The impact of random dopant fluctuation (RDF) on a 10-nm n-type silicon (Si) FinFET with a metal-insulator-semiconductor (M-I-S) source/drain (S/D) structure is investigated using three-dimensional TCAD simulation. To determine the optimal aspect ratio of the fin for a variation-robust FinFET with an M-I-S S/D structure, various metrics for device performance are quantitatively evaluated. It is found that variation in RDF-induced threshold voltage (V-th) in the FinFET can be suppressed with a taller fin (i.e., a fin with a higher aspect ratio) because of better gate-to-channel controllability and wider channel width. For a fin aspect ratio (i.e., fin height to fin width) of 5.25:1, the standard deviation for RDF-induced V-th in a FinFET with an S/D doping concentration (N-S/D) of 5 x 10(20) cm(-3) is 9.277 mV. In order to suppress RDF-induced V-th variation even further, an M-I-S structure with a heavily doped n-type ZnO interlayer can be introduced into the S/D region of the FinFET. For the tallest fin height, this M-I-S S/D structure (with an N-S/D = 5 x 10(19) cm(-3)) results in a standard deviation of 4.729 mV for RDF-induced V-th, while maintaining the on-state drive current (I-on) at a satisfactory level. Therefore, it is expected that a 10-nm n-type FinFET can be designed to be immune to Vth variation with the adoption of the proposed M-I-S S/D structure. (C) 2016 Elsevier B.V. All rights reserved.