This paper describes the use of the KLA STARlightTM 300 inspection system for advanced photomask manufacturing and development. STARlight's combination of state-of-the-art defect detectivity and high speed helps to streamline final mask inspection and improve product quality. For advanced development, previously undetected defects can now be identified, their effects on printability can be quantified, and strategies to eliminate them can be implemented.
With the increased resolution of today's lithography processes, reticle pinhole defects are much more printable. Measuring the size of small pinholes using the current SEM method often produces erroneous results when compared to pinhole energy transmission. This is mainly due to the fact that SEMs do not accurately account for edge wall angle and partial filling which can dramatically reduce the pinhole transmission and subsequent printability. Since reticle inspection tools, like wafer steppers and scanners, use transmitted illumination, pinhole detection performance based upon top surface SEM defect sizing is often erroneous for small pinhole diameters.This study first uses simulation to predict printability. Then, a pinhole test reticle is developed with a variety of sub-200nm pinholes. The reticle pinholes are measured with an improved method incorporating transmission and imaged to wafer in order to assess printability.
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