Influence of the negative oxygen ions on the structure evolution of transition metal oxide thin films

The energy distributions of O− ions of magnetron sputtered Nb, Ta, Zr, and Hf in an Ar∕O2 atmosphere were measured as a function of the oxygen partial pressure. Three ion populations were detected in the plasma: high, medium, and low energy ions, with energies corresponding to the target potential, half of the target potential, and <150eV, respectively. The ion energy distribution functions were compared to distributions obtained based on Sigmund’s linear collision cascade sputtering theory. If the surface binding energy is assumed to be equal to the heat of formation, good agreement between the experiment and theory was achieved. From correlating the measured ion energy distributions with previously published phase stability data [Ngaruiya et al., Appl. Phys. Lett. 85, 748 (2004)], it can be deduced that large fluxes of medium and high energy O− ions comparable to the fluxes of the low energy O− ions enable formation of crystalline transition metal oxide thin films during low temperature growth. The presented data here may be of general relevance for understanding the structure evolution of thin oxide films.