Wafer level response to mask deficiencies in 0.55-numerical aperture extreme ultraviolet photolithography

BackgroundThis study investigates the impact of 0.55-numerical aperture (NA) imaging on wafer defectivity when multilayer ripple is present in the extreme ultraviolet (EUV) mask.AimWe investigate the impact of 0.55-NA anamorphic imaging on one-dimensional (1D) and two-dimensional (2D) horizontal and vertical mask feature deficiencies on wafer defectivity. The information in the study is intended to guide experimentation to aid in setting standards for EUV mask blanks in 0.55-NA lithography.ApproachThis study stochastically simulated 1D and 2D horizontal and vertical features using an extreme ultraviolet mask with varied random multilayer ripple configurations. The photoresist critical dimension (CD) was measured from the simulated wafer and used to generate statistical analysis of the simulation.ResultsHorizontal 1D features show an ∼2.5 × improvement in failure ratio versus vertical 1D features. Vertical 2D features appear to have a lower failure ratio compared with 2D horizontal features, but the difference is not as clear as found in the 1D case. The light scattered from the leaf shaped illuminator into the pupil background region due to multilayer ripple from 2D features appears smaller than in the 1D case. Potentially mask deficient structures may benefit from orientating the CD vertically on an anamorphic system to reduce wafer level defectivity.ConclusionsThere appears to be a multilayer ripple saturation level for 1D and 2D features at which defectivity and CD variation become constant. Horizontal imaging appears to be preferable for all CDs. The roughness threshold computational shortcut to mask deficiency characterization may not be sufficient for 2D features. The 2D analysis in this study does not change previous mask standard suggestions.