Water adsorption in interfacial silane layers by neutron reflection: 2. Epoxy plus silane finish on silicon wafers

The interaction of water with an interphase composed of a common commercial glass cloth silane finish and an epoxy resin is explored by neutron reflec tion. The silane finish was applied to the oxide surfaces of polished silic on wafers. The epoxy resin (diglycidyl ether of bisphenol A with dicyandiam ide curing agent) was then roll-coated over the silane finish and cured. Pr ofiles of D2O in the interphase were measured by neutron reflection after v arying periods of exposure to air saturated with D2O at 22 degrees C and at 80 degrees C. A significant uptake of D2O into the interphase region is ob served after exposure at 80 degrees C for 3 days. The D2O profile in the in terphase can be described by a two-layer model composed of a thin (similar to 15 Angstrom) layer with similar to 50 vol% D2O next to the silicon oxide surface and a second layer corresponding to the remainder of the silane-ep oxy mixed layer with a much lower D2O level. No excess D2O is detected (det ection limit similar to 3%) in the interface region under the same conditio ns if the silane finish is not present. For samples conditioned at 22 degre es C, no D2O is detected in the silane interphase after exposure for 18 day s, but a significant uptake is observed after exposure for 6 months. The pr ofile in the latter case can again be described by a two-layer model with a thin D2O-rich layer near the silicon oxide surface. The nature of the inte raction of D2O with the interphase is further probed by exposing samples to vacuum following humidity conditioning. After evacuation for similar to 1 month, near complete removal of interfacial water is observed for samples c onditioned at 80 degrees C for 3 days and also at 22 degrees C for 6 months . These observations are interpreted in terms of a reversible chemical inte raction (hydrolysis) between water and the silane finish.