Optimization of laser anneal conditions for implanted shallow p/n-junctions

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Laser Thermal Processing (LTP) both at silicon melting and sub-melting powers have been studied for many years in order to achieve high levels of dopant activation and abrupt junctions thanks to extremely short annealing times with potential elimination of transient-enhanced diffusion.However, its introduction in a CMOS-like process is not achieved yet, since the laser energy can be destructive to other parts of the device, integration issues related to the introduction of effective reflecting layers to protect devices from laser have not been solved yet.In the present work we present a preliminary characterization in order to identify the most promising implantations and LTP process for both standard and emerging device. Both melting and sub-melting regime was investigated.A first characterization by transmission electron microscopy (TEM), time of flight secondary ion mass spectroscopy (TOF-SIMS) and sheet resistance measurements of LTP performances allowed to identify Boron as preferable to BF2 as doping species and to exclude non melting regime from further investigations. Indeed, in Boron implanted samples sheet resistance is found to be lower than in BF2 implanted samples for almost all energy densities, suggesting better activation. In both BF2 and B implants sheet resistance in sub-melted samples is too high to allow measurements.Junction depth seems to be steady in Boron implanted sample whereas it increases at BF2 implanted ones during thermal treatment. So Boron implanted samples show better control of diffusion with no drift of the profile at concentrations below 2*1019cm−3.This result is rather surprising, because dopant diffusion takes a large amount of doping at concentration below the solid solubility, so a lower sheet resistance is generally associated with a more diffused profile.In terms of silicon defectivity the Boron implanted sample treated with the highest laser energy is the only one where no dislocations rich layer is observed, on the contrary the silicon close to the surface appears perfectly crystalline.