Gate-last vs. gate-first technology for aggressively scaled EOT logic/RF CMOS

We report on gate-last technology for improved effective work function tuning with ~200meV higher p-EWF at 7Å EOT, ~2× higher f_max performance, and further options for channel stress enhancement than with gate-first by taking advantage of the intrinsic stress of metals and gate height dependence. Additional key features: 1) scavenging technique yielding UT-EOT down to ~5Å is demonstrated in gate-last, with high-k deposited first, through the use of an Etch-Stop-Layer with composite nature and similar TDDB reliability to gate-first; 2) controlled alloying for EWF engineering is obtained by careful material selection and tuned metals thicknesses ratio; 3) suppression of abnormal L_gate- and W_gate-dependence on J_G, EOT and NBTI for devices with both high-k and metal deposited last (L_gate≥35nm, W_gate≥80nm) demonstrates the potential for improved UT-EOT control down to small devices with this scheme.