A three-dimensional mesh generation method in which triangulation of the domain boundary is performed first is desirable since such a method would make it easier to achieve the requirements for the mesh around the boundary. We have developed a mesh generator for a 3D device simulator based on this approach. This mesh generator recursively subdivides a box that includes the whole domain into smaller boxes (cells), a method known as the octree technique. Although our mesh generator is similar to previously reported mesh generators in the sense that it utilizes recursive subdivision of elements, its major difference is that it constructs a triangular mesh upon boundaries of the domain first and this triangular mesh is not changed in the following processes. In order to generate a mesh suitable for the control volume method, a "forbidden region" is introduced and mesh points in the domain are allocated outside of this region. Since the triangular mesh is determined prior to tessellation of the domain, this method is suitable for handling layered mesh along the boundary, which is often necessary to estimate large flows parallel to the boundary precisely. A simple method to provide a layered mesh for a planar boundary is incorporated into the mesh generator. This mesh generator is integrated within our in-house three-dimensional device simulation system. The simulator's practicality is demonstrated through analysis of the reverse narrow channel effect for MOSFETs with LOCOS isolation structures. The effect of protection of the boundary by the layered mesh is also examined by calculating Id-Vg characteristics of a MOSFET with an oblique Si surface, and it is shown that protection of the whole surface of the channel region is necessary to estimate drain current correctly.

A realistic 3-D process/device simulation method was developed for investigating the fluctuation in device characteristics induced by the statistical nature of the number and position of discrete dopant atoms. Monte Carlo procedures are applied for both ion implantation and dopant diffusion/activation simulations. Atomistic potential profile for device simulation is calculated from discrete dopant atom positions by incorporating the long-range part of Coulomb potential. This simulation was used to investigate the variations in characteristics of sub-100 nm CMOS devices induced by realistic dopant fluctuations considering practical device fabrication processes. In particular, sensitivity analysis of the threshold voltage fluctuation was performed in terms of the independent dopant contribution, such as that of the dopant in the source/drain or channel region.