Grant: Discovery Grants Program - Individual

Micro- and nano-fabrication, the cornerstone of microelectronics, photovoltaics, and display technology relies greatly on the deposition of thin films using chemical vapour deposition (CVD) and atomic layer deposition (ALD). Metal thin films are particularly important as the wiring (i.e., metal interconnects) used in microelectronics, but also as electrical contacts and for optoelectronics. As microelectronics becomes further miniaturised, ALD has become increasingly important: it can handle the length scales (10 nm) of modern electronics much better than other fabrication techniques including CVD. Deposition processes by ALD rely heavily on the chemistry of volatile, metal-containing "precursor" compounds to deliver the components of the target film in the vapour phase. Novel chemical precursors are continually required to match the volatility and thermal stability required by ALD. Copper has been the interconnect metal of choice in microelectronics since 1997, but as the cross-section of this wiring has shrunk to accommodate smaller, more densely packed transistors and other devices, copper has started to fail. Copper metal will easily electromigrated in a current flux at small interconnect dimensions, causing poor conductivity and ultimately poor reliability. The proposed research will explore a framework in which to accurately and reproducibly measure these two key thermal parameters (volatilization and thermal decomposition) and proposes to use these to define the "thermal range" of a precursor: the temperature range over which the precursor has a high enough vapour pressure to be useful in ALD processes without thermally decomposing either in the delivery of the vapour precursor or at the gas-surface interface. Three medium-term projects are proposed: the development of precursors for gold and silver thin films for use in photonic applications like sensing and spectroscopy; the development of nickel and cobalt precursors as near-term replacements for copper as an interconnect material; and the development of precursors for tungsten and molybdenum, as high-temperature, high cohesion metals for future interconnect technology. These precursors will be designed with monoanionic, chelating ligands (amidinates, guanidinates, iminopyrrolidinates, diketiminates), monoanionic, monodentate ligands (amides, alkyls) and coordinative ligands (phosphines, carbenes). The designs will be compared using their effective "thermal range" and compared to investigate the effectiveness of each ligand in the design. Standard definitions of the temperatures for the "onset of volatility" and "thermal decomposition" will be used to compare them. Iterative precursor design will be used to develop and improve candidate precursors, and the most promising candidates will be used to develop ALD processes.