(Invited) The Chemical Composition of Low Dielectric Constant Films from Ion Beam Scattering Methodologies

Abstract

A suite of ion beam scattering methodologies is described for determining the atomic composition of the thin films commonly used as interlayer dielectric barriers (low-k) in next generation integrated circuits. These Si based films typically also contain light elements, such as O, C, and H, that are not easily detected with traditional elastic Rutherford backscattering spectrometry (RBS) and nuclear resonance enhanced RBS measurements when the thin film is supported on a substrate that also contain heavy elements like Si. To circumvent this difficulty, 2 MeV forward scattering (FS) spectrometry is used to enhance the light element sensitivity by separating their characteristic energies from those of the Si substrate and increasing their relative scattering cross-section. This allows an accurate determination the Si:O:C ratio. The absolute H abundance is determined from forward recoil spectrometry (FRES) on both the unknown low-k film and polystyrene (PS) reference film of known H content (defined by the stoichiometry and film thickness). The complete stoichiometry and atomic density of the low-k film are fit from either the RBS or grazing angle backscattering (GBS) spectrum using constraints implied by the absolute aerial H density and the Si:O:C ratio.