Can oxygen stabilize chromium nitride? Characterization of high temperature cycled chromium oxynitride

Stoichiometric CrO0.1N0.9 and CrO0.5N0.5 films were produced by r.f.-sputtering. Both compositions showed CrN (Fm-3m) structure in XRD. HT-XRD measurements during heat cycling up to 850 degreesC revealed a region of thermal healing of structural defects during the first heat cycle. For the oxygen rich films, a relevant reduction of crystallite size expansion during heating compared to the low oxygen film was observed, while both films did show no change in crystallite size in following cycles. An explanation for this behavior could be oxynitride formation during film deposition. This was proven by STEM pictures, which indicate amorphous oxygen rich films and a columnar structure for films with low oxygen contents. In addition, EELS (ELNES) spectra give evidence for oxynitride bonding. SIMS depth profiling revealed homogeneous films with a thin protective oxide layer on the surface. In XRD, Cr2O3 was only detected after high temperature treatment and also in FT-IR no absorption band at the corresponding values, but a wide band at higher wave numbers was detected. CGHE measurements point toward only one chemical state for oxygen in the films. UPS and XPS measurements after careful sputter etching of the surface oxidation layer deviate strongly from reference CrN spectra. The Cr 2p line is shifted to higher binding energies in the oxygen rich films. No Cr2O3 contribution to the spectra was observed. The O 1s line is shifted to higher binding energies in the oxygen rich films, too, and indicates N-Cr-O bonds. All the gained analytical information confirms the assumption of an oxynitride structure, which is known to stabilize amorphous films against recrystallization at elevated temperatures also for other compounds. No confirmation was found for the deposition of a two-phase CrN and Cr2O3 system. (C) 2003 Elsevier B.V. All rights reserved.