Studies on the optimisation of unbalanced magnetron sputtering cathodes

The optimisation is reported on the design of unbalanced magnetron (UBM) sp uttering cathodes. For the study, a planar circular cathode backed by a dou ble-coil electromagnet (compatible for a 100 mm diameter target) was develo ped. The variation of the structure and strength of the magnetic field in f ront of the target was investigated for different current combinations in t he electromagnetic coils, and its effect on the sputtering process was anal ysed. The observations on the magnetic held geometry revealed some interest ing features, such as the balancing point of the fields along the axis (nul l-point), and the zero axial region over the target surface (B-z = 0 ring). The positions of both could be controlled by adjusting the ratio of the el ectric current in the coils. The magnetic field null-point could be used as a reference for the region of homogeneous film growth. The B-z = 0 ring wa s the location where the glow discharge concentrated (or where the maximum target erosion occurred). The diameter of the ring determined the area cove red by the discharge and thus the sputtering efficiency. The optimum substr ate position can be fixed according to the position of the null-point and o ptimisation of sputtering can be achieved by adjusting the diameter of the B-z = 0 ring. The results of this study should be helpful in the designing of an ideal UBM using permanent magnets as well as electromagnets. (C) 1999 Elsevier Science Ltd. All rights reserved.