Structural and optical analysis of Cr₂N thin films prepared by DC magnetron sputtering

Chromium nitride (Cr₂N) thin films were prepared by a DC magnetron sputtering technique. The deposition temperature was raised from 50 to 300℃, and its influence on the film structure and refractive index was investigated. X-ray diffraction analysis shows that the crystalline structure of the films transforms from the (101) to (002) oriented hexagonal Cr₂N phase as the increase of substrate temperature above 50℃, and a highly textured film grows at 100℃. An empirical relation between the crystalline orientation and infrared active modes of the films is obtained, i.e., the Fourier transform infrared (FTIR) spectrum of the film prepared at 50℃ exhibits only A₁(TO) mode. The prominent peak in the FTIR spectra of the film prepared above 50℃ is assigned to the E₁(TO) mode and is correlated with the (002) or c-axis oriented hexagonal wurtzite phase of Cr₂N. In the surface analysis of atomic force microscopy, a transformation from the featureless surface to columnar-type morphology is observed with the increase of substrate temperature from 50 to 100℃, exhibiting c-axis oriented crystallite growth. A further increase in substrate temperature to 200℃ causes the c-axis crystallites to merge, resulting in the formation of voids. The refractive index (n) of the deposited films is obtained using spectroscopic ellipsometry.