Water adsorption in interfacial silane layers by neutron reflection: 1. Silane finish on silicon wafers

The interaction of water with a common commercial glass cloth silane finish is explored by neutron reflection. The silane coating is applied to the ox ide surfaces of polished silicon wafers. Detailed profiles of D2O within th e similar to 80 Angstrom silane finish layers are measured after exposure f or 48 hours to a saturated D2O atmosphere at either 22 degrees C or 80 degr ees C. The nature of the interaction of D2O with the finish layer is probed by exposing the samples to vacuum following adsorption. In both samples, t he profile of adsorbed D2O is composed of at least two distinct layers: a t hin (< 30 Angstrom) D2O-rich layer adjacent to the interface, and the bulk of the film in which only a low level of D2O is present. The amount of adso rbed D2O is greater for the sample conditioned at 80 degrees C than for the sample conditioned at 22 degrees C. In addition, adsorbed D2O within the i nterfacial layer is removed more slowly during evacuation for the sample co nditioned at 80 degrees C than for the sample conditioned at 22 degrees C. These latter two results are interpreted as indicating increased hydrolysis of siloxane bonds for the samples conditioned at 80 degrees C. Surprisingl y, after several months in vacuum the remaining D2O redistributes within th e layer, accumulating within a very thin layer at the interface in both sam ples. The nature of this redistribution is not understood.