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The challenges and the possibilities of colour image inspection are discussed from the viewpoint of optical imaging theory. Object models for 3-D wafer structures and faults were developed to realize test wafers and their imaging as a simulation tool. Coloured images are generated to analyse the colour properties of such structures and faults.

The influence of the new methods of superresolution lithography on resolution limit and DOF is discussed for line and space structures. It could be shown that SHRINC, CQUEST, optical filtering and Levensons method cannot increase the optical resolution limit, but that they differ in transferable contrast and the influence of defocus.

From the viewpoint of partially coherent imaging theory we discuss the possibilities of modern optical methods in superresolution lithography for imaging of isolated structures. It could be shown that small isolated structures are nonresolved structures in the understanding of optical imaging theory. They can be described approximately by point objects. This results in a nearly plane-wave illumination of the pupil plane, so that the image intensity is mainly determined by the special filter function.

Optical filter methods are used to enhance images with the aim of succesful digital image processing. A theoretical model of a spike defect is carried out to interprete and to demonstrate experimental results.

From viewpoint of partially coherent imaging theory we discuss resolution and depth of focus for L/S-structures and isolated structures. It could be shown that it is not possible to increase the transferable frequency for L/S-structures. The effect of resolution improvement for L/S-structures is caused by a contrast enhancement only. For isolated structures the pupil transmission is mainly responsible for the intensity distribution on the wafer.

Starting from the spatial frequency spectra of phase-shift structures sufficient filters are derived to enhance the resolution and the contrast of line imaging in photolithography. It is shown, that common mask structures in connection with suitable filters yield similar results like phase-shift techniques.

A model of deep groove structures as alignment marks in photolithography is proposed. The influence of coherence and aberrations like defocus and coma as well as the influence of the nonplanar resist is included. It is shown, that the image intensity of such alignment marks is mainly determined by the shape of the resist surface.

Three-dimensional transparent wafer structures can be modelled best using BPM. Then the image intensities are calculated for three waveleghths to discuss the colour properties in the image. Additionally the influence of sampling is analysed for CD- and overlay measurement by the help of simulated test wafer structures.