Comparative study on chemical stability of dielectric oxide films under HF wet and vapor etching for radiofrequency microelectromechanical system application

HF wet and vapor etching of dielectric oxide films, which were prepared by thermal atomic layer deposition (ALD) and plasma-enhanced ALD (PEALD), are examined for radiofrequency microelectromechanical system (RF MEMS) application. The chemical stability of oxide films was increased in the order of ALD–Al2O3 < PEALD–ZrO2 < PEALD–TiO2 ≈ ALD–Ta2O5 under wet etching in 6:1 buffered HF aqueous solution, but in a different order of Ta2O5 < ZrO2 < TiO2 ≈ Al2O3 under anhydrous HF/CH3OH vapor etching at 4 kPa. The unstable films were uniformly and completely etched under the wet etching, while transformed to have increased thickness or non-uniformly etched with thicker residue under the vapor etching. Al2O3 and TiO2 (Ta2O5 and TiO2) can be used for RF MEMS capacitive switch fabricated by using HF vapor (wet) etching of sacrificial SiO2.