JPS6177002A - Optical antireflecting film - Google Patents

Abstract

PURPOSE:To obtain an antireflecting film which is satisfactory with vacuum UV rays by laminating alternately 3 layers of low refractive index materials and intermediate refractive index material on a base body. CONSTITUTION:The 1st layer 2 consisting of the low refractive index material having <=1.5 refractive index with respect to light having 160-230nm wavelength, the 2nd layer 3 consisting of the intermediate refractive index material having 1.6-1.8 refractive index then the 3rd layer 4 consisting of the above- described low refractive index material are successively laminated on the base body 1 consisting of a material allowing the transmission of the above-mentioned light. The optical film thicknesses of the 1st layer 2-3rd layer 4 are preferably made respectively about (1/2)lambda0, about (1/4)lambda0 and about (1/4)lambda0 with respect to the optical design reference wavelength lambda0 within the range of the above- described wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a light antireflection film, and particularly to a film body having a good antireflection effect against vacuum ultraviolet rays.

[Prior art]

Semiconductor exposure equipment can be divided into contact (or gloximity) and projection printing systems based on the printing method.The resolution of the equipment is proportional to the square root of the light source wavelength in the case of contact exposure; In the case of , it is proportional to the light source wavelength.

Therefore, in order to improve the resolution of exposure equipment, it is increasingly necessary to shorten the wavelength of the light source, and currently the wavelength is 200 to 270nm.
A device using ultraviolet rays of 500 m has been put into practical use. However, in the future it will be necessary to further improve the resolution, and the wavelength will be 20.
It becomes necessary to use vacuum ultraviolet light of 0 nm or less.

By the way, in the illumination system of a semiconductor 1x device, there is a problem in that ghosts caused by reflection on the lens surface cause illumination unevenness on the image plane. For this reason, although it has been conventional practice to coat the lens surface with an antireflection film consisting of a single layer or multiple layers of dielectric material, there are almost no antireflection films that work in the vacuum ultraviolet region, and only a few 40668
No., Optical Engineering Vol-
18, AI (1979), etc., but these too cannot be said to have a sufficient antireflection function.

[Purpose of the invention]

One object of the present invention is to provide an antireflection film that has a good antireflection effect against vacuum ultraviolet rays.

Another object of the present invention is to provide an antireflection film that has a good antireflection effect against vacuum ultraviolet rays and is physically and chemically stable.

The above purpose is to use a low refractive index material with a refractive index of 1.5 or less and a refractive index of 1.6 to 1.5 nm for light with a wavelength of 160 to 230 nm.
8, a first layer made of the low refractive index material, a second layer made of the intermediate refractive index material, and then the low refractive index material on a substrate made of a material that transmits light of the wavelength. This is achieved by a light antireflection film characterized by having a three-layer structure in which a third layer made of a substance is laminated in this order.

[Detailed description of the invention]

For vacuum ultraviolet ray antireflection coatings, the coating material poses a major constraint in design and production. That is, the film material of the antireflection film must be transparent and stable to vacuum ultraviolet rays. As a vacuum ultraviolet transmitting material, MgF2. CaF2.
LiF, NaF, LaF3. Fluorides such as NdF3 are known. On the other hand, At203. SiO2, Hf
Some oxides, such as O2, are transparent up to relatively short wavelengths, but at wavelengths of 200 am or less, their absorption is so strong that they no longer transmit. ZrO2 is also used for anti-reflection coatings in the visible range.
, 'rio□, CeO2, etc. cannot be used because they absorb so much that they do not transmit.

Therefore, it is preferable that the light antireflection film of the present invention is mainly composed of a heptadide-based electrically shielding material.

Among these, the low refractive index substance used in the present invention is MgF2. CaF2. LiF, and Na3AtF
As the intermediate refractive index material, a material selected from LaF and NdF3 is suitable.

The antireflection film of the present invention has a three-layer structure as shown in FIG.

In FIG. 1, 1 is a substrate made of a substance that transmits light with a wavelength of 160 to 230 nm, specifically an optical device such as a lens made of synthetic quartz, artificial quartz, crystals such as CaF2, MgF2, etc. It is. Laminated on the substrate 1, 2 and 4 are layers of a low refractive index material, and 3 is a layer of an intermediate refractive index material, and these layers are usually formed using a vacuum evaporation method (
Includes ion blating, sputtering, etc.

) is used.

Although a flat film body is shown in FIG. 1, the shape of the film is not limited to this, and may be arbitrarily selected according to the shape of the base surface, such as cylindrical, spherical, concave, or convex. can be designed.

This is the design standard wavelength of laziness. ), and the first one is
The optical thickness of each of the first to third layers can be optimized, for example, by calculation using an electronic computer so that the reflectance takes a minimum value in a desired wavelength range.

The present invention will be explained in more detail below by way of examples.

Example 1 In the antireflection film shown in FIG. 1, the base 1 is a lens made of synthetic quartz, and the low refractive index substances 2 and 4 are MgF2.3.
The intermediate refractive index material was composed of LaFs, and these materials were coated using a vacuum evaporation method. The refractive index of the constituent materials is determined by the dispersion formula. In Table 1, λ = 1
The refractive index is shown when the wavelength is 90 nm. In vacuum deposition, the optical film thickness was optimized by calculation as shown in Table 1, and the vapor deposition was performed by the optical film thickness.

With MgF2 and LaFs used in this example, absorption can be almost ignored at film thicknesses shown in Table 1.

Further, fluoride has the advantage that there is no difference in structure between the bulk and the deposited film compared to oxide, and reproducibility is good.

Table 1 The spectral characteristics of the antireflection film thus obtained are shown in FIG. According to this, it was possible to suppress the reflectance to 1% or less in the wavelength range of 160 to 230 nm, particularly to 0.5% or less in the wavelength range of 165 to 215 nm. Therefore, since the vacuum ultraviolet rays normally used are around 180 nm, the antireflection film of the present invention can suppress the reflectance to a sufficiently low level.

Next, regarding durability, we used acetone, Inglovil alcohol, and methanol to clean the surface of the prepared lens with anti-reflection coating in a solvent resistance test, but no changes were observed in the spectral characteristics or appearance. It was confirmed that it had sufficient solvent resistance. Further, as a result of an adhesion test using Sconottigue and an abrasion resistance test using cotton cloth (cheese cloth), no external defects such as peeling or cracks, and no change in reflectance were observed. ” 45 regarding humidity
Even after being placed in a constant temperature and humidity chamber at 95% relative humidity for more than 1000 hours, no chemical changes such as a decrease in reflectance or corrosion occurred. Furthermore, there was no deterioration at all even when irradiated with vacuum ultraviolet light.

Example 2 λo-200nm, first layer film material (substance) was LIF'
A light antireflection film was tabulated in the same manner as in Example 1, except that the refractive index and the optimized optical film thickness shown in Table 2 were used.

The spectral characteristics of the anti-reflection film obtained by oxidation are shown in FIG. In this example as well, a light antireflection film having the same optical properties and chemical and physical stability as the light antireflection film of Example 1 was obtained.

Table 2 [Effects of the Invention] As explained above, the antireflection film of the present invention suppresses the reflection of the surface of a substrate such as a lens against light of a desired wavelength, including optical kit vacuum ultraviolet light, and It has excellent optical properties that solve problems such as ghosting. Furthermore, it is highly chemically stable with excellent solvent resistance and moisture resistance, and at the same time has excellent physical stability such as adhesion, n1Li abrasion resistance, and ultraviolet resistance, making it extremely useful for practical purposes.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the structure of the anti-reflection film of the present invention, and FIGS. 2 and 3 are curves showing the spectral characteristics of the anti-reflection film produced in Example 1-2. 0 1...Substrate, 2, 4...Low refractive index material layer, 3...
Intermediate refractive index material layer.

Claims (3)

[Claims] (1) The refractive index for light with a wavelength of 160 to 230 nm is 1.
A first layer made of the low refractive index material on a substrate made of a material that transmits light of the wavelength, using a low refractive index material of 5 or less and an intermediate refractive index material of 1.6 to 1.8. A light antireflection film having a three-layer structure in which a second layer made of the intermediate refractive index material and a third layer made of the low refractive index material are laminated in this order. (2) For any design reference wavelength λ_0 within the wavelength range of 160 to 230 nm, the optical thickness of the first to third layers is approximately 1/2λ_0, approximately 1/4λ_0, and approximately 1/2λ_0, respectively.
4λ_0. The antireflection film according to claim (1). (3) The low refractive index substance is MgF_2, CaF_2, Li
The anti-reflection film according to claim 1 or 2, wherein the material is a material selected from F and Na_3AlF_6, and the intermediate refractive index material is a material selected from LaF_3 and NdF_3.