With shrinking dimensions of semiconductor devices more and more effects arise which cannot be analyzed by two-dimensional simulations, since a two-dimensional simulation is not able to describe the influence of corners or other three-dimensional structures. In very small devices, which are already used in standard technologies, almost all regions of the devices, especially of critical devices, are located close to corners. Especially these critical devices require three-dimensional process and device simulations to be able to understand their behavior and the impact of processing steps.

Within the last year several tools have been developed at the Institute for Microelectronics for the three-dimensional simulation of semiconductor process steps. Among them are:

TOPO3D	a simulator for etching, deposition and mask transfer process steps
MCIMPL-II	an ion implantation simulator
FEDOS	a finite element based simulator for annealing processes

All these tools are fully compatible to each other since they are based on the Wafer-State-Server, a class of libraries which allows for a fast and convenient development of new tools since a large set of methods is already available.

TOPO3D provides the integration framework for various surface propagation algorithms (cellular, polygonal, level-set) with individual internal discretizations. An advanced simulation concept has been developed in which the moving front (generated by the surface propagation algorithms) is merged with the original structure at the end of the simulation. Thereby the drawback of structural conversion between various discretizations can be avoided, by maintaining, for instance, the benefit of the high stability of surface propagation on the basis of a cellular discretization. A simulation step of TOPO3D is always accompanied by an update of the volume mesh. Thereby a consistently volume-meshed structure results at the end of each topography simulation. Recently several empirical models have been implemented into TOPO3D for etching and deposition simulation on the basis of the cellular surface propagation algorithm. Additionally a link of the mask transfer models to the aerial image simulation has been established, which allows specific lithographic effects within a simulation flow to be considered.

MCIMPL-II comprises a Monte-Carlo module and has recently been extended by an analytical module. Calibrated (physically based) models have been implemented in both modules, offering a wide range of applicability. Another important research aspect in the field of three-dimensional ion implantation has been the topic of mesh generation/adaptation in order to be able to adequately resolve the implanted doping profiles while keeping the number of mesh nodes low. Various strategies have been worked out and are currently being evaluated.

FEDOS has been designed in an object-oriented concept which allows a convenient implementation of models. The simulator is designed to handle diffusion problems as well as oxidation problems. Recently a comprehensive set of models has been implemented which covers extrinsic as well as point defect assisted diffusion effects. Additionally a new approach for the simulation of oxidation processes based on a diffuse interface mechanism has been implemented. It has turned out that this approach is less demanding with respect to mesh generation. The applicability of the approach for three-dimensional applications considering critical aspects like stress and segregation is currently being investigated.