Infrared attenuated total reflection spectroscopy has been used to observe the surface chemistry of Si3N4 films (grown on Si by low-pressure chemical vapor deposition) under steady-state conditions during exposure to dilute aqueous HF solutions. Surfaces etched in HF do not exhibit rapid growth of an SiO2 layer when subsequently exposed to either humid room air at room temperature or to liquid H2O. However, some evidence is found for the formation of an ultrathin oxide-like layer when the etched surface is rinsed in deionized H2O. Removal of this layer in HF results in no detectable signal in the Si-H stretching region, unlike the case for Si subjected to a similar oxide-removal treatment. The presence of SiOH groups has been detected by observing their removal by reaction with aqueous acetic acid or HCl solutions, which suggests that SiHx groups are rapidly hydrolyzed. An attempt was made to detect surface NHx groups by protonation in aqueous acid to form NHx+1+, which should be more readily observable in the infrared spectrum. However, the surface coverage of NHx, if any, is too small to be detected by this means. (C) 2005 The Electrochemical Society.