Imaging Modes of Confocal Scanning Microscopy.

Available from UMI in association with The British Library. Requires signed TDF. The long term aim of the work carried out during the course of this thesis is to prepare the ground for the use of the scanning optical microscope for on-line micrometrology. The current resolution requirements in this area are right at the very limit of the performance of conventional microscopes. The theory of auto-focus and extended-focus imaging modes is presented and applied to the technologically significant structure of a straight edge with a coincident step change in both reflectivity and height. The range imaging mode, which is essentially a different representation of surface profilometry data, is also discussed. The effects of various imperfections in practical systems in use are explored for the case of a confocal microscope. This forms a major part of the work described in this thesis. Misalignment of the pinhole and its effect on both lateral and axial responses is investigated in detail. The bearing of the pinhole size on the behaviour of the microscope is analysed in depth and theoretical predictions are compared to experimental results. Images are presented illustrating the role of pinhole size in determining the axial response and the effects of flare light. Aberrations of the optical systems are considered theoretically with extensive checking of the theory derived against actual data. Primary aberrations are examined both individually and in combination. In particular, experimental results of the effects of such aberrations as detector pinhole size varies are presented. Two techniques are presented for imaging objects with significant detail available only as phase information. One involves stopping down the collector lens of the microscope. The other is a novel imaging mode which when applied to the confocal scanning optical microscope produces differential phase contrast or differential imaging while maintaining the optical sectioning property. Both of these techniques have the advantage that, unlike interferometric techniques, they are relatively easy to set up. Results are presented both using a biological specimen and an integrated circuit. Much of the work in this thesis is equally applicable to biological structures, many of which contain detail which is close to the resolution limit of the system used here. Finally, the properties of a number of pupil plane filters on the imaging performance of both conventional and confocal microscopes are examined. Theoretical results are derived and experimental data presented.