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Low-energy electron-induced damage in hexadecanethiolate (HDT) monolayers on gold substrates has been investigated using infrared reflection−absorption spectroscopy (IRAS), angle-resolved near edge X-ray absorption fine structure spectroscopy (NEXAFS), and advancing water contact angle measurements. HDT films were exposed to electrons of energies 10−100 eV and doses between 30 and 14 000 μC/cm2. The induced damage was monitored both “in situ” by NEXAFS measurements interleaved with electron irradiations and “ex-situ” by NEXAFS, IRAS, and contact angle measurements after exposure of the irradiated samples to air. A progressive film damage was observed with increasing electron energy and dose of irradiation. This damage was found to occur during irradiation in UHV and was not induced by chemical reactions with airborne molecules during subsequent exposure of the irradiated films to air. The damage starts in the region of the terminal methyl groups of the HDT films and propagates into the bulk of the film. An analysis of the IRAS and NEXAFS data shows that the conformational and orientational order within the HDT film are most sensitive to low-energy electron irradiation. Electron-induced cleavage of C−H and C−C bonds resulting in a partial desorption of the film constituents also occurs and leads to formation of CC double bonds in the film as inferred from the appearance of a π*-resonance in the C 1s NEXAFS spectra. The obtained results are of importance for both the optimization of self-assembled-monolayers-based lithography processes and for the general understanding of irradiation-induced changes in organic films.

In this article we describe the preparation and identification of an organosilane self-assembled monolayer (octadecyltrimethoxysilane:  OTMS) on chromium oxide. The formation of the OTMS monolayer was investigated by X-ray photoelectron (XPS) spectroscopy and water contact angle measurements. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was applied in order to determine the tilt angle of the alkyl chains in the monolayer. The degree of hydration of the chromium oxide surface was found to greatly influence the quality of the monolayer. Our work focuses on the suitability of OTMS/Cr for lithographic patterning with low-energy electrons. In addition to the sensitivity and selectivity of the SAM system, its contrast γ was determined by measuring the gradation curve of OTMS on a 20 nm thick chromium layer using an alkaline hexacyanoferrat solution as an etchant. The contrast was found to be γ ≈ 1, which is comparable to those of conventional electron resists. The structured chromium layer was used as a mask for a reactive ion etch (RIE) process to pattern a silicon substrate.

This article describes the limitations of proximal probe lithography due to electrons that are mirrored by the electric field between the tip and the surface. The incident beam generates two kinds of electrons at the sample surface: primary electrons which are elastically backscattered and secondary electrons which are produced in the resist/substrate system. The electric field confines the electrons emanating from the surface. The electron trajectories are bent in such a way that the electrons impinge on the sample surface in the vicinity of their origin. These reflected electrons contribute to the exposure of the resist and therefore, limit the resolution. For hexadecanethiol monolayers on gold substrates, we have measured the energy distribution of the mirrored electrons and the secondary electron yield as a function of the primary energy. With near edge x-ray absorption fine structure spectroscopy, we have investigated the relevance of low energy electrons in the exposure of hexadecanethiol films. Simulations of secondary electron trajectories can explain the occurrence of triple line structures observed in field emission proximal probe lithography.