2792 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 53, NO. 11, NOVEMBER 2006 Modeling the Well-Edge Proximity Effect in Highly Scaled MOSFETs Yi-Ming Sheu, Ke-Wei Su, Shiyang Tian, Sheng-Jier Yang, Chih-Chiang Wang, Member, IEEE, Ming-Jer Chen, Senior Member, IEEE, and Sally Liu Abstract—The well-edge proximity effect caused by ion scat- tering during implantation in highly scaled CMOS technology is explored from a physics and process perspective. Technology computer-aided design (TCAD) simulations together with silicon wafer experiments have been conducted to investigate the impact of this effect. The ion scattering model and TCAD simulations provided a physical understanding of how the internal changes of the MOSFETs are formed. A new compact model for SPICE is proposed using physics-based understanding and has been cali- brated using experimental silicon test sets. Index Terms—CMOS wells, high-energy ion implantation, ion scattering, MOSFETs, SPICE model, technology computer-aided design (TCAD) simulation. I. INTRODUCTION A S CMOS very large scale integration technology pro- gresses to the nanometer regime, several physical effects become significant as a result of aggressive layout scaling [1]–[3]. MOSFETs are formed during the front end of the fabrication process, which mainly consists of shallow trench isolation (STI), MOSFET wells, and MOSFET gate formation. The effect of the well-edge proximity to the MOSFET gates was first reported in [4] and originates from the lateral scattering of ion implantations at the photoresist edge when forming MOSFET wells, which in turn causes a change in the MOSFET threshold voltage. Fig. 1 schematically shows the reason for the well-edge proximity effect on MOSFET devices from a cross- sectional viewpoint. The high-energy ions scattered at the well photoresist edge introduce extra dopant atoms in the silicon near the well edge. As the MOSFET gate approaches the well edge, the dopant concentration of the MOSFET core area will increase, therefore causing a comparative increase in threshold voltage. The effect becomes of increasing importance as CMOS devices continue to shrink further. Manuscript received April 13, 2006; revised August 3, 2006. The review of this paper was arranged by Editor V. R. Rao. Y.-M. Sheu is with the Device Engineering Division, Taiwan Semiconductor Manufacturing Company, Hsinchu 300, Taiwan, R.O.C., and also with the Department of Electronics Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, R.O.C. (e-mail: ymsheu@tsmc.com). K.-W. Su, S.-J. Yang, C.-C. Wang, and S. Liu are with the Device Engineer- ing Division, Taiwan Semiconductor Manufacturing Company, Hsinchu 300, Taiwan, R.O.C. (e-mail: s_liu@tsmc.com). S. Tian is with Synopsys, Inc., Dallas, TX 75254 USA. M.-J. Chen is with the Department of Electronics Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, R.O.C. Color versions of Figs. 1–3 and 6–11 are available online at http:// ieeexplore.ieee.org. Digital Object Identifier 10.1109/TED.2006.884070 Fig. 1. Origin of well-edge proximity effect. High-energy dopant ions scatter at the well photoresist edge during well ion implantation, and the scattered ions are implanted in the MOSFET channel before the gate is formed. SC denotes the distance of the well photoresist edge to the MOSFET gate edge. In this paper, a silicon wafer experiment was performed using state-of-the-art CMOS technology to investigate this effect. Monte Carlo ion scattering and integrated technology computer-aided design (TCAD) simulation were conducted to evaluate the dopant profile variations of the well ion implan- tation. Calibrated process and device TCAD simulations were used to quantify the impact on MOSFET electrical charac- teristics. Utilizing a physics-based understanding and silicon experimental results, a new model that corrects the inaccuracies of current SPICE models is proposed. II. ION SCATTERING PHYSICS AND MODELING Moving ions (projectiles) in a solid loose their energy via two independent mechanisms. The first mechanism is elastic nuclear stopping, which causes the ions to be scattered away from their original paths. The second mechanism is inelastic electronic stopping, which acts as a drag force causing negligi- ble angular deflections of the moving ions. The principal assumption of the Monte Carlo model is that the interaction of the energetic ions with the solid may be separated into a series of distinct two-body collisions (binary collision approximation). Thus, Monte Carlo modeling of ion implantation consists of following the ions from one scatter- ing event to the next and properly accounting for all energy loss mechanisms and deflections. The Monte Carlo model for implants into crystalline silicon was described in detail in [5]. 0018-9383/$20.00 © 2006 IEEE