Critical dimension guarantee for the next generation photomasks with critical dimension scanning electron microscope

Abstract

Advanced critical dimension (CD)-scanning electron microscope was evaluated as a photomask CD guarantee tool. Measurement repeatability was 2.3 nm (3σ) for each measurement, and reproducibility (range of average value in five days) was 3 nm. The contamination effect was evaluated by measuring isolated Cr line and isolated space patterns. The contamination effect on measured CD value was estimated as 0.02 nm/scan (reticle scale) from the result of 500 scans at the same position. This result was quite different from the results of the aerial image of approximately 0.3 nm/scan (reticle scale) evaluated by MSM100 (λ=248 nm) and exposure results (λ=193 nm). The difference between these two evaluation results was probably due to the transmittance reduction of the electron beam scanning area of quartz substrate. This consideration was supported by atomic force microscopy and simulation results. There was no degradation on measurement repeatability and no image shift caused from the charging effect for the most severe condition (0.4 μm Cr isolated dot, global coverage of 20%, and local coverage of 0.05% under the magnification of 88 000×).