Ultra-shallow p-n junction formation by ion implantation at high energy?

Further CMOS device scaling beyond 0.13μm requires very shallow p-n junction formation for the source and drain extensions. Ultra-low energy ion implantation is the key process to achieve this goal. Two principal drawbacks of the process: sample surface proximity to the implanted species,and space proximity of the dopant atoms and radiation damages accompanied by the enhanced diffusion phenomena give rise to the complexity of the shallow junction formation. It is known that even at high energy implantation, a surface-related peak of dopants is clearly seen by SIMS in implanted samples. Some authors consider the peak as an artificial effect of the SIMS. However, there are several physical reasons in support of the surface peak really existing. If it is the case, it suggests a way to produce a super ultra shallow p-n junctions with relatively high energy ion implantation when the main area of the radiation damages and subsurface area are separated in space. B⁺, Li⁺, Na⁺ and P⁺ have been implanted at 40 - 200 keV into Si wafers to find out the conformations of the dopants surface peak reality. SIMS analysis has been used to estimate the dopant atoms depth distribution. Enhanced depth resolution of the SIMS technique used allows to prove the surface-related dopant atoms existence.