Application of electron beam evaporation -- preparation of TiO2 film by electron beam evaporation
Coating principle electron beam evaporation to prepare TiO2 film, using the INTEGRITY-39 automatic optical coating system with ion beam assisted electron beam evaporation as shown in the figure below.
1. Cooling water inlet; 2. Cooling water outlet; 3. Crucible; 4. Beam coil; 5. Electron beam transmitter; 6. Heating lamp; 7. Substrate frame; 8. The motor; 9. Monitoring film; 10. The working voltage of sample electron gun prepared by ion source plating is 10 kV, the current is 200 A, and the deposition temperature of vacuum chamber is 145 ~ 155℃. Black granular Ti2O3 with a purity of 99.99% was selected for the membrane material. Cc-105 cold cathode ion beam was used for auxiliary deposition. During deposition, the vacuum chamber was filled with O2 with a purity of 99.99% as the reaction gas. Before coating, the substrate is cleaned with glass solution, rinsed with deionized water, and blow-dried with nitrogen. Then, the substrate is cleaned with 99.9% acetone and anhydrous ethanol ultrasonic wave for 15 min each. After drying with special wipe paper, it is loaded into the vacuum chamber. When the vacuum is pumped to 6.5× 10-4pa by mechanical pump and diffusion pump, the automatic plating process is set. When the substrate is heated to the deposition temperature of 150℃, the ion source starts bombarding the substrate, and the energy is controlled at 60 ~ 90 eV for 10 min.
then, the electron gun is automatically started to heat and evaporate the film material, and the deposition rate is 0.38 ~ 0.42 nm/s. When the film is deposited to the design thickness of 440 nm, the program automatically closes the electron gun, and the plating is completed. After coating, the vacuum chamber was naturally cooled to room temperature and the sample was taken out. Spectral test of sample TiO2 was conducted with Lambda900(test range 175 ~ 3 300 nm) spectrophotometer. The actual thickness, extinction coefficient and refractive index of TiO2 film were calculated by Macleod software envelope method. The effects of different vacuum degrees on the film forming quality, refractive index and absorption coefficient of TiO2 were studied with different flows of high purity oxygen into the vacuum chamber. When TiO2 thin film is deposited by evaporation assisted by ion source at a high vacuum degree, the change of vacuum degree with the passage of oxygen is listed in the following table. As the oxygen molecules in the vacuum chamber are ionized into oxygen ions and react with Ti2O3 vapor molecules fully, the oxygen lost in the decomposition of Ti2O3 is replenished, and the resulting TiO2 in the film is relatively pure. However, if the oxygen supply is insufficient or the reaction between Ti2O3 and O2 is insufficient, the high-absorption titanium oxide film tino2n-1 (n=1, 2,... , 10). With the increase of oxygen flux, the collision probability between TiO2 vapor molecules and oxygen molecules in the process of evaporation rise increases and energy is lost, which reduces the kinetic energy of TiO2 deposited on the substrate surface and affects the adhesion and densification of the deposited film. For optical thin films, the ion source assist can increase the kinetic energy of the molecules on the substrate surface, not only has a significant impact on the refractive index of the film, but also can improve the film density and moisture resistance, and the film adhesion on the substrate is also significantly improved.
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