| Vertical scanning white light interferometry is significant in surface topographymeasurement. Based on the vertical scanning white light interferometry developed by thelab, some research on the key techniques, such as light source optimization, expand of thevertical measurement range, topography recovery algorithm and etc., is done to improve theperformance of the measurement system.The system employs a white LED as the illumination source and Mirau interferencemicroscope as the interference device. A diffraction grating measuring unit is introduced torealize the real-time displacement measurement. PZT is used to achieve the verticalscanning and interference fringe is captured by CCD.In consideration of the impacts of numeric aperture of objective and specific sourcespectrum, a computationally efficient method to simulate the interference signal for verticalscanning interferometry is proposed and through comparison with experimental results toverify the accuracy. Through this method, the interference signal caused by a white LED, ared LED, a blue LED and hybrid light source is simulated and compared to the results ofexperiments, which makes an optimization for the selection of light source.Cooperated with stepping motor and PZT, it realized the coarse-fine level scan andaccurate positioning in a large range, which overcomes the disadvantage of PZT. Thediffraction grating measuring unit is utilized as the metrology system for both the steppingmotor and PZT and achieves real-time feedback. Experiments are conducted to verify thefeasibility by making a comparison with the results of dual-frequency laser interferometer.At last, topography recovery algorithms are discussed. Study the accuracy of thesealgorithms through simulation. According to the specific characteristics of interferencesignal produced by white light LED, propose a method to improve the envelope curvefitting algorithm and experiments on the single scratch sample are conducted to verify theaccuracy and repeatability. |
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