Thin Polytetrafluoroethylene Organosilane Nanocomposite Films Used as Ultra Low Dielectric Constant Materials in Microel
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ABSTRACT Replacing 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. INTRODUCTION As the microelectronics industry continues its trend towards progressively more demanding applications, the need for low dielectric constant materials has become more important than ever. Since as the size of the semiconductor device features shrinks without an accompanying reduction in die size, the RC delay associated with materials and processes used in interconnects contributes an increasingly large delay to signal propagation speed. To allow the industry to realize continued device performance improvements, two basic approaches to RC time constant reduction have been: reduction of "R" by the transition from aluminum-based to lower resistivity copper-based interconnect metallization; and reduction of "C" by introduction of low dielectric constant materials to replace Si0 2. In many cases, both paths are being taken simultaneously to afford the largest possible benefit. PTFE is well known for its ultra low dielectric constant at full density, which makes it a promising candidate low-k material. Since 1995, W. L. Gore & Associates, Inc. has been developing a proprietary PTFE nanoemulsion (SPEEDFILM TM ) for ultra thin film coating applications. Previous work has proved that PTFE thin films cast from the Gore PTFE nanoemulsion have very good thermal stability up to 400°C, excellent electrical properties, as well as good chemical compatibility with all known chemicals currently used in the semiconductor industry' 2. However, there were also some noticeable problems with the first generation pu
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