Overview
The development of next-generation semiconductor interconnects requires atomically precise thin film synthesis. My work centers on ultra-high vacuum (UHV) physical vapor deposition (PVD) using DC and RF magnetron sputtering to grow epitaxial thin films of interconnect candidate materials on single-crystal substrates. The UHV environment (base pressure <10⁻⁹ Torr) minimizes contamination and enables high-quality crystalline growth essential for fundamental transport studies.
Materials Systems
Epitaxial Ru(0001) on Al₂O₃(0001)
Ruthenium thin films are deposited by DC magnetron sputtering onto c-plane sapphire substrates at elevated temperatures (typically 600–900 °C) to achieve single-crystal Ru(0001) epitaxy. Film thicknesses range from 5 nm to 330 nm, enabling systematic studies of the resistivity size effect. The epitaxial relationship Ru(0001)[11̅00] || Al₂O₃(0001)[11̅00] is confirmed by XRD pole figure analysis, with rocking curve widths as narrow as 0.1° indicating excellent crystallographic quality.
Transition Metal Nitrides: AlN and Mo₂N
Epitaxial AlN(0001) serves as both a diffusion barrier and a template layer for subsequent Ru growth. Reactive sputtering in Ar/N₂ mixtures at controlled partial pressures yields wurtzite AlN with atomically smooth surfaces (<0.3 nm RMS roughness). Mo₂N films are explored as alternative barrier materials with metallic conductivity, offering potential advantages over insulating barriers in ultra-thin interconnect stacks.
Topological Semimetal: NbAs
NbAs is a type-I Weyl semimetal with predicted ultra-high mobility and topological surface states. Thin film growth of NbAs via sputtering is challenging due to its complex crystal structure and tendency toward off-stoichiometry. My work develops deposition protocols using co-sputtering from Nb and As targets with careful control of substrate temperature and flux ratios to achieve oriented NbAs films suitable for transport measurements.
Ru Thickness Range
Continuous epitaxial films spanning two orders of magnitude for systematic size effect studies.
Base Pressure
Ultra-high vacuum environment ensuring contamination-free epitaxial growth.
XRD Rocking Curve
Exceptional crystallographic quality of epitaxial Ru(0001) on sapphire.
Deposition Techniques
The primary deposition system is a custom-built multi-target UHV sputtering chamber equipped with three magnetron guns, substrate heating to 1000 °C, RHEED for in-situ growth monitoring, and a residual gas analyzer for chamber diagnostics. Key process parameters optimized in this work include substrate temperature, sputtering power, working gas pressure, target-to-substrate distance, and deposition rate. For reactive sputtering of nitrides, the N₂ partial pressure is the critical parameter controlling stoichiometry and crystalline phase.
Impact
The ability to grow high-quality epitaxial films is the foundation upon which all transport measurements in this dissertation are built. Without single-crystal films free from grain boundary scattering, it would be impossible to isolate and quantify the surface scattering contribution to resistivity—the central goal of this research program. The deposition expertise developed here also translates directly to industrial PVD processes used in semiconductor fabrication.