Langmuir probe plasma parameters and kinetic rates in a Ar–SiH4–H2 plasma during nc-Si films deposition for photovoltaic applications

Abstract

An assessment of main electron-impact and secondary (homogeneous) gas-phase reaction rates of silane in an argon–silane–hydrogen plasma during nano-crystalline silicon deposition is presented.Radially resolved Langmuir probe plasma parameters (electron temperature and density) and electron energy distribution functions (eedfs) have been evaluated for Ar, Ar–H2 and Ar–SiH4–H2 plasma in a low-energy plasma-enhanced chemical vapour deposition reactor. Input flow rates of 50 sccm Ar, 10 sccm SiH4 and 0–50 sccm H2 have been used for a reactor pressure range 1–4 Pa.The eedfs are used to evaluate kinetic rate constants for electron-impact dissociative processes of SiH4 and H2 and to infer the amount of atomic H available for the silane–hydrogen gas-phase reaction, observing trends with an increase in H2 input flow.The evolution of silane kinetic rates with an increase in H2 input indicates that conditions corresponding to nc-Si deposition are characterized by a dominance of silane–hydrogen gas-phase rates over electron-impact dissociation rates up to about two orders of magnitude.