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.

Xerogel films of high porosity were fabricated using an ambient pressure technique. The same porosity can be obtained with different microstructures by varying the aging time of the films. The dielectric constant of these films as a function of porosity at 1 MHz follows correlations originally developed for bulk aerogels. Diffusion of copper is orders of magnitude faster in these xerogels than in the corresponding thermal oxide. An activation energy of 0.9 eV was estimated based on a convective diffusion model.

Surface modified silica xerogel films of high porosity (60 - 90 %) and uniform thickness (0.4–2 μm) were fabricated at ambient pressure on silicon and silicon dioxide. The rheological properties that govern film uniformity were determined. A relation between the final dried film thickness and spin speed was developed. The porosity and thickness of the films could be controlled independently. The same porosity could be obtained over a wide range of aging time and temperature combinations. Fracture toughness was measured using the edge-lift-off technique. The best values were comparable to concrete. Surface modification was affected by treating the film with trimethylcholorosilane (TMCS) and other modifiers. Moisture adsorption was studied at 100% RH using a quartz crystal microbalance technique. Depending upon the degree and kind of surface treatment, films absorbed as much as 32% or as little as 2% of their weight in water. Dielectric constants (K), losses and breakdown strengths were comparable to values for calcined, bulk aerogels. Thin (≤ 500 Å) films of Copper (Cu) and Tantalum (Ta) were deposited on xerogel films and subjected to thermal annealing. No diffusion was observed within the limits of RBS. High-density plasma etching showed that the films etch an order of magnitude faster than conventional SiO2 films.

Ion beam analysis techniques have become very useful for characterization of low k materials. Studies on several ion beam analysis techniques will be discussed. Rutherford Backscattering Spectrometry (RBS) provides a very powerful analytical technique for the thickness and porosity measurements on porous Si0 2 films. Nuclear Reaction Analysis (NRA) techniques for hydrogen and fluorine profiling are very useful to characterize fluorinated polymer and fluorinated oxide films. Examples of low k materials including Si02:F, Parylene-AF and Teflon-AF will be discussed. Fluorine diffusion in to metals and various interface effects between metal and low k materials will be presented.