The Nanomechanical Effect of Dendrimer Interlayers Underneath Cu Ultrathin Films
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The Nanomechanical Effect of Dendrimer Interlayers Underneath Cu Ultrathin Films Junyan Zhang, Micheal Curry, Shane Street Center for Materials for Information Technology and Chemistry Department University of Alabama, Tuscaloosa, AL 35487 ABSTRACT Two kinds of dendrimers, DAB and PAMAM (with the same terminal groups but different branched repeat units), were chosen as interlayers for Cu ultrathin films deposited on native oxide Si(100) wafers. 10 nm Cu thin films were deposited directly on the dendrimer monolayers by DC sputtering at room temperature. The nanomechanical results show that PAMAM and DAB have significant effects on the properties of the resulting films, with the DAB layer acting as a stiffer ‘spring’, compared to PAMAM, underneath the Cu films. Both dendrimer interlayers lower the hardness of the film, compared to Cu alone; the effect is greater for PAMAM than DAB interlayers. However, the introduction of either dendrimer monolayer significantly increased the elasticity of the Cu film. INTRODUCTION The metal-polymer interface has been studied extensively due to its importance in applications ranging from food and electronic packaging, to microelectronic mechanical system (MEMS)1-3. The requirements of future integrated circuits demand the continual shrinkage of device size to achieve higher performance. Polymers are seen as potential candidates to replace SiO2 low dialectrics in integrated circuits, and the interface between them and the metal conductors is critical4-6. Furthermore, with the rapid development of microelectronic mechanical systems (MEMS) and nanoelectronic mechanical systems (NEMS), new materials with improved properties are required. Dendrimers, a unique kind of self-contained polymer with globular shape, have recently attracted considerable interest as nanoscopic building blocks due to their highly branched three-dimensional structure and monodispersity 7-11. A dendrimer can be isolated as an essentially monodisperse single compound, in contrast to most linear polymers which have a range of molecular species differing in molecular weight. The number of dendrimer functional end groups increases exponentially with generation, or branching. Studies have investigated the behavior of dendrimer self-assembled monolayers, prepared by very simple methods, which indicate dendrimers have relatively strong physisorption to Au, SiO2 and other surfaces 12-15. Crooks and colleagues 16 have reported that the adhesion of an evaporated Au film to SiO2 was improved by the introduction of a dendrimer monolayer as interlayer. Street et al. reported 17 that the Au films on Si with and without the dendrimer interlayer show large differences in mechanical response. The nanoindentation hardness of the dendrimer-mediated Au film is, unusually, higher than the Au film layer without dendrimer interlayer. This effect has been attributed tentatively to the compressed nature of the dendrimer interlayer and the influence of the organic layer on the growth of the
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metal overlayer. The unique comp
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