Axially-resolved study of highly ionized magnetron sputtering

Summary form only given. A potential device for deposition of highly ionized metal consists of a dc magnetron which sputters atoms through a 13 cm-long region of high density argon plasma. The plasma is produced by an rf induction coil immersed in the deposition chamber. Electron densities produced in the induction plasma are 10/sup 11/-10/sup 12/ cm/sup -3/. This method of post-ionized sputter deposition (PSD) has produced aluminum ion flux fractions in excess of 80%. The introduction of aluminum atoms into the induction plasma is observed to decrease the electron temperature by more than 20% and reduce the electron density by >10% (as determined from microwave interferometry). The net result is a significantly decreased metal ionization fraction. Ultimately, this phenomena limits the maximum obtainable deposition rate (i.e., metal density). These measurements compare favorably with a simple, global model for the metal/inert gas plasma. Minimizing the distance between the magnetron and wafer is critical to obtaining an economical deposition rate. As the throw distance is decreased, however, the fraction of metal ions at the wafer also decreases. Spatially-resolved optical measurements of Al/sup +/ and Al emission show a nearly exponential rise in the relative ion fraction with distance from the sputter target. The experimental path length required for ionization will be related to the thermalization of the sputtered flux, measured electron temperature, and line-averaged electron density.