A quite simple numerical model for the wave-optical simulation of the interference in a grating lateral shearing
interferometer with a periodic light source and a large lateral shear is presented. Aberrations of the collimating lens will
generate a spatially varying modulation in the interference pattern. The model assumes that the light source itself is
completely spatially incoherent so that only the light from each point of the light source has to be propagated wave-optically
through the optical system. Then, the intensity distributions of all light source points in the detector plane can
just be added. The simulations are compared to theoretical calculations of partial coherence theory and also to
Mostly, the typical light distribution of a light source, as a LED or an excimer laser, is not suitable for the application. The excimer laser beam for example shows a distinct elliptical Gaussian profile. As another example the layout of the light emitting chip and the reflector of a LED form an extremely inhomogeneous luminescent area. To achieve a better adapted beam profile a homogenizing setup with beam shaping qualities can be used. In this talk two setups for homogenization with the help of refractive micro lens arrays are shown and compared. The main attention is turned on the influence of the numerical aperture of the micro lenses, the limitations due to the spatial coherence degree and the difficulties of the alignment of the systems. In addition, a diffractive solution of homogenization for spatial partially coherence is presented.
The physical limits of optical lithography are mainly determined by the aperture of the mask projection system and the wavelength of the light. In addition to the wavelength shift to the deep UV the application of special techniques to improve the processing window are required. This has furthered the application of the phase shift mask as a lithography tool. The generation of the exact intensity distribution needed in the plane of the wafer strongly depends on the accuracy of the phase shift introduced by the phase shift mask. However, one difficult issue is the reliable measurement of the phase shift introduced by the phase mask at the working wavelength. This is of course mainly due to the lack of suitable and simple interferometric devices for the deep-UV-region -- here 193 nm. We propose the use of a diffractive shearing interferometer as a way out. By combining two Ronchi-phase gratings it is possible to produce shear and phase shifts for the evaluation of the fringe patterns simply by axial and lateral shifts of the phase gratings relative to each other. Since the excimer laser emits spatially partial coherent light only the coherence issue is one of the physical problems dealt with in our experiments. The state of the art of our experiments so far reached will be presented.