Plasma and Fusion Research

Volume 16, 1406003 (2021)

Regular Articles

Effect of Hydrogen Ion Energy in the Process of Reactive Ion Etching of Sn Thin Films by Hydrogen Plasmas
Mengran JI, Ryo NAGATA and Kiichiro UCHINO
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasugakoen, Kasuga, Fukuoka 816-8580, Japan
(Received 28 September 2020 / Accepted 13 December 2020 / Published 8 February 2021)

Abstract

One of the problems in extreme ultraviolet (EUV) lithography is the deterioration in the reflectivity of the EUV mirror owing to the deposition of tin (Sn) debris. Such Sn adhesion films can be etched by hydrogen ions and atoms through a chemical reaction, forming a volatile SnH4 gas. In this study, the dependence of the hydrogen ion energy on the Sn etching was investigated. Samples covered by Sn thin films and with various applied bias voltages were exposed to hydrogen plasmas. The etched thicknesses of the Sn films were quantitatively analyzed using X-ray fluorescence. As a result, it was found that the threshold ion energy is approximately 7 eV, and that the peak of the Sn atom yield per hydrogen ion, which is the value indicating the efficiency of the reactive ion etching, is obtained at a hydrogen ion energy of approximately 14 eV.

Keywords

extreme ultraviolet lithography, Sn debris, thin film, hydrogen plasma, reactive ion etching, bias voltage

DOI: 10.1585/pfr.16.1406003

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