ZrO₂ Monolayer as a Removable Etch Stop Layer for Thermal Al₂O₃ Atomic Layer Etching Using Hydrogen Fluoride and Trimethylaluminum

Abstract

A ZrO2 monolayer was demonstrated as a removable etch stop layer (ESL) for thermal Al2O3 atomic layer etching (ALE) using HF and Al(CH3)3 (trimethylaluminum (TMA)) as the reactants. The ZrO2 ESL was deposited on Al2O3 using tetrakis(ethylmethylamido)zirconium (TEMAZ) and H2O. In situ quartz crystal microbalance (QCM) measurements showed that a ZrO2 coverage of ∼190 ng/cm2 completely blocked thermal Al2O3 ALE at 285 °C. This ZrO2 coverage is equivalent to approximately one ZrO2 monolayer. The inhibition of the Al2O3 etch rate was proportional to the ZrO2 fractional coverage. The ZrO2 ESL was effective for hundreds of thermal Al2O3 ALE cycles. In terms of the surface chemistry, the ZrO2 ESL is known to be fluorinated to a ZrOxFy or ZrF4 layer by HF exposure. This fluorinated layer restricts etching by preventing the ligand-exchange reaction with TMA. The fluorinated layer could be easily removed using thermal ALE with HF and AlCl(CH3)2 (dimethylaluminum chloride (DMAC)) as the reactants. The ZrO2 ESL could be deposited and removed repeatedly without changing the Al2O3 etch rate. X-ray photoelectron spectroscopy (XPS) studies observed no trace of Zr on the Al2O3 surface after 7–8 cycles of HF and DMAC sequential exposures. Area selective deposition of the ZrO2 ESL would lead to area selective etching using HF and TMA as the reactants.