Interconnects are crucial components of all microelectronic circuits as they provide the fabric that interlinks transistors and passive components by distributing signal, power, and clock. Today, interconnects are main determinants of the circuit performance and area and therefore interconnect research has become a vibrant field at the center of CMOS scaling efforts. In the near future, interconnect wires will reach widths of less than 10 nm. At such small dimensions, the properties of the interconnects are much degraded due to increased line resistance and reduced reliability, with strong adverse impact on the circuit performance. Current interconnect wires use Cu as the main conductor materials, which exhibits a strong increase in resistivity with decreasing wire width in the nanometer scale. Moreover, Cu requires diffusion barriers and liners for reliable operation. Such barriers and liners are difficult to scale and occupy an increasing fraction of the wire volume with little contribution to the conductivity.
Therefore, alternative metals have been researched that can replace Cu in advanced interconnects. Main properties of suitable alternative metals are a weaker size dependence of the resistivity and reliable wire operation without the need for barriers. Recently, Pt group metals, such as Ru, Ir, or Rh have been identified as materials with great potential. However, the quest is still ongoing to identify materials with even better properties at even smaller dimensions.
In the PhD thesis, the electrical, structural, and mechanical properties of thin films and nanowires of such alternative metals will be studied. A particular focus will be on the understanding of the scattering mechanisms (surface, grain boundaries) that dominate at small dimensions. Both Pt group metals as well as novel ternary carbides will be studied. The student will develop suitable deposition processes for the alternative metals, fabricate nanowires in collaboration with engineers in imec’s interconnect program, and characterize the thin films and nanowires. The desired outcome is the fundamental understanding of the materials properties at reduced dimensions (1D/2D) and small sizes, enabling the benchmarking and the downselection of materials for scaled interconnect systems in future microelectronic circuits.
The thesis will combine the deposition of thin films and the nanofabrication of nanowires with electrical, structural, and mechanical materials characterization. The development and assessment of advanced characterization methods (e.g. low-temperature magnetoresistance) and the physics-based modeling of the resistivity will play important roles. A background in materials science, (applied) physics, electrical engineering, or nanotechnology, together with interest in advanced interconnect applications and materials physics as well as enthusiasm for nanofabrication are ideal.
Required background: materials science, nanotechnology, physics, electrical engineering
Type of work: 60% experimental, 30% modeling, 10% literature study
Supervisor: Ingrid De Wolf
Daily advisor: Christoph Adelmann
The reference code for this PhD position is STS1712-09. Mention this reference code on your application form.