By Chris Jones, Edwards Vacuum
The energy-hungry nature and large carbon footprint of semiconductor manufacturing have received considerable attention in the context of reducing our emissions of planet-warming greenhouse gases. It turns out we are just as thirsty as we are hungry. Our industry consumes copious amounts of water, as much as 264 billion gallons per year, a resource likely to become more scarce in a changing climate. An individual fab can use tens of millions of gallons of water per day. To put this into perspective, average water usage in the U.S. is about 82 gallons (310 liters) per person per day, making 10 million gallons equivalent to the daily household water consumption of a small city (population 122,000). One needs only to glance at the headlines describing historic warming-driven drought conditions in numerous locations worldwide, including the US, Europe, and Asia, to understand the urgent need to conserve this essential resource.
Water use in a fab.
The largest use of water (about three-quarters) in a fab is process related, with much of that being converted to ultra-pure water (UPW) needed for production itself, followed by the facility scrubber and cooling tower (both about one-tenth) (Fig 1). Fabs typically have separate circuits for ultrapure water (UPW), which can be hot and cold, and lower purity (LP) water. UPW generation is a complex, multi-step process that also consumes significant amounts of power. Most fabs have some level of UPW reclamation, although rates vary widely among fabs and processes within a fab.
Figure 2 shows fab water usage (feedwater withdrawals in billions of liters per year) for several semiconductor-producing countries. The top five are all using well over 100 billion liters per year. The numbers at the right end of each country show the consumption per square centimeter of product. Various types of product are represented in the color key.
The primary use of water by Edwards products is in the abatement of process gases, where systems often include an integrated wet-scrubber. Abatement may account for 1% – 5% of the water recirculating through a fab’s wastewater and water recycling facility. The most immediate opportunities to reduce water consumption in this application lie in using water only as needed to scrub the processed gas and selecting materials to enable high concentrations of contaminants to be present. Materials selection can reduce water used for abatement by more than 75%. Switching the abatement system to idle mode, when a process tool signals it is not actively processing, can reduce abatement water usage by more than 98% during that idle period.
Water Use and Energy
Beyond the growing need to conserve water because it is increasingly scarce, many processes associated with water usage also contribute to the industry’s carbon footprint through their consumption of energy. The latest update to S23, SEMI’s guidance for energy use in the fab, assigns a value of 9kWh/m3 to generate cold UPW, and 92kWh/m3 for hot UPW. S23 does not declare a value for wastewater management. Internally, we have used 4.12kWh/m3 for water and wastewater to and from the abatement system. The energy requirement will be much higher if the water is extensively recycled. The energy required for wastewater management will vary according to the type of waste, the quantity, the recycle efficiency, and the waste management processes adopted. Any fab energy assessment must include facilities required for production, such as the use of chemicals and energy consumed in the wastewater management process.
Water use globally
Water access and availability vary from region to region. Unfortunately, many centers for semiconductor manufacturing lie in regions of high water stress (as expressed by the ratio of water withdrawn to water available). Let’s take a brief look at several of these centers to see what they are facing and how they are dealing with their water challenges.
Singapore, a small island nation with limited freshwater resources, is, in many ways, the poster child for proactive water management. They have invested heavily in desalination, and their NEWater program recycles wastewater for industrial use and drinking after further treatment. Since the fifth NEWater plant came online in 2017, the program has produced more than 40 billion gallons (150 million cubic meters) per year. Semiconductor manufacturing consumes 25.7 million gallons (~100 million liters)2 per day of potable and NEWater, constituting 11% of the country’s non-domestic water demand and equivalent to about 86,000 US households. All wafer fabrication plants in Singapore practice some form of water recycling, and recycling rates range from 23% to 65%, with an industry average of 45%. For semiconductor plants, the situation is more variable, with the recycling rates ranging from 0% to 80% and an average of 23%. They expect water demand to double from 430 to 860 Mg/day (1.6 to 3.2 billion liters per day) by 2060 and plan to meet 85% of that demand with desalination and recycled NEWater.
Taiwan, another island, has many fabs in high water stress areas. TSMC withdrew approximately 51 Mg/day in 2020i (197 Ml/day or 170,000 US households). Usage is increasing steadily, but they have an admirably high recycle rate, averaging over 85% from 2016 to 2020. Taiwan have implemented an integrated water resources management program to address planning for water quality, quantity, and resource control; shifting social perspectives on saving, reusing, recycling, diversifying sources, and storing and using rainwater; improving the efficiency of existing facilities and constructing a backup water supply network; and involving the private sector in desalination, recycling, and developing new sources.
Recent data for China is harder to come by. A 2016 report puts 40% of fab production in Jiangsu province, where water resources per capita are relatively low. A 2017 study attributed 27% of the water used by manufacturingto the semiconductor industry. SMIC reported 2020 withdrawals of about 11 Mg/day (42 Ml/day or 37000 US homes), with recycling rates between 65% and 72% from 2016 to 2020. Usage may be increasing, and it is unclear how recycling rates are calculated. China has made major investments in water-related projects, totaling $470 billion between 2014 and 2020. Its stated goals include increasing water supply by 32 trillion gallons (122 billion cubic meters) per year (20%), saving 6 trillion gallons (22 billion cubic meters) of irrigation water per year, increasing flood control capacity by 8.3 trillion gallons (31.6 billion cubic meters) and increasing its irrigated area by 10%.
Most fabs in South Korea are in areas of medium to high water stress. Samsung, the country’s largest producer, withdrew 103 Mg/d (390 Ml/d or 340,000 US homes) globally in 2020. It reuses nearly half of that. Recently Korea has enacted laws relating to integrated water management across local and national governments. A National Water Management Committee has been set up, and it has invested $20 million (2012-2019) in studies regarding the implementation of a smart water grid.
Many fabs in the US operate in highly water-stressed southwestern states. For example, of the three main fabs in Maricopa County, Arizona, the largest, Ocotillo (operated by Intel), withdrew 8.5 Mg/d (32Ml/d or 28,000 US homes) in the twelve months leading to the end of June this year. Intel has made major investments in a water recycle facility in Oregon that treated 6.6 Mg/d (25 Ml/d) in 2020.
Water supply challenges for the semiconductor industry
To paraphrase a well-known political adage, “All weather is local.” Only a few decades ago, a change of a degree or two in long-term global average temperature might have seemed unimportant to most of us. But that seemingly insignificant change in the global average belies the dramatic changes we are already seeing at the local level. It’s not that there is less rain – a warmer atmosphere actually holds more water. But that rain falls in different places. Like the weather, water too is local. If it’s not available when and where you need it, it might as well not exist. Ask the residents of Portland, Oregon who often endure seasonal water use restrictions while 650 million cubic meters of freshwater flow by the edge of town every day in the mighty Columbia River.
Water availability depends on various factors, from weather and climate to local infrastructure. The effects of climate change on water availability are equally broad, including reservoir/storage depletion, increased flood risk and frequency, rising sea level, declining seawater quality, and more. The news is full of reports of droughts and floods around the world. Sea levels will certainly rise on a warmer planet, unwelcome news for coastal plains where the problem may be compounded by subsidence caused by the over-extraction of groundwater.
In summary
Water is becoming more valuable and more scarce. Semiconductor manufacturing needs a lot of water, primarily to produce the ultrapure water for the process itself. There are many other uses for water in a fab: cooling, scrubbing, point-of-use abatement, and fire suppression, to name a few. A single fab can withdraw the same amount of water as tens of thousands of homes. Many fabs are sited in regions of high water stress.
What can we do? First, we need to raise awareness. For this, a common measure of water usage, reuse, treatment, and recycling would be useful – perhaps something modelled on an extension of SEMI’s S23 guidance for energy analysis. It would also be important to ensure that the energy conversion factors in S23 enable an accurate calculation and comparison of the energy consumed by the various systems deployed.
Climate change will have a negative impact on the availability of water in many regions where semiconductors devices are manufactured. It is also important to understand the balance between recycle efficiency, energy usage, and carbon footprint. Innovative approaches that involve the fabs, local, and national governments are needed to manage this water risk as production increases.
