Research On The Key Techniques Of Virtual Probe Based On Standing Wave

Nondestructive measurement of microscale features remains a challengingmetrology problem. With the development of industrial technology, for the highaspect ratio small hole, not only the inside diameter drops and the depth increases,but also the improves of measurement accuracy. Generally, to assess a high aspectratio small hole it is currently common to cut a cross section and stretch the probeinto the hole. For the first method, we usually measure the features of interest usingan atomic force microscope, scanning probe microscope, or scanning electronmicroscope. Typically, these metrology tools may be suitable for surface finishmeasurement but often lack the capability for dimensional metrology. For the secondone, the miniaturization of the probe is the main challenge to restricted theapplications of this way.The aim of this article is to discuss the development of a high aspect ratiomicroscale probe for measurement of microscale features. A200:1high aspect ratioprobe shank is fabricated with a7μm diameter, and attached at one end to anoscillator. The oscillator produces a standing wave in the oscillating probe shank asopposed to conventional probes that use a microscale sphere on the end of acomparatively rigid shank. As a result of the standing wave formed in steady statevibration, the free end of the shank generates an amplitude of oscillation greaterthan the probe shank diameter. Thus, the probe does not require a spherical ball toserve as the contact point and simply uses the contact diameter of the free end of thevibrating shank. This methodology is referred to as a virtual probe tip. The diamaterof the virtual probe tip is20μm~60μm.The theory of standing wave and the sensor mechanism of virtual probe arepresented in this article. Aimed at the tunning fork oscillator, we have researched themethod to make a virtual probe and to improve the performance of the probe sensor.A drive and detecting circuit are designed and a16-bit resolution data acquisitionsystem is employed to load data while maintaining bandwidths about500Hz.Through the experimental, the resolution of the data acquisition system is0.153mV.A piezoelectric actuator is used to test the performance of the probe, and the inside16-bit resolution capacitive gage is used to monitor the motion of the translator.Through the experimental demenstration of the performance of the virtual probesensor, its spatial sensitivity is45.7mV/μm and its spatial resolution is35nm. Therepeatability of the virtual probe is0.16μm.Furthermore, adhesion problems often encountered with micrometer scaled probes were not observed during measurements with this virtual probe which gives agood solution to the adhesion problem.