In situ measurements of sensor film dynamics by spectroscopic ellipsometry. Demonstration of back-side measurements and the etching of indium tin oxide

A new liquid flow cell design for in situ ellipsometric measurements on transparent multilayer samples using variable angle spectroscopic ellipsometry is presented. In this cell, films made on transparent substrates are in direct contact with liquid solution. Ellipsometry measurements are made through the transparent substrate, that is, from the back-side relative to the incident light so that films are in continuous contact with the liquid. This cell is not limited to just one angle of incidence of light allowing the films to be characterized at several angles before, during and after liquid contact. The spectral range of measurements is limited only by absorption of light in the underlying transparent substrate and not by the liquid solution that the film is in contact with. As a demonstration, we have measured and analyzed the dynamics of an indium tin oxide film on glass undergoing acid etching. Data from this in situ experiment were successfully modeled and the ITO layer thickness decreased uniformly during the etching process with an average etch rate of 0.23 nm/min.