Tungsten Thin Film Electron-Beam Evaporation for Electronic Device Fabrication Applications

Tungsten (W) is a heavy metal valued for its high melting point, electrical conductivity, and mechanical strength that makes it an ideal candidate for electronic device applications. While various physical vapor deposition (PVD) techniques like sputtering have enabled deposition of W thin films, electron-beam (e-beam) evaporation features directional deposition of metallic thin films, thus allowing for lift-off patterning which is a crucial process in fabricating micro- or nanoscale devices. However, Tungsten’s low vapor pressure makes it difficult to evaporate in a traditional process condition because it requires a very high-power output. This project sought to develop a process recipe for W e-beam evaporation by focusing on tungsten’s sublimation point (around 1,700C) and using a graphite liner that helps with thermal isolation. The results show that tungsten of up to 30 nm in thickness was successfully deposited on a silica-coated silicon wafer at the 57% power level. To assess the possibility of device fabrication that involves W patterning by lift-off such as phase change memory, a CAD layout with features as small as 10 microns was created and tested for photolithography followed by W evaporation and lift-off. This study will serve as an experimental foundation for designing and building nanoelectronic devices that are made of hard-to-evaporate metals.