We investigated the mechanism of premature etch stop in magnetic tunnel junction (MTJ) patterning using CO/NH3 plasma with a Ta mask to clarify the cause of etch-stop problem in high-density patterning due to mask deposition to a bottom space of a pattern. CO/NH3 plasmas consist of carbon monoxide, nitrogen, and hydrogen plasmas. To clarify the role of gas species in inducing this premature etch stop, the etching-depth difference of an MTJ with a Ru/CoFeB/MgO/CoFeB stack film was compared with CO/N2/H2, N2/H2, and N2/He plasmas at an electrode temperature of 200 °C. Premature etch stop was observed in the CO/N2/H2 plasma but not in the N2/H2 plasma. It was also observed in N2/He plasma, the position of which was found to be almost at the same level as the MgO layer. This etch stop is caused by the high etching durability of deposited Ta on the bottom space of the pattern, and oxidation of Ta enhances etching durability. Thus, the main reason for this type of etch stop is the oxidation of deposited Ta on the bottom space, and this oxidation is enhanced by two types of supplied oxygen, i.e., that from plasma when CO gas is added and that from MgO when the MgO surface is exposed by increasing the etching depth of an MTJ. Electrode temperature dependence in N2/H2 plasma as a function of the H2-mixing ratio indicates that this premature etch stop is suppressed by increasing the hydrogen content or the electrode temperature. Therefore, reducing oxygen by using hydrogen-including plasma was found to be effective in preventing the premature etch stop caused by oxidation of Ta, which is deposited to the bottom space of the pattern from the mask.

中文翻译：

---

使用带有 Ta 掩模的 CO/NH3 等离子体在高密度磁隧道结图案化中过早蚀刻停止的机制

我们研究了使用带有 Ta 掩模的 CO/NH3 等离子体在磁隧道结 (MTJ) 图案化中过早蚀刻停止的机制，以阐明由于掩模沉积到图案底部空间而导致高密度图案化中蚀刻停止问题的原因. CO/NH3 等离子体由一氧化碳、氮和氢等离子体组成。为了阐明气体种类在诱导这种过早蚀刻停止中的作用，将具有 Ru/CoFeB/MgO/CoFeB 叠层膜的 MTJ 的蚀刻深度差异与 CO/N2/H2、N2/H2 和 N2/He 进行比较等离子在 200 °C 的电极温度下进行。在 CO/N2/H2 等离子体中观察到过早蚀刻停止，但在 N2/H2 等离子体中未观察到。在 N2/He 等离子体中也观察到了这种现象，发现其位置与 MgO 层几乎处于同一水平。这种蚀刻停止是由沉积在图案底部空间上的 Ta 的高蚀刻耐久性引起的，Ta 的氧化增强了蚀刻耐久性。因此，这种类型的蚀刻停止的主要原因是底部空间上沉积的 Ta 的氧化，并且这种氧化被两种类型的供应氧增强，即当添加 CO 气体时来自等离子体的氧和来自 MgO 时的氧。通过增加 MTJ 的蚀刻深度来暴露 MgO 表面。N2/H2 等离子体中的电极温度依赖性作为 H2 混合比的函数表明这种过早的蚀刻停止可以通过增加氢含量或电极温度来抑制。因此，发现使用含氢等离子体减少氧气可有效防止由 Ta 氧化引起的过早蚀刻停止，