Cellular automaton (CA)-based device simulation is one of the most powerful tool to solve Boltzmann transport equation (BTE) of carriers in semiconductor devices. In comparison to the Monte Carlo (MC) method which suffers statistical noise problems, cell representation used in the CA method realizes noise free analysis of the carrier distribution function (DF) both in real and momentum space. However, CA requires more computer resources than MC in typical cases because cell sizes used for both real and momentum space are restricted to be small enough not to cause artificial diffusion (ADF). In this paper, a new scheme for calculation of flux among cells is proposed in which carrier distribution is interpolated between neighbor cells. The suppression of ADF is confirmed through comparisons to other simulation methods in homogeneous cases, an n/sup +/-p diode case and an n/sup +/-n-n/sup +/ structure case. Consistency with MC analysis is also demonstrated by analyzes of homogeneous cases and an n/sup +/-n-n/sup +/ case and also by a theoretical study. A speed up of at least two orders of magnitude can be obtained by introducing the new flux calculation whose accuracy is ensured with much less number of cells than conventional CA methods. Consequently, this CA method is drastically improved as a practical tool for semiconductor device modeling from the point of CPU time and accuracy.

A three-dimensional (3-D) process simulator, OPUS/3D, has been developed. It has access to two-dimensional (2-D) process simulation results. Impurity profiles and structural data simulated rigidly in 2-D space are expanded to 3-D space at an arbitrary stage of the simulation processes. 3-D simulation follows until the end of the process. The access to 2-D simulation results enables OPUS/3D to handle curved boundaries as seen in field oxides. OPUS/3D has three different methods for expanding 2-D results. Errors due to these expansions are discussed. OPUS/3D was applied to 3-D simulations of MOS devices at the corner edge of the active region and in the channel region near the source/drain. Computation time was drastically reduced by replacing part of the 3-D simulations by 2-D simulations. Some 3-D effects are confirmed by OPUS/3D.>

A general-purpose two-dimensional process simulator OPUS (Oki Process simulator for ULSI Structures) for arbitrary structures is discussed. By separating a preprocessor from a main processor, OPUS can simulate any kind of impurity or material with up to eight impurities and ten materials. OPUS utilizes a finite-difference method for diffusion analysis without any coordinate transformation. In order to minimize errors due to discretization around the curved boundaries, OPUS has introduced two kinds of boundaries. The first is true boundaries by strings. The other is quasi-boundaries formed through simplifying but retaining the shape of true boundaries as long as possible. The quasi-boundaries and resulting dummy cells are used for discretization of the diffusion equation. General features of OPUS are first introduced with special emphasis on dummy cells. Errors caused by dummy cells are discussed. The capacity of OPUS is then demonstrated through application to a trench process and to a full MOS process with a sidewall.>