Diffusion Suppression of Delta Doped Phosphorus in Germanium by Implantation of Nitrogen

Abstract

Influence of implanted monomer nitrogen (14N) on the diffusion of single delta-doped phosphorus (P) layer in epitaxial Ge (001) and its electrical activation by rapid thermal processing (RTP) is investigated. One µm thick intrinsic Ge with a P delta layer at 25nm from the surface with / without 14N co-implantation is annealed at peak temperature of 450°C to 800°C for 10s. The high P concentration gradient of up to 2nm/dec. yields strong diffusion and high surface concentration after RTP w/o 14N co-implantation. After 600°C RTP P is uniformly distributed in the first 60nm with an active carrier concentration of about 1x1019/cm³. The sheet resistivity (Rs) is reduced to the minimum of 207Ω/sq by broadened profile despite 20% P loss (up to 50% at 800°C). By 4x1014/cm³ 14N implantation the dopant loss is fully suppressed up to 750°C (20% at 800°C). The P diffusion length was reduced by a factor of four at 600°C. Formation of immobile and electrically inactive PN clusters lead to a reduction of the active carrier concentration of about 3.4x1018/cm³ and though to a higher Rs of 600Ω/sq. Lower 14N doses (4x1011/cm² to 4x1013/cm²) influence the Rs and the P profile only at temperatures below 600°C.