Contact resonance spectroscopy for on-the-machine manufactory monitoring

A piezo resistive, phase locked loop (PLL) controlled micro tactile measurement system for on-the-machine contact resonance spectroscopy (CRS) mapping of square centimetre-sized areas is developed and characterized. The CRS uses the influence of material parameters like the Young's modulus on the contact stiffness between probing tip and sample surface and thus, the resonance frequency of the in-contact cantilever. Recently, we showed a robust, large-dimension, piezo resistive silicon cantilever (5 mm × 200 μm × 50 μm) with a silicon tip at its free end for tactile probing of high-aspect-ratio geometries and high-speed topography scans (i.e., up to 15 mm/s). For CRS-based layer and material analysis, this cantilever can be excited into resonance by a piezo chip actuator as described in this work. A compact, LabVIEW-controlled, fully automated scanning system using a homemade, μ-controller-implemented software PLL for resonance frequency tracking and out-reading was realized. To verify the measurement principle, analytical modelling was done. Different layer thicknesses of photo resist (PR) on silicon (11 ± 2 nm to 1653 ± 76 nm), point-by-point line scans of material transitions with various Young's moduli (Si-PR-Si), bulk materials and nano-/micro-structures were investigated to validate the system. For optimization of the sensor sensitivity and efficiency, amplitude and phase were analysed under different conditions (contact force, excitation amplitudes). On-the-machine CRS with tools and work pieces can be a valuable method for quality assurance and reproducibility of future industrial manufacturing and just-in-time production.