BIC Formation and Boron Diffusion in Relaxed Si 0.8 Ge 0.2
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BIC Formation and Boron Diffusion in Relaxed Si0.8Ge0.2 R. T. Crosby, L. Radic, K. S. Jones, M. E. Law 1, P.E. Thompson 2, J. Liu 3, M. Klimov 4, V. Craciun 5 1 2 3 4
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SWAMP Center, University of Florida, Gainesville, FL Naval Research Laboratory, Code 6812, Washington D.C., 20375 Varian Semiconductors Equipment Associates, Gloucester, MA Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, FL Major Analytical and Instrumentation Center, University of Florida, Gainesville, FL
ABSTRACT The relationships between Boron Interstitial Cluster (BIC) evolution and boron diffusion in relaxed Si0.8Ge0.2 have been investigated. Structures were grown by Molecular Beam Epitaxy (MBE) with surface boron wells of variant composition extending 0.25 µm into the substrate, as well as boron marker layers positioned 0.50 µm below the surface. The boron well concentrations are as follows: 0, 7.5x1018, 1.5x1019, and 5.0x1019 atoms/cm3. The boron marker layers are approximately 3 nm wide and have a peak concentration of 5 x1018 atoms/cm3. Samples were ion implanted with 60 keV Si+ at a dose of 1x1014 atoms/cm2 and subsequently annealed at 675oC and 750oC for various times. Plan-view Transmission Electron Microscopy (PTEM) was used to monitor the agglomeration of injected silicon interstitials and the evolution of extended defects in the near surface region. Secondary Ion Mass Spectroscopy (SIMS) concentration profiles facilitated the characterization of boron diffusion behaviors during annealing. Interstitial supersaturation conditions and the resultant defect structures of ion implanted relaxed Si0.8Ge0.2 in both the presence and absence of boron have been characterized. INTRODUCTION In order to meet the technological demands of tomorrow’s CMOS design, SiGe has emerged as alternative material. To update models and processing steps accordingly, fundamental knowledge about dopant diffusion in SiGe is of extreme importance. It has been demonstrated that B diffusion is retarded in SiGe [1, 2], and B activation is comparable [3, 4]. Strain compensation and preferential Ge-B bonding can be attributed to this behavior, but to fully test these hypotheses, the defect morphology should be studied in conjunction with diffusion studies. Upon implantation and annealing, it has been demonstrated that immobile and inactive boron interstitial clusters will form in Si, which contribute to transient enhanced diffusion (TED) and the deactivation of B [5-8]. These defects are concentrated around the projected range of the implant where interstitial supersaturation is the highest. This paper will address the defect evolution of BICs in SiGe and also the associated diffusion of B in SiGe from interstitial injection.
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EXPERIMENTAL SETUP B-doped Si0.8Ge0.2 was grown atop of relaxed Si0.8Ge0.2 substrates with varying surface B well concentrations: 0, 7.5 x 1018 cm-3, 1.5 x 1019 cm-3, and 5.0 x 1019 cm-3. These B wells extend 0.25 µm, and will be utilized to access the evolution of BICs in the presence of
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