Extreme Ultraviolet Photoelectron Spectroscopy on Fluorinated Monolayers: towards Nanolithography on Monolayers

Abstract

The semiconductor industry plans to keep fabricating integrated circuits, progressively decreasing there features size, by employing extreme ultraviolet lithography (EUVL). With this method, new designs and concepts for photoresist materials need to be conceived. In this work, we explore an alternative concept to the classic photoresist material by using an organic self-assembled monolayer (SAM) on a gold substrate. The monolayer, composed of a richly fluorinated thiol sensitive to low-energy electrons, is adsorbed on the Au substrate which acts as main EUV-absorber and as the source of photoelectrons and secondary electrons. We investigate the stability of the SAM adsorbed on gold towards EUV radiation by means of in-situ photoelectron spectroscopy. The photoelectron spectra indicate that the monolayer attenuates a significant amount of primary electrons generated in the gold layer. The spectral evolution upon EUV irradiation indicates that the SAM loses a significant amount of its initial fluorine content (ca. 40% at 200 mJ/cm 2 ). We attribute these chemical changes mostly to the interaction with the electrons generated in the thiol/Au system.

Bottom-Up Nanofabrication with Extreme-Ultraviolet Light: Metal–Organic Frameworks on Patterned Monolayers

“…The hydrophobicity of HFDT monolayers originates from their high concentration of fluorine atoms. Thus, this hydrophobicity test supports our previous in-situ X-ray photoelectron spectroscopy (XPS) study, in which the F-loss was evidenced, 30 and reveals on a macroscopic scale, the chemical contrast between unexposed and exposed and exchanged areas. This fact also evidences that the replacement of thiols on exposed areas by a different thiol species is favored.…”

“…The qualitative comparison of the chemical composition of the various systems provides valuable insights into the mechanisms that take place during the procedure. Combined with the previously discussed hydrophobicity test, SEM inspection, and our previous F-loss studies, 30 these XPS results indicate that both desorption and incorporation of new species occur during the exchange procedure on areas irradiated by EUV photons.…”

“…The F 1s spectra show a significant decrease in intensity of the fluorine peak (687.6 eV, see also Figure S2 in the Supporting Information) in line with our previous in-situ irradiation studies, denoting the partial desorption of full HFDT molecules and/or outgassing of fluorine-containing fragments. 30 The +0.3 eV blue shift of the F 1s peak implies slight changes in the chemical environment of F atoms, presumably from structural reorganizations of the fluorocarbon chains of the monolayer upon exposure. 34 The 18 h exchange procedure yields a widening of the C 1s components assigned to C−H sp 2 /sp 3 carbon species as the dose increases.…”

“…Steps 1, 1′ and 2: EUV Exposure and Post-Exposure Exchange. In our previous study, 30 we showed that a thiol monolayer rich in fluorine, (3,4,5,6,7,8,9,10)-heptadecafluorodecanethiol (HFDT), on Au is chemically changed when exposed to EUV light and it was found that at a dose of 200 mJ/cm 2 , ∼40% of fluorine is lost. The secondary electrons and holes generated upon EUV absorption trigger these chemical changes.…”