(A)thermal migration of Ge during junction formation in s-Si layers grown on thin SiGe-buffer layers
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(A)thermal migration of Ge during junction formation in s-Si layers grown on thin SiGebuffer layers W. Vandervorst1,3, B.J. Pawlak2, T.Janssens1, B.Brijs1, R. Delhougne1, M. Caymax1, R.Loo1 1
IMEC, Kapeldreef 75, 3001 Leuven, Belgium Philips Research Leuven, Kapeldreef 75, 3001 Leuven, Belgium 3 also : INSYS, KULeuven, Belgium email: [email protected] 2
ABSTRACT Solid phase epitaxial regrowth (SPER) has been proven to be highly advantageous for ultra shallow junction formation in advanced technologies. Application of SPER to strained Si/SiGe structures raises the concern that the Ge may out diffuse during the implantation and/or anneal steps and thus reduce the strain in the top silicon layer. In the present studies we expose 8-30 nm strained silicon layers grown on thin relaxed SiGe-buffers, to implant conditions and anneal cycles, characteristic for formation of the junctions by solid phase epitaxial regrowth and conventional spike activation. The resulting Geredistribution is measured using SIMS. Based on the outdiffused Ge-profiles the Ge-diffusion coefficient has been determined in the temperature range of 800-1100C from which an activation energy of ~ 3.6 eV can be deduced. Up to 1050 C, 10 min, even a 30 nm strained film remains highly stable and shows only very moderate outdiffusion. We also have observed a far more efficient, athermal Ge-redistribution process linked to the implantation step itself. This was studied by analysing the Ge-redistribution following an Asimplant (2-15 keV, 5 1014 – 3 1015 at/cm2). It is shown that the energy of the implant species (or more specifically the position of the damage distribution function relative to the Ge-edge) plays a determining factor with respect to the Ge-migration. For implants whereby the damage distribution overlaps with the Ge-edge, a very efficient transport of the Ge is observed, even prior to any anneal cycle. The migration is entirely correlated with the collision cascade and the resulting (forward!) Ge-recoil distribution. The scaling with dose for a given energy links the observed Ge-profile with a broadening mechanism related to the number of atom displacements induced in the sample within the vicinity of the Si-SiGe-transition. INTRODUCTION The strained-Si/SiGe MOS-transistor is one of the approaches pursued to enhance the device performance by carrier mobility modification in the transistor channel such as by the formation of strained silicon layers on a Si1-xGex buffer [1]. Implementation of such a structure in a full process not only requires considerations on thermal stability but also on the impact of the source and drain junction formation process as this should not relax the strain in the channel. In this paper we investigate the role of the implant process and thermal budget separately for a s-Si on a thin relaxed SiGe-buffer layer. As such we investigate the thermal stability of the strained layer stack by measuring the Ge-diffusion coefficient over a wide temperature range (800-1100C). In addition the athermal Ge-redistribut
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