Plasma-enhanced atomic layer deposition of SiO2 film using capacitively coupled Ar/O2 plasmas: A computational investigation

Abstract

Plasma-enhanced atomic layer deposition (PE-ALD) is widely used for dielectric deposition in semiconductor fabrication due to its ability to operate at low temperatures while having high precision control. The PE-ALD process consists of two subcycles: precursor dosing and plasma exposure with gas purging and filling in between. In the PE-ALD of SiO2, a Si-containing precursor is first deposited on the surface, usually in a plasma-free environment. The surface is then exposed to an oxygen-containing plasma during which the residual components of the precursor are removed and the Si oxidized. Various factors affect the outcome of SiO2 PE-ALD, such as exposure times during each step, steric hindrance of the Si precursor, and plasma properties, such as the energy of ions incident onto the film. The results from computational investigations of the first layers of SiO2 PE-ALD at both reactor (cm) and feature (nm) scales are discussed in this paper. The example system uses bis(tertiary-butylamino)silane, SiH2[NH(C4H9)]2 as the silicon precursor during dosing and plasmas operating in Ar/O2 gas mixtures during the oxidation step. Parametric studies were performed for blanket deposition, as well as deposition in trenches and vias while varying power, pressure, plasma exposure time, aspect ratio, and ligand retention in the film. The general trends show that conditions that reduce the fluence of reactive oxygen species typically decrease the O/Si ratio, increase the vacancies in the films, and decrease the order of the film. Conditions that result in higher ion fluxes having higher energies produce the same result due to sputtering. The retention of ligand groups from the precursor significantly decreased growth rates while increasing vacancies and reducing the O/Si ratio.