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1 April 2010 Improving lithographic performance for 32 nm
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As optical lithography pushes towards the 32nm node and as the k1 factor moves toward 0.25, scanner performance and operational stability are the key enablers to meet device scaling requirements. Achieving these requirements in production requires stable lithography tools and processes. Stable performance is tracked with respect to pattern to pattern overlay, nominal focus and critical dimension uniformity (CDU). Within our paper we will characterize the intrinsic lithographic performance of the scanner and will discuss a new method of machine control to improve the stability and thus the overall performance of the lithographic solution. This is achieved by measuring specific monitor wafers, modeling the results by a new software algorithm and constantly feeding back corrective terms to the scanner. Diffraction-based optical dimensional scatterometry was selected because of its precision, its ability to measure overlay and focus with a single metrology recipe and its capability to generate greater amounts of measurement data in a shorter time period than other metrology techniques and platforms. While monitor wafer performance can be indicative, we will discuss the impact of the new control loop on product. We will take a closer look at possible interactions with the existing process control loops and work through the configuration of both internal and fab control loops. We will show improvements in the focus performance on product wafers by using scatterometry as well. Most importantly we will demonstrate that the newly implemented control loop resulted in a significant improvement of the CD and overlay performance of critical product layers. This had a very positive impact on overall process variation and the rework rate at lithography.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jens Busch, Anne Parge, Rolf Seltmann, Heike Scholtz, Bernd Schultz, Uwe Knappe, Matthias Ruhm, Marc Noot, Dieter Woischke, and Paul Luehrmann "Improving lithographic performance for 32 nm", Proc. SPIE 7638, Metrology, Inspection, and Process Control for Microlithography XXIV, 763805 (1 April 2010);


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