Use of Excimer Laser Test System for Studying Haze Growth

摘要

With the use of 193nm lithography, haze growth has increased and become a critical issue for photomask suppliers and wafer fabs. Currently, the industry uses various test methods to measure known contributions to crystal growth, such as ion chromatography of cleaning residues and environmental monitoring in steppers. The understanding of the conditions that create haze is limited to end user photomask lifetime experience, which is gathered under varying environmental conditions. A better method to understand the formation of haze is to create a controlled environment and vary experimental conditions. Once experimental factors are understood, product reliability can be verified through end-user feedback. A custom excimer laser test system capable of 193nm and 248nm wavelengths was built to accelerate haze growth and to better understand haze formation. A photomask is enclosed in a test chamber where the environmental atmosphere and exposure conditions are controlled and monitored throughout testing. The system is used to test various elements important to mask fabrication and use, including materials, mask fabrication processes, and environmental operating conditions. This paper details the investigation of haze performance with commercially available pellicles using controlled environmental conditions and varying exposure parameters, such as pulse rate, energy density, and exposure dose. Using this methodology, the conditions that create haze growth were identified.