JPH0544017B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photomask cover made of a thin resin film for protecting a photomask in a ring graph.

Photoresists that use ultraviolet rays as a light source in the phosphor-ray process for manufacturing integrated circuits are characterized by high resolution and high productivity, and are extremely useful particularly in the manufacture of highly integrated wafers or chips.

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 is used in which a photomask cover made of 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.

As a result of intensive research, the inventors discovered that by using a cellulose ester thin film to which no plasticizer was added as the thin film material for the photomask cover,
It has been recognized that a photomask cover suitable for protecting a photomask can be obtained, and the present invention has been developed.

The physical properties required of the thin film material used in the present invention are as follows.

b Specific area of light used for exposure (especially in this case)
UV range), with as little absorption as possible.

(b) Even if the film is thin, it has sufficient strength and does not cleave or shrink after being supported by a support frame.

C. Directionality should not be caused in transmitted light due to crystals or orientation.

D. There should be no substances that would have a negative effect on the photomask compared to the thin film.

The cellulose ester thin film of the present invention to which no plasticizer is added satisfies these conditions.

That is, in the present invention, cellulose ester without added plasticizer is dissolved in an organic solvent, and a thin film is cast on a smooth glass plate, peeled off in water, supported on a support frame in a wet state, and then dried. This is the photomask cover obtained by this method.

Cellulose ester is suitable as the membrane material used in the present invention, and cellulose ester is
Refers to cellulose nitrate, cellulose acetate, cellulose propionate, cellulose acetate butyrate, etc. Among these, cellulose nitrate is particularly suitable for the purposes of the present invention.

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 by regulating the solution concentration and casting thickness, a thin film with a predetermined finished thickness can be produced. For example, the photomask protective thin film has a thickness of 2.8±0.3μm or 4.5±
A material with a certain thickness such as 0.3 μm is used.

When a smooth glass plate is used as the casting substrate during casting, and the thin film is immersed in water after removing the solvent, the thin film is naturally peeled off from the glass plate and can be easily recovered. This thin film is mounted directly on an aluminum support frame, and when it is partially dry, a small amount of volatile solvent is applied along the contact area between the support frame and the membrane and dried. The membrane attempts to contract slightly, providing support under uniform tension.

Cellulose esters, including cellulose nitrate, are highly transparent and have low absorption in the UV region, making them optically excellent materials. In addition, although the crystallinity is originally low, the molecular structure is rigid, so there is dimensional stability after molding. It has various advantages such as a suitable casting solvent can be used, it has poor adhesion to the glass plate, so only the thin film can be collected without applying force, and the thin film swells very slightly with water. The present invention takes advantage of these advantages.

Generally, the processability of cellulose esters is improved by using plasticizers, but the use of plasticizers causes problems such as absorption in the UV region, adhesion to glass surfaces, cleaving properties, and contamination of photomasks due to volatilization of the plasticizer. This has unfavorable effects for the purposes of the present invention. According to the present invention, by using a cellulose ester thin film to which no plasticizer is added,
The objectives of the present invention can be achieved by utilizing the above-mentioned inherent properties of cellulose ester.

The following examples further illustrate the invention.

Example 1 Nitrified cotton RS-5 (manufactured by Daicel Chemical Industries, isopropanol wet cotton, solid content 70%) 64 g, methyl ethyl ketone 146 g, butyl acetate 120 g, and toluene 120 g
Using a percoater with a clearance of 50 μm, a nitrified cotton dope consisting of
Dry at ℃ for hours. The dried film-formed nitrified cotton was gently immersed together with the glass plate in clean water. After being left for a while, the nitrified cotton film naturally peeled off from the glass plate, so I scooped it up using a circular aluminum frame with a diameter of about 150 mm to keep its shape.
The inside of the frame was mounted on the upper surface of an aluminum support frame with an inner diameter of 100 mm, an outer diameter of 110 mm, and a thickness of 10 mm. The film was then adhered to the support frame by applying a small amount of methyl ethyl ketone along the contact interface of the film with the support frame and air drying. The part of the film protruding outside the support frame was cut off and dried at 60°C for 3 hours to obtain a photomask cover made of cellulose nitrate film with a thickness of 3 μm (specific gravity 1.6) and supported with uniform tension. .

Example 2 In place of the nitrified cotton dope in Example 1, acetic acid cotton LT
-105 (Daicel Chemical Industries) 60g, methylene chloride
A cellulose acetate film was produced according to Example 1 using acetic acid cotton consisting of 846 g and methanol 94 g. However, the casting thickness was 50 μm, and the solvent used for adhering the support frame to the film was a mixed solvent of methylene chloride/methanol = 9/1. Similarly, a photomask cover consisting of a film with a thickness of 3 μm (specific gravity 1.3) supported with uniform tension was obtained.

Example 3 Nitrified cotton RS-7 (manufactured by Daicel Chemical Industries, isopropanol wet cotton, solid content 70%) 20g, butyl acetate
50, isobutyl acetate 50g and cyclohexanone
A nitrified cotton dove weighing 90g was prepared.

The viscosity of this dove at 23°C was 480CP.

A film was prepared using this dope by a spin coating method. That is, a glass plate was set in a spinner, and while rotating at 70 rpm, the above dope was dropped onto the center of rotation over a period of 5 seconds.
Immediately after the completion of the dropwise addition, the rotational speed was increased to 1050 rpm (required start-up time: 0.2 seconds), centrifugal casting was carried out while maintaining this speed for 15 seconds, and then the rotation was stopped.

Next, remove the glass plate from the spinner, leave it to dry indoors (23℃, 60%RH) for 24 hours, and then
It was dried at 60°C for 1 hour. Thereafter, the glass plate was immersed in water in the same manner as in Example 1, and the produced film was peeled off from the glass plate, mounted on an aluminum support frame, and supported by adhesive. The supporting frame was dried at 60° C. for 3 hours to obtain a photomask cover made of cellulose nitrate film supported with uniform tension with an average thickness of 0.29 μm and thickness unevenness of 0.03 μm or less.

Example 4 Nitrified cotton RS-120 (manufactured by Daicel Chemical Industries, isopropanol wet cotton, solid content 70%) 10g, butyl acetate
47.6g of isobutyl acetate and 94.8g of cyclohexanone were prepared.

The viscosity of this dope at 23°C was 300 cp.

The procedure was the same as in Example 3 except that the above dope was used and the rotational speed of centrifugal casting was 780 rpm. A photomask cover made of cellulose film was obtained.

Example 5 Acetate cotton L-20 (manufactured by Daicel Chemical Industries, drying loss rate 5%) 18.5 g, ethylene glycol acetate monomethyl ether 91.2 g, cyclohexanone
45.6g, butyl acetate 22.8g and isobutyl acetate 22.8g
An acetic acid cotton dope consisting of

The viscosity of this dope at 23°C was 550 cp.

Using the above dope, the rotation speed when dropping onto the glass plate is 200 rpm, and the dropping time is 7 seconds.
A photomask cover consisting of a cellulose acetate film supported under uniform tension with an average thickness of 0.29 μm and thickness unevenness of 0.03 μm or less was prepared in the same manner as in Example 3, except that the rotational speed of centrifugal casting was 850 rpm. Obtained.

Claims (1)

[Claims] 1. A photomask cover comprising a non-oriented cellulose ester thin film held in a uniform tension state, characterized in that no plasticizer is added to the cellulose ester.