Avoiding nodule growth in reactive DMS of silicon based dielectric films

The growth of nodules on the target surface can become a serious problem in the reactive sputtering of oxide films.  They can be seen as local spots where material is deposited rather than eroded during sputtering and their growth has been observed e.g. in the deposition of ITO for flat panel displays and during sputtering of silicon based dielectric films in architectural glass coating. The target grain structure has been identified as one parameter affecting 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 to minimize the nodule growth and to ensure a stable coating process. The tests are carried out on a jumbo size dual magnetron with Si(Al) rotatable targets.