Bo-Huei Liao

Residual stress in obliquely deposited MgF2 thin films.

MgF(2) films with a columnar microstructure are obliquely deposited on glass substrates by resistive heating evaporation. The columnar angles of the films increases with the deposition angle. Anisotropic stress does not develop in the films with tilted columns. The residual stresses in the films depend on the deposition and columnar angles in a columnar microstructure.

Fluorine-doped tin oxide films grown by pulsed direct current magnetron sputtering with an Sn target

Fluorine-doped tin oxide (FTO) films have been deposited by pulsed DC magnetron sputtering with an Sn target. Various ratios of CF4/O2 gas were injected to enhance the optical and electrical properties of the films. The extinction coefficient was lower than 1.5×10(-3) in the range from 400 to 800 nm when the CF4O2 ratio was 0.375. The resistivity of fluorine-doped SnO2 films (1.63×10(-3) Ω cm) deposited at 300 °C was 27.9 times smaller than that of undoped SnO2 (4.55×10(-2) Ω cm). Finally, an FTO film was consecutively deposited for protecting the oxidation of indium tin oxide films. The resistivity of the double-layered film was 2.68×10(-4) Ω cm, which increased by less than 39% at a 450 °C annealing temperature for 1 h in air.

AlF(3) thin films deposited by reactive magnetron sputtering with Al target.

Aluminum fluoride thin films have been deposited by magnetron sputtering of an aluminum target with CF(4) , and CF(4) mixed O(2) as the working gas onto a room temperature substrate. The quality of the coated AlF(3) film applied with 25W sputtering power using CF(4) mixed 5% O(2) was better than for films deposited using conventional methods. The extinction coefficient of AlF(3) was smaller than 6.0x10(-4) in the wavelength range of 190nm to 250nm. Single layer antireflection coatings on both sides of a fused silica substrate increased the transmittance from less than 91% for a bare substrate to higher than 96% in the wavelength range between 190nm to 250nm.

Developing new manufacturing methods for the improvement of AlF 3 thin films

In this research, the plasma etching mechanism which is applied to deposit AlF(3) thin films has been discussed in detail. Different ratios of O(2) gas were injected in the sputtering process and then the optical properties and microstructure of the thin films were examined. The best optical quality and smallest surface roughness was obtained when the AlF(3) thin films were coated with O(2):CF(4) (12 sccm:60 sccm) at 30 W sputtering power. To increase the deposition rate for industrial application, the sputtering power was increased to 200 W with the best ratio of O(2)/CF(4) gas. The results show that the deposition rate at 200W sputtering power was 7.43 times faster than that at 30 W sputtering power and the extinction coefficients deposited at 200 W are less than 6.8 x 10(-4) at the wavelength range from 190 nm to 700 nm. To compare the deposition with only CF(4) gas at 200 W sputtering power, the extinction coefficient of the thin films improve from 4.4 x 10(-3) to 6 x 10(-4) at the wavelength of 193 nm. In addition, the structure of the film deposited at 200W was amorphous-like with a surface roughness of 0.8 nm.

Process for deposition of AlF 3 thin films

We fabricated aluminum fluoride (AlF3) thin films by pulsed DC magnetron sputtering with various CF4 flow rates and sputtering powers. Our method is distinct from the conventional deposition process in that we used inexpensive Al (99.99% purity) as the target instead of an expensive fluoride compound. The optical properties and microstructure of the thin films were examined. The optical quality of AlF3 thin films deposited at a 20 W sputtering power and injected 110 SCCM (SCCM denotes cubic centimeters per minute at standard temperature and pressure) CF4 flow at room temperature showed improvement with an extinction coefficient of less than 7×10-4 at 193 nm. The deposition of AlF3 thin films at different substrate temperatures and annealed by UV light was also investigated.

Fluoride antireflection coatings deposited at 193 nm

Antireflection coatings for 193 nm composed of low-index (MgF(2) and AlF(3)) and high-index (LaF(3) and GdF(3)) materials are deposited by the resistive heating boat method at a substrate temperature of 300 degrees C. The optical characteristics (reflectance and optical loss), microstructure (morphology and surface roughness), stress, and laser-induced damage threshold (LIDT) of the coatings are investigated and discussed. The related reflection at 193 nm of the four kinds of antireflection coatings is smaller than 0.2% and the optical loss is less than 0.15%. Of the fluoride antireflection coatings, AlF(3)/GdF(3) had the lowest stress value. Antireflection coatings with AlF(3) as the low-index material had higher LIDT values than when MgF(2) was used.

Antireflection coatings for deep ultraviolet optics deposited by magnetron sputtering from Al targets

We introduce an innovative technique for the deposition of fluorine doped oxide (F:Al(2)O(3)) films by DC pulse magnetron sputtering from aluminum targets at room temperature. There was almost no change in transmittance even after the film was exposed to air for two weeks. Its refractive index was around 1.69 and the extinction coefficient was smaller than 1.9 × 10(-4) at 193 nm. An AlF(3)/F:Al(2)O(3) antireflection coating was deposited on both sides of a quartz substrate. A high transmittance of 99.32% was attained at the 193 nm wavelength. The cross-sectional morphology showed that the surface of the multilayer films was smooth and there were no columnar or porous structures.

FTO films deposited in transition and oxide modes by magnetron sputtering using tin metal target.

Fluorine-doped tin oxide (FTO) films were prepared by pulsed DC magnetron sputtering with a metal Sn target. Two different modes were applied to deposit the FTO films, and their respective optical and electrical properties were evaluated. In the transition mode, the minimum resistivity of the FTO film was 1.63×10(-3)  Ω cm with average transmittance of 80.0% in the visible region. Furthermore, FTO films deposited in the oxide mode and mixed simultaneously with H2 could achieve even lower resistivity to 8.42×10(-4)  Ω cm and higher average transmittance up to 81.1% in the visible region.

Head-up display using an inclined Al2O3 column array

An orderly inclined Al2O3 column array was fabricated by atomic layer deposition and sequential electron beam evaporation using a hollow nanosphere template. The transmittance spectra at various angles of incidence were obtained through the use of a Perkin-Elmer Lambda 900 UV/VIS/NIR spectrometer. The inclined column array could display the image information through a scattering mechanism and was transparent at high viewing angles along the deposition plane. This characteristic of the inclined column array gives it potential for applications in head-up displays in the automotive industry.

Improving the optical and electrical properties of fluorine-doped tin oxide films by various post-annealing treatments

Transparent conducting Fluorine-doped tin oxide (FTO) thin films were deposited on glass substrates by pulsed DC magnetron sputtering from cost saving metal targets. We observed lower resistivity and higher average transmittance in the visible range after the application of various post heating treatments. The electrical and optical properties of FTO films were investigated. When the annealing temperature is 400°C in air, the average transmittance is 79.79% with the lowest resistivity of 1.38×10 -3 Ω-cm, carrier density of 2.27×10 20 cm -3 and mobility of 20 cm 2 / V-s. When the annealing temperature is 400°Cin a H 2 5%+N 2 95% atmosphere, the average transmittance is 79.75 % with the lowest resistivity of 1.26×10 -3 Ω-cm, carrier density of 2.17×10 20 cm -3 and mobility of 22.8 cm 2 / V-s. When the annealing temperature is 350 °C in vacuum, the average transmittance is 80.48% with the lowest resistivity of 1.23×10 -3 Ω-cm, carrier density of 4.40×10 20 cm -3 and mobility of 11.6 cm 2 / V-s.