Multichannel ellipsometry from 1.5 to 6.5 eV for real time characterization of wide band gap materials: Phase identification in boron nitride thin films

A recently developed real time spectroscopic ellipsometer with an ultraviolet-extended spectral range (1.5-6.5 eV) has been applied to investigate the sputter deposition of BN films with high cBN content. Based on the optical contrast between the two phases (sp² and sp³ bonded BN) above 4.5 eV, it has been possible to characterize the growth of these films using a two-layer isotropic optical model. In this model, the innermost layer represents the combined contribution from the sp² bonded material (aBN and hBN) denoted collectively as hBN, whereas the outermost layer represents the contribution of the predominantly sp³ bonded material denoted as cBN. The BN films were grown on crystalline silicon substrates using two processes: (i) r.f. magnetron sputtering of a BN target with pulsed d.c. substrate biasing; and (ii) pulsed d.c. sputtering of a B₄C target with r.f. substrate biasing. In both cases, the thickness evolution of the hBN and cBN layers as well as their dielectric functions over the extended spectral range have been determined. The cBN content deduced from the two-layer analysis is in good agreement with estimates from ex situ infrared transmission spectroscopy. © 2001 Elsevier Science B.V. All rights reserved.