Characterization of Nanoporous Low-K Thin Films by SANS Contrast Variation
R C. Hedden, Hae-Jeong Lee, Barry J. Bauer
Small-angle neutron scattering (SANS) contrast variation is applied to characterization of nanoporous low-dielectric constant (low-k) thin films. Films are exposed to saturated solvent vapor in air, whereby the pores fill with liquid by capillary condensation. The pores are filled with mixtures of hydrogen- and deuterium-containing solvents to vary the neutron contrast with the wall (matrix). The composition of the solvent mixture is systematically varied to identify a composition that minimizes the scattered intensity (contrast match point). From the contrast match point composition, film characteristics including matrix density and homogeneity are assessed. Four spin-on low-k materials including a methylsilsesquioxane (MSQ), an organic polymer, a xerogel, and a hydrogensilsesquioxane (HSQ), are characterized by the new technique. Calculated matrix mass densities are compared to independent density measurements obtained by an established specular X-ray reflectivity (SXR) technique.