Characterization of laser-annealed polysilicon by spectroscopic ellipsometry and comparison to other techniques

Structural and electrical quality of polysilicon layers obtained by laser annealing of amorphous silicon, is a key point for the electric properties of TFT devices. For precise optimization of the laser annealing process and on line quality control a non destructive toll capable to provide precisely at the same time the crystallinity, the thickness and the roughness of the polysilicon layers is of great interest. The paper will compare the possibilities of UV spectrometry and spectroscopic ellipsometry in the case of practical examples obtained in different conditions. The UV penetration depth of less than 20 nm investigates the channel depth of the TFT. Structural results obtained using this spectral range are then directly correlated with the mobility of the transistors. Results will be also related to Raman spectroscopy and imaging morphologies obtained by scanning microscopy. A practical procedure for using spectroscopic ellipsometry will be discussed in relation to electrical results obtained on TFT devices.