CD guarantee for the next-generation photomasks with CD-SEM

We evaluated an advanced CD-SEM as a photomask CD guarantee tool. Measurement repeatability was 2.3 nm (3 (sigma) ) for each measurement, and reproducibility (the range of average value in 5 days) is 3 nm. Contamination effect was evaluated by measuring some isolated Cr line and isolated space patterns. The contamination effect on CD measurement value was estimated as 0.02 nm/scan (reticle scale) from the result of 500 scans at the same position. The results were quite different from the results of the aerial image of around 0.3 nm/scan (reticle scale) evaluated by MSM100 ((lambda) equals 248 nm). Difference between these two evaluation results was considered to be due to the transmittance reduction of substrate. There were no degradation on measurement repeatability and no image shift from charging effect for most severe condition (0.4 micrometer Cr isolated dot, global coverage of 20%, and local coverage of 0.05% under the magnification of 88,000 X).