Study of the Phase Nature of Boron- and Nitrogen-Containing Films by Optical and Photoelectron Spectroscopy

This work considers the possible occurrence of two distinct phases in thin films of overall composition B1−xNx (0.21 ≤ x ≤ 0.47) grown by chemical vapor deposition from sequential pulses of diborane (B2H6) and ammonia (NH3). Two distinct peaks are identified in B1s x-ray photoelectron spectroscopy (XPS), related to two populations of B atoms with different oxidation states. The data are most consistent with a model in which one population mainly bonds to B atoms, and the other population mainly bonds to N atoms, as expected for a composite of B and BN. Based on peak broadening, interfaces between the two types contribute significantly to the spectra. Furthermore, spectroscopic ellipsometry (SE) found that the samples displayed optical absorption consistent with that of pure-B. This work, thus, developed a fit model to characterize the films optically by SE. Describing the films as composites of pure-B and BN, and using optical constants of reference layers thereof, the relative fractions could be estimated in reasonable agreement with XPS. Differences between the models and data in both SE and XPS are consistent with the effects of hydrogenation and the contribution of atoms in interface states. Evidence from SE suggests that the films may consist of stacked lamellar phases, which would indeed have a large surface-to-volume ratio.