Significant Threshold Voltage Shift Induced by Ge Penetration into PMOSFET Channel of 28-nm SRAM

A significant positive threshold voltage shift for the PMOSFET of a 28-nm SRAM is reported in this letter. For the first time, it is revealed that Ge atoms may penetrate into the channel of a PMOSFET with embedded SiGe (eSiGe) source/drain (S/D). It is proposed that the localized high content of hydrogen radicals causes the penetration, and these radicals are related to GeH₄ decomposition during eSiGe deposition. The penetration is eliminated by removing GeH₄ from the SiGe cap layer deposition.