Melting and solidification of the surface layer of single-crystal silicon heated by pulsed laser radiation

Abstract

The methods of optical probing and of detection of pulsed thermal radiation were used in a study of crystal ↔ melt phase transitions in silicon heated by nanosecond ruby laser radiation. An electron-diffraction investigation was made of the structural state of the semiconductor surface. Inhomogeneity of the phase transitions was demonstrated experimentally. Local variations of the melting and crystallisation rates result in roughness of the phase boundary. Probing of this boundary through the base revealed deviations from the specular reflection of the probe beam. A numerical solution of the Stefan problem provided a description of the dynamics of changes in the reflected radiation flux, governed mainly by the transient optical absorption in the heated layer of a single crystal. A possible reduction in the supercooling of the molten surface during epitaxial crystallisation was insignificant. The presence on the irradiated surface of foreign micron-size particles could result in local lateral crystallisation of the melt and formation of unoriented silicon inclusions in the thin surface layer of the single crystal.