翻译(非平衡磁控溅射阴极的优化研究)

Studies on the optimisation of unbalanced magnetron sputtering cathodes Abstract

The optimisation is reported on the design of unbalanced magnetron (UBM) sputtering cathodes. For the study, a planar circular cathode backed by a double-coil electromagnet (compatible for a 100mm diameter target) was developed. The variation of the structure and strength of the magnetic field in front of the target was investigated for different current combinations in the electromagnetic coils, and its effect on the sputtering process was analysed. The observations on the magnetic field geometry revealed some interesting features, such as the balancing point of the fields along the axis (null-point), and the zero axial region over the target surface (Bz=0 ring). The positions of both could be controlled by adjusting the ratio of the electric current in the coils. The magnetic field null-point could be used as a reference for the region of homogeneous film growth. The Bz=0 ring was the location where the glow discharge concentrated (or where the maximum target erosion occurred). The diameter of the ring determined the area covered by the discharge and thus the sputtering e¦ciency. The optimum substrate position can be Þxed according to the position of the null-point and optimisation of sputtering can be achieved by adjusting the diameter of the Bz=0 ring. The results of this study should be helpful in the designing of an ideal UBM using permanent magnets as well as electromagnets.

1. Introduction

The unbalanced magnetron (UBM) has been the focus of interest for the PVDcommunity for over a decade [1]. While the conventional magnetron sputtering has already made its impact on the thin-film coating industry, the” unbalanced” version proves more advantageous because it combines high deposition rates and low-energy ion bombardment at the substrate. The ion bombardment is achieved by modifying the conventional magnetron (CM) with an additional magnetic field, which deviates the trajectories of secondary electrons from the glow discharge region concentrated near the target, towards the substrate. This would create an ionised region near the substrate and hence causes ion bombardment on the growing film, thereby modifying the properties of the coating [1Ð4].

The first ever detailed study of the UBM, is due to Window and Savvides [5]. They analysed dfferent modes of unbalancing the magnetron using permanent magnets and electromagnets, and proved that a magnetic field which converges towards the substrate (Type II, as they designated) gives the desired unbalancing effect. This field distribution was found to maintain considerable ion bombardment over the substrate at low energies, with a high ratio of ion-to-deposited atom.