ON THE << ASYMMETRICAL » BEHAVIOR OF TRANSIENT ENHANCED DIFFUSION IN PRE-AMORPHISED Si WAFERS D. ALQUIER', N. E. B. COWERN 2 , P. PICHLER 3 , C. ARMAND 4 , A. MARTINEZ', D. MATHIOT 5 , M. OMRI6 and A. CLAVERIE 6 LAAS/CNRS, 7 avenue du Colonel Roche, 31077 Toulouse, France Philips Research Lab., Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands FhG IIS-S, Schottkystrasse 10, 91058 Erlangen, Germany 4 INSA, Complexe scientifique de Rangueil, 31400 Toulouse, France 5 ERM/PHASE/CNRS, ENSPS, Bd. S. Brant, 67400, Illkirch, France 6 CEMES/CNRS, BP 4347, 31055 Toulouse Cedex 2, France, claverie@cemes.fr ABSTRACT We have studied by SIMS the diffusion of boron in Ge-preamorphised silicon over a range of anneal temperatures and times, focusing on the influence of the depth of the boron profile relative to the crystalline-amorphous (c/a) interface. It is shown that, for all durations, transient enhanced diffusion (TED) occurs on both sides of the c/a interface. For short annealing times, the amplitude of TED varies by about two orders of magnitude between the surface and the end-of- range (EOR) defect band, formed just below the original c/a interface. We propose a model in which TED arises from the coupling between a Si-interstitial supersaturated << box >», the EOR defect region, whose supersaturation decreases with time as the EOR defects grow, and a surface whose recombination efficiency is close to that of a perfect sink. The model successfully describes the different behavior of deep and shallow boron profiles, without requiring the existence of a diffusion barrier. INTRODUCTION With the need for ultra-shallow junctions for deep sub-micron technologies, new research efforts are being made in the field of boron diffusion in pre-amorphised silicon. In the preamorphisation method, boron is implanted into an amorphous layer formed by implantation with a high dose of e.g. Si or Ge, giving a shallower as-implanted junction and an increase in electrical activation on annealing. During annealing, the amorphous layer rapidly regrows, leaving (in principle) a defect-free regrown layer, beyond which a heavily damaged "end-of-range' (EOR) layer is located. The question of whether the boron dopant in such a structure undergoes transient enhanced diffusion (TED) upon annealing is still controversial, and seems to depend strongly on the experimental conditions (1). For example, while some studies (2-3) have shown near-normal diffusion when the boron is confined within the regrown layer, others (4-7) have shown strong TED in this region. However, essentially all studies suggest that less TED occurs in the regrown layer than in the region beyond the original a/c interface (2, 8). To explain this << asymmetrical >> behavior, a popular idea is that a (partial) diffusion barrier exists, which inhibits the passage of Si interstitial atoms (Si(I)'s) from the damaged crystalline silicon beyond the original a/c interface, into the regrown region (2, 8). In particular, Jones has shown that the amount of TED in the regrown layer is related to the density of the EOR band formed just beyond the c/a interface during annealing (8). Jones proposed that the relevant mechanism is capture of interstitials, generated by damage in deeper silicon layers, at dislocation loops in the EOR band. In a recent study of Ge-preamorphized silicon, we have demonstrated a mechanism of nucleation and growth of EOR defects, which suggests that the EOR band is an active buffer and can also be a source of interstitials during TED (9). This result is at variance with the simple loop- barrier hypothesis, in which the EOR dislocation loops are seen as an essentially 'dead' sink for interstitials. For this reason, we have decided in the present study to investigate the asymmetrical behavior of TED in more detail. Our objective is to see whether a more consistent and physically meaningful model can be developed and tested. In our experiment, a strong asymmetry between the regrown and deeper layers is indeed observed, but sufficient diffusion takes place within the 67 Mat. Res. Soc. Symp. Proc. Vol. 532 0 1998 Materials Research Society