Supercritical fluid deposition of thin metal films: Kinetics, mechanics and applications
In order to meet the demands of the continuous scaling of electronic devices, new technologies have been developed over the years. As we approach the newest levels of miniaturization, current technologies, such as physical vapor deposition and chemical vapor deposition, are reaching a limitation in their ability to successfully fabricate nano sized electronic devices.
Supercritical fluid deposition (SFD) is a demonstrated technology that provides excellent step coverage for the deposition of metals and metal oxides within narrow, high aspect ratio features. This technique shows the potential to satisfy the demands of integrated circuit miniaturization while maintaining a cost effective process needed to keep the technology competitive. In order to complement SFD technology heuristics for scale-up, an understanding of the deposition mechanism and kinetics and resolution of integration issues such as interfacial film adhesion must be resolved.
It is critical to have a fundamental understanding of the chemistry behind the reaction process in supercritical fluid deposition. For this purpose, a detailed kinetic study of the deposition of ruthenium from bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (1,5-cyclooctadiene) ruthenium(II) is carried out so that growth rate orders and a mechanism can be established. These predictive kinetic results provide the means to control the reaction which allows for overall optimization of the process.
Reliability is of the utmost importance for fabricated devices since they must withstand harsh steps in the fabrication process as well as perform and last under standard and extreme usage conditions. One issue of reliability is assessed by addressing the adhesion of the metallization layers deposited by SFD. A quantitative determination of the interfacial adhesion energy of as deposited and pretreated copper metallization layers from SFD onto barrier layers is used to determine the potential for integration of these films for industry standards.
Extension of the basics of SFD by performing co-deposition of multiple compounds, layer-by-layer deposition for device fabrication and integration with other unique technologies for novel applications demonstrates the ability of this technique to satisfy a wide range of commercial applications and be used as the basis for new technologies. Co-depositions of Ce/Pt, Co/Pt, Ba/Ti and Nd/Ni for the fabrication of functional direct methanol fuel cell electrodes, magnetic alloys for media storage applications, high k dielectric films for alternative energy storage devices and alternative materials for solid oxide fuel cell cathodes, respectively, are performed. Layer-by-layer deposition with masking is used to fabricate nanometer scale capacitors. Finally, plasma spray technology is combined with the rapid expansion of supercritical solvents technique to form a novel, patent pending, process that is used to fabricate next generation photovoltaic cells.