Mask line roughness contribution in EUV lithography

In this paper, mask line edge roughness contribution to the final resist roughness is studied. For this purpose, dedicated line and space modules were designed. Both correlated and anticorrelated edge modulations were considered. For each modulation type, frequency and amplitude were varied. Two pitches were exposed with EUV ASML Alpha Demo Tool: 88 and 128nm in both horizontal and vertical direction. Analysis in the frequency domain was done by means of edge detection of top-down resist images. It was found that the lithographic optical system acts as a low pass filter for the mask line edge roughness frequency components: low frequencies mask roughness, lower that the optical system cut-off, were fully transferred on wafer, and characterized by power spectral density analysis. Moreover, it was established that high frequency mask roughness component had a detrimental effect on low frequency resist roughness, due to an aerial image degradation. Optical simulations were run to confirm experimental results.