Radiation-induced protective carbon coating for extreme ultraviolet optics

Abstract

A technique is described that uses radiation and a gas-phase species to produce a protective carbon coating on extreme ultraviolet (EUV) optics. A specific example is given in which a ∼5 Å carbon coating is deposited on EUV Mo/Si optics via coexposure to radiation (EUV photons, electrons) and ethanol vapor. Auger electron spectroscopy, sputter Auger depth profiling, and EUV reflectivity measurements are presented that suggest a carbon coating that is substantially void free and protects the optic from water-induced oxidation at the water partial pressures used in the tests (∼2×10−7 Torr). The coating is also resistant to atmospheric degradation, and to gasification by the combination of electrons and molecular oxygen. The protective coating reduces the relative reflectivity (ΔR/R0) of an optic by ∼0.5%.

Protection and reduction of surface oxidation of Mo∕Si multilayers for extreme ultraviolet lithography projection optics by control of hydrocarbon gas atmosphere

“…[3][4][5] It has been demonstrated that a carbonaceous film can be cleaned by using ozone 6 or atomic hydrogen. 12 Similar results have also been reported by Klebanoff et al 13 for a Si-capped multilayer sample that was irradiated mainly by a high-energy electron beam. The technology for a capping layer with which an oxidation-resistant Ru thin film was coated onto the surface of the mirror has been proposed and demonstrated.…”

Long-term stability of Ru-based protection layers in extreme ultraviolet lithography: A surface science approach

“…86,87 To understand this mitigation effect, one has to bear in mind that the addition of alcohols switches the originally oxidizing EUVL environment into a net reducing environment. 86,87 To understand this mitigation effect, one has to bear in mind that the addition of alcohols switches the originally oxidizing EUVL environment into a net reducing environment.…”

Atomic O and H exposure of C-covered and oxidized d-metal surfaces

“…Both in ambient conditions and during intense illumination in vacuum, background C x H y and H 2 O has been observed to adsorb and dissociate on the surface [5][6][7][8], resulting in condensed carbonaceous and oxide contaminants at the nanolayer surface [9][10][11]. Atomic hydrogen exposure (AHE) [12][13][14][15] and atomic oxygen exposure (AOE) [16,17] are two viable options to selectively remove these contaminants, respectively via rehydrogenation, or via oxidation to volatile molecules. AHE has been reported to produce both metal and semiconductor surfaces entirely free of contamination [18].…”