Etching of CoFeB Using CO∕NH[sub 3] in an Inductively Coupled Plasma Etching System

Abstract

A CoFeB thin film composing a magnetic tunneling junction of CoFeB/MgO/CoFeB was etched in an inductively coupled plasma ͑ICP͒ etching system using CO/NH 3 gas mixtures, and its etch characteristics were compared with those of the CoFeB thin film etched using Cl 2 /Ar. When Cl 2 /Ar was used to etch the CoFeB thin film, even though its etch rate was faster than that of the CoFeB thin film etched using CO/NH 3 , a rough CoFeB surface could be observed due to the corrosion of the CoFeB surface during exposure to the air in addition to the significant change of surface composition. On the other hand, no corrosion of the CoFeB thin film was observed after the etching using CO/NH 3. When the ratio of CO/NH 3 was varied, the highest etch rate of 12 nm/min could be observed at the ratio of 1:3 compared to about 4 nm/min for CO or NH 3 at the ICP source power of 700 W, bias power of 300 W, and 5 mTorr of operating pressure. The highest etch rate was related to the formation of volatile metal carbonyls between metal and CO, where NH 3 appeared to assist the easier formation of metal carbonyl by preventing the dissociation of CO into C and CO 2 .

STT MRAM patterning challenges

“…Min et al using Cl 2 /Ar plasma reported etched MTJ stacks with clean side-walls 4 . However, the key problem encountered is the material degradation, Cl x species absorbed on the side-walls inducing corrosion of the CoFeB layer 5 . E.H. Kim et al 9 studied the etching of MTJ stacks in HBr/Ar plasma's.…”

“…Regarding chemical induced damage, Cl radicals from Ar/Cl 2 plasma's have been reported to induce corrosion 5 . The latter triggered the exploration of alternative plasma chemistries.…”

Selective Etching of Magnetic Tunnel Junction Materials Using CO/NH3 Gas Mixture in Radio Frequency Pulse-Biased Inductively Coupled Plasmas

“…In this study, an RF pulse-biasing technique has been applied in the etching of MTJ materials, such as CoFeB and MgO, and W has been used as one of the hard mask materials and its effect on the etch characteristics was investigated in an ICP system using a CO/NH 3 gas mixture, which has been investigated to show high etch rates in previous studies. 30)…”

Negative electron-beam resist hard mask ion beam etching process for the fabrication of nanoscale magnetic tunnel junctions

“…8,9 For such device applications, pattering, and therefore etching, the component magnetic materials becomes a critical process for fabricating stable devices. Reactive ion etching (RIE) [10][11][12][13]15 based on chlorine and methanol gases has been used for nanoscale magnetic materials etching. But it shows after-corrosion and oxidation problems.…”