MANUFACTURING I MATERIALS
Table 1. Comparison of bond strengths for typical cleaning gases
Larger generators have been designed for supplying hundreds of tonnes per year. Although the process design remains the same, the form factor for these systems has grown to a separate on-site facility. This mirrors the way other on-site supply schemes work for example. nitrogen, oxygen and hydrogen, from which manufacturers benefit in cost of ownership as they scale their operations to achieve a critical capacity.
In January 2008, the international roadmap for semiconductors (ITRS) for voluntary reductions in the use and emission of high GWP gases [1]. Largest in volume among these is nitrogen
trifluoride (NF3), whose consumption has skyrocketed recently with the ramp in production of thin-film PV panels and LCD displays. Usage on this scale prompted Michael Prather, lead author of the Nobel Peace Prize winning Intergovernmental Panel on Climate Change, to label nitrogen trifluoride as “the greenhouse gas missing from Kyoto” [2].
Measurements by the Scripps Institute have indicated a quasi- exponential growth in the amount of nitrogen trifluoride present in the atmosphere with more than 10% of nitrogen trifluoride produced ultimately escaping into the atmosphere [3]. The US EPA has now included nitrogen trifluoride and other greenhouse gases commonly used in electronics industry to be included in their reporting rules. Manufacturers are therefore required not only to report the amount of individual greenhouse
Fab Cleaning Gas CO2 Equivalent Emissions A NF3 (tonnes/year) approximate usage per MW B GWP100 for NF3 (tons CO2eq) ref [1]
C NF3 lifecycle emission ref [2]: Scripps Institute measurements D NF3 CO2 eq lifecycle emission ref [3]: ECN/M&W-Z study E NF3 lifecycle emission [Linde estimate]
F Customers plant capacity MW Cleaning Gas Atmospheric Lifetime [years] CF4
C2F6 C3F8 SF6 NF3
50,000 10,000 2600 3200 740
Table 2. Comparison of GWP for typical cleaning gases
gases used but also to measure the gases at key stages. In contrast to nitrogen trifluoride, fluorine has a zero GWP as it does not absorb UV radiation and convert it to heat. Combined with the increased synthesis, handling, and distribution energy requirements of off-site nitrogen trifluoride, the total carbon footprint of on-site generated fluorine is many times less [4].
As there is no loss of high GWP starting material, the abatement requirement for fluorine cleaning is simplified, and any regulatory compliance burden is significantly reduced [see table 2].
1
17,200 tonnes 16%
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G Equivalent CO2 reduction at Schüco Großröhrsdorf using ref [2] = A x B x C x F H Equivalent CO2 reduction at Schüco Großröhrsdorf using ref [3] = A x D x F I Equivalent CO2 reduction at Schüco Großröhrsdorf using Linde estimate = A x B x E x F
Table 3. Potential CO2 reduction using Linde estimate 14
www.solar-pv-management.com I Issue IX 2011
2,200 kg CO2 per kg NF3 10%
60
165,120 tonnes per year 132,000 tonnes per year 103,200 tonnes per year
GWP [equivalent kg
CO2 / kg] 100 years
6500 9200 7000
23,900 17,200
F2 00
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