Real-time/in situ diffraction study of phase and microstructural evolution in sputtered β-Ta/Ta2O5 films

Abstract

The evolution of texture, grain size, and phase content in sputtered β-Ta/Ta2O5 films was studied and controlled in situ using a laboratory-based real-time x-ray diffraction system. The films were dc magnetron sputter deposited using sputter gas (Ar) pressures ranging from 2 to 20 mTorr. To collect diffraction data during growth, a grazing incidence x-ray scattering (GIXS) configuration was necessary. Because this configuration complicated the interpretation of texturing data, complete Schultz geometry pole figures were also used to characterize the films after growth, and the relationship between pole figure and GIXS data was examined. The film composition was evaluated using sputter profile x-ray photoelectron spectroscopy and secondary ion mass spectroscopy. It was found that the degree and rate of (002) out-of-plane texturing was systematically stronger in films grown at lower Ar pressures (< 10 mTorr). These films were predominantly β-Ta in composition and had relatively large grains (∼50 nm in diameter). Films grown using progressively higher Ar pressures had increasing amounts of Ta2O5, developed a (002) out-of-plane texture more slowly, and were nanocrystalline/amorphous in nature. Data from depositions where the Ar pressure was changed during growth showed that the deposition environment at the instant of layer formation determined the phase content, degree of texture, and grain size in the developing film; the characteristics of previous layers had little bearing on subsequent growth. This shows that tailored multilayer β-Ta/Ta2O5 films may be created and monitored in situ.