In addition to measurements of single structure dimensions for process control of semidonductor devices it is important as well to measure defect densitiy on the whole wafer. By knowing defect density and defect distribution on the wafer there is the possibility to set up compensation strategies for increasing the yield. Most metrology tools are not suitable for such measuring tasks because they are far too slow for achieving a representative sample of the whole wafer. Defectoscopy in contrast to e.g. Scatterometry is able to analyse a multitude of structures simultaneously. Starting point for the method isba microscopic image which of cause yields no resolved structure data if size is below wavelength. However the benefit of defectoscopy is that isolated defects still result in bright or dark pixels in the CCD-image bif certain illumination conditions are fullfilled. The reason for this is, that isolated defects of an otherwise periodic grating cause redistribution of electrical carges in these elementar cells.In order to distinguish between different types of defects, illumination conditions can be varied.bThe response on this variation can be used as a specific defect signature. Defectoscopy images can be calculated with our simulation tool "Microsim" so at the same time a newsemiconductor processes are introduced, procedures to detect new type pf defects are available.

simulated microscopic image of a cross grating including a defect

[1]	S. Rafler; T. Schuster; K. Frenner; W. Osten; U. Seifert: Improvements on the simulation of microscopic images for the defect detection of nanostructures, Proc. SPIE 6922 (2008) 692215