A highly selective photoresist ashing process for silicon nitride films by addition of trifluoromethane

Makoto Saito, Hideo Eto, Nobuaki Makino, Kayoko Omiya, Tetsuya Homma, Takao Nagatomo

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8 Citations (Scopus)


A highly selective photoresist ashing process was developed for the fabrication of thin-film transistor liquid-crystal displays (TFT-LCDs). This ashing process utilizes downflow plasma consisting of a carbon trifluoromethane/oxygen (CHF3/O2) gas mixture at a low temperature. The etching selectivity of photoresist films to silicon nitride (SiN) film increased when using the CHF3/O2 gas mixture plasma, as compared to that when using the carbon tetrafluoride/oxygen (CF4/O2) gas mixture plasma. At the CHF3 gas flow rate of 30 sccm, a high etching selectivity ratio of about 1080 for the photoresist films to the SiN films was achieved at room temperature. On the basis of surface analysis results for SiN films and plasma analysis results for the CHF3/O2 gas mixture, a mechanism for the high etching selectivity of the photoresist films was proposed. Reaction products that were formed on SiN films by the CHF3/O2 gas mixture plasma obstructed the etching of SiN films by fluorine (F) radicals resulting in the high selectivity. It was found that the CHF3/O2 gas mixture plasma reacted with SiN, resulting in the formation of a protective reaction product that is considered to be an ammonium salt such as (NH4)2SiF6.

Original languageEnglish
Pages (from-to)5271-5274
Number of pages4
JournalJapanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers
Issue number9 A
Publication statusPublished - 2001 Sept


  • Ashing
  • Downflow plasma
  • Photoresist
  • Silicon nitride
  • Trifluoromethane

ASJC Scopus subject areas

  • Engineering(all)
  • Physics and Astronomy(all)


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