Techniques And Theories Of Superresolving Phase Shift Confocal Scanning Microscopy And Polychromatic Differential Confocal Scanning Microscopy

Confocal microscopy is a kind of 3D optical microscopy which is useful for measurement of micron and sub-micron structures. It features no sample preparation being required, quick measurement, low cost, no damage to the surface being measured and direct measurement of step profile higher than half wavelength, therefore it has been widely used for measurement of 3D micro-structures in such fields as material science, micron-electronics, optics, bio-engineering and medicine, and it has become an important branch of modern micro-nanometer metrology and measurement science.The instrumentation science and technique can always be further promoted by improving measuring resolution, expanding measuring range and enhancing disturbance inhibiting ability. Because of the improving width precision and the increasing etching depth of curved substrates or large apertures micro-structural elements and the wide applications of micro-structural elements with hybrid or inclusion materials in recent years, modern stereo optical microscopy is expectative pushing forward the compatibility of 3D high resolution, wide measuring range, inhibition of jumping reflectivity disturbance and power drift disturbance of a laser source during a long time scanning process to satisfy the nondestructive measuring requirements for geometrical parameters of micro or sub-micro size profile. However, the compatibility of the above performance parameters of present confocal microscopes is obstructed by the conflicting relation between focal depth expansion of optical scanning objective and improvement of axial detection sensitivity, and the coherent relation between axial detection sensitivity and energy loss of measuring beam. Therefore, it is an urgent and significant subject for the development of modern confocal scanning microscopy to achieve the compatibility of 3D high resolution, wide measuring range and inhibition of non-uniform reflectivity disturbance.The purpose of the study on"Techniques and Theories of Superresolving Phase Shift Confocal Scanning Microscopy and Polychromatic Differential Confocal Scanning Microscopy"is to combine 3D high resolution, wide measuring range and inhibition of non-uniform reflectivity disturbance to provide the key techniques and basic theories for the nondestructive measurement of the micro-structural profile geometrical parameters of the elements with hybrid or inclusion materials, curved substrates or large apertures. The results of study can be further used for the nondestructive measurement of the micro-structural profile geometrical parameters of micro-structural optical elements, large scale integrated circuits, micro optical-mechanical-electronic elements, mechanical elements with micro grooves and light-sensitive chips of infrared detectors. The following are the major issues addressed by this study:Firstly, the study on the globally minimized side lobe control method based on convex function optimization theory is focused on the inhibition of noise in the superresolving process. The modulus of side lobe amplitude is transformed into a convex function through phase rotary transformation and variable replacement, and the order of objective function of filter design is then reduced for minimization of side lobe, so that a superresolving filter design method is given to satisfy the necessary and sufficient condition for the global minimization of side lobe. The sufficiency and preciseness is thus achieved using this method for the design of an N-zone constant annular superresolving filter in the whole complex amplitude definition domain, and the uniqueness of the globally minimized side lobe solution is proved in the analytic process as well.Secondly, a synthetic complex superresolving pupil filter is proposed by establishing the equivalent mathematic models between the phase parameters of phase plates in the synthetic complex filter and conventional complex modulation. The influence of misalignment in the branch optical path for the superresolving effect is analyzed and the superresolving principle is finally proved through experiments. It should be noted that the synthetic complex filter has such advantages as simple structure, high accuracy phase modulation and mass fabrication easy to achieve.Thirdly, superresolving phase shift confocal scanning microscopy is proposed to overcome the principle deficiencies of conventional confocal microscopy, so that the combination of high resolution, wide measuring range and inhibition of non-uniform reflectivity disturbance can be achieved at the same time and expatiated. Such performances and influences as phase shift error, re-confocal position error, axial range expansion, paraxial and non-paraxial applicability and edge position criterion are discussed in detail to discover the basic regularity of axial and transverse response performances. Experiment results indicate that axial resolution is 0.5nm and the comparison error of the line width measurement related to the calibrated width of the standard grating is less than 0.15μm when NA=0.85 andλ=632.8nm.Superresolving polychromatic differential confocal scanning microscopy is proposed at last to overcome the principle deficiencies of conventional confocal microscopy. Axial dispersion is used to construct two independent and alternative working linear ranges. Since inconsistency between the expansion of measuring range and improvement of axial detection sensitivity is overcome, and then the range is doubled without sacrificing of 3D measuring resolution. Additionally, by taking the ratio between the difference and sum values of two defocusing response signals as the confocal response function, the inhibition of non-uniform reflectivity disturbance and ultrahigh axial response sensitivity are both obtained. Experiment results indicate that the axial resolution is 1nm and the comparison error of the line width measurement related to the calibrated width of the standard grating is less than 0.1μm when NA=0.75 andλ=632.8nm.