Stabilité thermique des propriétés optiques, mécaniques et microstructurales des oxydes de tantale et de niobium fabriqués par plasma
Abstract (summary)
Tantalum and niobium oxide optical thin films were prepared at room temperature by Plasma-Enhanced Chemical Vapor Deposition (PECVD) using different modes of deposition (RF, MW and MW/RF) using tantalum and niobium pentaethoxide (M(OC2H5)5) precursors. They were then tested for their stability.
The evolution of the films' optical and microstructural properties as a result of annealing was studied over a broad temperature range from room temperature up to 900°C. The as-deposited films were amorphous, their refractive index, n, and extinction coefficient, k, at 550 nm were n = 2.13 and k < 10-4</super> for Ta2O5, and n = 2.24 and k < 10-4</super> for Nb2O 5. The films contained a small amount of residual carbon (∼ 2--6 at. %) bonded mostly to oxygen. During annealing, the onset of crystallization was observed at approximately TC = 650°C for Ta2O5 and at TC = 450°C for Nb2O5. Upon annealing close to T 1 (300°C for Nb2O5 and 400°C for Ta 2O5), n at 550 nm decreased by less than 1%. During annealing, a phase transition from the δ- (hexagonal) phase to the L- (orthorhombic) phase was observed between 800°C and 900°C for Ta2O5, and between 600°C and 700°C for Nb2O5. (Abstract shortened by UMI.)