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.