Auger electron spectroscopy (AES) sputter depth profiling of an ISO reference material of the GaAs/AlAs superlattice was investigated using low-energy Ar + ions. Although a high depth resolution of ∼1.0 nm was obtained at the GaAs/AlAs interface under 100 eV Ar + ion irradiation, deterioration of the depth resolution was observed at the AlAs/GaAs interface. The Auger peak profile revealed that the enrichment of Al due to preferential sputtering occurred during sputter etching of the AlAs layer only under 100 eV Ar + ion irradiation. In addition, a significant difference in the etching rates between the AlAs and GaAs layers was observed for low-energy ion irradiation. Deterioration of the depth resolution under 100 eV Ar + ion irradiation is attributed to the preferential sputtering and the difference in the etching rate. The present results suggest that the effects induced by the preferential sputtering and the significant difference in the etching rate should be taken into account to optimize ion etching conditions using the GaAs/AlAs reference material under low-energy ion irradiation.
An ultrahigh vacuum floating-type low-energy ion gun (UHV-FLIG) with a differential pumping system was developed. The developed UHV-FLIG ensured high ion current densities of ∼45 and ∼20 µA cm −2for Ar + ions of 300 and 100 eV, respectively, under the UHV condition of the analysis chamber below ∼4 × 10 −6 Pa. The application of the developed UHV-FLIG to Auger electron spectroscopy (AES) sputter depth profiling of a GaAs/AlAs superlattice material revealed that the ultimate high depth resolution of ∼1.0 nm was achieved by sputter etching using 100 eV Ar + ions. The present results confirmed that lowering the primary energy of Ar + ions to 100 eV is still significantly effective for achieving higher depth resolution in sputter depth profiling.
The dependence of the depth resolution on the primary energy of low-energy Ar + ions in Auger electron spectroscopy (AES) sputter depth profiling of an ISO reference material GaAs/AlAs superlattice was investigated for the ion incidence angle of 50°from the sample surface normal. The depth resolution was found to improve as the square root of the primary energy of the ions as the primary energy decreased from 1000 to 200 eV. In contrast, a deterioration of the depth resolution was observed at 100 eV, which was induced by the difference in the etching rates between GaAs and AlAs and preferential sputtering. Further investigation of AES sputter depth profiling under irradiation of 100-eV Ar + ions at the incident angle of 70°revealed that the difference in the etching rate and preferential sputtering could be suppressed by changing the incident angle from 50°to 70°, leading to a depth resolution of ∼1.3 nm with 100 eV. The present results confirmed that glancing incidence is effective in achieving higher depth resolution from the point of view of the reduction of not only atomic mixing but also the difference in the etching rates and preferential sputtering. Careful attention is required for optimizing conditions of low-energy ion irradiation in sputter depth profiling using the GaAs/AlAs reference material.
Sputter depth profiling of multiple short-period BN δ-doped Si on the basis of work function (WF) measurement using the secondary electron (SE) method was investigated. The concentration of boron in the sample was confirmed to be less than the detection limit of the current Auger electron spectroscopy system. The results revealed that BN δ-doped layers can be detected as a periodic change in the WF of the order of ∼0.01 eV. These results confirmed that sputter depth profiling on the basis of WF measurement using the SE method is effective for the characterization of dopant atoms in semiconductor devices with high lateral and depth resolutions.
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