Silicon damage studies due to ultra-low-energy ion implantation with heavyspecies and rapid thermal annealing

There have been many studies of electron volt implants of B+ into silicon. This focus on boron was due to enhanced diffusion phenomena and the particu lar difficulty in constructing high conductivity, very shallow layers with B+ light ion. We have also analysed some features of high-dose implantation of As+ to form n(+) layers with shallow junction depths (30-40 nm) with ca rrier concentration of > IE20 cm(-3). Some of our heavy ion work is present ed here. We characterised the surface damage region (SDR) and identified se veral non-linear phenomena. High-conductivity layers of 150-300 Omega /squa re can be made with rapid thermal annealing, The critical limiting factors are range shortening, sputtering and out-diffusion, The range shortening is evident in the saturation behaviour and the out-diffusion is seen as a bui ld up of non-substitutional arsenic in the oxide or the oxide-silicon inter face after annealing. We have used Rutherford backscattering (RBS), medium- energy ion scattering (MEIS) and high-resolution transmission electron micr oscopy (HRTEM) to study crystal micro-structure and damage, as well as seco ndary ion mass spectrometry (SIMS), spreading resistance profiling (SRP) an d sheet resistance methods to study both the diffusion and activation of th e dopant. We have observed new features in the diffusion profile with vario us implant temperatures and offer some explanations for this behaviour. We have also studied Sb+ and In+ implants because they are becoming increasing ly important, at moderate energies, for hyper-abrupt channel and channel en gineering with controlled lateral diffusion. Models have been developed to describe the non-linear behaviour of heavy ion doping at low energies and o ur results demonstrate that implants in the energy range 300 eV-2.5 keV can provide solutions when combined with short rapid thermal anneals for the m anufacture of very shallow junctions with high activation of dopant. Intere stingly, implants at room temperature do not produce the best results. (C) 2000 Elsevier Science Ltd. All rights reserved.