Abstract
Influences of phase defect structures on extreme ultraviolet (EUV) microscope images were examined. Phase defects on the bottom of a multilayer (ML) do not always propagate vertically upward to the ML’s top surface. For this study, two types of masks were prepared. One was an EUV blank with programmed phase defects made of lines in order to analyze the inclination angle of the phase defects. The other was an EUV mask that consists of programmed dot type phase defects 80 nm wide and 2.4 nm high with absorber patterns of half-pitch 88-nm lines-and-spaces. The positions of the phase defects relative to the absorber lines were designed to be shifted accordingly. Transmission electron microscope observations revealed that the line type phase defects starting from the bottom surface of the ML propagated toward the ML’s top surface, while inclined toward the center of the EUV blank. At the distances of 0 and 66 mm from the center of the EUV blank, the inclination angles varied from 0 to 4 deg. The impacts of the inclination angles on EUV microscope images were significant even though the positions of the phase defect relative to the absorber line, as measured by a scanning probe microscope, were the same.
Highlights
Extreme ultraviolet (EUV) lithography is considered to be the most promising next-generation lithography after the point where 193-nm immersion lithography would cease to deliver smaller features
According to our previous work, the path of a pit type phase defect propagating from the bottom of an ML and ending at the top is inclined toward the center of the mask.[28]
The fact that a phase defect does not always propagate in a vertical direction from the bottom surface of the ML to the ML’s top surface makes it necessary to examine the effect of the phase defect structures on an EUV microscope image of a mask pattern
Summary
Extreme ultraviolet (EUV) lithography is considered to be the most promising next-generation lithography after the point where 193-nm immersion lithography would cease to deliver smaller features. The reason is that for the EUV lithography generation, the device pattern feature size happens to be exceedingly small and calls for higher repairing accuracy than what has been achieved for optical lithography.[14,15,16] Regarding the types of defects, the nature of the pattern defects in the EUV mask is mostly the same as in the case of optical masks except for those defects that are classified as reflective multilayer (ML) defects, such as bump or pit phase defects that propagate through the ML during their deposition, and are hard to repair.[17] to minimize the effect of the phase defect on the printed images on wafer, two methods are suggested. To understand the influence of the propagation angle of the phase defect on the compensation strategy, a programmed phase defect EUV mask was prepared, and absorber lines with the phase defects were observed using SPM and EUV microscope
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