Pattern placement correction due to bending in EUVL masks

摘要

Extreme Ultraviolet Lithography (EUVL) masks have residual stress induced by several thin films on low thermalexpansion material (LTEM) substrates. The stressed thin films finally result in convex out-of-plane displacement (OPD)of several 100s of nm on the pattern side of the mask. Since EUVL masks are chucked on EUVL scanners differentlyfrom on e-beam writer, the mask pattern placement errors (PPE) are necessary to be corrected for to reduce overlayerrors. In this paper, experimental results of pattern placement error correction using standard chrome on glass (COG)plate will be discussed together with simulations. Excellent agreement with simple bending theory is obtained.Suitability of the model to compensate for other EUVL-related PPEs due to mask non-flatness will be discussed.