Formation of Nanoporous Features, Flat Surfaces, or Crystallographically Oriented Etched Profiles by the Si Chemical Dry Etching Using the Reaction of F2 + NO 鈫?F + FNO at an Elevated Tempe

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• 作者：Satomi Tajima ; Toshio Hayashi ; Kenji Ishikawa ; Makoto Sekine ; Masaru Hori
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：October 10, 2013
• 年：2013
• 卷：117
• 期：40
• 页码：20810-20818
• 全文大小：452K
• 年卷期：v.117,no.40(October 10, 2013)
• ISSN：1932-7455

文摘

Chemical dry etching of Si was performed using the reaction of F₂ + NO 鈫?F + FNO at an elevated temperature. The etched profile, surface morphology, and surface chemical bonding structures, measured by a scanning electron microscope, X-ray photoelectron spectroscopy (XPS), and a Fourier transform infrared spectrometer (FT-IR), were significantly changed when the substrate was heated at 27 and 300 掳C. Differences in total energies of Si before and after the chemical reaction with gas molecules in the etching apparatus were theoretically calculated by the density functional theory (DFT) using CAM-B3LYP/6-311G+(d,p) in Gaussian 09. The possible change in chemical bonding structures during and after the Si etching was considered by correlating the measured XPS and FT-IR spectra and the DFT calculation results. When the Si sample was heated at 2760 掳C, the nanoporous features were observed since molecules present in the gas phase remained in the condensed layer near the Si surface and they reacted with the Si surface at different rates. The chemisorbed F₂, F, and FNO promoted Si etching by cleaving different bonds to form dangling bonds, whereas NO and OH, produced from the reaction between H₂O and F, inhibited the etching by encapsulating dangling bonds. The etch rate was significantly reduced, and the evolution of the flat surface was observed at 60230 掳C due to the reduction of chemisorbed F₂, F, and FNO on the Si surface. When the Si sample was heated at above 230 掳C, the etch rate increased with the temperature due to the amplification of the reaction rate constants of F₂, F, and FNO with the Si surface. Unique orientation-dependent etching was observed at these temperatures due to the termination of dangling bonds by F without cleaving the Si鈥揝i lattice bonds. The contribution of NO and OH at above 230 掳C was ignored since they desorbed from the Si surface.