Incorporation of substitutional carbon in Si and SiGe by laser processing in methane and propylene

Abstract

Substitutional carbon is incorporated in Si and SiGe from methane or propylene in a laser process which involves a melting–solidification cycle at each laser pulse. The surface density and concentration of substitutional C are measured by i.r. absorption spectroscopy vs. the laser fluence and the number of pulses in two gas supply modes: (i) in a pulsed molecular beam at low pressure; (ii) in a static pressure regime at pressures of the order of 100 mbar. Chemisorption is shown to play a dominant role in the molecular beam mode. The substitutional carbon surface density increases with the total melting time up to a threshold (≈10 μs) above which only SiC precipitates are formed. The maximum surface densities and concentrations obtained by this technique in Si(100) are, respectively, 5×10 15 cm 2 and 0.6%. Both of them are three times lower in SiGe. Finally, the C local mode linewidth is shown to be narrower with the laser process than with MBE or SPE. We conclude that fast laser-induced crystallization leads to randomized Si(Ge)C alloys.