Development of a Discharge Pumped 13 nm Laser for Metrology of Projection Lithography Optics at the Manufacture-Site

摘要

A high power capillary discharge cadmium plasma source was developed to investigate the generation of 13.2 nm coherent radiation for metrology tasks in Extreme Ultraviolet Lithography. Excitation of a capillary channel filled with Cd vapor with a fast current pulse (190 kA, 15 ns risetime) resulted in the successful excitation of 13.2 nm radiation from the 4d ISO-4p 1P1 laser line of Nickel-like Cd (Cd XXI). Spectra of this capillary discharge plasma showed the emission from the 13.2nm laser line is the most intense in that spectral region. Detailed spectroscopic studies confirmed that the observed 13.2 nm line radiation corresponds to the Cd XXI laser line, and identified fifty-five Cd XXI lines in the 12.7-18.4 nm region which constitute a valuable diagnostics to optimize the gain in the 13.2 nm laser line using line intensity ratio techniques. The dynamics and symmetry of the capillary discharge Cd plasma column were also studied using an EUV pinhole camera . The pinhole images show that the plasma column presents a good degree of symmetry up to the time of maximum compression.