Deactivation of sub-melt laser annealed arsenic ultra shallow junctions in silicon during subsequent thermal treatment

The need of creating ultra shallow junction to realize source and drain extension in Si CMOS devices has brought to a wide use of arsenic as n-type dopant because of its lower diffusivity and good solid solubility. Furthermore, its high mass helps to create shallower charge carrier profiles when the dopant is introduced in Si by ion implantation. However, because the sheet resistance has to be maintained at low level, a very high dopant electrical activation is required. This may be produced exploiting nonequilibrium approaches like millisec or nanosec annealing (e.g. flash or laser annealing). When subjected to subsequent thermal treatment, arsenic is known to deactivate at temperatures between 500 and 800 °C saturating at a level one order of magnitude below the solid solubility limit. In this work, we report further studies about the deactivation of laser annealed ultra shallow arsenic distributions in silicon using Hall effect measurements, extended x-ray absorption fine structure spectroscopy (EXAFS) and secondary ion mass spectrometry (SIMS). Single crystal Si (100) was implanted with As ions at 2 keV energy with fluencies 1E14 cm-2, 3E14 cm-2, 1E15 cm-2 and 3E15 cm-2. Samples were then activated with a millisecond annealing at 1300 °C using a scanning diode laser annealing (LA) system under non-melt conditions in N2 atmosphere. The samples were then thermally treated in furnace in a N2 atmosphere for 10 minutes at 300, 500, 700 and 900°C temperatures. Electrical deactivation has been observed, but for the lowest dose, the higher the As dose the easier the deactivation, in particular after 700°C. At 900 °C in-depth diffusion and a relevant re-activation has been observed for samples implanted with 1E15 and 5E15 cm-2.