An Ellipsometric Model for Establishing Thickness of Thin Water Nanolayers on the Silicon Wafers

Abstract

Ellipsometry optical measurements are a very useful tool for obtaining information about details of layered structures in the nanoscale. By examining data obtained with silicon wafers in the room conditions we show how to obtain a reliable assessment of the thickness of the adhered water nanolayer. This effect is naturally caused by the hydrophilic character of the surface silica which is always present on the silicon surfaces. Since the film thickness, optical constants, and microstructure are all intermixed in the effective experimental ellipsometric data the issue of determining a unique and best-fit model for an investigated sample is of the decisive importance. Our optical model, based on four oscillators of the Tauc-Lorentz type for the silicon substrate, a small layer of SiO ₂ and a water layer is shown to work satisfactorily for room temperatures. Consequences of the presence and the amount of water on the silicon based parts of nanodevices like, for instance, the AFM tips, are discussed. key words: ellipsometric modeling, silica, silicon, water, surface,silicon surface, nanolayers, water adsorption, dielectric constants, refraction coefficient, silanol groups, nanotribology, thin film properties, optical properties