JPH0461892B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a resin thin film with excellent transmittance and durability for light in the deep ultraviolet region, and more particularly, to a resin thin film used for dust prevention in a printing exposure apparatus for manufacturing integrated circuits. [Prior Art] When dust adheres to the image surface of a photomask in a printing exposure device used for manufacturing integrated circuits,
An image of the dust is also projected onto the resist surface, imprinting defect information. As a countermeasure to this problem, a method has been considered in which a thin resin film is inserted into the optical path on the image side of the photomask to protect the photomask from the adhesion of dust. In this case, the dust adheres to the surface of the resin thin film instead of the photomask image surface, but by leaving a certain distance between the photomask image surface and the resin thin film, the dust image can be
No image is formed on the resist surface. In other words, it is possible to outfocus
-28716, JP-A-1965-196501, JP-A-58-
219023). The resin thin film used for this purpose needs to have high transmittance to the light beam used for exposure.
Further, the thickness must be 10 μm or less, be uniform over the entire area, and have sufficient self-sustainability. Regarding the light transmittance of the resin thin film, if this value is low, the energy reaching the resist surface will be low, resulting in loss. There are three possible causes for reducing the light transmittance of the thin film. The problems of absorption of light by thin film materials, interference of transmitted light, and reflection on the film surface are caused by the photochemical properties of the materials themselves, and the selection of materials is also the gist of the present invention.
The effect is minimized by having a smooth film surface and placing the film surface perpendicular to the optical path. Regarding light incident perpendicularly to the thin film, most of the light passes straight through the thin film (principal ray), while some light passes through the thin film at the resin/air interface.
Reflect twice and go straight. At this time, the twice reflected light causes an optical path difference of twice the film thickness with respect to the principal ray, and interferes with each other. That is, wavelength ranges that strengthen each other and wavelength ranges that weaken each other alternately appear. Normally, the influence that this interference has on light transmittance is approximately within ±8% of the center value of the amplitude due to interference, and for films that are transparent to visible light and have very small thickness unevenness, in the visible to near ultraviolet region. The magnitude of the interference is approximately constant. Therefore, it is practically acceptable to indicate the light transmittance by approximately the center value of the amplitude due to interference of the transmittance curve obtained by a spectrophotometer. Therefore, in the present invention, the light transmittance of a thin film for a specific wavelength is defined as the transmittance of light of that wavelength using the center value of the interference amplitude. [Problems to be Solved by the Invention] Conventionally, resin thin films used in printing exposure apparatuses have been used that have good transmittance to light in the near-ultraviolet region. Japanese Patent Publication No. 54-28716 describes polyoxyethylene terephthalate, cellulose nitrate, and parylene as suitable materials. Also, JP-A-58-
219023 states that in addition to cellulose nitrate, cellulose esters such as cellulose acetate, cellulose propionate, and cellulose acetate butyrate can be used. When the light source is changed from conventional visible to near-ultraviolet light to far-ultraviolet light with a shorter wavelength, the photosensitivity of the resist layer needs to be adjusted accordingly. Since the energy is large, it is relatively easy to deal with the resist layer.
However, a two-fold problem arises with dustproof thin films. First, even if a material is generally transparent to visible light, it absorbs light in the ultraviolet region, and there is a loss of exposure energy due to transmission through a thin film. Second, absorption of ultraviolet light by thin film materials causes deterioration of the thin film materials themselves. Conventionally known polyester,
Parylene has a low transmittance for ultraviolet light, and nitrocellulose has a better transmittance than the former two, but its quality deteriorates quickly due to irradiation and its lifespan is extremely short after repeated use. The present invention aims to solve these problems and provide a dustproof thin film that can be used in printing exposure apparatuses that use deep ultraviolet light as a light source. [Means for solving the problem] The inventors have discovered that it is possible to form a film by a casting method,
A thin film was formed using a highly transparent resin material, and the transmittance to spectral light including the far ultraviolet region up to 200 nm was measured. We also conducted an exposure test using far ultraviolet light as a light source to determine the appearance, infrared absorption spectrum,
Changes in light transmittance, etc. were investigated. The exposure light source used was 254 nm light from a low-pressure mercury lamp. the result,
Cellulose acetate, cellulose propionate, cellulose acetate butyrate, cellulose acetate, cellulose propionate, cellulose acetate butyrate, etc. are thin films that exhibit a transmittance of 90% or more for light near the G line and 80% or more for light around 254 nm. Ethylcellulose, cyanoethylcellulose, etc. were obtained. However, cyanoethylcellulose had the best durability against exposure to 254 nm light.
Although cellulose esters such as cellulose acetate have better ultraviolet transmittance than cyanoethylcellulose, their durability is slightly lower than that of cellulose esters because the quantum yield of the photochemical decomposition reaction that occurs upon exposure to light is lower than that of cellulose esters. It is thought that this is because it is larger in . The present invention was made based on this knowledge, and has a constant thickness within the range of 0.5 to 10 μm,
The present invention provides a resin thin film made of a cyanoethyl cellulose derivative having a light transmittance of 88% or more in the range of 350 to 500 nm and a light transmittance of 80% or more in the range of 250 to 350 nm. The cyanoethyl cellulose derivative used in the present invention is a cellulose ether or cellulose ester ether with a degree of polymerization of 50 to 1500 and a total degree of substitution of 2.0 to 3.0, and may only have a cyanoethyl group (-CH ₂ CH ₂ CN) as a substituent. However, in addition to this, an alkyl group represented by C _o H _2o+1 (n = 1 to 5) with a degree of substitution of 1.0 or less, a substitution degree of 1.0 or less

[Formula] Acyl group represented by (n = 1 to 10), HOC _o H _2o - (n = 1 to 4) with a degree of substitution of 1.0 or less
Hydroxyalkyl group represented by, degree of substitution 1.0
below

〔Example〕

The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. Example Cyanoethyl cellulose (degree of substitution 2.5, degree of polymerization
250) A cyanoethyl cellulose solution consisting of 7 g, cyclohexanone 50 g, and acetone 50 g was applied onto a smooth glass plate using a bar coater with a clearance of 50 μm, and left to dry at room temperature (23 °C) for 24 hours.
It was further dried at 50°C for 90 minutes. The dried film of cyanoethylcellulose was gently immersed together with the glass plate in clean water. When left for a while, the cyanoethylcellulose naturally peeled off, so it was collected. It was dried at room temperature to obtain a film with a thickness of about 3 μm. The obtained film was supported with an appropriate frame, and the spectral light transmittance and infrared absorption spectrum from 190 nm to 700 nm were measured. Furthermore, the same film was exposed to a low pressure mercury lamp (254nm light, illuminance
Continuous irradiation at 1.8mW/cm ² ); 100W・sec/cm ² ,
Changes over time at 250 W·sec/cm ² and 400 W·sec/cm ² were investigated. One shot of a normal printing exposure device is
Since it is about 50nmW/cm ² × 1 second, 10 ⁴ shots are
Equivalent to an exposure of 500W・sec/ ^cm2 . Comparative Example In place of the cyanoethyl cellulose used in Examples, the following resin materials were used to form films in the same manner. The materials and film forming conditions are shown below. Ethyl cellulose (STD10 manufactured by Dow Chemical)
10g/toluene 20g, xylene 30g, butanol
30g, ethanol 20g, cellulose acetate butyrate (#381 made by Eastman Kodak) 10g/cyclohexanone 50g, butyl acetate
50g cellulose propionate (#482-20 manufactured by Eastman Kodak) 10g / cyclohexanone 50g, butyl acetate 50g cellulose acetate (L-20 manufactured by Daicel Chemical)
10g/cyclohexanone 100g Cellulose nitrate (Daicel Chemical RS-7, wet cotton containing 30% isopropanol) 14.3g/cyclohexanone 43g, butyl acetate 43g Spectral light transmittance, infrared absorption spectrum, time course by low pressure mercury lamp irradiation as in the example Changes were measured. These results are summarized in Table 1.

[Table] The following is an explanation using cellulose nitrate as an example. When cellulose nitrate is irradiated with GHI mixed light, its appearance remains unchanged even when irradiated at 500 W/sec.
There is no change in the infrared absorption spectrum, which corresponds to a sufficient lifespan in a printing exposure apparatus that uses near-ultraviolet light as a light source. However, when irradiated with far-ultraviolet light, it was destroyed with only 10 W/sec. During this period, the infrared absorption spectrum changed significantly, with the absorption at 1650 cm ^-1 and 1280 cm ^-1 decreasing, and the absorption at 1730 cm ^-1 and 3400 cm ^-1 increasing. In contrast, cyanoethylcellulose was found to have practically sufficient durability against irradiation with far ultraviolet light.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are spectral light transmittance curves of sample thin films of approximately 3 μm thick made of cyanoethyl cellulose, cellulose acetate, and cellulose nitrate, respectively.

Claims (1)

[Claims] 1. Has a constant thickness within the range of 0.5 to 10 μm,
Light transmittance of 350 to 500 nm is 88% or more, and
A thin resin film made of a cyanoethyl cellulose derivative that has a light transmittance of 80% or more in the range of 250 to 350 nm.