Effect of fluorine implantation dose on boron thermal diffusion in silicon

Abstract

This paper investigates how the thermal diffusion of boron in silicon is influenced by a high energy fluorine implant with a dose in the range 5 ϫ 10 14 -2.3ϫ 10 15 cm −2 . Secondary Ion Mass Spectroscopy (SIMS) profiles of boron marker layers are presented for different fluorine doses and compared with fluorine profiles to establish the conditions under which thermal boron diffusion is suppressed. The (SIMS) profiles show significantly reduced boron thermal diffusion above a critical F + dose of 0.9-1.4ϫ 10 15 cm −2 . Fitting of the measured boron profiles gives suppressions of the boron thermal diffusion coefficient by factors of 1.9 and 3.7 for F + implantation doses of 1.4 ϫ 10 15 and 2.3ϫ 10 15 cm −2 , respectively. The suppression of boron thermal diffusion above the critical fluorine dose correlates with the appearance of a shallow fluorine peak on the (SIMS) profile in the vicinity of the boron marker layer. This shallow fluorine peak is present in samples with and without boron marker layers, and hence it is not due to a chemical interaction between the boron and the fluorine. Analysis of the (SIMS) profiles and cross-section Transmission Electron Microscope micrographs suggests that it is due to the trapping of fluorine at vacancy-fluorine clusters, and that the suppression of the boron thermal diffusion is due to the effect of the clusters in suppressing the interstitial concentration in the vicinity of the boron profile.

Reduced boron diffusion under interstitial injection in fluorine implanted silicon

“…15 Recent work on fluorine implantation into preamorphized silicon has also suggested that V-F clusters are responsible for the suppression of boron transient enhanced diffusion. 9 However, contradictory results have also been reported, 16 which indicate that for fluorine implants into crystalline SiGe, suppression of boron TED is also obtained even when the shallow SIMS peak due to V-F clusters is not present. These results suggest that mechanisms other than V-F clusters can contribute to the suppression of boron diffusion in Si and SiGe.…”

Deep electronic states in ion-implanted Si

“…Enhanced Diffusion (and thermal diffusion) of B in Si can be suppressed by F implantation, which may form larger defects that soak up interstitials [6] . However the detailed electrical activity of F clusters (with anything) is yet to be established.…”

“…A further solution may lie in the introduction of another ion which promotes vacancy formation or retention, thus reducing the interstitial population, and hence reducing all diffusion. A possible candidate species currently under investigation is F [6], but other elements such as C may also have the same effect. 9], but this has more recently been shown not to be the case [10].…”

Ultrashallow p[sup +]∕n Junction Prepared by Low Energy BF[sub 3] Plasma Doping and KrF Excimer Laser Annealing

“…10 Over the past few years there has been considerable interest in the effect of fluorine on boron diffusion in silicon to suppress boron diffusion. [11][12][13][14][15][16][17][18][19] Research on the effects of fluorine from a BF 2 + implant reveals that shallower junctions could be obtained when BF 2 + was implanted instead of boron. [11][12][13] Also, it has been reported that fluorine was implanted separately into the boron to characterize the effect of the fluorine on boron diffusion.…”

“…This work shows that the fluorine implant reduced boron TED and increased boron activity. [14][15][16][17][18][19] In conjunction with these studies, the deactivation of dopants also should be considered because the postannealing process is accompanied with the deactivation of dopants during device fabrication. In the case of boron, Takamura et al 20 have already shown that the deactivation of boron in laser-annealed silicon is stable.…”