Carbon co-implant is well known to Suppress boron transient enhanced diffusion (TED) in silicon. The modeling of carbon-interstitial clusters (CICs) has been extensively studied and is now widely used in Technology Computer Aided Design (TCAD). It has already been reported in literature that carbon implant in the channel of NMOS transistor is highly effective for the suppression of oxidation-enhanced diffusion (OED) of boron while leading to poor boron activation. In order to account for this deactivation, we need to consider that the active boron equilibrium concentration is modified by the presence of carbon in non-amorphized silicon region with high concentration of interstitials. In this paper, for the first time, we show the effective TCAD modeling of boron deactivation in the presence of carbon in a NMOS transistor. The model is based on boron-carbon-interstitial clusters formed in the non-amorphized silicon region, thereby reducing active boron concentration. The model can be applied to accurately predict variations of threshold voltage as a function of channel length for NMOS devices with carbon implanted into the channel or halo regions, The tool used in this work is a commercial simulator based on the continuum approach. (C) 2009 Elsevier Ltd. All rights reserved.