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With continuously shrinking device structure sizes the photomask suppliers are facing increasing linewidth metrology control requirements. Therefore it is becoming more and more important for equipment suppliers to provide mask metrology tools capable of measuring 0.5 tm and smaller critical dimension (CD) features with high accuracy and repeatability, while offering high throughput for systems to be used in the production environment. CD measurement results obtained on the Leica LWM 250UV will be presented showing not only the considerably improved resolution power and measurement accuracy but also an extension ofthe linearity range to smaller feature sizes using UV light of 365 nm (I-line) instead of white light for illumination in transmitted mode. Results obtained after a system calibration against SEM measurement data show a further extension of the linearity regime. The higher lateral resolution of I-line compared to white light measurements also leads to a CD range value reduction for long term repeatability.

It will be reported on technical details, present typical measurement results and the performance of new I-line Linewidth Metrology Systems. The Tools represent the latest results of the recently existing co-operation between Leica Microsystems, Wetzlar and MueTec, Munich on the area of High Performance Measurement Tools for CD measurement on photomasks. Up to now only Tools for measurements in the region of visible light (VIS) were available. In contrast to systems with visible illumination, I-line CD Tools basically have a clearly raised optical resolution power. They show essentially better linearity of the calibration curves and considerably better repeatability of measurements on structures in the submicron area, compared with systems which only work in the region of visible light. So now CD measurements on submicron structures can be canied out in a completely new quality. I-line measurement results will be confronted with some results in the region of visible light.

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