JPH07244217A - Antireflection film - Google Patents

Abstract

PURPOSE:To obtain an antireflection film having a wide antireflection band, capable of being applied to a lens with a small film thickness ratio and which is hardly affected by the variations in production, by forming the film with specified five layers and specifying the respective optical thickness of the first to third layers. CONSTITUTION:This antireflection film has the design center wavelength lambda0 in a region from 180 to 300nm. The film has five layers, the first layer 2, the third layer 4 and the fifth layers 6 from the substrate 1 have a low refractive index, and the second layer 3 and the fourth layer 5 have an intermediate refractive index. Namely, the antiflection film consisting of lambda0/2 (low refractive index layer), lambda0/2 (intermediate refractive index layer), lambda0/2 (low refractive index layer) is interposed between the substrate 1 and the antireflection film with two layers, and the optical film thickness of the first layer 2 to the third layer 4 by the design center wavelength lambda0 is controlled respectively to 0.40lambda0<=n1d1<=0.50lambda0. Consequently, an antireflection film having <=0.5% reflectance and having >=70nm antireflection band is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film formed on an optical substrate.

[0002]

2. Description of the Related Art For example, a case of manufacturing an LSI will be described. In such a case, in order to expose the LSI pattern on the semiconductor surface, a reduction projection exposure apparatus is used at present when integration is advanced. As the miniaturization of the LSI pattern progresses, higher resolution is required for the reduction projection exposure apparatus, and accordingly, the wavelength of the light source used is shortened,
Wavelength emitted from ArF excimer laser λ = 193.4 (nm)
And mercury lamps that emit bright lines in the vacuum ultraviolet region are being studied for practical use.

A reduction projection exposure apparatus usually has an illumination system and a reduction projection system each consisting of several tens of lens groups between a light source and a semiconductor substrate on which a pattern is formed. When these optical systems are composed only of lenses without an antireflection film, the amount of light reaching the semiconductor substrate is extremely small because the residual reflection is about 4 to 5% per lens surface, or Illumination unevenness occurs on the semiconductor substrate surface due to the ghost due to residual reflection. Therefore, it is common to form an antireflection film on the lens surface.

As the antireflection film used so far, for example, as described in JP-A-61-177001, low refractive index layers and intermediate refractive index layers are alternately laminated on a substrate such as a lens. It has a five-layer structure and has anti-reflection properties in the wavelength range of 160 nm to 230 nm. This is basically from the substrate _{side, λ 0/2 -λ 0/} 4 -λ 0/4
An anti-reflection film structure, of which the lambda _0/2 parts 3
It has a layered structure.

[0005]

However, since the lens surface generally has a curvature, the thickness of the antireflection film formed on the surface is inevitably different between the central portion and the peripheral portion. For example, in a convex lens, the film thickness becomes thinner from the central portion to the peripheral portion, and this tendency becomes larger as the radius of curvature of the lens becomes smaller. Therefore, the antireflection band in the peripheral portion of the lens is shifted to the short wavelength side by the amount that the film thickness is smaller than the antireflection band in the central portion of the lens. If the ratio of the film thickness in the peripheral part to the film thickness in the central part, that is, the film thickness ratio becomes smaller than a certain value, the effective antireflection band in the peripheral part of the lens deviates from the used wavelength range. Happens. In the conventional antireflection film, the antireflection band itself is narrow,
In particular, the first problem is that the antireflection band that can make the reflectance 0.5% or less is narrow, and the second problem that it can only be effectively used for lenses with a film thickness ratio of 0.8 or more between the central part and the peripheral part. Had a point. In addition, although the number of layers is λ / 2 due to the three-layer structure from the first layer to the third layer counted from the substrate side, there are variations in manufacturing of each layer compared to a single λ / 2 layer. (Especially the second layer), the antireflection band tends to narrow, or the antireflection effect decreases (reflectance is 0.
It also has a problem that it is easy to be 5% or more).

An object of the present invention is to solve such a problem.

[0007]

As a result of intensive research for solving the above problems, the present inventors have found that the first layer, the third layer, and the fifth layer counted from the substrate side have a low refractive index. The second layer and the fourth layer are antireflection films having a five-layer structure composed of intermediate refractive index layers, and the first layer to the third layer with respect to the design center wavelength λ ₀ . Optical thickness of 0.40 each
With the range of _{λ 0 ≦ n 1 d 1 ≦} 0.50λ 0, it found that can achieve an effective anti-reflection film, the present invention has been accomplished.

Therefore, the present invention is, firstly, "wavelength 180 nm
In an antireflection film having a design center wavelength λ ₀ within a wavelength range of 300 nm, the antireflection film has a five-layer structure, and the first layer, the third layer, and the fifth layer are counted from the substrate side. Is composed of a low refractive index layer, the second layer and the fourth layer are composed of an intermediate refractive index layer, and the optical film thickness of the first layer to the third layer with respect to the design center wavelength λ ₀ . Respectively 0.40λ ₀ ≤ n ₁ d ₁ ≤ 0.
And an antireflection film having a range of 50λ _0. Secondly, in the antireflection film according to claim 1,
Anti reflection refractive index n _m of the refractive index n _l and the intermediate refractive index layer of the low refractive index layer is characterized by satisfying the relative refractive index n _s of the substrate, the relationship of n _l ≦ n _s ≦ n _m Membrane ", third
, In "anti-reflection film of claim 1 wherein the material of the low refractive index layer, LiF, AlF _3, and the _{MgF 2, CaF 2, Na 3} AlF 6, any one of SiO _2, the intermediate refractive index The material of the layer is NdF ₃ ,
An antireflection film characterized by being any one of LaF ₃ , ThF ₄ , Al ₂ O ₃ and MgO.

[0009]

[Action] antireflection film in the present invention is basically between the anti-reflection film of the substrate and the second _{layer, λ 0/2 -λ 0/} 2 -λ 0/2
(Λ ₀ is the design center wavelength) is inserted in the antireflection film. In general, anti-reflection coating, to expand the antireflection band, it may be inserted a layer of lambda _0/2 of one layer between the substrate and the antireflection film is known as prior art. However, the effect is not sufficient by itself. Therefore, in the present invention, lambda _0/2 (low refractive index layer) between the antireflection film of the substrate and two layers 1-? _0/2 (middle refractive index layer)
1-? _0/2 was configured to insert a (low refractive index layer). Furthermore,
As a result of optimizing the optical film thicknesses of all the constituent layers so that the reflectance is minimized while ensuring the antireflection band, the optical film thicknesses from the first layer to the third layer are defined in claim 1. When the value is within the stated range, it says, "Antireflection band is 70 nm with reflectance of 0.5% or less.
It was found that an "antireflection film having the above performance" can be obtained. This is more than 20 nm wider than the antireflection band of the conventional antireflection film. As a result, in the conventional anti-reflection film, the film thickness ratio of the lens peripheral part to the lens central part is about 0.8.
Although it can be applied only to the above lenses, the antireflection film of the present invention can be applied to lenses having a film thickness ratio of 0.7.

[0010] In addition, the above-mentioned _{(λ 0/2 -λ 0/} 2 -λ 0/2)
The layer has an action of alleviating a decrease in the antireflection effect caused by manufacturing variations in the first to fifth layers. This action is also effective as a relaxation action only for the first to third layers of the first aspect. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0011]

EXAMPLE FIG. 1 is a conceptual diagram showing a vertical cross section of an antireflection film produced in this example. That is, an antireflection film was formed on the surface of the substrate with the structure shown in Tables 1 to 4, and the spectral reflectance characteristics of these were measured. The results are shown in FIG. 2 to FIG.
Shown in. From Figure 2 As can be seen from the spectral reflectance characteristic of Figure 5, for any design central wavelength lambda ₀ of the wavelength range of the antireflection film is 180 nm to 300 nm of the present invention, the designed center wavelength lambda ₀ It has been proved that the reflectance can be suppressed to 0.5% or less in the wavelength range of 70 nm or more.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

[Table 3]

[0015]

[Table 4]

[0016]

As described above, according to the present invention,
It has become possible to provide an antireflection film which has a wide antireflection band and can be applied to a lens having a small film thickness ratio, and is less susceptible to manufacturing variations.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a vertical cross section of an antireflection film manufactured in this example.

FIG. 2 is a diagram showing the results of spectral reflection characteristics of an antireflection film manufactured with the configuration shown in Table 1.

FIG. 3 is a diagram showing the results of spectral reflection characteristics of an antireflection film manufactured with the configuration shown in Table 2.

FIG. 4 is a diagram showing the results of spectral reflection characteristics of antireflection films manufactured with the configurations shown in Table 3.

5 is a diagram showing the results of spectral reflection characteristics of the antireflection film manufactured with the configuration shown in Table 4. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Low refractive index layer 3 ... Intermediate refractive index layer 4 ... Low refractive index layer 5 ... Intermediate refractive index layer 6 ... Low refractive index layer or more

Claims (3)

[Claims] 1. An antireflection film having a design center wavelength λ ₀ within a wavelength range of 180 nm to 300 nm, wherein the antireflection film has a five-layer structure, and the first and third layers are counted from the substrate side. The first layer and the fifth layer are composed of low refractive index layers, the second layer and the fourth layer are composed of intermediate refractive index layers, and the first layer to the first layer for the design center wavelength λ ₀ are arranged. An antireflection film, wherein the optical thickness of the third layer is in the range of 0.40λ ₀ ≦ n ₁ d ₁ ≦ 0.50λ ₀ . 2. The antireflection film according to claim 1, wherein the refractive index n _l of the low refractive index layer and the refractive index n _m of the intermediate refractive index layer are n _l ≦ n _{s with} respect to the refractive index n _{s of the} substrate. antireflection film that satisfies the relationship of ≦ n _m. 3. The antireflection film according to claim 1, wherein the material of the low refractive index layer is LiF ₃ , AlF ₃ , MgF ₂ , CaF ₂ , Na ₃ Al.
F ₆ or SiO ₂ , and the material of the intermediate refractive index layer is NdF ₃ , LaF ₃ , ThF ₄ , Al ₂ O ₃ , or MgO. film.