Calibration of physical resist models for simulation of extreme ultraviolet lithography

We have calibrated a physical resist model for extreme ultraviolet (EUV) lithography, and discuss model calibration and validation over a larger set of structures. The study is conducted on an extensive data set, collected at imec, for ShinEtsu resist SEVR-59 exposed on the ASML EUV alpha demo tool (ADT). The data set included more than a thousand measured feature widths (critical dimensions or CD) on wafer and mask. We address practical aspects of the calibration, such as the speed of calibration and selection of calibration input. The model is calibrated by simultaneously fitting 12 process windows of features with different mask CD (32, 36, 40 nm), orientation (horizontal, vertical), and pitch (dense, isolated). The smallest feature size at nominal process condition is a 32 nm CD at a dense pitch of 64 nm. Mask CD metrology was used to fit the model versus actually measured mask CD's. Cross-sectional scanning electron microscopy information was included in the calibration, to tune the simulated resist loss and sidewall angle. The achieved calibration root-mean-squared (RMS) error is similar to 1.0 nm. We discuss the elements that were essential to obtain a well calibrated model. We discuss the impact of 3-D mask effects on the Bossung tilt. We demonstrate that a correct representation of the flare level during the calibration is key in order to achieve a high CD predictability at various flare levels. Although the model calibration is performed on a limited subset of the measurement data collected on 12 different patterns (one dimensional structure process windows), its accuracy is validated on a large number of patterns used to calibrate models for optical proximity correction-several hundred different feature types, at nominal dose and focus conditions. These were not included in the calibration; validation RMS results as small as 1 nm can be reached. Furthermore, we study the model's extendibility to two-dimensional end of line structures. Finally, we show that we can correlate the experimentally observed fingerprint of the EUV ADT CD uniformity, to a CD fingerprint calculated using this resist model, where EUV tool and mask specific signatures are taken into account. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3533324]