Nondestructive stiffness and density characterization of porous low-k films by surface acoustic wave spectroscopy

Nanoporous methylsilsesquioxane (MSSQ) films are a leading candidate for low dielectric constant (k) materials for microelectronic interconnects. Mechanical strength reduces rapidly with lower k (increasing porosity) however, and there is a lack of techniques to characterize these properties in the k ≤ 2 range. This work reports surface acoustic wave spectroscopy characterization of density/porosity and Young´s modulus values of a range of methylsilsesquioxane films from different manufacturers. We show that the results are validated by independent measurements and that nanoindentation measurements consistently overestimate stiffness.