Study Of Double Hollow Cathode Discharge And Preparation Of Cu Thin Film On The Inner Surface Of Slender Tube

It has always been a difficult problem to conduct plasma surface modification treatment on the inner surface of slender tubes,because the inner diameter of the tubes is too small to transport plasma into the inner shell of the tubes.To solve this problem,a method using RF coupled DC hollow cathode discharge was proposed in this paper.Cu thin films were deposited in the treated tubes with length of 200 mm and inner diameter of 6?12 mm.In this paper,the plasma characteristics of the hollow cathode discharge near the planar workpiece and the inner slender tube were studied.The Cu films were deposited on the planar workpiece and the inner surface of the slender tube at a fixed point.The influence of the processing parameters on the structure and properties of the Cu films was studied.A phenomenon of secondary hollow cathode discharge(double hollow cathode discharge)was found in the experiment of this paper,and the influence of technological parameters on the excitation voltage and substrate current of secondary hollow cathode discharge was studied.The results of the research on the plasma characteristics of the radio frequency hollow cathode discharge show that the plasma density of the radio frequency hollow cathode discharge near the flat workpiece is lower than the plasma density under the confinement condition in the slender tube;the higher the coupling DC voltage and RF power,the higher the plasma density from hollow cathode discharge no matter whether it is confined.The intermediate-frequency voltage applied to the treated tube should be higher than 40 V to promote the discharge and atomic ionization in the tube;The hollow cathode discharge is the most intensive when the distance between the hollow cathode tube and the anode rod is 12 mm and the inner diameter of the treated tube is 10 mm,Research on the plasma characteristics and substrate current of the secondary hollow cathode discharge shows that when the intermediate-frequency voltage reaches a certain critical value,the treated tube around the discharge area can produce a secondary hollow cathode discharge between the hollow cathode and the anode rod.The plasma density in the treated tube and the peak substrate current is increased.After turning off the RF power supply,the intermediate-frequency power supply can still maintain the discharge steadily at a voltage that cannot ignite discharge itself.The lower the intermediate-frequency voltage,and the higher the coupled DC voltage,the higher the excitation voltage required for igniting secondary hollow cathde discharge.The higher the intermediate-frequency voltage,the higher the coupled DC voltage,and the lower the gas pressure,the greater the increase in the peak current of the substrate caused by the secondary hollow cathode.By using a radio frequency coupled DC power supply,Cu film with good bonding strength was successfully deposited on the surface of a 304 stainless-steel sample with size of 30mm×30mmand and of a slender 304 stainless-steel tube with the length of 200 mm and inner diameter of from 6 to 12 mm.The analysis results of XRD,SEM,AFM,etc.demonstrate that the Cu film prepared by radio frequency hollow cathode discharge is featured by a typical face-centered cubic structure and grows preferentially along the normal direction of the crystal plane(1 1 1).The higher the coupled DC voltage,the greater the thickness of the film,the lower the surface roughness,and the greater the wetting angle between distilled water and the film at room temperature.The maximum film thickness(about 1.7 ?m)with lowest surface roughness and largest the wetting angle has been achieved with the distance between the anode rod and hollow cathode of 12 mm and the inner diameter of the tube of 10 mm.