Study On The Magnetic Field Auxiliary Direct-current Sputtering Method On The Inner Surface Of Tubular Workpiece

During scientific research and production practice, the demand that the inner surface of tubular workpiece is working face is more and more. It is well known that deposition thin film on the inner surface of tube can significantly improve the performance of the workpiece, but it is very difficult to coat thin film in the inner wall of long-thin tube. In this paper a variety of previous coating methods are comprehensive reviewed, and an improved coating method is introduced. The improved coating method is magnetic field auxiliary direct-current sputtering method. In this coating method magnetic field is provided by excitation coil, which can control the sputtering range. With the movement of excitation coil along the tube, homogeneous thin film is deposited.In this paper, research method includes two parts, numerical simulation and experimental analysis. At first, the magnetic field distribution in the sputtering region was simulated and measured, in order to obtain the optimal length of the excitation coil. The simulation results obtained by COMSOL software were consistent with the trend of the actual measurement value. The magnetic flux density distribution in a large range of the tube (the tube length3/4) is uniform. The excitation coil length should not be too long, for controlling the discharge range. Secondly, the electric field distribution in the sputtering region was calculated. It was found that the electric field distribution was the field, and the trajectory of electron in the electromagnetic field was spiral line. Thirdly, the minimum diameter of the coated tube used in this experimental device should be greater than6mm, considering the trajectory of electron in the electromagnetic field and characteristic lengths of the magnetron glow discharge. Finally, the effects of magnetic flux density, cathode voltage and working pressure on plasma potential distribution and charged particle density distribution simulated by XOOPIC software in the discharge region. The simulation results illustrated that the magnetic field was obviously constraint of the charged particles, and weakening magnetic flux density or decreasing working pressure, the target discharge voltage could increase.In this project, the author designed and manufactured the tubular workpiece inner surface magnetic field auxiliary direct-current sputtering system. After commissioning the equipment runs well, under the conditions that magnetic flux density0-0.035T, discharge power2W to75W, discharge current7mA to180mA and discharge voltage range300V to450V.In this paper, with the designed magnetic field auxiliary direct-current sputtering system, the experimental study on sputtering Cu film on the inner surface of a stainless steel tube (inner diameter the Φ28mm length160mm) was carried out, and the in the inside surface of the of, and plasma optical emission spectroscopy (OES) was used to diagnose the coating process. The experimental results show that when the negative bias volt of the cathode target is higher than400V, the working pressure is less than2Pa and magnetic flux density is less than200G, Cu324.7nm line is obvious. At the same time, with higher working pressure, weaker magnetic flux density or negative bias volt of the cathode target less than400V, Cu324.7nm line is not obvious.The optimum operating parameters of the designed coating system are:the working pressure1.5Pa, magnetic flux density150G, the discharge voltage of430V, Power30W, the target power density10W/cm2.