Invited Paper PS1-ThA3
Spatio-temporally Resolved Optical Emission Spectroscopy for Investigating rf Plasmas and Micro-Discharges

Thursday, October 23, 2008, 2:40 pm, Room 304

Non-thermal low temperature plasmas are widely used for technological applications. Increased demands on plasma technology have resulted in the development of various discharge concepts based on different power coupling mechanisms. Despite this, power dissipation mechanisms in these discharges are not yet fully understood. Of particular interest are low pressure radio-frequency (rf) discharges and also more recently developed micro-discharges at elevated pressure. Optical measurements are a powerful diagnostic tool offering high spatial and temporal resolution. Improved advances in technology and modern diagnostics now allow much better temporal resolution and deeper insight into fundamental mechanisms. In low pressure rf discharges insight into the electron dynamics within the rf cycle can yield vital information. The optical emission from these discharges exhibits temporal variations within the rf cycle, requiring high temporal resolution on a nano-second time scale. These variations are particularly strong, in for example capacitively coupled plasmas (CCPs), but also easily observable in inductively coupled plasmas (ICPs), and can be exploited for insight into power dissipation. Interesting kinetic and non-linear coupling effects are revealed in capacitive systems. In the relatively simple case of an asymmetric rf CCP the complexity of the power dissipation is exposed and various mode transitions (gamma-, alpha-mode and wave-particle interactions) can be clearly observed and investigated. Multi-frequency plasmas, provide additional process control for technological applications. Through investigating the excitation dynamics in such discharges the limitations of functional separation is observed. Recently developed micro-plasmas provide reactive plasma environments for processing applications without the need for expensive vacuum systems. On the one hand they allow extremely localised treatment, e.g. localised surgery. On the other hand they can provide the opportunity for controlled and scalable large area treatment using array devices of thousands or millions of micro-plasmas. However, fundamental understanding of the important mechanisms in particular coupling effects between individual discharge devices is to date poorly understood. Time and space resolved optical emission spectroscopy reveal details of these mechanisms.