Carbon contamination of EUV mask and its effect on CD performance Sangsul Lee a , Jong Gul Doh a , Jae Uk Lee a , Inhwan Lee a , Chang Young Jeong b , Dong Gun Lee b , Seung-yu Rah c , Jinho Ahn a, * a Department of Materials Science and Engineering, Hanyang University, Seoul 133-791, Republic of Korea b Photomask Team, Memory Division, Samsung Electronics Co., LTD, Republic of Korea c Pohang Light Source, Republic of Korea article info Article history: Received 10 November 2010 Received in revised form 2 May 2011 Accepted 3 May 2011 Available online 14 July 2011 Keywords: EUVL Coherent scattering microscopy Carbon contamination Mask CD Reflectivity Shadowing effect abstract 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 contami- nation 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 w20 nm carbon depo- sition. 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  incident angle) as an EUV exposure tool. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Extreme ultra violet lithography (EUVL) is the most promising next generation patterning technology for 22 nm half-pitch node and beyond [1]. However, there remain some technical challenges for its application to high volume manufacturing (HVM). Among them, carbon contamination of EUV masks is a critical issue for EUV mask lifetime and imaging performance. EUV (wavelength: 13.5 nm) radiation is absorbed by all materials; EUVL is a vacuum-based technology that uses reflective optics using a Bragg reflecting multi-layer mirror structure. However carbon film deposition has been reported to degrade the reflectivity of the mask, which results in reduction of throughput and deterioration of critical dimension (CD) uniformity [2,3]. An EUV mask can be contaminated in the presence of high- energy EUV radiation and by contamination sources like hydro- carbons and water vapor in the exposure chamber [2e5]. The unsolved issues for EUVL insertion into HVM are methods of mitigating the carbon contamination and analyzing the impact of carbon contamination on the imaging performance [6e8]. In this paper, we present our work on these issues using coherent scattering microscopy (CSM) with an in-situ accelerated contamina- tion system (ICS) [9e12]. The mask CD and reflectivity change were investigated before and after accelerated carbon contamination. 2. System overview The CSM/ICS was installed on 11B EUVL bending magnet beam- line at Pohang Light Source (PLS) [15]. The white synchrotron radiation (SR) beam was monochromatized with Mo/Si multi-layer mirrors and zirconium (Zr) filters on nickel mesh. Fig. 1 shows the layout of the EUV CSM/ICS optic system used for studying the impact of carbon contamination on the imaging property of an EUV mask. The EUV mask was positioned for intentional carbon contamination and the monochromatized beam was illuminated onto the evaluation area of the mask. After executing the acceler- ated contamination, the EUV mask was transferred to the CSM imaging position, where the incidence angle of the mono- chromatized beam to the mask surface was set to 6  . 3. Experiments and discussion A typical EUVL mask consists of four main layers: the absorber for EUV absorption, the buffer for absorber etch stop and damage * Corresponding author. Tel.: þ82 2 2220 0407; fax: þ82 2 2291 1130. E-mail address: jhahn@hanyang.ac.kr (J. Ahn). Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2011.07.019 Current Applied Physics 11 (2011) S107eS110