Onset of Misfit Dislocation Generation in As-Grown and Annealed Si l-X Ge x /Si Films
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ONSET OF MISFIT DISLOCATION GENERATION INAS-GROWN AND ANNEALED Sil_xGex/Si FILMS M.P. Scott, S.S. Laderman, T.I. Kamins, S.J. Rosner, K.Nauka Hewlett Packard Co., Palo Alto, CA 94303-0867 D.B. Noble, J.L. Hoyt, C.A. King, C.M. Gronet, J.F. Gibbons Stanford Electronics Labs, Stanford, CA 94305 ABSTRACT X-ray topography and transmission electron microscopy were used to quantify misfit-dislocation spacings in as-grown Sil_ Ge films formed by Umited Reaction Processing (LRP), which is a chemical vapor dXposition technique. These analysis techniques were also used to study dislocation formation during annealing of material grown by both LRP and by molecular beam epitaxy (MBE). The thickness at which misfit dislocations first appear in as-grown material was similar for both growth techniques. The thermal stability of capped and uncapped0 films was also investigated after rapid thermal annealing in the range of 625 to 1000 C. Significantly fewer misfit dislocations were observed in samples containing an epitaxial silicon cap. Some differences in the number of misfit dislocation generated in CVD and MBE films0 were observed after annealing uncapped layers at temperatures between 625 and 825 C. INTRODUCTION The recent fabrication of near-ideal heterojunction bipolar transistors (1] has increased the need to understand the structural stability of Si1 Gex alloy thin films grown on silicon. It is important to prevent strain relaxation in t-Aese pseudomorphic device structures to preserve the desired band gap and avoid recombination currents associated with closely spaced misfit dislocations [2]. Measurements to date of the generation of misfit dislocations during growth of Si1 Ge, have focussed on epitaxial layers grown by MBE [3,4]. Some of these siudixes have used Rutherford backscattering (RBS) and x-ray diffraction to characterize the onset of strain relaxation. The sensitivity of these techniques is not sufficient to study the early stages of misfit dislocation generation. A combination of techniques has been used to characterize individual dislocations in as-grown MBE samples [5,6]. However, little experimental data has been presented concerning the onset of dislocation generation induced by post-growth annealing and no comparison has been made between Si1 _xGex formed by MBE and that formed by chemical vapor deposition. In the present report, results are presented on material grown by limited reaction processing (LRP), a CVD technique that relies on the rapid heating and cooling of the substrate to initiate and terinate growth [7]. Tlese SijxGex films have been found to contain approximately 10 oxygen atoms/cm . Previous reports [4,5] have shown that as-grown, MBE Sii xGex films are metastable with dislocation spacings larger than predicted by equilibrium theory. In the present study the thermal stability of both uncapped and epitaxial-silicon capped structures were characterized by x-ray topography and transmission electron microscopy. The observed stability was compared to the stability of the film predicted by equili
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