Surface brillouin scattering study of radio frequency sputtered hard thin films
Date
2018
Authors
Kuria, Jonah Muiru
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Abstract
Surface Brillouin Scattering (SBS) is used to investigate the elastic properties of NbN, TaN, and ZrN thin films deposited on Si substrates using rf magnetron sputtering. Influence of sputter power and hence the ad-atom energy on the elastic properties of NbN has been established for the films deposited at sputter powers ranging from 75 W - 250 W. TaN and ZrN thin films have been deposited at sputter powers of 150 W and 200 W respectively. For each sputter power, a sample set of eight films of thickness ranging from 50 nm - 800 nm has been used for the investigations.
From the measured SBS spectra, the SAW phase velocities were calculated and used to obtain the velocity dispersion curves for all the sample sets. The surface elastodynamic Green’s technique was used to simulate Brillouin spectra of the films. Theoretical SAW phase velocities and hence the velocity dispersion curves have been obtained from the simulations. In NbN and TaN films, the dominant RSAW is observed in all the sample sets with higher order peaks (Sezawa modes) emerging from film thicknesses of 150 nm above. For the ZrN thin films on Si, no guided modes are observed. Increasing film thickness for NbN and TaN leads to a stiffening of the acoustic modes. Elastic constants for the NbN films and TaN films have been determined from the velocity dispersion modes. A least square fitting procedure has been used to optimise the elastic constants obtained from the Green’s function approach. The uncertainties of the elastic constants have also been calculated from the same procedure. Picosecond ultrasonic technique has been used as a complementary technique for the extraction of elastic constants of ZrN films.
Description
A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, University of the Witwatersrand, Johannesburg, 10 September 2018
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Citation
Kuria, Jonah Muir (2018) Surface brillouin scattering study of radio frequency sputtered hard thin films, University of the Witwatersrand, Johannesburg, https://hdl.handle.net/10539/27329