Auger electron spectroscopy of surfaces during exposure to gaseous discharges

Abstract

Articles you may be interested inTracking electron-induced carbon contamination and cleaning of Ru surfaces by Auger electron spectroscopy J. Vac. Sci. Technol. A 30, 041401 (2012); 10.1116/1.4718426 Mass and Auger electron spectroscopy studies of the interactions of atomic and molecular chlorine on a plasma reactor wall Stability of Se passivation layers on Si(001) surfaces characterized by time-of-flight positron annihilation induced Auger electron spectroscopyThe authors report for the first time Auger electron spectroscopy ͑AES͒ of a surface while it is exposed to a high pressure, reactive environment: a 5 mTorr inductively coupled plasma. An anodized aluminum cylindrical substrate ͑a common plasma reactor coating͒ was rotated within the reactor wall. Differential pumping allowed the substrate to be exposed to the plasma, and then AES as little as 1 ms 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. O 2 plasmas are effective in removing Cl from Cl 2 plasma-conditioned surfaces; N 2 plasmas are not. During Cl 2 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 Cl 2 ͑detected by line-of-sight mass spectrometry͒, which decreases dramatically as the delay time becomes longer than the time for Langmuir-Hinshelwood ͑LH͒ recombination of adsorbed Cl. The adsorbed Cl participating in LH recombination is Ͻ10% of the total Cl coverage, which is estimated to be ϳ͑3-8͒ ϫ 10 14 cm −2 .

Experimental and modeling study of O and Cl atoms surface recombination reactions in O2 and Cl2 plasmas

“…The observation of low recombination coefficients on plasma-conditioned AA and SS surfaces with respect to those obtained on "bare" SS and AA result from the coating of sputtered silica on chamber walls due to the erosion of the silica discharge tube and viewports and the much lower γ O values on SiO x surfaces (e.g., γ O = 0.04 for sputtered silica, see [33]. Near real-time elemental analysis by in situ AES confirmed that the SS and AA surfaces became rapidly coated with a Si-oxide-based layer (Fe:Al:Si:O ≈ 1:1:3:8 for SS and Al:Si:O ≈ 2:1:3 for AA) [30,32]. The absolute concentration of Si determined by AES was comparable for SS (20 %) and AA (17 %) substrates, suggesting that the higher Auger pressure rises and thus the higher recombination coefficients for SS result from the presence of Fe on the surface.…”

“…As reported by several authors (see, e.g., refs. [57,58]), the surface became coated with a Si-oxychloride-based layer (Fe:Si:O:Cl ≈ 1:13:13:3 for SS and Al:Si:O:Cl ≈ 3:3:8:1 for AA) [30,34] due to Cl adsorption and the erosion of the silica discharge tube. In the case of AA, previous AES investigations indicated that the steady-state surface composition when going from a pure O 2 to pure Cl 2 plasma is reached in less than 300 s [37].…”

“…Desorption of Cl 2 with the plasma off can be attributed to either the physisorption-desorption of Cl 2 , or another mechanism involving dissociative adsorption of Cl 2 fol- lowed by surface recombination of adsorbed Cl atoms and desorption of Cl 2 . The approach to extract the portion of the pressure rise with the plasma on that is due to LH recombination of adsorbed Cl atoms, ΔP rec , was described in details previously [30]. It was calculated according to ΔP rec = ΔP on -(n on ) ΔP off , where ΔP on and ΔP off are the pressure rises with the plasma on and off, respectively.…”

“…A small, cylindrical substrate is rapidly rotated through skimmers such that a point of the surface is periodically exposed to the plasma and is analyzed in near real-time by surface diagnostics in separate, differentially pumped chambers. This paper reviews and compares previously published spinning-wall studies of the recombination dynamics of O and Cl atoms on plasma-conditioned AA and SS surfaces [28][29][30][31][32][33][34][35]. Cl atom recombination rate was also obtained by fitting an isothermal fluid model to measured degrees of dissociation of Cl 2 obtained in low-pressure, high-density Cl 2 plasmas sustained by traveling electromagnetic surface waves.…”

“…A "spinning-wall" technique was recently developed for studying surface reactions on plasma reactor walls [28][29][30][31][32][33][34][35][36][37]. This method couples the established ultra-high-vacuum techniques of desorption MS and AES to the high-pressure, high-charge-density plasma environment.…”