| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Friday Sessions |
| Session PS+NS+SS+TF-FrM |
| Session: | Atomic Layer Etching II |
| Presenter: | Younghee Lee, University of Colorado at Boulder |
| Authors: | Y. Lee, University of Colorado at Boulder S.M. George, University of Colorado at Boulder |
| Correspondent: | Click to Email |
Titanium nitride (TiN) is an important conducting material as a copper diffusion barrier and a gate electrode in semiconductor devices. Previous thermal atomic layer etching (ALE) studies have shown that TiN was not etched using fluorination and ligand-exchange reactions [1]. These results suggest that the ligand-exchange reactions do not produce stable and volatile reaction products.
In this work, a new etching mechanism based on sequential, self-limiting oxidation and fluorination reactions was developed for thermal TiN ALE. The oxidation reactant was either O3 or H2O2. 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 produces gaseous products such as NO. HF exposure to the TiO2 layer then yields TiF4 and H2O as volatile reaction products. The overall reaction can be written as: TiN + 3O3 + 4HF → TiF4 + 3O2 + NO + 2H2O.
Quartz crystal microbalance experiments 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 etch rate for TiN ALE was determined at temperatures from 150 to 350°C. The etch rates increased with temperature from 0.06 Å/cycle at 150°C to 0.20 Å/cycle at 250°C and stayed nearly constant for temperatures ≥250°C
The thermal ALE of many other metal nitrides should be possible using this new etching mechanism based on oxidation and fluorination reactions. This thermal ALE mechanism should also be applicable to metal carbides, metal sulfides, metal selenides, and elemental metals that have volatile metal fluorides.
[1] Y. Lee, C. Huffman and S.M. George, “Selectivity in Thermal Atomic Layer Etching Using Sequential, Self-Limiting Fluorination and Ligand-Exchange Reactions”, Chem. Mater. 28, 7657 (2016).