Cmos sidewall oxide-lightly doped drain process

Abstract

A CMOS process wherein lightly doped drain extensions are fabricated in the N-channel devices without any additional masking steps. The present invention requires a specific sequence of steps, after all steps through patterning of the polysilicon gate level have been completed: first, a light shallow N-type implant is performed overall. Next, oxide is deposited overall. Second, photoresist is patterned according to the P-type source/drain mask. The exposed conformal oxide is etched away completely, and the P-type source/drain implant is performed. Third, after the P-type source/drain photoresist is removed, the conformal oxide is anisotropically etched to leave sidewall oxide filaments, the N+ source/drain masking layer is applied, and the N+ source/drain implant is performed. This process results in short lightly doped drain extensions on the source/drain regions of the N-type devices only and not of the P-type devices. Alternatively, the conformal oxide is not deposited until after the pt source/drain resist is removed, so that the PMOS devices also have sidewall oxides (for better topography), but not lightly doped drain extension.