Channeling of implanted phosphorus through polycrystalline silicon

Abstract

Implanted phosphorus was found to penetrate phosphorus-diffused polycrystalline silicon (polysilicon or poly) gate masks during complimentary metal oxide semiconductor processing. The result is unwanted depletion mode (turned-on) N-channel metal oxide semiconductor transistors. The effect is interpreted as channeling of phosphorus through large-grain polysilicon. The channeling effects were eliminated when (1) the upper polysilicon atomic layers were made amorphous prior to 31P+ implantation, (2) thermal oxides were grown to a thickness which prevents high-energy 31P+ from entering the grains of the polysilicon, or (3) when the ion-energy-to-poly thickness ratio is reduced below about 200 keV/μm.