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9 July 2015 Influence of unit process interaction on EUV mask performance
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The EUV mask readiness is ranked under the top three challenges for successful introduction of EUV into high volume manufacturing. Whereas the basic mask manufacturing processes can be principally taken over from optical mask manufacturing, the big amount of new materials incorporated in the relatively complicated EUV mask stack is causing new effects either by their chemical and physical nature, or by their interaction with the processes. Some of the major challenges for EUV mask manufacturing compared to the optical mask is the EUV mask lifetime. First of those is the high illumination energy, which is expected to introduce changes in the mask stack, degradation of the pattern fidelity and reflectivity of the EUV mask. Also EUV mask manufacturing processes influence the mask lifetime. Few of those processes used over decade for successful manufacturing of optical mask can be used for manufacturing of EUV mask, which however will not perform very well and will impact mask lifetime. Interactions between unit processes were identified, influencing not only the pristine mask performance, but impacting their lifetime as well. In our work mainly the interaction between EUV etch and dedicated EUV cleaning process is investigated. Mainly the absorber etch process is dominantly determining the actinic reflectivity and its uniformity across the mask. Additionally the etch process is interacting with the clean process and limits the threshold for mask properties change due to clean process. Finally modification of surface layer and the presence (or absence) of Ru-based capping layer are critical factors for overall EUV mask properties and stability.
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Pavel Nesládek, Tereza Steinhartová, Haiko Rolff, Thorsten Schedel, and Markus Bender "Influence of unit process interaction on EUV mask performance", Proc. SPIE 9658, Photomask Japan 2015: Photomask and Next-Generation Lithography Mask Technology XXII, 965812 (9 July 2015);


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