Structural and electrical characterisation of ion-implanted strained silicon

The production of low resistance ultra-shallow junctions for e.g. source/drain extensions using low energy ion-implantation will be required for future CMOS devices [H. Wakabayashi, M. Ueki, M. Narihiro, T. Fukai, N. Ikezawa, T. Matsuda, K. Yoshida, K. Takeuchi, Y. Ochiai, T. Mogami, T. Kunio, Trans. Electron Devices 49 (2002) 89–94]. This architecture will require implants which demonstrate high electrical activation and nm range depth profiles. We investigate the properties of Sb implants in tensile strained silicon due to their potential to satisfy these criteria and the mobility enhancements associated with tensile strained silicon. Low energy (in this case 2keV) implants coupled with Sb’s large atomic radius are capable of providing ∼10nm implant depths. In addition to this, Sb demonstrates higher electrical activation in the presence of tensile strain, when compared with the more traditional n-type dopant As [N.S. Bennett, N.E.B. Cowern, A.J. Smith, R.M. Gwilliam, B.J. Sealy, L. O’Reilly, P.J. McNally, G. Cooke, H. Kheyrandish, Appl. Phys. Lett. 89 (2006) 182122]. We now report on the initial results of an ongoing systematic study over a wide silicon tensile strain range (from 0.4% to 1.25% strain) in order to establish clear strain-related trends. Graded Si1−xGex virtual substrates (VS) with 0.1≤x≤0.3 were used as template substrates upon which tensile Si layers were grown. Prior to implantation the quality of the strained layer and SiGe buffer is assessed using UV micro-Raman spectroscopy (μRS), synchrotron X-ray topography (SXRT) and high-resolution X-ray diffraction (HR-XRD). For measurements of strain following implantation, HR-XRD is found to be more useful than μRS because of additional carrier-concentration induced Si Raman peak shifts. These shifts obscure small changes in the strain state, and are a result of the degenerate doping levels achieved in these samples (∼7×1020cm−3). Using X-ray techniques, at Ge concentrations >23% (i.e. ɛ>0.9%) we find clear evidence of tilt in the SiGe VS, which impacts on the quality of the strained Si. Additionally, stacking faults have been detected non-destructively in the higher strain samples (ɛ=1.25%, VS=Si0.7Ge0.3) using SXRT in transmission mode.