Mo2C / Ge multilayer film reflector and preparation method thereof

Abstract

The invention relates to the technical field of optical thin film manufacturing, in particular to a Mo2C / Ge 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 germanium films and molybdenum carbide films which are alternately stacked, and the first layer and the last layer are germanium films; in one period of the periodic multilayer film, the thickness of the germanium film is 17-21 nm, and the thickness of the molybdenum carbide film is 7-12 nm; the cap layer is made of molybdenum carbide, and the thickness of the cap layer is 2-4 nm. The number of cycles of the periodic multilayer film is 18-25, and the thickness of each cycle is 24-33 nm. And a direct-current magnetron sputtering method is adopted for alternate lamination preparation. The Mo2C / Ge multilayer film reflector has the advantages that the Mo2C / Ge multilayer film reflector has relatively small interface diffusion and relatively good stability; and meanwhile, the reflectivity at frequency doubling and long wave positions is relatively low, and the out-of-band reflectivity inhibition is better.

Description

Technical Field

[0001] The present invention relates to the technical field of optical thin film manufacturing, and in particular to a Mo2C / Ge multilayer film reflecting mirror and a preparation method thereof. Background Art

[0002] Currently, the mechanisms of solar activity remain controversial. The Sun is divided into the photosphere, chromosphere, transition region, and corona. The transition region, with a temperature ranging from 0.02 MK to 0.8 MK, is a dynamic, inhomogeneous region with drastic magnetic field fluctuations. Existing observations indicate that the transition region is a key factor in the transfer of matter and energy between the quiet solar atmosphere and solar eruptions. The VII 46.5nm emission line of the element neon, corresponding to a temperature of approximately 0.5 MK, is the strongest emission line in the transition region, possessing extremely high observational value. my country's Solar Upper Transition Region Imager (SUTRI), launched in 2022, observes this 46.5nm line and has obtained excellent images of the Sun.

[0003] Multilayer mirrors are key optical components of EUV payloads, reflecting the observed spectral lines and providing partial filtering. The SUTRI payload, which detects the 46.5nm spectral line, utilizes a Si / Sc EUV multilayer mirror with a Sc ratio of 0.283 to the period thickness, a bandwidth of 3.7nm, and a reflectivity of approximately 30% at 46.5nm. The theoretical reflectivity of this film system is 53.1% with a bandwidth of 4.7nm. The significant discrepancy between experimental and theoretical results is primarily due to interfacial diffusion between the Si and Sc layers. The roughness of the Sc and Si layers is approximately 0.75nm and 1.11nm, respectively. The Si / Sc material combination was first proposed by Uspenskii in 1998. Subsequently, researchers have proposed using W, B4C, ScN, CrB2, Cr, and C as spacer / buffer layers to address the significant interfacial diffusion and stability issues between the Si and Sc layers. These interfaces have been manipulated, resulting in some improvements in thermal stability, but the reflectivity performance has remained unchanged. Another drawback of this material combination is that the Sc element is highly reactive and can react with water, posing a significant threat to its optical performance and placing high demands on the storage and operating environment of the multilayer mirror. Its reflectivity at the harmonic frequency of 25.0nm is 21.5%, and at 1000nm it is 38.3%, with a relatively high out-of-band reflectivity. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a Mo2C / Ge multilayer film reflector and a preparation method thereof.

[0005] The first object of the present invention is to provide a Mo2C / Ge multilayer film reflector, which comprises a substrate, a periodic multilayer film and a cap layer stacked closely in sequence from bottom to top; The periodic multilayer film includes alternating germanium films and molybdenum carbide films, with the first and last layers both being germanium films. Within one period of the periodic multilayer film, the thickness of the germanium film is 17 to 21 nm, and the thickness of the molybdenum carbide film is 7 to 12 nm. The cap layer is made of molybdenum carbide with a thickness of 2~4nm.

[0006] Preferably, the number of periods of the periodic multilayer film is 18 to 25, and the thickness of each period is 24 to 33 nm.

[0007] Preferably, the thickness of each period of the periodic multilayer film is 27.7 nm.

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

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

[0010] The second object of the present invention is to provide a method for preparing a Mo2C / Ge multilayer film reflector, which specifically comprises the following steps: S1. Substrate Cleaning and Testing: Ultrasonic cleaning of the substrate followed by centrifugal drying. Detection of particles attached to the substrate to ensure that there are less than 10 particles per square millimeter with a diameter exceeding 300 nm. S2. Substrate coating: Using the DC magnetron sputtering method, germanium films and molybdenum carbide films are alternately stacked on the substrate to form a periodic multilayer film. A cap layer is then plated on the surface of the periodic multilayer film to obtain a Mo2C / Ge multilayer film reflector.

[0011] Preferably, the frequency of ultrasonic cleaning in step S1 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 the molybdenum carbide film and the cap layer are both 80~120W, and the deposition rate is 0.04~0.06nm / s; the coating power of the germanium film is 45~55W, and the deposition rate is 0.03~0.05nm / s; the purity of the germanium and molybdenum carbide targets is ≥99.9%.

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

[0014] Compared with the prior art, the present invention can achieve the following beneficial effects: This invention provides a Mo2C / Ge multilayer reflector and its preparation method. The Mo2C and Ge materials used are commonly used in the extreme ultraviolet (EUV) band. They are chemically stable, inactive, and exhibit minimal interfacial diffusion, thus avoiding the stability issues associated with the use of more reactive metals such as Sc, which react with water. The combination of Mo2C and Ge ensures both reflectivity and stability. Furthermore, the reflectivity is lower at the doubled frequency and long wavelengths, and out-of-band reflectivity is better suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the cross-sectional structure of a Mo2C / Ge multilayer film reflector provided according to an embodiment of the present invention.

[0016] Figure 2 This is a measured reflectivity diagram of the Mo2C / Ge multilayer film reflector provided according to an embodiment of the present invention.

[0017] Figure 3 1. Transmission electron microscope (TEM) images and analysis images of a Mo2C / Ge multilayer film reflector provided according to an embodiment of the present invention; (a) is a transmission electron microscope image; (b) is an analysis image.

[0018] Figure 4 This is an X-ray small-angle diffraction pattern of the Mo2C / Ge multilayer film reflector provided according to an embodiment of the present invention.

[0019] Figure 5 1 is a comparison result of the theoretical reflectivity of the Mo2C / Ge multilayer film reflector provided according to the embodiment of the present invention and the Si / Sc multilayer film reflector provided in the comparative example.

[0020] Reference numerals: 1. base; 2. Periodic multilayer films; 201. Germanium film; 202. Molybdenum carbide film; 3. Cap layer. DETAILED DESCRIPTION

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

[0022] In order to make the purpose, 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 and do not constitute a limitation of the present invention.

[0023] The present invention provides a Mo2C / Ge multilayer film reflector, which comprises a substrate, a periodic multilayer film and a cap layer which are stacked closely in sequence from bottom to top; Specifically, the substrate is a fused quartz substrate, a glass substrate or a silicon substrate; the substrate roughness is less than 0.8 nm; In a specific embodiment, the substrate is a fused quartz substrate, which is cleaned by ultrasonic cleaning at an ultrasonic frequency of 40 kHz; dried by a centrifuge at a speed of 3000 rpm; and the cleaned substrate is inspected using a dark field microscope. The substrate is qualified if there are less than 10 particles with a diameter exceeding 300 nm per square millimeter.

[0024] The periodic multilayer film includes alternating layers of germanium (Ge) and molybdenum carbide (Mo2C) films, with the first and last layers both being germanium films. The periodic multilayer film has 18 to 25 periods, with each period having a thickness of 24 to 33 nm. The MoC film accounts for 29 to 36% of the period thickness; that is, within one period, the Ge film has a thickness of 17 to 21 nm, and the MoC film has a thickness of 7 to 12 nm. In a specific embodiment, the number of periods of the periodic multilayer film is 20, the period thickness is 27.7 nm, and the molybdenum carbide film accounts for 0.315 of the period thickness; within one period, the Ge thickness is 19 nm and the Mo2C thickness is 8.73 nm.

[0025] The cap layer is made of molybdenum carbide and has a thickness of 2-4 nm. In a specific embodiment, the cap layer has a thickness of 3 nm.

[0026] The preparation method of the Mo2C / Ge multilayer film reflector specifically comprises the following steps: S1. Substrate Cleaning and Testing: Ultrasonic cleaning of the substrate followed by centrifugal drying. Detection of particles attached to the substrate to ensure that there are less than 10 particles per square millimeter with a diameter exceeding 300 nm. Specifically, the frequency of ultrasonic cleaning is 30-50 kHz, and the centrifugal speed 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 frequency of ultrasonic cleaning is 40 kHz, and the centrifugal speed is 3000 rpm.

[0027] S2. Substrate Coating: Using DC magnetron sputtering, alternately layer germanium and molybdenum carbide films on a substrate to form a periodic multilayer film. A cap layer is then deposited on the surface of the periodic multilayer film to form a Mo2C / Ge multilayer reflector. Specifically, the DC magnetron sputtering coating parameters are as follows: the coating power of the molybdenum carbide film and the cap layer is 80~120W, and the deposition rate is 0.04~0.06nm / s; the coating power of the germanium film is 45~55W, and the deposition rate is 0.03~0.05nm / s; the working gas is Ar gas, and the purity of Ar gas is ≥99.99%; the vacuum value is less than 5×10-4 Pa; working pressure ≤ 0.1Pa; purity of germanium and molybdenum carbide target ≥ 99.9%; In a specific embodiment, the coating power of the molybdenum carbide film and the cap layer is 100 W, and the deposition rate is 0.05 nm / s; the coating power of the germanium film is 50 W, and the deposition rate is 0.04 nm / s.

[0028] Example 1 This embodiment provides a Mo2C / Ge multilayer film reflector, see Figure 1 A schematic structural diagram of the present invention, comprising, from bottom to top, a substrate 1, a periodic multilayer film 2 and a cap layer 3 that are tightly stacked in sequence; The substrate 1 used was fused quartz; The periodic multilayer film 2 includes alternating stacked germanium films 201 and molybdenum carbide films 202, with the first and last layers both being germanium films 201. The two materials are alternately stacked to form a periodic film system. The number of periods is 20, the period thickness is 27.7 nm, and the molybdenum carbide film 202 accounts for 0.315 of the period thickness. Within one period, the thickness of the germanium film 201 is 19 nm, and the thickness of the molybdenum carbide film 202 is 8.73 nm. The cap layer 3 is made of molybdenum carbide and has a thickness of 3 nm.

[0029] The preparation method specifically comprises the following steps: S1. Substrate Cleaning and Testing: Substrate 1 was ultrasonically cleaned and then centrifuged for drying; the ultrasonic cleaning frequency was 40 kHz and the centrifugal speed was 3000 rpm. The number of particles attached to substrate 1 was determined using dark-field microscopy to ensure that the number of particles with a diameter exceeding 300 nm per square millimeter was less than 10; S2. Substrate Coating: Using DC magnetron sputtering, alternately layer germanium and molybdenum carbide films on a substrate to form a periodic multilayer film. A cap layer is then deposited on the surface of the periodic multilayer film to form a Mo2C / Ge multilayer reflector. The DC magnetron sputtering deposition parameters are as follows: the deposition power for the MoC film and the cap layer is 100 W, and the deposition rate is 0.05 nm / s; the deposition power for the Ge film is 50 W, and the deposition rate is 0.04 nm / s; the working gas is Ar gas, and the purity of Ar gas is ≥99.99%; the vacuum value is less than 5×10 -4 Pa; working gas pressure ≤ 0.1Pa; purity of germanium and molybdenum carbide targets ≥ 99.9%.

[0030] Figure 2 The measured reflectivity of the Mo2C / Ge multilayer mirror is shown in the figure. The results show that the reflectivity of the Mo2C / Ge multilayer mirror is about 30.6% at 46.5nm, which is comparable to that of Si / Sc.

[0031] Figure 3The transmission electron microscope (TEM) images of Mo2C / Ge multilayer mirrors are given ( Figure 3 (a) and analysis diagram ( Figure 3 In (b), compared with Si / Sc, Mo2C / Ge has a smaller interface roughness of about 0.4nm / 0.3nm, which is only 1 / 4 of Si / Sc.

[0032] Figure 4 The X-ray small-angle diffraction pattern of the Mo2C / Ge multilayer mirror is shown, showing more than 12 sharp diffraction peaks. This indicates that the material has an excellent periodic structure, a clear interface, minimal interfacial diffusion, and improved stability.

[0033] Comparative Example 1 The Si / Sc multilayer film reflector is 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.

[0034] Comparing the theoretical reflectivity curves of Mo2C / Ge multilayer reflector and Si / Sc multilayer reflector, the results are as follows Figure 5 As can be seen from the figure, the reflectivity of the Mo2C / Ge multilayer mirror is 6.6% at the double frequency of 24.1nm and 16.5% at 1000nm. The reflectivity of the Si / Sc multilayer is 21.5% at the double frequency of 25.0nm and 38.3% at 1000nm. The theoretical reflectivity curve of the Mo2C / Ge multilayer mirror shows a theoretical reflectivity of 40% at 46.5nm and a bandwidth of 6.7nm. Compared with the Si / Sc multilayer, the Mo2C / Ge multilayer mirror has better out-of-band reflectivity suppression capabilities at the double frequency and long wavelengths.

[0035] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0036] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A Mo2C / Ge multilayer reflector, characterized in that: From bottom to top, it includes a substrate, a periodic multilayer film and a cap layer that are tightly stacked in sequence; The periodic multilayer film includes alternating germanium films and molybdenum carbide films, with the first and last layers both being germanium films. Within one period of the periodic multilayer film, the thickness of the germanium film is 17 to 21 nm, and the thickness of the molybdenum carbide film is 7 to 12 nm. The cap layer is made of molybdenum carbide with a thickness of 2~4nm.

2. The Mo2C / Ge multilayer reflector according to claim 1, characterized in that: The periodic multilayer film has a period number of 18 to 25, and a thickness of each period of 24 to 33 nm.

3. The Mo2C / Ge multilayer reflector according to claim 2, characterized in that: The thickness of each period of the periodic multilayer film is 27.7 nm.

4. The Mo2C / Ge multilayer reflector according to claim 1, characterized in that: The substrate is a fused quartz substrate, a glass substrate or a silicon substrate.

5. The Mo2C / Ge multilayer reflector according to claim 4, characterized in that: The substrate is a fused quartz substrate with a roughness less than 0.8 nm.

6. The method for preparing a Mo2C / Ge multilayer film reflector according to any one of claims 1 to 5, characterized in that: The specific steps include: S1. Substrate Cleaning and Testing: Ultrasonic cleaning of the substrate followed by centrifugal drying. Detection of particles attached to the substrate to ensure that there are less than 10 particles per square millimeter with a diameter exceeding 300 nm. S2. Substrate coating: Using the DC magnetron sputtering method, germanium films and molybdenum carbide films are alternately stacked on the substrate to form a periodic multilayer film. A cap layer is then plated on the surface of the periodic multilayer film to obtain a Mo2C / Ge multilayer film reflector.

7. The method for preparing a Mo2C / Ge multilayer film reflector according to claim 6, characterized in that: The frequency of ultrasonic cleaning in step S1 is 30-50 kHz, and the centrifugal speed is 2500-3500 rpm.

8. The method for preparing a Mo2C / Ge multilayer film reflector according to claim 6, wherein: The DC magnetron sputtering coating parameters in step S2 are as follows: the coating power of the molybdenum carbide film and the cap layer is 80-120 W, and the deposition rate is 0.04-0.06 nm / s; the coating power of the germanium film is 45-55 W, and the deposition rate is 0.03-0.05 nm / s; the purity of the germanium and molybdenum carbide targets is ≥99.9%.

9. The method for preparing a Mo2C / Ge multilayer film reflector according to claim 8, characterized in that: The working gas for the DC magnetron sputtering is Ar gas, and the purity of the Ar gas is ≥99.99%; The vacuum value is less than 5×10 -4 Pa; working pressure ≤0.1Pa.

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