Carbon addition for low resistivity in situ doped silicon epitaxy

Abstract

Embodiments of the present invention generally relate to methods of forming epitaxial layers and devices having epitaxial layers. The methods generally include forming a first epitaxial layer including phosphorus and carbon on a substrate, and then forming a second epitaxial layer including phosphorus and carbon on the first epitaxial layer. The second epitaxial layer has a lower phosphorus concentration than the first epitaxial layer, which allows for selective etching of the second epitaxial layer and undesired amorphous silicon or polysilicon deposited during the depositions. The substrate is then exposed to an etchant to remove the second epitaxial layer and undesired amorphous silicon or polysilicon. The carbon present in the first and second epitaxial layers reduces phosphorus diffusion, which allows for higher phosphorus doping concentrations. The increased phosphorus concentrations reduce the resistivity of the final device. The devices include epitaxial layers having a resistivity of less than about 0.381 milliohm-centimeters.