Time-resolved investigations of pulsed microwave excited plasmas

Abstract

Pulsed microwave excited (2.45 GHz) argon plasmas generated by a slot antenna type plasma source are investigated by various diagnostic tools. Through the combined use of time-resolved planar optical emission spectroscopy (TPOES), microwave interferometry (MWI) and Langmuir probes the temporal behaviour of the electron density, n e (t), and effective electron temperature, T e (t), for the pulse frequency range of 0.2-20 kHz are measured. Additionally, from TPOES maps of Ar * and Ar + , the qualitative spatially and time-resolved electron temperature distribution is derived. The n e (t) and T e (t) rise and decay times are almost constant throughout the examined frequency range. A n e (t) rise time of 1 ms and a decay time of 0.6 ms is derived from probe and MWI data at 5 Pa. A T e (t) rise time between 5 and 10 µs and a decay time between 50 µs and 80 µs is derived from TPOES and probe measurements at 5 Pa. The maximum time-averaged electron density, ne , at 5 Pa is obtained at a pulse frequency f of 200 Hz. With increasing pressure and power the pulse frequency f at which a maximum of ne is reached decreases to f ≈ 50 Hz. The temporal n e (t) and T e (t) behaviour for the investigated pressure range is described by a simple set of equations based on the 'Global Model' of pulsed plasmas. It can be concluded that the electron loss rate ν loss controls both the rise and decay times of n e (t). The ν loss is in the first order a function of the plasma system dimensions and geometry. The decay of T e (t) depends on ν loss and the losses due to inelastic scattering.

Rapid surface treatment of polyamide 12 by microwave plasma jet

“…Numerous studies have been performed concerning kinetics of neutrals, excited species as well as charged particles [11][12][13][14][15][16].…”

Time resolved optical emission spectroscopy in power modulated atmospheric pressure plasma jet

“…Moreover, studying the plasma kinetics in modulated and pulsed discharges offer the possibility to understand the mechanisms and processes involved from a fundamental point of view. Plentiful articles have already been published on plasma kinetics of active species in plasma, using time resolved measurements [9][10][11][12][13].…”

Microwave Plasma Sources ‐Applications in Industry

“…High aspect ratio, very low substrate temperature change, cleaning of organic traces or very high etch rates up to 20 μm per minute can be achieved with the same set-up only by variation of the plasma parameters [5,6]. The plasma generation with a high density of excited neutrals is observed in addition with long lifetime in pulsed microwave plasmas [13][14][15]. To solve that problem, each PET-bottle needs a barrier layer to prevent the gas exchange and its negative consequences.…”

“…With the relaxation of the excited state, the emitted photons will do the photo curing. The plasma generation with a high density of excited neutrals is observed in addition with long lifetime in pulsed microwave plasmas [13][14][15]. The remaining difficulty between plasma photo curing and the application was how to get a car body pumped to vacuum and how to excite a plasma in such a large volume to treat a car body with short cycle time.…”