Scatterfield Microscopy and the Fundamental Limits of Optical Defect Metrology

摘要

Defect inspection remains a critical manufacturing challenge due to the competing requirements between throughput and very high resolution. Currently only optical methods provide an acceptable solution, although there are a number of process layers and defect types that cannot be measured adequately. As a result there has been a continued drive to push optical methods to new levels of performance and sensitivity without compromising throughput. In this paper we describe several advanced optical engineering methods that improve resolution and extend optical techniques. Fourier control methods applied to both the illumination field and the imaged field offer the possibility to optimize sensitivity in a conventional or high angle optical system. This combined with polarization control is the current approach to extend conventional techniques. Recent advances that capture and use the full 3-D scattered field have recently been shown to improve detectability by up to nearly an order of magnitude. Although there are throughput costs to 3-D imaging, these costs may be mitigated if the 3-D data used to find best focus are also used in the volumetric analysis. Advances in wavelength scaling and coherence will also be contrast with existing methods.