Etching of transition metals is one of the major challenges in magnetoresistive random-access memory (MRAM) device fabrication. In this work, atomic layer etching of iron and cobalt surfaces with halogen and an organic molecule was studied. We successfully performed etching of Fe and Co thin films via forming volatile metal complexes at low temperature with cyclic sequential reactions of Cl2 and acetylacetone (acacH) or hexafluoroacetylacetone (hfacH). The etching reaction mechanism of acac and hfac reacting with Clorine-modified Fe and Co surfaces was investigated: the surface was first activated with Cl2 gas, and subsequently, the top layer of chlorinated metal was removed by reaction with a diketone (acacH/hfacH). The extent of Cl2 reaction determines the etching rate of the metal. At substrate temperatures lower than 135°C, acac could remove the chlorinated Fe metal layer from Fe surfaces, but not chlorinated Co from Co surfaces. In-operando X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) simulation shows that the reaction of acacH or hfacH with chlorinated Fe or Co surfaces is likely following a complex reaction pathway instead of simple diketone substitution for the metal chloride. The removal rate of metal chloride is close to a first order reaction kinetics with repect to diketone precursor which implies a higher diketone pressure facilitates a faster etching rate. Diketone decomposition plays an important role in the etching process. Furthermore, a significant surface smoothing process demonstrated via AFM surface topographic imaging is happening (Figure 3). The aforementioned results have important applications in the processing and fabrication of memory and semiconductor devices .

In operando XPS study on atomic layer etching of Fe and Co using Cl2 and acetylacetone or hexafluoroacetylacetone

ACS Spring Meeting 2021

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