On the Ion Implantation Models for Simulation of Fond Devices

The fully overlapped nitride mask defined (FOND) MOSFETs¹⁾ exhibit a much better immunity with respect to hot carrier degradation compared to conventional LDD devices. The reason for the better reliability performance of these devices is the special shape of the LDD extentions formed by the FOND process. In order to simulate electrical properties and hot carrier degradation characteristics of FOND devices, reliable descriptions of the doping distributions in the LDD regions must be available. The task of this paper is to investigate how the simulated electrical parameters of FOND devices depend on the approximations involved in ion implantation models and what are the critical properties of the ion implantation models needed to predict the dopant distributions in the LDD regions. To elucidate the problems associated with the simulation of the drain extensions in a submicron FOND device, we performed a number of process and device simulations of an n-channel MOS FOND device¹⁾, changing approximations involved in the ion implantation models. The process simulation was performed with STORM²⁾ and the device simulation with HFIELDS³⁾. Advanced ion implantation models implemented in STORM have been used together with range moments for implantation into cristalline silicon generated by Monte Carlo simulations performed with the MCIMPL module of the VISTA⁴⁾ framework. A strong influence of the crystalline structure of polysilicon on LDD profiles and electrical performance of the FOND device is demonstrated which cannot be taken into account with the standard simulation software.