New Results from DUV Water Immersion Microscopy Using the CD Metrology System LWM500 WI with a High NA Condenser

New results using the world's first optical DUV mask CD (critical dimension) metrology system based on water immersion (WI) technology (Vistec LWM500 WI) are presented. In order to improve repeatability and linearity, especially for feature sizes smaller than 300 nm, a new condenser with an increased numerical aperture (NA) was integrated and qualified. Comparative investigations between the previously used 0.55 NA condenser and the new 0.8 NA condenser are shown and the resulting improvements by the high NA condenser are discussed. This report focuses on results obtained on ArF half tone phase shift masks which are more critical than KrF half tone or binary masks due to the mismatch between measurement and exposure wavelengths.