JPS63285501A - Reflection preventive file - Google Patents

Abstract

PURPOSE:To obtain a preventive film which is effective to light in a wide ultraviolet range by employing a four-layer structure consisting of materials which differ in refractive index from an incidence medium side to a substrate side. CONSTITUTION:The four-layer structure consists of a 1st layer 1 which has a lower refractive index than the lens substrate 5, a 2nd layer 2 which has a 1.5-1.8 refractive index and is made of an intermediate refractive index material, a 3rd layer 3 made of a low refractive index material having a lower refractive index than the substrate 5, and a 4th layer made of an intermediate refractive index material whose refractive index is 1.5-1.8 successively from the incidence medium side. Consequently, this structure functions effectively to light in a 160-400nm wide ultraviolet range.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an antireflection film that is effective against light in the ultraviolet region.

BACKGROUND OF THE INVENTION Recently, semiconductor exposure apparatuses for projection exposure using a light source in the ultraviolet region (for example, 365 r+ amount) have been put into practical use.

Since the resolving power of a semiconductor exposure device for projection type exposure is proportional to the wavelength of the light source, the wavelength of the light source has been shortened, and 193 ng+, 2
Ultraviolet rays such as 48n- or 308nm are used.

However, since the exposure apparatus described above usually has an illumination system and a reduction system composed of a large number of lenses (15 to 20 lenses), ghosts and the like caused by reflections from each lens surface in these systems cause uneven illuminance in the image. In order to prevent such reflection, it is possible to provide an anti-reflection film made of a material that does not absorb the above light, but most of the anti-reflection films used in conventional camera lenses absorb in the ultraviolet region. Anti-reflection materials cannot be used as is.

On the other hand, antireflection films that are effective against light in the vacuum ultraviolet region with a wavelength of 160 to 230 nm are disclosed, for example, in JP-A-61-770oI, JP-A-61-77002, or JP-A-61.
It is disclosed in Japanese Patent No.-77003. The above technology uses a material with a low refractive index (n<1.5) that transmits light in the vacuum ultraviolet region and a material with an intermediate refractive index (n=1).

6 to 1.8) This article relates to an antireflection film laminated in three or five layers with a predetermined thickness using a substance.

In addition, in the center and periphery of a lens with a curved surface, 1 piece 1! ! Apart from forming an anti-reflection film alone, when forming an anti-reflection film for mass production, a film with different thickness is formed depending on the radius of curvature of the lens or the distance between the lens and the evaporation source. Therefore, the effective antireflection wavelength range at the center of the lens is different from that at the periphery. Therefore, in the case of an anti-reflection coating with a narrow six effective wavelength range, it is difficult to provide anti-reflection coatings that are effective in the same wavelength range over the entire lens surface on many lenses at once. The narrower the effective wavelength range, the more difficult it becomes.

Problems to be Solved by the Invention The present invention was made in view of the above circumstances, and its purpose is to provide an antireflection film that is effective against light in a wide range of ultraviolet regions. With the goal.

Means for Solving the Problems In other words, the present invention provides a first layer made of a low refractive index material having a refractive index 6 lower than that of the substrate in order from the incident medium side to the substrate side, and the refractive index is 1.5 to 1.8. a second layer made of an intermediate refractive index material of , a third layer made of a low refractive index material having a refractive index lower than that of the substrate, and a fourth layer made of an intermediate refractive index material with a refractive index of 1.5 to 1.8. It consists of a 4-layer structure with 160 layers m~
The present invention relates to an antireflection film that is effective in a wavelength range of 400 layers.

The antireflection film of the present invention functions effectively against light in a wide range of ultraviolet regions of 160 to 400 layers.

As shown in FIG. 1, the antireflection film of the present invention includes a film made of a low refractive index material (hereinafter simply referred to as a low refractive index material) having a smaller refractive index than the substrate (5) from the incident medium side.
layer (1), a film made of an intermediate refractive index material (hereinafter simply referred to as intermediate refractive index material) having a higher refractive index than the substrate;
A layer (2), a film made of a low refractive index material as a third layer (3), and a film made of a high refractive index material as a fourth layer (4) are formed on a lens substrate (5).

The lens substrate (5) that can be used in the present invention is a material having a refractive index of 1.47 to 1.60, specifically 5IC).
A material composed of e, CaFt, BK-7, etc. can be used.

As the low refractive index material, a material having a refractive index of 1.6 or less, such as MgFg, Cart, or Sin, can be used, and MgFg is particularly preferred.

Intermediate refractive index materials include materials with a refractive index between 1.5 and 1.8, such as LaFa, l'JdFs, S
tot, A(box, MgO, YtOs, etc.) can be used, with LaF, . . . A Q *Os being particularly preferred.

In the present invention, depending on the type of lens substrate, MgF is used as a low refractive index material, and LaFs is used as an intermediate refractive index material.
Alternatively, it is preferable to use A Q t Os in combination.

Further, 5lot is effective for both low refractive index materials and intermediate refractive index materials, but in order to obtain the effects of the present invention, Sio* cannot be used for both the low refractive index material and the intermediate refractive index material.

The fourth layer on the substrate is made of an intermediate refractive index material different from that of the substrate, and has a thickness of approximately 0.50λo (λo is the designed dominant wavelength).
to form. In the present invention, the thickness of the fourth calendar is ±0.0
An error within the range of 5λo is acceptable. The error is ±
When it is larger than 0.05λo, the antireflection effect deteriorates.

The third layer is formed of a low refractive index material with a thickness of about 0.50λo on the fourth layer. The thickness is allowed to have an error within the range of ±0°05λo. The error is ±0.05λ
When it is larger than o, the antireflection effect deteriorates.

It is possible to use the same material as the substrate as the low refractive index material for forming the third layer.

The second layer is formed on the third layer of an intermediate refractive index material with a thickness of about 0.25λo. An error in the film thickness within a range of ±0.05λo is acceptable. The error is ±0.05
When it is larger than λo, the antireflection effect deteriorates.

The intermediate refractive index material for forming the second layer can be the same as or different from the intermediate refractive index material used for forming the fourth layer, but it is possible to use as few materials as possible to improve manufacturing efficiency. For reasons such as ease of handling, the fourth
Preferably, the same material as the layer is used.

The first layer is made of a low refractive index material and has a thickness of about 0.25 mm on the second layer.
formed at λo. An error in the film thickness within the range of ±0605λo is acceptable. If the error becomes larger than ±0.05λo, the antireflection effect deteriorates.

The low refractive index material for forming the first layer can be the same as or different from the low refractive index material used for forming the third layer, but it is possible to use as few types of materials as possible to improve manufacturing efficiency. For reasons such as ease of handling, it is preferable to use the same material as the third layer.

As a manufacturing method for the first to fourth layers, a known method, for example, a vacuum deposition method such as an ion blasting method or a sputtering method can be used.

When forming an anti-reflection film using a vacuum evaporation method, it is preferable to install the evaporation source at a sufficient distance from the lens. The coating thickness (d,) and the coating thickness (d,) at the lens periphery are dt # d, aoBθ, (
The film is formed according to the relationship between the central axis on the periphery of the lens and the normal line on the coating film, so that the film is thinner at the periphery. Therefore, the effective wavelength range for antireflection differs between the center and the periphery of the lens. but,
Since the antireflection film of the present invention is essentially effective against ultraviolet rays in a wide range of wavelengths, the wavelength ranges effective for antireflection overlap between the center and the periphery.

Therefore, although the effective wavelength range for preventing reflection on the entire lens surface becomes narrower as a result, the antireflection film can be effectively used in the narrower wavelength range or in a specific wavelength range within that range. This advantage particularly applies to the antireflection coating of the present invention.
It is effective when forming on a lens with a large lens curvature or when mass-producing it industrially.

An antireflection film having a film structure shown in Tables 1 to 8 was formed on the Example lens substrate.

The antireflection properties of the obtained lenses are shown in FIGS. 2 to 9.

Table 1 (Film configuration 1) λo=255na: Incident angle θ=09 Table 2 (Film structure 2
) Table 3 (Film configuration 3) λo=255 nm; incident angle θ=θ.

Table 4 (Film configuration 4) λ, = 255 nm; Incident angle θ = 09 Table 5 (Film configuration 5) λo-320 nm; Incident angle θ・0° Table 6 (Film configuration 6
) λo=320 nm; Incident angle θ=0° Table 7 (Film configuration 7
) λo-190n; Incident angle θ=o'' Table 8 (Film configuration 8) λo=L9Qnm; Incident angle θ: 0 The antireflection properties are shown in FIGS. 2 to 9.

As is clear from FIG. 2, for example, the antireflection film of the present invention was able to suppress the reflectance to 1% or less over a wide wavelength range of 210 to 340 nn+.

Effects of the Invention The antireflection film of the present invention is effective in a wide range of ultraviolet wavelength regions.

When the anti-reflection film of the present invention is used at a specific wavelength or in a narrow wavelength range, the anti-reflection film of the present invention has manufacturing advantages such as when forming a lens with a large lens curvature or when mass-producing it industrially. You can get the feeling.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of the structure of the antireflection film of the present invention. FIGS. 2 to 9 are diagrams showing antireflection characteristics. ■... 1st layer 2... 2nd layer 3... 3rd layer 4... 4th layer 5... Lens board patent applicant Minolta Camera Co., Ltd. Agent Patent attorney Said Sho et al. 2 people Figure 1 Input Horomata J Output spiral 91 Figure 2 Trench + nmJ Figure 3 3 degrees -1i (nml 4th factor line length + nm + Figure 5 Wire length fnml Figure 6 Line length fnm + Figure 7 Figure 8 Essay (nml Figure 9 a-

Claims (1)

[Claims] 1. In order from the incident medium side to the substrate side, a first layer made of a low refractive index material having a refractive index lower than that of the substrate;
a second layer made of a medium refractive index material having a refractive index of 5 to 1.8; a third layer made of a low refractive index material having a refractive index lower than that of the substrate; and a medium refractive index material having a refractive index of 1.5 to 1.8. An antireflection film having a four-layer structure with a fourth layer consisting of: 2. The antireflection film according to claim 1, wherein the low refractive index substance has a refractive index of 1.6 or less. 3. Low refractive index material is MgF_2, CaF_2, SiO_
The intermediate refractive index material is LaF_3, NdF_3, SiO_2, Al_
2. The antireflection film according to claim 1, which is a material selected from the group consisting of 2O_3, MgO, and Y_2O_3, and in which SiO_2 is not simultaneously selected as the low refractive index material and the intermediate refractive index material. 4. The first layer and the second layer each have an optical thickness of about 0.25λ_o with respect to the designed dominant wavelength (λ_o), and the third layer and the fourth layer have an optical thickness of about 0.25λ_o with respect to the designed dominant wavelength (λ_o). The antireflection coating of claim 1, each having an optical thickness of about 0.50λ_o.