ArF excimer laser epitaxy of SixGe1-x alloys studied by XRD and XPS

The formation of SiGe alloys was obtained by ArF excimer laser induced epitaxy of thin a-Ge films deposited by Laser-CVD on Si(100) substrates. The alloying process was studied as a function of the thickness of the Ge overlayer, which ranged between 10 and 70 nm. In order to investigate the early stage of the Ge and Si intermixing, single pulse irradiation was performed at fluence (0.49 J/cm2) appropriate to melt the Ge overlayer and a certain thickness of the underlying substrate. XRD and XPS depth profile analysis revealed the formation of graded alloys, showing high Ge content in the near-surface layer and Si rich alloy regions in the proximity of the alloy/substrate interface. Although Ge was redistributed over lengths predictable by heat flow numerical model calculation, other mechanisms (such as Ge segregation and/or strain field effects) besides diffusion, seem to regulate the observed alloy concentration profiles. The altered surface morphology exhibited after laser processing by the sample having the thickest Ge overlayer sets an upper limit for the thickness of the a-Ge film, which in the present irradiation conditions is about 40 nm.