Determination of the CD Performance and Carbon Contamination of an EUV Mask by Using a Coherent Scattering Microscopy/In-situ Contamination System

Abstract

The impact of carbon contamination on imaging performance was analyzed using an in-situ accelerated contamination system (ICS) combined with coherent scattering microscopy (CSM) at the 11B extreme ultraviolet lithography (EUVL) beamline of the Pohang Accelerator Laboratory (PAL). The CSM/ICS is composed of the CSM for measuring imaging properties and the ICS for accelerating the carbon contamination. The CD (critical dimension) and the reflectivity of the mask were compared before and after carbon contamination through acceleration exposure. The reflectivity degradation was 1.3%, 2.1%, and 2.5% after 1-, 2-, and 3-hour exposures, respectively, due to carbon contamination of 5, 10, and 20 nm as measured by using a Zygo interferometer. The mask CD change of an 88-nm line and space pattern was analyzed using CSM and CD SEM (scanning electron microscope), and the result showed a similar trend, but a different absolute value. This difference confirmed the importance of the actinic inspection technique, which employs exactly the same imaging condition as the exposure tool.