Dynamic wetting behavior of silicon wafers in alkaline solutions of interest to semiconductor processing

Alkaline solutions based on ammonium hydroxide and quaternary ammonium hydroxides are used widely in the wet processing of silicon wafers for control of ionic and particulate impurities following etching in acidic or buffered fluoride solutions. Etched silicon is hydrophobic in nature and alkaline solutions, because of their capacity to etch silicon, will probably alter its wettability. In this paper, the wettability of silicon in choline (2-hydroxyethyl trimethyl ammonium hydroxide) and ammonium hydroxide solutions as investigated by a dynamic contact angle analysis technique is discussed. Specifically, it has been found that silicon exhibits a profound hysteresis in wettability during the first immersion/emersion cycle in dilute choline as well as in ammonia solutions Ellipsometric and XPS (X-ray photoelectron spectroscopy) analyses have shown that exposure of choline-treated surfaces to air results in the oxidation of Si to SiO₂.