Wavelength Characterization of a Molecular F2 Laser at 157 nm for DUV Lithography
Craig J. Sansonetti, Joseph Reader
The wavelengths of six spectral lines emitted by a molecular fluorine (F2) laser at 157 nm were measured to high accuracy with the 10.7-m normal-incidence vacuum spectrograph at the National Institute of Standards and Technology. Lines from a Pt/Ne hollow cathode lamp served as wavelength standards. Spectra of the laser and the Pt/Ne lamp were photographed simultaneously through an uncoated CaF2 beam splitter. The optical paths were arranged so as to avoid shifts in line positions arising from possible differences in illumination of the grating by the two sources. The strongest lasing line was found to have a wavelength of 157.63094(10) nm. Changes in wavelength for variations in gas mixture, total gas pressure, and voltage were also measured.