Fluorine effect on boron diffusion of p/sup +/ gate devices (MOSFETs)

A device characteristics instability in MOSFETs associated with fluorine incorporation in the p/sup +/-gate fabrication is reported. MOSFETs with BF/sub 2/ or boron-implanted polysilicon gates are fabricated identically except at gate implantation. A substantial shift and fluctuation in the threshold voltages of MOSFETs with BF/sub 2/-implanted gates are observed, even under moderate annealing conditions, while the boron-implanted gate devices still exhibits normal characteristics. The threshold voltage is found to shift more positively, and the subthreshold swing shifted to a large value as the fluorine concentration increased in the gate. The physical causes accounting for the threshold voltage shift are identified to be the fluorine-enhanced boron penetration and/or negative charge generation.<
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