Paper PS+EM+TF-ThA2
Thermal Atomic Layer Etching of HfO₂ Using HF for Fluorination and TiCl₄ for Ligand-Exchange

Thursday, October 25, 2018, 2:40 pm, Room 104C

Thermal atomic layer etching (ALE) can be accomplished using sequential fluorination and ligand-exchange reactions. HF has been a typical fluorination reactant. Various metal precursor s have been used for ligand-exchange such as Sn(acac)₂, Al(CH₃)₃ and AlCl(CH₃)₂ and SiCl₄. This study explored TiCl₄ as a new metal chloride precursor for ligand-exchange. Thermal HfO₂ ALE using TiCl₄ and HF as the reactants was studied using in situ quartz crystal microbalance (QCM) measurements from 200 - 300 °C. The HfO₂ films were etched linearly versus number of TiCl₄ and HF reaction cycles. The sequential TiCl₄ and HF reactions were also self-limiting versus reactant exposure. The QCM studies observed a mass change per cycle (MCPC) of -10.2 ng/(cm² cycle) at 200 °C and -56.4 ng/(cm² cycle) at 300 °C. These MCPCs correspond to HfO₂ etch rates of 0.11 Å/cycle at 200 °C and 0.59 Å/cycle at 300 °C. To explore the selectivity of thermal ALE using TiCl₄ and HF as the reactants, spectroscopic ellipsometry (SE) measurements were also employed to survey the etching of various materials. The SE results revealed that HfO₂ and ZrO₂ were etched by TiCl₄ and HF. In contrast, Al₂O₃, SiO₂, Si₃N₄, and TiN were not etched by TiCl₄ and HF. QCM studies also revealed that TiCl₄ and HF were able to etch Ga₂O₃. The etching selectivity can be explained by the reaction thermochemistry and the stability and volatility of the possible etch products. Al₂O₃ can also serve as an etch stop for HfO₂ ALE.