Characterization of carbon contamination under ion and hot atom bombardment in a tin-plasma extreme ultraviolet light source

TL;DR

This study investigates carbon film formation on EUV lithography collectors under tin plasma bombardment, revealing inert, diamond-like carbon characteristics influenced by water and plasma conditions.

Contribution

It provides the first detailed chemical and structural characterization of carbon contamination films formed under ion and hot atom bombardment in EUV sources.

Findings

Carbon film is chemically inert and hydrogenated.

The film is predominantly sp3 hybridized, diamond-like carbon.

Water plays a significant role in film formation.

Abstract

Molecular contamination of a grazing incidence collector for extreme ultraviolet (EUV) lithography was experimentally studied. A carbon film was found to have grown under irradiation from a pulsed tin plasma discharge. Our studies show that the film is chemically inert and has characteristics that are typical for a hydrogenated amorphous carbon film. It was experimentally observed that the film consists of carbon (~70 at. %), oxygen (~20 at. %) and hydrogen (bound to oxygen and carbon), along with a few at. % of tin. Most of the oxygen and hydrogen are most likely present as OH groups, chemically bound to carbon, indicating an important role for adsorbed water during the film formation process. It was observed that the film is predominantly sp3 hybridized carbon, as is typical for diamond-like carbon. The Raman spectra of the film, under 514 and 264 nm excitation, are typical for hydrogenated diamond-like carbon. Additionally, the lower etch rate and higher energy threshold in chemical ion sputtering in H2 plasma, compared to magnetron-sputtered carbon films, suggests that the film exhibits diamond-like carbon properties.