Thermal Atomic Layer Etching of Titanium Nitride Using Sequential, Self-Limiting Reactions: Oxidation to TiO2 and Fluorination to Volatile TiF4

Abstract

The thermal atomic layer etching (ALE) of TiN was demonstrated using a new etching mechanism based on sequential, self-limiting oxidation and fluorination reactions. The oxidation reactant was either O3 or H2O2, and the fluorination reactant was hydrogen fluoride (HF) derived from HF-pyridine. In the proposed reaction mechanism, the O3 reaction oxidizes the surface of the TiN substrate to a TiO2 layer and gaseous NO. HF exposure to the TiO2 layer then produces TiF4 and H2O as volatile reaction products. The overall reaction can be written as TiN + 3O3 + 4HF → TiF4 + 3O2 + NO + 2H2O. Quartz crystal microbalance studies showed that HF can spontaneously etch TiO2 films. Spectroscopic ellipsometry and X-ray reflectivity analysis showed that TiN films were etched linearly versus the number of ALE cycles using O3 and HF as the reactants. The TiN etching also occurred selectively in the presence of Al2O3, HfO2, ZrO2, SiO2, and Si3N4. The etch rate for TiN ALE was determined at temperatures from 150 to 350 °C. Th...