A Model for Boron T.E.D. in Silicon: Full Couplings of Dopant with Free and Clustered Interstitials

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A MODEL FOR BORON T.E.D. IN SILICON : FULL COUPLINGS OF DOPANT WITH FREE AND CLUSTERED INTERSTITIALS. F. Boucard1,2,3, D. Mathiot1, E. Guichard2, and P. Rivallin3 Laboratoire PHASE-CNRS, 23 rue du Loess, F-67037 Strasbourg Cedex 2, France 2 SILVACO DATA SYSTEMS , 55, rue Blaise Pascal, F-38330 Montbonnot, France 3 CEA-LETI, 17 Av. des Martyrs F-38054 Grenoble cedex 9, France 1

ABSTRACT In this contribution we present a model for transient enhanced diffusion of boron in silicon. This model is based on the usual pair diffusion mechanism including non-equilibrium reactions between the dopant and the free point defects, taking into account their various charge states. In addition to, and fully coupled with the dopant diffusion we model the growth and dissolution of the interstitials and boron interstitials clusters associated with the anneal of the self-interstitial supersaturation created by the implantation step. It is thus possible to simulate a rather large set of experimental conditions, from conventional predeposition steps, to RTA after low energy implantation.

INTRODUCTION One of the most important challenges in developing ULSI technology today is to shrink device sizes to their limit. Each generation requires a large effort in research and development, where technological computer aided design (TCAD) can play a key role. Ion implantation is the common technique used for doping advanced silicon devices in microelectronics. However this technique induces a huge supersaturation of point defects in the Si crystal which leads to an anomalous broadening of the dopant profile during the high temperature activation anneal. This phenomenon, known as transient enhanced diffusion (TED) is particularly noticeable and embarrassing for boron diffusion, where it is a serious issue for the formation of the ultra shallow junctions needed for next generation of devices. It is also now well established that TED is strongly correlated with the evolution of the self-interstitial supersaturation governed by the nucleation and evolution, during the high temperature anneal, of a variety of extended defects structures like boron interstitial clusters (BIC) [1] or interstitials clusters (IC) [2]. Thus, predictive process modeling, needed for deep submicron MOSFET technologies, requires the development of accurate diffusion models taking into account the full set of interactions between the dopant and the point or extended defects (clusters). The purpose of this contribution is to show that it is possible to extend the usual dopant pair diffusion model to take into account these interstitial-related clusters. Special attention is paid on the fact that the "new" model is fully consistent with the equilibrium "normal" model.

BASIC DIFFUSION MECHANISM As a starting point of our modeling effort we used an extension of the basic dopant pair diffusion model proposed several years ago by one of us [3]. Briefly, the basic idea of this model is that isolated substitutional boron atoms (BS) are immobile. The dopant diffusion occurs only via the