In situ measurement of stress during deposition of boron nitride films

A two-beam laser deflection system has been setup for real-time measurement of the stress in thin films during processing. The curvature of a Si-cantilever, laser reflectivity and real time spectroscopic ellipsometry data are recorded simultaneously. Reliable real time film thickness data are essential for the calculation of the instantaneous stress from the bending force per unit width measured. Instantaneous stress data with a depth resolution in the nanometer range provide detailed information on growth processes. It is demonstrated that force per unit width or global stress data, as calculated by applying the simple form of Stoney's equation, are not appropriate for the analysis of the stress in layered structures like boron nitride films.
The depth distribution of the instantaneous stress in boron nitride films recorded during growth by ion beam assisted deposition has been analyzed. The layer sequence of interfacial turbostratic BN layer / mixed (t-BN+c-BN) transition layer / cubic BN can be clearly identified in the instantaneous stress data. The instantaneous stress has been found to depend sensitively upon fluctuations in the boron deposition rate which in turn cause variations in the ion/atom arrival ratio. Real time global stress data recorded during ion implantation into c-BN films have revealed for the first time two mechanisms being involved.