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.

Silicon Nitride Surface Modification by Ion Bombardment with Physisorbed Hydrofluorocarbons: Theoretical Assessment

“…Primarily, these defects are undercoordinated sites resulting from bombardmentinduced bond cleavage, but the creation of relatively unfavorable 5-fold coordinated Si centers is possible as well. In agreement with our previous results, 19,21 we observe relatively few thermal reactions between HFCs and the SiN substrate, with the bulk of reactions occurring during the short time periods following ion bombardment events. Most critically, we find evidence that initial surface modification can result in the formation of surface functional groups, which themselves can be further reactants given subsequent ion bombardment.…”

“…Here, it is useful to note that little evidence of thermal reactions between undissociated HFCs and the SiN surface has been predicted by our simulations, even at the elevated surface temperatures associated with ion-induced thermal spikes. Further details on this can be found in our work assessing this specifically . Thus, we expect the reactivity in this system to almost entirely be a result of ion-driven interactions or highly reactive HFC fragments.…”

“…Further details on this can be found in our work assessing this specifically. 21 Thus, we expect the reactivity in this system to almost entirely be a result of ion-driven interactions or highly reactive HFC fragments.…”

A density functional tight-binding based strategy for modeling ion bombardment and its application to Ar bombardment of silicon nitride

“…These above are a combination of standard assumptions in this field along with recently investigated properties of ion-induced thermal spikes, which has been detailed in a separate work. 19 B. Computational details…”