Selective Etching of Magnetic Tunnel Junction Materials Using CO/NH3 Gas Mixture in Radio Frequency Pulse-Biased Inductively Coupled Plasmas
The etch characteristics of magnetic tunneling junction (MTJ) materials and the etch selectivity over W have been investigated using RF pulse-biased conditions in addition to the continuous wave (CW) bias condition with a CO/NH 3 gas combination in an inductively coupled plasma system. By using a ti...
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| Published in | Jpn J Appl Phys Vol. 52; no. 5; pp. 05EB03 - 05EB03-6 |
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| Main Authors | , , , , , |
| Format | Journal Article |
| Language | English |
| Published |
The Japan Society of Applied Physics
25.05.2013
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| Online Access | Get full text |
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| Summary: | The etch characteristics of magnetic tunneling junction (MTJ) materials and the etch selectivity over W have been investigated using RF pulse-biased conditions in addition to the continuous wave (CW) bias condition with a CO/NH 3 gas combination in an inductively coupled plasma system. By using a time-averaged substrate DC bias voltage condition for the RF pulse biasing, the etch rates of MTJ materials for the RF pulse-biased conditions were generally similar to those etched using the CW RF bias condition even though the etch rates were slightly decreased with decreasing the duty percentage of the RF pulse biasing. However, the use of the RF pulse biasing improved the etch selectivity of the MTJ materials over mask materials such as W. When the surface roughness and the residual thickness remaining on the etched surface of the MTJ material such as CoFeB were investigated by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively, it was clear that the use of the RF pulse biasing instead of CW RF biasing also decreased the residual thickness and the surface roughness. This is believed to be related to the formation of a more uniform chemically reacted layer on the etch CoFeB surface during the RF pulse-biased etching condition. |
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| Bibliography: | Schematic diagram of the ICP etching system used in this study. (Color online) (a) CW RF biasing at $-300$ V of constant DC bias voltage condition. (b) and (c) show the rf pulsed biasing with the 50% duty ratio at $-300$ V of DC bias voltage condition for instant DC biasing and time-averaged DC biasing, respectively. (Color online) Etch characteristics of MTJ-related materials and W as a function of pulse duty percentage at a fixed DC bias voltage of $-300$ V. (a) Etch rates of MTJ materials and W and (b) etch selectivities of MTJ materials over W. The pulse frequency was kept at 50 kHz. The ICP power, the process pressure of CO (12.5 sccm)/NH 3 (37.5 sccm), and the substrate temperature were also maintained at 500 W, 5 mTorr, and 20--30 °C, respectively. As the constant DC bias voltage during the pulsing, the instant DC bias voltage condition and the time-averaged DC bias voltage condition were used. (Color online) XPS narrow scan data of Co 2p, Fe 2p, and B 1s during the depth profiling of the CoFeB surface etched with CW and 30% pulse duty percentage. The samples were etched for 3 min with the time-averaged DC bias voltage condition of $-300$ V and the other etch conditions are the same as those in Fig. . (Color online) Relative atomic percentages of the etched CoFeB surface measured by XPS depth profiling as a function of Ar + ion sputter etch time for the CoFeB samples etched for various pulse duty percentages including the CoFeB etched with the CW biasing. (a) CW, (b) DR 70%, (c) DR 50%, and (d) DR 30%. The etch conditions are the same as those in Fig. . (Color online) AFM surface roughness of the etched CoFeB as a function of pulse duty percentage using a CO/NH 3 gas combination in the ICP system. The etch conditions are the same as those in Fig. . (Color online) Schematic drawing of one of the possible reaction mechanisms during the etching using CW biasing (100% pulse duty cycle) and 50% pulsed duty cycle. |
| ISSN: | 0021-4922 1347-4065 |
| DOI: | 10.7567/JJAP.52.05EB03 |