INFRARED OPTICAL-PROPERTIES OF MIXED-PHASE THIN-FILMS STUDIED BY SPECTROSCOPIC ELLIPSOMETRY USING BORON-NITRIDE AS AN EXAMPLE

We present a microstructure-dependent anisotropic infrared-optical die lectric function model for mixed-phase polycrystalline material from w hich we derive the transverse and longitudinal-optical modes observabl e in thin films. Infrared ellipsometry over the wavelength range from 700 to 3000 cm(-1) is then used to determine the phase and microstruct ure of polycrystalline and multilayered hexagonal and cubic boron nitr ide thin films deposited by magnetron sputtering onto (100) silicon. T he ellipsometric data depend on the thin-film multilayer structure, th e layer-phase composition, and the average orientation of the hexagona l grain c axes. In particular, we demonstrate the existence of spectra l shifts of longitudinal optical phonons as a function of microstructu re, i.e., the average grain crystallographic orientation within the mi xed-phase material.