EUV-induced low pressure hydrogen and H2/Sn plasmas

Abstract

The continuing decrease in feature size in microelectronics fabrication has been enabled by a progressive decrease in the wavelengths for photolithography. The recent deployment of extreme ultra-violet (EUV) lithography systems with photon wavelengths centered at 13.5 nm has enabled feature sizes below 10 nm. One method to produce EUV photon fluxes is to ablate and ionize tin droplets with pulsed lasers. A possible consequence of the ablation is that the resulting tin vapor may coat optical components. By filling the chamber with low-pressure H 2 gas that does not significantly absorb the EUV photons, a low-density plasma is produced by the EUV photon flux that dissociates and ionizes the hydrogen. Tin films on optics can then be etched by H atoms and ions producing stannane (SnH 4 ), which can then be pumped away. In this paper, results from a computational investigation of the plasma formation that occurs by EUV photon fluxes (13.5 nm, 92 eV) passing through low pressure H 2 and tin vapor are discussed. Electron energy distributions produced by the photo-generated primary electrons and the resulting plasma densities are discussed as a function of the background gas pressure, metal vapor and pulse power format.