J Comput Electron (2008) 7: 107–110 DOI 10.1007/s10825-008-0214-6 Surface roughness induced device variability: 3D ab initio Monte Carlo simulation study Craig L. Alexander · Asen Asenov Published online: 28 February 2008 © Springer Science+Business Media LLC 2008 Abstract It is expected that published results from drift dif- fusion simulation of oxide thickness fluctuations in nano- scale devices underestimates the true intrinsic device pa- rameter variation by neglecting local variations in surface roughness scattering. We present initial results from 3D ‘bulk’ Monte Carlo simulation including an ab initio treat- ment of surface roughness scattering capable of capturing such transport variation. The scattering is included directly through the real space propagation of carriers in the fluctuat- ing potential associated with a randomly generated interface. We apply this approach to simulate inversion layer mobility in order to validate the model before its possible application in device variability simulations. Qualitative agreement is found with universal mobility data and avenues for possible calibration of surface and simulation parameters are high- lighted. Keywords Monte Carlo · Surface roughness scattering · Device parameter variation 1 Introduction Inherent device variability increasingly plays a more impor- tant role in limiting device integration with each new tech- nology node. The accurate estimation of variability in nano- scale devices and its impact on circuit performance [1] then becomes increasingly valuable during the technology design stage. The most comprehensive method to achieve this is C.L. Alexander ( ) · A. Asenov Dept. E&EE, Device Modelling Group, University of Glasgow, 80 Oakfield Ave., Glasgow G12 8LT, UK e-mail: c.alexander@elec.gla.ac.uk through the three-dimensional simulation of statistical en- sembles of devices that incorporate random discrete varia- tions. To this end, drift diffusion (DD) simulation has been suc- cessfully applied to study a wide range of sources of vari- ability [2]. However, recently [3] it has been shown that DD simulation underestimates the true magnitude of device pa- rameter variation by only capturing the electrostatic effect of discrete fluctuations on carrier concentration, while not treating associated variations in carrier transport. Transport variations are naturally incorporated within 3D Monte Carlo (MC) simulation when the appropriate interac- tion potential is resolved and applied within the simulation domain. While the proper resolution of additional current variations due to random discrete dopants was successfully demonstrated in 3D MC simulations and shown to be signifi- cant [3], this paper addresses the effect of transport variation associated with oxide thickness fluctuations. Work carried out on ab initio scattering from the related effect of body thickness fluctuations in double gate devices [4] has paved the way to incorporate this effect in MC. We present here an ab initio model of surface roughness scattering and for the first time its application to the simulation of the universal mobility in Silicon. We show a qualitative agreement with experimental data, and we further look to the application of this approach to study transport variations in real devices. 2 Ab initio surface roughness scattering Device variation associated with interface roughness and the corresponding oxide thickness fluctuations as estimated from DD simulation has been reported in the past [5]. In such simulations, unique variation in the oxide thickness