Elastic and anelastic properties, internal stress and thermal expansion coefficient of cubic boron nitride films on silicon

The values of Young's modulus, internal friction, internal stress and linear thermal expansion coefficient of c-BN thin films have been estimated from mechanical spectroscopy (vibrating-reed technique, 175 Hz-12 kHz). The thin films were deposited by reactive sputtering onto microstructurized silicon cantilever substrates. The measured Young's modulus and thermal expansion coefficient are roughly in accordance with the few literature data on bulk material and with theoretical estimates. The internal stress of approximately 5 GPa is hardly affected by thermal treatments of the film up to 620°C. An interesting anelastic damping peak is detected at approximately 50°C (at 650 Hz) with an activation energy of 0.45 eV which is suggested to arise from the piezo-electric and semiconducting properties of the c-BN film.