The goal of our work is to calculate the variation in mask reflectivity due to various sources of inaccuracies using Monte Carlo simulations. Such calculation is necessary as small changes in the thickness and optical properties of the high-Z and low-Z materials can cause substantial variations in reflectivity. This is further complicated by undesirable intermixing between the two materials used to create the reflector.5 One of the key contributors to mask reflectivity fluctuation is identified to be the intermixing layer thickness. We also investigate the impacts on OPC when the wrong mask information is provided, and evaluate the deterioration of overlapping process window. For a hypothetical N7 via layer, the lack of accurate mask information costs 25% of the depth of focus at 5% exposure latitude. Our work would allow the determination of major contributors to mask reflectivity variation, drive experimental efforts of measuring such contributors, provide strategies to optimize mask reflectivity, and quantize the OPC errors due to imperfect mask modeling.
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Yulu Chen, Obert Wood, Jed Rankin, Eric Gullikson, Julia Meyer-Ilse, Lei Sun, Zhengqing John Qi, Francis Goodwin, Jongwook Kye, "Monte Carlo sensitivity analysis of EUV mask reflectivity and its impact on OPC accuracy," Proc. SPIE 10143, Extreme Ultraviolet (EUV) Lithography VIII, 101431S (27 March 2017);