Abstract
Ruthenium (Ru) is a next-generation metal interconnect material, and the demand for precise etching is on the rise. This study explores anisotropic atomic layer etching (ALE) of Ru, utilizing various oxygen adsorption methods (O radical, oxygen plasma, or O2 molecule) and two types of plasma sources: inductively coupled plasma (ICP) and ion beam source. Through ICP ALE, an etch per cycle (EPC) of ∼ 1.5 Å/cycle was achieved using oxygen plasma for adsorption. For ion beam ALE, EPC values of ∼ 0.8 Å/cycle were obtained using oxygen radical, and ∼ 0.4 Å/cycle through physisorption using oxygen molecule without plasma generation. The higher EPC with the ICP ALE was attributed to spontaneous etching during oxygen adsorption during the oxygen plasma generation. Conversely, the lower EPC with ion beam ALE during oxygen adsorption using O2 molecule without plasma generation resulted from nonuniform oxidation of Ru during the adsorption step. Among the three ALE methods, optimal Ru ALE with 100 % ALE synergy was achieved with ion beam ALE, likely due to the absence of ion bombardment during oxygen adsorption and the precise Ar+ ion energy for removing RuOx formed on the surface.
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