Water Adsorption in Interfacial Silane Layers by Neutron Reflection: 2. Epoxy + Silane Finish on Silicon Wafers

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Abstract
The interaction of water with an interphase composed of a common commercial glass cloth silane finish and an epoxy resin is explored by neutron reflection. The silane finish was applied to the oxide surfaces of polished silicon wafers. The epoxy resin (diglycidyl ether of bisphenol A with dicyandiamide curing agent) was then roll-coated over the silane finish and cured. Profiles of D2O in the interphase were measured by neutron reflection after varying periods of exposure to air saturated with D2O at 22°C and at 80°C. A significant uptake of D2O into the interphase region is observed after exposure at 80°C for 3 days. The D2O profile in the interphase can be described by a two-layer model composed of a thin (∼15 Å) layer with ∼50 vol% D2O next to the silicon oxide surface and a second layer corresponding to the remainder of the silane-epoxy mixed layer with a much lower D2O level. No excess D2O is detected (detection limit ∼3%) in the interface region under the same conditions if the silane finish is not present. For samples conditioned at 22°C, no D2O is detected in the silane interphase after exposure for 18 days, but a significant uptake is observed after exposure for 6 months. The profile 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 interaction of D2O with the interphase is further probed by exposing samples to vacuum following humidity conditioning. After evacuation for ∼1 month, near complete removal of interfacial water is observed for samples conditioned at 80°C for 3 days and also at 22°C for 6 months. These observations are interpreted in terms of a reversible chemical interaction (hydrolysis) between water and the silane finish.

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