Energy-dispersive x-ray reflectivity and the measurement of thin film density for interlevel dielectric optimization

A novel method for determining thin film electron density by energy-dispersive x-ray reflectivity is demonstrated for a commercial spin-on-glass dielectric. The effects of sample misalignment limit the accuracy of x-ray reflectivity as typically practiced. These effects may be properly accounted for by measuring the critical angle for reflection at many different x-ray wavelengths simultaneously. From this measurement, the thin film electron density can be ascertained with much improved accuracy. The electron density can be converted to a mass density with knowledge of the film composition.