Effect on Critical Dimension Performance for Carbon Contamination of Extreme Ultraviolet Mask Using Coherent Scattering Microscopy and 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) which was installed at 11B extreme ultraviolet lithography (EUVL) beamline of the Pohang Accelerator Laboratory (PAL). The CSM/ICS is composed of CSM for measuring imaging properties and ICS for implementing acceleration of carbon contamination. The mask critical dimension (CD) and reflectivity were compared before and after carbon contamination through accelerated exposure. The reflectivity degradation was measured as 1.3, 2.0, and 2.8% after 1, 2, and 3 h exposure, respectively, due to carbon contamination of 5, 10, and 20 nm as measured by Zygo interferometer. The mask CD change for 88 nm line and space pattern was analyzed using CSM and a CD scanning electron microscope (SEM), and the result shows CD-SEM and CSM give large difference of 3.8 times in mask Delta CD after carbon contamination. This difference confirms the importance of using actinic inspection technique that employs exactly the same imaging condition as exposure tool.