High speed and highly accurate tip-scanning atomic force microscope for large samples

Abstract

The Atomic Force Microscope (AFM) is a powerful instrument in the nanometer-scale science and technology. Since its invention in 1986, the AFM has evolved significantly; refining its capabilities and conveniences. A sample scanner can move a sample to within a few nm of resolution within a certain range. Early AFM models kept the probing unit (including a micro-machined cantilever) stationary and controlled the sample position with the scanner. The “sample-scanning” design can handle only small and light samples. Large and heavy samples such as silicon wafers and Liquid Crystal Display panels require a “tip-scanning” AFM. In this thesis, a novel high speed and highly accurate tip scanning AFM (TS-AFM) head which uses a flexure guided xy and z scanning system has been developed. Moreover, additional components including a coarse z-stage, an optical microscope with a motorized focus stage and structural frames are also developed to evaluate the feasibility for application for large samples for example, Liquid Crystal Displays and wafers. The scanning speed of AFMs which use lock-in amplifiers for non-contact imaging is determined by a settling (decaying of a transient response) time of cantilever. So, system bandwidths of xy and z scanners are chosen according to the settling time of cantilever. The system bandwidth is determined by a “separation frequency” not by a first resonant frequency. The separation frequency is enhanced via an appropriate preload. In this thesis, a preloading effect on a flexure guided nano-positioner (scanner) is proven by theory and experiments. The xy and z scanning system which uses flexure guides and multilayered PZT actuators is optimally designed by used the concept of separation frequency. A highly sensitive optical lever for nulling sensor is designed by using a systematic approach and a commercial optic simulation program. The coarse z-stage which uses a preloaded ball screw, a cross roller guide and a harmonic drive five ...