Using point-defect engineering to increase stability of highly doped ultrashallow junctions formed by molecular-beam-epitaxy growth

Abstract

Stability of p+/n junctions remains a critical issue for device performance. We report that the technique of point-defect engineering (PDE) can substantially increase the stability of ultrashallow junctions formed by molecular-beam epitaxy. It is shown that an as-grown 15 nm, 2×1020/cm3 B-doped Si layer becomes unstable during 10 min thermal anneal above 650 °C. The thermal stability can be increased by performing a 5×1015/cm2 1 MeV Si ion implantation. The B profile with the MeV Si implant does not show significant diffusion during annealing up to 750 °C, and the final junction depth after an 800 °C/10 min anneal is about half that of an annealed unimplanted sample. Although with Mev implantation the as-implanted B profile becomes slightly deeper due to recoil implantation, and some of the B has been electrically deactivated by the MeV implantation, PDE is advantageous for postgrowth thermal processes above 700 °C. The mechanism causing the instability is discussed.

Formation of p+ shallow junctions using SiGe barriers

“…With the elimination of band gap narrowing and strain as factors reducing the B diffusion, point defect engineering remains as a viable option. Shao et al [15][16][17][18] have demonstrated that it is possible to reduce boride-enhanced diffusion by injecting vacancies near the surface using MeV implantation. During the postimplant anneal the interstitials and vacancies recombine, reducing the concentration of interstitials available for B diffusion.…”