Laser-induced breakdown spectrometry of titanium dioxide antireflection coatings in photovoltaic cells

Silicon photovoltaic cells have design and material requirements different from those of most other silicon electronic devices. Not only are nearly ideal silicon surfaces required, but also the bulk properties must be of uniform high quality for high-energy conversion efficiency. In this paper, emission spectra of laser-generated plasmas from titanium dioxide antireflection coatings in solar cells are reported, A pulsed nitrogen laser at 337.1 nm was used with a pulse width of 10 ns and a laser fluence of 8.6 J/cm(2) onto the sample. The plasmas were detected using a charge-coupled device. Depth profilings from several samples with different thicknesses of titanium dioxide have been studied. A method for measuring thin TiO2 films based on the observation of such profiles was developed. The effect of the laser fluence on the sensitivity of the present method has been examined. Depth resolutions are fluence-dependent but are on the order of 40 nm. The dependence between titanium dioxide plasma intensity and material reflectivity at the laser wavelength is discussed. Another valuable aspect of the technique is the ability to perform measurements in a contactless manner at room temperature and atmospheric pressure on wafer-sized samples.