Microfabricated inductively coupled plasma-on-a-chip for molecular SO2 detection: a comparison between global model and optical emission spectrometry

Abstract

In this work the molecular SO₂ detection limit obtained using a microfabricated inductively coupled plasma-on-a-chip (mICP) system is compared with a volume-averaged plasma model. The miniature ICP system consists of a planar plasma source that is microfabricated on a glass wafer and a miniature aluminium vacuum chamber. The plasma operates from 0.1 to 10 Torr, and requires less than 4 W of power at a frequency of 493 MHz. Molecular detection limits were measured using the SO₂ MUV2 band (Ã(¹B₁), ã(³B₁) → X(¹A₁)). Detection limits improve with increase of both the operating power and pressure due to increases in electron and metastable state Ar densities, with the best DL value being 45 ppb. A global plasma model is developed to calculate the metastable Ar density, electron temperature, and SO₂ excitation rates in the mICP. Excitation rates for electron-impact collisions and the quenching reaction with Ar metastables, together with the known sensitivity of the optical system, allow one to calculate detection limits for molecular SO₂ excitation. Calculated DLs are in reasonable agreement with experimental OES results.