Uniformity of Plasma Density and Film Thickness of Coatings Deposited Inside a Cylindrical Tribe by Radio Frequency Sputtering

Plasma surface modification of the inner wall of a slender tube is quite difficult toachieve using conventional means.In the work described here,an inner coaxial radio frequency(RF)copper electrode is utilized to produce the plasma and also acts as the sputtered targetto deposit copper films in a tube.The influence of RF power,gas pressure,and bias voltageon the distribution of plasma density and the uniformity of fihn thickness is investigated.Theexperimental results show that the plasma density is higher at the two ends and lower in themiddle of the tube.A higher RF power and pressure as well as larger tube bias lead to a higherplasma density.Changes in the discharge parameter only affect the plasma density uniformityslightly.The variation in the film thickness is consistent with that of the plasma density along thetube axis for different RF power and pressure.Although the plasma density increases with highertube biases,there is an optimal bias to obtain the highest deposition rate.It can be attributed tothe reduction in self-sputtering of the copper electrode and re-sputtering effects of the depositedfilm at higher tube biases.