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.
With the continuous resolution shrinking in cutting edge semiconductor industry such as memory device, on product overlay (OPO) control has become more and more challenging. Reticle heating is a critical impact to OPO when DUV light exposes to the reticle, as the thermal expansion of the reticle induces nanos of overlay error on wafer level which directly impacts device function. Reticle heating control functions has been developed to compensate overlay error in current advanced scanners for normal full reticle, of which one layer mask occupies one reticle. However, the heating effect of Multilayer Reticle (MLR), wherein one reticle consists of multiple mask layers, is less discussed. In this paper, we investigated the reticle heating effect to OPO on MLR, and the methods for MLR heating control is proposed.
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