Metal epitaxy for ultimate low-resistivity conductors in advanced microelectronic devices

In today’s semiconductor devices, metals are ubiquitous as conductors in interconnects, gates, and contacts. Their performance has a strong impact on device performance both on power consumption and computing throughput. Therefore, research on novel metals and their properties has become increasingly important in the last decade and can be considered as a key topic in materials research for semiconductor devices.

A key property of metals is their conductivity since it determines the power dissipation and the bandwidth in, e.g., an interconnect line. In the near future, the characteristic dimensions of metallic interconnects in state-of-the-art microelectronic chips will reach 10 nm and less. At such small scales, the conductivity in polycrystalline wires is strongly degraded due to the scattering of the charge carriers at grain boundaries as well as at the (rough) surrounding surfaces. Since grain boundary scattering is typically the dominant mechanism in nanostructures of many metals and grain sizes are expected to decrease at smaller dimensions, this problem will become even more aggravated in the future. Even currently, resistivities of metallic nanostructures are much larger than those of the corresponding bulk metals.

To alleviate the observed rapid degradation of the conductor properties in metallic nanostructures, the grain size must thus be increased as much as possible. Epitaxial single crystal metals form a limiting case of films without grain boundaries and are thus ideal systems to study the ultimate limitations of thin film resistivity. The goal of this PhD thesis will the development of epitaxial metals that are relevant as conductors in microelectronic devices. This will include elemental metals (Co, Ru) but also intermetallic compounds, e.g. binary aluminides or ternary MAX carbides. The films will be deposited by physical vapor deposition and atomic-layer deposition. The films will then be characterized using structural, electrical, mechanical, and thermal measurement techniques. The final goal of this study is to understand in depth the conductivity limitations of such epitaxial metal films and their potential in advanced interconnect structures. The characterization results will be correlated to deposition parameters with the aim to optimize the thin film electrical and thermal conductivity.

The student will learn to use state-of-the art equipment to deposit and characterize epitaxial metal films, including the processing of the necessary measurement test structures. She or he will additionally learn about the material science of epitaxial metals. A background in materials science, (applied) physics, or nanotechnology is ideal, together with an interest in thin film deposition and characterization of advanced materials.