Dong-Xu Zhang

Evolution of optical constants of silicon dioxide on silicon from ultrathin films to thick films

A series of SiO2 films with thickness range 1–600 nm have been deposited on crystal silicon (c-Si) substrates by electron beam evaporation (EBE) method. Variable-angle spectroscopic ellipsometry (VASE) in combination with a two-film model (ambient-oxide-interlayer substrate) was used to determine the optical constants and thicknesses of the investigated films. The refractive indices of SiO2 films thicker than 60 nm are close to those of bulk SiO2. For the thin films deposited at the rate of ~1.0 nm s−1, the refractive indices increase with decreasing thickness from ~60 to ~10 nm and then drop sharply with decreasing thickness below ~10 nm. However, for thin films deposited at the rates of ~0.4 and ~0.2 nm s−1, the refractive indices monotonically increase with decreasing thickness below 60 nm. The optical constants of the ultrathin film depend on the morphology of the film, the stress exerted on the film, as well as the stoichiometry of the oxide film.

Application of image spectrometer to in situ infrared broadband optical monitoring for thin film deposition

A path-folded infrared image spectrometer with five sub-gratings and five linear-array detectors was applied to a broadband optical monitoring (BOM) system for thin film deposition. Through in situ BOM, we can simultaneously acquire the thickness and refractive index of each layer in real time by fitting the measured spectra, and modify the deposition parameters during deposition process according to the fitting results. An effective data processing method was proposed and applied in the BOM process, and it shortened the data processing time and improved the monitoring efficiency greatly. For demonstration, a narrow band-pass filter (NBF) at 1540 nm with ~10 nm full width at half-maximum (FWHM) had been manufactured using the developed BOM system, and the results showed that this BOM method was satisfying for monitoring deposition of thin film devices.

Temperature-Dependent Optical Properties of Titanium Oxide Thin Films Studied by Spectroscopic Ellipsometry

The electron-beam evaporation method was devoted to fabricate anatase-phase TiO2 thin films on silicon substrate. The optical constants of the thin films determined by spectroscopic ellipsometry in the spectral range from 300 to 800 nm were studied in a temperature range from 293 to 533 K. The refractive indices decrease apparently with increasing temperature, and the thermal expansion and electron–phonon interaction can be introduced to elucidate this phenomenon. The absorption edge in extinction coefficient spectra shows a redshift at elevated temperature, which is attributed to thermally driven band gap shrinkage and electron lifetime loss of optical electron transition.