Solid Phase Recrystallization and Strain Relaxation in Ion-Implanted Strained Si on SiGe Heterostructures
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Solid Phase Recrystallization and Strain Relaxation in Ion-Implanted Strained Si on SiGe Heterostructures M.S. Phen1, R. T. Crosby1, V. Craciun1, K. S. Jones1, M.E. Law2, J.L. Hansen3 and A.N. Larsen3 1
Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 Department of Electrical & Computer Engineering, University of Florida, Gainesville, FL 32611 3 Department of Physics and Astronomy, University of Aarhus, Aarhus, Denmark 2
ABSTRACT The relaxation process of strained silicon films on silicon-rich relaxed SiGe alloys has been studied. Experimental structures were grown via Molecular Beam Epitaxy (MBE) growth techniques and contain a strained silicon capping layer approximately 50 nm thick. The relaxed SiGe alloy compositions range from 0 to 30 at.% germanium. A 12 keV Si+ implant at a dose of 1x1015 atoms/cm2 was used to generate an amorphous layer ~30 nm thick, which was confined within the strained silicon capping layer. Upon annealing at 500 ºC, it was found that the solid phase epitaxial regrowth process of the amorphous silicon breaks down for high strain levels and regrowth related defects were observed in the regrown layer. In addition, high-resolution X-Ray diffraction results indicate a reduction in strain for the silicon capping layer. This study addresses the critical strain regime necessary for the breakdown of solid phase epitaxial recrystallization in silicon.
INTRODUCTION Strained silicon technology offers the advantage of enhanced carrier mobility without a need for scaling gate length (1-2). Strain in the capping layer arises from the lattice mismatch between the SiGe substrate and the silicon film. Si/SiGe heterostructures are typically grown at low temperatures. The subsequent anneal to activate dopants and regrow amorphous layers could decrease the strain energy in these structures and cause them to relax by forming misfit and threading dislocations. In previous works it has been shown that the strained silicon on relaxed SiGe relaxes after high thermal processing via misfit dislocations, threading dislocations, and Ge interdiffusion (3-5). Ion implantation creates point defects which may act as nucleation sites for relaxation-induced dislocations and/or may assist Ge interdiffusion by an interstitial mediated mechanism. In recent years, many studies have been reported on silicon recrystallization and regrowth in SiGe/Si and Si systems (6-8). However, the stability of strained silicon post recrystallization is not well understood. In this study, we focus on recrystallization kinetics and relaxation due to implantation and thermal processing of the strained silicon layer.
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EXPERIMENTAL DESIGN Strained silicon was grown on top of relaxed Si1-xGex via Molecular Beam Epitaxy (MBE). The relaxed Si1-xGex was grown to a thickness of 630 nm, with a compositional graded buffer layer incorporating 10 at.% germanium/micron. The germanium concentrations were 0, 10, 20 and 30 at.%. Subsequently, a 50 nm strained silicon capping layer was grown upo
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