Shape Measurement Technology And Theory Of Confocal Microscopy Based On Medium Layer Scatterring

With the development of ultra-precision manufacturing technology, the level of machining accuracy of component surface improves constantly, and the processing technology of complex micro-structure and macro-free-form surface become mature, meanwhile, the demand of corresponding measurements of these components are put forward. In the measurement of the shape of specimen with high-curved and steep surface, the existing measurement methods based on optical stitching te chnology and mechanical scanning technology introduce much freedom of scan and motion, which not only increases the cost of the instrument, but also restrict the system accuracy. Thus, the accurate measurements of these components are not possible. Moreover, the light signals are blocked by local structure of the specimen when measuring micro structure with high-curved and steep surface, even introducing multi-dimensional mechanical scanning in the measurement system one cannot obtain the local shape of this kind of specimen. Optical imaging and measurement of high-curved and steep surface is one of the challengeable problems to be solved currently in the field of optical metrology.In the subject “Shape measurement technology and theory of confocal microscopy based on medium layer scattering”, imaging mechanism of conventional confocal contour instrument for high-curved and steep surface was studied and shape measurement method based on medium layer scattering confocal microcopy was proposed for high-curved and steep surface measurement. This thesis made deep study for peak extraction localization as well which is a core issue in confocal measurement technology. The main research contents of this dissertation are as follows:Firstly, the mechanisms for imaging high-curved and steep surfaces using confocal microcopy were studied based on the principles of linear Fourier optics and confocal imaging theory. The analysis includes the following points. The limited collection aperture cannot collect enough lights, which lower the theory resolution and signal to noise ratio. The confocal imaging ability for t he smooth oblique reflection sample was analyzed with two aspects, the axial response and three-dimensional transfer functions.Secondly, to solve the problem that the rotation of signal lights normal generated by specular reflection of the high-curved surface leads to the decrease of effective collection aperture, and even no collection ability in the traditional measuring method based on the reflection and diffraction, the shape measurement technology and theory of confocal microscopy based on medium layer scattering for high-curved and steep surfaces was carried out. This method deposits a fluorescent layer with nan scale thickness on the surface to be measured to build an isotropy fluorescent scattering surface and overcome the center normal of signal li ght rotation caused by specular reflection. Thus, the scattering signals that carry the surface location information can always fill the imaging pupil, rather than change with the variation of surface angles. Low resolution and immeasurable problems in measuring high-curved and steep surface are solved. In the case of NA=0.75, the tilt angle that can be measured is up to 88.4°, which is 82% larger than that can be measured using conventional imaging method based on bright field confocal microscopy. At the same time, the thickness errors of medium layer were correct using the shift of axial peak location and expand of axial envelope in confocal axial response with medium layer, so the theoretical rigor of confocal measurement based on medium layer scattering was solved.Thirdly, aiming at extracting peak value location of confocal axial response curve(the common core technology in confocal contour measurement), the sinc2 function axial response model of confocal system with high numerical aperture is analyzed. The availability of sinc2 model is expended from the case in low numerical aperture to high numerical aperture. The sinc2 fitting method is proposed for confocal axial response peak localization based on this model, which can achieve higher precision than Gaussian model in accuracy and efficiency. The height measurement experiment for standard step proved that the consumed time for sinc2 fitting method is 21.3% less than Gaussian function fitting method in average.Lastly, equipment integration of confocal measurement instrument was carried out, which provide approach for profile measurement of high-curved and steep surface samples, and provides technique preparations for developing novel super resolution microscopes as well. Key technology of laser scanning confocal microscopy system and equipment integration was stated. The confocal measurement instrument with mediation layer scattering method was set up, which included the laser beam scanning, the multi-channel laser illumination, the wide spectrum detection, and the wide-field imaging module, etc. The typical high-curved micro structured specimen was tested and analyzed. The scanning imaging and 3D contour test of fluorescent specimen and auto-fluorescence biological specimen were carried out.