Mg2Si / Sc multilayer film reflector and preparation method thereof

Abstract

The invention relates to the technical field of optical thin film manufacturing, in particular to an Mg2Si / Sc multilayer film reflector and a preparation method thereof. The structure comprises a substrate, a periodic multilayer film and a cap layer which are tightly stacked in sequence from bottom to top, the periodic multilayer film comprises magnesium silicide films and scandium films which are alternately overlapped, the first layer is the magnesium silicide film, and the last layer is the scandium film; in one period of the periodic multilayer film, the thickness of the magnesium silicide film is 13-18nm, and the thickness of the scandium film is 7-12nm; the material of the cap layer is magnesium silicide, and the thickness of the cap layer is 2-4 nm. The number of cycles is 18-25, and the thickness of each cycle is 20-30 nm. The Mg2Si / Sc multilayer film reflector has the advantages that the Mg2Si / Sc multilayer film reflector is smaller in interface roughness, higher in reflectivity at 46.5 nm, narrower in bandwidth, better in out-of-band reflectivity inhibition capability, excellent in periodic structure, clear in interface, smaller in interface diffusion and better in stability.

Description

Technical Field

[0001] The invention relates to the technical field of optical thin film manufacturing, and in particular to a Mg2Si / Sc multilayer film reflecting mirror and a preparation method thereof. Background Art

[0002] Solar activity has a profound impact on the survival and life of organisms on Earth. Human space exploration and research on solar activity is an important research content of space physics. Solar activity includes solar eruptions, coronal mass ejections, prominences and solar wind. The sun is divided into the photosphere, chromosphere, transition layer and corona according to the activity area. Among them, the transition layer is the key factor in the transfer of matter and energy between the quiet solar atmosphere and the solar eruption. The temperature of the transition layer is 0.02~0.8 MK. It is a dynamic and inhomogeneous region with drastic changes in the magnetic field. The VII 46.5nm of the neon element is the strongest emission line in the transition region, corresponding to a temperature of about 0.5MK, and has extremely high observation value. The 46.5nm extreme ultraviolet solar imager (Solar Upper Transition Region Imager, SUTRI) launched by my country in 2022 observes the 46.5nm spectral line and obtains better solar images.

[0003] The extreme ultraviolet multilayer reflector is one of the key optical components of the short-wave space detection payload. It plays the role of reflecting the detection spectrum and filtering. That is, the reflector is required to have a high reflectivity at the working wavelength, a narrow bandwidth, and a low reflectivity outside the band. In addition, there are a large number of high-energy particles in the space environment, and the multilayer film is also required to be resistant to high-energy particle irradiation and have good stability. In the SUTRI payload, the material pair used for the extreme ultraviolet multilayer reflector is Si / Sc, and the ratio of the Sc film thickness in the period is 0.283. The theoretical reflectivity at 46.5nm is about 50.0%, and the bandwidth is about 4.7nm. However, the actual measured reflectivity is only about 30.0%, and the bandwidth is about 3.7nm. The bandwidth of the multilayer film is slightly wider, and the theoretical reflectivity of the frequency doubling (25.0nm) processing reaches 21.5%. The reflectivity is high in the long-wave band, and the reflectivity suppression outside the band is poor. This is because Sc is an active metal, and there is a large interface diffusion with Si, and the interface roughness is about 0.75nm / 1.11nm. The Si / Sc material combination was first proposed by Uspenskii in 1998. In response to the large interface diffusion and stability issues between Si and Sc film layers, people subsequently proposed using W, B4C, ScN, CrB2, Cr, and C as spacer / buffer layers to regulate their interfaces, and their thermal stability was improved to a certain extent, but the reflective performance was still not improved. Summary of the invention

[0004] To solve the above problems, the present invention provides a Mg2Si / Sc multilayer mirror and a preparation method thereof.

[0005] The first object of the present invention is to provide a Mg2Si / Sc multilayer mirror, which includes a substrate, a periodic multilayer film and a capping layer that are tightly stacked in sequence from bottom to top; The periodic multilayer film includes alternately stacked magnesium silicide films and scandium films. The first layer is a magnesium silicide film and the last layer is a scandium film. Within one period of the periodic multilayer film, the thickness of the magnesium silicide film is 13 - 18 nm, and the thickness of the scandium film is 7 - 12 nm; The capping layer is made of magnesium silicide and has a thickness of 2 - 4 nm.

[0006] Preferably, the number of periods of the periodic multilayer film is 18 - 25, and the thickness of each period is 20 - 30 nm.

[0007] Preferably, the thickness of each period of the periodic multilayer film is 24.9 nm.

[0008] Preferably, the substrate is a fused silica substrate, a glass substrate or a silicon substrate.

[0009] Preferably, the substrate is a fused silica substrate with a roughness less than 0.8 nm.

[0010] The second object of the present invention is to provide a preparation method of a Mg2Si / Sc multilayer mirror, which specifically includes the following steps: S1. Substrate cleaning and detection: The substrate is ultrasonically cleaned and then centrifugally dried; the number of particles attached to the substrate is detected to ensure that the number of particles with a diameter exceeding 300 nm per square millimeter is less than 10. S2. Substrate coating: Using the DC magnetron sputtering method, magnesium silicide films and scandium films are alternately deposited on the substrate to form a periodic multilayer film; then a capping layer is deposited on the surface of the periodic multilayer film to obtain a Mg2Si / Sc multilayer mirror.

[0011] Preferably, in step S1, the ultrasonic cleaning frequency is 30 - 50 kHz, and the centrifugal speed is 2500 - 3500 rpm.

[0012] Preferably, the coating parameters of DC magnetron sputtering in step S2 are as follows: the coating power of both the magnesium silicide film and the capping layer is 70 - 80 W, and the deposition rate is 0.01 - 0.03 nm / s; the coating power of the scandium film is 45 - 55 W, and the deposition rate is 0.04 - 0.06 nm / s; the purity of the magnesium silicide and scandium target materials is ≥99.9%.

[0013] Preferably, the working gas for DC magnetron sputtering is Ar gas, and the purity of Ar gas is ≥99.99%; the vacuum value is lower than 5×10 -4 Pa; the working gas pressure is ≤0.1 Pa.

[0014] Compared with the prior art, the present invention can achieve the following beneficial effects: The present invention provides an extreme ultraviolet Mg2Si / Sc multilayer mirror, which has the characteristics of narrow bandwidth, second harmonic generation and low reflectivity at long wavelengths. The theoretical reflectivity of the Mg2Si / Sc multilayer is only 10.7% at the second harmonic of 23.7 nm and only 4.8% at 100 nm. Mg2Si / Sc has better out-of-band reflectivity suppression ability than the Si / Sc multilayer. The reflectivity of the Mg2Si / Sc multilayer mirror is about 22.7% at 46.5 nm, and the bandwidth is only 3.4 nm. Compared with Si / Sc, Mg2Si / Sc has a smaller interface roughness, only 1 / 4 of that of Si / Sc. The Mg2Si / Sc material has an excellent periodic structure, clear interfaces, small interface diffusion, and good stability. Description of the Drawings

[0015] Figure 1 is a schematic cross-sectional structure diagram of the Mg2Si / Sc multilayer mirror provided by an embodiment of the present invention.

[0016] Figure 2 is the theoretical reflectivity result of the Mg2Si / Sc multilayer mirror provided by an embodiment of the present invention and the Si / Sc multilayer mirror provided by the comparative example.

[0017] Figure 3 is the measured reflectivity diagram of the Mg2Si / Sc multilayer mirror provided by an embodiment of the present invention.

[0018] Figure 4 is the transmission electron microscope (TEM) analysis diagram of the Mg2Si / Sc multilayer mirror provided by an embodiment of the present invention.

[0019] Figure 5 is the small-angle X-ray diffraction diagram of the Mg2Si / Sc multilayer mirror provided by an embodiment of the present invention.

[0020] Reference Signs: 1. Substrate; 2. Periodic Multilayer; 201. Magnesium Silicide Film; 202. Scandium Film; 3. Capping Layer. Detailed Embodiments

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same modules are denoted by the same reference signs. In the case of the same reference signs, their names and functions are also the same. Therefore, their detailed descriptions will not be repeated.

[0022] To make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

[0023] The present invention provides a Mg2Si / Sc multilayer mirror, which includes a substrate, a periodic multilayer film and a cap layer that are tightly stacked in sequence from bottom to top; Specifically, the substrate is a fused silica substrate, a glass substrate or a silicon substrate; the roughness of the substrate is less than 0.8 nm; In a specific embodiment, the substrate is a fused silica substrate, which is ultrasonically cleaned at an ultrasonic frequency of 40 kHz; dried by centrifugation at a rate of 3000 rpm; the cleaned substrate is inspected with a dark field microscope, and if there are less than 10 particles with a diameter exceeding 300 nm per square millimeter, it is considered qualified.

[0024] The periodic multilayer film includes alternately stacked magnesium silicide (Mg2Si) films and scandium (Sc) films. The first layer is a magnesium silicide film, and the last layer is a scandium film; the number of periods of the periodic multilayer film is 18 - 25, the thickness of each period is 20 - 30 nm, and the scandium film accounts for 37 - 40% of the period thickness; that is, within one period, the thickness of the magnesium silicide film is 13 - 18 nm, and the thickness of the scandium film is 7 - 12 nm; In a specific embodiment, the number of periods of the periodic multilayer film is 20, the period thickness is 24.9 nm, and Sc accounts for 0.381 of the period thickness. Within one period, the thickness of Sc is 9.5 nm, and the thickness of Mg2Si is 15.4 nm.

[0025] The material of the cap layer is magnesium silicide, and the thickness is 2 - 4 nm; in a specific embodiment, the thickness of the cap layer is 3 nm.

[0026] A method for preparing a Mg2Si / Sc multilayer mirror specifically includes the following steps: S1. Substrate cleaning and detection: The substrate is ultrasonically cleaned and then centrifugally dried; the number of particles attached to the substrate is detected to ensure that the number of particles with a diameter exceeding 300 nm per square millimeter is less than 10; Specifically, the ultrasonic cleaning frequency is 30 - 50 kHz, and the centrifugal rate is 2500 - 3500 rpm; a dark field microscope is used to detect the number of particles attached to the substrate; in a specific embodiment, the ultrasonic cleaning frequency is 40 kHz, and the centrifugal rate is 3000 rpm.

[0027] S2. Substrate coating: Using the direct current magnetron sputtering method, magnesium silicide films and scandium films are alternately laminated on the substrate to form a periodic multilayer film; then a cap layer is coated on the surface of the periodic multilayer film to obtain a Mg2Si / Sc multilayer mirror; Specifically, the coating parameters of DC magnetron sputtering are as follows: the coating power of magnesium silicide film and capping layer is both 70 - 80W, and the deposition rate is both 0.01 - 0.03nm / s; the coating power of scandium film is 45 - 55W, and the deposition rate is 0.04 - 0.06nm / s; the working gas is Ar gas, and the purity of Ar gas ≥ 99.99%; -4 the vacuum value is lower than 5×10 Pa; the working pressure ≤ 0.1Pa; the purity of magnesium silicide and scandium targets ≥ 99.9%;

[0028] In a specific embodiment, the coating power of magnesium silicide film and capping layer is both 75W, and the deposition rate is both 0.02nm / s; the coating power of scandium film is 50W, and the deposition rate is 0.05nm / s.

[0029] Embodiment 1 This embodiment provides a Mg2Si / Sc multilayer mirror. Referring to Figure 1 the structural schematic diagram, from bottom to top, it includes a substrate 1, a periodic multilayer film 2 and a capping layer 3 stacked closely in sequence; The used substrate 1 is fused quartz; The periodic multilayer film 2 includes alternately stacked magnesium silicide films 201 and scandium films 202; the first layer is a magnesium silicide film 201, and the last layer is a scandium film 202. The two materials are alternately stacked to form a periodic film system; the number of periods is 20, the period thickness is 24.9nm, and Sc accounts for 0.381 of the period thickness; within one period, the thickness of the magnesium silicide film 201 is 15.4nm, and the thickness of the scandium film 202 is 9.5nm; The material of the capping layer 3 is Mg2Si, and the thickness is 3.0nm.

[0030] The preparation method specifically includes the following steps: S1. Substrate cleaning and detection: The substrate 1 is ultrasonically cleaned and then centrifugally dried; the frequency of ultrasonic cleaning is 40kHz, and the centrifugal rate is 3000rpm; a dark field microscope is used to detect the number of particles attached to the substrate 1, ensuring that the number of particles with a diameter exceeding 300nm per square millimeter is less than 10; S2. Substrate coating: Using the DC magnetron sputtering method, magnesium silicide films and scandium films are alternately deposited on the substrate to form a periodic multilayer film; then a capping layer is deposited on the surface of the periodic multilayer film to obtain a Mg2Si / Sc multilayer mirror; The coating parameters of DC magnetron sputtering are as follows: the coating powers of magnesium silicide film and capping layer are both 75 W, and the deposition rates are both 0.02 nm / s; the coating power of scandium film is 50 W, and the deposition rate is 0.05 nm / s; the working gas is Ar gas, and the purity of Ar gas ≥ 99.99%; the vacuum value is lower than 5×10 -4 Pa; the working gas pressure ≤ 0.1 Pa; the purities of magnesium silicide and scandium targets ≥ 99.9%.

[0031] Figure 2 The theoretical reflectivity curve of the Mg2Si / Sc multilayer mirror is given. The theoretical reflectivity at 46.5 nm is 50%, and the bandwidth is 3.6 nm; the theoretical reflectivity at the second harmonic 23.7 nm is 10.7%, and the theoretical reflectivity at 100 nm is 4.8%.

[0032] Figure 4 The transmission electron microscope (TEM) analysis diagram of the Mg2Si / Sc multilayer mirror is given. Compared with Si / Sc, Mg2Si / Sc has a smaller interface roughness, with values of about 0.4 nm / 0.3 nm, only 1 / 4 of that of Si / Sc.

[0033] Figure 5 The small-angle X-ray diffraction pattern of the Mg2Si / Sc multilayer mirror is given. There are more than 12 diffraction peaks, and the peaks are very sharp. This material has an excellent periodic structure, clear interfaces, small interface diffusion, and good stability.

[0034] The above results show that the extreme ultraviolet Mg2Si / Sc multilayer mirror of the present invention has the characteristics of narrow bandwidth, low reflectivity at the second harmonic and long wavelengths.

[0035] Comparative Example 1 A Si / Sc multilayer mirror was prepared. The difference from Example 1 is that the periodic multilayer film includes alternately stacked silicon films and scandium films; the other preparation conditions are the same as those in Example 1.

[0036] Compare the theoretical reflectivities of the Mg2Si / Sc multilayer mirror and the Si / Sc multilayer mirror. The results are as Figure 2 . It can be seen from the figure that the theoretical reflectivity of the Mg2Si / Sc multilayer film at the second harmonic 23.7 nm is only 10.7%, and the theoretical reflectivity at 100 nm is only 4.8%; while the reflectivity of the Si / Sc multilayer film at the second harmonic 25.0 nm is 21.5%, and the reflectivity at 100 nm is 38.3%. Mg2Si / Sc has better out-of-band reflectivity suppression ability than the Si / Sc multilayer film. At 46.5 nm, the theoretical reflectivities of both are about 50.0%. It shows that the Mg2Si / Sc multilayer mirror of the present invention has more advantages than the commonly used Si / Sc multilayer mirror.

[0037] Figure 3 The measured reflectivity diagram of the Mg2Si / Sc multilayer mirror is given. The reflectivity of the Mg2Si / Sc multilayer mirror is about 22.7% at 46.5 nm, which is comparable to that of the Si / Sc multilayer mirror, and the bandwidth is only 3.4 nm. It is 0.3 nm smaller than the 3.7 nm bandwidth of the Si / Sc multilayer mirror used in the SUTRI payload.

[0038] It should be understood that various forms of the processes shown above can be used, steps can be reordered, added or deleted. For example, the steps recited in the disclosure of the present invention can be executed in parallel, sequentially or in a different order, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and no limitation is made herein.

[0039] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A Mg2Si / Sc multilayer mirror, characterized in that: From bottom to top, it includes a substrate, a periodic multilayer film, and a capping layer that are tightly stacked in sequence; The periodic multilayer film includes alternately stacked magnesium silicide films and scandium films. The first layer is a magnesium silicide film, and the last layer is a scandium film. Within one period of the periodic multilayer film, the thickness of the magnesium silicide film is 13 - 18 nm, and the thickness of the scandium film is 7 - 12 nm; The capping layer is made of magnesium silicide with a thickness of 2 - 4 nm.

2. The Mg2Si / Sc multilayer mirror according to claim 1, characterized in that: The number of periods of the periodic multilayer film is 18 - 25, and the thickness of each period is 20 - 30 nm.

3. The Mg2Si / Sc multi-layer mirror according to claim 2, characterized in that: The thickness of each period of the periodic multilayer film is 24.9 nm.

4. A Mg2Si / Sc multilayer mirror according to claim 1, characterized in that: The substrate is a fused quartz substrate, a glass substrate, or a silicon substrate.

5. The Mg2Si / Sc multilayer mirror according to claim 4, characterized in that: The substrate is a fused quartz substrate with a roughness less than 0.8 nm.

6. The preparation method of a Mg2Si / Sc multilayer mirror according to any one of claims 1-5, characterized in that: Specifically, it includes the following steps: S1. Substrate cleaning and detection: The substrate is ultrasonically cleaned and then centrifugally dried. The number of particles attached to the substrate is detected to ensure that the number of particles with a diameter exceeding 300 nm per square millimeter is less than 10; S2. Substrate coating: Using the direct current magnetron sputtering method, magnesium silicide films and scandium films are alternately laminated on the substrate to form a periodic multilayer film. Then, a capping layer is coated on the surface of the periodic multilayer film to obtain a Mg2Si / Sc multilayer mirror.

7. The preparation method of a Mg2Si / Sc multilayer mirror according to claim 6, characterized in that: In step S1, the frequency of ultrasonic cleaning is 30 - 50 kHz, and the centrifugal speed is 2500 - 3500 rpm.

8. The preparation method of an Mg2Si / Sc multi-layer film mirror according to claim 6, characterized in that: In step S2, the coating parameters of direct current magnetron sputtering are as follows: The coating power of both the magnesium silicide film and the capping layer is 70 - 80 W, and the deposition rate is 0.01 - 0.03 nm / s; the coating power of the scandium film is 45 - 55 W, and the deposition rate is 0.04 - 0.06 nm / s; the purity of the magnesium silicide and scandium target materials is ≥99.9%.

9. The preparation method of a Mg2Si / Sc multilayer mirror according to claim 8, characterized in that: The working gas for the direct current magnetron sputtering is Ar gas, and the purity of the Ar gas is ≥99.99%; The vacuum value is lower than 5×10 -4 Pa; the working air pressure ≤ 0.1 Pa.

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