Plasma-free approach to remove SiN:H surface inhibitor (HCl) at room temperature

Our study explores a plasma-free approach to remove H+/Cl− pairs, a common reaction by-product, after chlorosilane-type Si precursors (such as dichlorosilane and SiH2Cl2) dissociate on a hydrogen-terminated SiN surface. Although previous studies have suggested that H radicals in NH3 and CH3NH2 plasma may remove some Cl impurities, these methods have limitations that in high-aspect-ratio structures, the recombination of radicals may be too fast rendering them unable to reach the trench bottom intact[H. C. M. Knoops et al., J. Electrochem. Soc. 157, G241 (2010)]. This may lead to Cl accumulation at the trench and passive layer formation, which inhibits further film growth and reduces conformality. Introducing polar molecules, such as NH3, N2H4, CH3NH2, and (CH3)2NH, is an alternative solution. Density functional theory calculations show that when these polar molecules interact with the surface, they first abstract H+ from the H+/Cl− pair and capture Cl−, which may then be solvated by surrounding polar molecules to form a “microsolvation cluster.” This cluster is energetically stable and envelops Cl− while weakening the interactions between Cl− and surface amine groups, creating a pathway for HCl desorption with a lower energy cost. Our metadynamics simulations show that when the surface is saturated with CH3NH2 molecules, the energy barrier for HCl desorption can be reduced significantly from 0.5 to 0.3 eV at 300 K, resulting in a ∼5000 times increase in the desorption rate, assuming an Arrhenius rate expression. Our findings suggest that by-products generated by halogen-containing precursors can be removed at room temperature via “microsolvation cluster” formation, without requiring plasma assistance.