New SPM concept for accurate and repeatable tip positioning

Abstract

In routine scanning probe microscopy (SPM) measurements either the tip is hidden underneath the cantilever and thus the position of the tip is only known with a very low accuracy (>5 μm) or a high aspect-ratio tip is used which is visible but is very fragile. Furthermore, for electrical applications, visible tips are simply coated with a thin layer of active material that wears fast in case of high pressure applications such as scanning spreading resistance microscopy (SSRM). In this work we present a novel approach for fabricating SPM probes with tips that can be located with sub-micrometer accuracy. A fully-integrated batch fabrication process was developed and used to make low aspect-ratio tips entirely made of hard metal (TiN) with an uncertainty on the tip position below 200 nm. We evaluated our fabricated tips in tapping mode topography atomic force microscopy (AFM) and SSRM analysis. A reference sample of SrTiO 3 was used for tip evaluation in tapping mode AFM and SSRM measurements were performed on an n-type GaAs staircase test structure with different doping levels. From the topography measurements we calculated a tip radius below 40 nm for our fabricated tips and we were able to resolve all of the different layers in the GaAs reference sample.