The Activity of HF/H₂O Treated Silicon Surfaces in Ambient Air Before and After Gate Oxidation

A strong correlation is observed among surface charge, contact angle, and native oxide thickness in which up to 10,000 min of exposure time to ambient air, the liquid-HF/H₂O and vapor-HF/H₂O treated surfaces seem to undergo three distinct periods of evolution. The results indicate that the vapor-HF/H₂O treatment yields surfaces with greater activity in ambient air. The trends, which are explained by considering the reaction between unpassivated trivalent silicon and hydroxyl groups, are shown to be consistent with XPS data on surface carbon, fluorine, and oxygen. Following thermal oxidation, the total oxide charge, oxide thickness, and contact angle are stable over time. This is possibly due to the complete surface oxide coverage. The thermal oxide thicknesses of liquid-HF/H₂O and vapor-HF/H₂O treated surfaces are different and can be correlated to preoxidation surface XPS results. Following thermal oxidation, no differences between vapor-HF/H₂O and liquid-HF/H₂O are detected in terms of oxide charge and contact angle as a function of ambient air exposure time. However, results indicate that an increase in the waiting period prior to oxidation in ambient air results in lower oxide charge values. This is attributed to the increase in hydroxyl coverage as a function of waiting period.