Auger electron spectroscopy of surfaces during exposure to gaseous discharges

Abstract

The authors report for the first time Auger electron spectroscopy (AES) of a surface while it is exposed to a high pressure, reactive environment: a 5mTorr inductively coupled plasma. An anodized aluminum cylindrical substrate (a common plasma reactor coating) was rotated within the reactor wall. Differential pumping allowed the substrate to be exposed to the plasma, and then AES as little as 1ms thereafter. Electron-beam-induced charging, a severe problem for conventional Auger analysis of insulators, is remediated in this experiment because the plasma maintains the surface at a constant floating potential. Chlorine, oxygen, and nitrogen plasmas were investigated. O2 plasmas are effective in removing Cl from Cl2 plasma-conditioned surfaces; N2 plasmas are not. During Cl2 plasma exposure, Cl coverage does not decrease with increasing delay time between plasma exposure and Auger analysis, varied by varying the substrate rotation frequency. This is contrary to desorption of Cl2 (detected by line-of-sight mass spectrometry), which decreases dramatically as the delay time becomes longer than the time for Langmuir-Hinshelwood (LH) recombination of adsorbed Cl. The adsorbed Cl participating in LH recombination is <10% of the total Cl coverage, which is estimated to be ∼(3–8)×1014cm−2.