Moving boundary problems and solution strategies in semiconductor process simulation

One important topic in numerical semiconductor process simulation is the thermal oxidation of silicon. The process step can be described as a transient coupled system of equations for oxidant diffusion, chemical reaction and large mechanical displacement. A moving interface between oxide and silicon renders the whole system a free boundary problem. Moreover, a volume expansion during oxidation by a factor of more than two causes the overall domain of computation to change during simulation. The approach which is presented in this paper, uses the idea of a distributed reaction zone between silicon and oxide. A finite element discretization for this formulation shows significant advantages over conventional approaches. In numerical examples an excellent agreement of the simulated results with microscopical photographs of real structures is demonstrated.