Electron impact-assisted carbon film growth on Ru(0001): Implications for next-generation EUV lithography

Carbonaceous deposits produced on Ru-capped multilayer mirrors under extreme ultraviolet (EUV) irradiation in the presence of adventitious gaseous hydrocarbons are a major obstacle to process implementation of EUV lithography, the key to fabrication of next generation semiconductor chips. The technical problem has been simulated by examining graphitic film growth on Ru(0001) under low-energy electron irradiation in the presence of 1-butene, C5-C8 linear alkanes, and toluene. We show that this provides a practical and reliable means of simulating the photon-induced chemistry and of distinguishing between benign and harmful species. Linear alkanes up to n-heptane are relatively benign, whereas n-octane and toluene are much more harmful, giving rise to rapid growth of graphitic films of a thickness sufficient to seriously impair mirror reflectivity. 1-Butene exhibits behavior in between these extremes. These properties may be understood in terms of the surface residence lifetimes of the various adsorbates on graphitic surfaces.