Atomic layer etching of ultra-thin HfO₂ film for gate oxide in MOSFET devices

Precise etch depth control of ultra-thin HfO₂ (3.5 nm) films applied as a gate oxide material was investigated by using atomic layer etching (ALET) with an energetic Ar beam and BCl₃ gas. A monolayer etching condition of 1.2 /cycle with a low surface roughness and an unchanged surface composition was observed for ultra-thin, ALET-etched HfO₂ by supplying BCl₃ gas and an Ar beam at higher levels than the critical pressure and dose, respectively. When HfO₂-nMOSFET devices were fabricated by ALET, a 70% increase in the drain current and a lower leakage current were observed compared with the device fabricated by conventional reactive ion etching, which was attributed to the decreased structural and electrical damage.