JP2831349B2 - Multilayer reflector for X-ray or vacuum ultraviolet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to optical devices, in particular, light having a wavelength of 200 nm or less called vacuum ultraviolet rays from X-rays, and a normal incidence whose incidence angle is almost perpendicular to a mirror surface. It relates to a reflector. [Prior art] Conventionally, for light with a shorter wavelength than the region called vacuum ultraviolet, there is no reflector such as having a high reflectance when incident on the surface at an angle close to or perpendicular thereto, At an incidence angle close to normal incidence, only a reflectance of 1% or less was obtained. On the other hand, in a grazing incidence reflecting mirror having a relatively high reflectivity, it is necessary to adjust the incident angle to 1 ° or less or 2 to 3 ° from the mirror surface. In addition, a very large shape is required even for a thin light beam in order to make it incident on a surface at a small angle, and its use has been difficult and limited. In addition, the oblique incidence mirror has a small degree of freedom in the optical system, and there are many difficulties in actual use, such as polishing and holding the reflective mirror so as to have a highly accurate flatness over a large area. In order to eliminate such a drawback, there has been proposed a reflecting mirror having a multilayer structure using interference of multilayer thin films. By the way, in the region of X-rays and vacuum ultraviolet light, the reflectance of most substances is a complex refractive index (n) having an imaginary part k representing absorption.
+ Ik, hereinafter referred to as the refractive index), and the real part n is approximately 1.0 (n = 1−δ, δ = 10 ⁻¹ to 10 ⁻³⁾ , so that the reflectance of Fresnel at the boundary between the vacuum and the material thin film Is very small, on the order of 0.1% or less, and the reflectivity does not exceed several percent per single interface even at the boundary of the laminated thin film of dissimilar materials. By adopting a film thickness configuration that maximizes the reflectance of the multilayer film as a whole, the reflections from the respective layer boundaries are strengthened by interference, and a high reflectance can be achieved. It is known that a reflector having a high reflectance can be realized by selecting a combination of different materials so that the difference in the refractive index between the layers becomes large, and by combining with the above-mentioned film thickness configuration. The combination of materials
Transition metals have been used as low-refractive-index materials, and many high-refractive-index materials have used semiconductor elements such as carbon and silicon. A typical example is tungsten (W)
And carbon (C) and molybdenum (Mo) and silicon (Si). [Problems to be Solved by the Invention] However, when a reflector using these combinations is actually irradiated with light having a high intensity such as synchrotron orbital radiation, it is locally heated, and a low-density material layer is formed. There is a disadvantage that the multilayer structure is easily broken due to a low melting point. Therefore, as a characteristic that the multilayer mirror should have, it has resistance to local heating, and in addition, the material of each layer is a high melting point material,
In addition, it is required that the material be chemically stable and not diffuse even when the temperature rises. The present invention has been made in view of the above problems, and an object of the present invention is to provide a multilayer reflector for X-ray or vacuum ultraviolet light which has a condition that the reflector should have excellent heat resistance and does not cause blur between layers. Is to do. [Means for Solving the Problems] The object of the present invention is to provide an X-ray or vacuum ultraviolet multilayer film reflecting mirror having a multilayer structure composed of alternating layers of two kinds of substances having different refractive indexes. 2000 melting point for the substance
Using a melting point substance exceeding ℃, the above-mentioned two kinds of substances are used to reduce the complex refractive index of the substance of the first layer. The complex refractive index of the material in the second layer When Δn = | n ₁ −n ₂ |, a combination satisfying Δn ≧ 10 ⁻³ or a combination satisfying | k ₁ −k ₂ |> Δn when Δn <10 ^−3. This is achieved by a multilayer reflector for X-rays or vacuum ultraviolet rays. According to this method, the material of each layer is excellent in heat stability and chemically stable, so that even after heating after forming the multilayer film, there is no deterioration such as peeling of layers and diffusion between layers. The present invention uses a high-melting-point compound as a constituent material of a layer so as to maintain the performance as a reflecting mirror even when locally heated by irradiation with high-intensity light such as synchrotron orbital radiation. , Especially such materials have a melting point
Aluminum nitride (AlN), beryllium nitride (Be ₃ N ₂ ), titanium nitride (Ti
N), niobium nitride (NbN), vanadium nitride (VN), zirconium nitride (ZrN), boron nitride (BN), hafnium nitride (HfN), tantalum nitride (TaN, Ta ₂ N), aluminum boride (AlB ₁₂₎ , Titanium boride (TiB ₂ ), vanadium boride (V ₃ B ₄ , VB), tungsten boride (WB), hafnium boride (HfB ₂ ), zirconium boride (Zr
B ₂ ); boron carbide (B ₄ C), molybdenum carbide (Mo ₂ C),
Beryllium carbide (Be ₂ C), silicon carbide (SiC), vanadium carbide (V ₂ C), tungsten carbide (WC, W ₂ C), hafnium carbide (HfC), niobium carbide (NbC), tantalum carbide (TaC), Titanium carbide (TiC), zirconium carbide (Zr
C), aluminum oxide (Al ₂ O ₃ ), beryllium oxide (Be
O), chromium oxide (Cr ₂ O ₃ ), hafnium oxide (HfO ₂ ),
It is preferable to use titanium oxide (Ti ₂ O ₃ ), cerium oxide (CeO ₂ ), zirconium oxide (ZrO ₂ ), or the like. Of the substances listed above, the refractive index of the substance in the first layer
₁ = n ₁ + ik ₁ , and the refractive index of the substance of the second layer is ₂ = n ₂ + i
A combination that satisfies Δn = | n ₁ −n ₂ | ≧ 10 ^-3 when k ₂ is set,
Or, in the case of Δn = | n ₁ −n ₂ | <10 ⁻³ , | k ₁ −k ₂ |> Δ
What is necessary is just to select two kinds of substances and form an alternating layer so that it may become n combinations. FIG. 1 is a schematic view of an embodiment of a multilayer reflector for X-ray or vacuum ultraviolet rays according to the present invention. The X-ray or vacuum ultraviolet multilayer film reflecting mirror of the present invention shown in FIG. 1 is a substrate 1 having a flat or curved surface (for example, a roughness of 10 ° or less in rms) polished sufficiently smoothly compared to the wavelength used. , And layers 3, 5, 7,... Of the second material are alternately laminated. The reflectivity exhibited by the multilayer mirror for X-ray or vacuum ultraviolet rays of the present invention is the difference between the refractive indices of two substances having different refractive indices forming the alternating layers, the absorptivity of each layer, and the number of layers to be laminated. Although it differs depending on the wavelength of the light to be irradiated, the difference in the refractive index is practically at least 0.0 if the number of layers is 100 layers.
Preferably there is at least one. In order to make each layer of the alternating layer have a difference in refractive index, the alternating layer may be formed using a substance having a high refractive index and a substance having a low refractive index with respect to light in the region of X-rays or vacuum ultraviolet rays. Materials having a high refractive index and a high melting point include borides, nitrides, carbides and oxides of transition metals, and materials having a high refractive index and a high melting point include nitrides, carbides of beryllium or aluminum or boron or silicon, Oxides.
Here, transition metals are elements that have electron vacancies in the 3d, 4d, and 5d orbitals: scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), nickel (Ni), and cobalt. (Co), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), rhodium (R
h), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), and 3d,
4d, 5d orbital filled copper (Cu), palladium (Pd),
It represents silver (Ag) and gold (Au). The thickness d ₁ , d ₂ ,... Of each layer is about / 4 of the wavelength used, and the layers are alternately laminated films of the same material. Either satisfy the condition of constructively interfering with each other, or satisfy the condition that the decrease in reflectance of the multilayer film as a whole is smaller when comparing the absorption loss in each layer and the reflectance decrease due to phase shift. Alternatively, it is determined by both. At this time, the film thickness may be the same for all the same material layers, or may not be the same so that the reflectance is maximized by changing the film thickness of each layer. As the structure of the lamination, it is desirable to select a material that has a large difference between the refractive index of the final layer which is a layer in contact with gas or vacuum and the refractive index of gas or vacuum. Further, it is preferable that the difference in the refractive index between the substrate and the layer in contact with the substrate is increased. The reflectivity increases as the number of the alternating layers increases, and the number of layers is preferably 5 or more. However, when the number is too large, the influence of the absorbing layer becomes remarkable. It is good to have a layer pair. Further, a protective layer made of a stable material having a small number of series may be provided on the final layer. As a film forming method for producing the multilayer mirror for X-ray or vacuum ultraviolet rays of the present invention, an electron beam method in an ultra-high vacuum is preferably used. The sputtering method in a vacuum having a sufficiently small amount of the above is an effective method. Further, needless to say, a multi-layer film may be formed by using an ion plating method or a metal organic chemical vapor deposition (MOCVD) method, which has attracted attention in the production of semiconductor superlattices, as a method of forming a film having high film strength. Nor. EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention. Example 1 100 μm thick silicon carbide (SiC) optically polished to a surface accuracy of λ / 20 (λ = 6328 °) and a surface roughness of 7 ° (rms value)
Are formed on a silicon substrate 1 coated with a first layer 2,4 of hafnium nitride (HfN) which is a low refractive index material.
(Thickness 23.0 mm), a total of 41 alternately laminated second layers 3,5 ... (thickness 38.8 mm) made of silicon carbide (SiC), a high refractive index material (HfN: 21 layers, SiC : 20 layers). The final layer of the alternate layers was hafnium nitride, and carbon (C) was further laminated thereon as a protective film A by 10 °. A layer of hafnium nitride,
Silicon carbide layers in ultra-high vacuum (<10 ^-6 P
In a), evaporation was performed by electron beam evaporation. The deposition rate was set to be 0.2 mm / sec for both materials.
The protective layer was formed by an electron beam method. When light having a wavelength of 124.0 ° was perpendicularly incident on the reflecting surface, a reflectance of 29.8% was obtained. When the film thicknesses of hafnium nitride and silicon carbide were 23.8 ° and 41.9 °, respectively, when light having a wavelength of 124.0 ° was incident at an incident angle of 20 °, a reflectivity of 31.5% was obtained. [Example 2] A first layer 2, 4 made of tantalum nitride (TaN), which is a low refractive index material, is formed on a silicon substrate coated with 100 μm thick silicon carbide polished in the same manner as in Example 1.
(Thickness: 21.7 mm), 41 layers of second layers 3,5 ... (thickness: 40.1 mm) made of silicon carbide (SiC) which is a high refractive index material are alternately laminated (TaN: 21 layers, SiC : 20 layers). The last layer of the alternating layers was tantalum nitride having a large difference in refractive index from vacuum, and a carbon film as a protective film A was further laminated thereon by 10 °. Both the low-refractive-index material layer and the high-refractive-index material layer were formed by electron beam evaporation in an ultra-high vacuum (<10 ⁻⁶ Pa). The deposition rate was set to be 0.2 mm / sec for both materials.
When light of 124.0 ° was vertically incident on this, a reflectance of 31.3% was obtained. In addition, tantalum nitride and silicon carbide had a film thickness of 22.1Å and 43.5Å, respectively, and a total of 41 layers were alternately laminated. When light with a wavelength of 124.0Å was incident at an incidence angle of 20 ゜ from the normal line, 32.8% Was obtained. [Effects of the Invention] As described above, the multilayer mirror for X-rays or vacuum ultraviolet rays of the present invention not only has a high reflectivity to soft X-rays and light in the vacuum ultraviolet ray range, but also has a conventional synchrotron. Irradiation with orbital synchrotron radiation (SR) has caused significant damage in a short period of time, but now has a sufficiently long durability. In particular, by combining a plurality of flat or curved reflecting mirrors, a reducing / enlarging optical system in the X-ray region, a soft X-ray, a reflecting mirror of a laser resonator in a vacuum ultraviolet region, and a reflecting mirror having a grating can be used. The present invention greatly contributes to the expansion of the field of application of optical components as a new optical component in the field of X-ray optics, such as a reflective dispersion element having a structure, which has not existed before.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing a layer structure of an embodiment of a multilayer reflector for X-ray or vacuum ultraviolet rays according to the present invention. 1: substrate 2, 4: the first layer 3, 5: second layer A: protective layer _{d 1, d 2, d 3} : thickness of the layer

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shigetaro Ogura 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-60-7400 (JP, A) JP-A-59 -26704 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G21K 1/06 G02B 5/08 G02B 5/28

Claims (1)

(57) [Claims] In a multilayer mirror for X-ray or vacuum ultraviolet radiation having a multilayer structure composed of alternating layers of two substances having different refractive indices, a melting point substance having a melting point exceeding 2000 ° C. is used as a constituent material of the layer. The material is the complex refractive index of the material in the first layer The complex refractive index of the material in the second layer When Δn = | n ₁ −n ₂ |, a combination satisfying Δn ≧ 10 ⁻³ or a combination satisfying | k ₁ −k ₂ |> Δn when Δn <10 ^−3. X-ray or vacuum ultraviolet multilayer reflector. 2. The two substances forming the alternating layers are both melting point compounds, and one of the substances is selected from the group consisting of transition metal borides, nitrides, carbides, and oxides, and the other substance is used as the other substance. 2. The multilayer mirror for X-ray or vacuum ultraviolet rays according to claim 1, wherein one of a substance selected from nitride, carbide, and oxide of beryllium, aluminum, boron, or silicon is used. 3. The two substances forming the alternating layers have a melting point of 2000 ° C.
Aluminum nitride (AlN), which is a melting point compound exceeding
Beryllium nitride (Be ₃ N ₂ ), titanium nitride (TiN), niobium nitride (NbN), vanadium nitride (VN), zirconium nitride (ZrN), boron nitride (BN), hafnium nitride (Hf
N), tantalum nitride (TaN, TaN ₂ ); aluminum boride (AlB ₁₂ ), titanium boride (TiB ₂ ), vanadium boride (V ₃ B ₄ ), tungsten boride (WB), hafnium boride (HfB ₂ ), zirconium boride (ZrB ₂ ), boron carbide (B ₄ C), molybdenum carbide (Mo ₂ C), beryllium carbide (B
e ₂ C), silicon carbide (SiC), vanadium carbide (V ₂ C),
Tungsten carbide (WC, W ₂ C), hafnium carbide (Hf
C), niobium carbide (NbC), tantalum carbide (TaC), titanium carbide (TiC), zirconium carbide (ZrC), aluminum oxide (Al ₂ O ₃ ), beryllium oxide (BeO), chromium oxide (Cr ₂ O ₃ ) , Hafnium oxide (HfO ₂ ), titanium oxide (Ti ₂
O ₃ ), cerium oxide (CeO ₂ ), zirconium oxide (Zr
_{2. The} multi-layer reflecting mirror for X-rays or vacuum ultraviolet rays according to claim 1, wherein two kinds of substances are selected from O ₂ ) so as to have different refractive indexes.