| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS2-ThM |
| Session: | Plasma Processing of Challenging Materials |
| Presenter: | Masaki Yamada, Hitachi High-Technologies Corporation, Japan |
| Authors: | M. Yamada, Hitachi High-Technologies Corporation, Japan M. Satake, Hitachi High-Technologies Corporation |
| Correspondent: | Click to Email |
The RIE etching of p-MTJ (Perpendicular Magnetic Tunnel Junction) device is one of big issues to realize the high density STT-MRAM (Spin Transfer Torque Magnetoresistive Random Access Memory). In the view point of high etching selectivity or corrosion-less, Ar/CH3OH or CO/NH3 is generally used in MTJ etching. On the other hand, according to recently report, the hydrogen plasma in etching gas may cause the electrical degradation [1]. In this study, we investigate the influence of hydrogen plasma on magnetic properties by using thin CoFeB blanket film.
The stacked film structure is Ta(tTa) / MgO (2.0nm) / CoFeB(tCoFeB) / Ta(5nm) / substrate, which were deposited on Si substrate by UHV RF-sputtering apparatus. In this study, CoFeB film thickness tCoFeB were varied from 1.0 nm to 2.0 nm. Then they were annealed at 300 degC for 1 hour with μ0H = 0.6 mT. After that, the hydrogen plasma was irradiated to the film for 5 min through Ta capping layer by using Inductively Coupled Plasma etcher. The magnetization of blanket CoFeB films were evaluated by using Vibration Sampling Magnetometer.
At first we evaluate the CoFeB film thickness dependence of magnetic anisotropy. Without plasma irradiation, the magnetization of CoFeB film shows a perfect perpendicular anisotropy at tCoFeB = 1.2 nm and its coercivity μ0Hc is obtained as μ0Hc = 0.8 mT. On the other hand, when the hydrogen plasma is irradiated to stacked film, the coercivity decreases down to μ0Hc = 0.2 mT. And also its effective perpendicular anisotropy field μ0Hk also decreases from μ 0Hk = 330 mT to μ0Hk = 220 mT with hydrogen plasma irradiation. In the case of tCoFeB = 1.4 nm, the magnetization shows weak perpendicular anisotropy before plasma irradiation. In this situation, the magnetization drastically changes from the weak perpendicular to in-plane anisotropy by hydrogen plasma irradiation. These results imply that the interfacial perpendicular anisotropy energy decreases by hydrogen plasma irradiation. Next we evaluate capping layer thickness tTa dependence of magnetic anisotropy. In the case of tTa < 20 nm, the coercivity of CoFeB film increases with increasing Ta capping film thickness with hydrogen plasma irradiation. And it shows approximately constant value at tTa > 50 nm even with hydrogen plasma irradiation. This behavior is well described by the hydrogen plasma diffusion model in Ta capping layer, which is calculated by Monte Carlo simulation. From present study, we found that hydrogen plasma may attack to MgO layer chemically and it may deteriorate the perpendicular magnetization of CoFeB.
[1] J. H. Joeng, et al., J. Appl. Phys., vol.115, 17C727 (2014)