Amorphous Regions and Thermal Stability of RF-Sputtered Films in the SiO<sub>2</sub>-CaO System

Abstract

Amorphous regions and thermal stability of sputtered films in the SiO2-CaO system were determined. The results are summarized as follows. (1) The amorphous region in the SiO2-CaO system by the sputtering method (100W, 25h) was found in the composition range CaO=0-89mol%, which is slightly larger than that of the SiO2-MgO system. (2) Crystallization temperature TC was determined from the DTA measurements of the sputtered amorphous films and melt-quenched glasses. (3) Thermal stability of the amorphous films and glasses was evaluated from the TC/TL ratio. TC/TL is highest 0.8 at CaO=0mol%. It passes maxima and minima as CaO content is increased and reaches the lowest value 0.44 at CaO=71.5mol%. Melt-quenched glasses showed similar compositional dependence of TC/TL ratio to that of sputtered films. (4) According to the empirical relationship between TC/TL and critical cooling rate for glass formation Q*, the TC/TL ratio of 0.44 corresponds to Q*=108.5°C/s which is well within the estimated quenching rate by the sputtering method.