Pure water, semiconductors and the recession

Subscription required

As a guest you can read up to 3 full articles before a subscription is required.

You can read a further 2 articles for free.

Subscribe Now, Sign up for a Free Trial, Log In

Pure water is vital for the survival of the $250 billion global semiconductor industry. Cost pressures brought on by the recession are filtering through to water treatment equipment manufacturers, as Gord Cope finds out.

The manufacture of semiconductors represents one of the largest industrial sectors on Earth. In 2008, the industry had worldwide sales of approximately $249 billion, and KPMG estimates that when the effect on the whole electronics value chain is taken into account, the industry enables the generation of some $1.2 trillion in electronic systems business and $5 trillion in services, representing close to 10% of world GDP.

Water is central to the manufacture of semiconductors, and the impact that the global recession has had on the semiconductor industry has had a knock-on effect on suppliers of water and wastewater treatment equipment. The cyclical nature of the semiconductor market can lead to unpredictable revenue fluctuations, but the modern world’s dependence on microelectronics means that each trough has always been followed by a new boom.

“Water is vital to producing today’s microchips, and microchips are critical to today’s communication lifestyle,” says Alan Knapp, director of semiconductor and solar global sales and marketing for Siemens Water Technologies. The cornerstone of the semiconductor industry is the humble transistor, which is used to amplify or switch electronic signals. A semiconductor device is a miniaturized electronic circuit containing a myriad of transistors. Through a complex series of steps, semiconductors are built on pure silicon wafers into integrated circuits (also called microcircuits, microchips and silicon chips) that are used in a wide assortment of consumer electronic devices, from computers to cellphones. They range in size from a few square millimeters to the size of a large dinner plate, with up to 1 million transistors per square millimeter.

The semiconductor industry is global in nature, with dominant manufacturers including Intel, Texas Instruments, IBM, AMD, Micron and Freescale in the US, as well as STMicroelectronics of Europe, Samsung of Korea and NEC of Japan. Semiconductors are manufactured in fabrication plants (“fabs”), each one costing upwards of $2.5 billion. While many fabs are located in Taiwan, South Korea and Japan, where they serve national consumer device manufacturers, about 65% of semiconductor manufacturing is located in the US. Out of about 400 fabrication units worldwide, more than 250 are located in the US. Most fabs manufacture semiconductors on small wafers of 135mm diameter, but around 150 manufacture circuits on larger 200mm and 300mm wafers.

The process starts with the manufacture of extremely pure silicon ingots that are grown in cylinders of up to 300mm in diameter. The ingots are then sliced into wafers less than 1mm thick and polished to create a f lat, smooth surface. The wafers are then treated in a series of steps, or ‘tools’, in which the materials that will form the electronic circuits are deposited, etched and polished. Many modern circuits have eight or more levels produced in over 300 sequenced processing steps, and the entire manufacturing process from start to packaged chips ready for shipment takes six to eight weeks.

Cleaner than clean
Ultrapure water (UPW) plays an essential role in the manufacturing of integrated circuit semiconductor chips. “There are many steps in processing a wafer,” says Tom Diamond, director of environmental health and safety for the Semiconductor Industry Association (SIA), which represents 75-80% of the semiconductor industry capacity in the US.

“One common step is called a ‘chemmech’, short for chemical-mechanical polish. The chemical part is a slurry of fine grit, and the mechanical part is a polishing pad. Once the surface has been polished, the slurry needs to be washed off with ultrapure water. The circuits are very small, in some cases only 32nm wide (one nanometre is one billionth of a metre), and they are crammed in there as tightly as possible.

“When you wash your car with potable water, you see spots after the water has evaporated. Those spots are from minerals dissolved in the water. These molecules of minerals could short out hundreds of circuits. That’s the reason the water must be so pure.”

The treatment process needed to create ultrapure water depends on the quality of the source and the requirement of the manufacturing process, Diamond explains. “The amount of ultrapure water needed depends on many factors. 200mm wafers use less than 300mm wafers. And memory chips require fewer layers than logic chips. The more layers, the more water is needed.”

Industry statistics indicate that creating an integrated circuit on a 300mm wafer requires approximately 2,200 gallons of water in total, of which 1,500 gallons is ultrapure water.

Industry participants estimate the annual spend of the semiconductor industry on water and wastewater systems and services to be around $1 billion, with half of that figure relating to capital equipment sales. While many companies supply a wide assortment of filters and other components, only a handful of companies supply complete UPW systems to the semiconductor industry. The largest suppliers include Siemens Water Technologies, GE Water, Christ Water Technology, Kurita Water Industries, Nomura Micro Science and Organo Corporation. Together, they account for about 60% of the global industry.

UPW flow rates for a fab plant can range from 500 to 2,000 gallons per minute, and a complete system (including wastewater capture and recycling) can cost 1.0-1.5% of a plant’s capital costs, or $25-40 million. While some Asian semiconductor manufacturers opt for the build-ownoperate (BOO) model, most prefer turnkey systems.

The needs for each plant are unique, although UPW water systems follow a common schematic f low, such as the following, outlined by Christ. In the pre-treatment stage, raw water is run through multi-media filtration and microf locculation to remove suspended matter and reduce the fouling index (raw water can also be passed through ultrafiltration membranes). Activated carbon is used to reduce total organic compounds (TOC) and oxidants.

The next step is ion removal. RO removes the bulk of ions, bacteria particles and remnant TOC. Depending on the source water, ion exchange (IX) may also be used. Oxygen and some volatile organics are then removed using a twostage vacuum degasifier or membrane degasifier. The water is then run through mixed-bed ion exchangers and electrodeionization. The final polishing loop generally consists of a UV unit to destroy remaining TOC. An additional degasser is also often employed, as is a second mixedbed ion exchange system.

In order to clean semiconductors with a component standard of 65nm, UPW must have a resistivity of under 18.2 microOhm-cm, with total SiO2 under 0.1 ppb, TOC under 1 ppb, O2 under 10 ppb, critical metals under 1 ppt, critical ions under 10 ppt, and no bacteria.

Purity is maintained through strategically placed filters and purifiers, as well as point-of-use filters right in the tool to eliminate trace contaminants from entering the process.

Wafer waste
Manufacturing semiconductors results in various levels of wastewater being generated. The industry faces two challenges: reducing the amount of water consumed, and cleaning up eff luent.

A host of toxic materials are used in the fabrication process, including arsenic, antimony, phosphorous, hydrogen peroxide, nitric acid, sulphuric acid and hydrof luoric acid. Arsenic in the form of arsine gas is implanted in the wafers in molecular amounts as part of the manufacturing process. Little if any of this material washes off – much of the waste material is the slurry paste used for polishing, while some acids and caustics also end up in the wastewater stream.

The semiconductor industry is governed by strict legislation, including the EPA’s Clean Water Act and state regulations in the US. All wastewater is captured, though suspended particles in wastewater, the majority of which are under 150nm across, complicate separation by conventional methods (e.g. coagulation, settling, centrifuge).

Hollow-fibre membranes are used to remove these suspended solids without the need for f locculating chemicals, improving the operating costs and overall efficiency of IX, ED and RO systems. Acids and caustics are neutralized, and other contaminants that are in solution are removed by other treatment processes. “Following the treatment processes, the solids that are filtered out are nonhazardous and can be sold or used for other things, such as material for roadways,” says the SIA’s Diamond.

Semiconductor eff luent can contain a host of valuable metals. “We had a semiconductor tool manufacturer based in Silicon Valley approach us to assist in the design of a copper waste treatment system,” says Siemens’ Knapp. “Any traditional method using a two-stage precipitation/clarification system produces copper sludge, which would be required to be handled as hazardous waste in the state of California. That’s very costly, and there are environmental concerns.”

Siemens Water Technologies looked at another approach which would remove the copper prior to particle f locculation and precipitation. They used an IX process to remove copper from wastewater without the need to remove solids. The copper-free wastewater could be then sent to a classical precipitation system for f locculation and coagulation of the solids remaining. After some initial start-up adjustments, the 20 gpm system worked effectively. Analysis of the solids showed copper levels below the 1 ppm level, allowing for non-hazardous landfill disposal.

“It saved any environmental impact, and the copper trapped by the IX was sold,” says Knapp.

In many places, the expansion of semiconductor production is restricted due to a limited water supply. The cost of water and surcharges for excessive consumption or discharge are growing. Most importantly, regulatory agencies are increasingly demanding that water consumption be reduced.

“Most water is recycled in some way,” says Diamond. The three Rs (Reduce, Reuse, Recycle) can also add to the bottom line: Pall Corp., a filter manufacturer, estimates that the reduction, reclamation and recycling of water from fabs would save the industry over $100 million per year due to reduced capital and operating costs.

Recently, GE, working with National Semiconductor Ltd., was able to make dramatic reductions in both water usage and energy consumption at the firm’s fab plant in Scotland. A typical site recovery rate for a reverse osmosis (RO) system would be approximately 75-80%, but by reusing the reject streams from the existing RO and electro-deionization (EDI) phases, National Semiconductor’s ultrapure water plant was able to reduce its waste and improve water recovery to 99%.

The innovation cut annual water usage by 40 million gallons and reduced the plant’s carbon footprint by 200 tonnes per year. Overall energy savings are projected to be more than 500,000kW per year.

“We will continue to work with National Semiconductor to further realize additional water and energy savings and increased efficiency,” said Jeff Fulgham, chief marketing officer of GE Water. The project earned National a GE ecomagination Leadership Award.

Expensive rejects
Several trends are expected to affect semiconductor UPW systems in the near future. For example, a component standard scale in the 10nm region is being investigated for some applications. Dr Vivien Krygier, senior vice president of marketing for Pall Corp’s microelectronics division, says that building integrated circuits on the same scale as human DNA poses tremendously tight specs on UPW.

“There’s a concern for the critical removal of particles, especially photolithography. You want tight removal. It reduces the number of rejects [rejected wafers] and electrical shorts [shortcircuits]. When you have a wafer with 18 layers, rejects get very expensive.”

As the ability of testing labs to detect ever more exotic compounds at ever smaller concentrations improves, the semiconductor industry will face new mandates to make discharge water cleaner. “The semiconductor industry has a history of not only dealing well with environmental (as well as health and safety) regulations, it often takes action prior to being regulated,” says the SIA’s Diamond.

“There are PF (perf luorinated) organics that are critical in the use of photolithography. We use them in very small concentrations, but it turns out they are very widespread in the environment due to their widespread use in the consumer market. We have put together a memorandum of understanding to eliminate all non-critical uses and to invest in research to invent or discover a replacement that will eliminate their use.”

Suppliers of UPW equipment also face a number of challenges. “There are cost pressures,” says Knapp. “The industry is saying to us: ‘Our selling prices are way down, and the cost of plants is increasing, so you have to deliver your systems to us at a lower price.’”

The next few years will also see the introduction of 450mm wafers. “The prediction is the need for fewer fabs at 450mm, so tool suppliers and the supply chain may see less business in the future.” The uncertainties of new technologies also rest upon the far distant horizon. Recently, scientists investigating nanotechnology at the University of California, Berkeley, were able to create a memory cell by placing a particle of iron 2nm in length into a carbon nanotube.

“You never know about the next generation of fabs,” says Knapp. “They might one day come up with a water-free manufacturing technology.”

The global recession has had a profound impact on the semiconductor industry. SIA industry statistics for 2009 show that global chip sales are down about 20% from 2008. “Our industry is driven by the consumer market, so when people are not buying cellphones, computers and videogames, our sales are down,” observes Diamond.

“The recession has really slowed everything down,” says Krygier. “OEMs are down 50% or more. We have seen revenues drop 50%.”

“In a good year, you might see 20 plants being built,” says Knapp. “But 2009 has been one of the worst years in terms of capital spending.”

When the global recession eventually abates, the need for semiconductors will grow again. “It’s a good strong industry, and our companies are very aggressive when it comes to environment, health and safety (EHS),” says Diamond

“I’m a lot more optimistic than I was four months ago,” says Krygier. “But it won’t be for a few years that we see the numbers we saw in 2008.”

Semiconductors and water

* In 2008, the semiconductor industry had worldwide sales of approximately $249 billion. The industry enables the generation of some $1.2 trillion in electronic systems business and $5 trillion in services.

* Dominant manufacturers include Intel, Texas Instruments, IBM, AMD, Micron and Freescale of the US, as well as STMicroelectronics of Europe, Samsung of Korea and NEC of Japan.

* Each semiconductor plant can cost upwards of $2.5 billion. There are over 250 fabrication units in the US, out of a total of about 400 worldwide.

* Semiconductor chips contain components smaller than 65 nanometres across. The manufacturing process requires ultrapure water (UPW) for cleaning in order to prevent trace molecules from shorting circuits and causing defects.

* Manufacturing a large integrated circuit requires approximately 2,200 gallons of water in total, of which 1,500 gallons is ultrapure water.

* UPW flow rates for a fab plant can range from 500 to 2,000 gpm, and a complete system can cost between 1.0-1.5% of capital costs, or $25-40 million.

* The semiconductor industry spends approximately $1 billion on water and wastewater systems and services every year, around half of which is capital equipment sales. The largest technology suppliers include Siemens Water Technologies, GE Water, Christ Water Technology, Kurita, Nomura Micro Science and Organo.

* Wastewater from semiconductor plants contains small amounts of arsenic, antimony and phosphorous, hydrogen peroxide, nitric acid, sulphuric acid and hydrofluoric acid. All wastewater is captured; toxic chemicals are removed and acids neutralized.

* Pall Corp. estimates that reduction, reclamation and recycling of water from semiconductor plants would save the industry over $100 million per year due to reduced capital and operating costs.