INTERPRETATION OF OPTICAL DIAGNOSTICS FOR THE ANALYSIS OF LASER CRYSTALLIZATION OF AMORPHOUS SILICON FILMS

Abstract

The focus of this investigation is on optical diagnostics of melting and solidification during excimer laser crystallization of a-Si. Although optical techniques are effective for probing the laser annealing process, the analysis of the results is not straightforward due to temperature variation of the optical properties, phase change, and interference effects. These effects are clarified by analyzing the front and back, s- and p-polarized reflectivity traces at the lambda=633-nm and 1,520-nm laser wavelengths. Ellipsometry was utilized to measure the temperature-dependent spectral optical properties of the deposited 50-nm a-Si films. Spectral optical properties of laser-annealed poly-silicon were also measured at room temperature. These optical properties were used in the optical models constructed for the melting and solidification processes. Comparison with the experimental results unveiled evidence of spontaneous volumetric nucleation for laser fluences sufficiently high to impart complete melting of the a-Si film.