Improved Etch Characteristics of Magnetic Tunneling Junction Materials by Using Helium

Abstract

The etch characteristics of magnetic tunneling junction (MTJ) materials for spin transfer torque magnetic random access memory (STT-MRAM) using He inductively coupled plasma (ICP) were compared with the etch characteristics of ICP using Ar or CO/NH3 (1:3). The ICP etching using He showed a higher etch selectivity of CoFeB over W and a more anisotropic etch profile compared to the etching using Ar at similar etch rates. The sputter etch characteristics of CoFeB and W were also investigated using the Stopping and Range of Ions in Matter (SRIM) simulation program. The results showed higher sputter etch selectivity of CoFeB over W in addition to narrower angular distribution of the sputtered atoms than those obtained using Ar. The etching of MTJ materials using CO/NH3 (1:3) ICP exhibited good MTJ etch characteristics comparable to He ICP, however, the MTJ etched using CO/NH3 (1:3) showed the lowest saturation magnetization (MS) measured by a vibrating-sample magnetometer (VSM) possibly due to the sidewall oxidation of MTJ while the MS values of the MTJ etched using He and Ar are similar. It is found that, by etching the MTJ materials using He ICP with the ion energy near the hardmask sputter threshold energy, highly anisotropic etch profiles could be obtained without forming the sidewall redeposited materials and without significant degradation of magnetic properties.