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Title:
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The carbon footprint of PECVD chamber cleaning using fluorinated gases
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Author(s):
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Published by:
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Publication date:
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ECN
Solar Energy
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5-9-2008
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ECN report number:
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Document type:
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ECN-M--08-058
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Conference Paper
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Number of pages:
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Full text:
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5
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Download PDF
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Presented at: 23rd European Photovoltaic Solar Energy Conference and Exhibition, Valencia, Spain, 1-5 september 2008.
Abstract:
Fluorinated gases like CF4, C2F6, SF6, NF3, F2 by on-site generation can be used by the semiconductor and photovoltaic industry for etching silicon wafers and (PE)CVD chamber cleaning. Avoidance of the emission of the gases CF4, C2F6, SF6 and NF3 is required because they have a high global warming effect and high atmospheric life-time. In this work a comparison is made of the carbon footprint from the use of these gases in chamber cleaning.
The carbon footprint is calculated as the total greenhouse gas emissions over the whole life-cycle of the gases.
The steps in the life cycle are the following: production of the compounds, transportation, distribution in the fab (connection of cylinders), use in the process, abatement to destroy the unreacted gases and take-back of cylinders. Emissions from each step can be direct (from emission of the fluorinated gases) or indirect (from energy use).
Preliminary results (excluding SF6 onsite recycling), partly based on best guesses, indicate that the life-cycle greenhouse gas emissions are dominated by rest emissions of the fluorinated gases after abatement in the usage phase, followed by fugitive emissions during downtime of the abatement system and cleaning of the not completely empty returned cylinders.
The use of on-site generated F2 turns out to be clearly in advantage over the other fluorinated compounds because F2 has a global warming potential of zero. Possible improvement options to minimize the use and emission of fluorinated gas are (1) strict procedure for connection of cylinders, (2) complete usage or reliable abatement of the gas from the bottle, (3) the recovery or reliable abatement of unused gases from the process and (4) good end-point detection of the process.
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