Research On Heterodyne Interferential Displacement Measurement Of Scanning Probe System

As the development of high-density and high performance of the electronic industry,it is needed that the surface of the component has nanometer-level accuracy.In this dissertation,microprobe scanning and dual-frequency laser heterodyne interference were combined to measure the ultra precision surface detection at nano-scale.The micro-probe was used to improve the lateral and normal resolution.In this dissertation,the domestic and foreign surface inspection methods and the measurement of the probe vibration signals were summarized and compared.Based on this,the scanning probe heterodyne interferometric displacement detection system was proposed.This dissertation represents the overall plan of the measurement system and the frame of subsystems.The measurement system is composed of four parts: the micro-probe system,the laser measurement system,the data acquirement and feedback system and the sample scanning system.The scanning micro-probe is used to sense the scratch of the sample and is deflected because of the atomic force between it and the sample.As the sample is moved beneath the micro-probe vibrates near its resonant frequency and laser is focused on the back of it,then reflected to the detector to get the amplitude.When the sample is scanned,firstly,the sample is kept in the same position as the imaging working point.Then,Change in amplitude due to the unevenness surface of the sample,the amplitude of the probe is measured by the dual-frequency interference system,and the profile information of the sample is obtained.Based on the the analysis of the probe vibration signal,the fundamental frequency can be used to characterize the change of the displacement of the probe,and the second harmonic is generated due to the probe-sample contact.The dissertation establishes the nonlinear equation of probe-sample vibration,simulates the variation of amplitude with probe-sample distance,In the area of repulsion,the variation of the amplitude changes linearly with the decrease of the probe sample distance.In this dissertation,the thermal noise analysis method is used to study the characteristics of the probe vibration system.The driving voltage can control the distance between probe-samples,on this basis,we can get the amplitude rule of scanning probe.When the voltage value is 1.44 V,the amplitude of the vibration signal changes linearly with the voltage,and the linearity reaches 0.9463.The 1.44 V voltage can be used as a pre-set point to realize ultra-precise surface nano-scale topography measurement.