Integrated tip strain sensor for use in combination with a single axis

Abstract

An integrated tip strain sensor is combination with a single axis atomic force microscope (AFM) for determining the profile of a surface in three dimensions. A cantilever beam carries an integrated tip stem on which is deposited a piezoelectric film strain sensor. A high-resolution direct electron beam (e-beam) deposition process is used to grow a sharp tip onto the silicon (Si) cantilever structure. The direct e-beam deposition process permits the controllable fabrication of high-aspect ratio, nanometer-scale tip structures. A piezoelectric jacket with four superimposed elements is deposited on the tip stem. The piezoelectric sensors function in a plane perpendicular to that of a probe in the AFM; that is, any tip contact with the linewidth surface will cause tip deflection with a corresponding proportional electrical signal output. This tip strain sensor, coupled to a standard single axis AFM tip, allows for three-dimensional metrology with a much simpler approach while avoiding catastrophic tip 'crashes'. Two-dimensional edge detection of the sidewalls is used to calculate the absolute value or the linewidth of overlay, independent of the AFM principle. The technique works on any linewidth surface material, whether conductive, non-conductive or semiconductive.