Magnetically confined microplasma for localized submillimeter-scale sputter deposition in vacuum

Plasma processing is crucial in the fabrication of microelectronic and photonic devices, enabling deposition of thin films, etching of materials, and surface cleaning/modification. Typical semiconductor thin-film deposition systems are designed to deposit blanket coatings on large-area substrates and generate plasmas on a centimeter length scale. This work describes the design and demonstration of a tool that generates a microplasma for localized direct-write deposition of submillimeter-scale metallic features via a motorized stage that moves the substrate independently of the write head. Plasma confinement and increased sputter yield were achieved with the incorporation of a neodymium rare-earth ring magnet to generate an axially oriented magnetic field. The micro-sputter direct-write head (micro-sputter head) was designed and optimized using magnetohydrodynamic equations, multiphysics finite element method simulations, and Monte Carlo simulations. The tool was used to deposit submillimeter aluminum and gold features that were characterized with profilometry, scanning electron microscopy, energy dispersive x-ray spectroscopy, and focused ion beam/scanning transmission electron microscopy (STEM). Aluminum spots of 0.8–1.2 mm diameter and thickness of 100–192 nm, and a gold spot with 0.4 mm diameter and a thickness of 535 nm, were deposited. The deposition rates for aluminum and gold were 3.2 and 8.9 Å/s, with volumetric throughputs of 74.9 and 21.5 μm3/s, respectively. This prototype direct-write micro-sputtering system is relevant for a range of applications, including materials discovery, packaging, circuit repairs, and feature definition without photolithography.