Influence of low ion bombardment energy on interface formation and thin film growth in a plasma-CVD environment

We show that ion bombardment in the range of a few hundreds of eV used in ion- and plasma-assisted deposition processes leads to significant interface broadening due to ion mixing during the initial stages of film deposition. First, we study the modifications of a c-Si (100) target exposed to an O ₂ plasma at the radio frequency powered electrode using in situ real time spectroscopic ellipsometry (RTSE). We detect important ion-bulk interactions, such as implantation, damage recoils, and oxidation to a depth of up to ∼10 nm, which we confirm and validate with Monte-Carlo TRIDYN simulations based on binary collision calculations assuming plasma as a broad energy ion source. RTSE was then used to monitor TiO₂ deposition on SiO₂ under similar ion bombardment conditions, we observed formation of a 3 to 4 nm thick interfacial layer, while TRIDYN simulations show that ion bombardment results mainly in ion mixing of Ti and Si atoms. Simulated interface thickness scales as a square root of ion fluence, in agreement with ion mixing laws for light elements with Z < 20. At high ion-to-neutral ratios, simulations predict that the majority of Ti atoms are knocked into the bulk, suggesting that a substantial part of film deposition occurs below the growth surface.