Titanium Nitride Coating of RF Ceramic Windows by Reactive DC Magnetron Sputtering
Résumé
LAL-Orsay is developing an important effort on R&D and technology studies on RF power couplers for superconductive cavities. These are complex and high technology devices due to their basic functions: vacuum and temperature separation form the environment to the cavity. One of the most critical components of high power couplers is the ceramic RF window that allows the power flux to be injected in the coaxial line. The presence of a dielectric window on a high power RF line has in fact a strong influence on the multipactor phenomena, a resonant electron discharge that is strongly limiting for the RF components performances. The most important method to reduce the multipactor is to decrease the secondary emission yield of the ceramic window. Due to its low secondary electron emission coefficient, TiN thin film is used as a multipactor suppressor coating on RF ceramic coupler windows. In the framework of the EU program FP6 the LAL-Orsay and the LNL-Legnaro establish a collaboration to develop a coating bench that takes into account the different strong constraints on stoechiometry and film coating thickness given by coupler operating conditions. Reactive magnetron sputtering technology was chosen to obtain such deposit. A full description of a sputtering bench recently installed in LAL, and its main characteristics are given. Stoechiometric TiN films are obtained by optimization of reactive gas flow (N2), for a given bias and a given ionisation gas flow (Ar). XRD analysis was performed to control film composition. From the data obtained, lattice parameter is calculated for each deposit and film stoechiometry is determined. XPS analysis of stoechiometric film had shown the existence of oxygen and carbon mainly in the surface. However, it shows also that the ratio Ti/N in atomic percentage is equal to 1.
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