Throughput of steppers with off-axis illuminators: analysis and experiments

As manufacturing critical dimensions continue to shrink towards 0.35 μm, the exposure of IC critical levels requires increasingly effective techniques. Demand for such techniques facilitates acceptance of off-axis illumination as a way to better control the process window of 0.35 μm design rule. We focus our attention on issues related to optimization of exposure related factors influencing stepper throughput. We analyzed exposure conditions of one critical level commonly encountered in a variety of IC design. First, we present the result of process modeling and optimization of the critical level exposure. We then review the results of extensive proof-of-principle work done in support of modeling