Adsorption mechanism of hexachlorodisilane for low-temperature atomic layer deposition of silicon nitride

Abstract

Thin films of silicon nitride (SiN_x) are used as dielectric layers, passivation coatings, and barrier layers, which are crucial for enhancing the performance, reliability, and durability of semiconductors and display devices. Due to increasing miniaturization of devices, atomic layer deposition (ALD) of SiN_x is gaining large interest. Especially, thermal ALD of SiN_x at lower temperature is desirable to minimize damage of the substrates and to ensure excellent conformality. While hexachlorodisilane (Si₂Cl₆) is one of few precursors that can enable low-temperature thermal ALD of SiN_x, its surface chemical reaction mechanism has not been clarified yet. In this study, the surface reaction mechanisms of silicon tetrachloride (SiCl₄) and Si₂Cl₆, representative precursors for SiN_x ALD, are compared. Using density functional theory (DFT) calculations, the mechanisms of precursor adsorption on SiN_x surface and subsequent reactions with the counter-reactant NH₃ were investigated. Higher reactivity of Si₂Cl₆ was identified during both the precursor adsorption and removal of Cl by NH₃ co-reactant, attributed to the Si-Si bond present in Si₂Cl₆. Current results suggest that the presence of the direct Si-Si bond within the precursor molecule can be a crucial factor for enabling low-temperature ALD processes.