SiO2 etching and surface evolution using combined exposure to CF4/O2 remote plasma and electron beam

Abstract

Electron-based surface activation of surfaces functionalized by remote plasma appears like a flexible and novel approach to atomic scale etching and deposition. Relative to plasma-based dry etching that uses ion bombardment of a substrate to achieve controlled material removal, electron beam-induced etching (EBIE) is expected to reduce surface damage, including atom displacement, surface roughness, and undesired material removal. One of the issues with EBIE is the limited number of chemical precursors that can be used to functionalize material surfaces. In this work, we demonstrate a new configuration that was designed to leverage flexible surface functionalization using a remote plasma source, and, by combining with electron beam bombardment to remove the chemically reacted surface layer through plasma-assisted electron beam-induced etching, achieve highly controlled etching. This article describes the experimental configuration used for this demonstration that consists of a remote plasma source and an electron flood gun for enabling electron beam-induced etching of SiO2 with Ar/CF4/O2 precursors. We evaluated the parametric dependence of SiO2 etching rate on processing parameters of the flood gun, including electron energy and emission current, and of the remote plasma source, including radiofrequency source power and flow rate of CF4/O2, respectively. Additionally, two prototypical processing cases were demonstrated by temporally combining or separating remote plasma treatment and electron beam irradiation. The results validate the performance of this approach for etching applications, including photomask repair and atomic layer etching of SiO2. Surface characterization results that provide mechanistic insights into these processes are also presented and discussed.

Near-Plasma Chemical Surface Engineering

“…It can thus be postulated that NPC results in less destructive conditions at the substrate surface, while a similar yet more-defined chemistry is promoted, supported by electron instead of ion interactions. Indeed, it has recently been discussed that electron interactions during plasma chemical etching in a remote plasma without ion bombardment can reduce surface damage, including atom displacement, surface roughness, and the removal of undesired materials [ 26 ]. Furthermore, the influence of trapped charges should be considered for aging effects [ 35 ].…”

“…These approaches benefit from the plasma production of radicals, dealing with the fabrication [ 23 ] or modification [ 24 ] of nanostructures in a mild environment. However, due to its afterglow nature, only those long-living plasma species characterized by large mean free paths likely play a role in this process, highly decreasing its deposition [ 25 ] and etching rates [ 26 ]. Therefore, parts of the benefits of plasma surface engineering are lost.…”

Transformer coupled toroidal wave-heated remote plasma sources operating in Ar/NF3 mixtures

“…The ferrite guides and focuses the magnetic field, which is delivered to the plasma chamber where a toroidal electric field is induced producing the plasma. Prior studies have addressed transformer coupled RPSs in continuous-wave operation employing electronegative gas admixtures including NH 3 [2,22], NF 3 [4,[23][24][25], CF 4 [26], O 2 [24] and SF 6 [27]. A typical system layout of the RPS and, for example, a plasma etching chamber receiving its output will strategically optimize the length of the flow tube between the RPS and the chamber [25].…”