Suppression of boron penetration in BF2-implanted p-type gate MOSFET by trapping of fluorines in amorphous gate

This paper reports the use of amorphous/polysilicon gate electrode in BF₂-implanted poly-gated P-MOSFETs to suppress the boron penetration. SIMS analysis clearly illustrates that fluorine prefers to accumulate in the layer of amorphous silicon. The retardation of boron diffusion is therefore achieved by the trapping of fluorine in the amorphous layer of stacked amorphous/polysilicon (SAP) p-type gate due to a lower diffusion rate of fluorine in the amorphous silicon layer. Polysilicon depletion effect did not become more severe by introducing the amorphous silicon. In addition, gate oxide reliability is not degraded by using this gate structure. Results show that the structure is a promising gate electrode for future dual-poly gate CMOS technology development.