in transmitted light or generation of ghosts in reflected images. .

Example 4 The upper surface of hard aluminum with double-sided adhesive tape was attached to the surface of the dried nitrified cotton thin film prepared on a glass plate in the same manner as in Example 2, and cutters were used to cut along the outer periphery of the hard aluminum support frame. The thin film was cut.

After that, water droplets 7 are sprayed on the outer periphery and inside of the hard aluminum support frame as shown in FIG. I got it. Separating the thin film from the glass was very easy and took about 15 seconds.

Comparative Example 1 After forming a thin film with a uniform thickness on a glass plate in the same manner as in Example 1, the thin film was separated from the glass plate in water, collected, and supported on a support frame in a wet state. When recovering the thin film separated from the plate, the thin film was easily torn, and the recovery rate was about 64%.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams illustrating the process of wetting a thin film in the present invention. 1...thin film, 2...glass plate, 3a...adhesive, 3b...double-sided adhesive tape, 4...hard aluminum support frame, 5...stainless steel container, 6...
Warm water, 7...drops of water.

Claims (1)

[Claims] 1. A step of casting a solution of cellulose ester dissolved in an organic solvent onto a smooth substrate, removing the solvent to form a thin film of uniform thickness on the smooth substrate, and placing the thin film on a support frame. A method for producing a resin thin film for protecting a photomask, comprising the steps of adhering the thin film to a substrate, bringing saturated steam or water droplets into contact with the thin film to moisten it, and separating the thin film from a smooth substrate in a wet state. 2. The method for producing a resin thin film according to claim 1, wherein the cellulose ester is cellulose nitrate, cellulose acetate, or cellulose acetate butyrate.