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 oxide surfaces of polished silicon wafers. Detailed profiles of D2O within the ∼80 Å silane finish layers are measured after exposure for 48 hours to a saturated D2O atmosphere at either 22°C or 80°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, the profile of adsorbed D2O is composed of at least two distinct layers: a thin (< 30 Å) 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 adsorbed D2O is greater for the sample conditioned at 80°C than for the sample conditioned at 22°C. In addition, adsorbed D2O within the interfacial layer is removed more slowly during evacuation for the sample conditioned at 80°C than for the sample conditioned at 22°C. These latter two results are interpreted as indicating increased hydrolysis of siloxane bonds for the samples conditioned at 80°C. Surprisingly, after several months in vacuum the remaining D2O redistributes within the layer, accumulating within a very thin layer at the interface in both samples. The nature of this redistribution is not understood.