Co diffusion and precipitation in Si/SiGe heterostructures

Abstract

Several Si/Si1−xGex multilayer structures, grown by molecular-beam epitaxy (MBE) or synthesized by high-dose Ge implantation into Si substrates, have been implanted with Co atoms at doses of typically 1.0×1015 and 1.0×1016 ions/cm2. These samples are annealed at elevated temperatures (typically 850 °C) to study the diffusion and precipitation of the Co atoms. Depth distributions of Co atoms are measured with secondary-ion mass spectrometry. X-ray diffraction is used to measure the strain evolution of the Si/Si1−xGex MBE multilayers during processing. Channeling Rutherford backscattering spectrometry is used to study the lattice position of the Co atoms after heat treatment. Upon annealing, Co atoms are observed to diffuse out of the Si1−xGex layers. The efficiency of this outdiffusion process strongly depends on the implantation dose. The released Co atoms are gettered by the Si layers adjacent to the Si1−xGex layers and, in case of the MBE samples, at the interface between the substrate and MBE-grown bufferlayer. A physical model to explain these observations is presented.