Etch characteristics of magnetic tunnel junction materials using H₂/NH₃ reactive ion beam

Abstract

Magnetic tunneling junction (MTJ) materials such as CoFeB, Co, Pt, MgO, and the hard mask material such as W and TiN were etched with a reactive ion beam etching (RIBE) system using H-2/NH3. By using gas mixtures of H-2 and NH3, especially with the H-2/NH3( 2:1) ratio, higher etch rates of MTJ related materials and higher etch selectivities over mask materials (>30) could be observed compared to those etching using pure H-2( no etching) and NH3. In addition, no significant chemical and physical damages were observed on etched magnetic materials surfaces and, for CoPt and MTJ nanoscale patterns etched by the H₂/NH₃( 2:1) ion beam, highly anisotropic etch profiles >83 degrees with no sidewall redeposition could be observed. The higher etch rates of magnetic materials such as CoFeB by the H₂/NH₃( 2:1) ion beam compared to those by H₂ ion beam or NH₃ ion beam are believed to be related to the formation of volatile metal hydrides (MH, M = Co, Fe, etc) through the reduction of M-NHx( x = 1 similar to 3) formed in the CoFeB surface by the exposure to NH₃ ion beam. It is believed that the H₂/NH₃ RIBE is a suitable technique in the etching of MTJ materials for the next generation nanoscale spin transfer torque magnetic random access memory (STT-MRAM) devices.