As the feature size gets smaller, the accuracy requirement for rigorous simulators becomes more stringent. While an accuracy of 1% in the aerial image may be enough for large feature sizes, an accuracy of better than 1% is needed for the small feature sizes encountered in advanced lithography. This means that the diffraction orders themselves should be accurate to three decimal places.

At Fastlitho, we take great care to make sure that our rigorous simulator gives accurate results. To verify the accuracy, we compare our results with those of the rigorous coupled wave analysis (RCWA) method, which is widely regarded as the gold standard for accuracy. Furthermore, to ensure complete objectivity in the comparison, we use a third-party RCWA tool for reference.

Until recently, a third-party RCWA tool may cost hundreds, if not thousands of dollars. Hence, such a tool was not readily available for use as a reference. However, recently, a very popular RCWA tool, GSolver, was released to the public free of charge. This means that users can now check the accuracy of their own rigorous simulators by comparing with this free, third-party RCWA tool.

However, since RCWA can be very time consuming for two-dimensional problems, it can be used to generate reference solutions accurate to four decimal places only for one-dimensional grating problems. So, we suggest that any rigorous simulator accurate enough for advanced lithography simulation should agree with RCWA to three decimal places for one-dimensional grating problems.

To see how accurate Fastlitho's rigorous simulator is compared to RCWA, click the links below for DUV and EUV examples:

DUV grating example
EUV grating example

Note: Some simulators' results may need to be adjusted for normalization before comparison with GSolver.