Use of gas-phase ethanol to mitigate extreme UV/water oxidation of extreme UV optics

Abstract

A technique is described that uses a gas-phase species to mitigate the oxidation of a Mo/Si multilayer optic caused by either extreme UV (EUV) or electron-induced dissociation of adsorbed water vapor. It is found that introduction of ethanol (EtOH) into a water-rich gas-phase environment inhibits oxidation of the outermost Si layer of the Mo/Si EUV reflective coating. Auger electron spectroscopy, sputter Auger depth profiling, EUV reflectivity, and photocurrent measurements are presented that reveal the EUV/water- and electron/water-derived optic oxidation can be suppressed at the water partial pressures used in the tests (∼2×10−7–2×10−5 Torr). The ethanol appears to function differently in two time regimes. At early times, ethanol decomposes on the optic surface, providing reactive carbon atoms that scavenge reactive oxygen atoms before they can oxidize the outermost Si layer. At later times, the reactive carbon atoms form a thin (∼5 Å), possibly self-limited, graphitic layer that inhibits water adsorption on the optic surface.

Assumptions and trade-offs of extreme ultraviolet optics contamination modeling

“…It is imperative to understand and theoretically predict the growth of a carbonaceous layer to prolong mirror lifetime using various mitigation and cleaning techniques. 10,11,12,13 Two different mechanisms cause carbon contamination of the optics. In the presence of EUV radiation, adsorbed hydrocarbon molecules on the surface can dissociate by absorbing photons.…”

Aromatic structure degradation of single layer graphene on an amorphous silicon substrate in the presence of water, hydrogen and Extreme Ultraviolet light

“…To reduce the influence of residual gases -mainly water and hydrocarbons -the pressure is increased to a few Pa, by adding hydrogen [22]. The balance between hydrogen as a reducing agent and water as an oxidizing agent allows a dynamic equilibrium between competing processes to be managed [23]. However, the conditions under which such a balance can be achieved varies from material to material.…”

Metrology Related to the Multilayer Mirrors in an Extreme-Ultraviolet Stepper

“…Each of these reactions would likely depend differently on water vapor pressure, EUV intensity and irradiation dose. Results 4,5 show that the two processes, oxidation and carbon growth, appear to compete and mutually offset the damage done by the other. Even if these were all simple first-order processes, the interaction of the reactants and products could result in non-linear behavior and produce results such as those seen in Figures 2 and 3.…”