Alignment scheme for through‐the‐lens alignment

A real‐time through‐the‐lens alignment system that locks the mask and wafer together via a feedback system on a deep ultraviolet (DUV) camera is described. The mask can be moved to actively track wafer motions even when the resist is being exposed. In support of this, we have devised a novel, high sample rate alignment system. Bench top experiments have verified the basic principles behind the design, emphasizing the ‘‘active’’ alignment mode. A one‐dimensional aligner will be installed on a stepper to test the concept with exposures on silicon wafers. The goal is to produce an alignment system that improves both overlay accuracy and throughput on DUV steppers.