Validation of the predictive power of a calibrated physical stochastic resist model

Abstract

A newly developed stochastic resist model, implemented in a prototype version of the PROLITH lithography simulation software is fitted to experimental data for a commercially available immersion ArF photoresist, EPIC 2013 (Dow Electronic Materials). Calibration is performed only considering the mean CD value through focus and dose for three line/space features of varying pitch (dense, semi-dense and isolated).An unweighted Root Mean Squared Error (RMSE) of approximately 2.0 nm is observed when the calibrated model is compared to the experimental data. Although the model is calibrated only to mean CD values, it is able to accurately predict LER through focus to better than 1.5 nm RMSE and highly accurate CDU distributions at fixed focus and dose conditions. It is also shown how a stochastic model can be used to the describe the bridging behavior often observed at marginal focus and exposure conditions.

Predictive linewidth roughness and CDU simulation using a calibrated physical stochastic resist model

“…The first feature of interest was a 50nm line in a 100nm pitch imaged at 36.0 mJcm -2 and 0.05μm ('Best' focus). It should be noted that the standard deviation of the distribution for both experimental and simulation data is around 50% lower than that reported in the previous study [2]. This stems from a change in the way mean CD was determined for each sample.…”

“…In previous studies [2,3] it has been shown that repeated runs of the stochastic resist model under identical process settings yield slightly different resist profile results. Since these variations are related to probabilistic statistics, repeated runs can be used to synthetic CDU distributions.…”

“…In the original EPIC 2013 study [2] only a very limited amount of line-based experimental CDU data was available. For this work, a much larger number of CD measurements were made and the linewidth data was augmented with 2D line-end shortening mask patterns.…”

“…In a previous study [2], the same prototype model was calibrated to a comprehensive experimental data set for a commercially available immersion ArF photoresist, EPIC2013 (Dow Advanced Materials) to validate its ability to describe other experimentally observed lithographic behaviors, e.g. Focus-Dose CD response across pitch and CD uniformity (CDU).…”

Selection approach of critical patterns for calibrating the physical resist model based on spectrum coverage

“…Different imaging characteristics are observed due to the varying pitch-to-CD ratio values. Dense and isolated line/space patterns are frequently used for resist modeling 27 , 28 , 30 – 32 and calibration 33 – 38 due to the significant differences in imaging characteristics between them. Consequently, the EXP-method 1 selects the patterns with the smallest and largest pitch-to-CD ratios as the critical patterns.…”