Corporate Environmental Report

Water



Water plays a critical role in the manufacture of semiconductor products and because of the extreme sensitivity of processes, only ultra-pure water can be used. This is created by reverse osmosis and de-ionization.
In addition, the water is specially treated and this consumes both energy and chemicals.

Water conservation is a general ST corporate goal, but it is an imperative at several STMicroelectronics manufacturing sites where water supplies are scarce or diminishing - Malta, Rancho Bernardo, Phoenix, Catania and Singapore, for example. At a corporate level, STMicroelectronics has substantially cut its use of water, reducing the cubic meters used per million dollars of standard production value from 11,300 in 1994 to 7,800 cubic meters in 1998. Last year we met 95% of the Decalogue goal, mainly due to the production level decrease during 1998.
Especially for those sites with shortage of fresh water, reduction in water consumption has been made through recycling activities.

For all manufacturing operations, reach a level of 50% recycled water by end 1997 and 90% by end 1999.

A simple example of water consumption reduction comes from our manufacturing site in Rancho Bernardo in San Diego, California.

In 1998 the site initiated and completed a K$70 capital project to reuse waste water. The system was based primarily on an advanced waste water treatment system with filters and chlorination.

Instead of discharging waste water from the neutralization system, the water is reused for a variety of industrial processes including air emission scrubbers, bottle washing, and cooling water for the thermal processing units (TPU). This reuse of waste water accounts for over 10% of the site's total water use.

In Malta, large volumes of water are used during silicon wafer cutting. In the slicing process, silicon dust is too fine to be captured by traditional filters. The site installed a microfiltration unit to remove the fine particles and the water was then further purified by passage through ion-exchange resin columns. It was then clean enough to be recycled for operations requiring extremely high purity water. As a result, city water used was reduced by some 13,000 cubic meters per year.

A system was also developed for recycling the waste brine, discharged by the plant's Electrodialysis Reverse water purification. The concentrate waste was collected and, after filtration and chlorination, the water became suitable for non-potable use in toilet flushing. A separate storage and distribution system now directs this water to more than 90 toilet units in the facility. City water consumption dropped by a further 6,500 cubic meters.

During the second quarter of 1998, the Malta site made a major effort to recycle waste water from its electroplating operations. During this process, residual metals always pollute the water. It makes sense to recover the valuable metal and clean the water for reuse whenever technically and economically feasible. The new design uses ion-exchange resins to recover the metals and reverse osmosis to further purify the water. 80% of the waste water effluent is now recovered with a saving of 60,000 cubic meters annually, equivalent to 50% of the present water intake.

The final component in the site's comprehensive water conservation strategy was the installation of a rainwater capture and recycling system. By the second quarter, the facility had reduced its consumption from city mains from 183,000 cubic meters per year down to 52,000 cubic meters &emdash; a remarkable reduction of 72%.