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 D 2 O within the ∼80 Å silane finish layers are measured after exposure for 48 hours to a saturated D 2 O atmosphere at either 22°C or 80°C. The nature of the interaction of D 2 O with the finish layer is probed by exposing the samples to vacuum following adsorption. In both samples, the profile of adsorbed D 2 O is composed of at least two distinct layers: a thin (< 30 Å) D 2 O -rich layer adjacent to the interface, and the bulk of the film in which only a low level of D 2 O is present. The amount of adsorbed D 2 O is greater for the sample conditioned at 80°C than for the sample conditioned at 22°C. In addition, adsorbed D 2 O 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 D 2 O redistributes within the layer, accumulating within a very thin layer at the interface in both samples. The nature of this redistribution is not understood.