Highly Selective Photoresist Ashing by Addition of Ammonia to Plasma Containing Carbon Tetrafluoride

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

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


A highly selective photoresist ashing process performed at low temperature using a downflow plusma consisting of a carbon tetrafluoride/oxygen (CF4/O2) gas mixture was developed for the fabrication of thin film transistor liquid crystal displays (TFTLCDs). Although the ashing rate was increased by using the CF4/O2 gas mixture plasma, the etching selectivity for underlying amorphous silicon (a-Si:H) films containing hydrogen decreased. The etching rate of a-Si:H films was decreased by the addition of ammonia (NH3). Since the etching rate of a-Si:H films decreased to zero at NH3 flow rates higher than 15 standard cubic centimeters per minute, an infinitely high etching selectivity for the photoresist films was achieved at room temperature. On the basis of the surface analysis results for a-Si:H films, a mechanism for the high etching selectivity of the photoresist films was proposed. Reaction products that were formed on a-Si:H films by the addition of NH3 gas to CF4/O2 gas mixture plasma obstructed the etching of a-Si:H films by fluorine (F) radicals, resulting in the high selectivity, It was found that the NH3, gas that was added to CF4/O2 gas mixture plasma reacted with a-Si:H. resulting in the formation of a protective reaction product which is considered to be an ammonium salt such as (NH4)2 SiF6

Original languageEnglish
Pages (from-to)G59-G62
JournalJournal of the Electrochemical Society
Issue number2
Publication statusPublished - 2001 Dec 1

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Materials Chemistry


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