High-repetition-rate lasers for advanced DUV exposure tools

摘要

Abstract: KrF lasers with up to 500 Hz repetition rate and a bandwidth of about 1 pm are in use for DUV-microlithography. Increasing resist sensitivity demands even higher repetition rate in order to allow precise dose control. In some cases step & scan exposure tools apply reflective optics instead of refractive ones. This diminishes the bandwidth requirements by about two orders of magnitude, but a high polarization degree of $GREQ 98% is a basic requirement for the laser light source. Dose control and statistics define the second basic requirement for the laser. A dose accuracy of less than 2% demands small energy increments, i.e., for pulse energy in the 10 to 20 mJ range. Throughput requires 10 to 20 W of average laser power. Therefore, the repetition rate must be in the 1 kHz range. !0