Graduation Year

2020

Document Type

Thesis

Degree

M.S.M.E.

Degree Name

MS in Mechanical Engineering (M.S.M.E.)

Degree Granting Department

Mechanical Engineering

Major Professor

Mike Cai Wang, Ph.D.

Committee Member

Nathan Gallant, Ph.D.

Committee Member

Rasim Guldiken, Ph.D.

Keywords

Black's Equation, Diffusion, Moore's Law, Nanomanufacturing, Semiconductors

Abstract

Electromigration in metal interconnects remains one of the most prominent challenges in the state-of-the-art semiconductor industry. A phenomenon defined as the momentum transfer from electrons in an electric current to the metal atoms in a conductor, electromigration creates voids and hillocks that ultimately cause failures in nanoelectronics due to short or open circuits. Additionally, electromigration induces undesirable diffusion of metal atoms into the dielectric material, forcing the need for a barrier material that can mitigate such adverse effects of the phenomenon. However, extremely tight dimensional control of modern transistor designs imposes reduced dimensions of the interconnects in order to accommodate the volume needed by the barrier layer. Overall, there is a growing demand for BEOL-compatible integration of ultrathin passivation layers that can effectively mitigate electromigration without significant reduction in interconnect dimensions.

In light of such challenges, two-dimensional layered materials (2DLMs) have recently shown vast potential for application in novel nanoscale mechanical/chemical/electrical devices. Given their ultimate surface-to-volume ratio that render them ideal for space-constrained applications added to their ‘two-sided’ nature, precise control over the interfacial phenomena that arises from the contact surface of a 2DLM with other materials is crucial in exploiting the unprecedented properties of 2DLMs to the full potential. Additionally, the inherent impermeability of select 2DLMs drives immense potential for their application as a diffusion barrier with sub-nanometer thinness. In this thesis, we present interfacial phenomena exhibited by 2DLM-metal interfaces that demonstrate the feasibility of improved electrical performance in integrated circuits. Additionally, we discuss various material preparation techniques employed in preparing mono- to few-layer 2DLMs and ensuring ultraclean interfaces in 2DLM-metal interfaces, which were crucial in ensuring the maximum possible improvement in electrical performance induced by the contact between the 2DLM and metal.

More specifically, we fabricated Cu interconnects coated by large-area hexagonal boron nitride (hBN) crystals with nanometer-scale thinness. Carefully designed experiments allowed for the observation of contrast in electrical performance between Cu interconnects that were passivated with hBN and those that were uncoated. A maximum improvement in breakdown current density of 39.01% and an average improvement in the said parameter of 35.09% was observed. With an hBN passivation layer thickness of approximately 2.5 nm as opposed to previously investigated metal alloy-based barrier thickness of 10-20 nm, the potential 2DLMs as a highly efficient barrier material was demonstrated. The research presented in the following chapters show promising results for the application of 2DLMs in various interface-driven nanoscale devices, while serving as a foundation for the investigation of novel, 2DLM-based electric structures as an alternative to metal-based semiconductor devices.

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