Structural Comparison of Hydrogen Silsesquioxane Based Porous Low-k Thin Films Prepared with Varying Process Conditions

The structures of hydrogen silsesquioxane based porous low dielectric constant (low- k ) films (XLK) prepared with varying process conditions are characterized using a combination of high-energy ion scattering, X-ray reflectivity, and small-angle neutron scattering. We measure the film thickness, average mass density, density depth profile, wall density, porosity, average pore size, pore spacing, pore connectivity, and atomic composition. We compare samples with varying dielectric constants and degrees of cure or Si−H bonding fraction. The structural parameters are correlated with the chemical bond structure as measured by Fourier transform infrared spectroscopy. The density profiles of the porous films were uniform, with a slight densification observed at the film surface. Films with similar k values but varying degrees of cure have almost identical structural characteristics. Lower dielectric constant films have larger porosities and average pore sizes but lower wall densities. The process conditions used to alter the dielectric constant affect not only the porosity but also many other structural parameters such as the wall density.