Simulation of front-end processing is a critical component of integrated-circuit (IC) technology development. Today's electronics are so small that characterization of their material parameters is very difficult and expensive. Simulation is often the only effective tool for exploring the lateral and vertical doping profiles of a modern device at the level of detail required for optimization. Additionally, the cost of fabrication and test lots increases with each technology generation; for this reason, simulation becomes especially costeffective, if it can be made accurate. Increasingly, process simulation is being performed by harnessing a hierarchy of tools. Ab initio and molecular-dynamics (MD) codes are used to generate insight into the physics of individual particle reactions in the silicon lattice. This information can be fed to kinetic Monte Carlo (MC) codes to establish the dominant, critical mechanisms. Finally, traditional continuum codes can make use of this information and couple with the other process steps to simulate the entire process flow. Both MC and continuum codes can be compared with experiment in order to validate the calculations.