Beam-power heating effect on the synthesis of graded composition epitaxial Si 1− xGe x alloy layers

Abstract

Formation of epitaxial Si 1− x Ge x layers by high-dose Ge + implantation into Si has been investigated under different beam-power densities regimes. Ge + ions with incident energies of 200 and 250 keV were implanted into (100) Si. Ion fluences were between 0.5 × 10 16 and 1 × 10 17Ge +/cm 2, with current densities varied between 0.2 and 12 μA/cm 2. In one set of samples a second amorphizing 500 keV Si + implant was also performed at low temperature (< −50°C) before Solid Phase Epitaxial (SPE) regrowth. As implanted and thermal processed layers have been studied by cross-sectional Transmission Electron Microscopy (XTEM) and Rutherford Backscattering Spectrometry and ion-Channeling (RBS-C). In the low beam-power density regime (⋍ 0.2 W/cm 2) small variations in the current density value have been found to affect dramatically the crystalline quality of the SPE regrown layers. This has been attributed to beam-power heating occurring during the synthesis of the layers which determines the quality of the amorphous/crystalline (a/c) interface and of the crystalline seed for SPE regrowth. The implantation temperature for different beam-power densities has been measured and a method to control the a/c interface quality by using a double-step Ge + implant process has been demonstrated. Samples implanted with high beam-power densities (⋍ 2 W/cm 2) resulted in highly damaged crystalline materials. The high-temperature annealing required to remove the implantation damage is limited by the Ge diffusion, while appreciable recovery of the crystal quality is achieved if a post amorphization process by low temperature Si + implant is used in conjunction with SPE regrowth.