Suppression of reverse short channel effect by a buried carbon layer

Transient diffusion in epitaxial silicon can be suppressed by incorporating high concentrations of carbon. However, the presence of carbon at this level inside the depletion regions of a device leads to increased leakage. We show that a carbon profile tailored to give reduction of transient diffusion (TED) while minimizing carbon concentration in the depletion layer avoids the problems associated with carbon while maintaining the advantages. Such a profile can be achieved by ion implantation. Before C is able to reduce TED a high temperature annealing step is required that removes the C-implant damage. SIMS measurements verify that the expected reduction in transient diffusion occurred, while NMOS devices fabricated with a buried carbon layer have no RSCE and a shift in threshold voltage indicating suppression of TED. The impact on device leakage is minimal.