Preparation method of ten-micron-level amorphous chalcogenide thin film for superlens

Abstract

The application discloses a preparation method of a ten-micron amorphous chalcogenide film for a superlens, and has the following characteristics: a step of starting an electron beam thermal evaporation deposition system, and loading materials to be evaporated into a crucible with an evaporation hole; a step of vacuumizing the chamber until the chamber pressure is lower than 6.6*10 ‑4 Pa, and then starting a sample stage heating temperature control module, setting the target temperature to be 15-25 DEG C lower than the glass transition temperature of the amorphous chalcogenide material to be evaporated; a step of adjusting the position of a circular spot generated by an electron beam to the center position of the crucible, and then opening a sample stage shutter to evaporate after the evaporation rate is stable, so as to obtain a ten-micron amorphous Ge-Se-Te film, and the method has the advantages of fast speed, stability, high film forming quality, high evaporation efficiency, good film forming quality and the like on the basis of keeping the performance of the original glass material, and can be used for subsequent processing of a micro-nano structure of the superlens.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of semiconductor materials, and particularly relates to a preparation method of a ten-micron amorphous chalcogenide film for a superlens. BACKGROUND

[0002] Micro-nano integration of optical systems is an important trend in the development of new generation information technology. Planar superlenses composed of subwavelength nanostructures can overcome most of the existing challenges and provide a revolutionary technology for the miniaturization of imaging systems. Chalcogenide glasses belong to a large category of inorganic non-oxide glass materials, which have excellent mid-infrared optical properties. They are widely used in phase change memory, infrared thermal imaging technology, infrared detectors, optical waveguides and other fields. Amorphous chalcogenide materials can also meet the material requirements of super surface lens in the far infrared band. They have high refractive index, high transmittance, low thermal expansion coefficient and low refractive index temperature coefficient in theory.

[0003] In the preparation of amorphous chalcogenide materials for mid-infrared superlenses, there are two methods. One is to directly prepare micro-nano structures on a suitable substrate, but the focusing efficiency of the superlens made by this method is relatively low. The second method is to coat a thin film of mid-infrared material on a low refractive index substrate for micro-nano processing. This method has the characteristics of low reflection loss and high focusing efficiency. Therefore, it is necessary to prepare chalcogenide glass bulk material into a thin film on a substrate for the next step of superlens micro-nano structure processing.

[0004] Amorphous chalcogenide films can usually be prepared by conventional thin film preparation techniques, including thermal evaporation, magnetron sputtering, chemical vapor deposition, sol-gel and laser pulse deposition. However, the above-mentioned thin film preparation methods have certain disadvantages. For example, thermal evaporation may cause the material to vaporize into a mixture of different compounds or single elements, resulting in a large deviation between the actual composition of the thin film and the composition of the original material. Although the composition deviation is small and the thickness control is accurate in magnetron sputtering, it is difficult to quickly coat the required thickness due to the need for thick films (theoretically, continuous sputtering for several days is required), which has the problems of low efficiency and high cost. Chemical vapor deposition requires materials that can react in a gaseous state, which has a large limitation. The sol-gel method produces thin films with poor density and poor quality. Laser pulse deposition is prone to particle defects and high loss, which is not conducive to large-area thin film preparation. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a preparation method of a ten-micron amorphous chalcogenide film for a superlens, which has a fast rate, is stable and has high film quality.

[0006] The application solves the above technical problems by adopting the technical scheme of a preparation method of a ten-micron amorphous chalcogenide film for a superlens, comprising the following steps:

[0007] (1) The substrate is sequentially cleaned in an ultrasonic cleaner using isopropyl alcohol, anhydrous ethanol and deionized water for 10 minutes, and then dried with a nitrogen gun, and cleaned and dried for storage;

[0008] (2) The electron beam thermal evaporation deposition system is started, the substrate is fixed to the sample table of the chamber, and then the covered crucible containing the amorphous Ge-Se-Te material is placed in the crucible groove of the chamber, and a plurality of evaporation holes are arranged on the cover;

[0009] (3) The vacuum system is started to perform vacuum treatment on the chamber until the chamber pressure is lower than 6.6*10 -4 Pa;

[0010] (4) The sample table heating and temperature control module of the electron beam thermal evaporation deposition system is started, the target temperature is set to be 15-25℃ lower than the glass transition temperature of the amorphous Ge-Se-Te material to be evaporated, the heating current is adjusted to 1.2A, and the sample table temperature is raised to the target temperature;

[0011] (5) The electron beam control system is started, the filament is preheated, the filament preset current is set to 0.5A, the electron gun high voltage button is turned on, the control electron gun high voltage number is 8.11, the electron beam current number is 0.007-0.011, the filament voltage is 81.5-82.5V, and the filament current is 1.2A, and the electron gun generates an electron beam;

[0012] (6) The circular spot position of the electron beam is adjusted to the center position of the crucible, pre-evaporation is performed for 5-10 minutes, after the film thickness instrument shows that the evaporation rate is stable, the sample table shutter is opened for evaporation, the evaporation time is controlled to be 10-20 minutes, after evaporation, the electron beam control system, the sample table heating and temperature control module and the vacuum system are sequentially turned off, and after the sample table temperature naturally cools down to room temperature, a ten-micron amorphous chalcogenide film is obtained.

[0013] Further, the substrate is any one of a silicon wafer, a quartz wafer, NaCl and BaF2.

[0014] Further, the evaporation holes are uniformly distributed on the cover.

[0015] Further, the cover uniformly distributes eight evaporation holes with a diameter of 3mm on a concentric circle with a center radius of 8mm.

[0016] Further, the amorphous Ge-Se-Te material is Ge 20 Se 20 Te 60.

[0017] Further, the material of the crucible and the cover is tungsten, which has low cost and enough quality to avoid the vapor to open the cover during evaporation.

[0018] Compared with the prior art, the preparation method of the ten-micron-level amorphous Ge-Se-Te film for a superlens has the advantages that the film is evaporated by the electron beam thermal evaporation method. The electron beam thermal evaporation technology uses a high-energy electron beam to quickly and accurately heat raw materials, and can provide very high heat for the to-be-evaporated raw materials, so the evaporation rate is very fast. The electron beam positioning is accurate, which can avoid the evaporation of the crucible material and eliminate the film pollution, and greatly improve the film quality. However, the general evaporation object of the electron beam is metal, and the melting temperature is much higher than the glass transition temperature and the melting temperature of amorphous Ge-Se-Te, so the electron beam directly hitting the amorphous Ge-Se-Te material will cause the rate to be too fast to control the film thickness, and the too fast evaporation rate will affect the film quality and increase unnecessary residual stress. On this basis, the crucible cover with an evaporation hole designed by the applicant is added, which can effectively control the problem of too fast evaporation of the amorphous Ge-Se-Te material and improve the film quality. In addition, the electron beam energy is large enough, and compared with the traditional thermal evaporation and magnetron sputtering method, the evaporation rate is faster. At the same time, the film is in-situ annealed during evaporation, the temperature of the film during evaporation is maintained at a suitable annealing temperature, and then the film is naturally cooled to remove residual stress. The technology maintains the performance of the glass raw material, so that the film maintains good characteristics in the subsequent micro-nano processing process.

[0019] In summary, the preparation method of the ten-micron-level Ge-Se-Te film for a superlens is provided, the cover with the evaporation hole is added to the crucible containing the evaporation material, the in-situ annealing process is performed during evaporation, and the electron beam thermal evaporation deposition method is used to prepare the ten-micron-level thickness of the amorphous Ge-Se-Te film, so that the film with stable composition and high film quality is obtained, the performance of the original glass material is maintained, and the film has the characteristics of high evaporation efficiency and good film quality, and can be used for subsequent processing of the micro-nano structure of the superlens. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The schematic diagram of the crucible suitable for the electron beam evaporation deposition system of the embodiment is shown in the figure;

[0021] Figure 2 The schematic diagram of the cover of the crucible suitable for the embodiment is shown in the figure;

[0022] Figure 3 The Ge 20 Se 20 Te 60Microscope (bright field) image of the film surface after evaporation;

[0023] Figure 4 Ge 20 Se 20 Te 60 Microscope (dark field) image of the film surface after evaporation;

[0024] Figure 5 Ge 20 Se 20 Te 60 X-ray diffraction (XRD) test pattern of the film;

[0025] Figure 6 Ge 20 Se 20 Te 60 Cross-sectional image of the film under scanning electron microscope (SEM) observation;

[0026] Figure 7 Ge 20 Se 20 Te 60 Energy dispersive X-ray spectroscopy (EDS) test pattern of the film;

[0027] Figure 8 Ge 20 Se 20 Te 60 Refractive index and absorption coefficient pattern of the film tested by infrared variable angle spectroscopic ellipsometry;

[0028] Figure 9 Ge 20 Se 20 Te 60 Raman spectroscopy pattern of the film tested by Raman spectrometer;

[0029] Figure 10 Ge 20 Se 20 Te 60 Transmittance spectrum (1000~2500nm) of the film tested by spectrophotometer;

[0030] Figure 11 Ge 20 Se 20 Te 60 Transmittance spectrum (1000~2500nm) of the glass tested by spectrophotometer;

[0031] Figure 12 Ge 20 Se 20 Te 60 Transmittance spectrum (2.5~25µm) of the film tested by Fourier infrared spectrometer;

[0032] Figure 13 Ge for Ge 20 Se for Se 20 Te for Te 60 The Fourier infrared spectrometer of the glass tests the transmission spectrum (0~25µm);

[0033] Figure 14 Ge for Ge 20 Se for Se 20 Te for Te 60 The dilatometer of the glass tests the thermal expansion coefficient-temperature change graph. DETAILED DESCRIPTION

[0034] The application will be described in further detail below with reference to the embodiments and the accompanying drawings. I. Embodiments

[0036] A ten-micron amorphous chalcogenide film for a superlens is prepared using a high-vacuum electron beam evaporation thin film deposition system (Shenyang Keyi, Model DZS500) for alloy electrode applications, and the specific material used is Ge 20 Se 20 Te 60 The evaporation material is loaded into a crucible (see Figure 1 ), and a cover with holes (see Figure 2 ) is placed on it, and the preparation method steps are as follows:

[0037] (1) The substrate is cleaned in an ultrasonic cleaner with isopropanol, anhydrous ethanol, and deionized water for 10 minutes, and then dried with a nitrogen gun. After washing, it is dried and stored;

[0038] (2) Turn on the electron beam thermal evaporation deposition system, fix the substrate to the sample stage in the chamber, and then place the crucible with the amorphous chalcogenide material in the chamber crucible slot, and set several evaporation holes on the cover;

[0039] (3) Turn on the vacuum system to perform vacuum treatment on the chamber until the chamber pressure is lower than 6.6*10 -4 Pa;

[0040] (4) Then turn on the sample stage heating and temperature control module of the electron beam thermal evaporation deposition system, set the target temperature to be 15-25℃ lower than the glass transition temperature of the amorphous chalcogenide material to be evaporated, adjust the heating current to 1.2A, and wait until the sample stage temperature rises to the target temperature; wherein the glass transition temperature of Ge 20 Se 20 Te 60 is 145℃, and the target temperature is set to 120℃;

[0041] (5) Turn on the electron beam control system, and perform filament presetting. Set the filament presetting current to 0.5 A, turn on the electron gun high voltage button, and rotate the power knob (the filament voltage and current will rise accordingly) until the electron gun high voltage reading is 8.1 (that is, 8000 V, if the electron beam energy is too large, the instrument is easy to be damaged, and if the electron beam energy is too small, the electron beam cannot be generated), the electron beam current reading is 0.011, the filament voltage reading is 82.0 V, and the filament current is 1.2 A (this is a relatively stable evaporation intensity range for amorphous sulfur materials, and too large an intensity will cause rapid evaporation, and the molten material will splash, and too small an intensity will result in low evaporation efficiency), at this time the electron gun generates an electron beam;

[0042] (6) After the electron gun generates an electron beam, a circular light spot appears on the experimental platform. Observe and adjust the light spot position to be at the center of the crucible. Pre-evaporate for 10 minutes, and then open the sample stage shutter to start evaporation after the film thickness meter shows that the evaporation rate is stable (the reading fluctuation is less than 0.1 angstrom). Evaporate for 20 minutes, then turn off the electron beam control system, the sample stage heating and temperature control module, and the vacuum pumping system. After the sample stage temperature naturally cools to room temperature, a ten-micron-level Ge 20 Se 20 Te 60 amorphous thin film is obtained.

[0043] The evaporation holes are uniformly distributed on the cover, that is, the cover uniformly distributes eight evaporation holes (circular holes) with a diameter of 3 mm on a concentric circle with a center radius of 8 mm. The materials of the crucible and the cover are tungsten, which is low in cost and has sufficient quality to avoid the vapor from opening the cover during evaporation. The substrate can be any one of a silicon wafer, a quartz wafer, NaCl, and BaF2.

[0044] II. Analysis of experimental results

[0045] The performance of the above-mentioned thin film is tested and explained as follows:

[0046] 1. The surface quality of the thin film is shown in FIGS. 1 and 2. The thin film surface is clean under bright field and only a few small white spots can be seen under dark field, which is caused by unavoidable pollution when placing the substrate. The thin film surface is clean overall, and has a sufficient area for superlens superstructure surface construction. Figure 3 Figure 4 2. The film thickness is measured using a step meter. Five different positions are measured, and the average value of the data is calculated. The calculated thickness is 9.57 µm, which meets the ten-micron-level thickness requirement, and is more efficient than other commonly used amorphous sulfur coating technologies.

[0047] 2. The film thickness is measured using a step meter. Five different positions are measured, and the average value of the data is calculated. The calculated thickness is 9.57 µm, which meets the ten-micron-level thickness requirement, and is more efficient than other commonly used amorphous sulfur coating technologies.

[0048] ​3. X-ray diffraction (XRD) confirmed that the thin film is amorphous, such as... Figure 5 As shown in the figure, no sharp diffraction peaks appear, which indicates that the film is indeed amorphous and there is no crystallization phenomenon.

[0049] 4. Cut the sample film and observe the cross-section of the film using a scanning electron microscope (SEM), such as... Figure 6 As shown in the figure, the cross-section of the film is very uniform and clean, with no obvious delamination. This also verifies that the film thickness is consistent with the data measured by the profilometer.

[0050] 5. Figure 7 The distribution of thin film components measured by X-ray energy dispersive spectroscopy (EDS) is shown. In this embodiment, the ratio of each atomic content Ge:Te:Se is shown in Table 1. It is close to the ratio of the original evaporated glass material (20:60:20) with a small error. Compared with the traditional thermal evaporation method, it has the advantage of more precise component control.

[0051] Table 1

[0052]

[0053] 6. The refractive index of the thin film was tested using an ellipsometer, such as... Figure 8 As shown, it is easy to see that in the mid-infrared band (8-12μm), the refractive index of the thin film is higher than 3.0, and its high refractive index characteristic meets the requirements for fabricating superlenses.

[0054] 7. Raman spectroscopy was used to test the bonding between various atoms, such as... Figure 9 As shown in the figure, there are clearly three vibrational peaks, which, from left to right, correspond to the corner-sharing (CS) GeTe4 tetrahedral structure, Te... n Vibrations of GeTe4 tetrahedral structures with chain-like and edge-sharing (ES) structures.

[0055] 8. The transmittance of the thin film and glass raw materials in the near-infrared band (1000~2500nm) was measured using a spectrophotometer. The thin film substrate was a quartz sheet. Figure 10 , Figure 11 As shown, the transmittance of the two films is similar, but because the film is thicker, the interference is greater, thus producing a wave pattern.

[0056] 9. The transmittance of the thin film sample and the glass raw material in the mid- and far-infrared bands was measured using a Fourier transform infrared spectrometer. The thin film substrate was NaCl. Figure 12 , Figure 13As shown, similarly, the transmittance of both is similar, because the film is thicker, the interference is larger, so the fluctuation pattern is generated, and it can be seen that the transmittance in the middle and far infrared wave band is also good, and it can be used for the preparation of superlenses.

[0057] 10. The thermal expansion coefficient a of the thin film original glass material is tested by using a thermal dilatometer, from which it can be seen that the order of magnitude is 10 Figure 14 -6 / °C, which is much smaller than that of the substrate. -5 Therefore, the evaporation is carried out on the low-refractive infrared material substrate such as BaF2, so that the thermal expansion coefficients of the two match, and the phenomenon of excessive stress leading to film cracking does not occur.

[0058] The above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or replacements made by ordinary skilled in the art within the essential scope of the present application shall also belong to the protection scope of the present application.

Claims

1. A method for preparing a ten-micrometer-scale amorphous chalcogenide thin film for superlenses, characterized in that... Includes the following steps: (1) The substrate was cleaned in an ultrasonic cleaner for 10 minutes in sequence with isopropanol, anhydrous ethanol and deionized water, and then dried with a nitrogen gun. After cleaning, it was dried and stored. (2) Turn on the electron beam thermal evaporation deposition system, fix the substrate to the sample stage of the chamber, and then place the lidded crucible containing amorphous chalcogenide material into the crucible tank of the chamber. The lid has several evaporation holes, wherein the lid has eight evaporation holes with a diameter of 3 mm evenly distributed on a concentric circle with a central radius of 8 mm. The amorphous chalcogenide material is Ge. 20 Se 20 Te 60 ; (3) Turn on the vacuum system to evacuate the chamber until the chamber pressure is below 6.6*10. -4 Pa; (4) Turn on the sample stage heating and temperature control module of the electron beam thermal evaporation deposition system, set the target temperature to be 15-25°C lower than the glass transition temperature of the amorphous chalcogenide material to be deposited, and adjust the heating current to 1.2A to make the sample stage temperature rise to the target temperature. (5) Turn on the electron beam control system to preheat the filament, set the filament preset current to 0.5A, turn on the electron gun high voltage button, control the electron gun high voltage reading to 8.11, the electron beam current reading to 0.007-0.011, the filament voltage to 81.5-82.5V, the filament current to 1.2A, and the electron gun to generate an electron beam; (6) Adjust the position of the circular spot generated by the electron beam to the center of the crucible, pre-deposit for 5-10 minutes, and after the film thickness gauge shows that the deposition rate is stable, open the sample stage baffle to perform deposition, control the deposition time to 10-20 minutes, and after the deposition is completed, turn off the electron beam control system, the sample stage heating temperature control module and the vacuum system in sequence, and wait for the sample stage temperature to naturally cool down to room temperature to obtain a ten-micron amorphous chalcogenide film.

2. The method for preparing a ten-micrometer-scale amorphous chalcogenide thin film for a superlens according to claim 1, characterized in that: The substrate is any one of silicon wafer, quartz wafer, NaCl, and BaF2.

3. The method for preparing a ten-micrometer-scale amorphous chalcogenide thin film for a superlens according to claim 1, characterized in that: Both the crucible and the lid are made of tungsten.

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