Impact of fluorine co-implantation on B deactivation and leakage currents in low and high energy Ge preamorphised p+n shallow junctions

D. Girginoudi and C. Tsiarapas
2008. Materials Science and Engineering, B 154–155, 268–274. doi: 10.1016/j.mseb.2008.09.040

Abstract: The impact of fluorine (F) co-implantation on boron (B) deactivation and B TED, as well as on the I–V characteristics of p+n shallow junctions, have been studied for low (10 keV) and high (70 keV) energy Ge preamorphised (PAI) n-type Si samples, that were annealed at 600 °C and 700 °C. Transmission electron microscopy revealed the existence of 〈3 1 1〉 defects and dislocation loops (DLs) in the EOR region. It has been found that F stabilizes the EOR defect population via the increase of EOR defect density and the percentage of the stable DLs. This phenomenon is more pronounced when the preamorphisation is shallow (10 keV Ge energy). SIMS and sheet resistance measurements showed the formation of BICs, which implies B deactivation and increased B TED, especially in the shallow PAI samples and at the 700 °C annealing temperature. The role of F on B deactivation is multiplex: in the 70 keV PAI samples, and at 600 °C annealing temperature, F forms clusters with B causing further B deactivation. In the case of 700 °C annealing temperature, F probably forms fluorine–vacancy (F–V) clusters that trap silicon interstitials (Is), thus reducing the possibility of forming BICs and, therefore, resulting in B re-activation and suppression of B TED. Conversely, in the 10-keV PAI samples, and irrespective of the annealing temperature, F improves significantly the sheet resistance, and we suggest that this is a result of the contribution of two physical mechanisms: in the EOR region, F is trapped into DLs, which release less Is than other types of defects. In the amorphous part of Si, there are probably F–V clusters that trap the Is released from the EOR region. Although F in most cases improves B deactivation, it increases the reverse leakage currents, probably due to the stabilization of the EOR defects. As regards the carrier-transport mechanisms, it has been found that the dominant mechanism is the generation–recombination process under forward bias as well as under the larger part of the reverse-bias voltage conditions.

Keywords: Fluorine co-implantation, TEM, SIMS, B deactivation mechanisms, Leakage current