Comparison Of At-Wavelength Inspection, Printability, And Simulation Of Nm-Scale Substrate Defects In Extreme Ultraviolet Lithography (Euvl).

We report on the comparison of defect printability experimental results with at-wavelength defect inspection and printability modeling at extreme ultraviolet (EUV) wavelengths. Two sets of EUV masks were fabricated with nm-scale substrate defect topographies patterned using a sacrificial layer and dry-etch process, while the absorber pattern was defined using a subtractive metal process. One set of masks employed a silicon dioxide film to produce the programmed defects, whereas the other set used chromium films. Line-, proximity- and point-defects were patterned and had lateral dimensions in the range of 0.2 mu m x 0.2 mu m to 8.0 mu m x 1.5 mu m on the EUV reticle, and a topography in the range of 8 nm - 45 nm. Substrate defect topographies were measured by atomic force microscopy (AFM) before and after deposition of EUV-reflective Mo/Si multilayers. The programmed defect masks were then characterized using an actinic inspection tool. All EUVL printing experiments were performed using Sandia's 10x-reduction EUV Microstepper, which has a projection optics system with a wavefront error <1 nm, and a numerical aperture of 0.088. Defect dimensions and exposure conditions were entered into a defect printability model. In this investigation, we compare the simulation predictions with experimental results.