Surface reaction during thermal atomic layer etching of aluminum oxide films using fluorine radicals and trimethylaluminum

Abstract

We investigated the surface reaction of the thermal atomic layer etching (ALE) of Al2O3 film using fluorine (F) radicals and trimethylaluminum (TMA). As a strong fluorination source to replace HF, we used NF3 remote plasma to generate F radicals without spontaneous or anisotropic etching by ion bombardment. The mass was increased by F radicals and decreased by TMA. X-ray photoelectron spectroscopy (XPS) analysis showed that AlF3 and AlOxFy were formed by F radicals, and all AlF3 and a significant portion of AlOxFy were removed by TMA. At 250 °C, the etch per cycle (EPC) was fully saturated at 1.58 Å/cycle for the NF3 remote plasma of 4 s and the TMA pulse time of 3 s. Based on the saturation behavior, isotropic etching was demonstrated for the Al2O3 film prepared on a trench pattern. The EPC increased progressively with temperature from 0.1 Å/cycle at 198 °C to 4.2 Å/cycle at 320 °C. Since the thickness of the fluorinated layer did not increase significantly with increasing temperature, the removal step determined the EPC.