Phase transformation in chromium nitride films

The phase transformation of CrN films prepared on (100) Si substrates by cathodic arc plasma deposition was investigated at various temperatures using x-ray diffraction and stress measurements. The films were annealed in a $N2/H2=9$ reducing atmosphere over the temperature range of 300–1200 °C. X-ray diffraction results showed that an additional $Cr2N$ phase appeared both at temperatures above 1100 °C and over temperatures between 500 and 650 °C. Thermodynamics can explain the formation of $Cr2N$ at temperatures above 1100 °C but not that in the low temperature range. Nevertheless, the residual stresses in the films were determined and found to be relaxed largely over such a low temperature range. The stress states of the films were strongly correlated to the phase transformation of the films. It is concluded that the formation of $Cr2N$ at such low temperatures is mainly due to a nonthermodynamic factor—large stress relaxation occurring in the films. More experimental proof of the stress relaxation-induced phase transformation is presented.