Direct Water Reuse in PoU Gas Abatement applications
Joerg Winter
The semiconductor fabrication industry is aware of its dependence on water. Many manufacturers, thus, set ambitious goals with respect to the reduction of water consumption. Water recycling plays a key role in that context. A centralized approach where a broad mixture of wastewaters is treated to a water quality that fits a broad range of applications is the most direct way to reach water recycling goals. However, complementing that approach with decentralized solutions where selected contaminants are removed from specific wastewater streams to a ‘fit for purpose’ quality for reuse in particular applications can save resources with a more minimal impact on fab infrastructure.
One area for direct water recycling is the treatment of wastewater from point of use gas abatement for the reuse in those gas-abatement systems (i.e. wet scrubbers, burn-wet systems, dust removal systems). The appropriate water treatment thereby depends on the waste gas and consequently the wastewater characteristics, with salt and particle loads being main parameters.
The present abstract focuses on applications where the water usage is governed by water exchange in the gas abatement with the purpose of limiting particle concentration.
Potential manufacturing processes where the latter applies are:
• MOCVD processes
• W-CVD processes
• PV processes
In the water, the metals are typically present as oxides (e.g. alum-oxide, zinc-oxide, tin-oxide etc.). The concentration of those particles should be kept within certain limits in the gas abatement system to minimize maintenance intervals and maximize uptime. To date, this is commonly done by the usage of fresh water. DAS has developed a water treatment system that receives the wastewater from the gas abatement systems, filters the water to reject the particles and provides the gas abatement system with the treated water on demand.
The system is currently being tested in the field with the possibility to vary filter selectivity for system optimization. At production scale, the system will be equipped with membrane filters with the optimal pore-size. With those systems, water savings and reduction of wastewater produced from approximately 30 L/h to 1,400 L/h per point of use abatement systems can be achieved.