New technologies and processes help companies strive for net-zero.
Fabs, OSATs, and equipment makers are accelerating their efforts to consume less water while recycling more material waste in a trend toward better sustainability.
With chips, sustainability is heavily focused on carbon emissions, and energy consumption is a significant contributor. But there is an equal effort underway to reduce water consumption and pollution. Across the globe, the number of regions where water is considered scarce is growing. Some 75% of the United States qualifies. And while large manufacturers always have managed their material waste and wastewater, they now are setting more aggressive goals which drives change.
“We recognize the importance of a healthy environment, and we are committed to preserving our natural resources, improving sustainability, and contributing to the quality of life in the communities where we operate,” said HyeJu Lee, vice president of compliance at Amkor Technology. “At present, our key sustainability goals are to reduce GHG (greenhouse gas) emissions, water usage, and waste generated by 20% by 2030, from the baseline average of 2018 to 2020. We continue to monitor our progress, and we are on track to meet our goals.”
Sustainability efforts often are classified by intensity, which is a measurement per revenue. For example, companies report water withdrawal intensity in gallons of water used per $1 million revenue.
This reaches far beyond manufacturing, though. To meet sustainability goals for everyone in the supply chain, collaboration is needed.
“We launched the Semiconductor Climate Consortium (SCC) [1] at COP27 last November,” said Mousumi Bhat, vice president of sustainability programs at SEMI. “The consortium is working to accelerate chip industry value chain efforts to reduce greenhouse gas emissions in member company operations and in other sectors of the value chain. These companies have made a commitment to band together to leverage their best skills and resources as a collective. To accelerate the journey to net zero, companies are addressing the toughest climate issues. As part of the overall SEMI Sustainability Initiative, our circularity working group is addressing water usage and waste management — two areas central to a cradle-to-cradle circular economy.” [2]
Material management
Both wafer fab and assembly factories generate material waste. Hazardous waste requires disposal procedures that meet government regulation requirements. In the case of the U.S., those requirements are set by the Environmental Protection Agency. Net-zero means 0% of materials used or produced by operations winds up in a landfill. In striving toward that goal, the options available include reduction, reclamation, and incineration. Incineration can be used to generate energy or not. In their annual reports, companies provide detailed numbers in terms of tons of waste per year, intensity, and handling methods.
“Our company is committed to minimizing waste generated from our facilities worldwide and promoting sustainable waste management practices,” said Amkor’s Lee. “We have implemented a comprehensive waste reduction program focusing on waste segregation, recycling, and reuse. As part of our environmental impact, we continue to monitor the waste generated in our manufacturing process so we can best implement reduction and recycling strategies. We strive to recycle materials to the extent possible as part of our efforts to manage the waste generated. To give an example, we collect plastic packing materials (trays, leadframe cases, wire inner boxes and spools, wafer cassettes, etc.) separately and send them back to suppliers for reuse. Our total waste generation intensity decreased by 19% from 2021 to 2022.”
Recycling and reuse may involve adopting/adapting existing processes or developing new processes.
In May 2023, UMC announced that it is building a Circular Economy & Recycling Innovation Center in Tainan, Taiwan.[3] In phase one, the foundry will process IC manufacturing waste to be re-used or sold, such as turning sludge into industrial-grade products and using thermal cracking to turn waste solvents into fuel. (Thermal cracking uses temperature and pressure (450-700°C, 70 atm) to turn larger hydrocarbons into lighter, smaller hydrocarbons.) In phase two, the center will further develop thermal cracking to process plastics. UMC estimates the facility will reduce waste by one-third and generate ~NT$100 million (USD $3.2 million) in value-added products. The center enables collaboration with raw material suppliers and waste management providers in developing new recycling methods.
In parallel, third-party auditing organizations are assisting companies in determining additional actions that will help companies meet waste reduction goals.
“In 2022, our teams identified strategies to better manage and reduce non-hazardous waste,” said Shawn Covell, director of ESG strategy at Lam Research. “They partnered with a third party to conduct reporting and internal audits, which resulted in key recommendations for efficient waste management practices. We are now engaging employees to implement these practices globally. Our teams have implemented key waste minimization activities such as silicon reuse, wood crate take-back programs, and on-site composting. Lam also has joined SEMI’s circularity working group to share best practices and to collaborate and advance further industry innovations.”
In its 2022-23 report, Intel noted it is targeting 60% of the company’s manufacturing waste streams to be diverted from landfills, with some of it focused on circular economy. For the year 2022, the company reported that 120,000 metric tons of GHG emissions was avoided by taking solvent wastes and implementing methods to recover, recycle, and fuel blend rather than incinerate.[4]
Many improvement strategies
Achieving net-zero waste involves multiple strategies — in particular, for the hazardous waste.
“We have a Zero Waste-to-Landfill program and have been Green Circle Certified Zero Waste-to-Landfill for seven years,” said Rory McCarthy, environmental manager at Brewer Science. [5,6] “Over 12 tons of construction debris from a new building was collected and sent for energy recovery. Over 3,000 pounds of scrap metal from the construction was collected for recycling.”
With its Alerion program, Brewer Science re-uses solvent waste to clean tanker cars, after which it is sent to cement kilns. In its 2022/23 CSR report, the company noted that improving its separation of solvent waste resulted in 64% increase in hazardous waste being used.[6]
Fuel blending has become a common method for handling some hazardous waste materials. By processing hazardous waste into fuels derived from liquid and solid waste, facilities can replace some coal and natural gas usage in certain applications.
Fig. 1: Hazardous materials treatment in pounds of waste. Source: Brewer Science
Water management
Semiconductor manufacturers are striving for net-zero water impact. They can accomplish this via conserving and reclaiming water or investing in regional water projects. Semiconductor manufacturing consumes a large amount of water, especially during wafer fabrication.
One fab can use tens of millions of gallons per day. Three-quarters of that water supports wafer fabrication processes. The next 20% is used by its facilities scrubbers and chillers. Such levels place a strain on a region’s water resources, and many fabs are located in water-constrained regions throughout the globe. So it’s imperative that factory water systems reclaim water for other uses. Treatments for hazardous containments need to be included.
“We recognize that water conservation is increasingly important for our company and remains a critical aspect of our sustainability efforts. We have implemented a thorough water management program at our manufacturing facilities worldwide,” said Amkor’s Lee. “As part of this effort, we continue to operate reverse osmosis systems at our facilities, allowing us to purify the process water and re-use the water in our manufacturing process. Reverse osmosis systems are combined with electro-deionization (EDI) systems, and it uses less than 95% of the chemical products used in the conventional ion exchange processes. This helps to reduce freshwater usage, improve water efficiency, and protect the environment. We continue to reduce our water usage and contribute to the preservation of water resources. Our total water withdrawal intensity decreased by 12% from 2021 to 2022.”
To achieve water use efficiency, ASE Group adopted the ISO 46001 Water Efficiency Management System [7], which assists engineering teams in identifying risks and opportunities for improvements. In 2021 ASE Kaohsiung facility became the first OSAT in Taiwan to earn the ISO 46001 certification. ASE then achieved certification at its ChungLi facility.[8]
It’s not just factories paying attention to water. Equipment and materials suppliers also are stepping up conservation efforts.
“As part of our ESG strategy, we continue to make strides in achieving water savings,” said Lam Research’s Covell. “In 2022, we exceeded our goal to achieve 17 million gallons of water savings in water-stressed regions from a 2019 baseline by 2025. [9] As part of setting this goal, we used the World Resource Institute Aqueduct Water Risk Atlas to identify which of our facilities were in water-stressed regions. To date, we have identified six sites throughout California, South Korea, India, and Malaysia.”
With infrastructure and process improvements, Brewer Science saved 1.16 million gallons of wastewater in 2021. In 2022, facility upgrades enabled 150,000 fewer gallons of water used per month.
A fab’s water management system consists of multiple systems for different water types – ultrapure water (UPW) and lower purity water (hot and cold) — and for the management of multiple water waste streams. Wafer production equipment has a high reliance upon ultrapure water [10].
“The ultrapure water system is an intricate system that includes many integrated units,” explained Slava Libman, CEO of FTD Solutions. “When the system runs out of capacity, the water pressure goes down, which results in not much water going to the tool. There are two ways of increasing capacity. One is to build another system. An alternative way is fine tuning the existing ultrapure water system to maximize capacity utilization. It takes a little bit of engineering expertise to look at each unit’s operation capacity and identify bottlenecks. For example, certain equipment may need an upgrade or a modification in operating recipe.”
Libman highlighted how one customer increased water reuse from 30% to 65% by optimizing its existing infrastructure, thereby avoiding capital expenditures of ~$30 million.
Fig. 2: Illustration of a fab water system management. Source: FTD Solutions
Wastewater streams often are segregated because that reduces the cost and complexity of treatment. Each wastewater stream requires multiple, specific process steps from the point of waste generation to returning water back to the utility, or to be reclaimed within the factory. Government regulations set limits on containment levels that are environmentally safe to discharge.
Over the last 40 years, reverse osmosis (RO) has been a technology of choice for purifying water. In RO, a semi-permeable membrane filters contaminants as water passes through under a pressurized system. From a saline stream the process can recover up to 50% fresh water. But more fresh water could be recovered.
One path for increasing the recovery amount involves machine learning. “With semi-batch reverse osmosis, the increase in water recovery can move from 50% to 65%,” said Prakash Govindan, co-founder and CTO at Gradiant. “This comes from applying a machine learning algorithm developed for this mode of operation. It uses the data to squeeze a little extra out of the existing equipment. Instead of a continuous feed and bleed approach, with the semi batch approach, we send water out of the system only after a set period of time. With that small innovation the effectiveness of machine learning can be applied.”
Due to fundamental limits of the cross-flow process, reverse osmosis is limited to 50% to 65% recovery. The osmotic potential curve versus concentration is an exponential function, i.e., the required osmotic pressure increases dramatically with an increase in concentration. It is nearly impossible to manufacture a membrane to withstand these higher pressures.
But reverse osmosis also can achieve significantly higher recovery. “Counterflow reverse osmosis is a paradigm change in how reverse osmosis works,” Govindan said. “If you look at the fundamental equations, you realize that you can get flux of freshwater through the membrane as a function of the delta osmotic pressures. It requires a counter-flow arrangement, where the output side of the membrane has slightly salinated water. The osmotic pressure of that slightly saline water cuts the osmotic pressure of your concentrated feed coming through. By just maintaining a 70-atmosphere barometric pressure in your system, you can almost achieve salt saturation. This requires a cascaded, multistage arrangement. In six stages, we can achieve 95% to 98% salinity.”
Using counterflow reverse osmosis, fabs in Singapore, Taiwan and the U.S. have achieved up 99% of wastewater recovery.
Fig. 3: Counter-flow reverse osmosis process, and multi-stage implementation. (MLD brine = Minimum Liquid Discharge brine; CFRO = counter-flow reverse osmosis). Source: Gradiant
Removing copper
During post-damascene CMP of wafers, both chemical oxidation and mechanical abrasion remove copper. This results in wastewater with a high concentration of copper sulfates mixed in with hydrogen peroxide, organics, and silica. This mix of containments complicates treatment and requires multiple steps prior to removing the copper. The EPA sets the copper discharge target at <2.07 ppm per liter of water.
Fabs can truck their copper wastewater offsite to be processed at a third-party facility. Or, within their own wastewater treatment facilities, they can use several treatment options to achieve safe copper levels.
Chemical precipitation and flocculation processes adds chemicals to precipitate the copper into a sludge, and then the water is removed. However, that still requires trucking the sludge off-site.
Another option is to use ion exchange resins to capture the copper. The tradeoffs come with resin reuse. The additional contaminants need to be removed first in order to reuse the resins. Otherwise, they can only be used once. This step impacts maintainability.
Electrowinning is another option, which electroplates the copper onto the surface by passing an electrical current through the wastewater. While this method supports copper reuse, it does not remove enough metal to reach discharge levels, so additional steps are needed.
For several reasons electro-ceramic desalination (ECD) presents the most attractive alternative technology. “We can knock out two to three stages of a traditional treatment process, which makes it far more cost-effective,” said Paul Humphreys, senior vice president of business development at Membrion. “When you go from three to one process step, you also reduce the amount of service and consumables. Also, you’re using less operator time, because there is less equipment to worry about and maintain.”
With respect to maintenance, the ceramic membrane used in ECD lasts much longer than traditional materials. For instance, ion exchange resins could last three to four weeks, while a ceramic membrane can last for several years.
“Our technology uses ECD to remove salts, metals, or minerals from a variety of different wastewater streams,” said Greg Newbloom, president and CEO of Membrion. “In the semiconductor industry we focus on the treatment of metal wastewaters — in particular, copper wastewater. The challenge with copper wastewater is what comes along with it, which makes it difficult for traditional water treatment technologies to work effectively. Copper wastewater is often at low pH. Frequently you find some level of oxidizers, and these can break down the components of wastewater treatment technologies. These wastewater particulates (micron- or nano-sized) can clog and foul components. Chelating agents can foul membrane surfaces. In the midst of all contaminants in the water, ECD selectively pulls the copper out of the wastewater. This allows the remaining wastewater to be combined with their general waste stream and then process it much more efficiently.”
So how does it work? “Our ceramic membranes are designed to have really small pores that only transport ions,” Newbloom explained. “You have wastewater on one side of the membrane, and you apply electricity across the membrane. The positively charged copper moves toward the negative electrode into a secondary stream that becomes very concentrated over time. The flow rates on either side of the membrane must be the same. We actually use a fairly small volume of liquid that just gets recirculated over and over again, because it takes time for the concentration to slowly build up in the other compartment.”
Fig. 4: Electro-ceramic deionization process, implementation, product. Source: Membrion
Conclusion
Water is essential for life and for semiconductor manufacturing. Without clean water, neither can exist. Facilities are optimizing existing wastewater treatment options and adopting new treatment technologies, which enables higher reuse and higher purity levels. With all new technologies on the horizon, net-zero within two decades appears to be attainable.
While CO2 equivalent emission has become the popular measurement of a semiconductor company’s impact on the global climate, efforts to reduce material waste and clean water usage are equally important. Using fewer materials, re-using them in some capacity, and recycling processes are continuing to gain momentum.
References:
Related Reading
Managing Water Supplies With Machine Learning
Fabs need to understand their water supply and segregate sources that require different levels of treatment.
Goals Of Going Green
Net zero goals target energy, emissions, water, and factory efficiencies.
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