Tunable optical and electrical properties of thermal and plasma-enhanced atomic layer deposited Si-rich Si _xTi_(1-x)O_2 thin films

摘要

Ternary dielectrics with varying composition formed by alloying two binary oxides can enable tunable optical and electrical properties for advanced technological applications. Atomic layer deposition (ALD) gives precise control over ternary dielectric composition through the ability to finely tune the precursor pulsing ratio. This work presents ALD development of Si-rich Si_xTi_(1-x)O_2 dielectrics with varying composition (x), along with spectroscopic and electrical characterization of their properties. Stoichiometry of the Si_xTi_(1-x)O_2 films was determined using X-ray photoelectron spectroscopy. Their composition-dependent refractive index, energy bandgap, and reflectance show promise for diverse optical applications ranging from anti-reflective coatings in photovoltaics to optical waveguides. This work also reports a first comparative study of Si_xTi_(1-x)O_2 films prepared by thermal (T-) and plasma-enhanced (PE-) ALD with varying Si composition and deposition temperatures. Deposition rates of 0.67-0.92 Å/cycle were obtained for Si_xTi_(1-x)O_2 films with x = 0.5-0.91 deposited using PE-ALD at 250 °C, which were higher than that of T-ALD at 200 °C (0.42-0.05 Å/cycle). PE-ALD also exhibited a high deposition rate of 0.81 A/cycle for Si_xTi_(1-x)O_2 film with x = 0.91 at a low growth temperature of 150 °C. The PE-ALD Si-rich silica-titania films show substantially lower (100×) leakage current densities than the thermally deposited films, along with higher breakdown fields for decreasing deposition temperature. A dielectric constant as low as ～5 was achieved for PE-ALD Si_xTi_(1-x)O_2 films with high Si (x = 0.91) content.