 On the other hand, a single exposure only offers a single illumination.For example, in a cross-pitch source-mask optimization for 7nm node, for 40-48 nm pitch and 32 nm pitch, the quality as determined by the normalized image log slope was insufficient (NILS<2), while only 36 nm pitch was barely satisfactory for bidirectional single exposure.The underlying situation is that EUV patterns may be split according to different illuminations for different pitches, or different pattern types (e.g., staggered arrays vs. regular arrays).