Temperature dependence of the optical properties and coefficient of thermal expansion in (001) Al2O3 substrate
Manil Kang and Sok Won Kim
(001) Al2O3 has a hexagonal structure and is optically uniaxial and optically anisotropic. It is very important to investigate the thermal and optical anisotropies of the substrate for accurate characterization of the film properties. This study characterized the temperature-dependent anisotropy of the optical properties and coefficient of thermal expansion (CTE) of (001) Al2O3 substrate using spectroscopic ellipsometry (SE) and thermal expansion measurements. XRD results show an increase of d-spacing in the c-axis of the Al2O3 substrate, and the d-spacing at 100°C increased by 0.046%. The thermal expansion rate with respect to temperature is larger in the through-plane direction, and the anisotropy of CTE increases with the temperature. The transmittance at 540 nm shows an increment of 4.2% due to thermal expansion. The in-plane (ne) and through-plane (no) refractive index spectra show a considerable change at 82°C. The results show that the thermal and optical anisotropies of (001) Al2O3 substrate strongly depended on the temperature.
Keywords: Al2O3, thermal expansion coefficient, optical anisotropy, spectroscopic ellipsometry