Atomic layer controlled electron beam induced etching of molybdenum using sequential O2 and HCl exposures with positive sample voltage

Atomic layer controlled molybdenum (Mo) etching was performed at <100 °C using alternating exposures of O2 and HCl combined with simultaneous electron exposures and positive sample voltage. Electron exposures at ∼100 eV were derived from a hollow cathode plasma electron source. The Mo surface was oxidized to MoOx using concurrent O2 and electron beam exposures. The Mo oxidation rate increased dramatically when a positive voltage of +20 V was applied to the sample stage. Subsequently, the MoOx layer was linearly etched during synchronous HCl and electron exposures when a positive voltage of +20 V was also applied to the sample stage. No enhancement of the oxidation or etching was observed with a negative voltage of −20 V on the sample stage. The oxidation and etching enhancement in the presence of the positive sample voltage suggested that low energy electrons or anions dominated the reaction. The primary electrons at ∼100 eV can produce low energy electrons by ionization of Ar in the reactor and also by secondary electron yield from the Mo substrate. Low energy electrons can form O− or Cl− anions via dissociative electron attachment. Low energy electrons and anions can then be pulled to the sample stage at +20 V. Alternating oxidation and chlorination steps were applied in a digital fashion to define the Mo etching process. An etch per cycle of 1.3 Å/cycle was measured using in situ spectroscopic ellipsometry. The ellipsometric measurements could separately measure the MoOx growth, MoOx removal, and Mo film thickness loss during each etching cycle.