Amorphous tantalum oxide (Ta2O5) films were deposited on Si substrate for application as the gate dielectric in metal-oxide-semiconductor field-effect transistors (MOSFETs). Prior to Ta2O5 deposition, the Si substrate was nitrided in an N2O+NH3 plasma at 450 °C to form a passive silicon oxynitride (SiOxNy) layer. In this work, spectroscopic ellipsometry was used to determine the complex refractive index and the thickness of the SiOxNy and Ta2O5 layers. To determine the composition of the dielectric stack, the Bruggeman effective medium approximation (EMA) model was applied to each layer for fitting the ellipsometry data. Using X-ray photoelectron spectroscopy (XPS) as a complementary method to verify the film composition and thickness, we have found that the EMA model explains the composition of the two mixed phases (SiO2 and Si3N4) in the SiOxNy layer, as well as the off-stoichiometry in the Ta2O5 layer.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Surfaces and Interfaces
- Surfaces, Coatings and Films
- Metals and Alloys
- Materials Chemistry