Analysis of Amorphous Alumina Thin Film Etching by Phosphate Buffer Using Surface Plasmon Resonance

Abstract

The optical surface plasmon resonance (SPR) phenomenon was used to estimate the etching rate for inorganic films. The etching rate for amorphous alumina films deposited by atmospheric chemical vapor deposition using a phosphate buffer (PB) solution was estimated by the SPR method using a multilayer structure of alumina/gold/chromium/optical glass. To demonstrate that the SPR technique can be used to measure film thickness, the decrease in the thickness of a film as a result of etching was confirmed by measuring the thickness by the X-ray reflectivity (XRR) technique. The alumina/silicon samples were immersed in PB solution, and the film thicknesses obtained by the XRR technique changed from 46 to 35 nm when etched by the 0.3 M PB solution for 5 h. In SPR experiment, the same concentration of PB was used for the multilayer structure of alumina, and it was observed that the thickness changed from 26.3 to 9.8 nm in 5 h. It was found that the etching rates determined by both techniques for each PB concentration were in agreement. These results indicate that the SPR technique, which is an easy and safe technique compared with the XRR technique, could be used to estimate the etching rate for multilayer structures.