Novel sacrificial gate stack process for suppression of boron penetration in p-MOSFET with shallow BF₂-implanted source/drain extension

A novel process flow employing a sacrificial tetraethyl orthosilicate/polycrystalline silicon (TEOS/poly-Si) gate stack is proposed for fabricating fluorine-enhanced-boron-penetration-free p-channel metal oxide semiconductor field effect transistors (p-MOSFET's) with shallow BF₂-implanted source/drain (S/D) extension. With the presence of the sacrificial TEOS/poly-Si gate stack as the mask during the shallow BF₂ implant, the incorporated fluorine atoms are trapped in the sacrificial TEOS top layer and can be subsequently removed. The new process thus offers a unique opportunity of achieving an ultra shallow S/D extension characteristic of the BF₂ shallow implant, while not suffering from any fluorine-enhanced boron penetration normally accompanying the BF₂ implant. Excellent transistor performance with improved gate oxide integrity has been successfully demonstrated on p-MOSFET's fabricated with the new process flow.