Instrumental aberrations of a parallel-beam diffractometer equipped with a rotating anode X-ray source, a single-reflection collimating multilayer optic and a parallel-plate collimator in front of the detector have been investigated on the basis of standard measurements (i.e. employing stress-and texture-free isotropic powder specimens exhibiting small or negligible structural diffraction line broadening). It has been shown that a defocusing correction, which is a major instrumental aberration for diffraction patterns collected with divergent-beam (focusing) geometries, is unnecessary for this diffractometer. The performance of the diffractometer equipped with the single-reflection collimating multilayer optic (single-reflection mirror) is compared with the performance of the diffractometer equipped with a Kirkpatrick-Baez optic (cross-coupled Gö bel mirror) on the basis of experimental standard measurements and ray-tracing calculations. The results indicate that the use of the single-reflection mirror provides a significant gain in photon flux and brilliance. A high photon flux, high brilliance and minimal divergence of the incident beam make the setup based on the single-reflection mirror particularly suitable for grazing-incidence diffraction, and thus for the investigation of very thin films (yielding low diffracted intensities) and of stress and texture (requiring the acquisition of large measured data sets, corresponding to the variation of the orientation of the diffraction vector with respect to the specimen frame of reference). A comparative discussion of primary optics which can be used to realise parallel-beam geometry shows the range of possible applications of parallelbeam diffractometers and indicates the virtues and disadvantages of the different optics. research papers J. Appl. Cryst. (2008). 41, 124-133 M. Wohlschlö gel et al. Single-reflection collimating multilayer optic 125

The effect of lens aberrations on the process windows of a 248nm stepper is presented for multiple locations within the exposure field and for various illumination conditions. It is shown that the effect on the process window depends on the field location and the illumination condition. The common process window for multiple field locations is significantly reduced from the single location result. Process window data obtained with one illumination condition is shown to be useful in predicting results with other illumination conditions.

No abstract