Paper SS-TuP2
Uncovering the Mechanism of Thermal Dry Etching of Cobalt Thin Films Using Hexafluoroacetylacetone (hfacH)

Tuesday, October 23, 2018, 6:30 pm, Room Hall B

The initial steps of thermal dry etching of cobalt thin films with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (hexafluoroacetylacetone, hfacH) as the organic precursor were studied with in situ temperature-programmed desorption (TPD) and with X-ray photoelectron spectroscopy (XPS) supplemented with microscopic investigations. Comparison of the reaction of hfacH with oxidized and clean (sputtered) cobalt thin films suggested that partial surface oxidation is essential in designing dry etching schemes of this metal. On a clean surface, decomposition of the organic precursor molecule was the primary surface process. The oxidized cobalt surface can be reduced by a reaction with hfacH, releasing Co(hfac)₂ and water (as a side product). However, the thermal chemistry occurred at temperatures significantly higher than those required for industrial applications. The kinetic contribution to the overall etching process was investigated by exposing the oxidized cobalt films to hfacH at several temperatures and following the chemical and morphological changes of a surface. It was determined that exposure to hfacH affected the nanostructuring of the surface even at room temperature (making the surface rougher). Annealing this surface to 800 K produced a much smoother film following Co(hfac)₂ and water removal; however, at that point the films also started to produce microscopic level defects (pits). The optimization of surface temperature placed the upper limit of the process, before substantial surface decomposition of the hfacH precursor molecule and significant morphological changes took place, at 650 K. Further studies are required to explain the experimentally observed possibility of cobalt surface etching at temperatures as low as 440 K.