| Considerable attention has been focused on exploring novel low dielectric constant (k) materials to replace the traditional interconnect dielectric material, silicon dioxide, in order to reduce capacitive signal delay from the back end of line (BEOL) and power consumption. Among all ultra low-k (ULK) materials, SiCOH is the most popular and mature material for integration. It has been generally agreed that incorporating porosity is necessary to decrease the dielectric constant below 2.5 for future technology nodes. However, while incorporation of carbon and porosity benefit dielectric properties, the mechanical properties degrade simultaneously. Therefore, material composition, matrix structure and porosity must be carefully controlled to optimize dielectric properties without sacrificing mechanical robustness.;As porous low-k dielectric thin films begin to be investigated, new challenges are posed on metrologies. When mechanical properties are evaluated using nanoindentation, the 'substrate effect', which evolves from the contribution of elastic strain of substrate, causes an overestimation of film intrinsic mechanical properties. The use of cube corner tip instead of Berkovich tip is proposed to minimize the substrate effect. The experimental results show that the use of cube corner tip enhances the critical depth from below 10% of the film thickness to 40%.;The characterization of porosity of porous low-k dielectric films is a challenge posed on metrologies due to the limited sampling volume. The application of three non-destructive porosimetry techniques, Positron Annihilation Lifetime Spectroscopy (PALS), Ellipsometric Porosimetry (EP) and X-ray Reflectivity (XRR) to characterize xviii porous low-k thin films are examined. The advantages and limitations of each technique, especially the sensitivity to pore interconnectivity, are discussed.;The optimization of SiCOH low-k dielectrics are conducted from two aspects; optimization of deposition conditions and modification of precursor chemistry. The effects of Plasma Enhanced Chemical Vapor Deposition (PECVD) deposition conditions, e.g. O2 flow, substrate temperature and RF power, on matrix composition and structure and the consequent dielectric and mechanical properties are studied. The dependence of dielectric and mechanical properties on composition and structure, i.e. Si-CH3 incorporation, Si-CH 2-Si bridge, and the fraction of cage SiO are also studied.;Inserting a carbon bridging unit into the network is proposed to stiffen the network and enhance the mechanical properties of low-k dielectrics. The corresponding effect on dielectric properties of introducing carbon from an alkane bridge instead of a methyl group is studied. The experimental results show that the incorporation of the carbon bridging unit indeed enhances the elastic modulus of low-k dielectrics, but the dielectric constant reduction is not as effective as the methyl group.;To sum up, the work in this dissertation focused on the addressing the challenges on metrologies to characterize low-k dielectrics and developing new precursors to produce low-k dielectrics with higher modulus with low dielectric constant for future technology nodes. |
