MELTING AND SOLIDIFICATION OF THE SURFACE -LAYER OF SINGLE-CRYSTAL SILICON SUBJECTED TO PULSED-LASER HEATING

The methods of optical probing and of detection of pulsed thermal radi ation were used in a study of crystal <-> melt phase transitions in si licon subjected to nanosecond ruby laser pulses. An electron-diffracti on investigation was made of the structural state of the semiconductor surface. Inhomogeneity of the phase transitions was demonstrated expe rimentally. Local variation of the melting and crystallisation rates p roduced an uneven phase boundary. Probing of this boundary through the base revealed deviations from the specular reflection of the prove be am. A numerical solution of the Stefan problem provided a description of the kinetics of changes in the reflected radiation flux, which were governed mainly by the transient optical absorption in the heated lay er of a single crystal. A possible reduction in the supercooling of th e molten surface during epitaxial crystallisation was slight. The pres ence on the irradiated surface of foreign micron-size particles could result in local lateral crystallisation of the melt and formation of t he unoriented silicon inclusions in the thin surface layer of the sing le crystal.w