Etch characteristics of CoFeB thin films and magnetic tunnel junction stacks in a H2O/CH3OH plasma

Review Article: Plasma–surface interactions at the atomic scale for patterning metals

“…Halogen chemistries were used in conjunction with Ar or the aforementioned H 2 , while incorporation of numerous organics, such as CH 4 , CH 3 OH, and CH 3 COOH, were also employed but suffered from undesirable carbon deposition or oxidation caused from methanol and acetic acid fragmentation. [45][46][47][48] None of the chemistries reported exhibits etch rates higher than 20-30 nm/min, with moderate selectivity to Ti or TiN masks.…”

Inductively coupled plasma reactive ion etching of CoFeB magnetic thin films in a CH3COOH/Ar gas mixture

“…The results suggest that chemical reactions occurred between the CO radicals in the plasma and metal compounds of the film. Xiao et al and Hwang et al reported the etching of CoFeB in CH 3 OH/ Ar and CH 3 OH/H 2 O gas mixtures [8,9]. They found that etching proceeded mainly via physical sputtering of the film assisted by minor chemical reactions between the gas species and the film (such as oxidation), and that the etch rate ranged from 2 to 10 nm/ min.…”

Inductively Coupled Plasma Reactive Ion Etching of Magnetic Tunnel Junction Stacks in a CH3COOH/Ar Gas

“…4,13 Recent studies have focused on developing etching processes that employ non corrosive gas mixtures containing C, H, O and N, such as CO/NH 3 , CH 3 OH/Ar, CH 3 OH/H 2 O, CH 4 /Ar and CH 4 /O 2 /Ar. [5][6][7][8][9][10][11][12] MTJ stacks etching in such non corrosive gas mixtures mainly proceeds via oxidation of metals in the MTJ stack that compose each layer, formation of a protective layer and ion bombardment, which enables moderate etch rates and good etch profiles without any post etch degradation of the MTJ stacks. However, the lack of chemically reactive species in the plasma chemistry that can produce volatile etch byproducts results in heavy sidewall redeposition under certain conditions.…”

“…However, previous studies reported the formation of a protective layer and oxidation of the etched material. [9][10][11] The improved etch profile is attributed to partial oxidation of the film, which allows easy sputtering of the oxide layer and formation of a protective layer on the sidewall. Owing to fast etch rates and good etch profiles, 25% CH 3 COOH was selected as the standard concentration for the investigation of the etch profile evolution as a function of time.…”