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Proceedings Paper

Directional and selective patterning of Ni for next generation EUV absorber (Conference Presentation)
Author(s): Xia Sang; Jane P. Chang

Paper Abstract

Ni is a promising candidate for future EUV absorber material due to its superior optical properties. However existing reports on gas phase patterning of Ni are limited and not precise enough to support the application. In this work, we present a two-step reaction ion etch (RIE) and atomic layer etching (ALE) process, in which the a cyclic exposure to chlorine and hydrogen plasmas in the RIE stage removes the bulk of the majority of the exposed Ni thin films, and a cyclic exposure to oxygen plasma and gas phase formic acid tailors the surface chemical contrast to form a directional etching profile. In the ALE step, the final sidewall angle is defined by directional ions that simultaneously control the subsequent etching selectivity and anisotropy. Specifically, the oxygen plasma exposure converts the surface to an oxide layer which has a large chemical reactivity contrast to the organic acid, therefore the reaction self-terminates upon the complete removal of the oxides, leaving an exposed metallic surface on the sidewall with great verticality. The self-limiting nature of this process is backed by the removal rate difference of over 100:1 between etching NiO x and Ni using formic acid vapor. The effect of acid exposure pressure is studied, and a higher pressure results in a more vertical sidewall profile. Structures of post-etch patterns were measured using AFM, SEM and TEM while the chemical compositions are confirmed by XPS and EDS. This approach is free of noble ion bombardment – greatly reducing adventitious sputtering – and has a much more forgiving process windows comparing to other reported approaches. A final sidewall angle of 87 has been observed for the first time using this highly selective self-limiting technique, which can be further improved with process optimization.

Paper Details

Date Published: 24 March 2020
Proc. SPIE 11323, Extreme Ultraviolet (EUV) Lithography XI, 1132312 (24 March 2020); doi: 10.1117/12.2554150
Show Author Affiliations
Xia Sang, Univ. of California, Los Angeles (United States)
Jane P. Chang, Univ. of California, Los Angeles (United States)

Published in SPIE Proceedings Vol. 11323:
Extreme Ultraviolet (EUV) Lithography XI
Nelson M. Felix; Anna Lio, Editor(s)

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