A miniaturized, high frequency mechanical scanner for high speed atomic force microscope using suspension on dynamically determined points.

Rodolf Herfst,Bert Dekker,Will Crowcombe,Dorus De Lange,Gert Witvoet,Hamed Sadeghian

doi:10.1063/1.4935584

Abstract

One of the major limitations in the speed of the atomic force microscope (AFM) is the bandwidth of the mechanical scanning stage, especially in the vertical (z) direction. According to the design principles of "light and stiff" and "static determinacy," the bandwidth of the mechanical scanner is limited by the first eigenfrequency of the AFM head in case of tip scanning and by the sample stage in terms of sample scanning. Due to stringent requirements of the system, simply pushing the first eigenfrequency to an ever higher value has reached its limitation. We have developed a miniaturized, high speed AFM scanner in which the dynamics of the z-scanning stage are made insensitive to its surrounding dynamics via suspension of it on specific dynamically determined points. This resulted in a mechanical bandwidth as high as that of the z-actuator (50 kHz) while remaining insensitive to the dynamics of its base and surroundings. The scanner allows a practical z scan range of 2.1 μm. We have demonstrated the applicability of the scanner to the high speed scanning of nanostructures.

Highlights

The increase of the imaging speed in atomic force microscopy (AFM) is of interest in several practical applications, including wafer inspection in semiconductor applications[1–5] and visualizing dynamic behavior of proteins in a physiological environment.[6,7]dynamics of the high speed z-stage is insensitive to its base and surrounding dynamics
We have developed an AFM scan head, in which the high speed z-stage is designed in such a way that at the interface between the z-stage and the surrounding frame, there is no motion while actuating
Considering the listed requirements on the rest of the scan head, a 50 kHz eigenfrequency for the entire stage is considered infeasible. This is driven by a higher mass and lower stiffness of the bulk of the scan head compared to the high speed mechanical z-stage

Summary

INTRODUCTION

The increase of the imaging speed in atomic force microscopy (AFM) is of interest in several practical applications, including wafer inspection in semiconductor applications[1–5] and visualizing dynamic behavior of proteins in a physiological environment.[6,7]. Dynamics of the high speed z-stage is insensitive to its base and surrounding dynamics. We have developed an AFM scan head, in which the high speed z-stage is designed in such a way that at the interface between the z-stage and the surrounding frame, there is no motion while actuating. We have achieved very high speed AFM measurements, whilst maintaining the image quality.

ARCHITECTURE OF THE AFM HEAD

HIGH SPEED MECHANICAL Z-STAGE

EXPERIMENTAL RESULTS

CONCLUSIONS