A set of cross sections and transport coefficients for electrons in HBr O. Šašic ´ a,b,⇑ , S. Dujko a , T. Makabe c , Z.Lj. Petrovic ´ a a Institute of Physics, Belgrade, P.O. Box 68, 11080 Zemun, Belgrade, Serbia b Faculty of Transport and Traffic Engineering, University of Belgrade, Vojvode Stepe 305, 11000 Belgrade, Serbia c Department of Electronics and Electrical Engineering, Keio University, Hiyoshi 3-14-1, Yokohama, Japan article info Article history: Available online 26 August 2011 Keywords: HBr Swarms Cross sections Transport coefficients Fluid models Plasma etching abstract We have compiled a set of electron collision cross sections for HBr. It will be useful for a fluid modeling of HBr plasmas together with transport coefficients in both DC and RF, E and E  B fields. The calculation made use of a Monte Carlo technique. The transport coefficients are rather unstructured because the total cross section resembles that of a constant collisonal frequency model. Additional measurements of swarm parameters are required in order to obtain more acurate set of cross sections. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Control of plasma chemistry and physical properties of ions reaching the surface as well as surface chemistry by radical species are critical to achieving appropriate functionality of plasma process- ing in the micro (nano) electronics industry [1,2]. In order to achieve proper adjustment of those properties, accurate and stable control of plasma reactors should be achieved. Contemporary plasma devices for nanoelectronic technologies are designed, modeled and under- stood and even operated by using equally complex plasma modeling codes. These plasma models [3–6] need to include atomic and molecular collision data base, electron ion and fast neutral transport data base, self consistent field calculation, general plasma physics stage, chemical kinetics of plasma, representation of boundaries be- tween plasma and surfaces and also a section describing surface interactions and modifications. The surface set would have to in- volve modeling of the growth of structures, charging and also dam- age to the substrate and manufactured circuits. The foundation for the entire scheme is the set of cross sections and transport data. Hydrogen bromide has been used in plasma processing of inte- grated circuits (ICs) for many different purposes [7–9] including: etching of poly Si [10–12], of III–V semiconductors [13], of high k gate dielectrics [14] and etching of low k oxides for interconnects [15]. HBr is used for plasma etching in various mixtures: combined with Ar [16], Br 2 ,F 2 [17], Cl 2 [10], with SF 6 –O 2 [18,19], SiCl 4 –SiF 4 [20], BCl 3 , CH 4 [21],H 2 , and even as a pure gas [13]. HBr was shown to possess all the required properties such as fast etching rate, selectivity and anisotropy except for side-wall passivation for etch- ing applications [10,18,20,22–24]. Pushing into the realms of nano- technologies control of etching induced surface roughness may prove to be critical [25,26]. In spite of the wide spread use and importance, to our knowl- edge, there have been no models of HBr-processes due to lack of basic electron collision and transport data. In some cases, when plasma models were developed, data for Cl 2 were used instead of HBr (with adjustment for the different mass ions) [27,28]. Thus it seemed to us that compiling a set of cross sections from the liter- ature and adjusting them to form a complete (in terms of number, momentum and energy balances) set of data, together with the integrated transport data, would be a worthwhile endeavor. The data may prove to be useful for modeling plasmas involving HBr and reveal the basic characteristics of the transport coefficients. The present set of cross sections may encourage further experi- mental measurements needed to improve cross section and trans- port coefficient sets. Recent focus of the very few remaining swarm experiments has been towards gases used in applications [29] but one may need to develop a specialized apparatus for reactive gases in order to measure the data for gases like HBr. The calculations of the transport coefficients were made for DC electric fields and also for crossed E and B, DC and RF fields. Preliminary reports of our work have been presented elsewhere [30,31]. 2. The cross section data Low energy elastic scattering by HBr molecules has not been the subject of many experiments, but there have been several theoret- ical studies [32–35]. The momentum transfer (and total elastic) 0301-0104/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2011.08.019 ⇑ Corresponding author at: Faculty of Transport and Traffic Engineering, Univer- sity of Belgrade, Vojvode Stepe 305, 11000 Belgrade, Serbia. Tel.: +381 113091371. E-mail addresses: o.sasic@sf.bg.ac.rs, vomsasic@open.telekom.rs (O. Šašic ´). Chemical Physics 398 (2012) 154–159 Contents lists available at SciVerse ScienceDirect Chemical Physics journal homepage: www.elsevier.com/locate/chemphys