CHEMICAL-REACTIONS AT SOLID SOLID INTERFACES INDUCED BY PULSED LASER ANNEALING

Al thin films (thickness < 1000 Å) evaporated on the (111) face of an Sb single crystal, and Al-Sb multilayer thin films (thickness < 1000 Å) evaporated on glass and quartz substrates were irradiated in UHV by the pulsed beam of an excimer laser. The samples were characterized in-situ during the growth of the films and after the irradiations by Auger and photoelectron spectroscopies without breaking the vacuum, and later, by scanning electron microscopy. The formation of the AlSb compound is observed above the fluence threshold previously reported. Lateral transport of matter and inhomogeneous reaction are observed after irradiation of the Al films deposited on Sb crystals, leading to the formation of an inhomogeneous surface with holes and particles. A strong chemical reaction between the substrate and the films also leads to a partial oxidation of the film evaporated on quartz or glass. We observed the same behaviour under the IR laser beam from a Q-switched Nd:YAG laser. One has taken advantage of fast thermal processes of thin films induced by pulsed or scanned CW laser beams for applications like synthesis of compounds by laser alloying, oxidation of thin films, planarization, and phase changes in optical data storage media. The relevant parameters needed to predict the evolution of the film/substrate interface under strong laser irradiation using the thermal model are not only: (i) the thermal properties of the substrate, and (ii) the optical characteristics of the film-substrate system, but also (iii) the chemical stability of the interface, and (iv) the free surface energies of the substrate and of the film, at least above the melting fluence threshold or if thermal cycling is expected over large periods of time. © 1990.