The carbon contamination on extreme ultraviolet (EUV) masks is a critical issue causing throughput degradation and unexpected effects on imaging performance. In this work, a series of carbon contamination experiments were performed on a patterned EUV mask. The impact of carbon contamination on imaging performance was analyzed using actinic EUV coherent scattering microscopy (CSM) combined with an in-situ accelerated contamination system (ICS), which was installed on 11B EUVL beam-line at Pohang Light Source (PLS). In addition, the topography of the carbon contamination on the patterned mask was inspected with a scanning electron microscope (SEM). The mask critical dimension (CD) and reflectivity were compared before and after carbon contamination through accelerated exposure. The reflectivity degradation was measured as 5.5% after 3 h exposure which caused similar to 20 nm carbon deposition. A mask CD change of 88 nm line and the space pattern showed a similar trend but different absolute values as measured by CSM and CD-SEM. This difference confirms the importance of actinic inspection technique which emulates the practical imaging condition (6 degrees incident angle) as an EUV exposure tool. (C) 2011 Elsevier B. V. All rights reserved.