Voltage‐assisted sodium ion incorporation and transport in thin silicon dioxide films

Na+ is a well-known contaminant in metal-oxide-semiconductor field effect transistor devices, which may cause severe changes in their input characteristics. This work is addressed to investigate the incorporation and transport behavior of mobile Na+ ions in SiO2, representing a material of major importance in semiconductor technology. We design an appropriate model system, to deliberately incorporate Na+ ions into a thin SiO2 film, which is attached on an n-doped Si wafer. A spin-coated thin polymer film, doped with sodium triflate in a low concentration, serves as external Na+ host matrix. The incorporation is assisted by means of an external voltage. Time of flight–secondary ion mass spectrometry is chosen as the tool for determination of Na+ ion location and distribution in SiO2. Measurements show that once Na+ was incorporated, the enormous internal electrical field in the bulk SiO2 causes an immediate drift of these ions toward the SiO2/Si interface, where a pile up of Na+ occurs. The related diffusion part can therefore be neglected. However, this accumulation has a counteracting effect on the electrical field and thus influences the incorporation rate. A comparison between the detected number of Na+ ions from potentiostatic and spectrometric data shows good agreement. Copyright © 2010 John Wiley & Sons, Ltd.