鈷鐵硼磁性穿隧結元件之自對準製程研究及磁阻特性分析

The investigation of self-aligned process and magnetoresistance of CoFeB-based magnetic tunnel junction devices

賴國豪(Guo-Hau Lai)

指導教授 ： 吳仲卿

國立彰化師範大學/理學院/物理學系/碩士(2017年)

摘要

近年來基於自旋電子學的材料及物理的蓬勃研究，推動了新型自旋電子元件的研發和應用。尤其於感測層和參考層中具有正交磁異向性之磁性穿隧結，因為其潛在的應用價值，如微波產生器、微波偵測器、及磁場感測器等，已經引起了科學與工業界的重視。本論文主要探究具有正交磁異向性之磁性穿隧結的磁特性，並透過大陣列製程完成奈米尺度元件之蝕刻樣貌分析。磁性穿隧結膜層結構由下而上為Ta 5nm/ NiFe 5nm/ IrMn 10nm (AFM)/ Co80Fe20 2.5nm (pinned layer)/ Ru 0.9nm/ Co40Fe40B20 2.5nm (reference layer)/ MgO 1.0nm/ Co40Fe40B20 1.2nm (free layer)/ Ta 5nm/ Ru 5nm，其製備是透過超高真空磁控濺鍍系統完成，再經由調變不同的熱退火參數，並使用交替式梯度測磁儀量測磁滯曲線，以確認具有正交磁異相性之感測層和參考層。電流垂直膜面之微米級元件及奈米級點狀大陣列皆是透過由上而下的方式完成製作，其主要製程技術包括黃光微影術、電子束微影技術及雙角度離子蝕刻技術，製程上尤其以雙角度離子蝕刻的步驟，以避免蝕刻反鍍而造成側壁短路的問題。
微米級元件的磁阻特性探究主要透過直流電性四點量測法，量測磁阻與平行膜面高磁場的響應行為，並且將磁阻特性曲線與磁滯曲線共同比較，可以清楚地了解不同磁性層之間的磁矩翻轉行為。其磁阻變化率(MR %)約莫15 %，電阻面積乘積值約960 Ω．μ㎡。
調控元件蝕刻參數及烘烤電子阻劑(man-2405)之溫度對於奈米尺度之元件的形貌分析是本論文的另一項重點，研究發現烘烤溫度於110℃蝕，能使得man-2405硬化成為良好之遮罩，使得蝕刻之元件具有最佳的圖案轉移效果，且最小尺寸可達略小於150奈米直徑之元件，有助於後續沉積上電極製程之接觸，可以順利完成奈米尺度之磁性穿隧結元件。

關鍵字

磁性穿隧結 ； 正交磁異相性 ； 電流垂直膜面元件製程 ； 大陣列製程 ； 奈米尺度磁性穿隧結元件 ； 雙角度離子蝕刻

並列摘要

Due to the vigorous development of materials and physical properties of spintronics recently, a variety of potential applications of new spintronic components has been conceived and promoted. Especially magnetic tunnel junctions (MTJs) with orthogonal magnetic anisotropies in sensing-layer and reference-layer have acquired many interests due to its cutting edge application, such as microwave generator, microwave detector, magnetic field sensors, and many others. The objective of this thesis focuses on the magnetic and magnetoresistive characteristic of a MTJ with orthogonal magnetic anisotropies and an analysis of etching technique for making nano-scaled MTJ devices. The stack films, consisting of “Ta 5nm/ NiFe 5nm/ IrMn 10nm (AFM)/ Co80Fe20 2.5nm (pinned layer)/ Ru 0.9nm/ Co40Fe40B20 2.5nm (reference layer)/ MgO 1.0nm/ Co40Fe40B20 1.2nm (sensing layer)/ Ta 5nm/ Ru 5nm”, were deposited by using an ultrahigh vacuum magnetron sputtering system and tested for various annealing process to acquire the orthogonal magnetic anisotropies in sensing-layer and reference-layer, which was identified through the hysteresis loop measurement using an Alternating Gradient Magnetometer. Micron-sized MTJ devices with current-perpendicular-to-plane configuration and dots array in nanoscale were fabricated with a top-down process. The key techniques used are including photolithography, E-beam lithography, and dual-angle ion-milling process. Care was taken by using a dual-angle ion beam milling in order to avoid edge shorting during the etching process.
Magnetoresistance (MR) was measured via a DC four-probe measurements and the results were in close comparison with hysteresis loops. The basic magnetization reversal behavior of each ferromagnetic layer was clearly understood and identified. The MR ratio was almost 15% and the resistance-area (RA) ratio was 960 Ω．μ㎡.
Adjusting the etching parameters and the baking temperature of the photoresist (man-2405) are important issues making nano-scaled MTJ device. By adopting the baking temperature of 110℃, the photoresist was hardened and became a good soft-mask. As a result, MTJ pillars in 150 nm scale show a best pattern transfer effect which will avoid bad contact issue on the top electrode sputtering. Accordingly, nano-scaled MTJ can be successfully completed.

並列關鍵字

Magnetic Tunnel Junctions ； Orthogonal magnetic anisotropies ； CPP-MTJ ； fabrication of large array ； nano-sacled MTJ ； dual-angle etching

參考文獻

1.3 參考文獻

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