Paper PS+AS+SS-MoA8
Ultra-high Si₃N₄ to SiO₂ Selective Etching by Fluorocarbon Based Remote Plasma

Monday, October 30, 2017, 4:00 pm, Room 23

Plasma etching processes capable of highly selective Si₃N₄ to SiO₂ removal are increasingly required in fabrication of current integrated circuit devices. We report fluorocarbon (FC) based remote plasma etching processes for Si₃N₄ and SiO₂ substrates using inductively coupled plasma (ICP) and electron cyclotron wave resonance (ECWR) plasma reactors. For the remote plasma operating conditions direct ion bombardment of the sample surface is prevented and etching is primarily due to chemical reactions by neutral radicals. Such conditions can be realized by either high processing pressure for a remote ICP source or a neutralization plate for an ECWR source. Combinations of fluorocarbon gases, e.g. CF₄, with O₂ and N₂ additives have been evaluated. Etching behavior and surface properties are monitored using in situ ellipsometry. Optical emission spectroscopy (OES) has been used to evaluate the plasma gas phase chemistry. We show that ultra-high Si₃N₄ to SiO₂ etching selectivity can be achieved under remote plasma conditions in both reactors, and that control of the feed gas chemistry plays a key role. As is well-known, low levels of O₂ increase oxidation of FC gases and atomic F generation, which leads to increasing Si₃N₄ etch rate, whereas for high O₂ levels the F concentration is reduced and surface oxidation takes place. For these F-rich remote plasma conditions, SiO₂ is hardly etched and Si₃N₄ to SiO₂ etching selectivity of 7 and 87 were observed for the ICP and ECWR system, respectively. The observed etching behavior will be discussed using surface chemical studies of Si₃N₄ and SiO₂ by vacuum transferred x-ray photoelectron spectroscopy (XPS).