ZHAOHUI YAN, Global Market Segment Lead for Microelectronics at DuPont Water Solutions
Water is fundamental in the manufacture of microelectronics, with large volumes of water required at every stage of the fabrication process. As one of the world’s most water-intensive industries, it is understandable why it is in the spotlight as water scarcity becomes an increasingly pressing issue. In addition to sustainability considerations, water stress can increase operating costs for foundries as they compete with local communities for local resources, plus it may expose them to reputational, regulatory, and litigation risks.
“In the midst of increasing regional water scarcity and raw material costs, we’re seeing end-users increase their reclamation of wastewater for reuse back into their process streams—and recycling other valuable resources through minimum or zero liquid discharge strategies,” said Veronica Garcia Molina, Global Marketing Leader, Industrial Water & Energy at DuPont Water Solutions. “We’re seeing a shift from reuse being viewed as aspirational to something that is now necessary.”
The semiconductor industry is undergoing an evolutionary shift from simply striving to meet increasingly stringent regulatory requirements on discharge, to reusing wastewater, and is now embracing the reclamation of resources from wastewater as part of the treatment processes that enable reuse. This shift reflects the general principle of 3Rs; reducing pollutants and freshwater consumption, reusing water, and recycling resources.
The scale of the challenge
Producing a typical 12-inch wafer will generate around 10 m3 of wastewater containing valuable minerals, including approximately 3.5 Kg NH4+, 1.0 Kg TMAH, 50 g valuable metals, and 100 g of silicon particles. This wastewater is generated during many different front and back-end process stages, with its composition varying greatly, requiring different treatment approaches for maximum efficiency (FIGURE 1).
For example, TSMC classifies its process wastewater [1] into 38 types according to their composition and concentration of specific compounds (FIGURE 2). Low-concentration wastewater most suitable for reuse is divided into three categories which directed wastewater streams for treatment by nine recycling systems.
Treatment Technologies: The wide world of membrane filtration and ion exchange resins
Membrane filtration is a flexible and proven method for the concentration of liquids and separation of materials. This technological approach is often faster and easier to manage than energy-intensive centrifugal separation or evaporation solutions. The precise nature of the separation is determined by the membrane’s chemistry:
- semi-permeable membranes rely on a combination of size exclusion and solution/diffusion permeation to achieve separation.
- microporous membranes can be used to separate targeted components from a feed stream dependent on pressure and the target molecular weight.
It is certainly not a case of one size fits all; there is a huge variety of membranes available on the market, developed for different industries, applications, and treatment approaches. The different grades and properties of these membranes determine not just their efficiency and performance characteristics, but also their resistance to fouling.