Evolution of etch profile in etching of CoFeB thin films using high density plasma reactive ion etching

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

“…The decrease in etch rate of both CoFeB and TiN thin films as the CH 3 COOH concentration in the gas mixture increased can be attributed to a reduction in the effect of sputtering onto the film owing to reduced Ar ion bombardment and/or the formation of a C x H y inhibition layer that hindered the etching process. The decreasing etch rates suggest that the conventional RIE mechanism is not followed; however, C and O containing etching gases are known to form metal oxides, which could easily be removed by the subsequent ion bombardment [8,14,15]. Fig.…”

“…[CO] radicals are known to chemically react with several magnetic materials including NiFe, CoFe and IrMn [8]; however, as CH 3 COOH concentration increased, etch rate decreased, suggesting a passive role of [CO] species due to the hindering of any chemical reactions by the formation of a C x H y inhibition layer on the CoFeB film surface.…”

“…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.…”

Etch characteristics of magnetic tunnel junction materials using substrate heating in the pulse-biased inductively coupled plasma

“…However, the etching of MTJ materials using halogen gas mixtures has faced problems due to these chemistries corroding the metal alloy and providing poor selectivity to typical metal hard mask materials such as TiN and W. 9,10 To overcome these etch problems, several research groups have investigated the etching of magnetic materials using noncorrosive gas mixtures instead of halogens and have attempted to increase the formation of volatile compounds between the etchant gas, such as CO/NH 3 , CH 3 OH, and CH 4 /Ar, and MTJ materials by forming stable and volatile metal compounds possibly related to metal carbonyls. [11][12][13][14][15] However, the noncorrosive etch gas mixtures do not form stable and volatile carbonyl compounds easily and tend to show very low etch rates due to difficulty in reacting with the MTJ materials using the typical etching methods. As a result, the etch products are redeposited on the etched MTJ surface during etching, causing problems including low etch selectivity, sloped etch profiles, formation of a thick etch residue on the MTJ feature sidewall, high MTJ leakage current, and etch stop during the nanoscale MTJ pattern etching.…”

Structural and magnetic etch damage in CoFeB

“…3,4 Several studies have shown that capping CoFeB with MgO minimizes the magnetic damage in the CoFeB. 2,[4][5][6] Although much work has been done to minimize structural damage in CoFeB during etching, [7][8][9][10][11] the exact nature of the magnetic damage due to common etch methods is still unknown. With this in mind, we prepared a CoFeB sample with an etched surface and studied the structural and magnetic depth profiles with polarized neutron reflectometry (PNR) and cross-sectional transmission electron microscopy (TEM).…”