Low-cost batch fabrication method of high aspect ratio AFM tips

原子力显微镜(AFM)是扫描探针显微镜(SPM)家族中最常用的表征工具。与扫描电子显微镜(SEM)相比，AFM的成本更低，如果样品是平的，则在z方向和x-y方向的精度要高得多(高一个数量级)，并且可以与绝缘样品甚至在液体环境中同样好地工作。然而，在表面结构表征方面，扫描电子显微镜仍然比原子力显微镜更受欢迎，这主要是因为在绘制非平坦表面(例如，深而窄的孔/沟槽)时，AFM图像的内在限制，其中尖端不能完全跟随样品表面。克服这个问题的自然解决方案是使用薄的和高纵横比的尖端，这样可以更精确地跟踪样品表面。 本项目的目标是开发高深宽比原子力显微镜针尖的制造工艺。该技术的关键特征是它是一种低成本、高成品率的批量制造工艺。该过程从一片包含380个规则金字塔形尖端的AFM尖端开始，并同时对它们进行加工，以在顶端产生细小且高深宽比的柱子。 目前所有商用的高深宽比AFM针尖都是以缓慢且昂贵的方式一个接一个地制造的。相反，我们的工艺是批量制造工艺，因此具有更高的生产能力和更低的每尖端制造成本。

Atomic force microscope (AFM) is the most popular characterization tool among the scanning probe microscope (SPM) family. Compared to scanning electron microscope (SEM), AFM has lower cost, much more accurate (by one order) in the z-direction and x-y direction if the sample is flat, and can work equally well with insulating sample or even inside a liquid environment. Nevertheless, SEM is still far more popular than AFM for topographical structure characterization, mostly because of the intrinsic limit in the AFM image when mapping a none-flat surface (e.g a deep and narrow hole/trench) where the tip cannot fully follow the sample surface. The natural solution to overcome this issue is by using thin and high aspect ratio tips that can follow the sample surface more precisely. The objective of this project is to develop the fabrication process for high aspect ratio AFM tips. The key feature of the technology is that it is a low-cost batch fabrication process with high yield. The process starts from a wafer of AFM tips containing 380 regular pyramid-shaped tips, and process them simultaneously to produce fine and high aspect ratio pillars at the tip apex. Currently all the commercially available high aspect ratio AFM tips are made one by one, in a slow and costly manner. On the contrary, our process is a batch fabrication process, and is thus with much higher throughput and much lower fabrication cost per tip.