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23 March 2020 Accuracy improvement in advance lithography focus control
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To handle upcoming advanced technology nodes, the spec of focus control continues to tighten to satisfy more stringent CD uniformity (CDU). In high volume manufacturing (HVM) nowadays, yield at wafer edge suffers from CDU degradation due to process variation like edge roll-off topography. Advance focus control using diffraction-based focus (DBF) was proposed as one solution; we can apply the focus compensation values, which are determined from DBF measurement. However, the confidence of the focus compensation depends on the accuracy of focus measurement, which is a widely recognized challenge in the industry. In this paper, we have investigated the performance and the accuracy of two different designs of DBF marks by collecting full maps of DBF measurements. The measurement shows different signatures cross wafer from the two designs. For focus accuracy validation, CDU maps of several focus sensitive patterns have been collected and analyzed against the defocus measurement results. Our results demonstrate that with the accuracy improved DBF design and focus correction per exposure (CPE) schematic, the CDU is improved by 20%, at the wafer edge. We find that the dimension of the DBF main pattern (W1) dominates the accuracy of focus measurement. A DBF design guideline is proposed that the main pattern dimension (W1) should be close to device focus sensitive pattern size to capture its defocus signature more effectively. The accuracy of focus measurement benefits from designs that are close to device weak point patterns, which in turn improves the overall CD uniformity.
Conference Presentation
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Chris Hsu, Dongyue Yang, Cassidy Dineen, Xueli Hao, Young Ki Kim, Poya Hsu, and Bradley Morgenfeld "Accuracy improvement in advance lithography focus control", Proc. SPIE 11327, Optical Microlithography XXXIII, 113270O (23 March 2020);

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