Etch residue removal of CoFeB using CO/NH₃ reactive ion beam for spin transfer torque-magnetic random access memory device

Using a reactive ion beam etching (RIBE) system, the possibility of removing the sidewall residues remaining on etched nanoscale CoFeB features and the W hard mask after using a conventional inductively coupled plasma etching system was investigated. Upon increasing the ion energy of the Ar beam, a similar sputter yield increase was found for both CoFeB side wall residues and the W hard mask. Hence, increasing the ion beam energy to improve etch residue removal efficiency at the same time induces a degradation of the CoFeB profile because of the W hard mask erosion. However, when CO/NH₃ was used as the RIBE gas mixture, at ion energy in the range of 90-110 eV, the effective residue removal from CoFeB etched features without etching the W hard mask. When the ion energy of the CO/NH₃ RIBE exceeds 140 eV, again similar sputter yields are found for both CoFeB side wall residues and the W hard mask.