Accurate analysis of indium-zinc oxide thin films via laser-induced breakdown spectroscopy based on plasma modeling

We report on accurate analysis of indium-zinc oxide thin films via laser-induced breakdown spectroscopy (LIBS) based on the calculation of the spectral radiance of the nonuniform laser-produced plasma. A thin film sample with variable elemental composition was irradiated with ultraviolet nanosecond laser pulses and the plasma emission spectra were characterized using time-resolved optical emission spectroscopy. Thus, the spectrum recorded with an Echelle Spectrometer coupled to a gated detector was compared to the spectral radiance computed for a plasma in local thermodynamic equilibrium conditions. The time evolution of the plasma was studied to find optimized recording conditions for which the self-absorption of spectral lines is minimized. In addition, the time-resolved measurements allowed us to determine the Stark broadening parameters of spectral lines used for the LIBS analysis. The metal fractions measured via LIBS were found to be in good agreement with the values obtained by complementary measurements using energy dispersive X-ray spectroscopy. The relative decay between fractions measured with both methods was smaller than 5% over the entire measurement range that implied the variation by a factor of four in the case of zinc. The present results show that LIBS measurement procedures based on plasma modeling could be used for fast quality control in the industrial production of thin films.