Atomic-Scale Mechanisms of SiO$_2$ Plasma-Enhanced Chemical Vapor Deposition Revealed by Molecular Dynamics with a Machine-Learning Interatomic Potential

TL;DR

This study uses molecular dynamics with a machine-learning interatomic potential to reveal atomic-scale mechanisms of SiO$_2$ PECVD, showing how gas ratios and plasma conditions influence film growth, composition, and surface roughness.

Contribution

It introduces a machine-learning-based molecular dynamics approach to simulate SiO$_2$ PECVD, providing detailed atomic insights into growth mechanisms and effects of process parameters.

Findings

Oxidation of Si-H groups forms Si-OH, leading to network growth.

Higher oxidant ratios reduce hydrogen incorporation and saturate Si/O ratio.

High-energy plasma species can etch SiO$_2$, affecting growth and surface quality.

Abstract

Plasma-enhanced chemical vapor deposition (PECVD) of silicon dioxide (SiO$_2$) is widely used for low-temperature fabrication of dielectric thin films, yet its atomic-scale growth mechanisms remain incompletely understood. In this work, we investigate SiO$_2$ PECVD using silane and N$_2$O as source gases via molecular dynamics simulations driven by a machine-learning interatomic potential. By systematically varying the oxidant-to-silane-derived species ratio $r$, we elucidate the evolution of film stoichiometry, density, and hydrogen content. Formation of the Si-O-Si network primarily proceeds via oxidation of surface Si-H groups to form Si-OH species, followed by condensation of neighboring Si-OH groups that produces H$_2$O as the dominant byproduct. At low $r$, H$_2$ formation via reactions between Si-H and Si-OH groups also contributes to the network formation. Increasing oxidant supply promotes the network formation through oxidation of residual Si-H species, suppressing hydrogen incorporation and leading to saturation of the Si/O ratio. Rapid chemisorption of silane-derived species, together with steric hindrance from pre-deposited species, results in localized growth and surface roughness. We further show that high-kinetic-energy plasma species can etch SiO$_2$ films, which potentially limits growth rates and enhances surface roughness under high RF-power conditions. These results provide atomic-scale insight into PECVD growth and guidance for optimizing film composition and quality.