Plasma Composition by Mass Spectrometry in a Ar-SiH4-H2 LEPECVD Process During nc-Si Deposition

Abstract

Mass spectrometry has been used to assess plasma composition during a low-energy plasma-enhanced chemical vapor deposition (LEPECVD) process using argon-silane-hydrogen (Ar-SiH4-H2) gas mixtures with input flows of 50 sccm Ar, 2–20 sccm SiH4 and 0–50 sccm H2 at total pressures of 1–4 Pa. Energy-integrated ion densities, residual gas analysis and threshold ionization mass spectrometry have been used to characterize the transition from amorphous (a-Si) to nano-crystalline silicon (nc-Si) deposition at constant LEPECVD operating parameters. While relative ion densities have a marked decrease with H2 input, the densities of SiHx (x < 4) radicals show evolution trends depending on the SiH4 and H2 input. For conditions leading to nc-Si growth a turning point is reached above which SiH is the main radical. Observed SiHx density trends with H2 input are explained based on kinetic reaction rates calculated from previously obtained Langmuir probe data.