Fabrication of high aspect ratio (HAR) atomic force microscopy (AFM) probes by one step e-beam lithography and AFM cantilever patterning using grafted monolayer brushes

Abstract

Atomic force microscopy (AFM) allows imaging individual atoms where a very sharp tip touches and feels the substrate. Although a regular AFM tip can achieve atomic resolution, it produces false images on substrates with tall and dense features because of the shape and dimensions of the tip. To solve this problem, high aspect ratio (HAR) AFM tips have emerged. However, the HAR AFM tips are often fabricated individually with the need for expensive instruments such as focused ion beam causing low throughput and high cost. In this thesis, several processes are developed for the batch fabrication of HAR AFM tips to reduce the cost and increase the throughput where HAR tips with tip apex diameter down to 9 nm without oxidation sharpening have been obtained by our methods.

Moreover, there are cantilever-based devices demanded in a wide range of applications such as tip-enhanced Raman spectroscopy. Our one-step e-beam lithography technique is capable of forming arbitrary patterns for a variety of applications. Alternatively, a process based on grafting polystyrene monolayer brush has been developed to pattern irregular substrates like cantilevers with e-beam lithography where both negative and positive tone behaviors are obtained under different development conditions. That is, the process enables the fabrication of both recessed and protruded features on both nonflat and very small surfaces. As a result, an AFM cantilever is patterned with high resolution on both top and sidewalls at the same time.