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Effect of Oxygen Permeability of Electron Beam Evaporated TiO2 Film on Optical Properties of Film

2021-02-23 18:24  Times of view:

The effects of different oxygen fluxes on the optical properties of TiO2 films deposited by electron beam evaporation were studied. As the oxygen flow rate increases from 37.4×10-3 Pa·m3·s-1 to 61.2×10-3 Pa·m3·s-1, the vacuum degree of the vacuum chamber changes from 1.4×10-3 Pa to 2.5 × 10-3 Pa, titanium dioxide films with different optical properties can be obtained. The spectrum was tested with a spectrophotometer, and it was found that the peak transmittance of the TiO2 film increased as the vacuum degree decreased, and the refractive index and extinction coefficient first increased and then decreased as the vacuum degree decreased. Under the process conditions of vacuum degree 2.0×10-3 Pa, the film quality is the best, the transmittance is 92%, the refractive index is between 2.50-2.20, and the extinction coefficient is below 10-4. According to the Cauchy equation to fit its dispersion law, the fitted curve and the curve calculated by the envelope method coincide well. The formula for the change of refractive index with wavelength is n(λ)=2.17+6.12×104/λ2+ 2.98×108/λ4.

Introduction

TiO2 is an important optical film material. It not only has excellent characteristics such as high refractive index, high light transmittance, friction resistance, corrosion resistance, and high hardness, but also its chemical stability is very good, and it is transparent in the entire visible and near infrared regions.

With the development of optical film thickness control technology and computer simulation design film technology, non-λ/4 film systems have become very extensive. The basic condition for plating non-λ/4 film system is that the refractive index of the film material is stable, so as to ensure that the non-λ/4 film system computer simulation design requirements can be achieved through the control process. The stability of the refractive index of the TiO2 film is closely related to the evaporation material used, the preparation process and related parameters. Therefore, the coating process must be ensured when TiO2 is used to plate a hard film with a high refractive index in a non-λ/4 multilayer film system. The structure, composition and process parameters of the medium evaporation material are stable.

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TiO2 films can be prepared by a variety of deposition techniques, including sol-gel, magnetron sputtering, reactive evaporation, and ion beam assisted deposition techniques. The TiO2 films prepared by different methods have different optical properties. Because TiO2 material decomposes and loses oxygen when heated and evaporated in a vacuum, it is easy to form a highly absorbing titanium suboxide film. Therefore, the preparation process is different, and the refractive index and extinction coefficient of the prepared TiO2 film are also very different. Therefore, the TiO2 film is studied The influence of the film-forming process on its optical performance is very important to further improve the application of TiO2 film.

This article studies the influence of the oxygen flux of ion beam assisted electron beam evaporation coating on the performance of the TiO2 film to obtain the best coating process and the best optical properties of the film.

1. Sample plating

Electron beam evaporation coating TiO2 film, using the INTEGRITY-39 automatic optical coating system with ion beam assisted electron beam evaporation as shown. The system is equipped with two electron guns. The film thickness and deposition rate adopt the Leybold Inficon IC/5 quartz crystal monitoring system. The substrate holder is on the top of the vacuum chamber, and the vertical distance from the evaporation source is 85 cm. It is rotated by planetary rotation to increase the film. The uniformity. The working voltage of the electron gun of the plated sample is 10 kV, the current is 200 A, and the deposition temperature of the vacuum chamber is 145-155 ℃. The film material is black granular Ti2O3 with a purity of 99.99%, and CC-105 cold cathode ion beam is used for assisted deposition. During the deposition, the vacuum chamber is filled with O2 with a purity of 99.99% as the reaction gas, and it is controlled by a 1179A MKS mass flowmeter. The flow rate of reaction gas O2, the substrate is round K9 glass with a diameter of 25 mm.

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Schematic diagram of ion beam assisted electron beam evaporation automatic optical coating system

Before coating, the substrate is cleaned with liquid glass, rinsed with deionized water, dried with nitrogen, then cleaned with 99.9% purity acetone and absolute ethanol for 15 minutes each by ultrasonic, dried with special wiper paper, and then put into the vacuum chamber.

When the vacuum degree is 6.5×10-4 Pa with mechanical pump and diffusion pump during plating, automatic plating program is set. When the substrate is heated to a deposition temperature of 150 ℃, the ion source begins to bombard the substrate, the energy is controlled at 60-90 eV, and the time is 10 min. Then automatically start the electron gun to heat the evaporated film material and deposit the film at a deposition rate of 0.38~0.42 nm/s. When the film is deposited to the designed thickness of 440 nm, the program automatically turns off the electron gun to complete the plating.

After coating, the vacuum chamber is naturally cooled to room temperature and the sample is taken out, and the Lambda900 (test range is 175-3 300 nm) spectrophotometer is used to measure the TiO2 spectrum of the sample. The Macleod software package is used to calculate the actual thickness, extinction coefficient and refraction of the TiO2 film. rate. The vacuum chamber was filled with high-purity oxygen with different flow rates, and the effects of different vacuum degrees on the film quality, refractive index and absorption coefficient of TiO2 were studied.

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When TiO2 film is deposited by ion source-assisted evaporation under high vacuum, the change of vacuum with the amount of oxygen is listed in Table 1. As the oxygen molecules charged into the vacuum chamber are ionized into oxygen ions to fully react with Ti2O3 vapor molecules, the oxygen lost by the decomposition of Ti2O3 is replenished, so that the TiO2 component in the resulting film is relatively pure, but if the amount of oxygen is insufficient or Ti2O3 and Ti2O3 Insufficient O2 reaction will form a highly absorbing titanium suboxide film TinO2n-1 (n=1, 2, ……, 10). With the increase of oxygen flow, the collision probability of TiO2 vapor molecules with oxygen molecules increases during the evaporation process and loses energy, which reduces the kinetic energy of TiO2 deposited on the substrate surface, which affects the adhesion and compactness of the deposited film. For optical films, the use of ion source assistance can increase the kinetic energy of the film molecules on the substrate surface, which not only has a significant impact on the refractive index of the film, but also improves the density and moisture resistance of the film. Adhesion has also improved significantly.

Table 1 Corresponding vacuum degree under different O2 flow

The corresponding vacuum degree under different O2 flow

3. Conclusion

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The oxygen flux has an important influence on the optical properties of the TiO2 film. By controlling the oxygen flow to adjust the vacuum degree in the vacuum chamber, the peak spectral transmittance of the TiO2 film increases as the vacuum degree decreases, and the refractive index and extinction coefficient first increase and then decrease as the vacuum degree decreases; when the vacuum degree is 2.0× At 10-3 Pa, the prepared TiO2 film has high transmittance in the visible spectral region, with a maximum transmittance of 92%, a refractive index between 2.50 and 2.20, and an extinction coefficient below 10-4. The square of the correlation coefficient between the fitting curve and the envelope method is 0.999 46, and the Cauchy dispersion equation of the refractive index is n(λ)=2.17+6.12×104/λ2+2.98×108/λ4 .

Founded in 2015,Zunhua Baorui Titanium Equipment Co.,Ltd. is a manufacturer specializing in pvd vacuum ion coating equipment. The company’s products mainly include large plate coating machine, large tube collating machine, tool coating machine and LOW-E glass production line. Mr.Wang baijiang ,general manager of the company ,has been engaged in vacuum coating industry for more than 30 years. He continuously improve production technology, improve product performance and devote himself to provide customers with better product experience and higher production efficiency.

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