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Emissions to Air
Almost all semiconductor manufacturing processes use chemicals and gases that can be harmful to the environment. For example, the wet etch process uses acids such as hydrochloric, hydrofluoric, or sulfuric acid. Without treatment, emissions could acidify the environment.
Scrubbers are installed at most of our manufacturing facilities to abate emissions such as acids, alkalis and solvents. All scrubbers are equipped with variable frequency drives to conserve energy and to maintain the standard exhaust pressure needed by the equipment.
Each site monitors the air emissions parameters to ensure they are within the corporate specification limit. These are based on the most stringent regulations of any country where we operate. Monitoring of critical parameters is continuous.
EXAMPLES
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At our Carrollton site in Texas, USA, a system was installed in 2000 to segregate acids, VOCs and ammonia exhaust emissions for treatment. Over 95% of all VOCs are removed. The treatment involves VOC emissions being absorbed on a rotating wheel, then separated out and destroyed in a thermal oxidizer. This system has already been replicated in our new 8-inch wafer fab in Rousset (France) and project studies are running at other ST sites. |
NET PFC EMISSIONS TRENDS
(Calculated with IPCC Tier 2c method)
PERFLUORINATED COMPOUNDS (PFCs)
PFCs are greenhouse gases, which trap heat in the earth’s atmosphere and contribute to climate change. A number of gases have been identified as GHGs - they have varying impacts on global warming, depending on their different properties. The unit used to measure their impact is known as the global warming potential. PFCs are very stable and have a long life time in the atmosphere. However, they are non-toxic and do not damage the ozone layer.
PFCs are widely used in the semiconductor industry for CVD chamber cleaning and etching processes. The semiconductor industry uses several types of PFCs with global warming potentials ranging from 6,500 to 23,900 times the CO2 equivalent. The World Semiconductor Council (WSC) where ST leads the European participation, has set a challenging goal of reducing the aggregate absolute PFC emissions to 10% below 1995 levels by 2010. This aggressive target is expressed in absolute emissions (rather than emissions per unit) to assess the real benefit for environment. ST’s emissions are expected to increase up to 2003-2004, after which they will decrease.
ST will contribute to the program by reducing its emissions to 10% below 1995 levels by 2008, at least two years before the WSC deadline.
We have already cut our emission rate, expressed in kg of carbon equivalent per wafer, by roughly 50%, compared with the 1995 baseline.
EXAMPLES
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Around 80 PFC point-of-use abatement systems have already been installed in our manufacturing sites. Alternatives such as C3F8 have been widely tested and implemented in several of our locations in Europe, US and Asia. Substituting C3F8 reduces PFC emissions by 40-70% compared with traditional processes. New equipment using NF3, which can reduce emissions by more than 95%, is now operating in at advanced front-end manufacturing sites. |
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