Plasma distribution in the slender bore excited by coaxial rf electrode

A metal coaxial radio-frequency (rf) electrode has been utilized to produce plasma and deposit the coating onto the inner wall of the tubes. The inner electrode acts both as a plasma source and as a sputtering target to achieve plasma-based IBAD. The non-uniformity of thickness of deposited films and plasma density in the bore has been investigated for tubes with different lengths and inner diameters. The experimental results demonstrate that plasma density is higher at two ends of the tube and lower in the middle section of the tube. The uniformity of plasma density may increase with the inner diameter of tubes increasing, but will decrease with the length of tubes increasing. Copper films have been deposited using this technique and the variation of film thickness agrees with the distribution of plasma density along the bore axis. It is also observed that the uniformity of plasma density is higher than that of film thickness due to diffusion behavior of plasmas.