To protect an EUV mask from contamination, a pellicle can be used. However, the pellicle membrane must be very thin due to EUV absorption. As a result, a pellicle support structure is needed to avoid deflection of the membrane by gravity. Previous authors have shown that such a structure would produce a non-uniform intensity distribution on the wafer. In this paper, we use simulation to re-examine the issue. The results show that, when coherent illumination is used, a pellicle support structure would have an undesirable effect on the aerial image. However, we also show that, when partially coherent illumination is used, the intensity non-uniformity caused by the pellicle support structure can be effectively smoothed out, resulting in a perfectly acceptable aerial image.
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