In situ diagnostics of stress evolution and relaxation at BN deposition by IBAD

Boron nitride films are grown by ion beam assisted deposition (IBAD). Si cantilevers are used as substrates. Intrinsic stress data are derived from dynamic simultaneous measurement of cantilever bending and film thickness during growth. The cantilever bending was measured with a two-beam laser deflection system for real time measurement of the stress in thin films during processing. The curvature of the cantilever, laser reflectivity, quartz thickness monitoring and real time spectroscopic ellipsometry data are recorded simultaneously. Instantaneous stress knowledge with a depth resolution in the nanometer scale provide detailed information on growth processes. 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 measured stress depends sensitively on fluctuations in the boron evaporation rate which in turn cause variations in the ion/atom arrival ratio. The global stress in turbostratic and cubic boron nitride films is studied during annealing up to 670°C. It is observed that the stress relaxation starts when the deposition temperature is exceeded. It is demonstrated that the intrinsic stress of cubic boron nitride films can be relaxed during growth by simultaneous medium energy implantation. For simultaneous implantations with an ion energy of several keV it is shown that the stress in the growing film can be reduced below 2 GPa, resulting in high quality c-BN.