Laser-induced structural or compositional modifications of Si or IV-IV surface: planarization, pulsed-laser-induced epitaxy, carbon incorporation, and chemical etching

Laser induced structural or compositional modifications of Si or IV-IV surface:planarization, pulsed laser induced epitaxy, carbon incorporation, chemical etchingJ. Boulmer' ,B. Dragnea3, C. Guedj', D. Debarre', A. Bosseboeuf', E. Finkman2, B. Bourguignon3I Institut d'Electronique Fondamentale, associe au CNRS, Bat. 220, Universite Paris—Sud, 91405, Orsay, France2 Department of Electrical Engineering and Solid State Institute, Technion, Haifa, 32000 Israel3 Laboratoire de Photophysique Moleculaire du CNRS, Bat. 213, Universite Paris—Sud, 91405, Orsay, FranceABSTRACTWe examine experimentally the modifications induced at the surface of silicon and IV-IV alloys by an excimer laserabove the melting threshold fluence. Laser irradiation takes place under vacuum, or in the presence of a gas. The resultingprocesses are respectively: laser induced planarization, pulsed laser induced epitaxy (PLIE), incorporation of atoms from thegas phase, and laser chemical etching. In turn, the laser induced surface modifications and the presence of adsorbates on thesurface cause important changes in the melting I solidification cycle. We describe a model calculation which takes intoaccount non-equilibrium heat diffusion, phase change, atom diffusion, segregation and desorption. The model is applied to thelaser chemical etching process, and its results are compared to the experimental data. This simulation brings information onthe segregation ofchlorine and on the dynamics of desorption.Keywords: laser processing, Si, SiGeC, IV-IV alloy, laser induced processes, chemical etching, planarization, epitaxy, Cincorporation, desorption, segregation, diffusion, melting.I. INTRODUCTIONThe modifications induced at the surface of an irradiated material are of major importance in many laser processingtechniques which are useful for the fabrication of electronic circuits, micro-electro-mechanical or micro-optical systems, andfor the thin film deposition or the spectroscopic analysis techniques based on laser ablation. In the present paper, we reviewour experimental observations of the modifications induced on Si or IV-lV (SiGeC) samples by a pulsed laser involvingrepeated melting /solidification cycles. Our experiments are performed with an XeC1 excimer laser (X 308 nm, pulseduration 20 ns) operated in vacuum or in the presence of a gas. The laser fluence ranges from 0.3 to 1 .5