Evaluation of Alignment Performance of Different Exposure Tools Under Various CMP Conditions

摘要

The downscaling of IC design rule has increasingly imposed tighter overlay tolerances together with high cost of lithography equipment. Foundries are required to optimize tools utilization in order to be cost effective. To run with the same process flow using different exposure tools, the effect of the different process parameters needs to be characterized. This paper explores the feasibility of using the same W-CMP process for two different alignment systems employing different alignment marks. An evaluation of the alignment performance was done using marks placed in the scribe line of Tower's products. Exposures were performed using two different DUV scanners at BEOL layers, with process splits performed prior to the W-CMP phase. Robustness of alignment mark is critical, as the scanner's alignment system requires accurate signal to precisely align a pattern layer to a pervious layer. Data taken by the scanners on various tool/mark/recipe combinations is analyzed to provide indication of the overlay performance robustness to the process parameters. To investigate the effect of different W-CMP processes on alignment marks in back-end processing, an evaluation was performed through which both mark design and process parameters were varied. The robustness of typical long-term process variation at the W-CMP step in a production environment was evaluated.