Surface Analysis of AlGaN Treated with CF<sub>4 </sub>and Ar Plasma Etching

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To understand the surface damage of AlGaN film caused by plasma etching in detail, we etched AlGaN film with CF4 and Ar plasmas. The intensity of ultraviolet (UV) light emitted from the CF4 plasma was very weak at each gas pressure investigated. However, in the case of Ar, a certain degree of UV intensity was observed at gas pressures between 50 and 100 mTorr. The surface etched with the CF4 plasma was as smooth as that of the as-grown film. In the case of Ar, surface roughening occurred at gas pressures between 50 and 100 mTorr. The Al/N and Ga/N ratios of the AlGaN surface etched with Ar plasma increased more significantly than those of the surface etched CF4 plasma, as determined by X-ray photoelectron spectroscopy (XPS). The peak shape of the near-edge X-ray absorption fine structure (NEXAFS) spectra in the N-K absorption edge was broadened by the plasma etching with increasing processing-time. The broadening observed in the case of Ar etching was greater than that during CF4 plasma etching. The observed changes in the surface morphology and crystalline structure of the AlGaN are considered to be caused by the synergistic effect of UV light irradiation from the plasma and ion bombardment of the sample surface. The changes in surface composition, surface roughening, and the disordering of the crystalline structure were found to occur within a shallow region from the surface, and did not occur in deeper regions of the sample. F atoms (ions) were found to penetrate the surface to a depth of about 10 nm in the AlGaN etched with CF4 plasma. [DOI: 10.1380/ejssnt.2015.481]

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