JPH09166703A - UV and visible light range back mirror - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rear mirror having high reflectivity, light resistance, gas resistance and laser resistance by successively laminating multilayered fluoride films consisting of intermediate-refractive index materials and low- refractive index materials, metallic film, multilayered fluoride films and metallic film on the rear of an optical substrate. SOLUTION: The multilayered fluoride films consisting of the intermediate- refractive index layers of LaF3 3 and the low-refractive index layers of MgF2 2 alternately laminated in five layers, Al4 as the metallic film and a protective film of Cu5 so as to hermetically close the multilayered fluoride films and the metallic film are successively formed on the surface of synthetic quartz glass 1 which allows the transmission of light from a UV region to a visible light region. The optical film thicknesses of the multilayered fluoride films consisting of LaF3 3 and MgF2 2 are respectively λ/4 (λ=250μm). The film thickness of Al metallic film 4 is about 1000 to 1500 angstrom and the film thickness of the protective film 5 consisting of Cu is about 1000 to 1500 angstrom. The high reflectivity from the UV region to the visible light region is obtd. in such constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective optical element having high reflectance, light resistance, gas resistance, and laser resistance in a wavelength range from an ultraviolet range to a visible light range.

[0002]

2. Description of the Related Art There are known two types of conventional reflective optical elements in the ultraviolet to visible light range. The first reflective optical element has a structure as shown in FIG. 5, and is made of aluminum (A
l) 7 is vapor-deposited, and a single layer of magnesium fluoride (MgF ₂ ) 8 is overcoated for the purpose of protecting the surface of Al 7 from excimer laser gas which is a corrosive gas and increasing the reflectance in the ultraviolet range. ing. The Al metal film 7 has a thickness of about 1000 to 1500 angstroms, and the overcoated MgF ₂ 8 has an optical film thickness of λ / 4 (λ =
250 nm). The spectral reflectance is shown in FIG.

This reflective optical element has the advantage that it can be used in the entire wavelength range because the reflectance has little wavelength dependence. The second reflective optical element has a structure as shown in FIG. 7, and has a structure in which a fluoride multilayer film made of LaF ₃ 10 and MgF ₂ 11 is formed on the substrate 9. The optical film thickness of each of the fluoride multilayer films made of LaF ₃ 10 and MgF ₂ 11 is λ / 4 (λ = 250 nm). The spectral reflectance is shown in FIG.

This reflective optical element has high reflection in the ultraviolet region and has a strong laser resistance of about 4 J / cm ² .

[0005]

The first reflective optical element has the advantage that it can be used in the entire wavelength range because the reflectance has little wavelength dependence, but it has a weak film strength because it is formed at room temperature. Since MgF ₂ 8 has a low packing density, impurities are eroded into the film and the metal film is corroded, so that it is unsatisfactory with respect to gas resistance.

Further, the film deteriorates with the passage of time,
There is a problem that the reflectance decreases (low light resistance). Further, the laser resistance of the film when irradiated with an excimer laser is very weak, about 0.1 J / cm ² , because the metal film has a property of absorbing the laser, which is not sufficiently satisfactory.

The second reflective optical element is highly reflective in the ultraviolet range and has a strong laser resistance of about 4 J / cm ² , but has a very narrow high reflectivity band and a low reflectivity in the visible light range. There is a problem that it will end up. It is possible to increase the reflectance in the visible light region by increasing the number of layers in the fluoride multilayer film, but in the fluoride multilayer film, the stress of the film also increases as the film thickness increases and cracks Occurs.

The present invention has been made in view of the above problems, and provides a reflective optical element having high reflectance, light resistance, gas resistance, and laser resistance in a wavelength range from the ultraviolet range to the visible light range. The purpose is to do.

[0009]

SUMMARY OF THE INVENTION The first aspect of the present invention is to provide a "multilayer fluoride film, a metal film, and at least two layers of a medium refractive index material and a low refractive index material on the back surface of the optical substrate, which are on the back surface. Provided is a rear-view mirror for ultraviolet and visible light regions, in which a fluoride multilayer film and a metal protective film are sequentially laminated so as to seal the metal film (claim 1).

In the second aspect of the present invention, "the intermediate refractive index substance is LaF ₃ , NdF ₃ or YbF ₃ alone or in a mixture, and the low refractive index substance is MgF ₂ , CaF ₂ or Al.
The rear surface mirror for ultraviolet and visible light regions according to claim 1 (claim 2), which is a single substance or a mixture of F ₃ or Na ₃ AlF ₆ .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an embodiment of the present invention.
It is sectional drawing of the back surface mirror for ultraviolet rays and a visible light range. this is,
Fluoride multi-layered film and metal film composed of five intermediate layers of LaF ₃ 3 and MgF ₂ 2 having a low refractive index layer alternately laminated on the surface of synthetic quartz glass 1 transmitting from the ultraviolet range to the visible range As described above, a protective film of Cu5 is sequentially formed so as to seal Al4, the fluoride multilayer film, and the metal film.

The optical film thickness of the fluoride multilayer film composed of LaF ₃ 3 and MgF ₂ 2 is λ / 4 (λ = 250). The film thickness of the Al4 metal film is about 1000 to 1500 angstroms, and the film thickness of the Cu5 protective film is about 1000 to 1500 angstroms. The spectral reflectance in the configuration of FIG. 1 is shown in FIG. It can be seen that a high reflectance can be obtained from the ultraviolet region to the visible light region.

In addition, as an intermediate refractive index layer, LaF ₃ ,
Examples include NdF ₃ or YbF ₃ simple substance or mixture, and the low refractive index layer include MgF ₂ , CaF ₂ , AlF ₃ or Na ₃ AlF ₆ simple substance or mixture. The metal protective film is required to have a high filling rate to prevent corrosion of the metal film, and SiO can also be used.

The fluoride multilayer film is formed by vacuum vapor deposition, the substrate temperature is 200 ° C. to 300 ° C., the film is formed in an atmosphere of 1 × 10 ⁻⁵ Torr, and the vapor deposition rate is 0.2 to 15 Å / sec
It is. The method for forming the metal film and the metal protective film is a vacuum deposition method, and the substrate temperature is about 30 ° C. and 5 × 10 ⁻⁶ Torr without heating.
The film is formed in the following atmosphere and the deposition rate is 0.2 to 20Å /
sec.

To seal the fluoride multilayer film and the metal film with the metal protective film, first, after forming the fluoride multilayer film and the metal film on the substrate using a mask having a diameter slightly smaller than the diameter of the substrate, This is performed by forming a metal protective film by a wraparound phenomenon using a mask having the same diameter as. Further, in order to control the film quality, the ion beam assist method (Ar,
Gas such as N ₂ is ionized and accelerated to irradiate the substrate during vapor deposition to improve the film quality by the kinetic energy of the ion beam), ion plating method (Ar, N ₂ etc. at an appropriate pressure in the vacuum chamber) Gas is introduced and plasma is generated by RF discharge, and the deposited material is activated and deposited on the substrate to improve the film quality).

The filling rate of the film can also be obtained by a method which does not use the vacuum evaporation method, that is, a method in which atoms and molecules are knocked out (sputtered) from the sample target by the kinetic energy of ions without evaporating the sample by heating. It is possible to improve the film quality. FIG. 3 shows the laser resistance to an excimer laser of the rear-view mirror for ultraviolet and visible light regions according to the present invention having the structure shown in FIG. 1 and the conventional Al metal film reflecting mirror having the structure shown in FIG. It is a measurement result of measuring whether or not it can withstand.

It can be seen that the laser resistance of the back mirror for the ultraviolet and visible light regions according to the present invention is improved as compared with that of the conventional Al metal film. As a method for evaluating the laser resistance, a method of irradiating a laser beam whose energy density was changed while changing the location on the sample surface as a spot and inspecting for damage was used.

[0018] At this time, E _ND: maximum energy density does not cause damage _{^{(J / cm 2) E D}} : the element of LDT represented by the following equation using the minimum energy density of occurrence of damage (J / cm ²⁾ It is the amount (laser proof strength) that indicates how much energy density can be endured. LDT = (E _ND + E _D ) / 2 (J / cm ² ) FIG. 4 shows a schematic diagram of an apparatus for measuring this LDT.

After shaping the laser beam, the beam diameter is changed to an arbitrary size with a zoom expander. This changes the amount of energy per unit area and irradiates the sample surface with the objective lens. The light energy at this time can be constantly monitored by a detector. In the structure according to the present invention, since the fluoride multilayer film and the metal film are sealed by the optical substrate and the metal protective film, no corrosive gas is eroded into the film, and the gas resistance and the light resistance are excellent.

Optically, light in the ultraviolet region is transmitted through the optical substrate and then reflected by the fluoride multilayer film, and light in the visible region is transmitted through the optical substrate and the fluoride multilayer film, and then the metal film. Since it is reflected by, it is possible to maintain a high reflectance from the ultraviolet region to the visible light region. Further, the laser proof strength is high because the excimer laser enters the optical substrate, the fluoride multilayer film, and the metal film in this order, and the ratio of the light intensity of the excimer laser reflected by the metal film decreases.

[0021]

As described above, in the rear-view mirror for the ultraviolet and visible light range according to the present invention, since the fluoride multilayer film and the metal film are sealed by the optical substrate and the metal protective film,
Corrosion gas impurities did not erode into the fluoride multilayer film and the metal film, and the gas resistance and light resistance (the reflectance with respect to ultraviolet rays did not decrease with the lapse of use time) were improved.

Further, it has become possible to maintain a high reflectance in a wide band from the ultraviolet range to the visible range. Further, the laser resistance against the excimer laser is improved as compared with the conventional Al metal film reflecting mirror.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a backside mirror for ultraviolet and visible light according to the present invention.

FIG. 2 is a diagram showing a spectral reflectance of a rear-view mirror for ultraviolet and visible light according to the present invention.

FIG. 3 is a result of measurement of laser proof strength against excimer laser between the rear surface mirror for ultraviolet and visible light regions according to the present invention having the structure shown in FIG. 1 and the conventional Al metal film reflecting mirror having the structure shown in FIG. Is.

FIG. 4 is a schematic diagram of an apparatus for measuring LDT.

FIG. 5 is a cross-sectional view of a structure of a conventional Al metal film reflecting mirror.

FIG. 6 is a diagram showing the spectral reflectance of a conventional Al metal film reflecting mirror.

FIG. 7 is a sectional view showing a structure of a conventional fluoride multilayer film reflecting mirror.

FIG. 8 is a diagram showing a spectral reflectance of a conventional fluoride multilayer film reflecting mirror.

[Explanation of symbols]

1 ... Quartz glass substrate _2, 8, 11 ... MgF ₂ 3, 10 ... LaF ₃ 4, 7 ... Al 5 ... Cu 6, 9 ... Optical substrate

Claims (2)

[Claims] 1. A fluoride multilayer film comprising at least two layers of an intermediate refractive index substance and a low refractive index substance, a metal film, and the fluoride multilayer film and the metal film are hermetically sealed on the back surface of the optical substrate with respect to the incident surface. A rear-view mirror for the ultraviolet and visible light regions, which is formed by sequentially laminating metal protective films. 2. The intermediate refractive index material is LaF ₃ , NdF ₃ or YbF ₃ alone or a mixture, and the low refractive index material is MgF ₂ , CaF ₂ , AlF ₃ or Na ₃ AlF ₆ alone or a mixture. The back mirror for ultraviolet and visible light regions according to claim 1, wherein