Phase changes of CrN films annealed at high temperature under controlled atmosphere

Abstract

CrN films were deposited onto (100) Si wafers by cathodic arc plasma deposition. After that, the films were annealed between 400 and 1200°C for 2 h in air, N 2, and N 2/H 2=9, which possess dramatically different P n 2 and P o 2. XRD results showed that oxidation of CrN films occurred above 700°C in all gases but the relative amount of the resultant oxide Cr 2O 3 decreased with rising ( P n 2/ P o 2) ratio in the gases for a given temperature. The driving force for oxidation of the nitride is the Gibbs free energy changes in the oxidation reaction. Meanwhile, the β-Cr 2N phase appeared at 500°C, diminished at 700°C, and showed up again at 1100°C under all atmospheres. The reason for the presence of β-Cr 2N at temperatures above 1100°C is that Cr 2N is thermodynamically more stable than CrN in the high temperature range, as analyzed from thermodynamics. The phase transforming from CrN to Cr 2N in the low temperature range is possibly due to the large stress relaxation occurring in the film during annealing, as observed in the in situ stress measurements.