Chemical Bonding, Permittivity and Elastic Properties in Locally Modified Organosilicate Glass

Abstract

AbstractChanging local electronic polarizability and chemical bonding in OSG in such a way that the effective permittivity - and consequently the electrical performance of the Cu/low-k structure - deteriorates only slightly and that adhesion and stiffness are improved significantly is an extremely challenging task [1], [2]. As the interconnect line spacings continue to shrink, optimization of the electrical and mechanical properties of the ILD material becomes increasingly important for Cu/low-k integration since the effect of thin regions that have been modified by special treatments on the effective material properties, e. g. keff, increases. Composition and chemical bonding, changed by plasma or beam treatments, effect the materials properties significantly. Plasma processes for resist stripping, trench etching and post-etch cleaning remove C and H containing molecular groups from the near-surface layer of OSG. Electron-beam interaction with OSG changes the chemical bonding in the low-k material. In this paper, the effect of chemical bonding on permittivity and elastic modulus is studied. Compositional analysis and chemical bonding characterization of structured ILD films with nanometer resolution is done with electron energy loss spectroscopy (EELS). The fine structure near the C-K electron energy loss edge, allows to differentiate between C-H, C-C, and C-O bonds, and consequently, between individual low-k materials and their modifications. Dielectric permittivity changes are studied based on VEELS (valence EELS) measurements and subsequent Kramers-Kronig analysis. The elastic modulus is determined with atomic force microscopy (AFM) in force modulation (FM) mode. Nanoindentation was applied as a complementary technique to obtain reference data.