Comparison of chemical stability and corrosion resistance of group IV metal oxide films formed by thermal and plasma-enhanced atomic layer deposition

摘要

The wide applications of ultrathin group IV metal oxide films (TiOsub2/sub, ZrOsub2/sub and HfOsub2/sub) probably expose materials to potentially reactive etchants and solvents, appealing for extraordinary chemical stability and corrosion resistance property. In this paper, TiOsub2/sub ultrathin films were deposited on Si at 200?°C while ZrOsub2/sub and HfOsub2/sub were grown at 250?°C to fit their growth temperature window, by thermal atomic layer deposition (TALD) and plasma-enhanced ALD (PEALD). A variety of chemical liquid media including 1?mol/L Hsub2/subSOsub4/sub, 1?mol/L HCl, 1?mol/L KOH, 1?mol/L KCl, and 18 MΩ deionized water were used to test and compare chemical stability of all these as-deposited group IV metal oxides thin films, as well as post-annealed samples at various temperatures. Among these metal oxides, TALD/PEALD HfOsub2/sub ultrathin films exhibit the best chemical stability and anti-corrosion property without any change in thickness after long time immersion into acidic, alkaline and neutral solutions. As-deposited TALD ZrOsub2/sub ultrathin films have slow etch rate of 1.06?nm/day in 1?mol/L HCl, however other PEALD ZrOsub2/sub ultrathin films and annealed TALD ones show better anti-acid stability, indicating the role of introduction of plasma Osub2/sub in PEALD and post-thermal treatment. As-deposited TiOsub2/sub ultrathin films by TALD and PEALD are found to be etched slowly in acidic solutions, but the PEALD can decrease the etching rate of TiOsub2/sub by ~41%. After post-annealing, TiOsub2/sub ultrathin films have satisfactory corrosion resistance, which is ascribed to the crystallization transition from amorphous to anatase phase and the formation of 5% Si-doped TiOsub2/sub ultrathin layers on sample surfaces, i.e. Ti-silicate. ZrOsub2/sub, and TiOsub2/sub ultrathin films show excellent corrosion endurance property in basic and neutral solutions. Simultaneously, 304 stainless steel coated with PEALD-HfOsub2/sub is found to have a lower corrosion rate than that with TALD-HfOsub2/sub by means of electrochemical measurement. The pre-treatment of plasma Hsub2/sub to 304 stainless steel can effectively reduce interfacial impurities and porosity of overlayers with significantly enhanced corrosion endurance. Above all, the chemical stability and anti-corrosion properties of IV group metal oxide coatings can be improved by using PEALD technique, post-annealing process and plasma Hsub2/sub pre-treatment to substrates.