טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentRubin Eyal
SubjectMultidimensional Topography Sensing for Frequency
Modulated AFM
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Izhak Bucher
Full Thesis textFull thesis text - English Version


Abstract

Atomic force microscopy (AFM) is widely used in the semiconductor industry for inspection and quality control. The basic mechanical concept of an AFM is a micro-cantilever with a sharp stylus at its tip, excited at or near resonance. Frequency modulated AFM (FM-AFM) extracts the surface topography features by measuring the frequency shift created by the Van der Waals (VdW) interaction forces between the tip and the sample. To improve the measurement speed and address complex geometries emerging in industrial microchip constructions, several enhancements are introduced. While most FM-AFM devices operate in a single vibrating mode, this research proposes a method for multidimensional sensing using frequency modulation of orthogonal vibration modes simultaneously. The concept was tested on a large-scale experimental system, where VdW forces were replaced by strong magnetic forces, using a magnetic tip and ferromagnetic samples. To emulate the VdW forces accurately, the ratio between the base frequency and frequency shift was designed to be similar to that experienced in a real AFM. The Autoresonance (AR) control scheme for faster excitation and curve fitting frequency estimation algorithm were used for sensing several modes simultaneously without waiting for steady state settling of the cantilever.  Experimental results employ 3D relevant topographies such as inclined surfaces, steep walls and trenches that were reconstructed experimentally with 4 (µm) precision or better. Downscaling to typical AFM dimensions would theoretically yield sub-nanometer precision.