Actinic phase defect detection and printability analysis for patterned EUVL mask

Multilayer defects embedded in EUV mask blanks are of primary concern in making usable mask because the multilayer defects as small as 1.5 nm in height cause phase shifts and are most likely to be printable on wafers. To detect such phase defects, we have developed an actinic (at wavelength) full-field EUV mask blank inspection tool equipped with dark-field imaging optics. Inspection performance was demonstrated by a full-field mask blank inspection of a test mask blank to detect its programmed phase defects and native phase defects. A potential of detecting phase defects among the absorber patterns was also explored by inspecting masks with dot bump defects sitting among the absorber lines and line bump defects perpendicular to the absorber lines. For the phase defect printability study, the test mask was exposed using an EUV exposure tool (EUV1) at Selete. Simulation of projected image was also conducted using FDTD method. Multilayer defect printability for varying location of the multilayer phase defects relative to the absorber line patterns were evaluated