Jung Ku Youl, Min Byoung-Chul, Ahn Chiyui, Choi Gyung-Min, Shin Il-Jae, Park Seung-Young, Rhie Kungwon, Shin Kyung-Ho
Center for Spintronics Research, Korea Institute of Science and Technology, Seoul 136-791, Korea.
J Nanosci Nanotechnol. 2013 Sep;13(9):6467-70. doi: 10.1166/jnn.2013.7616.
We present a fabrication method for nano-scale magnetic tunnel junctions (MTJs), employing e-beam lithography and lift-off process assisted by the probe tip of atomic force microscope (AFM). It is challenging to fabricate nano-sized MTJs on small substrates because it is difficult to use chemical mechanical planarization (CMP) process. The AFM-assisted lift-off process enables us to fabricate nano-sized MTJs on small substrates (12.5 mm x 12.5 mm) without CMP process. The e-beam patterning has been done using bi-layer resist, the poly methyl methacrylate (PMMA)/ hydrogen silsesquioxane (HSQ). The PMMA/HSQ resist patterns are used for both the etch mask for ion milling and the self-aligned mask for top contact formation after passivation. The self-aligned mask buried inside a passivation oxide layer, is readily lifted-off by the force exerted by the probe tip. The nano-MTJs (160 nm x 90 nm) fabricated by this method show clear current-induced magnetization switching with a reasonable TMR and critical switching current density.
我们提出了一种用于纳米级磁性隧道结（MTJ）的制造方法，该方法采用电子束光刻技术以及由原子力显微镜（AFM）的探针尖端辅助的剥离工艺。在小尺寸衬底上制造纳米尺寸的MTJ具有挑战性，因为难以使用化学机械平面化（CMP）工艺。AFM辅助的剥离工艺使我们能够在不使用CMP工艺的情况下，在小尺寸衬底（12.5毫米×12.5毫米）上制造纳米尺寸的MTJ。电子束图案化是使用双层抗蚀剂，即聚甲基丙烯酸甲酯（PMMA）/氢倍半硅氧烷（HSQ）来完成的。PMMA/HSQ抗蚀剂图案既用于离子铣削的蚀刻掩膜，也用于钝化后顶部接触形成的自对准掩膜。埋在钝化氧化层内的自对准掩膜，很容易被探针尖端施加的力剥离。通过这种方法制造的纳米MTJ（160纳米×90纳米）显示出清晰的电流感应磁化翻转，具有合理的隧穿磁电阻（TMR）和临界翻转电流密度。
