Ultra-shallow junction formation using conventional ion implantation and rapid thermal annealing

The major trends in conventional ion implantation and rapid thermal annealing (RTA) in recent years have been the use of ultra-low energy implants and spike anneals for the formation of ultra-shallow junctions. These trends have allowed the conventional technologies to continue to be used to form nand p-type source/drain extensions that meet the ITRS requirements for at least the 100nm gate-length technology. While the necessity of ultra-low energies (sub-keV for B) is well accepted, the lowest implant energy that will be required in practice has not been decided. Data showing the effects of physical phenomena such as sputtering, enhanced dopant diffusion and dopant out-diffusion suggest that approximate to0.5keV might be a sufficiently low energy. It is shown here that indeed junction depths achieved by 0.2-keV implants can be matched by lower dose 0.5-keV implants. Similarly, in RTA processing, while the necessity of spike anneals, characterized by a minimized soak-time at peak temperature and fast temperature ramp rates, has been accepted, the optimum ramp-up rate has not been agreed upon. Through a combination of experimental data and diffusion simulations, the effect of the ramp rates on junction diffusion has been reviewed here. The relative contribution of the ramp- and soak-time portions of the anneal has been quantified through thermal budget calculations.