Silent discharges for the generation of ultraviolet and vacuum ultraviolet excimer radiation
Excimers, known from electron beam experiments and UV lasers, can also fomi in silent discharges, a discharge type used for large-scale ozone production. In this high pressure non-equilibrium discharge a dielectric barrier leads to the formation of localized short-lived microdischarges. Inside the microdischarge filaments energetic electrons can excite rare gas (RG) atoms which, under appropriate conditions, react to form RG/RG dimers or RG/halogen dimers. With the pure RG dimers Ar2*, Kr2*, Xe2*, their chlorides ArCl*, KrCl*, XeCl* and their fluorides ArF*, KrF*, XeF* a number of narrow-band UV sources can be obtained in the wavelength region between 120 nm and 360 nm. The physical parameters of the microdischarges and the reaction kinetics of excimer formation in silent discharges are discussed. The potential of these new UV sources for industrial UV processing is demonstrated. As an example of an application for such incoherent excimer UV sources structured and large-area metal deposition induced by the 172 nm radiation from a silent discharge in xenon is shown. Patterned thin palladium films could be produced by irradiating a palladium acetate coating through a contact mask. In a second step thicker copper layers were deposited on top of the palladium patterns by an elec@oless plating process.