JP3069641B2 - Dielectric multilayer film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric multilayer film used as an optical element such as a high-efficiency light reflecting mirror, an antireflection film, and an optical filter, and more particularly to a highly durable dielectric multilayer film.

[0002]

2. Description of the Related Art A dielectric multilayer film has been widely used as an optical element such as a high-reflectance mirror for light, an antireflection film, and a filter. FIG. 3 shows a cross section of the dielectric multilayer film. Substrate 20
A plurality of dielectric film layers 1, 2, 3,...
Are formed to form a dielectric multilayer film 100. The substrate 200 is typically made of glass or the like. Dielectric film layer 1,
.. Can be appropriately formed by sequentially forming a plurality of dielectric materials using, for example, vacuum evaporation, sputtering, ion beam sputtering, or the like. The principle that the dielectric multilayer film 100 functions as an optical element will be described below. When the dielectric multilayer film 100 is used as an optical element, light passes through the dielectric multilayer film 100. Since the refractive index differs among the dielectric layers 1-2, 2-3,..., Fresnel reflection occurs at the boundaries between the dielectric film layers 1, 2, 3,. By setting the refractive index and thickness of each of the dielectric film layers 1, 2, 3,... To appropriate values, the Fresnel reflected waves generated between a plurality of layers interfere with each other so as to strengthen each other or weaken each other. You can control the state. Dielectric multilayer film 1
Reference numeral 00 functions as a reflector in an interference state where the Fresnel reflected waves mutually reinforce each other, and as an antireflection film in an interference state where the Fresnel reflected waves mutually weaken. Further, when the reflected waves weaken each other within a certain wavelength range and reinforce each other in other wavelength ranges, they function as a wavelength selection filter that passes only light in that wavelength range.

The dielectric multilayer film 100 utilizes Fresnel reflection and does not use light absorption in principle. The dielectrics 1, 2, 3,... Are generally materials having extremely low light absorption. For this reason, it is known that an optical element with extremely high efficiency can be manufactured using the dielectric multilayer film 100. For example, SiO ₂ and TiO ₂ are 110 nm and 69 n, respectively.
Dielectric multilayer film 100 in which 21 layers are laminated with a thickness of m
If the extinction coefficient of the dielectric film layers 1, 2,... 21 is neglected, it can be a reflecting mirror having a high reflectivity of almost 99.99% at a wavelength of 632.8 nm, which is almost 100%. This reflection spectral characteristic is shown by a solid line in FIG. In the graph of FIG. 4, the horizontal axis represents light wavelength, and the vertical axis represents reflectance. FIG. 4 shows a simulation result.
Actually, a dielectric multilayer film having substantially the same characteristics as the above can be manufactured. However, if the dielectric multilayer film deteriorates, light absorption increases and the efficiency of the optical element decreases. For example, the above SiO
When SiO ₂ and the extinction coefficient of the TiO ₂ is to become 0.01 in the multilayer films of ₂ and TiO ₂ of 21 layers due to deterioration of the dielectric multilayer film 100, the wavelength as shown in broken line in FIG. 4 632.8 nm Reflectivity to 98.4%. The deterioration of the dielectric multilayer film 100 is particularly strong,
It is easy to occur when light of high energy enters. For this reason, the life of an optical element that handles high-intensity and high-energy light is extremely short, which has been a cause that the optical element must be frequently replaced.

[0004]

As described above, the dielectric multilayer film can constitute an optical element with extremely high efficiency.
Deterioration of the dielectric multilayer film makes it difficult to enjoy the advantage of high efficiency. SUMMARY OF THE INVENTION An object of the present invention is to provide a high yield strength dielectric multilayer film which reduces deterioration of the dielectric multilayer film and maintains high efficiency for a long time even in an environment using high intensity or high energy light.

[0005]

According to the present invention, a dielectric film containing hydrogen is used for forming a dielectric multilayer film.

[0006]

In the present invention, the hydrogen contained in the dielectric film compensates for lattice defects in the dielectric which cause light absorption, thereby extending the life of the dielectric multilayer film.

[0007]

FIG. 1 shows an embodiment of the present invention. FIG. 1 shows a cross section of a dielectric multilayer film 100, and a SiO ₂ film 1 A containing hydrogen on a substrate 200.
Dielectric film 10 in which a TiO ₂ film 2A and a TiO ₂ film 2A are alternately laminated
0 is formed. SiO ₂ and TiO containing hydrogen
There are various methods for forming the _second film. For example, Si
Heat treatment in a hydrogen atmosphere after forming a film of O ₂ and TiO ₂ ,
Alternatively, it can be performed by hydrogen ion implantation using an ion gun. The heat treatment and the ion implantation can be performed after the formation of the dielectric multilayer structure. It is also possible to carry out each time each layer is formed, which is more effective for reducing deterioration of the dielectric multilayer film. This is because the amount of hydrogen contained is closely related to the degree of deterioration reduction as shown below,
This is because if the hydrogen content is different in each layer, the layer having a low hydrogen content may deteriorate first. However, on the other hand, in consideration of the dielectric material of each layer, it may be effective to prevent the deterioration of the dielectric multilayer film as a whole by including more hydrogen in a material that is easily deteriorated. As another example, there is a method of forming a SiO ₂ or TiO ₂ film in a hydrogen atmosphere. In this method, since the formation of the film and the inclusion of hydrogen are performed simultaneously, a dielectric multilayer film containing hydrogen can be efficiently formed. At this time, by adjusting the concentration of the hydrogen atmosphere for each material of the film to be laminated, it is possible to effectively prevent deterioration of the entire dielectric multilayer film as described above.

Next, the effect of reducing deterioration due to hydrogen content will be described. FIG. 2 shows a SiO ₂ film containing hydrogen and a Si film not containing hydrogen.
The result of irradiating a high-energy light pulse having a wavelength of 193 nm with an ArF excimer laser to each O ₂ film is shown. The hydrogen concentration in the hydrogen-containing SiO ₂ film is about 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ . The horizontal axis of the graph in FIG. 2 indicates the number of irradiated light pulses, that is, the total irradiation amount, the left vertical axis indicates the E ′ lattice defect concentration in the film, and the right vertical axis indicates the NBOHC lattice defect concentration in the film. Show. Here, the E ′ lattice defect is “≡Si.”, That is, NBOHC indicates that an unbonded bond is generated at a silicon atom.
Lattice defects mean “≡Si—O.”, That is, the occurrence of unbonded bonds at oxygen atoms. It is known that such a lattice defect causes light absorption. Light absorption at a wavelength of 215 nm is caused by an increase in the concentration of the E ′ lattice defect, and a wavelength of 26 nm is caused by an increase in the concentration of the NBOHC lattice defect.
The light absorption at 0 nm respectively increases. If the light absorption increases, the light reflection and transmission characteristics of the entire dielectric multilayer film deteriorate as described above. From the graph of FIG. 4, it can be seen that the inclusion of hydrogen reduces E ′ lattice defects by more than an order of magnitude, while NBOHC lattice defects are not generated. The mechanism of this lattice defect reduction is based on the fact that lattice defects caused by breaking of bonds between atoms by light irradiation are combined with hydrogen atoms and compensated. As described above, the content hydrogen concentration was set to 10 ¹⁸ c
It can be seen that the light proof strength of the dielectric film can be greatly improved by setting it to the order of m ⁻³ . Since the improvement in proof stress is due to the fact that lattice defects are associated with hydrogen atoms, it can be applied not only to SiO ₂ but also to a wide range of dielectrics in general, such as metal oxide dielectrics such as TiO ₂ and Al ₂ O _3. .

[0009]

As described above, according to the present invention, since each layer or one layer of the dielectric constituting the dielectric multilayer film contains hydrogen, it has a higher strength than a dielectric not containing hydrogen.
It is possible to provide a dielectric multilayer film with less deterioration with respect to high-energy light. An optical element composed of this dielectric multilayer film can handle high-intensity or high-energy light for a long time without any change in optical characteristics.

[Brief description of the drawings]

FIG. 1 is an embodiment of the present invention, showing a cross section of a dielectric multilayer film including a dielectric containing hydrogen together with a substrate.

2 is a graph showing the relationship between the light pulses and the lattice defect concentration when irradiated with light pulses in the SiO ₂ material containing no SiO ₂ material and hydrogen ArF excimer laser containing hydrogen.

FIG. 3 is a diagram showing a cross section of a dielectric multilayer film.

FIG. 4 is a graph showing the spectral reflection characteristics of a dielectric multilayer film in which SiO ₂ and TiO ₂ are laminated, where a solid line indicates a case where the extinction coefficient of the dielectric is negligible, and a broken line indicates the extinction due to deterioration of the dielectric The case where the coefficient becomes 0.01 is shown.

[Explanation of symbols]

1: Dielectric film layer 2: Dielectric film layer 3: Dielectric film layer 1A: Hydrogen-containing SiO ₂ film layer 2A: Hydrogen-containing TiO ₂ film layer 100: Dielectric multilayer film 200: Substrate

Claims (3)

(57) [Claims] 1. A dielectric multilayer film comprising a plurality of dielectric films having different refractive indexes stacked, wherein at least one of the dielectric films is a dielectric film containing hydrogen. Body multilayer film 2. The dielectric multilayer film according to claim 1, wherein the hydrogen-containing dielectric film is made of SiO ₂ , Al ₂ O ₃ , Ti
A dielectric multilayer film comprising a dielectric film containing hydrogen in any of O ₂ , Ta ₂ O ₅ , HfO ₂ , and ZrO ₂ 3. The dielectric multilayer film according to claim 1, wherein the hydrogen-containing dielectric film has a hydrogen concentration of 1 × 10 ¹⁷ cm.
^-3 or more dielectric multilayer film