Fundamental investigations of the hysteresis effect in magnetically enhanced reactive sputter processes*

Capacitively coupled radio-frequency plasmas are frequently used in the industry to facilitate the processing of surfaces by e.g. etching and/or deposition. A typical process conducted in such a discharge is the deposition of aluminum oxide layers which can be facilitated by using an aluminum target and introducing oxygen to the inert gas background such as argon. In these discharges, a hysteresis effect on basic plasma parameters, e.g. electron density, DC self-bias, symmetry parameter, is observed when the oxygen flux is increased or decreased, respectively. In this work, we examine this hysteresis experimentally. A magnetron-like magnetic field configuration is added to the powered electrode to increase the heavy particle flux to the target. Using a variety of diagnostic tools, namely VI probe, Lambda probe (partial pressure of oxygen), Multipole Resonance Probe (electron density), retarding field energy analyzer (ion energy distribution function), and phase resolved optical emission spectroscopy (electron dynamics), a new aspect of the hysteresis effect is investigated: It is found that the electron dynamics are altered by the surface conditions of the target which leads to a change of the discharge symmetry and, hence, of the ion flux. Finally, the resulting layers at different operation points are analyzed with a profilometer (grow rate) and energy-dispersive X-ray spectroscopy (composition of the films).