Design, analysis and application of confocal self-interference microscopy

Abstract

Confocal microscopy has been widely used in many research and industrial applications due to its optical sectioning ability and higher resolution. It has been usually used in the biomedical researches, but nowadays it is also applied to the industrial applications, such as inspection of semiconductor circuits and measurement of critical dimensions of nano-patterned surfaces. Confocal microscopy has advantages over atomic force microscopy or electron microscopy: real-time scanning speed, no need of preprocessing of specimens, non-contact style of measurement, and cost-effectiveness. In confocal microscopy, the lateral resolution is limited by the diffraction effect. There have been several researches done on the improvement of the lateral resolution in confocal microscopy. Though some confocal microscopes in fluorescence mode have achieved the ultimate resolution of the far-field light microscopy on the order of several 10 nm, these microscopes can not be used in the reflection mode, which is widely used in the industrial metrology. In reflection mode, some confocal microscopes have improved the resolution by using the pupil plane filters. However, the improvement obtained by these methods was not large, or there were significant sidelobes generating artifacts in images. In this thesis, confocal self-interference microscopy (CSIM) is proposed to enhance the lateral resolution. CSIM uses the self-interference optics in the detection optics. The self-interference optics is composed of two polarizers crossed to each other, and a calcite plate. Since the calcite is a birefringent material, the entering beam splits into two perpendicularly polarized beams, which have different optical path lengths to each other. This difference of optical path length generates the optical path difference between two beams, and this optical path difference is a function of the incidence angle on the calcite plate. And the incidence angle is proportional to the object coordinate in the...