JP2712447B2 - Exposure mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] An exposure mask, particularly a mask suitable for exposure to far ultraviolet rays, is a pattern made of a light absorber on a substrate such as CaF ₂ having a high transmittance for far ultraviolet rays. A non-hygroscopic protective film is formed on a supporting substrate, and a mask substrate made of a material that is transparent to the irradiation light for exposure and that has a hygroscopic property is provided. An opening through which the irradiation light passes is formed by forming a second non-hygroscopic protection film on the mask substrate layer and selectively removing a central portion of the support substrate. Forming a support frame having a peripheral portion coupled to a peripheral portion of the mask substrate.

[Industrial applications]

The present invention relates to a mask or reticle for exposure, and more particularly to a mask or reticle suitable for exposure using far ultraviolet rays.

[Conventional technology]

With the increase in the density of semiconductor integrated circuits, exposure technology in the sub-micron region is becoming essential. For this reason, instead of the conventional ultraviolet exposure method using a G-ray or an I-ray generated from a high-pressure mercury lamp, an exposure technique using ultraviolet light of a shorter wavelength generated by an excimer laser attracts attention. In an excimer laser, light having wavelengths of 306 nm, 248 nm and 198 nm, respectively, is stimulated emitted from a dimer of a rare gas such as XeCl, KrF or ArF and a halogen gas. Among them, the stimulated emission light having a wavelength of 306 nm from the XeCl excimer laser is close to the light of the I-line having a wavelength of 396 nm, and thus has little advantage for use in exposing fine patterns. Therefore, K
248nm emitted by rF or ArF excimer laser respectively
Light of a shorter wavelength called deep ultraviolet (Deep-UV) such as 198 nm and 198 nm is considered useful for exposing fine patterns.

On the other hand, when light having a short wavelength as described above is used, light absorption becomes large, so that selection conditions for an exposure atmosphere, a material of an exposure optical system such as a projection lens, and a material of a mask substrate on which a mask pattern is formed are strict. Become.

[Problems to be solved by the invention]

Among them, quartz, which has been used in conventional ultraviolet exposure, cannot be used as a mask substrate material because of its large light absorption in a short wavelength region of 250 to 150 nm. Materials having high light transmittance in the far ultraviolet region include halides of alkali metals or alkaline earth metals such as lithium fluoride (LiF) and calcium fluoride (CaF ₂ ). However, these materials have high deliquescence or hygroscopicity and cannot be used in a normal exposure atmosphere. That is,
When the above material is used as a substrate and a light-shielding mask pattern made of a thin film of chromium or the like is formed on it, if moisture adsorbs on the substrate exposed at the opening of the mask pattern, the surface becomes cloudy and the light scattering property And the transmittance decreases. As a result, a desired transmitted light pattern cannot be obtained. Further, when the mask substrate material has a high hygroscopicity or deliquescent, the chromium thin film is peeled off or moves on the substrate surface due to a decrease in the adhesive strength to the substrate, so that a predetermined pattern accuracy cannot be maintained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a mask for deep ultraviolet exposure, which protects a mask substrate having a hygroscopic property or a deliquescent property such as CaF ₂ from the influence of moisture in an exposure atmosphere.

[Means for solving the problem]

The object of the present invention is to provide a mask substrate made of an alkali metal or alkaline earth metal halide which is transparent to far ultraviolet rays for exposure, and silicon oxide, silicon nitride or silicon nitride covering at least the open front and back surfaces of the mask substrate. The present invention is attained by an exposure mask according to the present invention, comprising a protective thin film made of aluminum oxide.

Such an exposure mask forms, for example, a non-hygroscopic transparent protective film on a supporting substrate, and is made of an alkali metal or alkaline earth metal halide which is transparent to the irradiation light for exposure and has a hygroscopic property. Forming a second non-hygroscopic transparent protective film on the mask substrate, and selectively removing a central portion of the supporting substrate, thereby forming the mask substrate. It is manufactured by forming a support frame having an opening through which light passes and a peripheral portion coupled to a peripheral portion of the mask substrate.

(Operation)

Both sides of a mask substrate exhibiting high transmittance in the deep ultraviolet region made of an alkali metal or alkaline earth metal halide such as LiF or CaF ₂ are coated with SiO ₂ , Si ₃ N ₄ , or Al.
By covering with a non-hygroscopic transparent protective film material such as ₂ O ₃ and shielding from the exposure atmosphere containing moisture, the pattern accuracy of the mask pattern formed on this mask substrate and the opening of the mask pattern are improved. The light transmittance of the exposed mask substrate can be stably maintained.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Figure 1 is a fragmentary cross-sectional view showing an embodiment of a structure of an exposure mask of the present invention, a thickness of 100μ consisting CaF ₂
On both surfaces of a mask substrate 1 having a thickness of 1000 m or less, a transparent protective film 2 made of, for example, SiO ₂ and having a thickness of 1000 to 2000 ° is formed.
As the mask substrate 1, a thin plate-shaped crystal is cut out from a CaF ₂ , BaF ₂ or LiF crystal ingot prepared by a method such as the Bridgman method, and the surface thereof is mirror-polished by a known method and has a thickness of 100 μm or less. What is processed may be used. Then, on the mirror-polished surface, a well-known CV
By using the D method or the sputtering method, a thin film of SiO ₂ , Si ₃ N ₄ or Al ₂ O ₃ is deposited in a thickness of 1000 to 2000 mm to form the transparent protective film 2. Thereafter, a not-shown chromium thin film, for example, is formed as a light shield on one side of the transparent protective film 2.
This is processed into a predetermined mask pattern by using a lithographic technique, whereby an exposure mask applicable to far ultraviolet exposure is completed.

FIG. 2 shows another embodiment of the structure of the exposure mask of the present invention, for example, a thickness of 1 to 100 μm formed by a CVD method.
Both surfaces of a mask substrate 5 made of CaF ₂ are coated with transparent protective films 4 and 6 made of, for example, SiO ₂ and having a thickness of 1000 to 2000 °, and the periphery of the mask substrate 5 is made of, for example, a silicon plate. It is supported by the support frame 3. The support frame 3 is provided with an opening 10 through which irradiation light for exposure passes at the center thereof, and its peripheral edge is connected to the peripheral edge of the mask substrate 5. For example, a mask pattern (not shown) made of a gold or chromium thin film is formed on the transparent protective film 6.

FIG. 3 is a sectional view of an essential part for explaining an embodiment of a method of manufacturing an exposure mask according to the present invention. As shown in FIG. 3A, for example, a support substrate made of A1 and having a thickness of about 1 mm. On one side of 3 ′, a transparent protective film 4 having a thickness of 1000 to 2000 mm, which is a film made of any one of SiO ₂ , Si ₃ N ₄ and Al ₂ O ₃ N, or a composite film thereof, is provided on the support substrate 3 ′. An etching mask 7 'having a thickness of 1000 to 2000 mm is formed on the back surface. The transparent protective film 4 and the etching mask 7 'may be formed by using a known CVD technique. Next, on the transparent protective film 4, a film made of any of CaF ₂ , BaF ₂ , LiF or the like, or a mask made of a composite film thereof, by using a known thin film technique such as a CVD method, a sputtering method or a vapor deposition method. A substrate 5 is deposited, and a film made of any one of SiO ₂ , Si ₃ N ₄ , and Al ₂ O ₃ N, or a transparent protective film having a thickness of 1000 to 2000 mm, which is a composite film thereof, is formed on the mask substrate 5. 6 is deposited.

The supporting substrate 3 'is a substrate on which the mask substrate 5 is to be formed, and is made of a material similar to the thermal expansion coefficient of the mask substrate 5 (approximately 19 × 10 ^-6 / ° C. for a CaF ₂ mask substrate). It has a thermal expansion integer, for example, aluminum (Al), copper (C
u), a plate made of nickel (Ni) or the like with a thickness of 1 mm or less is used. Thereby, the residual stress generated in the mask substrate 5 due to a temperature change during the film formation of the mask substrate 5 is reduced, and the accuracy of the mask pattern can be stably maintained.

Following the above, the central portion of the etching mask 7 'is selectively removed by using a well-known Si ₃ N ₄ lithographic technique,
As shown in FIG. 3 (b), an etching mask pattern 7 made of Si ₃ N ₄ is formed. Then, using the etching mask pattern 7 as a mask, the Al support substrate 3 'is selectively etched using, for example, a sodium hydroxide solution,
An Al support frame 3 having an opening 10 in the center is formed. After that, for example, a chromium thin film (not shown) is formed on the surface of the transparent protective film 6, for example, and this is etched by using a well-known lithographic technique, thereby forming a mask pattern in a region corresponding to the opening 10. The exposure mask of the present invention is completed.

In the present specification, the term “exposure mask” has been used.
It goes without saying that a reticle used in the reduction projection exposure method is also included.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, there exists an effect which can provide the mask for exposure comprised using the mask board | substrate which shows high transmittance | permeability with respect to the light of the deep ultraviolet region which has a hygroscopic or deliquescent property.

[Brief description of the drawings]

1 and 2 are cross-sectional views of essential parts showing an embodiment of the structure of an exposure mask of the present invention. FIG. 3 is a cross-sectional view of main parts for explaining an embodiment of a method of manufacturing an exposure mask of the present invention. It is a figure. In the figure, 1 and 5 are mask substrates, 2 and 4 and 6 are transparent protective films, 3 is a support frame, 3 'is a support substrate, 7 is an etching mask pattern, 7' is an etching mask, and 10 is an opening.

Claims (1)

(57) [Claims] 1. A mask substrate made of an alkali metal or an alkaline earth metal halide which is transparent to far ultraviolet rays for exposure, and silicon oxide and silicon nitride covering at least the open front and back surfaces of the mask substrate. Alternatively, an exposure mask comprising a protective thin film made of aluminum oxide.