Point defect–dislocation interactions in BEOL-compatible Ge-on-Si epitaxy

Abstract

Reduced thermal budget is required for back-end-of-line (BEOL) integration of application specific functionality into the multilevel metal stack of a processor “substrate.” We report 400 °C BEOL-compatible Ge-on-Si growth (LT Ge) that is epitaxial and single crystalline with a defect density similar to high temperature growth and a small 0.05% tensile strain. Room temperature methanol–iodine passivation is employed pre-growth in lieu of the typical 800 °C oxide removal step. Undoped LT Ge exhibits p-type conductivity initially and n-type conductivity conversion upon annealing. Hall effect measurements following post growth heat treatment between 400 and 600 °C reveal an acceptor removal reaction that follows first-order kinetics with an activation energy of 1.7 ± 0.5 eV and a pre-exponential factor of 2.3×107 s−1 consistent with a point defect, diffusion limited process. We also observe that 90° sessile dislocations identified via transmission electron microscopy are annihilated in the same temperature regime, which is evidence for point defect-mediated climb. Ensuring high-quality epitaxy by characterizing defect reactions in a BEOL-compatible Ge-on-Si process flow is key to enabling vertical integration of optical interconnects.