The compact excimer laser - light source for optical (mask) inspection systems

摘要

The discharge pumped excimer laser is a gas laser providing ultra violet (UV) radiation with well defined spectral, temporal and spatial properties. The fast development of excimer lasers in recent years has succeeded in designing very compact, turn-key systems delivering up to 10 W of radiation at 248 nm (5 W at 193 nm and 1 W at 157 nm) with repetition rates up to 1000 Hz [1]. Experimental data on important beam properties of excimer lasers hi the field of mask inspection are being presented and discussed. Relevant parameters are spectral bandwidth, energetic pulse-to-pulse stability, pulse duration, beam pointing stability, beam direction stability, beam dimension, beam profile and coherence. We will compare the excimer laser with lamp sources and continuous wave (CW) lasers in the framework of these parameters. The discussion will show future opportunities of compact excimer lasers in optical inspection as well as in mask writing systems, improving resolution and throughput.