Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0021, Japan.
Nanotechnology. 2011 Jan 28;22(4):045302. doi: 10.1088/0957-4484/22/4/045302. Epub 2010 Dec 20.
We introduce a novel three-step procedure for precise niobium (Nb)-etching on the nanometer-scale, including the design of high contrast resist patterning and sacrifice layer formation under high radio frequency (RF) power. We present the results of precise slit fabrication using this technique and discuss its application for the production of superconducting devices, such as superconductor-semiconductor-superconductor (S-Sm-S) Josephson junctions. For the reactive ion etching (RIE) of Nb, we selected CF(4) as etchant gas and a positive tone resist to form the etching mask. We found that the combination of resist usage and RIE process allows for etching of thicker Nb layers when utilizing the opposite dependence of the etching rate (ER) on the CF(4) pressure in the case of Nb as compared to the resist. Precise slit-width control of 80 and 200 nm thick Nb apertures was performed with three kinds of ER control, for the resist, the Nb, and the underlying layer. S-Sm-S Josephson junctions were fabricated with lengths as small as 80 nm, which can be considered clean and short and thus exhibit critical currents as high as 50 µA. Moreover, possible further applications, such as for apertures of superconducting light emitting diodes (SC LEDs), are addressed.
我们介绍了一种新颖的三步法，可实现纳米级铌（Nb）精确刻蚀，包括在高射频（RF）功率下设计高对比度抗蚀剂图案和牺牲层形成。我们展示了使用该技术精确狭缝制造的结果，并讨论了其在超导器件生产中的应用，例如超导-半导体-超导（S-Sm-S）约瑟夫森结。对于 Nb 的反应离子刻蚀（RIE），我们选择 CF(4)作为刻蚀气体，正性光刻胶作为刻蚀掩模。我们发现，当使用 Nb 的刻蚀速率（ER）对 CF(4)压力的相反依赖性与抗蚀剂相比时，抗蚀剂的使用和 RIE 工艺的组合允许对较厚的 Nb 层进行刻蚀。使用三种 ER 控制方法，对 80nm 和 200nm 厚的 Nb 孔径进行了精确的狭缝宽度控制，用于控制抗蚀剂、Nb 和底层的 ER。制造了长度小至 80nm 的 S-Sm-S 约瑟夫森结，这些结可以被认为是干净和短的，因此表现出高达 50µA 的临界电流。此外，还讨论了可能的进一步应用，例如用于超导发光二极管（SC LED）的孔径。
