Vacuum ultra-violet spectroscopic ellipsometry study of single- and multi-phase nitrideprotective films

Abstract

This paper reports on a systematic investigation of the optical properties ofTa1−xZrxN single-phase and ZrN–Ag multi-phase films fabricated by unbalanced magnetron sputteringusing vacuum ultraviolet spectroscopic ellipsometry (VUV-SE). VUV-SE is a newlydeveloped technique that was used to evaluate the strength and energy of the interbandelectronic excitations/transitions in these films. The energy of the interband transition wasfound to be altered by any changes in the elemental composition for single-phasematerials. For example, it was found to increase with the increase in the covalentcharacter of the bond as more Zr atoms are substituted for by Ta atoms in the ZrNrock-salt structure. In contrast, the peak positions did not vary in the multi-phasestructures because the constituent phases were immiscible and retained their electronicstructure. However, the strength and width of the interband transition were found tochange to reflect changes in phase composition and microstructure. The optical andelectronic properties of these materials were simulated using density functionaltheory (DFT) within the generalized gradient approximation. The calculatedrefractive indices and density of states were in good agreement with the VUV-SEdata.