Full chip correction of EUV design

Extreme Ultraviolet Lithography (EUVL) is currently the most promising technology for advanced manufacturing nodes: it recently demonstrated the feasibility of 32nm and 22nm node devices, and pre-production tools are expected to be delivered by 2010. Generally speaking, EUVL is less in need of Optical Proximity Correction (OPC) as compared to 193nm lithography, and the device feasibility studies were indeed carried out with limited or no correction. However, a rigorous optical correction strategy and an appropriate Electronic Design Automation (EDA) infrastructure is critical to face the challenges of the 22nm node and beyond, and EUV-specific effects such as flare and shadowing have to be fully integrated in the correction flow and properly tested. This study aims to assess in detail the quality of a full chip optical correction for a EUV design, as well to discuss the available approaches to compensate for EUV-specific effects. Extensive data sets have been collected on the ASML EUV Alpha-Demo Tool (ADT) using the latest IMEC baseline resist Shin-Etsu SEVR59. In total about 1300 CD measurements at wafer level and 700 at mask level were used as input for model calibration and validation. The smallest feature size in the data set was 32nm. Both one-dimensional and two-dimensional structures through CD and pitch were measured. The mask used in this calibration exercise allowed the authors to modulate flare by varying tiling densities within the range expected in the final design. The OPC model was fitted and validated against the CD data collected on the EUV ADT. The shadowing effect was modeled by means of a single bias correction throughout the design. Horizontal and vertical features of different type through pitch and CD were used to calibrate the shadowing correction, and the extent of the validity of the single bias approach is discussed. In addition, the quality of the generated full-chip flare maps has been tested against experimental results, and the model has been validated in the full flare range available within the mask. The model calibration yielded an RMS of about 1nm, and a EUV mask fully corrected for OPC, flare and shadowing was finally fabricated and qualified.