LASER SINGLE-PHOTON IONIZATION MASS-SPECTROMETRY MEASUREMENTS OF SICLAND SICL2 DURING THERMAL ETCHING OF SI(100)

Pulsed laser single-photon ionization time-of-flight mass spectrometry is used to investigate the etch products resulting from thermal etchi ng of Si(100) with molecular chlorine over a temperature range of 1023 -1373 K and a pressure range of 10(-5)-10(-4) Pa. In this regime, two thermal etch products, SiCl2 and SiCl, are directly observed by ioniza tion without fragmentation using 118 nm light. Over this temperature a nd pressure range, the desorption fluxes of SiCl2 and SiCl are proport ional to the dosing chlorine pressure. A phenomenological activation e nergy of 0.36+/-0.03 eV is observed for the SiCl desorption flux from an Arrhenius plot. The SiCl2 product flux exhibits a complex temperatu re dependence, first. increasing and then decreasing, and thus this ra te is controlled by at least two pathways. One pathway in the lower te mperature regime may be a direct desorption channel. The other process at higher temperatures may be a competing reaction that limits the pr ecursor species, most likely SiCl, for the formation of SiCl2 on the s urface. The ability to detect the radical species without mass spectra l cracking provides the potential to unravel such complex pathways. (C ) 1997 American Vacuum Society.