Phase transformation in chromium nitride films

Abstract

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.