In operando x-ray photoelectron spectroscopy study of mechanism of atomic layer etching of cobalt

The reaction mechanism of atomic layer etching (ALE) process of Co thin films using Cl-2 gas and diketone organic precursor hexafluoroacetylacetone (Hfac) has been investigated. In operando XPS featuring a reaction chamber directly connected to the XPS surface analysis chamber allows the study of the mechanism of ALE process of Co thin films with minimum surface contamination. Chlorine activated Co surfaces were investigated using in operando XPS that confirms the formation of CoCl2 and CoCl3. Hfac reacts with chlorinated Co surfaces to perform thermal etching surface chemical reactions at 140 degrees C. The chlorine removal rate upon exposure to Hfac follows a first order kinetics at 140 degrees C. The reaction mechanism elucidated by in operando XPS reveals that Hfac decomposes on chlorine activated Co surfaces suggesting a more complex reaction mechanistic pathway other than a simple adsorbate substitution reaction between chlorine and Hfac on Co surfaces. Moreover, the Co surface becomes smoother during the etching process.