The role of dc self-bias potential in the control of rf sputtering

For rf, as with dc sputtering, the deposition rate may be uniquely related to the power delivered to the target electrode. The power delivered to the electrode is less than the power delivered by the rf generator by an amount equal to the rf losses in the system. These losses can be substantial and quite variable, even when a good match is indicated at the generator. It is shown that an important source of such losses is seemingly insignificant amounts of series inductance between the matching network and the powered electrode. Deposition rate cannot then, in general, be related reproducibly to the power delivered by the generator. Data are presented which show that, for a given discharge mode, the dc self-bias potential is uniquely related to the power delivered to the electrode and hence to the deposition rate. Implications of this observation as they relate to control of the sputtering process are discussed.