In situ determination of dielectric functions and optical gap of ultrathin amorphous silicon by real time spectroscopic ellipsometry

We have developed techniques to determine the near-infrared to near-ultraviolet dielectric function and optical gap of ultrathin amorphous silicon [a-Si:(H)] using real-time spectroscopic ellipsometry during preparation and processing. The techniques have been applied to ∼50 Å a-Si:H films prepared by plasma-enhanced chemical vapor deposition, and to ∼250 Å pure a-Si chemically modified by atomic H exposure. For the latter, the time evolution of the bonded H content can be estimated along with the evolution of the gap.