An oxide masked p+ source/drain implant for VLSI CMOS

A process innovation is proposed to help eliminate the p+ implant mask in VLSI CMOS process. After the resist masked n+ source/drain implant, a wet oxidation is done. Thick oxides are grown on the n+ single crystal and polysilicon, while a thin oxide is grown on the p-substrate. The thick oxides are used to mask the n+ regions from the blanket boron implant during the subsequent p+ source/drain formation. Small geometry CMOS devices are fabricated with this technique and give performance similar to those made with the conventional two mask source/drain processing.