Numerical investigation of the effect of variation of gas mixture ratio on density distribution of etchant species (Br,
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Numerical investigation of the effect of variation of gas mixture ratio on density distribution of etchant species (Br, Br+, Cl, Cl+, and H) in HBr/Cl2/Ar plasma discharge Muhammad Majeed1 , Banat Gul2,a , Gulfam Zia1 , and Aman-ur-Rehman1 1 2
Department of Nuclear Engineering, PIEAS, Nilore, Islamabad, Pakistan Department of Basic Sciences, Military College of Engineering, NUST, Risalpor Campus, Risalpor, Pakistan Received 14 December 2019 / Received in final form 4 March 2020 Published online 11 June 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. A self-sustained fluid model is used to study the effect of variation of noble gas fraction (Ar) and variation of gas mixture ratio (HBr/Cl2 /Ar) on density distribution of important etchant species (Br, Br+ , Cl, Cl+ , and H) in HBr/Cl2 /Ar capacitive coupled plasma discharge that is being vastly used for dry etching of Si, GaAs, GaSb and other group III and IV semiconductor materials. A comprehensive set of 80 reactions in this plasma discharge is presented which contains electron impact reactions, neutral– neutral reactions, ion–ion reactions, and charge transfer reactions. Based on simulation results, it is found that densities of neutral species have normal distribution curve; density is higher at center of the reactor and decreases as we move towards electrode surface, while densities of charged species follow bimodal distribution in which peaks occur near electrodes. Furthermore, the addition of Ar in HBr/Cl2 causes electron density to increase which promotes ionization and dissociation. It was found that at constant supply of Cl2 gas, by increasing Ar fraction (HBr/Cl2 /Ar from 80/10/10 to 10/10/80) densities of Br, Br+ and H will go down and at constant supply of Ar gas, raising Cl2 fraction in feedback gases (HBr/Cl2 /Ar from 70/20/10 to 20/70/10) promoted the production of Cl and Cl+ while densities of Br, Br+ , and H are dropped-off. Hence, densities and fluxes of important etchant species – for chemical vs. physical etching – can be controlled by tuning of mixture ratio.
1 Introduction Plasma based etching plays a vital role in manufacturing of micro- and nano-electronics devices in IC industry. In this process, the surface is exposed to gaseous molecules and etch products evaporate into gas phase. Low temperature and low pressure capacitive coupled halide-based plasmas – such as fluorine (F), chlorine (Cl), or bromine (Br) – are used for dry etching of silicon for said purpose [1–4]. To optimize the performance of plasma source, the chemistry of the discharge needs to be understood either by using experiments or by carrying out simulations [5]. Hydrogen halide based plasma sources are usually preferred for silicon etching because of their high etch rate [2]. Furthermore, volatile halide products form in this process that can easily be removed. Each of these plasmas offer it’s own merits and demerits for Si etching; fluorine offers
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