Abstract

Researchers occasionally use a single photomask to create a stacked structure with identical patterns. This method is cost-effective but also challenging for precise overlay control, due to the lack of coupled overlay marks between successive layers. In this paper, an innovative approach has been developed to address this problem. By shifting the exposure field with a specific offset, the outer overlay mark of the previous layer and the inner overlay mark of the current layer are aligned to the same coordinate position, allowing for accurate measurement of the overlay error. The raw overlay measurement values are then modeled using polynomials and compensated during subsequent runs. The effectiveness of this method has been demonstrated with experiment wafers, and PFA (Physical Failure Analysis) result further confirmed its feasibility for achieving precise overlay in such applications.