Radicals and Non-Equilibrium Processes in Low-Temperature Plasmas

Abstract

This volume is a selection from papers presented at the 5th EU – Japan Symposium. Unfortunately not all of the authors invited to prepare a review could finalize their papers in time for publication. Thus this book displays only a part of what has been enjoyed by the audience during the conference and what was expected to be in the book. On the other hand it provides the possibility to view some of the issues in greater detail and a chance for those who attended the meeting to revisit some of the presentations and discussion. The particular value of this symposia series is the opportunity for participants to discuss the issues confronting modern plasma physics and evolve a collaborative strategy to address these issues. The resulting synergism from having the leading researchers in this field all in the same room unfortunately could not be captured in this book but will certainly be reflected in the results presented at future symposia.The 29 invited lectures and 4 progress reports (with the addition of 10 posters) presented at the conference came from 12 different countries from 4 continents. A similar distribution is maintained in the 21 articles in this book. All the papers presented here have been refereed according to the standards of the conference and the journal, first by selecting the renowned invited speakers and selecting the topics of their presentations and later on by reviewing the articles. However we still leave the responsibility (and honors) for the contents of the papers to the authors. The papers in this book are review articles giving a summary of the already published work or presenting the work in progress that will be published in full at a later date (or both). The EU – Japan Symposia were initiated in 2003 and have been held in Japan and in Europe (so far only in European countries starting with the letter `S': Sweden, Slovakia, Serbia). The 5th EU – Japan Joint Symposium on Plasma Processing was organized in Belgrade, 6–9 March at the Serbian Academy of Sciences and Arts and Institute of Physics, Belgrade. Each Symposium has sought to highlight a key topic of plasma research and the 5th EU – Japan symposium explored the role of Radicals and Non-Equilibrium Processes in Low-Temperature Plasmas since these are key elements of plasma processing. Other aspects of technologies for manufacturing integrated circuits were also considered. Unlike bio-medicine and perhaps politics, in plasma processing free radicals are `good radicals' but their kinetics are difficult to understand since there remains little data on their collisions with electrons and ions. One of the goals of the symposium was to facilitate communication between experimentalists and theorists in binary collision physics with plasma modellers and practitioners of plasma processing in order to optimize efforts to provide much needed data for both molecules and radicals of practical importance. The non-equilibrium nature of plasmas is critical in the efficient manufacturing of high resolution structures by anisotropic plasma etching on Si wafers since they allow separate control of the directionality and energy of ions and provide a high level of separation between the mean energies of electrons and ions. As nanotechnologies become practical, plasma processing may play a key role, not only in manufacturing of integrated circuits, but also for self-organization of massively parallel manufacturing of nanostructures. In this Symposium the key issues that are hindering the development of such new, higher resolution technologies were discussed and some possible solutions were proposed. In particular, damage control, fast neutral etching, processes at surface and modeling of profiles were addressed in several of the lectures.A wide range of topics are covered in this book including atomic and molecular collision physics – primarily focused towards formation and analysis of radicals, basic swarm data and breakdown kinetics, basic kinetics of RF and DC discharges, plasma chemistry – particularly in oxygen containing plasmas, modeling of plasmas and plasma surface interactions in complex comprehensive plasma codes, modeling of the development of surface profiles and kinetics of surface collisions, plasma treatment of materials, plasma processing and applications in thin film deposition, nanoscale device production and many other applications. Yet all the papers, one way or the other, address the key issues of the next generation of plasma technologies in the micro and nano electronic industry.The issue of radicals and also of electron molecule collisions is addressed by J Tennyson who presents a guide into using a code for R-matrix calculations of electron–molecule collisions at low and intermediate energies. Related experimental results are presented by T Field who showed recent measurements of electron radical attachment cross sections, by T Märk who discusses electron impact ionization/dissociation of molecules and subsequent production of energetic radicals, and by M Kimura and his coauthors who discuss productions of radicals and ions by electron and photon impacts on CH4. Finally T Maddern and M Brunger share with us the first results from the new very complex system for comprehensive measurements of electron radical cross sections, the first example being CF2. B Marinković mainly focuses on recent results of his group having in mind the data needs for plasma modeling. Collisions at surfaces are addressed by P Tegeder and more specifically she presents here the evolution of negative ion resonances at surfaces. The electron swarm data as projected onto gaseous dielectrics but also having application in plasma processing is covered by J De Urquijo who attempted to answer the question whether CF3I is a better dielectric than SF6. The basic processes leading to the gas breakdown have been addressed by D Marić and Z Lj Petrović who focus on the transition from Townsend to constricted–normal glow regime while trying to project the recent results onto the standard Townsend theory and phenomenology.New developments in plasma diagnostics are given by U Czarnetzki who studies application of the plasma series resonance effect in RF-discharges and by J Röpcke who describes the recent progress in understanding kinetics of molecular plasmas using laser absorption techniques. Theoretical description of the two frequency operation of capacitively coupled plasmas in CF4 mixtures is provided by Z Donko.Different plasma sources are well covered. First S Popović discusses microwave discharges in oxygen and the role of the oxygen metastable, K Becker analyzes UV production in dielectric barrier discharges while K Tachibana and O Sakai show results on generation and applications of atmospheric pressure glow discharges by integration of microplasmas Plasma surface interactions are addressed from the viewpoint of the surface processes (etching of organic dielectrics and Si in particular) by S Hamaguchi while the recent numerical techniques in predicting 3D etched profiles are presented by B Radjenović who discusses coupling of the profile charging and the level set calculations in 3D profile evolution simulations. A detailed study of SiO2 etching in two frequency plasma is provided by F Hamaoka, T Yagisawa and T Makabe.Plasmas may not only be used in their destructive (etching) mode, they may be used to build (deposit) new materials or structures. Thus plasma assisted growth of ultrathin oxides and nitrides on Si surfaces for CMOS applications is described in the paper by P Morgen and coworkers while E Neyts et al discuss reaction mechanisms and thin a-C:H film growth from low energy hydrocarbon radicals. Finally M Shiratani describes control of nano-strucutures produced by plasma CVD films and its application in development of novel photovoltaic devices.Although the major applications discussed in this Symposium were related to nano-electronics, much of the basic research was relevant for the development of a wide range of other nano-technologies. The former is certainly well documented but the relevance of plasma processing for massively parallel self-organized manufacturing of nanostructures has yet to be proven. While, in stressing the importance of plasmas in nano-technologies we may sound like one of the seven blind men/women who went to India to `see' (observe) an elephant and each identified elephant with the part of its body that he/she was able to touch, but we still believe that plasma technologies will provide the possibility for transfer of a large number of bottom-up nano-technologies to the industrial environment. The results presented at this conference are therefore applicable to a broader range of nano-applications in future.During the Workshop, a round table discussion: `Network of Excellence between EU and Japan in the era of globalization' was organized. A strategy for further research and joint applications for funding was developed between the EU and Japanese groups, also involving collaborative research with groups from Australia and USA.We therefore believe that the symposium was one of the best aggregations of leading researchers in the field in the last few years and was a highly successful conference. While this volume cannot capture all that was going on at such a conference, we are still confident that it will prove to be a useful reference on numerous topical issues, a guide for young researchers into the scientific issues of this field and a reminder for the participants of the symposium itself and all the interactions they had with their colleagues. Most of the things that we observe exist in non-equilibrium and life is one of its manifestations. Our desire to predict and describe even these, very complex aspects of nature is an attempt to create and control non-equilibrium. Therefore we hope that our attempts, as described in this proceedings, which are focused on one aspect of nature that we understand very well, sometimes almost exactly, may put us in position ask some fundamental questions while contributing to the benefit of mankind. We are grateful to all the members of the Gaseous Electronics Laboratory for organization of the event, in particular the members of the organizing committee and the staff of the Academy of Science and Institute of Physics. Finally and above all we acknowledge the great efforts of all the participants who have invested a lot of funds, their time and effort to join us, sometimes travelling from distant continents. The conference was primarily supported by ESF Program Electron Induced Processing at the Molecular Level. Additional funding and facilities were provided by the COE Optical and Electronic Device Technology for Access Network (Keio University), Ministry of Science of the Republic of Serbia; Academy of Sciences and Arts of Serbia, Institute of Physics Belgrade, COE Nonequilibrium processes in plasma physics and environmental science and Hiden Analytical. Zoran L J Petrović, Nigel Mason, Satoshi Hamaguchi and Marija Radmilović-Radjenović Editors