Formation of integrated circuit structure using one or more silicon layers for implantation and out-diffusion in formation of defect-free source/drain regions and also for subsequent formation of silicon nitride spacers

Abstract

A process is described for using a silicon layer as an implant and out-diffusion layer, for forming defect-free source/drain regions in a semiconductor substrate, and also for subsequent formation of silicon nitride spacers. A nitrogen-containing dopant barrier layer is first formed over a single crystal semiconductor substrate by nitridating either a previously formed gate oxide layer, or a silicon layer formed over the gate oxide layer, to form a barrier layer comprising either a silicon, oxygen, and nitrogen compound or a compound of silicon and nitrogen. The nitridating may be carried out using a nitrogen plasma followed by an anneal. A polysilicon gate electrode is then formed over this barrier layer, and the exposed portions of the barrier layer remaining are removed. An amorphous silicon layer of predetermined thickness is then formed over the substrate and polysilicon gate electrode. This amorphous layer is then implanted with a dopant capable of forming a source/drain region in the underlying silicon substrate by subsequent diffusion of the implanted dopant from the amorphous silicon layer into the substrate. The structure is then annealed to diffuse the dopant from the implanted silicon layer into the substrate to form the desired source/drain regions and into the polysilicon gate electrode to dope the polysilicon. The annealing further serves to cause the amorphous silicon layer to crystalize to polycrystalline silicon (polysilicon). In one embodiment, the polysilicon layer is then nitridized to convert it to a silicon nitride layer which is then patterned to form silicon nitride spacers on the sidewalls of the polysilicon gate electrode to electrically insulate the gate electrode from the source/drain regions. The process may be further modified to also create LDD or HDD source/drain regions in the substrate (depending on the concentration of the dopant), using multiple implants into the same silicon layer or by the sequential use of several silicon layers, each of which is used as an implantation and out-diffusion layer.