Transformation of amorphous Si0.9Ge0.1 and Si films by laser annealing

Abstract A report is given on the transformation of amorphous Si 0.9 Ge 0.1 films into polycrystalline films by laser annealing. The films have been electron-gun evaporated onto glass substrates. 308 nm radiation of an excimer laser with pulse lengths of about 10 ns was used for the laser annealing. Whereas the diameter of the laserspot is about a few millimetres, the target can be moved by a computer-controlled scanner adjusting the energy density and covering a large area of a sample by stepping it laterally to the laser beam. For characterization of the amorphous-polycrystalline transformation we used the spectral dependencies of the optical constants with the different phases which were deduced by measurements of transmissivity and reflectivity applying a computer-aided fitting. We observed that especially the alloy films were transformed inhomogeneously by annealing only once. To achieve homogeneous transformation a process of repeated annealing with increasing energy density is necessary. Furthermore, melting times of pure Si films were measured by analyzing the increased reflectivity of the UV-radiated area of the sample due to the liquid state of Si. These melting times allow one to determine the melting depth and the surface temperature by applying a numerical model.