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MODELING OF DAMAGE ENHANCED DIFFUSION OF IMPLANTED BORON IN SILICON V.C. LO*, S.P. WONG** AND Y.W. LAM ** *Department of Applied Physics, Hong Kong Polytechnic, **Department of Electronic Engineering, The Chinese Kong, Hong Kong.

Kowloon, Hong Kong University of Hong

ABSTRACT Modeling of the damage enhanced diffusion (DED) behaviors of implanted In his boron in silicon of Powell's experiment [1] has been performed. silicon experiment, Powell showed that the diffusion of implanted boron in was dependent on implantation dosage as well as on the annealing conditions. For low dose boron implantation, the extent of boron diffusion 0 after 15 second RTP is less than that of furnace annealing at 900 C for 30 But the reverse is true for the high dose case, and a two-step minutes. implantation annealing leads to least and minimal diffusion. In this work, induced excess self-interstitials which generate mobile boron atoms at the intersititial sites are considered the dominant point defect species responsible for the DED. Both the local relaxation and diffusion of these excess self-interstitials are considered. The features of the DED reported by Powell are successfully reproduced and explained.

INTRODUCTION A few years ago, Powell [1] reported some experimental results on the damage enhanced diffusion (DED) of implanted boron in silicon which showed that the extent of boron diffusion is dependent both on implantation dosage as well as the annealing conditions. In his experiment, 49 keV BF2 + ion impltgtatioý into pre-amorphized silf9on w~fers was performed at two doses: cm" (high dose, HD), respectively. 2xlO cm (low dose, LD) and 6x10 furnace The wafers were then subjected to different thermal treatments: annealing (FA), rapid thermal process (RTP), or two-step annealing (TSA). While FA was performed at 9000C for 30 minutes, for RTP, the wafers were exposed to the radiation emitted from a graphite heater heated to 1250°C for 15 seconds, resulting a temperature of about 11000C at the wafer 0 surface. In TSA, wafers were first annealed at 550 C for two hours, and then subjected to rapid exposure to the radiation as in RTP. The results showed that while for the low dose case, RTA produced less diffusional broadening in the boron profile than FA did, however, for the high dose case, the reverse was true and TSA gave the least and minimal diffusion. It is the aim of this work to understand these DED behaviors of implanted boron in silicon. It is generally believed that the DED features decribed above are defects attributed to the transient transport of the excess point (2-5] has introduced by implantation. Experimental investigation of boron in demonstrated that the oxidation enhanced diffusion (OED) silicon is accompanied with the growth of oxidation stacking faults (OSF). This OSF effect is believed to be the evidence of supersaturation of selfinterstitials. On the other hand, excess vacancies generated during thermal nitridation of silicon are related to the simultaneously observed retarded diffusion of boron [5]. These ar