Pattern inspection of etched multilayer EUV mask

Susumu Iida; Ryoichi Hirano; Tsuyoshi Amano; Hidehiro Watanabe

doi:10.1117/12.2203123

23 October 2015 Pattern inspection of etched multilayer EUV mask

Susumu Iida, Ryoichi Hirano, Tsuyoshi Amano, Hidehiro Watanabe

Proceedings Volume 9635, Photomask Technology 2015; 96350Y (2015) https://doi.org/10.1117/12.2203123
Event: SPIE Photomask Technology, 2015, Monterey, California, United States

Abstract

Patterned mask inspection for an etched multilayer (ML) EUV mask was investigated. In order to optimize the mask structure from the standpoint of not only a pattern inspection by using a projection electron microscope (PEM), but also by considering the other fabrication processes using electron beam (EB) techniques such as CD metrology and mask repair, we employed a conductive layer between the ML and substrate. By measuring the secondary electron emission coefficients (SEECs) of the candidate materials for conductive layer, we evaluated the image contrast and the influence of charging effect. In the cases of 40-pair-ML, 16 nm sized extrusion and intrusion defects were found to be detectable more than 10 sigma in hp 44 nm, 40 nm, and 32 nm line and space (L/S) patterns. Reducing 40-pair-ML to 20-pair-ML degraded the image contrast and the defect detectability. However, by selecting B₄C as a conductive layer, 16 nm sized defects remained detectable. These defects were also detected after the etched part was refilled with Si. Moreover, the simulation shows a high sensitivity for detecting the residual-type defects (etching residues). A double layer structure with 2.5-nm-thik B₄C on metal film used as a conductive layer was found to have sufficient conductivity and also was found to be free from the surface charging effect and influence of native oxide.

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Susumu Iida, Ryoichi Hirano, Tsuyoshi Amano, and Hidehiro Watanabe "Pattern inspection of etched multilayer EUV mask", Proc. SPIE 9635, Photomask Technology 2015, 96350Y (23 October 2015); https://doi.org/10.1117/12.2203123

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KEYWORDS

Silicon

Defect detection

Extreme ultraviolet

Photomasks

Inspection

Modulation transfer functions

Etching

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