EUV mask observations using a coherent EUV scatterometry microscope with a high-harmonic-generation source

In extreme ultraviolet (EUV) lithography, the three-dimensional (3D) structure of the EUV mask, which has an absorber layer and a Mo/Si multilayer on a glass substrate, strongly affects the EUV phase. EUV actinic metrology is required to evaluate the feature of defect printability and the critical dimension (CD) value. The 3D structure modulates the EUV phase, causing the pattern position and focus shift. A microscope that observes in phase contrast necessary. We have developed a coherent EUV scatterometry microscope (CSM) for observing EUV patterns with quantitative phase contrast. The exposure light is coherent EUV light. For the industrial use, we have developed a laboratory coherent source of high-harmonic-generation (HHG) EUV light. High harmonics is pumped by a scale of a Ti:Sapphire laser. In the previous study, a very long exposure time of 1000 s was necessary to detect We upgraded the relay optics. The detection performance of an absorber defect using the new relay optics is We observed the line-end oversize defect and the oversize defect in the 112 nm hole pattern and 180 nm hole pattern. The upgraded system has a detection size limit of a line-end 24-nm-oversize defect with 10 s exposure time, which is 2,688 nm2 (52 × 52 nm2) absorber defect. This result shows high performance capability of HHG-CSM for detecting small defect.

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