Quantification of microstructural evolution in sputtered a-Si thin films by real time spectroscopic ellipsometry

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Abstract
We have undertaken a real time spectroscopic ellipsometry (SE) investigation of amorphous silicon (a‐Si) sputtered under conditions leading to the highest bulk bond‐packing density. The spectral range for our observations is 1.5–4.5 eV, and the time resolution and repetition rate for complete spectra are ∼3 and ∼15 s, respectively. From the real time measurements, we have deduced the complete optical functions and band gap of the growing material. The real time data also provide quantitative information on the microstructural evolution during initial nucleation and growth. For a‐Si on thermally oxidized c‐Si, we find that the first monolayer covers ∼15% of the surface, and the first bulk density monolayer is formed after a cluster thickness of 21 Å. The advantage of SE over the single photon energy approach, is that void fractions and layer thicknesses can be deduced from each pseudodielectric function independently. This leads to unambiguous microstructural information at an unprecedented level of detail, in a compact, easily assimilated form for future comparisons with film growth simulations.

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