Target effective emission coefficients during reactive sputtering of oxides and nitrides

Presented by R. De Gryse, Taiyuan University of Technology

In the field of magnetron sputtering, reactive sputtering is becoming more and more important as it allows to widen the scope of materials that can be deposited. Not only high quality metal coatings can be deposited, but also a wide variety of compounds such as oxides and nitrides can be obtained by adding a reaction gas, for instance oxygen or nitrogen to the sputtering gas. By doing this, compounds are not only deposited on the substrate, and inner walls of the equipment but also on the cathode or target. On the target surface the growth of this compound layer is the result of the competition between shallow implantation of reaction gas ions, chemisorption and knock-on implantation and the sputter etching of the surface by essentially sputter gas ions. This effect of target coverage is called poisoning and affects the deposition speed, discharge stability and cathode or discharge voltage. The discharge voltage is a very sensitive parameter for controlling the composition of the growing compound layers on the target. The understanding of its behaviour is important for controlling the reactive sputter process. This discharge voltage, which is an easily accessible quantity, is closely related to a more fundamental quantity, i.e. the ion induced secondary electron emission
coefficient or , and gives the average number of electrons ejected out of a particular material upon impact by an ion.