Epi process margin improvement using co-implantation to control Phosphorus diffusion in a DRAM manufacturing

Co-implantation has been proven to be an effective method to reduce Transient Enhanced Diffusion (TED). In this paper, the effect of Carbon co-implant energy, dose, and combined with Fluorine implants were investigated to control TED for a contact Phosphorus. With optimized co-implant conditions, Dynamic Random Access Memory (DRAM) device wafers were used to verify that the Epi process window can be enlarged due to better control of Phosphorus TED. The study revealed that Carbon suppresses the Phosphorus diffusion tailing and reduces Gate Induced Drain Leakage (GIDL) without degrading Vt and contact resistance performances. With the reduction of Phosphorus diffusion and GIDL, thinner selective Epi layer can be tolerated, resulting in widened process window of Epi final thickness and increased selective Epi process margin.