Research of Nanometer White-light Phase-shifting Interferometry and Instrumentation Used for Micro-surface Topography Measurement
|Keywords||Micro-surface togography White-light phase-shifting interferometer Mirau interferometer Central obscuration Numerical aperture Piezoelectric Transducer (PZT)|
The exit various methods used to measure the micro-surface topography andphase measurement methods in optical interferometry are described. The researchfocus and tend are introduced. A vertical-shaft-type Mirau white-light phase-shiftinginterferometer is developed based on white-light phase-shifting interferencemicroscopy. The interferometer is composed of the interference imaging andillumination part, Piezoelectric transducer (PZT) in the vertical direction,two-dimensional scanning part in the test surface, image capture and interferogramsanalyse part.The model for white-light interference microscope is developed and the spectrumwidth condition for white-light interference and monochrome interference is derived.The two-wavelength measurement and synthetic source measurement are analyzed.The Mirau interference objective is optimized developed based on infinity tubemicroscope structure. The interference intensity is balanced and the influence ofcentral obscuration by reference surface on the system performance is investigated.The reflected self-collimated structure is adopted in the illumination system. The twodimensional scanning are realized by the movement of precision motorized stage. Themicrocontroller serial circuit to control the step-motor is completed. The LED(light-emitting diode) constant current drive circuit and the mechanical structure areaccomplished. The sensitivities of different phase-shifting algorithms to thephase-shifting error and detector nonlinearity error are investigated. The numericalaperture effect is analyzed and calibrated. The lateral, vertical resolution andmeasurement range are determined. The surface topography of fiber optic connector ismeasured and the repeatability is less than 2nm.Major innovations of this dissertation:1. The model for white-light interference microscope is developed. Both thenumerical aperture and the spectrum distribution of light source have an effect onthe envelope of interferograms. The spectrum width condition for white-lightinterference and monochrome interference is derived.2. The geometrical optics of Mirau white-light phase-shifting interferometer isresearched. The intensity of the interference pattern is balanced using beamsplitters with different transmission/reflection ratio. The relations of Strehlcriterion, resolution limitation, modulation transfer function (MTF), remainderaberration and effective numerical aperture to central obscuration are analyzed.The numerical aperture correction factor in the Mirau interferometer is obtained.3. The three-dimensional scanning, multi-aperture stitching, two-wavelengthmeasurement and synthetic sources measurement are realized in the Mirauwhite-light phase-shifting interferometer. Three-dimensional scanning iscomposed of two-dimensional motorized stage and vertical dimensionalPiezoelectric transducer. Multi-aperture stitching extends the measurement range.4. The instrumentation of white-light phase-shifting interference microscopy iscompleted. The whole design, component arrangement, optical system,mechanical structure, circuit and soft design in the Mirau interferometer areaccomplished. The surface topography of fiber optic connector is measured.