Enhanced degradation of PMOSFETs with BF sub 2 implanted poly gate.

PMOSFET transistors with both boron and BF sub 2 implanted gate are fabricated with the same process except gate implantation. We observe that the boron implanted gate transistors still exhibit normal characteristics, the heavily BF sub 2-implanted poly Si gate transistors have shown a positive shift in threshold voltage. We suspect that the cause of the threshold voltage reduction is associated with the high flourine concentration introduced by BF sub 2 gate implantation. The physical degradation mechanism involving flourine is actively under investigation.