DBD-based VUV source for advanced photolithography

As the semiconductor industry pushes toward smaller and smaller chip feature size (below 0.1 μm), shorter and shorter wavelengths are sought for the photolithographic process. Here, we present a novel deep UV source based on a high-pressure, cylindrical DBD discharge [1], for advanced photolithography applications. The discharge unit consists basically of a hollow tube made of a dielectric material with two loop-electrodes wrapped around the outside wall of the tube. The discharge is generated inside the tube by means of a 13.56 MHz RF source. For good RF power transfer, an impedance matching network is introduced between the RF source and the discharge unit. Emissions at two wavelengths, 130 nm and 121.6 nm, are of particular interest. To generate 130 nm radiation, argon with a small admixture of oxygen (less than 0.1%) was used. Resonant energy transfer from argon dimers to atomic oxygen allows the emission of oxygen triplet lines around 130 nm [2]. To generate 121.6 nm radiation, neon with a small admixture of hydrogen (less than 0.1%) was used. The hydrogen Lyman-α line at 121.6 nm was emitted via near-resonant energy transfer between neon excimers and H₂, which leads to the dissociation of H₂ and the excitation of atomic hydrogen [3]. Spectra, as measured by a 0.2 m McPherson Scanning Monochromator (1200 G/mm, 0.1 nm resolution), will be presented. The influence of the operating pressure, gas mixture ratio, and the applied RF power on the emission spectra, the emitted optical power, and the stability of the source will be discussed.