Imaging performance optimization for hyper-NA scanner systems in high volume production

The introduction of lithographic systems with NA=1.35 has enabled the extension of optical lithography to 45 nm and below. At the same time, despite the larger NA, k1-factors have dropped to 0.3 and below. Defining the appropriate strategies for these high-end lithographic processes requires the integration and co-optimization of the design, mask and imaging parameters. This requires an in-depth understanding of the relevant parameters for imaging performance during high volume manufacturing. Besides the Critical Dimension Uniformity (CDU) budget for the baseline lithographic system, it is crucial to realize that system performance may vary over time in volume manufacturing. In this paper the CDU budget will be restated, with all the well-known contributors, and extended with some new terms, such as volume manufacturing effects. Experimental low-k1 results will be shown from NA=1.35 lithographic tools and compared to model-based predictions under realistic volume manufacturing circumstances. The combination of extreme NA and low k1 makes it necessary to introduce computational lithography for scanner optimization. The potential of using LithoCruiserTM and TachyonTM for optimising scanner source and OPC will be described. Also, using the fast scanner correction mechanisms to compensate for reticle, track and etch fingerprints and variations will be discussed.