Theoretical analysis of thermal spikes during ion bombardment of amorphous silicon nitride surfaces

Abstract

Ion bombardment of amorphous silicon nitride (a-SiN) was simulated with self-consistent-charge density functional tight binding. These simulations were used to study bombardment-induced local heating events (often called “thermal spikes”). A model for estimating the thermal conductivity (k) of a locally heated area was implemented, yielding a predicted k of 3 W/m K for a small region of the a-SiN substrate around an ion impact site. Based on the estimated k, a bombardment-induced thermal spike is predicted to return to the baseline substrate temperature after only 0.2 ps. Consequently, no cumulative heating would occur in substrates with similar k values, given a typical ion flux of less than 1 × 1018 s−1 cm−2. Our simulations also show that surface reactions toward molecular adsorbates are not significantly facilitated by the thermal spike, largely due to its short duration.