Thin Polytetrafluoroethylene Organosilane Nanocomposite Films Used as Ultra Low Dielectric Constant Materials in Microelectronics

ABSTRACTReplacing the current on-chip dielectric materials such as silicon dioxide, which has a dielectric constant of approximately 4.0, with low dielectric constant materials can greatly improve the performance of high density VLSI device by reducing crosstalk and capacitive delay. Polytetrafluoroethylene (PTFE) has the lowest dielectric constant (k < 2.0) of any full density material, which makes it a promising candidate for this IC application. Pure PTFE thin films cast from PTFE nanoemulsion containing sub-20nm PTFE particles, though thermally stable, have some inherent sub-optimal properties. These include adhesion to other inorganic materials and mechanical strength at high processing temperatures. In order to improve these properties, we have developed a PTFE / silicon compound nanocomposite material. Initial tests have shown that this nanocomposite material has significantly improved high temperature mechanical properties and interfacial properties between the composite and inorganic materials such as silicon, silicon oxide, silicon nitride and some metals. The surface roughness of the thin film coatings is also reduced compared to pure PTFE thin film coatings. The coatings require no separate adhesion promoter to be applied to the substrate prior to deposition. Characterization work has been carried out with different techniques such as DMA, ToF-SIMS, XPS and AFM with hydrofluoric acid (HF) selective etching, in order to understand this novel nanocomposite and its surface and interfacial properties.