| With the continuous progress of advanced manufacturing technology,micro nano scale processing technology and process represented by ultra precision machining technology,lithography technology,micro optics technology and MEMS technology have developed rapidly.The key factor affecting the performance of micro structure devices is the micro surface morphology and structure characteristic size.Generally,the resolution of measurement instruments is required to be nanometer,and the measurement range is tens of microns,which objectively puts forward higher requirements for the existing measurement methods and means.Focusing interferometric confocal microscopy plays an important role in the field of micro surface topography measurement.Compared with the phase-shifting interferometry,this method solves the problem that the height of the adjacent point to be measured must be less than λ/4 Compared with confocal measurement,it gets rid of the limitation of resolution by numerical aperture,so it is of great significance to study this technology.The research content of this topic is divided into the following points(1)Aiming at the problem that the amplitude of interference signal gradually decays with the increase of defocusing distance,which affects the accuracy of interference measurement,the measurement principle of focusing synchronous phase-shifting interferometry is deeply studied.Firstly,the necessity of using four channel phase shifting interferometry in focusing interferometry is demonstrated.According to the knowledge of geometrical optics and Marius law,a positive and negative defocusing interference model is established with defocusing distance as independent variable and interference intensity as dependent variable.Through simulation and experiment,the effects of defocusing distance,lens numerical aperture and aperture size on interference intensity are analyzed;At the same time,it is proved that the single channel defocusing model can still be used for four channel phase-shifting interference with grating.(2)The heterodyne confocal interferometric fusion measurement system is designed and analyzed.Firstly,aiming at the problem of mutual coupling between focusing interference and confocal subsystem measurement signals,a variable area detection method of focusing interference confocal subsystem is proposed.It is demonstrated that the influence of mutual coupling between interference and confocal subsystem can be removed by using CCD as detection device and selecting different areas for interference and confocal subsystem to calculate light intensity,According to the designed measuring device,the measurement steps of fusion measurement and the process of variable area detection by CCD are given.Secondly,the error of the focusing synchronous phase-shifting interferometry system is analyzed,and the influence of the light intensity and the phase-shifting error on the final phase measurement is analyzed.According to the theory of grating and focusing interference,the size of the aperture is obtained;Through error analysis,the allowable value of X or Y direction installation offset is 0.04mm;The angle difference between two adjacent polarizers is 45°± zero0.9°,The tilt angle of the whole phase-shifting array is less than 16°(3)The experimental device of focusing synchronous phase-shifting interferometry is built,and the principle experiment,system performance index experiment and variable area detection experiment are carried out.The experimental results verify the focusing interference model.For the measurement objective with the equivalent numerical aperture NA = 0.02,the focusing interference model is established ± three hundred μ The amplitude attenuation of the interference signal is reduced from 83.2% to 19.0%.The serious problem of optical signal attenuation is effectively suppressed;The theory of soft pinhole variable region detection proposed in this paper is verified by the contrast experiment of focusing synchronous phaseshifting interferometry.The experimental results show that the performance of the system is in the range of [-300μm,+300 μ m],The nonlinear error is within 10nm;The stability of the system shows that the standard deviation within 2min is 2nm and that within 4 min is 4nm;The repeatability is 3 nm and the axial resolution is 5nm. |
