Precise control of ion and radical production using electron beam generated plasmas

Abstract

Precise control over both the relative and absolute flux of plasma species as well as their energy deposition at surfaces is critical to enabling the plasma processing of materials with atomic layer precision. In addition to the need for low damage, the complex device structures proposed for next generation nanoelectronics will also require control over radical to ion ratio. Electron beam generated plasmas are capable of generating a wide range of charged particle densities (109–1012 cm−3), while maintaining low electron temperatures (0.1–1.0 eV) and in reactive gas backgrounds, a relatively low radical production rate compared to discharges. These characteristics provide the ability to precisely control both the ion energy at adjacent surfaces and the ion to radical flux ratio. The latter capability is realized by coupling an electron beam generated plasma with an auxiliary plasma source designed to promote radical production. In this work, optical emission spectroscopy and Langmuir probe measurements are combined to measure the positive ion and fluorine atom densities in electron beam generated Ar/SF6 plasmas coupled to a remote, inductively coupled plasma source operating in the same environment. The results indicate that the approach can be used to independently control the positive ion and F radical densities such that the ion to radical density ratio can be varied over a range of 2–3 orders of magnitude.