Physical mechanisms of transient enhanced dopant diffusion in ion-implanted silicon

Abstract

Copper centers in copper-diffused n-type silicon measured by photoluminescence and deep-level transient spectroscopy Appl. Phys. Lett. 101, 042113 (2012) Bonding and diffusion of nitrogen in the InSbN alloys fabricated by two-step ion implantation Appl. Phys. Lett. 101, 021905 (2012) Shift of Ag diffusion profiles in CdTe by metal/semiconductor interfaces Appl. Phys. Lett. 100, 171915 (2012) Diffusion of co-implanted carbon and boron in silicon and its effect on excess self-interstitials Implanted B and P dopants in Si exhibit transient enhanced diffusion ͑TED͒ during annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy ͑MBE͒. Damage from nonamorphizing Si implants at doses ranging from 5ϫ10 12 to 1ϫ10 14 /cm 2 evolves into a distribution of ͕311͖ interstitial agglomerates during the initial annealing stages at 670-815°C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of interstitials from the damage region involves the dissolution of ͕311͖ defects during Ostwald ripening with an activation energy of 3.8Ϯ0.2 eV. The excess interstitials drive substitutional B into electrically inactive, metastable clusters of presumably two or three B atoms at concentrations below the solid solubility, thus explaining the generally observed immobile B peak during TED of ion-implanted B. Injected interstitials undergo retarded diffusion in the MBE-grown Si with an effective migration energy of ϳ3.5 eV, which arises from trapping at substitutional C. The concept of trap-limited diffusion provides a stepping stone for understanding the enormous disparity among published values for the interstitial diffusivity in Si. The population of excess interstitials is strongly reduced by incorporating substitutional C in Si to levels of ϳ10 19 /cm 3 prior to ion implantation. This provides a promising method for suppressing TED, thus enabling shallow junction formation in future Si devices through dopant implantation. The present insights have been implemented into a process simulator, allowing for a significant improvement of the predictive modeling of TED.

Vacancy and interstitial depth profiles in ion-implanted silicon

“…It has been established that anomalous diffusion of B and P during postimplant annealing is due to the excess of point defects generated by the implantation. [2][3][4][5][6][7] Hence, knowledge about the initial distributions of excess point defects is crucial in order to understand and model the enhanced dopant diffusion.…”

Atomistic modeling of ion implantation technologies in silicon

“…One of the main limitations of this simplistic view is the uncertainty in the critical point defect concentration value: due to the steepness of the damage profile, a little variation in the predicted depth of the amorphous-crystal interface can lead to changes up to 50% in the residual damage concentration. The exact amount of this residual damage is of great relevance as it significantly affects dopant diffusion and activation [4].…”

Elastic interaction energy between a silicon interstitial and a carbon substitutional in a silicon crystal

“…Carbon is therefore added to provide a sink for the self-interstitials, inhibiting the diffusion of boron. 2,5,6 But carbon itself diffuses fast; it is even more diffusive in silicon than boron. 7 Like boron, carbon diffuses by kick-out and kick-in reactions with silicon interstitials 8 in which a silicon interstitial kicks a substitutional carbon atom out from a lattice site moving the carbon atom into an interstitial site.…”

“…1 and diffuses particularly fast during annealing. 2 Diffusion of dopants is undesirable; the dopant profile needs to be kept sharply steplike and this becomes more important as device sizes reduce. Carbon is therefore added to provide a sink for the self-interstitials, inhibiting the diffusion of boron.…”

“…2 Ion implantation also introduces defects into the crystal which are repaired by annealing at a temperature of about 800°C. Boron diffuses by kick-in and kick-out reactions with silicon interstitials, 3,4 as illustrated in Fig.…”