Organic gases cause carbon depositions on the multi-layer mirrors by Extreme Ultra Violet (EUV) light irradiations in EUV lithography tool. The dependences on organic gas species, organic gas pressure and EUV light intensity in the carbon deposition were researched in order to understand this reaction. EUV light was irradiated on a (Si/Mo) multilayer mirror sample injecting organic gas like buthane, buthanol, methyl propionate, hexane, perfluoro octane, decane, decanol, methyl nonanoate, diethyl benzene, dimethyl phthalate and hexadecane. X-ray photoelectron spectroscopy measurements revealed that organic gases with heavier molecule weight or higher boiling temperature caused faster carbon deposition rates. Carbon deposition rates increased linearly with organic gas pressures. Dependence on EUV light intensity was estimated from comparisons between an EUV light profile and carbon distributions on irradiated samples. Carbon deposition rates increased rapidly, but became saturated at higher EUV light intensities. Three chemical reactions, an adsorption, a desorption and a carbon deposition by EUV light irradiation, were taken into account to explain the behavior of the carbon deposition. Electron irradiation on a mirror sample revealed that photoelectrons emitting from the mirror surface played an important role in carbon deposition.
Determination of bonding structure of Si, Ge, and N incorporated amorphous carbon films by near-edge x-ray absorption fine structure and ultraviolet Raman spectroscopy
It is very important to mitigate oxidation of multilayer mirrors (MLMs) and carbon deposition onto MLMs to extend the lifetime of EUV exposure tool. In order to estimate the lifetime, we have to figure out scaling law. Previous results at EUVA have shown that carbon deposition rate on MLMs is not proportional to every hydrocarbon partial pressure and every EUV intensity 3-4 . In this study we focused on carbon deposition on Si-capped multilayer mirror. We made experiments of EUV irradiation to the MLMs using two different apparatuses. One is connected to a beamline (SBL-2) of synchrotron radiation facility Super-ALIS in the NTT Atsugi research and development center, and the other is connected to a beamline (BL9) of synchrotron radiation facility New SUBARU in the University of Hyogo. As the result of experiments, we found that different carbon deposition rate occurred on the different beamlines, although they have the same average EUV intensity. We present differences of carbon deposition rate on MLMs between two different beamlines and estimation of carbon deposition rate on EUV tool analyzing dependences of carbon deposition rate on characteristics of EUV source.
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