Process optimization for preventing boron-penetration using P or as co-implant in p-poly gate of P-MOSFETs

A comprehensive study of the phosphorus dosage and annealing condition dependencies of boron-penetration and poly-depletion is presented. The experimental results show that the boron-penetration in BF₂ implanted poly-gate is significantly reduced as the dose of co-implanted phosphorus increases. The phosphorus dose of about 1.5×10¹⁵cm^-2 in p⁺-poly gate can effectively retard the penetration of boron in BF₂ 3 to 5×10¹⁵cm^-2 doped poly gate under 900°C, 60min annealing (30min reflow anneal, and 30min post-contact implant anneal). The performance of boron-penetration-free phosphorus co-implanted p⁺-poly gate MOSFETs is also shown to be much better than the device with boron-penetration. In arsenic Co-implanted p-poly gate, it also appears that arsenic co-implant would also retard boron penetrating through thin gate oxide. An optimal and effective gate processing for preventing boron-penetration is proposed for dual-gate CMOS devices.