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Photomask contamination inspections, whether performed at maskshops as an outgoing
inspection or at wafer fabs for incoming shipping and handling or progressive defect monitoring,
have been performed by KLA-Tencor STARlight systems for a number of design nodes.
STARlight has evolved since it first appeared on the 3xx generation of KLA-Tencor mask
inspection tools. It was improved with the TeraStar (also known as SLF) based tools with the
SL1 algorithm. SL2 first appeared on the TeraScan systems (also known as 5xx) and has been
widely adopted in both mask shops and wafer fabs.
Design rules continue to advance as do inspection challenges. Advances in computer processing
power have enabled more complex and powerful algorithms to be developed and applied to the
STARlight technology. The current generation of STARlight, which is known as SL2+,
implements improved modeling fidelity as well as a completely new paradigm to the existing
STARlight technology known as HiRes5, or simply "H5". H5 is integrated seamlessly within
SL2+ and provides die-to-die-like performance in both transmitted and reflected light, in addition
to the STARlight detection, in unit time. It achieves this by automatically identifying repeating
structures in both X and Y directions and applying image alignment and difference threshold.
A leading mask shop partnered with KLA-Tencor in order to evaluate SL2+ at its facility. SL2+
demonstrated a high level of sensitivity on all test reticles, with good inspectability on advanced
production reticles. High sensitivity settings were used for 45 nm HP and smaller design rule
masks and low false detections were achieved. H5 provided additional sensitivity on production
plates, demonstrating the ability to extend the use of SL2+ to cover 32 nm DR plate inspections.
This paper reports the findings and results of this evaluation.
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