Ammonium chloride (–NH3+Cl-) salt formation from dichlorosilane decomposition and its potential impact on silicon nitride atomic layer deposition

Plasma-enhanced atomic layer deposition (PEALD) has been demonstrated to be a promising technique for controlled growth of silicon nitride (SiNx) thin films. Based on first-principles calculations, we present the effects of by-product production on the reaction of dichlorosilane (DCS) as the Si precursor with a hydrogen-terminated N-rich surface created upon ammonia (NH3) plasma treatment relevant to thin film growth. The presence of amines, especially primary amines (–NH2), plays a key role in DCS decomposition by generating H and Cl atoms as by-products. Our work clearly demonstrates that the by-products can be strongly bound to the surface by forming stable –NH3+Cl- complexes, which may in turn affect the SiNx ALD process. The HCl desorption reaction, i.e., –NH3+Cl- → –NH2 + HCl(g), is predicted to be endothermic by 1.1–1.2 eV, depending on HCl surface coverage. The large HCl binding energy suggests that a high thermal energy would be required for its removal from the surface, as evidenced by results from experimental spectroscopic analysis. We also discuss how the by-product presence inhibits DCS adsorption and decomposition, leading to a decrease in the SiNx growth rate.