Optical components and optical devices

Abstract

An optical component and an optical device are disclosed. The optical component includes: a substrate; and a multilayer film, including a first layer group located on the substrate and a second layer group located between the first layer group and the substrate. The second layer group includes a first dielectric layer and a second dielectric layer stacked alternately, and the first layer group includes a third dielectric layer and a fourth dielectric layer stacked alternately. The first dielectric layer has a higher refractive index than the second dielectric layer, and the third dielectric layer has a higher refractive index than the fourth dielectric layer.

Description

Technical Field

[0001] The present disclosure relates to optical assemblies. Background Art

[0002] Since multilayer films formed of multiple dielectric layers have high design flexibility, they are widely used for antireflection films, reflection films, and filter films in optical components.

[0003] Japanese Patent Laid-Open No. 2005-345492 and Japanese Patent Laid-Open No. 7-244205 disclose an optical device including a dielectric multilayer film.

[0004] In the techniques described in Japanese Patent Laid-Open No. 2005-345492 and Japanese Patent Laid-Open No. 7-244205, research into improving the optical characteristics of optical devices is insufficient. Summary of the invention

[0005] An optical component according to a first aspect of the present disclosure includes: a substrate; and a multilayer film, including a first layer group located on the substrate and a second layer group located between the first layer group and the substrate, wherein the second layer group includes first and second dielectric layers stacked alternately, the first layer group includes third and fourth dielectric layers stacked alternately, the first dielectric layer has a higher refractive index than the second dielectric layer, the third dielectric layer has a higher refractive index than the fourth dielectric layer, and at least one of (i) and (iii) is satisfied: (i) the third dielectric layer has a higher refractive index than the first dielectric layer, and (ii) the difference between the refractive index of the third dielectric layer and the refractive index of the fourth dielectric layer is greater than the difference between the refractive index of the first dielectric layer and the refractive index of the second dielectric layer, and (iii) the third dielectric layer has a lower density than the first dielectric layer.

[0006] An optical component according to a second aspect of the present disclosure includes: a substrate; and a multilayer film located on the substrate, wherein the multilayer film includes a first dielectric layer, a second dielectric layer, a third dielectric layer and a fourth dielectric layer, the first dielectric layer is located between the second dielectric layer and the substrate, and the distance between the first dielectric layer and the second dielectric layer is less than the thickness of the first dielectric layer, the third dielectric layer is located between the fourth dielectric layer and the substrate, and the distance between the third dielectric layer and the fourth dielectric layer is less than the thickness of the third dielectric layer, the first dielectric layer contains ytterbium fluoride, the third dielectric layer contains at least one of neodymium fluoride, lanthanum fluoride, gadolinium fluoride, samarium fluoride, cerium fluoride and aluminum oxide, and each of the second dielectric layer and the fourth dielectric layer contains at least one of magnesium fluoride, aluminum fluoride, sodium fluoride, lithium fluoride, calcium fluoride, barium fluoride, strontium fluoride, silicon oxide, cryolite and cone cryolite.

[0007] An optical component according to a third aspect of the present disclosure includes a substrate and an ytterbium fluoride layer on the substrate, wherein the ytterbium fluoride layer has a refractive index of 1.65 or greater for light having a wavelength of 193 nm.

[0008] Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic diagram of the optical components.

[0010] Figure 2 It's the periodic table.

[0011] Figure 3A and Figure 3B is a schematic diagram of the optical components, and Figure 3C It is a graph of reflectivity characteristics.

[0012] Figure 4 is a schematic diagram of the optical device. DETAILED DESCRIPTION

[0013] Below, the embodiments of the present disclosure are described with reference to the accompanying drawings. In the following description and drawings, similar reference numerals represent similar components. Sometimes common parts are described with reference to multiple drawings without further notice. Parts with common reference numerals may not be described again.

[0014] The present disclosure provides advantageous techniques for improving the optical properties of optical components.

[0015] refer to Figure 1 The optical component 30 is described. The optical component 30 includes a substrate 10 and a multilayer film 20 located on the substrate 10. The optical component 30 can be used so that light enters the multilayer film 20 from the side of the multilayer film 20 opposite to the substrate 10. Alternatively, the optical component 30 can be used so that light enters the multilayer film 20 from the substrate 10. The multilayer film 20 in the optical component 30 can be used as a reflective film to reflect light of a predetermined wavelength. Alternatively, the multilayer film 20 in the optical component 30 can be used as a filter film to selectively transmit light of a predetermined wavelength. Alternatively, the multilayer film 20 can be used as an anti-reflective film to prevent reflection from the optical component 30.

[0016] The multilayer film 20 includes a dielectric layer group 27 and a dielectric layer group 28. The dielectric layer group 27 is located between the dielectric layer group 28 and the substrate 10. In addition, the multilayer film 20 may include a dielectric layer group 29 ( Figure 3B The dielectric layer group 28 is located between the dielectric layer group 27 and the dielectric layer group 29 .

[0017] The multilayer film 20 includes a dielectric layer 21, a dielectric layer 22, a dielectric layer 23, and a dielectric layer 24. In addition, the multilayer film 20 may include a dielectric layer 25 and a dielectric layer 26, and does not necessarily include at least one of the dielectric layer 25 and the dielectric layer 26. The multilayer film 20 is formed of a large number of dielectric layers, and thus may be referred to as a dielectric stacked film or a dielectric multilayer film.

[0018] Dielectric layer group 27 includes dielectric layer 21 and dielectric layer 22. Dielectric layer 21 is located between dielectric layer 22 and substrate 10. In dielectric layer group 27, dielectric layer 21 and dielectric layer 22 are preferably stacked alternately. Dielectric layer group 28 includes dielectric layer 23 and dielectric layer 24. Dielectric layer 23 is located between dielectric layer 24 and substrate 10. In dielectric layer group 28, dielectric layer 23 and dielectric layer 24 are preferably stacked alternately. The phrase "first layers and second layers are stacked alternately" used herein means that at least one second layer is located between two first layers, and at least one first layer is located between two second layers. Therefore, the alternately stacked first and second layers include at least four layers. For the sake of brevity, Figure 1 The dielectric layer group 27 in the multilayer film 20 includes only two different types of layers: dielectric layers 21 and 22. Although the multilayer film 20 includes the dielectric layer group 27 and the dielectric layer group 28 in the present embodiment, a combination of the dielectric layer 21, the dielectric layer 22, the dielectric layer 23, and the dielectric layer 24 may be repeatedly stacked. The dielectric layer group 29 includes the dielectric layer 25 and the dielectric layer 26. In the dielectric layer group 29, the dielectric layer 25 and the dielectric layer 26 may or may not be alternately stacked.

[0019] The dielectric layer 21 is located between the substrate 10 and the dielectric layer 23. The refractive index Na of the dielectric layer 21 is higher than the refractive index Nb of the dielectric layer 22 (Na > Nb). The distance Db between the dielectric layer 21 and the dielectric layer 22 is less than the thickness Ta of the dielectric layer 21 (Db < Ta). This means that the dielectric layer 21 and the dielectric layer 22 are positioned close to each other (adjacent to each other). Although the dielectric layer 22 is usually in contact with the dielectric layer 21 and the distance Db is 0, other dielectric layers (not shown) may be located between the dielectric layer 21 and the dielectric layer 22. The refractive index Nc of the dielectric layer 23 is higher than the refractive index Nd of the dielectric layer 24 (Nc > Nd). The distance Dc between the dielectric layer 22 and the dielectric layer 23 depends on the number of layers between the dielectric layer 22 and the dielectric layer 23 of interest and may be less than 1 μm. The distance Dc may be greater than the thickness Tb and the thickness Tc. The distance Dd between the dielectric layer 23 and the dielectric layer 24 is less than the thickness Tc of the dielectric layer 23 (Dd < Tc). Usually, the dielectric layer 24 is in contact with the dielectric layer 23 and the distance Dd is 0. Other dielectric layers (not shown) may be located between the dielectric layer 23 and the dielectric layer 24. The distance Df between the dielectric layer 25 and the dielectric layer 26 is less than the thickness Te of the dielectric layer 25 (Df < Te). Usually, the dielectric layer 26 is in contact with the dielectric layer 25 and the distance Df is 0. Other dielectric layers (not shown) may be located between the dielectric layer 25 and the dielectric layer 26. The distance De between the dielectric layer 24 and the dielectric layer 25 depends on the number of layers between the dielectric layer 24 and the dielectric layer 25 of interest and may be less than 1 μm. The distance De may be greater than the thickness Td and the thickness Tf.

[0020] The dielectric layer 21 contains a compound of the metal element Mtla. The dielectric layer 23 contains a compound of the metal element Mtlc. The metal element Mtlc is different from the metal element Mtla. Two different elements have different atomic numbers, and two identical elements have the same atomic number. Figure 2 A periodic table with element symbols and atomic numbers is shown. The shaded elements are metal elements, while the unshaded elements are non-metal elements.

[0021] The dielectric layer 21 and the dielectric layer 23 have different compositions. The term "composition" as used herein refers to at least one of the combination of all elements and the ratio of all elements that make up the dielectric layers 21 and 23.

[0022] The dielectric layers 21 and 23 have a higher refractive index than their corresponding adjacent dielectric layers 22 and 24. Among the two adjacent dielectric layers, the dielectric layer with a higher refractive index (dielectric layers 21 and 23) is called a high refractive index layer, and the dielectric layer with a lower refractive index (dielectric layers 22 and 24) is called a low refractive index layer. The physical thickness required for the dielectric layers 21 and 23 whose optical thickness is within a predetermined range can be less than the physical thickness required for the dielectric layers 22 and 24 whose optical thickness is within a predetermined range. This increases the degree of freedom of film thickness and material selection. Therefore, the dielectric layers 21 and 23 are suitable for making their compositions different. The optical thickness of each of the dielectric layers 21, 22, 23 and 24 can be appropriately set according to the wavelength λa of the light transmitted or reflected, and is generally less than the wavelength λa, for example, λa / 8 to 3λa / 8. The optical thicknesses of the dielectric layers 21, 22, 23 and 24 can be different or the same.

[0023] In the dielectric laminate film, the reflectivity at the interface between the low refractive index layer and the high refractive index layer is preferably high to utilize the interference of reflected light at the interface between the low refractive index layer and the high refractive index layer and achieve the desired optical properties. In the low refractive index layer and the high refractive index layer that are close to each other (e.g., forming an interface), the low refractive index layer has a refractive index Nt, and the high refractive index layer has a refractive index Nk. The reflectivity R between the low refractive index layer and the high refractive index layer (e.g., at the interface) is simply expressed as R = {(Nk-Nt) / (Nk+Nt)} 2 Therefore, the reflectivity R increases as the sum of the refractive index Nt of the low refractive index layer and the refractive index Nk of the high refractive index layer decreases, and increases as the difference between the refractive index Nt of the low refractive index layer and the refractive index Nk of the high refractive index layer increases.

[0024] The concentration Ccc of the metal element Mtlc in the dielectric layer 23 may be different from the concentration Cca of the metal element Mtlc in the dielectric layer 21 (Ccc≠Cca). The concentration Ccc of the metal element Mtlc in the dielectric layer 23 is preferably higher than the concentration Cca of the metal element Mtlc in the dielectric layer 21 (Ccc>Cca). In a typical example, the dielectric layer 21 may not contain the metal element Mtlc, and the concentration Cca of the metal element Mtlc in the dielectric layer 21 may be zero. In a modified example, the dielectric layer 21 may contain a compound of the metal element Mtlc and a compound of the metal element Mtlc, and the dielectric layer 23 may also contain a compound of the metal element Mtlc and a compound of the metal element Mtlc.

[0025] The concentration Caa of the metal element Mtla in the dielectric layer 21 may be different from the concentration Cac of the metal element Mtla in the dielectric layer 23 (Caa≠Cac). The concentration Caa of the metal element Mtla in the dielectric layer 21 is preferably higher than the concentration Cac of the metal element Mtla in the dielectric layer 23 (Caa>Cac). In a typical example, the dielectric layer 23 may not contain the metal element Mtla, and the concentration Caa of the metal element Mtla in the dielectric layer 21 may be zero. In another example, the dielectric layer 21 may contain a compound of the metal element Mtla and a compound of the metal element Mtlc, and the dielectric layer 23 may also contain a compound of the metal element Mtla and a compound of the metal element Mtlc.

[0026] The metal element Mtla may be a transition element. The metal element Mtlc may be a transition element. Figure 2 In the periodic table shown in , the elements within the thick frame are transition elements, and the elements outside the thick frame are typical elements. Comparing compounds of the same non-metallic element, compounds of transition metal elements generally have a higher refractive index than compounds of typical metal elements, and are therefore suitable as materials for high refractive index layers. However, at least one of the metal element Mtla and the metal element Mtlc may be a typical element.

[0027] The compound in the dielectric layer 21 is, for example, a compound of a metal element Mt1a and a non-metal element Nt1a, for example, a boride, a carbide, a nitride, an oxide, a fluoride, a sulfide, a phosphide or a chloride, usually an oxide or a fluoride. The compound in the dielectric layer 23 is, for example, a compound of a metal element Mt1c and a non-metal element Nt1a, for example, a boride, a carbide, a nitride, an oxide, a fluoride, a sulfide, a phosphide or a chloride, usually an oxide or a fluoride. The non-metal element Nt1c may be the same as the non-metal element Nt1a, or the non-metal element Nt1c may be different from the non-metal element Nt1a.

[0028] The metal element Mt1a may be a rare earth element. The metal element Mt1c may be a rare earth element. Rare earth elements are elements having atomic numbers of 21, 39, and 57 to 71. The dielectric layer 21 may contain a fluoride. The compound in the dielectric layer 21 may be a fluoride of the metal element Mt1a. The dielectric layer 23 may contain a fluoride. The compound in the dielectric layer 23 may be a fluoride of the metal element Mt1c.

[0029] Many metal fluorides absorb less ultraviolet radiation than many metal oxides. Therefore, in the optical component 30 that utilizes ultraviolet light by transmission or reflection, the metal fluoride contained in at least one of the dielectric layers 21 and 23 is effective in improving the efficiency of using ultraviolet light.

[0030] The dielectric layer 23 may include at least one of neodymium fluoride (NdF3), lanthanum fluoride (LaF3), gadolinium fluoride (GdF3), samarium fluoride (SmF3), cerium fluoride (CeF3), and aluminum oxide (Al2O3). The dielectric layer 21 may include ytterbium fluoride (YbF3).

[0031] In another example, the metal element Mt1a may be a Group 4 element or a Group 5 element.

[0032] The metal element Mtlc may be an element of Group 4 or Group 5. When the metal element Mtla or the metal element Mtlc is titanium, zirconium or hafnium, and when the non-metal element Ntla or Ntlc is oxygen, the dielectric layers 21 and 22 contain titanium oxide, zirconium oxide or hafnium oxide.

[0033] In another example, the metal element Mtla may be a Group 12 element or a Group 13 element. The metal element Mtlc may be a Group 12 element or a Group 13 element. When the metal element Mtla or the metal element Mtlc is zinc, aluminum, gallium, or indium, and when the non-metal element Ntla or Ntlc is oxygen, the dielectric layers 21 and 22 contain zinc oxide, aluminum oxide, or gallium oxide.

[0034] The different compositions of dielectric layer 21 and dielectric layer 23 can improve the function of multilayer film 20. The different compositions of dielectric layer 21 and dielectric layer 23 result in different optical, chemical and mechanical properties of the dielectric layers. As optical properties, the refractive index or extinction coefficient can be different. As chemical properties, the diffusion constant or adhesion can be different. As mechanical properties, the surface profile, thermal expansion coefficient or elastic modulus can be different. The combination of these properties can improve the function of multilayer film 20.

[0035] In the dielectric laminate film, the reflectivity between the high refractive index layer and the low refractive index layer (e.g., at the interface) is preferably high to utilize the interference of reflected light at the interface between the high refractive index layer and the low refractive index layer and achieve the desired optical properties. For this purpose, the refractive index ratio (Nk / Nt) or the refractive index difference (Nk-Nt) of the high refractive index layer to the low refractive index layer is preferably large, and the sum of the refractive indices of the high refractive index layer and the low refractive index layer (Nk+Nt) is preferably small.

[0036] The reflectivity Ra at the interface between the dielectric layer 21 and the dielectric layer 22 is given by Ra={(Na-Nb) / (Na+Nb)} 2 The reflectivity Rc at the interface between the dielectric layer 23 and the dielectric layer 24 is expressed by Rc={(Nc-Nd) / (Nc+Nd)} 2It is expressed that the condition for Ra < Rc is Na / Nb < Nc / Nd, and the condition for Ra > Rc is Na / Nb > Nc / Nd.

[0037] For example, when light enters the multilayer film 20 from the side opposite to the substrate 10 and when light of a predetermined wavelength is reflected by the multilayer film 20, it is preferably satisfied that Rc > Ra. This is because it is advantageous to place the reflective surface (interface) with a higher refractive index closer to the light incident surface (the upper surface 202) to increase the reflectivity of the multilayer film 20. When light enters the multilayer film 20 from the substrate 10 and when light of a predetermined wavelength passes through the multilayer film 20, it is also preferably satisfied that Rc > Ra. This is because it is advantageous to place the reflective surface (interface) with a higher refractive index farther from the light incident surface (the upper surface 202) to increase the transmittance of the multilayer film 20.

[0038] The ratio Nc / Nd of the refractive index Nc of the dielectric layer 23 to the refractive index Nd of the dielectric layer 24 can be greater than the ratio Na / Nb of the refractive index Na of the dielectric layer 21 to the refractive index Nb of the dielectric layer 22 (Nc / Nd > Na / Nb). Satisfying Nc / Nd > Na / Nb is advantageous for satisfying Rc > Ra.

[0039] The difference Nc - Nd between the refractive index Nc of the dielectric layer 23 and the refractive index Nd of the dielectric layer 24 can be greater than the difference Na - Nb between the refractive index Na of the dielectric layer 21 and the refractive index Nb of the dielectric layer 22 (Nc - Nd > Na - Nb). The reflectivity Rc increases as the difference Nc - Nd increases.

[0040] The sum Nc + Nd of the refractive index Nc of the dielectric layer 23 and the refractive index Nd of the dielectric layer 24 can be less than the sum Na + Nb of the refractive index Na of the dielectric layer 21 and the refractive index Nb of the dielectric layer 22 (Nc + Nd < Na + Nb). The reflectivity Rc increases as the sum Nc + Nd decreases.

[0041] The refractive index Nc of the dielectric layer 23 can be higher than the refractive index Na of the dielectric layer 21 (Nc > Na). If Nc > Na and Nd ≤ Nb, then Nc / Nd > Na / Nb and Nc - Nd > Na - Nb are satisfied. Even if Nd > Nb, it is preferably satisfied that Nc > Na.

[0042] For example, when light enters the multilayer film 20 from the substrate 10 and when light of a predetermined wavelength is reflected by the multilayer film 20, it is preferably satisfied that Rc < Ra. This is because it is advantageous to place the reflective surface (interface) with a higher refractive index closer to the light incident surface (the lower surface 201) in order to increase the reflectance of the multilayer film 20. When light enters the multilayer film 20 from the side of the multilayer film 20 opposite to the substrate 10 and when light of a predetermined wavelength passes through the multilayer film 20, it is also preferably satisfied that Rc < Ra. This is because it is advantageous to place the reflective surface (interface) with a higher refractive index farther from the light incident surface (the upper surface 202) in order to increase the reflectance of the multilayer film 20.

[0043] The ratio Nc / Nd of the refractive index Nc of the dielectric layer 23 to the refractive index Nd of the dielectric layer 24 can be less than the ratio Na / Nb of the refractive index Na of the dielectric layer 21 to the refractive index Nb of the dielectric layer 22 (Nc / Nd < Na / Nb). Satisfying Nc / Nd < Na / Nb is advantageous for satisfying Rc < Ra.

[0044] The difference Nc - Nd between the refractive index Nc of the dielectric layer 23 and the refractive index Nd of the dielectric layer 24 can be less than the difference Na - Nb between the refractive index Na of the dielectric layer 21 and the refractive index Nb of the dielectric layer 22 (Nc - Nd < Na - Nb). The reflectance Rc increases as the difference Nc - Nd increases.

[0045] The sum Nc + Nd of the refractive index Nc of the dielectric layer 23 and the refractive index Nd of the dielectric layer 24 can be greater than the sum Na + Nb of the refractive index Na of the dielectric layer 21 and the refractive index Nb of the dielectric layer 22 (Nc + Nd > Na + Nb). The reflectance Rc increases as the sum Nc + Nd decreases.

[0046] The refractive index Nc of the dielectric layer 23 can be lower than the refractive index Na of the dielectric layer 21 (Nc < Na). If Nc < Na and Nd ≥ Nb, then Nc / Nd < Na / Nb and Nc - Nd < Na - Nb are satisfied. Even if Nd < Nb, it is preferably satisfied that Nc < Na.

[0047] Although the light absorption of the dielectric layers 21, 22, 23, and 24 is preferably small, light absorption materials can also be selected, for example, to satisfy the refractive index relationship with other dielectric layers. The dielectric layer 21 has an extinction coefficient Ka, the dielectric layer 22 has an extinction coefficient Kb, the dielectric layer 23 has an extinction coefficient Kc, and the dielectric layer 24 has an extinction coefficient Kd. The extinction coefficients are applied to light of a predetermined wavelength processed by the multilayer film 20.

[0048] For example, when light enters the multilayer film 20 from the side opposite to the substrate 10, it is preferably satisfied that Ka≥Kc rather than Ka<Kc. In addition, it is preferably satisfied that Kb≥Kd rather than Kb<Kd. This is because it is advantageous to place the dielectric layer with less light absorption closer to the light incident surface (the upper surface 202) in order to reduce the light absorption of the multilayer film 20.

[0049] For example, when light enters the multilayer film 20 from the substrate 10, it is preferably satisfied that Ka≤Kc rather than Ka>Kc. In addition, it is preferably satisfied that Kb≤Kd rather than Kb>Kd. This is because it is advantageous to place the dielectric layer with less light absorption closer to the light incident surface (the lower surface 201) in order to reduce the light absorption of the multilayer film 20.

[0050] Each dielectric layer of the multilayer film 20 may have a specific surface profile depending on its crystallinity (crystal grain size), film formation conditions, etc. The dielectric layers of the multilayer film 20 are sequentially stacked on the substrate 10. Therefore, the surface profile of each dielectric layer can reflect not only its specific surface profile but also the profile of its underlying layer. In the multilayer film 20, the interface between two adjacent dielectric layers is preferably as flat as possible to improve the optical properties. This is because the light scattering loss at the interface can be reduced. For this purpose, the underlying profile of each dielectric layer is preferably flat. For dielectric layers with different surface profiles, it is more effective to improve the surface flatness of the lower dielectric layer closer to the substrate 10 than to improve the surface flatness of the upper dielectric layer farther from the substrate 10. When the lower dielectric layer has a specific surface profile with large irregularities, the upper dielectric layer formed on the lower dielectric layer may have a specific surface profile with large irregularities that reflects the irregularities of the lower dielectric layer in addition to the specific surface profile of the upper dielectric layer. However, when the lower dielectric layer has a surface profile with small irregularities, the upper dielectric layer formed on the lower dielectric layer may have a surface profile similar to the specific surface profile of the upper dielectric layer. Therefore, the surface (the surface opposite to the substrate 10) of the dielectric layer 21 is preferably flatter than the surface (the surface opposite to the substrate 10) of the dielectric layer 23. Similarly, the surface (the surface opposite to the substrate 10) of the dielectric layer 22 is preferably flatter than the surface (the surface opposite to the substrate 10) of the dielectric layer 24. For example, the surface (the upper surface 202) of the multilayer film 20 opposite to the substrate 10 may have a surface roughness in the range of 1.0 to 3.0 nm RMS. The materials of the dielectric layers 21 and 22 can be selected such that the dielectric layers 21 and 22 have a specific surface profile flatter than that of the dielectric layers 23 and 24.

[0051] Each dielectric layer of the substrate 10 and the multilayer film 20 may have a different density. The dielectric layer 21 has a density ρa, the dielectric layer 22 has a density ρb, the dielectric layer 23 has a density ρc, and the dielectric layer 24 has a density ρd. In general, materials with higher densities tend to have higher stresses. In addition, dielectric layers with greater physical thickness tend to have higher stresses. Stress in the dielectric layer may cause the dielectric layer to peel or crack. Therefore, a dielectric layer with a greater physical thickness may have a lower density than a dielectric layer with a smaller physical thickness. This can reduce the difference in the absolute value of stress. This may be preferred when two adjacent dielectric layers have opposite stresses (positive: tensile stress or negative: compressive stress), but this may also be effective when two adjacent dielectric layers have the same positive or negative stress. When the low refractive index layer has a greater physical thickness than the high refractive index layer, the low refractive index layer may have a lower density than the high refractive index layer. For example, the density ρb of the dielectric layer 22 is preferably lower than the density ρa of the dielectric layer 21 (ρb<ρa). The density ρd of the dielectric layer 24 is preferably lower than the density ρc of the dielectric layer 23 (ρd<ρc). The term "density of the dielectric layer" as used herein refers to at least one of the intrinsic density of the substance and the film density depending on the formation conditions (filling rate) of the dielectric layer. Theoretical densities may be compared, or film densities may be compared. At similar theoretical densities, the density increases as the filling rate increases. At similar filling ratios, the density increases as the theoretical density increases.

[0052] The upper dielectric layer preferably has a lower density than the lower dielectric layer to prevent cracking or peeling in the multilayer film 20. Generally, the substrate 10 is thicker than the multilayer film 20 and tends to have a higher stress. Therefore, the lower dielectric layer preferably has a higher absolute stress. For example, the density ρc of the dielectric layer 23 may be less than the density ρa of the dielectric layer 21 (ρc<ρa). The density ρd of the dielectric layer 24 may be less than the density ρb of the dielectric layer 22 (ρd<ρb). When the substrate 10 does not have such a high stress, the upper dielectric layer may have a higher density than the lower dielectric layer, and the density may be ρc>ρa and / or ρd>ρb.

[0053] Each dielectric layer of the substrate 10 and the multilayer film 20 may have a different melting point. The dielectric layer 21 has a melting point Ma, the dielectric layer 22 has a melting point Mb, the dielectric layer 23 has a melting point Mc, and the dielectric layer 24 has a melting point Md. When the dielectric layer is formed by a vapor deposition method, the formation of the upper dielectric layer may increase the temperature of the dielectric material of the lower layer. Therefore, it is preferable to design the vapor deposition device so that the temperature does not exceed the melting point of the lower dielectric layer.

[0054] Among two adjacent dielectric layers (a high refractive index layer and a low refractive index layer), the dielectric layer with a larger physical thickness tends to have a longer film formation time. When the low refractive index layer has a larger physical thickness than the high refractive index layer, the low refractive index layer can thus have a lower melting point than the high refractive index layer. For example, the melting point Mb of the dielectric layer 22 is preferably lower than the melting point Ma of the dielectric layer 21 (Mb < Ma). The melting point Md of the dielectric layer 24 is preferably lower than the melting point Mc of the dielectric layer 23 (Md < Mc).

[0055] The upper dielectric layer also preferably has a lower melting point than the lower dielectric layer. For example, the melting point Mc of the dielectric layer 23 can be lower than the melting point Ma of the dielectric layer 21 (Mc < Ma). The melting point Md of the dielectric layer 24 can be lower than the melting point Mb of the dielectric layer 22 (Md < Mb). When the temperature rise of the dielectric material of the lower layer during the formation of the upper dielectric layer has a small effect on film formation, for example, when the melting point of the lower layer or the lower dielectric layer is 1000 °C or higher, the melting points can be Mc > Ma and / or Md > Mb.

[0056] The dielectric layer 22 can contain a compound of the metal element Mtlb. The metal element Mtlb in the compound in the dielectric layer 22 can be a typical element. The dielectric layer 24 can contain a compound of the metal element Mtld. The metal element Mtld in the compound in the dielectric layer 22 can be a typical element. The metal element Mtlb in the compound in the dielectric layer 22 and the metal element Mtld in the compound in the dielectric layer 24 can be the same element (Mtlb = Mtld). The metal element Mtlb can be different from the metal element Mtld.

[0057] The metal element Mtlb can be a typical element. The metal element Mtld can also be a typical element. Comparing compounds of the same non-metal element, compounds of typical metal elements generally have a lower refractive index than compounds of transition metal elements, and are thus suitable as materials for the low refractive index layer. However, at least one of the metal element Mtlb and the metal element Mtld can be a transition element.

[0058] The compound in the dielectric layer 22 is, for example, a compound of the metal element Mtlb and the non-metal element Ntlb, such as boride, carbide, nitride, oxide, fluoride, sulfide, phosphide, or chloride, and is usually an oxide or a fluoride. The compound in the dielectric layer 24 is, for example, a compound of the metal element Mtld and the non-metal element Ntld, such as boride, carbide, nitride, oxide, fluoride, sulfide, phosphide, or chloride, and is usually an oxide or a fluoride. The non-metal element Ntld can be the same as the non-metal element Ntlb, and the non-metal element Ntld can be different from the non-metal element Ntlb.

[0059] The dielectric layer 22 may contain fluoride. The compound in the dielectric layer 22 may be a fluoride of the metal element Mtlc. The dielectric layer 24 may contain fluoride. The compound in the dielectric layer 24 may be a fluoride of the metal element Mtld.

[0060] Many metal fluorides absorb less ultraviolet radiation than many metal oxides. Therefore, in the optical component 30 that utilizes ultraviolet light by transmission or reflection, the metal fluoride contained in at least one of the dielectric layers 22 and 24 is effective in improving the efficiency of using ultraviolet light.

[0061] Each of dielectric layer 22 and dielectric layer 24 may include magnesium fluoride (MgF2), aluminum fluoride (AlF3), sodium fluoride (NaF), lithium fluoride (LiF), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF3), silicon oxide (SiO2), cryolite (Na3AlF6), and chiolite (Na5Al3F6). 14 ) at least one of.

[0062] The compound in any one of the dielectric layers 21, 22, 23, 24, 25 and 26 may be a silicon compound rather than a compound of a metal element. Any one of the dielectric layers 21, 22, 23 and 24 may be silicon carbide, silicon nitride or silicon oxide. Any one of silicon carbide, silicon nitride and silicon oxide may be silicon oxycarbide, silicon nitride carbide or silicon oxynitride.

[0063] The substrate 10 has a front surface 101 facing the multilayer film 20 and a rear surface 102 opposite to the multilayer film 20. The front surface 101 may be in contact with the multilayer film 20. The shape of the rear surface 102 may be the same as or different from that of the front surface 101. The front surface 101 may be flatter than the rear surface 102.

[0064] The multilayer film 20 has a lower surface 201 facing the substrate 10 and an upper surface 202 opposite to the substrate 10. The lower surface 201 of the multilayer film 20 may have the same shape as the front surface 101 of the substrate 10. The lower surface 201 of the multilayer film 20 facing the substrate 10 may be flatter than the upper surface 202 of the multilayer film 20 opposite to the substrate 10. The upper surface 202 of the multilayer film 20 opposite to the substrate 10 may have a surface roughness in the range of 1.0 to 3.0 nm RMS.

[0065] The dielectric layer 21 has a lower surface 211 facing the substrate 10 and an upper surface 212 opposite to the substrate 10. The dielectric layer 23 has a lower surface 231 facing the substrate 10 and an upper surface 232 opposite to the substrate 10. The upper surface 212 of the dielectric layer 21 opposite to the substrate 10 can be flatter than the upper surface 232 of the dielectric layer 23 opposite to the substrate 10. The lower surface 211 of the dielectric layer 21 facing the substrate 10 can be flatter than the lower surface 231 of the dielectric layer 23 facing the substrate 10.

[0066] The substrate 10 can be a conductor, a semiconductor, or an insulator. The substrate 10 can be a single crystal, a polycrystal, or an amorphous material. The substrate 10 can be a single crystal or a polycrystal. The substrate 10 can be, for example, a metal polycrystal, a semiconductor single crystal, a semiconductor polycrystal, or an insulator single crystal. The substrate 10 can contain at least one of calcium fluoride (CaF2), magnesium fluoride (MgF2), barium fluoride (BaF2), silicon oxide (SiO2), CLEARCERAM (registered trademark), Zerodur (registered trademark), and BK7. The substrate 10 can be fluorite. The substrate 10 can be glass or plastic.

[0067] The multilayer film 20 can include a dielectric layer 25. The dielectric layer 21, the dielectric layer 22, the dielectric layer 23, and the dielectric layer 24 are located between the dielectric layer 25 and the substrate 10. The refractive index Ne of the dielectric layer 25 can be lower than the refractive index Nc of the dielectric layer 23 (Ne < Nc). The refractive index Ne of the dielectric layer 25 can be higher than the refractive index Nd of the dielectric layer 24 (Ne > Nd). The dielectric layer 25 and the dielectric layer 24 can have different compositions.

[0068] The dielectric layer 25 can contain a compound of a metal element Mtle. The metal element Mtle of the compound in the dielectric layer 25 can be a typical element. The metal element Mtle of the compound in the dielectric layer 25 and the metal element Mtld of the compound in the dielectric layer 24 can be the same element (Mtle = Mtld). The metal element Mtle can be different from the metal element Mtld.

[0069] The compound in the dielectric layer 25 is, for example, a compound of a metal element Mtle and a non-metal element Ntle. For example, boride, carbide, nitride, oxide, fluoride, sulfide, phosphide, or chloride, usually an oxide or a fluoride. The non-metal element Ntle can be the same as the non-metal element Ntld, or the non-metal element Ntle can be different from the non-metal element Ntld.

[0070] The dielectric layer 25 can contain at least one of magnesium fluoride, aluminum fluoride, sodium fluoride, lithium fluoride, calcium fluoride, barium fluoride, strontium fluoride, silicon oxide, cryolite, and chionite.

[0071] The multilayer film 20 may include a dielectric layer 26. The dielectric layers 21, 22, 23, and 24 are located between the dielectric layer 26 and the substrate 10. The refractive index Nf of the dielectric layer 26 may be higher than the refractive index Ne of the dielectric layer 25 (Nf>Ne). The dielectric layer 26 and the dielectric layer 23 may have the same composition.

[0072] The dielectric layer 26 may contain a compound of a metal element Mtlf. The metal element Mtlf of the compound in the dielectric layer 26 may be a transition element. The metal element Mtlf of the compound in the dielectric layer 26 and the metal element Mtlc of the compound in the dielectric layer 23 may be the same element (Mtlf=Mtlc). The metal element Mtlf may be different from the metal element Mtlc.

[0073] The compound in the dielectric layer 26 is, for example, a compound of a metal element Mtlf and a non-metal element Ntlf, such as a boride, a carbide, a nitride, an oxide, a fluoride, a sulfide, a phosphide or a chloride, usually an oxide or a fluoride.

[0074] The dielectric layer 23 may include at least one of neodymium fluoride, lanthanum fluoride, gadolinium fluoride, samarium fluoride, cerium fluoride, ytterbium fluoride, and aluminum oxide.

[0075] Figure 3A A more suitable embodiment of the optical component 30 is shown. The multilayer film 20 includes a dielectric layer group 27 and a dielectric layer group 28. The dielectric layer group 27 is located between the dielectric layer group 28 and the substrate 10. The multilayer film 20 may include a dielectric layer group 29. The dielectric layer group 28 is located between the dielectric layer group 27 and the dielectric layer group 29.

[0076] The dielectric layer group 27 includes i (i ≥ 2) dielectric layers 21 (dielectric layers 21-1 to 21-i). Each of the i dielectric layers 21 of the dielectric layer group 27 includes at least two elements included in one dielectric layer 21 (eg, dielectric layer 21-2) among the i dielectric layers 21.

[0077] The dielectric layer group 27 includes i dielectric layers 22 (dielectric layers 22-1 to 22-i). The i dielectric layers 22 in the dielectric layer group 27 include at least two elements included in one dielectric layer 22 (for example, dielectric layer 22-2) among the i dielectric layers 22. In the dielectric layer group 27, when the i dielectric layers 21 and the i dielectric layers 22 are alternately stacked, i is at least 2.

[0078] The dielectric layer group 28 includes j (j≥2) dielectric layers 23 (dielectric layers 23-1 to 23-j). Each of the j dielectric layers 23 in the dielectric layer group 28 contains at least two elements included in one of the j dielectric layers 23 (for example, dielectric layer 23-2). The dielectric layer group 28 includes j dielectric layers 24 (dielectric layers 24-1 to 24-j). The j dielectric layers 24 in the dielectric layer group 28 contain at least two elements included in one of the j dielectric layers 24 (for example, dielectric layer 24-2). In the dielectric layer group 28, when the j dielectric layers 23 and the j dielectric layers 24 are alternately stacked, j is at least 2.

[0079] Preferably, i and j are not extremely different from each other. More preferably, it is preferably satisfied that 0.2≤i / j≤5. It is preferably satisfied that i≤j, and more preferably satisfied that i<j. This is because the dielectric layer group 27 is closer to the substrate 10 than the dielectric layer group 28 and is thus less affected by the shape of the underlying layer. For narrowband wavelength dependence, at least one of i≥3 and j≥3 is satisfied, and more preferably at least one of i≥10 and j≥10 is satisfied. To simplify the film formation step and reduce the thickness of the multilayer film 20, it is preferably satisfied that i≤30 and j≤30.

[0080] The dielectric layer group 28 includes one dielectric layer 25 and two dielectric layers 26 (dielectric layers 26-1 and 26-2). The dielectric layer 25 is located between the dielectric layer 26-1 and the dielectric layer 26-2.

[0081] The optical component 30 can be applied to various optical devices EQP. Examples of the optical device EQP including the optical component 30 include a camera lens, a telescope, a projector, an exposure device, and a measuring device. In particular, the optical component 30 is suitable for optical devices including a light source such as a projector, an exposure device, and a measuring device. This is because the multilayer film 20 of the optical component 30 can be designed to match the wavelength of the light source, so that the optical component 30 transmits and / or reflects the light from the light source. The light from the light source can be infrared light, visible light, or ultraviolet light. Many metal fluorides absorb less ultraviolet light than other metal compounds and are thus suitable when the light source is ultraviolet light.

[0082] Figure 4: is a schematic diagram of an exposure device as an example of an optical device EQP. The optical device EQP as an exposure device includes mirrors 2 and 3 constituting an illumination optical system and a light source 1. The optical device EQP also includes a mask stage 5 for supporting a reticle 4, a projection optical system 6 for projecting a pattern of the mask 4, and a substrate stage 8 for supporting a substrate 7. Exposure light 9 from the light source 1 is reflected by the mirrors 2 and 3 of the illumination optical system and guided to the mask 4. The exposure light 9 having the pattern of the mask 4 is focused by the projection optical system 6 and projected onto the substrate 7. The pattern formed on the mask 4 by the light source 1 and the optical component 30 is projected onto the substrate 7. A photoresist is applied to the substrate 7 and exposed to the exposure light 9. The substrate 7 may be a semiconductor wafer or a glass substrate for a flat panel display (FPD). The exposure light of the exposure device is generally ultraviolet light. The wavelength of the exposure light is 436 nm in a g-line light source or about 365 nm in an i-line light source. The wavelength of the exposure light is about 248nm in a KrF excimer laser light source, about 193nm in an ArF excimer laser light source, or 10 to 20nm in an extreme ultraviolet (EUV) light source. Although the optical component 30 is used for the mirrors 2 and 3 of the illumination optical system in the present embodiment, the optical component 30 can be used for the lens of the projection optical system. In addition, the projection optical system can be composed of a mirror, and the optical component 30 can be used for the mirror. The projection optical system can be a reduced projection type, a one-to-one projection type, or an enlarged projection type. Although the mask 4 is a transmission type in the present embodiment, the mask 4 can also be a reflection type. The projection optical system can be a refractive type using a lens or a reflective type using a mirror. The optical component 30 can be used for a mirror of a reflective reduced projection optical system in an exposure device equipped with an EUV light source.

[0083] Exemplary Embodiments

[0084] The semiconductor exposure device controls the optical path by reflecting the excimer laser beam emitted from the light source with a mirror and refracting the excimer laser beam with a lens, and reduces and projects the fine pattern formed on the mask onto the silicon wafer. The light source is a KrF excimer laser with a wavelength of about 248nm, an ArF excimer laser with a wavelength of about 193nm, etc.

[0085] The mirror is formed by a multilayer film including a high refractive index layer and a low refractive index layer alternately stacked on a substrate material, and the reflectivity is increased by utilizing the interference of light. The reflectivity of the mirror can increase with the increase of the difference in the refractive index between the high refractive index material and the low refractive index material. Due to the low ultraviolet absorption and high laser resistance of the metal fluoride, it is suitable for the high refractive index layer and the low refractive index layer of the mirror for the ultraviolet laser. For example, the metal fluoride with a high refractive index can be lanthanum fluoride (LaF3), gadolinium fluoride (GdF3) or neodymium fluoride (NdF3). The metal fluoride in the low refractive index layer can be aluminum fluoride (AlF3) or magnesium fluoride (MgF2).

[0086] For example, 20 pairs of alternating layers of LaF3 and AlF3 are stacked on a substrate, and LaF3, MgF2, and LaF3 are stacked thereon. This structure can theoretically have a reflectivity of 99% or more at 193nm. However, LaF3 used as a high refractive index layer has crystallinity, and in particular, when a multilayer film is formed by a vacuum deposition method, the multilayer film has considerable interface or surface roughness. An interface or surface with large roughness scatters laser light and rarely has theoretical reflectivity characteristics. Therefore, the reflectivity of the mirror actually manufactured is several percentage points lower than the theoretical reflectivity. The same is true when other materials such as GdF3 or NdF3 are used for high refractive index films.

[0087] Therefore, in this embodiment, an optical component that can be used as a mirror for an ArF excimer laser having a laser wavelength of 193 nm or an ultraviolet laser having a light incident angle of 45 degrees is described below. It should be noted that the present disclosure is not limited to this exemplary embodiment.

[0088] A 35 mm×47 mm×5 mm fluorite (CaF2) substrate polished to a surface roughness of 0.8 nm RMS or less was used as the base material. In the present exemplary embodiment, the surface roughness was measured at 512 points×512 points in a grid shape within a range of 1 μm×1 μm using an atomic force microscope (AFM).

[0089] M (0≤M≤24) pairs of ytterbium fluoride layers (hereinafter referred to as YbF3) and aluminum fluoride layers (hereinafter referred to as AlF3) are stacked on a fluorite substrate. In addition, L (L=24-M) pairs of lanthanum fluoride layers (hereinafter referred to as LaF3) and AlF3 are stacked thereon. In addition, LaF3, magnesium fluoride layers (hereinafter referred to as MgF2) and LaF3 are stacked thereon in sequence. In this way, a multilayer film consisting of a total of 51 dielectric layers is formed. M (M=n / 2) pairs of YbF3 / AlF3 constitute the first to nth layers, and L (L=24-M=24-n / 2) pairs of LaF3 / AlF3 constitute the n+1th to 48th layers.

[0090] In this exemplary embodiment, a vacuum evaporator is used to form a metal fluoride film. The present disclosure is not limited to vacuum deposition methods and is also applicable to known physical vapor deposition methods (molecular beam vapor deposition method, ion plating method, ion beam vapor deposition method, sputtering method, etc.).

[0091] Below, the outline of the vacuum evaporator used in this exemplary embodiment is described. Four containers (molybdenum boats) in the vacuum chamber are filled with YbF3 as vapor deposition material α, AlF3 as vapor deposition material β, LaF3 as vapor deposition material γ and MgF2 as vapor deposition material δ. These four vapor deposition materials are placed on concentric circles with a radius of 250mm from the substrate resistance axis located at the center of the cavity, and are equipped with a resistance heating mechanism. The substrate is fixed to the substrate holder and rotates and revolves at a height of 1100mm from the vapor deposition material. The phrase "rotation and revolution" used in this article means that the substrate rotates around the substrate rotation axis and revolves around the substrate revolution axis at the same time. The substrate rotates 2.54 times per revolution. A shield mask is set at 100mm below the substrate and is pre-processed into a designed shape to form a film of uniform thickness on the substrate. During film formation, the substrate can be heated by a substrate heating mechanism. The film formation rate is monitored using a film thickness monitor placed at the center of the revolution plane of the substrate, and a mechanism for controlling the current value of resistance heating so that the film formation rate is constant is provided.

[0092] During the film formation, the pressure in the vacuum chamber was 5.0×10 -5 Pa, and the substrate temperature is 280°C. According to the film design shown in Table 1, the vapor deposition material is continuously formed into a film with a predetermined thickness. For YbF3, the film formation rate is controlled to be 0.6nm / s, for AlF3, the film formation rate is controlled to be 0.2nm / s, for LaF3, the film formation rate is controlled to be 0.2nm / s, or for MgF2, the film formation rate is controlled to be 0.2nm / s. Each of the YbF3, LaF3, AlF3 and MgF2 dielectric layers has a tensile stress.

[0093] Density (theoretical density) in LaF3 is 5.9 g / cm 3 , 2.9 g / cm in AlF3 3 , 3.2 g / cm in MgF2 3 , or 8.2 g / cm in YbF3 3 The melting point is 1490°C in LaF3, 1040°C in AlF3, 1248°C in MgF2, or 1159°C in YbF3.

[0094] The refractive index of the film formed under the above film forming conditions is 1.69 for LaF3, 1.41 for AlF3, 1.44 for MgF2, or 1.68 for YbF3. These refractive indices are for light having a wavelength of 193 nm.

[0095] The refractive index of each material was calculated as follows. A single layer film of each material with a thickness ranging from 50 to 100 nm was formed on a fluorite substrate of φ15 mm×2 mmt, and the reflectivity was measured using a spectrometer at a light incident angle of 15 degrees in a wavelength range of 180 to 240 nm. The optical thin film analysis and design software FilmWizard was used. TM The reflectivity was analyzed and the refractive index of the single layer film was calculated.

[0096] The YbF3 film formed by the vapor deposition method has a refractive index of about 1.63 when formed at a standard film formation rate. The inventors of the present invention have found through extensive research that at a higher film formation rate, the refractive index can be increased to 1.65 or greater, for example, 1.68, for a wavelength of 193nm. The inventors of the present invention have found that a YbF3 film formed at 0.6nm / s using a vapor deposition device with a standard film formation rate of 0.2nm / s can have a refractive index of 1.68. Although the reason for the greatly increased refractive index of the YbF3 film formed by the vapor deposition method at an increased film formation rate is unclear, this high-speed film formation can prevent the mixing of impurities. Therefore, in an optical component including a substrate and an ytterbium fluoride layer located on the substrate, the ytterbium fluoride layer can have a refractive index of 1.65 or greater for light with a wavelength of 193nm. For light with a wavelength of 193nm, the ytterbium fluoride layer can have a refractive index less than 1.69.

[0097] Metal fluorides may have a surface roughness that depends on the type of compound. For example, as a high refractive index material (refractive index: 1.50 or greater), LaF3 has a surface roughness of 5.8nm RMS, GdF3 has a surface roughness of 6.3nm RMS, SmF3 has a surface roughness of 8.9nm RMS, and YbF3 has a surface roughness of 1.1nm RMS. As a low refractive index material (refractive index: 1.50 or less), AlF3 has a surface roughness of 0.9nm RMS, and MgF2 has a surface roughness of 2.2nmRMS. The surface roughness (RMS) of each monolayer film was measured by AFM using the same vapor deposition apparatus, wherein the substrate was placed so that the deposited particles were formed at an incident angle of 70 degrees relative to the substrate, and a monolayer film with a thickness of 100nm was formed.

[0098] Generally, metal fluorides are crystalline, and their crystal grains increase surface roughness. AlF3 is amorphous and has a small roughness. High refractive index materials LaF3, GdF3 and SmF3 have a large roughness (greater than 3.0nm RMS). Although YbF3 is a high refractive index material, the roughness of YbF3 is as small as AlF3, which is amorphous, among the metal fluorides. The high refractive index material of the metal fluoride not described herein is also a crystalline film like LaF3, GdF3 and SmF3, and therefore may have a large surface roughness. Therefore, among the metal fluoride high refractive index materials, YbF3 has a very smooth inherent characteristic.

[0099] The use of YbF3 with a refractive index of 1.68 as a high refractive index layer is studied by changing the logarithm M and the number of layers n. YbF3 is a high refractive index layer with a small roughness, but has a refractive index smaller than the refractive index (1.69) of LaF3. Therefore, YbF3 and LaF3 should be appropriately combined to form a multilayer film. More specifically, YbF3 is used for the high refractive index layer of the multilayer film near the substrate where a relatively small amount of light arrives, and LaF3 is used for the high refractive index layer of the multilayer film near the atmosphere where a large amount of light arrives. In this structure, the YbF3 with a small roughness near the substrate can reduce the roughness of the entire multilayer film mirror, and the LaF3 used for the layer near the atmosphere can increase the theoretical reflectivity. Therefore, a mirror with a high reflectivity can be finally produced.

[0100] Table 1 shows films of type A to C with different numbers of alternating layers of YbF3 / AlF3 and different numbers of alternating layers of LaF3 / AlF3.

[0101] Table 1

[0102]

[0103] Type A

[0104] n / 2 pairs of YbF3 and AlF3, 24-n / 2 pairs of LaF3 and AlF3, and LaF3, MgF2, and LaF3 are stacked in sequence on a fluorite substrate. Table 1 shows the physical thickness of each layer at 193 nm. The physical thickness of each layer makes the optical thickness 26% to 29% of 193 nm.

[0105] Type B

[0106] 24 pairs of LaF3 and AlF3 and LaF3, MgF2 and LaF3 are stacked in sequence on a fluorite substrate. Table 1 shows the physical thickness of each layer at 193 nm. Each layer in type B is formed under the same conditions as the same film type in type A.

[0107] Type C

[0108] 24 pairs of YbF3 and AlF3 and LaF3, MgF2 and LaF3 are stacked in sequence on a fluorite substrate. Table 1 shows the physical thickness of each layer at 193 nm. Each layer in Type C is formed under the same conditions as the same film type in Type A.

[0109] Evaluate

[0110] Table 2 shows the comparison results of the reflectivity and surface roughness of the optical components of Types A, B and C. Table 2 shows the characteristics of Type A for different values ​​of n. Figure 3C The reflectivity characteristics of Type A and B are shown, and at a wavelength of 193 nm, the reflectivity of the mirror of Type A may be approximately 0.7% higher than that of Type B. The reflectivity of each mirror is measured using a spectrometer at a light incident angle of 45 degrees.

[0111] Table 2

[0112] n Reflectivity(%) Surface roughness (nmRMS) Type A 8 97.6 2.4 Type A 16 97.7 1.9 Type A 24 97.6 1.3 Type A 32 97.2 1.3 Type A 40 97.0 1.2 Type B 4 96.9 3.1 Type C 44 96.5 1.1

[0113] Comparing type A with type B, type B has a larger difference between the high refractive index layer and the low refractive index layer, and theoretically has a higher reflectivity. However, the roughness of the top surface measured by AFM is 3.1nm RMS in type B and 2.4nm RMS in type A. Therefore, in type A, the surface roughness of the surface opposite to the substrate of the multilayer film ranges from 1.0 to 3.0nm RMS. Type B has a larger roughness and a larger scattering loss. Therefore, even if type B has a higher theoretical reflectivity, type A with a smaller roughness has a higher actual reflectivity. This may be due to the smaller roughness of YbF3 than other metal fluoride high refractive index films.

[0114] At a refractive index of 1.63, even if the roughness is small, simply replacing the high refractive index layer from LaF3 to YbF3 cannot obtain a reflectivity higher than that of type B. However, when the refractive index can be increased to 1.68, depending on the combination of materials of the dielectric layer, the reflectivity can be higher than type B. In the combination of dielectric layers shown in type A, the reflectivity can be equal to or higher than type B. In contrast, type C, in which all pairs of 48 layers are YbF3 / AlF3 alternating layers, has a small roughness but has a low reflectivity.

[0115] The present exemplary embodiment can reduce the roughness of interfaces and surfaces in a multilayer film, thus providing a mirror for an ultraviolet laser having high reflectivity.

[0116] The present disclosure may provide advantageous techniques for improving the optical characteristics of optical components.

[0117] These embodiments can be modified appropriately without departing from the technical idea.It should be noted that the disclosure of this specification includes not only the contents described herein but also all matters that can be understood from this specification and the drawings attached to this specification.

[0118] The disclosure of this specification also includes the supplement of each concept described herein. More specifically, for example, even if the description "A is not greater than B" is omitted, the description "A is greater than B" in this specification also discloses "A is not greater than B". This is because the description "A is greater than B" takes "A is not greater than B" into consideration as a prerequisite.

[0119] Although the present invention has been described with reference to exemplary embodiments, it is to be understood that the present disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A mirror optical assembly, comprising: substrate; as well as A multilayer film comprising a first layer group located on a substrate and a second layer group located between the first layer group and the substrate, The second layer group includes m first dielectric layers and m second dielectric layers stacked alternately, wherein m is at least 2, The first layer group includes n third dielectric layers and n fourth dielectric layers stacked alternately, wherein n is at least 2, The first dielectric layer has a higher refractive index than the second dielectric layer, The third dielectric layer has a higher refractive index than the fourth dielectric layer, The third dielectric layer has a higher refractive index than the first dielectric layer, The difference between the refractive index of the third dielectric layer and the refractive index of the fourth dielectric layer is greater than the difference between the refractive index of the first dielectric layer and the refractive index of the second dielectric layer, and wherein the first dielectric layer comprises ytterbium fluoride, wherein the first layer group and the second layer group are used to reflect light entering from the side of the multilayer film opposite to the substrate, and Therein, the material used for the first dielectric layer is selected so that the first dielectric layer has a specific surface profile that is flatter than that of the third dielectric layer.

2. The mirror optical assembly according to claim 1, wherein: The first dielectric layer has a different composition than the second dielectric layer, and The first dielectric layer contains a compound of a first metal element, and the third dielectric layer contains a compound of a second metal element different from the first metal element.

3. A mirror optical assembly comprising: substrate; as well as A multilayer film comprising a first layer group located on a substrate and a second layer group located between the first layer group and the substrate, The second layer group includes m first dielectric layers and m second dielectric layers stacked alternately, wherein m is at least 2, The first layer group includes n third dielectric layers and n fourth dielectric layers stacked alternately, wherein n is at least 2, The first dielectric layer has a higher refractive index than the second dielectric layer, The third dielectric layer has a higher refractive index than the fourth dielectric layer, The third dielectric layer has a lower density than the first dielectric layer, wherein the first dielectric layer comprises ytterbium fluoride, wherein the first layer group and the second layer group are used to reflect light entering from the side of the multilayer film opposite to the substrate, and Therein, the material used for the first dielectric layer is selected so that the first dielectric layer has a specific surface profile that is flatter than that of the third dielectric layer.

4. The mirror optical assembly according to any one of claims 1 to 3, wherein: The first metal element is a rare earth element, and The second metal element is a rare earth element.

5. The mirror optical assembly according to any one of claims 1 to 3, wherein: The first dielectric layer comprises a fluoride, and The third dielectric layer includes fluoride.

6. The mirror optical assembly according to any one of claims 1 to 3, wherein: The third dielectric layer includes at least one of neodymium fluoride, lanthanum fluoride, gadolinium fluoride, samarium fluoride, cerium fluoride, and aluminum oxide.

7. The mirror optical assembly according to any one of claims 1 to 3, wherein: The second dielectric layer includes a compound of a metal element, and The fourth dielectric layer includes a compound of a metal element.

8. The mirror optical assembly according to claim 7, wherein: The metal element of the compound in the second dielectric layer is a typical element, and The metal element of the compound in the fourth dielectric layer is a typical element.

9. The mirror optical assembly according to any one of claims 1 to 3, wherein: The second dielectric layer includes a fluoride, and The fourth dielectric layer includes fluoride.

10. The mirror optical assembly according to any one of claims 1 to 3, wherein: Each of the second dielectric layer and the fourth dielectric layer includes at least one of magnesium fluoride, aluminum fluoride, sodium fluoride, lithium fluoride, calcium fluoride, barium fluoride, strontium fluoride, silicon oxide, cryolite, and pyroxene.

11. The mirror optical assembly according to any one of claims 1 to 3, wherein: A surface of the first dielectric layer opposite to the substrate is flatter than a surface of the third dielectric layer opposite to the substrate.

12. The mirror optical assembly according to any one of claims 1 to 3, wherein: the multilayer film comprises i (i≥2) dielectric layers each comprising at least two elements comprised in the first dielectric layer, The multilayer film includes j (j≥2) dielectric layers each containing at least two elements contained in the third dielectric layer, and 0.2≤i / j≤5 is satisfied.

13. The mirror optical assembly according to any one of claims 1 to 3, wherein: The surface of the multilayer film opposite to the substrate has a surface roughness ranging from 1.0 to 3.0 nm RMS.

14. The mirror optical assembly according to any one of claims 1 to 3, wherein: The multilayer film includes a fifth dielectric layer, The first dielectric layer, the second dielectric layer, the third dielectric layer and the fourth dielectric layer are located between the fifth dielectric layer and the substrate, and At least one of (a) and (b) is satisfied: (a) the fifth dielectric layer has a lower refractive index than the third dielectric layer and a higher refractive index than the fourth dielectric layer, and (b) The fifth dielectric layer includes magnesium fluoride.

15. The mirror optical assembly according to any one of claims 1 to 3, wherein: The substrate is single crystal or polycrystalline.

16. The mirror optical assembly according to any one of claims 1 to 3, wherein: The substrate comprises calcium fluoride.

17. An optical device comprising: light source; as well as The mirror optical assembly according to any one of claims 1 to 16, Therein, the mirror optical assembly reflects light from the light source.

18. The optical device according to claim 17, wherein: The light is ultraviolet light.

19. The optical device according to claim 17, further comprising: a first stage configured to support a mask; as well as a second stage configured to support the substrate, Therein, a pattern formed by a light source, mirror optics and a mask is projected onto a substrate.

20. A mirror optical assembly comprising: substrate; as well as A multilayer film on a substrate, wherein the multilayer film comprises a second layer group and a first layer group, the second layer group comprises a first dielectric layer and a second dielectric layer, and the first layer group comprises a third dielectric layer and a fourth dielectric layer, The first dielectric layer is located between the second dielectric layer and the substrate, and the distance between the first dielectric layer and the second dielectric layer is less than the thickness of the first dielectric layer. The third dielectric layer is located between the fourth dielectric layer and the substrate, and the distance between the third dielectric layer and the fourth dielectric layer is less than the thickness of the third dielectric layer. The first dielectric layer comprises ytterbium fluoride, The third dielectric layer includes at least one of neodymium fluoride, lanthanum fluoride, gadolinium fluoride, samarium fluoride, cerium fluoride, and aluminum oxide, and Each of the second dielectric layer and the fourth dielectric layer contains at least one of magnesium fluoride, aluminum fluoride, sodium fluoride, lithium fluoride, calcium fluoride, barium fluoride, strontium fluoride, silicon oxide, cryolite, and pyroxene, wherein the first layer group and the second layer group are used to reflect light entering from the side of the multilayer film opposite to the substrate, and Therein, the material used for the first dielectric layer is selected so that the first dielectric layer has a specific surface profile that is flatter than that of the third dielectric layer.

21. The mirror optical assembly of claim 20, wherein: The first dielectric layer is located between the substrate and the third dielectric layer.

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