Anomalous rapid diffusion of phosphorus caused by heavily implanted carbon in pre-amorphized ultrashallow junctions

Anomalous enhancement of phosphorus diffusion in pre-amorphized ultrashallow junctions was observed when the dose for carbon co-implantation was increased to 5 × 10¹⁵ cm⁻² at 5 keV. Simulation was performed to verify the diffusion mechanism and mimic the experimental box-shaped profiles of phosphorus. The enhanced diffusion was dominated by the rapid diffusion in the residual amorphous layer as the rate of solid-phase epitaxial regrowth was severely retarded at the peak region of the implanted carbon profile. The diffusion in the amorphous silicon layer did not show concentration dependence. No evident phosphorus segregation was observed at the interface of the amorphous layer and the bulk crystalline silicon. The rapid diffusion in the amorphous layer produced a flat profile near the surface region while a steep phosphorus profile near the amorphous/crystalline interface was observed due to low diffusivity in the bulk crystalline region. This explains similar box-shaped profiles at low temperatures because the phosphorus redistribution was mainly controlled by the thickness of the residual amorphous layer.