Overview
Understanding the relationship between film microstructure and electrical transport requires a multi-technique characterization approach. My work integrates crystallographic analysis (XRD, XRR, RHEED), surface and compositional analysis (XPS, AFM, SEM), and electrical transport measurements to build a complete picture of how deposition conditions affect interconnect-relevant properties.
Crystallographic Characterization
X-ray Diffraction and Reflectivity (XRD/XRR)
High-resolution XRD is used for phase identification, texture analysis, and crystallographic quality assessment via rocking curve measurements. Pole figures confirm epitaxial relationships between films and substrates. XRR provides precise thickness measurements (accuracy better than 0.5 nm) and surface/interface roughness quantification through fitting of Kiessig fringes — essential for correlating surface roughness with electron specularity in the Fuchs-Sondheimer framework.
RHEED (In-Situ)
Reflection high-energy electron diffraction during growth provides real-time feedback on surface crystallinity, growth mode (layer-by-layer vs. island), and epitaxial quality. RHEED oscillations are used to calibrate deposition rates at the monolayer level.
Surface and Chemical Analysis
X-ray Photoelectron Spectroscopy (XPS)
XPS provides surface chemical composition and oxidation state information critical for understanding interface chemistry. During my internship at Applied Materials, I developed advanced XPS analysis workflows using CasaXPS for characterizing plasma etch products (TiN, TiSi, tungsten oxide), training a team of engineers on quantitative peak fitting, background subtraction, and depth profiling interpretation.
Atomic Force Microscopy (AFM)
AFM surface roughness measurements are directly correlated with electron surface specularity. For epitaxial Ru films, RMS roughness values ranging from 0.2 nm (atomically smooth) to several nm (rough) are systematically measured and correlated with resistivity data to extract the roughness-specularity relationship. This represents a key experimental contribution: quantifying how surface morphology at the atomic scale affects electrical transport at the nanometer film thickness regime.
Electrical Transport Measurements
Temperature-dependent resistivity measurements from 10 K to 300 K using four-point probe and van der Pauw geometries enable Fuchs-Sondheimer analysis by separating the temperature-dependent (phonon) and temperature-independent (defect + surface) contributions to resistivity. For nano-wire geometries, focused ion beam (FIB) milling creates precise wire cross-sections for size-dependent transport measurements.
Temperature Range
Cryogenic to room temperature resistivity measurements for Fuchs-Sondheimer analysis.
XRR Precision
Sub-angstrom thickness accuracy from X-ray reflectivity fitting.
Smoothest Ru Surface
Atomically smooth epitaxial Ru surfaces achieved for maximum electron specularity.
FIB-SEM Fabrication
Focused ion beam scanning electron microscopy (FIB-SEM) is used both for cross-sectional imaging and for fabricating nano-scale wire geometries from single-crystal materials. For the CoSn kagome metal study, FIB milling combined with gas injection system (GIS) platinum deposition creates four-terminal nano-wire devices for direct resistivity size effect measurements. Electron beam lithography (EBL) provides an alternative patterning approach for materials sensitive to Ga+ ion damage.
Impact
The characterization expertise developed in this work spans both academic research and industrial process control. The XPS analysis skills applied at Applied Materials for plasma etch characterization demonstrate direct industry relevance, while the fundamental structure-property correlations established for epitaxial thin films advance the science of interconnect scaling.