臺灣博碩士論文加值系統

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。

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.

口試委員會審定書 iii
誌謝 iv
摘要 v
ABSTRACT vi
CONTENTS vii
LIST OF FIGURES x
LIST OF TABLES xv
Chapter 1 Introduction 1
1.1 Magnetoresistance (MR) 1
1.1.1 Giant magnetoresistance (GMR) 1
1.1.2 Tunneling magnetoresistance (TMR) 2
1.2 Magnetic tunnel junction (MTJ) 4
1.2.1 Introduction of MTJ 4
1.2.2 Spin-transfer-torque 5
1.2.3 Spin-orbit-torque 6
1.2.4 Types of MTJ 8
1.2.5 Typical MTJ layer structure 9
1.3 Resistance-area product 11
1.4 Capping layers of MTJ 12
1.5 Redeposition effect 13
1.6 Motivation of this work 14
Chapter 2 Fabrication 16
2.1 Thin film deposition 16
2.1.1 Magnetron sputtering 16
2.1.2 Electron beam (E-beam) evaporator 17
2.2 Etching system 18
2.2.1 Ion beam etching (IBE) 18
2.2.2 Endpoint detector 21
2.3 MTJ fabrication 23
Chapter 3 Measurement 30
3.1 Resistance measurement 30
3.2 TMR measurement 30
3.2.1 Two-probe lock-in measurement 30
3.2.2 TMR characterization on a standard MTJ device 32
3.3 Lock-in voltage – current 35
Chapter 4 Results 37
4.1 Influence of 2nd etching time on yield rate 37
4.1.1 Fabrication 37
4.1.2 B-B and T-B resistance 38
4.1.3 Yield rate 40
4.1.4 Lock-in voltage – current measurement 41
4.2 Ta capped MTJ result 42
4.2.1 Fabrication 42
4.2.2 B-B and T-B resistance 43
4.2.3 Yield rate 45
4.2.4 TEM image 46
4.3 Pt capped MTJ result 49
4.3.1 Fabrication 49
4.3.2 B-B resistance 52
4.3.3 T-B resistance 54
4.3.4 Yield rate 57
4.3.5 Lock-in voltage – current measurement 58
4.3.6 Annealing process 59
4.4 ITRI MTJ 61
4.4.1 Fabrication 61
4.4.2 B-B and T-B resistance 61
4.4.3 TMR measurement 62
4.4.4 TEM images 63
Chapter 5 Conclusion 65
REFERENCE 66

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