Three-dimensional Atomic Force Microscopy Based On The Probe With Flared-tip

In recent years,the demand for investigation of the morphology and topography on high quality products,which mainly features the critical dimensions of semiconductor devices,has made the true three-dimensional(3D)mesurement technology of micro-nano structures get more and more attention.3D atomic force microscope(3D-AFM)that performs at high resolution,does little damage to sample,and has the potential to detect steep sidewalls,is a ture 3D measurement technology with latent capability.However,this kind of instrument is more complicated than traditional AFM in terms of system structures and control methods.As of this writing,there is still room for improvement of critical technologies and universal applications.This paper mostly focuses on the research of 3D-AFM.One distinctive 3D-AFM measurement platform based on the probe with flared-tip coupled with 3D-scanning strategy are designed respectively.The main achievements include the following:1.The development status of 3D-AFM technology is discussed.Working principles of two classic 3D measurement techniques,including tilt-scanning method and flared-tip-based method,are described in detail.The research route of this article is consequently determined after comparing the advantages and disadvantages of these approaches.2.The model used to explain the contact force between flared-tip and sample is constructed.Based on the Lennard-Jones potential theory and the Maugis-Dugdale model of elastic contact,the mechanical behavior is analyzed as the probe gets close to sample in different directions.From the numerical calculation results,theoretical curves of force-displacement are plotted.These fundamental analyses can help to forecast the probe deformation and be useful for the improvement of 3D measurement method.3.A scheme aiming to reduce the lateral contact force applied on the flared-tip during measurement is proposed.Based on elastic mechanics and finite element simulation,the deformation of commercial probe with flared-tip is analyzed.By tailoring the cantilever shape,the torsional rigidity of the probe reduces and the lateral sensitivity increases.At the same time,a trigger-control method of monitoring both the deflection and torsional deformation is designed to further reduce the lateral force.4.A novel 3D scanning method based on adaptive vector approaching technique is proposed.In this way,the slope of local surface is calculated according to the previous measurement results.The approaching vector of probe is implemented by one doublefeedback control mechnism.As a result,the true 3D topography with uniform pixel density,including horizontal surfaces and opposite sidewalls,can be acquired in a single scanning.5.A 3D-AFM prototype based on flared-tip is developed and verified functionally.This homebuilt apparatus is equipped with a follow-up optical detector as well as a combined 3D scanning stage.Additionally,high-speed electronic controller with multi input/ouput channels and automated GUI are developed respectively.The system noise(RMS)is better than 0.1nm,the scanning range reaches 100μm×115μm×25μm and the repeatability(peak-to-peak)of measurement of the height/width is less than 2.5nm.Finally,true 3D images of the grating standard and the nanoimprint pattern are well obtained using this prototype.