Self-matching plasma sources using 2.45 GHz solid-state generators: microwave design and operating performance

ABSTRACT

In connection with recently published results, two 2.45 GHz microwave plasma sources were designed: a coaxial electron cyclotron resonance-type operating between 0.01 and 10 Pa and a collisional-type for higher pressure range, 1–100 Pa. The primary goal was to build self-matched plasma sources, which can maintain low reflected power levels without any impedance matching component. The microwave field was supplied to each plasma source via a coaxial feed from a solid-state microwave generator with adjustable power between 0 and 200 W and adjustable frequency from 2.4 to 2.5 GHz. The adjustable frequency of the generator is intended to be used as backup matching means if the reflected power increases above a set value; an automatic adjustment loop enables the microwave generator to start sweeping the frequency band until the lowest reflected power level is found. The modelling method used to obtain self-adapted plasma sources is explained; the performance of each source is evaluated by measuring the efficiency of the microwave power transmitted inside the plasma vs. gas pressure, gas type and microwave forward power level. Results of plasma source testing in industrial applications such as nanocrystalline diamond deposition on 4 inch silicon wafers and stainless steel nitriding are presented.

KEYWORDS:

• Microwave plasma
• electron cyclotron resonance
• collisional plasma
• plasma source
• solid-state microwave generator
• microwave modelling
• impedance matching

Acknowledgments

This work has been funded in the framework of the project PAUD contract No I 1202009W and CTI project 16867.2 PFNM-NM. The authors thank Dr. D. Rats, NeoCoat SA, La-Chaux-de-Fond, CH for providing diamond seeded silicon substrates and Dr. F. Haüg, EPFL, PV-lab, Neuchatel, CH for access to the UV-Raman spectrometer.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Reflected power ratio is defined as the reflected microwave power divided by generator's microwave output power (forward power).

Additional information

Funding

CTI project: 16867.2 PFNM-NM and PAUD: I 1202009W.

Notes on contributors

Louis Latrasse

Dr Louis Latrasse has a masters degree in engineering (Material Science, Institut National Polytechnique de Grenoble, 2003) and a PhD in physics and nanophysics (Université Joseph Fourier de Grenoble, 2006). For several years he worked on ECR Ion Source design for particles accelerators. Since 2010 he is Sairem's plasma R&D manager. He designs innovative microwave plasma sources like low pressure coaxial plasma sources for large scale processing, surface wave plasma sources, resonant cavity for diamond deposition, etc. He also performs microwave modelling and plasma characterization, general microwave modelling of cavities, tunnels, and various applicators. His recent developments is in plasma: ECR coaxial plasma source Aura-Wave -- high pressure coaxial plasma source Hi-Wave and a new industrial surface wave compact plasma source S-Wave. Dr Latrasse is a member of the European Physical Society.

Marilena Radoiu

Dr Marilena Radoiu, chartered chemist (CChem) and member of the Royal Society of Chemistry (MRSC), received her MSc in organic technological chemistry from the Polytechnic University of Bucharest in 1993 and a PhD in radiochemistry and nuclear chemistry from the same university in 1998. She has extensive work experience in different international academic and industrial environments. She has worked for 20 years in Romania, Canada, UK, and France in the development of microwave-assisted technologies with applications to chemical synthesis, biomass extraction, plasma etc. Her work has included engineering and development of novel industrial and scientific standard and custom products, such as Zenith Etch and Sirius6000 (microwave plasma reactors for semiconductor gas cleaning) and MiniFlow 200 and Minilabotron 2000 (microwave assisted laboratory equipment). Dr. Radoiu is also a member of several professional associations, including the Association for Microwave Power, Education and Research in Europe (AMPERE).

Thomas Nelis

Dr. Thomas Nelis is a professor of physics at the Bern University of applied Sciences, Switzerland (BFH) since 2011. He received PhD in 1989 at the Institute of Applied Physics of the University of Bonn. Since then, prior to joining BFH, he has worked at various locations, in industry, academia and as an independent researcher. During this time his main research and development topics have been related to combination of spectroscopy and plasma physics in view of industrial applications. On joining the BFH, he created the plasma surface engineering group as part of the institute of applied laser, photonics and surface technologies (ALPS) at the BFH. The focus of this research group is process development in the field of industrial plasma application for surface modification, both deposition and functionalizing.

Olivier Antonin

Olivier Antonin received his MSc degree in instrumentation and measurement-analysis in 2007 and engineer specialist in measurement-analysis and industrial control in 2008 from the Conservatoire National des Arts et Métiers, France. Since 2014 he is a PhD student in plasma physics and engineering at the University of Toulouse III, France with main thesis topics related to PE-CVD microwave plasma in matrix of elementary plasma source (MEPS) for nano-crystalline diamond (NCD) growth at low power density, low pressure and low temperature. His previous interests included PVD magnetron plasma discharges in DC, RF and HiPIMS. In 2002 he joined Centre National de la Recherche Scientifique, France.