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Linde On-Site F2 Generator
DESCRIPTION
On-site fluorine generators are sized according to the total volume required at the production fab, and all rely on the same simple, low pressure, low temperature and low inventory process design.
Anhydrous HF, supplied in either the gas or liquid phase, is the very low-cost feed material
The working fluid, KHF2.HF, is liquid only above 70°C, and is contained in a fluorine-resistant alloy vessel, which also serves as the cathode. Current applied through the anodes determines the rate of fluorine production, and the evolved fluorine and hydrogen are physically separated to prevent recombination. Hydrogen is diluted for direct disposal, or can be easily and completely abated in-situ with proprietary passive catalytic oxidation. Fluorine is filtered, purified of residual vapour-phase HF to levels below 10 ppm and can then be used at its nominally atmospheric production pressure, or compressed and buffered to a safe working pressure of up to 1.4 bar g. To supply processes developed using diluted sources of fluorine, a near-zero pressure drop blender can supply on-demand blends of fluorine and inert gases such as argon and nitrogen in a 0 to100% range of dilution.
Neutral fluorine radicals are the chemical agent responsible for chamber cleaning, and so chamber cleaning gases, like F2 or NF3, must be activated by decomposing them to their atomic components. Because there is less energy in F2 bonds vs NF3 or SF6 bonds, the decomposition takes much less energy, and therefore activation can proceed much faster or with less expensive equipment.
Proprietary design of the electrolytic cell and proprietary operating principles allow the units to operate safely and reliably - uptime is in excess of 99%. With more than 10 years of service, Linde on-site F2 generation systems have proved to be highly effective in the demanding semiconductor, display, and thin-film PV industries
INNOVATIVE ASPECT
Replacing NF3 with Fluorine in a 500MW thin film Si fab would result in elimination of NF3 consumption with an untreated global warming potential equivalent to over 8 million tonnes of CO2 per year. Linde’s proven technology for generating F2 on-site and on-demand eliminates the need for large volume storage and addresses all the safety requirements for handling this reactive material. In addition to its environmental benefit, F2 reduces the time for chamber cleaning, thereby increasing plant productivity, through a more efficient etching process, and ultimately lowers cost per watt.p
BENEFITS
(Please attach all relevant documents and reports).
Reduced carbon footprint payback time for thin film modules
Based on recent independent studies of NF3 concentration in the atmosphere, the resulting Global Warming Potential of NF3-based cleaning processes alone adds significantly to the carbon footprint payback time, or time the solar module needs to function and displace cabon-based fuels in order to have a net positive impact. Typically 1 tonne of NF3 is required for chamber cleaning for each MWp nameplate capacity solar fab. So for example, these modules, when deployed in Germany, add approximately 2 years to the carbon payback time. Because the GWP of F2 is zero, the carbon payback time due to F2-based cleaning is nearly zero.
Reduced cost per watt
The use of on-site F2 generation reduces the cost per watt through reduced mass consumption, faster clean times, and reduced capital expenditure, with savings of 3 to 5 ¢/W for a typical thin-film PV fab. Because only the fluorine atoms are responsible for chamber cleaning, 20% less F2 is required vs NF3; for less efficient activation processes, this savings can be significantly greater. Chamber cleaning with NF3 can take from 15 to 25% of the total amount of time a CVD tool is in operation. Cleaning with F2 can reduce chamber cleaning times by a factor of 2 to 4, and therefore greatly increase the throughput on a critical step of thin-film PV production. And because much less energy is required to activate F2 vs NF3, smaller, less expensive equipment can be used for activating F2.
ADDITIONAL INFORMATION:
Please see the following attached files in support of our entry:
1. Sustainable Chamber Cleaning Solutions -Semiconductor International, Jan 2008
2. Carbon footprint chamber cleaning PECVD - Photovoltaics International, Nov 2008
3. NF3, the greenhouse gas missing from Kyoto - Prather and Hsu, Jun 2008
4. Nitrogen trifluoride in the global atmosphere – Weiss etc, Oct 2008
5. Fluorine cleaning of a-Si PV Process on ULVAC PECVD tool – AIST Japan, Spring 2008
6. Going green with on site generated fluorine - Photon 4th Equipment Conference, March 2009
7. Flex-F80 product data sheet
PECVD Chamber Cleaning challenges
