COBALT DISILICIDE AS DOPANT DIFFUSION SOURCE FOR POLYSILICON GATES IN MOS DEVICES

In this paper, a novel p-channel metal oxide semiconductor (PMOS) device fabrication process using BF2-implanted CoSi2 as a boron diffusion source for both polycrystalline-silicon (polysilicon) gate doping and shallow source/drain junction formation is studied. Important issues including thermal stability of the CoSi2/polysilicon stacked layer and boron redistribution in the CoSi2/polysilicon stacked layer are discussed in detail. The data show that the thermal stability of CoSi2/polysilicon stacked layers can be significantly improved by using as-deposited amorphous silicon films rather than as-deposited polysilicon films. Samples with 120 nm CoSi2 on 180 nm polysilicon are thermally stable up to 1000-degrees-C for 60 s in a N2 ambient. Secondary ion mass spectroscopy analyses show that degenerately doped polysilicon gates and shallow source/drain junctions can be achieved simultaneously. Furthermore, a simple method to study the electrically active dopant redistribution in CoSi2/polysilicon gates using MOS capacitors is proposed.