Light wave measurements make circuits better

Talk about precision. New measurements of key wavelengths of ultraviolet light — down to a few millionths of a nanometer — are among the most precise ever reported and are improving calibrations of microlithography tools used in making integrated circuits such as those in computer chips.

The dimensions involved are 10,000 times smaller than hydrogen atoms, the smallest of all atoms.

To make the measurements, physicists at the National Institute of Standards and Technology (NIST) used a spectrometer so sophisticated that it is one of only five of its kind in the world, two of which are at NIST. The spectrometer, which separates and detects specific wavelengths of light radiation, provides 10 times better resolution than similar instruments used in calibrations for highly demanding applications such as the Hubble Space Telescope. The work is reported in the February issue of the Journal of the Optical Society of America B.

The scientists measured the wavelengths of light emitted by excited atoms of iron, germanium and platinum. These elements are used as reference standards for calibrating argon flouride (ArF) excimer lasers, among the latest tools for printing integrated circuits on silicon wafers. ArF lasers are tunable over a range of approximately 0.7 nanometer (nm) centered at 193.4 nm. Precise calibration ensures that the laser light is focused properly to produce the desired circuit patterns. Improved calibrations are expected to help the semiconductor industry make circuits smaller.

The measurements were partially funded by Lambda Physik, a major supplier of lasers for microlithography applications. The results have been incorporated into commercial laser systems.