Ultrahigh purity conditions for nitride growth with low oxygen content by plasma-enhanced atomic layer deposition

Ultrahigh purity (UHP) reactor conditions provide a process environment for growth of nitride thin films with low oxygen content by plasma-enhanced atomic layer deposition (PEALD). In particular, UHP conditions correspond to partial pressures below 10-8 Torr for impurities within the PEALD process environment to limit incorporation before, during, and after film growth. In this article, we identify the various sources of background oxygen species and describe the measures taken to obtain UHP reactor conditions. For example, in situ ellipsometry results are presented that reveal the impact of oxygen incorporation on film resistivity during and after titanium nitride PEALD due to elevated levels of oxygen impurities in the argon process gas. A model is also developed that shows the significance of water permeation through elastomer vacuum seals. These examples demonstrate the importance of process gas purification and elimination of elastomer permeation toward achieving a UHP environment. X-ray photoelectron spectroscopy (XPS) depth profile data for titanium, aluminum, and silicon nitride by PEALD reveal bulk oxygen levels below 1 at. %, thereby demonstrating the effectiveness of UHP reactor conditions at reducing oxygen incorporation. Consistent with XPS, depth profile secondary ion mass spectroscopy results for titanium nitride PEALD confirm bulk oxygen content less than 1 at. %, further establishing the effectiveness of a UHP background for high purity nitride film growth.