| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Thursday Sessions |
| Session PS+VT-ThA |
| Session: | Plasma Diagnostics, Sensors and Control |
| Presenter: | Ivan Shchelkanov, University of Illinois at Urbana-Champaign |
| Authors: | I.A. Shchelkanov, University of Illinois at Urbana-Champaign D. Qerimi, University of Illinois at Urbana-Champaign A. Hayes, University of Illinois at Urbana-Champaign J.T. Wegner, University of Illinois at Urbana-Champaign D.N. Ruzic, University of Illinois at Urbana-Champaign |
| Correspondent: | Click to Email |
Among plasma diagnostics one of the most difficult tasks is getting an estimate of radical gas species concentration in the ground state without plasma presence in the diagnosed volume. This is probably the major task for characterisation of downstream plasma composition in various areas of applied plasma technology and the requirements for characterisation tool are very strict. The ultimate device should have a good spatial resolution, relatively high response time, operate in highly reactive plasmas and in presence of sputtering flux materials, should be capable to characterize species of unknown geometrical distribution and composition.
The idea of a tool, which could satisfy most of the mentioned requirements, was proposed more than ten years ago [1] but only recently the Center for Plasma Materials Interaction was able to develop a complex system which can measure composition and density of radical species with 1 cm spatial-resolution and response time of 15 seconds in the presence of high intensity RF fields and flux of sputtered material. The system can measure density of oxygen, nitrogen, and hydrogen radicals, when different species present in the chamber at the same time. For vacuum chamber of 13 inch in diameter and 46 inches tall, which is equipped with 1 kW Helicon plasma source , the measured density at ~75 mTorr, 1kW power and 10 inch from the source, the density of radical species of hydrogen was 0.7 [±0.5] *1021 m-3 and of nitrogen radicals it was 1.1 [±0.7] *1020 m-3. Additional comparison with zero dimensional model showed a match with-in an errorbar between an experiment and the model.[2]
The principle of the radical species concentration measurement is the following. The thermocouple tip is coated with a particular catalytic metal. Once the probe is exposed to the gas atoms, recombination of gas atoms occurs on the surface of the probe tip. The catalytic surface provides efficient recombination thus more energy is delivered to the surface from the recombination reaction [3] compared to a probe tip without the catalytic surface. By measuring the temperature of the probe it becomes possible to quantify the amount of gas atoms in the probe vicinity. Different radical species can be distinguished by using catalytic surfaces particular to the species in question. Current work is focused on radical probe system capabilities, physical limitations, and examples of characterized plasmas.
References:
1. M. Mozetic / Vacuum V.47 #6-8 pages 943 to 945 (1996)
2. D.T. Elg / J. Micro/Nanolith. MEMS MOEMS, 16, 023501 (2017)
3. M. Mozetic / Surface & Coatings Technology 201 (2007) 4837–484