needs and challenges in atomic and molecular data

MODELING ETCHING PLASMAS: NEEDS AND CHALLENGES IN ATOMIC AND MOLECULAR DATA Joëlle Margot Department of physics, Université de Montréal, Montréal, Québec, Canada [email protected]

Domain: Low temperature laboratory plasma and industrial plasmas Chlorine- and fluorine-containing plasmas are routinely used for the etching of a large variety of materials, including those intended for novel applications such as ferroelectric, electro-optic, photonic and agile materials. In contrast to the huge effort devoted to the ad-hoc implementation of plasmas for etching purpose, relatively modest information is available concerning the characterization of the gas phase plasma and of its interaction with surfaces despite their importance for optimizing the etching processes. Over the last decade, our group has been pursuing various investigations related to the characterization of high-density plasmas intended for materials etching, in various gases like argon, chlorine, sulfur hexafluoride and their mixtures. When possible, in order to provide scientific insight into the physical and chemical mechanisms involved during plasma materials interaction, the results of these experiments were supported by models. One of the difficulties encountered when developing such models is related to the lack of various reaction rates either in the gas phase or for describing the interaction of the plasma with the materials to be etched and with the plasma reactor walls. Because of its relative simplicity as compared to other etching gases and because its relevant reaction rates and/or cross-sections are relatively well documented, chlorine was chosen as a test gas for the development of a simple fluid model intended for the understanding of the driving kinetics of neutral and charged species in high-density plasmas.1 Among the important results of this analysis, it was shown that many reactions occurring in the plasma bulk could be neglected in the particle balance of charged species, namely, electron-impact detachment, polar dissociation, and dissociative ionization of Cl2. It was also demonstrated that the dominant charged carriers are closely linked to the dissociation level of Cl2 molecules. As both Cl2 molecules and Cl atoms can yield different volatile reaction products when interacting with surfaces, the degree of dissociation of Cl2 plays an important role in the etching selectivity and therefore for determining the quality of the etched profiles. The results also demonstrate the importance of the assumed wall recombination coefficient of Cl atoms in predicting the neutral and ion composition of the plasma, because in low-pressure conditions atom recombination is more likely to occur on the chamber walls or wafer surface than through three body gas phase reactions. This presentation will review in details the results obtained in chlorine high-density plasmas and will discuss the challenges concerning plasma characterization and modeling in other relevant etching complex gases like SF6. * Work supported by the National Science and Engineering Research Council

1 L. Stafford, J. Margot, F. Vidal, M. Chaker, K. Giroux, J.-S. Poirier, A. Quintal-Léonard, J. Saussac, "Kinetics driving high-density chlorine plasmas”, J. Appl. Phys. 98, 063301 (2005)