Dopant Activation and Deactivation Phenomena during Advanced Millisecond Anneal Cycles

Achieving very high concentrations of electrically active dopants is essential for minimizing parasitic resistances in advanced CMOS devices. Existing methods are severely challenged by the limits on electrical activation of dopants imposed by their solid solubility, electrical deactivation, segregation at silicon/SiO2 interfaces and by the need to limit process temperatures to allow integration of new materials. This paper investigates the factors in the design of millisecond annealing (MSA) temperature cycles with peak temperatures below 1200ºC that can still improve electrical activation of high doses of As or P atoms ion-implanted in preamorphized silicon. High dose P doping was found to display better activation than could be achieved with As, where activation decreased for higher doses. MSA pulse length was found to have a weak influence on activation. Higher preheat temperatures degraded activation, as might be expected from the consequent increase in the post-pulse thermal budget. The effects of different cooling profiles after the pulsed heating were investigated, but were found to be insignificant for cooling cycle temperatures < 725ºC. The preheating conditions offer further room for optimization because they can affect dopant diffusion and activation during the regrowth of the amorphized layer.