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Chemicals
| Recycle the most used chemicals - e.g. for sulfuric acid recycle > 30% by end 1997 and 80% by end 1999. |
The semiconductor manufacturing processes require significant amounts of chemicals. ST is working in all directions to save these hazardous substances by substitution, process optimization, hardware modifications, on-site generation, recycling for reuse, and the installation of Total Chemical Management (TCM) in partnership with key suppliers, to name a few. This will improve the management of chemicals in terms of safety, tracking system and cost.
Engineers working on wet processes (cleaning processes using chemicals) are at the forefront of our efforts in chemical saving programs.
In addition to the undeniable benefits to the environment, health and safety the initiatives bring significant savings in cost, as well as better process performance.
In 1998, a global chemical survey was conducted to identify priorities in chemical savings. Three criteria were used: environment health and safety parameters, cost and global consumption. Photoresists, developers, sulfuric acid, nitric compounds, fluoride compounds, ammonia and hydrogen peroxide were identified as priorities. Several additional chemicals used in specific applications are also targeted : xylene, phosphoric acid, isopropyl alcohol (IPA) and acetone.
 Central R&D in our Agrate site in Italy is already preparing the long term with a strategic and revolutionary process known as "Twin Clean". Once in effect, this process will bring about significant reductions in the use of ammonia, hydrogen peroxide and sulfuric acid. The process will also bring a 50% increase in throughput, de-ionized water will be reduced by a factor of three, with an appreciable diminution in footprint of machinery.
At Crolles, in France, many different optimizations have been successful. Half pitch carriers have been installed and chemical consumption has been reduced by half. With the optimization of tools, the lifetime of chemicals has increased by 15%. The isopropyl alcohol (IPA) reduction program brought a 40% reduction in consumption, with the IPA emission being divided by ten. Annual savings are $K100. The implementation of a new post ash-clean and photoresist stripping strategy reduces costs by one third, with the total chemical consumption reduced by half.
At several ST sites in France, the United States and in Italy, depending on the chosen process, savings ranging from $K400 to $K1200 are being made thanks to a process which optimizes the low flow pick up in equipment. At Ang Mo Kio in Singapore, resist dispense systems were upgraded with an original new design, with savings of $1.2 million per year.
Also at Ang Mo Kio, a sulphuric acid recycling system &emdash; including collection, reprocessing and distribution &emdash; has enabled the site to reduce its annual requirements for sulphuric acid by 95%. The consumption of H2SO4 was 500 liters per day. An additional 571 liters per day of NaOH were used to neutralize it in the waste water treatment plant. The implementation of a recycling project cut the consumption of H2SO4 and NaOH, resulting in a total project payback in less than 1.5 years.
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