Diagnostics of SF6 plasmas by energy-resolved mass spectrometry: influence of the electrode material on internal plasma parameters

Abstract

Abstract A detailed understanding of physical and chemical processes in plasmas and plasma sheaths can be achieved by measuring the energy distributions of all ions (IED) at the place where the plasma species interact with a substrate. In order to measure IEDs in the reactive ion etching processes an energy-resolved quadrupole mass spectrometer (E-QMS) was assembled underneath the powered electrode (cathode) of a diode reactive ion etcher. To examine the influence of the electrode material, we used brass, steel and aluminium as cathode materials. The plasma ions reach the QMS through an orifice in the cathode with a diameter of a 100 μm. The ion energy distributions of SF + x ( x =0…5), F + and F + 2 ions from sulfur hexafluoride (SF 6 ) plasmas in the pressure range 0.1–5 Pa at different DC bias potentials between −50 and −250 V and a frequency of 13.56 MHz were investigated. Marked differences in the IEDs of all ionic species appeared for the three different electrode (cathode) materials. A model is developed which explains these experimental results with different secondary electron coefficients of the electrode materials.