Self-aligned double patterning (SADP) process even-odd uniformity improvement
Self-aligned spacer double patterning (SADP) scheme has been proposed as an alternative to litho-etch-litho-etch (LELE) scheme because if its superior control of the lines that are patterned by a uniform and conformal deposition of a spacer layer along sidewalls of the sacrificial patterning lines. However, it adds process complexity in the film stacks and extra challenges on both the linewidth and overlay variations induced by film thickness and etch uniformity, which was also called even-odd bias induced by the spacer. Effects of lithography and etch process deviations during sacrificial core formation are thought to be predominantly for the final space even-odd performance. In this paper, we will present an experimental study of process effect on the space even-odd uniformity, including the lithographic critical dimension uniformity (CDU), sacrificial core etch, spacer etch, hard mask etch and final Si etch. The contribution to the even-odd uniformity will be focused and analyzed step by step. DOMA application on 3X nm FLASH process was also carried out to improve the sacrificial core CDU, and its contribution and limitation to the final even-odd uniformity will be clarified as well.