JPH10227903A - Wide-band antireflection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain antireflection films having a sufficient antireflection effect in a wide band with a smaller number of layers by forming at least layers consisting of fluororesins varied in refractive indices in a film thickness direction. SOLUTION: The wide-band antireflection films are obtd. by forming at least the fluororesin layers 2 varied in the refractive indices in the film thickness direction on a substrate 1. Deposition conditions, for example, substrate temps. and vapor deposition rates, are controlled in order to execute deposition in such a manner that the refractive indices change in the film thickness direction. Materials (fluororesins and dielectric materials) having a good adhesion property to the fluororesins are formed on and/or under the fluororesin layers, by which the optical characteristics are improved. The examples of the fluororesins include tetrafluoroethylene resins (PETE), trifluorochloromethylene resins (PCTFE), polyvinyl fluoride (PVF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinylidene fluoride (PVDF) and polyacetal (POM).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband antireflection film.

[0002]

2. Description of the Related Art The refractive index of a conventional vapor-deposited substance is a value peculiar to the substance. Considering practicalities such as absorption loss, scattering, and peeling of a film, the refraction is largely controlled by controlling a film-forming method and film-forming conditions. It was difficult to change the rate. for that reason,
It is difficult to obtain a material having an optimum refractive index in designing an optical thin film, and a material having a relatively close refractive index has been used instead.

Further, in order to obtain a sufficient antireflection effect and broaden the band in the antireflection film, a material having a lower refractive index is required. The deposition material was magnesium fluoride, which did not provide sufficient spectral characteristics. For this reason, broadening of the band has been attempted by increasing the number of laminated antireflection films.

[0004]

However, there is a limit to widening the band by increasing the number of layers, and scattering increases as the number of layers increases. There has been a problem that demands for high transmittance and broadband in the most advanced region at present cannot be sufficiently achieved.

Further, when the number of layers increases, there is another problem that moisture easily penetrates into the film and the spectral characteristics change.
Therefore, the present invention has been made to solve such a problem, and an object of the present invention is to provide an antireflection film having a sufficient antireflection effect over a wide band with a small number of layers.

[0006]

According to the present invention, there is firstly provided a broadband antireflection film characterized by having at least a layer made of a fluororesin whose refractive index is changed in a film thickness direction. "I will provide a. In addition, the present invention provides a second method wherein the fluororesin layer is made of ethylene tetrafluoride resin (PTFE), methylene trifluoride chloride resin (PCTFE), vinyl fluoride resin (PVF), ethylene tetrafluoride-hexafluoride Propylene copolymer (FEP), vinylidene fluoride resin (PVD)
F), a polyacetal (POM), which provides a broadband antireflection film according to claim 1 (claim 2).

[0007]

FIG. 1 shows a broadband antireflection film according to an embodiment of the present invention. The broadband antireflection film of the embodiment according to the present invention is obtained by forming at least a fluororesin layer 2 having a refractive index varying in a film thickness direction on a substrate 1. When a film is formed by using a fluororesin as a vapor deposition material so that the refractive index changes in the film thickness direction, a thin film having a refractive index of 1.13 to 1.33, which cannot be obtained by a conventional dielectric thin film, is obtained.

In order to form a film so that the refractive index changes in the film thickness direction, film forming conditions, for example, a substrate temperature and a deposition rate are controlled. Further, by forming a substance (fluororesin, dielectric substance) having good adhesion to the fluororesin above and / or below the fluororesin layer, the optical characteristics can be further improved.

As the fluorine resin, ethylene tetrafluoride resin (PTFE), methylene trifluoride chloride resin (PCTF)
E), vinyl fluoride resin (PVF), ethylene tetrafluoride
-Propylene hexafluoride copolymer (FEP), vinylidene fluoride resin (PVDF), polyacetal (POM).

[0010]

Embodiments of the present invention will be described below with reference to the drawings. [Embodiment 1] FIG. 2 is a schematic sectional view of a broadband antireflection film of Embodiment 1. Magnesium fluoride layer 4 (first layer) having an optical thickness of 125 nm and a refractive index of 1.39 on a quartz glass substrate 1; an optical thickness of 1500 °; refraction in the thickness direction as shown in FIG. Fluororesin layer 2 with the ratio changed from 1.12 to 1.27 (Teflon AF2400, manufactured by DuPont)
(Second layer), the optical film thickness is 6.3 nm, and the refractive index is 1.5.
This is a three-layer structure in which eight neodymium fluoride layers 3 (third layers) are sequentially laminated.

FIG. 4 is a spectral characteristic diagram of the broadband antireflection film of the first embodiment. It was possible to achieve a transmittance of 99.5% or more in a wide wavelength range from 250 nm to 1000 nm. Using a vacuum deposition method, the first layer has a degree of vacuum of 4 × 1
^0-4 Pa, a substrate temperature of 250.degree. C., a deposition rate of 2.degree./sec., A second layer having a degree of vacuum of 4.times.10.sup.- ⁴ Pa and a substrate temperature of 25.
The third layer was formed at a degree of vacuum of 4 × 10 ⁻⁴ Pa, a substrate temperature of 250 ° C., and a deposition rate of 1 ° / sec.

By controlling the film forming conditions, the refractive index in the thickness direction of the fluororesin layer could be easily controlled.

[0013]

As described above, the antireflection film according to the present invention has an antireflection effect over a wide band with a smaller number of layers than ever before.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a broadband antireflection film according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of a broadband antireflection film of Example 1.

FIG. 3 is a diagram showing a change in the refractive index of a fluororesin layer in Example 1 in the thickness direction.

FIG. 4 is a spectral characteristic diagram of the broadband antireflection film of Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Fluororesin layer which changed refractive index in the film thickness direction 3 ... Neodymium fluoride layer 4 ... Magnesium fluoride layer

Claims (2)

[Claims] 1. A broadband anti-reflection film comprising at least a layer made of a fluororesin whose refractive index is changed in a thickness direction. 2. The method according to claim 1, wherein the fluororesin layer is made of ethylene tetrafluoride (PTFE) or methylene trifluoride chloride (PCTF).
E), vinyl fluoride resin (PVF), ethylene tetrafluoride
The broadband antireflection film according to claim 1, wherein the antireflection film is a propylene hexafluoride copolymer (FEP), a vinylidene fluoride resin (PVDF), or a polyacetal (POM).