磁性穿隧元件之製程優化與研究

Optimization of a fast-track fabrication process for magnetic tunnel junctions

陳建平(Chien-Ping Chen)

指導教授 ： 白奇峰

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102018

摘要

自旋軌道轉矩式記憶體 (SOT-MRAM) 具有非揮發性、讀寫速度快、低耗能、可微縮等等的特性，也優於另一個具有潛力的自旋轉移力矩式記憶體 (STT-MRAM) 的架構，避免寫入時的大電流破壞絕緣層的嚴重問題，已然成為次世代記憶體的候選人之一。因此，磁性穿隧元件 (MTJ) 之結構與製程就顯得至為關鍵。在本論文中，透過二次蝕刻時間的掌握、精準向下蝕刻至氧化鎂層、小角度蝕刻的技術，克服了再沉積所造成的邊際短路效應，達到優化微米尺寸磁性穿隧元件的目標。除此之外，我們使用鉑 (Pt) 作為覆蓋層，避免以鉭 (Ta) 作為覆蓋層時，因其在空氣中自然氧化，進而造成串聯高穿隧電阻的重大缺點，促使我們得以研究電阻-面積乘積 (resistance-area product) 對上氧化鎂膜層厚度的重要資訊，本研究中所成長之磁性穿隧膜層之元件的電阻-面積乘積的範圍為104 到106 (Ω μm2)，分別對應於氧化鎂為0 奈米至1.5 奈米的厚度，過程中氧化鎂膜層的實際厚度也經由高解析度穿隧電子顯微鏡的證實。最後我們使用工業技術研究院所提供的高品質磁性穿隧膜層，成功製作微米級的元件，驗證了本研究所發展的磁性穿隧元件製程的可靠性。總體而言，製程優化的達成是透過精準蝕刻至氧化鎂層、小角度蝕刻、以及合適的覆蓋層。

關鍵字

自旋軌道矩式記憶體 ； 磁性穿隧元件 ； 再沉積效應 ； 穿隧式磁阻 ； 電阻面積乘積

並列摘要

Spin-orbit-torque (SOT) magnetic random-access memory (MRAM) is a prime
candidate for the next-generation memory due to its non-volatility, fast operation speed, low power consumption, and high storage density. Besides, the reliability issue of spin-transfer-torque (STT) MRAM can also be overcome by SOT-MRAM. Therefore, the fabrication of three-terminal magnetic tunnel junction (MTJ) is very important because it is the basic component of SOT-MRAM. In this thesis, the 2nd etching time of fabrication process is optimized with the micron-scale MTJs and we provide a stop-on-MgO solution to prevent the redeposition effect. Also, the influence of the capping layer on tunneling resistance has been investigated. Ta would be oxidized when it serves as the capping layer,
which would lead to high tunneling resistance. However, for Pt-capped MTJ, the
tunneling resistance would not be affected by capping layer. Thus, the dependence of the RA product on MgO thickness can be observed, in which the RA product ranges from 104 to nearly 106 (Ω μm2), and the MgO thickness ranges from 0.9 to 1.5 nm, verified from HRTEM images. The fabrication process is also verified by the thin film provided by Industrial Technology Research Institute (ITRI). In summary, the optimization of the fabrication process for MTJ has been achieved by the stop-on-MgO etching technique, small-angle-etching and the choice of a proper capping layer.

並列關鍵字

spin-orbit-torque MRAM ； magnetic tunnel junction ； redeposition effect ； tunneling magnetoresistance ； resistance-area product

參考文獻

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