Formation and Characterization of Self-assembled Monolayers of Octadecyltrimethoxysilane on Chromium: Application in Low-Energy Electron Lithography

Abstract

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.