Comparison of B and BF2 source/drain extension implants for PMOS transistors with thin gate oxides

Boron penetration from the gate electrode into the Si substrate, through the thin gate oxide, presents a significant problem in advanced PMOS device fabrication. Boron penetration, which causes a degradation of many transistor parameters, is further enhanced when BF₂ is used to dope the gate electrode. It is known that pile-up of fluorine from the BF₂ gate implant at the polysilicon/gate oxide interface is responsible for the enhanced boron penetration. However, no reports have been made that address enhanced boron penetration due to fluorine from the source/drain implants. It is shown here that fluorine from the source/drain extension implants is also a significant problem, degrading transistor performance for gate oxide thickness less than 27 Å and gate lengths less than 0.5 μm