The chemical nature of Si surfaces treated with ammonium fluoride (NH 4F) has been investigated using photoemission and surface infrared spectroscopy. On the surface after treatment in NH4F solution, there remain ammonium compounds such as NH4F and NH4F.HF. Photoemission data demonstrate that under the atmospheric environment, the ammonium compounds remaining on the NH4F-treated Si surface react with the Si substrate to generate the hexafluorosilicate salt, (NH 4)2SiF6. We propose that the formation of (NH4)2SiF6 or SiF62- ions is the dominant reaction pathway in the NH4F etching of Si crystals.
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