Strain Relaxation of Ion-implanted Strained Silicon on Relaxed SiGe
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Strain Relaxation of Ion-implanted Strained Silicon on Relaxed SiGe R. T. Crosby, K. S. Jones, M. E. Law, A. F. Saavedra 1, J. L. Hansen, A. N. Larsen 2, and J. Liu 3 1
SWAMP Center, University of Florida, Gainesville, FL Department of Physics and Astronomy, University of Aarhus, Aarhus, Denmark 3 Varian Semiconductor Equipment Associates, Gloucester, MA. 2
ABSTRACT The relaxation processes of strained silicon films on silicon-rich relaxed SiGe alloys have been studied. Experimental structures were generated via Molecular Beam Epitaxial (MBE) growth techniques and contain a strained silicon capping layer of approximately 50 nm. The relaxed SiGe alloy compositions range from 0 to 30 atomic% germanium. Samples received two distinct types of silicon implants. A 12 keV Si+ implant at a dose of 1x1015 atoms/cm2 was used to generate an amorphous layer strictly confined within the strained Si cap. An alternate 60 keV Si+ implant at a dose of 1x1015 atoms/cm2 was employed to create a continuous amorphous layer extending from the sample surface to a position 50 nm into the bulk SiGe material. The strain relaxation and regrowth processes are quantified through High Resolution X-Ray Diffraction (HRXRD) rocking curves and Cross-sectional Transmission Electron Microscopy (XTEM). The role of injected silicon interstitials upon the strain relaxation processes at the Si/SiGe interface after annealing at 600oC is investigated. INTRODUCTION Strained Si is becoming an essential component in device applications due to its enhanced carrier mobility [1-4]. Strained Si on a relaxed SiGe buffer layer on (001) Si is typically grown at low temperatures. However, these layers may experience and will have to withstand further processing, i.e. annealing and ion-implantation to be fully incorporated into modern-day Si-based technology. It has been demonstrated that strained Si relaxes via misfit and threading dislocation propagation and Ge interdiffusion [5-7] after high temperature post annealing. To fully access the stability of these layers, the influence of ion implantation must be ascertained. Ion implantation can create point defects, which can serve as nucleation sites for relaxation-induced defects or aid in the interdiffusion of Ge; thus, relaxation can be accelerated. There have been many studies on the regrowth and recrystallization of ionimplanted SiGe/Si layers [8-11]; however, the regrowth process for strained Si remains unclear. This experiment will determine if strained Si structures can withstand the duress of solid phase epitaxial regrowth.
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EXPERIMENTAL DESIGN Strained Si was grown on top of relaxed SiGe virtual substrates via MBE methodology. The relaxed SiGe was grown with a compositionally graded buffer incorporating 10% Ge/micron. Then a constant composition SiGe layer was grown with a thickness of 630 nm upon which a 50 nm strained Si cap was grown. The Ge concentrations were 0, 10, 20, and 30%. Figure 1 (a) displays the HRXRD rocking curves of the starting material.
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