Formation of Al₂O₃-Ta₂O₅ Double-Oxide Thin Films by Low-Pressure MOCVD and Evaluation of Their Corrosion Resistances in Acid and Alkali Solutions

Electrochemical Society Active Member Al₂O₃-Ta₂O₅ double-oxide thin films with different cationic mole fractions of Ta, X_Ta, were formed by metallorganic chemical vapor deposition using aluminum tetraisopropoxide [Al(O-i-C₃H₇)₃] and tantalum pentametoxide [Ta(OCH₃)₅] as source gases and oxygen as a reaction gas. The corrosion resistances of the films were examined in 6 and 12 M HCl and l M NaOH at 298 K by the ellipsometric measurement of thinning rates of the films. The Al₂O₃-Ta₂O₅ films having X_Ta values between 0.0 and 1.0 showed homogeneous amorphous structures. The thinning rate of the films in HCl solutions decreased with increasing X_Ta value and reached the analytical limit of ellipsometry. The films with X_Ta values larger than 0.35 hardly dissolved in 6 M HCl and those with X_Ta values larger than 0.45 in 12 M HCl. The corrosion resistance of the Al₂O₃-Ta₂O₅ films in l M NaOH increased significantly with an increase in X_Ta: the dissolution rate of the Al₂O₃-Ta₂O₅ film with X_Ta value of about 0.5 is lower than that of pure Al₂O₃ film by six orders of magnitude.