Nodule formation on sputtering targets: Causes and their control by MF power supplies

The growth of nodules on the target surface can become a serious problem in the reactive sputtering of oxide films. The target grain structure has been identified as one parameter determining their formation, and sprayed targets behave different from cast targets in this respect. However, the conditions during target operation also play an important role. Nodules on the target surface lead to excessive arcing and hence to yield loss and reduced tool up-time. The growth process itself can be traced back to the arcing, which apparently makes it a self-augmenting phenomenon. In this contribution we investigate factors promoting or avoiding nodule formation. A modern power supply can provide several turning knobs which can contribute to minimize nodule growth and which may help to ensure a stable coating process for some materials and some target production methods. The tests are carried out on a jumbo size dual magnetron with Si(Al) rotatable targets.