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SiO 2 -based xerogels are highly porous materials that may enhance the performance of microelectronic devices due to their extremely low dielectric constants (ε=1.36–2.2). Conventional xerogel and aerogel manufacturing techniques include an expensive and hazardous supercritical drying step to deposit crack free, high porosity films. Ambient drying techniques have recently been developed and in this article, we discuss how the process parameters in the ambient drying process affect the properties of a spin-coated film. Successful spin-on deposition of highly porous (>70%), thick (>1 μm), crack-free, xerogel films was accomplished using a solvent saturated atmosphere during spinning and aging. The saturated atmosphere allowed for the isolation of each processing step and a better understanding of the effects of process variable changes. The film porosity was controlled by varying the extent of silylation (surface modification), the aging time, or the initial water/silane ratio. Fourier transform infrared spectra demonstrated that silylation of xerogel films helps eliminate bound moisture in these films and renders them hydrophobic. Finally, the dielectric constants extrapolated from refractive index measurements were in good agreement with those obtained from our conventional electrical measurements.

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The microscopic details of fluid flow and heat transfer near the contact line of an evaporating extended meniscus of heptane formed between a horizontal substrate and a “washer” were studied at low heat fluxes. The film profile in the contact line region was measured using ellipsometry and microcomputer-enhanced video microscopy, which demonstrated the details of the transition between a nonevaporating superheated flat thin film and an evaporating curved film. Using the augmented Young-Laplace equation, the interfacial properties of the system were initially evaluated in situ and then used to describe the transport processes. New analytical procedures demonstrated the importance of two dimensionless parameters. Both fluid flow and evaporation depend on the intermolecular force field, which is a function of the film profile. The thickness and curvature profiles agreed with the predictions based on interfacial transport phenomena models. The heat flux distribution and the pressure field were obtained. Since there are significant resistances to heat transfer in this small system due to interfacial forces, viscous stresses, and thermal conduction, the “ideal constant heat flux” cannot be attained. The description of the pressure field gives the details of the coupling between the disjoining and capillary pressures.

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A Kelvin–Clapeyron change-of-phase heat transfer model is used to evaluate experimental data for an evaporating meniscus. The details of the evaporating process near the contact line are obtained. The heat flux and the heat transfer coefficient are a function of the film thickness profile, which is a measure of both the intermolecular stress field in the contact line region and the resistance to conduction. The results indicate that a stationary meniscus with a high evaporative flux is possible. At equilibrium, the augmented Young–Laplace equation accurately predicts the meniscus slope. The interfacial slope is a function of the heat flux.

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