August 18, 2006 — /FDA News/ — The U.S. Food and Drug Administration (FDA) today ordered Donor Referral Services (DRS), a human tissue-recovery firm, of Raleigh, NC, and its owner, Philip Guyett, to immediately cease all manufacturing operations, and to retain human cells, tissues, and cellular and tissue-based products (HCT/Ps) after an inspection found serious deficiencies in its manufacturing practices, including those governing donor screening and record keeping.

The order to cease manufacturing and retain HCT/Ps requires DRS and Philip Guyett to immediately suspend any and all manufacturing steps, including but not limited to the recovery and shipment of HCT/Ps. FDA’s inspection identified serious violations of the regulations, including the failure to establish and maintain procedures for manufacturing steps performed by DRS. In addition to the above stated violations, FDA also found several instances where records provided by DRS to another HCT/P establishment were at variance with the official death certificates FDA had obtained from the state where the death occurred.

“Patient safety is at the forefront of today’s action,” said Margaret O’K Glavin, Associate Commissioner, Office of Regulatory Affairs. “Allowing the firm to continue to manufacture would present a danger to public health by increasing the risk of communicable disease transmission.”

Firms that recover HCT/Ps obtain tissue from human donors and send the tissue to establishments that process it for use in implantation or transplantation. HCT/Ps are used in a variety of procedures that can save lives, repair limbs, relieve pain or enhance a patient’s quality of life.

This action to protect public health is being taken under the agency’s new tissue regulations which took effect on May 25, 2005. Among other mandates, the regulations require firms to properly screen and test donors and, when needed, they enable FDA to take swift action in the interest of public health.

“While most tissues are obtained and manufactured using appropriate protections, some operators are not following acceptable practices,” said Jesse L. Goodman, MD, MPH, director of FDA’s Center for Biologics Evaluation and Research. “Today’s action is a clear sign of FDA’s intent to put a stop to any practices which place patients at unneeded risk.”

The regulations require that establishments process HCT/Ps in a way that does not cause contamination or cross-contamination and that prevents the introduction, transmission, or spread of communicable disease through the use of the HCT/P. To date, FDA has not received reports of adverse reactions (e.g., transmission of communicable disease to recipients) in any patients who may have received the tissues in question. All tissue products initially recovered from human donors by DRS have been recalled. The agency will continue to investigate DRS’ activities, monitor the recalls to account for all distributed tissue and work cooperatively with tissue processors and appropriate federal, state and local authorities. FDA will take further actions as needed.

You can view a copy of the DRS Order of Cessation at: www.fda.gov/cber/compl/drs081806.htm

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By Hank Hogan

Smaller than today’s 65-nanometer state-of-the-art manufacturing, the 45 nm semiconductor processing node looms just a few years ahead. And, when it comes to manufacturing tomorrow’s chips, more than cleanrooms must be ready. Several announcements from July’s SEMICON West trade show illustrate the industry’s response to this challenge and its contamination control requirements.

Laser maker Cymer Inc. (San Diego, Calif.) unveiled its XLR 500i at the show, touting the argon fluoride (ArF) 193 nm wavelength laser as the light source for next-node photolithography. In an announcement, Cymer pointed to laser module modifications that resulted in a 50 percent improvement in energy stability performance and a 20 percent reduction in the cost of ownership for the new product as compared to previous ones.

The Starlith® 1900i system from Carl Zeiss SMT boasts a numerical aperture of 1.35, reportedly the highest NA available on the market. It will be part of ASML’s new TWINSCANTM XT:1900i, which will be shipped mid-2007. Photo courtesy of Carl Zeiss SMT.Click here to enlarge image

Behind the scenes were other changes. “We have made continuous improvements in a number of contamination technologies,” says Nigel Farrar, Cymer’s vice president of technical marketing.

Farrar notes that, at 193 nm, light can cause surface damage, as well as surface deposits. To minimize both problems, Cymer uses an approved list of low-contamination materials in the product, purges the beam lines and optics with high-purity nitrogen, and filters the purge gas for hydrocarbons. By design, the device filters the chamber gas to minimize particulate contamination and, during operation, Cymer periodically replaces the chamber gas.

In another announcement, Carl Zeiss SMT (Oberkochen, Germany) revealed its Starlith 1900i (see photo). A second generation of the lens system at the heart of immersion steppers, the product reportedly has the highest possible practical numerical aperture, 1.35. The lens is thus capable of imaging 40 nm features. The manufacture of the 1900i requires control of the surface of single lens elements at the scale of a few atoms, notes Wolfgang Rupp, lithography optics division vice president of systems at Carl Zeiss SMT.

Achieving the necessary level of contamination control is accomplished with a number of strategies. These include purging of the assembled lens with an inert gas, as well as manufacturing in cleanrooms with bunny-suit-clad employees. “Additionally, we precisely control the environment, macro- and microenvironments, and temperature during assembly and adjustment of the lenses,” says Rupp.

Finally, filter maker Pall Corp. (East Hills, N.Y.) announced a number of new products designed to help clean up photoresist and other manufacturing chemicals. These new offerings include filters with variable pore sizes, a design that reduces the pressure drop across the material. The company also introduced its tightest filter ever, one with a 10-nanometer rating for use with 193 nm photoresists. Tony Shucosky, vice president of marketing for Pall Microelectronics’ global chemical products, notes that the semiconductor technology roadmap lists the critical particle size as about half the technology node. So for the 45 nm node, that would put the critical size at 22 nm.

Shucosky points out that attention to contamination control during assembly is critical, and that this need extends to the component materials and the final packaging. In the case of Pall’s products, assembly takes place in cleanrooms and often includes post-assembly cleaning. “These steps include flushing with ultrapure water and may also include chemical washing with acid or other proprietary chemical treatments,” he says.

These methods put the total ion metal extractables near one part per billion in a typical 10-inch filter, according to Shucosky. Such cleanliness is essential, he says, given that his company’s semiconductor customers are now measuring contamination as the number of atoms per square centimeter.

The Institute of Environmental Sciences and Technology (IEST) recently announced that the International Organization for Standardization (ISO) has published ISO 14644-8, Cleanrooms and associated controlled environments – Part 8: Classification of airborne molecular contamination. IEST serves as Secretariat for ISO Technical Committee 209, which developed the International Standard as part of a series of documents to serve the needs of the global contamination control community.

The new document is designed for use in a wide range of industries-such as microelectronics, pharmaceuticals, medical devices, and others-that may be adversely affected by airborne molecular contamination (AMC). It assigns ISO classification levels to specify the limits of AMC concentrations within cleanrooms and associated controlled environments where the product or process is at risk from such contamination.

According to the IEST, the ISO standard covers the classification of AMC in terms of specific chemical species (individual, group, or category) and considers concentrations of AMC between 100 and 10-12 g/m3 under cleanroom operational conditions. The document provides a protocol to include test methods, analysis, and time-weighted factors within the specification for classification. The annexes cover topics such as parameters for consideration, typical contaminating chemicals and substances, typical methods of measurement and analysis, and considerations of specific requirements for separative enclosures.

ISO 14644-8 is available from the IEST. For more information, visit www.iest.org.

GW Plastics (Bethel, Vt.; www.GWPlastics.com), a high-precision injection molding provider, recently hosted Mexico President Vicente Fox. President Fox visited the company’s state-of-the-art El Marques manufacturing park in Querétaro, about two hours northwest of Mexico City.

President Fox learns about sophisticated process technologies such as insert, multi-shot, and cleanroom molding. GW Plastics’ newest plant will share with all other GW Plastics plants high standardization in equipment, operating practices and quality systems, including ISO 9001:2000 and TS certification. Photo courtesy of GW Plastics.Click here to enlarge image

The plant boasts fully automated, insert molding systems with real-time process monitoring. According to Ben Bouchard, V.P. of international marketing for GW Plastics, “We designed the plant to use the most advanced technology available. This gives our customers a tremendous competitive advantage. Not only do they get the advantage of low cost country (LCC) manufacturing, they get the added benefit of improved efficiency and quality through automated processes, using the latest molding technology not typically seen in the region.”

With a focus on process technologies such as insert, multi-shot, and cleanroom molding, GW Plastics’ newest plant is an ultramodern 52,000-square-foot facility. It was designed to support existing GW Plastics customers, but according to the company, it’s expanding rapidly with new markets and customers in the growing region of central Mexico.

The initial footprint of the plant can accommodate up to 25 highly automated conventional and insert molding machines, but has room for value-added assembly operations and the capacity to expand to 40 machines. GW Plastics also plans to add an ISO Class 8 (Class 100,000) cleanroom to serve the growing medical device customer base in Mexico.

According to a recent announcement by Andrew C. von Eschenbach, acting commissioner of the Food and Drug Administration, the FDA will establish a new nanotechnology task force to examine the agency’s regulatory approaches with regard to nanomaterials used in FDA-regulated products. To ensure and encourage the continued safe development of such products, the task force will identify knowledge or policy deficiencies and recommend ways to address them.

“As this exciting new area of science develops, FDA must be positioned to address both health promotion and protection challenges that it may present,” said Dr. von Eschenbach. “Through this task force, we are leveraging our expertise and resources to guide the science and technology in the development of nanotechnology-based applications.”

One of the main goals of the task force will be to improve the agency’s ability to evaluate possible adverse health effects resulting from FDA-regulated products using nanomaterials. In addition, the task force will explore opportunities to foster innovation using nanotechnology materials to develop safe and effective drugs, biologics and devices, and to develop safe foods, feeds, and cosmetics. It will continue to strengthen the relationship between the FDA and other collaborating parties, including the agencies participating in the National Nanotechnology Initiative as well as foreign government regulatory bodies, international organizations, healthcare professionals, industry, consumers, and other stakeholders, to gather information regarding nanotechnology materials used in FDA-regulated products.

Next month, the task force will chair a public meeting to further the agency’s understanding of developments in nanotechnology materials pertaining to FDA-regulated products. The meeting is scheduled for October 10. The task force will submit its findings to the FDA within nine months of the event.

Ionizers, remote sensors, monitoring, and material choices all contribute to control

By Sarah Fister Gale

For a lot of cleanroom operators, any static is too much static. Disk drive manufacturers are leading the downward spiral toward zero tolerance for electrostatic-related events in the cleanroom, with semiconductor, flat panel, medical electronics, and pharmaceutical manufacturers close on their heals.

As with all things manufactured in a cleanroom, shrinking geometries are leading to greater sensitivities, and in the case of electrostatic charge, that means even a few volts of static electricity can result in serious impacts on yield.

Most disk drive makers have tolerances of two volts or less in the cleanroom-down from five volts just a year ago, says Steve Heymann, CEO of Novx Corporation (San Jose, Calif.), supplier of instrumentation and software for universal monitoring and control solutions in cleanrooms, manufacturing, and ESD-sensitive work areas. “It takes a lot of experience to create a cleanroom environment with control to that level.”

To help manage this static-free environment, the disk drive industry follows ESD standards, produced by the International Disk Drive Equipment & Materials Association (IDEMA; Santa Clara, Calif.), that standardize procedures for testing and set the correlation and benchmarking of products. The IDEMA documents include a packaging standard for disk drives and components that includes materials requirements for the various stages of disk drive manufacture, and a human body model (HBM) document that addresses the issue of testing magnetoresistive (MR) head products for qualification prior to shipping.

AC/DC ionization

Meeting a one- or two-volt sensitivity limit requires a complex ionization program that begins with a room system ionizer. Ionizers in the cleanroom are the first defense against static and, as sensitivity levels drop, ionization equipment is getting more attention.

Room system ionizers output clusters of airborne molecules that are bound by polarization forces to a charged (typically single) nitrogen or oxygen molecule, increasing the conductivity of the air with the charged gas molecules. When ionized air comes in contact with a charged surface, the surface attracts ions of the opposite polarity. As a result, the static electricity is neutralized.

There are three common ionization methods used in commercial air ionizers: corona, alpha and photoelectric. Each method generates air ions, but corona ionization is the most commonly used method in cleanrooms.

AC and DC high voltage is used to generate corona ionization. High voltage is applied to a sharp emitter point (see Fig. 1) or a small-diameter emitter wire, resulting in an electric field around the emitter. This high-voltage field interacts with the electrons in the nearby gas molecules, resulting in positive or negative ions, depending on the type of high voltage that is applied.

Figure 1. High voltage is applied to a sharp emitter point (shown above), creating an electric field around the emitter that interacts with the electrons in the nearby gas molecules, resulting in positive or negative ions, depending on the type of high voltage that is applied. Photo courtesy of ITW/Simco.Click here to enlarge image

Unlike AC corona ionization, which emits both positive and negative ions from the same emitter point, DC corona ionizers emit ions from separate positive and negative emitter points, creating less recombination of ions.

“Since ions are emitted independently for each polarity, it’s possible to monitor and control the amount and the equality of ions emitting from the positive and negative emitter points,” says Arnold Steinman, a member of the board of directors for the ESD Association and chief applied technologist at MKS, Ion Systems (Alameda, Calif.), provider of process control solutions for advanced manufacturing processes. “Various types of monitoring and control systems are available for DC corona ionizers. As a result, ionizers using DC corona offer great degrees of control and fine-tuning. The high level of system sophistication along with the low ion recombination rate also means that DC corona ionizers are appropriate for ESD-sensitive and contamination-critical technology applications.”

There are two types of DC corona ionization: pulsed DC and steady-state DC. Steady-state DC continuously applies positive high voltage to half of the emitter points and negative high voltage to the other half. The ionizer may contain a single pair of emitters (as in blow-off guns or nozzles, and in ceiling emitters), an array of pairs of emitters (DC blowers), or a straight line of emitter pairs (DC bars). Steady-state DC ionization may be employed with low or high airflow, depending on how far apart the emitter points are spaced. Steady-state DC ionization is commonly used in cleanroom systems, laminar flow hoods, blowers, and blow-off guns.

Pulsed DC ionizers allow positive and negative emitter points to be turned on and off alternately, creating clouds of positive and negative ions. Ionizers using pulsed DC ionization may be finely tuned to allow timing cycles and polarities to operate precisely for a specific application. Positive and negative emitters may be set to alternate in time periods of seconds. In certain areas, a greater proportion of one polarity may be needed over the other, or the time that the voltages are on may be stretched to prevent any recombination.

Local ionization requires balance

For many cleanrooms, a generic room ionizer is just the beginning of a complete ionization system. “Cleanroom operators used to assume that if they had an ionizer, everything was okay with regard to ESD, but that’s not true anymore,” Heymann says. “The problem with ESD technology is that simply installing it doesn’t mean it’s still working a day, a week, or a month later.”

Now, lower sensitivity thresholds are forcing cleanroom operators to add to their general room ionization systems, which can knock the atmosphere from 1,000 to 100 volts. Incorporating additional ionizers inside process tools and around critical areas of the environment can get voltages down under 10 volts. Workstation ionizers, including bar ionizers, blowers, and compressed-gas blow-off devices, are used in these defined work areas (see Fig. 2). Whether the ionizer is mounted above or directly on the work surface, the distance separating it from the ESD-sensitive product is much smaller than with room systems-typically less than 1 meter.

Figure 2. Incorporating additional ionizers inside process tools and around critical areas of the environment can further reduce voltages. Bar ionizers, such as the one shown here, are typically installed in minienvironments and tools. Photo courtesy of MKS, Ion Systems.Click here to enlarge image

For extremely critical environments, ionizing blowers are used in place of pulsed DC systems, which normally have a voltage swing that can’t be adjusted to zero (see Fig. 3). The problem, however, is that although the blower eliminates static, it interferes with other elements of the clean environment, Steinman explains. “Blowers affect air turbulence and can become a source of contamination,” he says. “A collaboration has to occur between contamination control and ESD management to be sure you are meeting all required levels.”

Figure 3. For extremely critical environments, ionizing blowers are used in place of pulsed DC systems. Blowers are typically installed on benchtops and inside tools. They can be used in test, assembly, and packaging areas, as well as in hard disk drive manufacturing. Photo courtesy of MKS, Ion Systems.Click here to enlarge image

To prevent the negative effects of blowers, Ion Systems uses emitter points made from its patented single-crystal silicon material that is “on the edge of meeting ISO Class 1 standards,” Steinman says. “Other materials for emitter points are just not as clean.”

Early warning systems

Adding to the challenge of controlling ESD is the fact that, in many cases, manufacturers don’t realize an event has caused damage until late in the production process. The failure may not show up until a disk drive is assembled, or it could be a latent failure in which ESD weakens or wounds the component but not enough to cause a malfunction during testing. Over time, however, the wounded component will cause poor system performance and eventually complete system failure. Because latent failures occur after final inspection or in the hands of customers, the cost for repair is very high.

To combat this problem, cleanroom operators are using remote sensors to continually monitor the atmosphere and determine the number of positive or negative ions required to neutralize the air, says Carl Newberg, general chairman of the ESD Association Symposium and president of Rivers Edge Technical Services, a materials testing firm in Rochester, Minnesota. “This is important because without sensors an ionizer can create a balance offset that makes matters worse.”

There has also been a growing trend toward independent monitoring in the process areas around key workstations to make sure the ionization process is working. These independent monitors gather and collect ESD data, giving operators ongoing reports about the cleanroom environment that detail any spikes or trends in ESD events during critical points in the manufacturing process.

This allows them to address problems in the cleanroom before they cause serious impacts to yield. For example, the resulting reports may show spikes during certain times of the day correlating to changes in personnel, placement or movement of tools or materials, or faults in grounding of equipment. By tracking the events and their locations, operators can identify where the problems are and what’s causing them.

“When sensitivity levels get that critical, you need to put these sensors directly in front of your ionizers in key target areas and use the feedback to maintain balance,” says Jim Curtis, business unit manager for the electronics manufacturing group of ITW/Simco (Hatfield, Pa.), a manufacturer of cleanroom ionization systems. “They are constantly striving for zero.”

But documenting events and trends isn’t enough to protect yields from ESD damage. Some monitors may only have a red or green light to show they are operating. Although data about events may be sent to a central database, if the sensors don’t actively alert operators when an issue arises, days or weeks could go by before it’s noticed, Heymann says. “If you’re making three drives per minute, how many will be made before you realize there’s a problem?”

Such questions have resulted in the implementation of proactive sensors that respond with an alarm the instant an event occurs, such as an ionizer needing maintenance or equipment becoming ungrounded. In more advanced systems, the monitors have a direct tool interface enabling them to shut down a tool or the entire production line when static levels rise out of specification, giving operators a chance to solve the problem and pull products off the line for evaluation before continuing. “Now, if the product is dead you can toss it before you put it through fifty more process steps,” Heymann says. “With this kind of proactive control, you don’t produce a single bad drive, panel or IC.”

Although it may seem extreme and costly, the payoff can be huge, says Curtis. He’s seen several clients realize dramatic increases in yield as the result of improving their ionization programs, including one RFID manufacturer that went from 60 to 90 percent yield after installing and tweaking a new ionization system. “The first guy in charge of the operation didn’t see the value of ionization,” he says. “They had ionization, but it wasn’t installed properly and it wasn’t in the right places.”

Another client, who debated investing in a $100,000 ionization system for two years because of the price, ultimately agreed the system paid for itself in one day, Curtis says. “Ionization systems are underappreciated, but you can’t argue with real-world results.”

S20.20 guides industry

For semiconductor manufacturers, the ESD crisis hasn’t yet reached critical urgency. Depending on the operation, they can tolerate 30 to 200 volts without damage; however, semiconductor manufacturers are already facing many of the same problems disk drive makers faced just a few years ago.

“The semiconductor industry invented ESD,” Newberg says. “When things started blowing up in the 70s, they quickly figured that ESD was causing it and learned how to put ESD protection on the chips.”

However, in the last few years semi manufacturers have whittled that protection away, giving up safety for speed and increased IC functionality. “It’s dropped their sensitivity levels dramatically.”

Novx’s Heymann agrees. “Semiconductors are trending in the same direction as the disk drive manufacturers. They dropped from 3,000 or 4,000 volts to 300 volts or less almost overnight because they gave up the oxide thickness that protected wafers against ESD.”

Heymann also points out that concern about ESD is disparate between the front and back ends of the semiconductor manufacturing process. “On the back end, where they cut the chips, they know they need to watch out for ESD, but there’s still a misconception that wafers are not ESD-sensitive at the front end of the process.”

Like the disk drive industry, semiconductor manufacturers follow standards for managing ESD. The ANSI/ESD S20.20-1999 standard, Development of an Electrostatic Discharge Control Program, covers the requirements necessary to design, establish, implement and maintain an ESD-control program to protect electrical or electronic parts, assemblies and equipment susceptible to ESD damage from HBM discharges greater than or equal to 100 volts. The areas covered by this standard will expand and overlap as industries progress along their technology roadmaps, and an update is expected next year.

ANSI/ESD S20.20 is a guidance document created using the industry’s experience with the ISO 9000 and ISO 14000 standard, says Steinman. The guidance is gaining worldwide acceptance as an international standard and is currently going through translation and draft status at the International Electrotechnical Commission (IEC).

It’s useful as a global standard in part because it was designed to work within ISO parameters. “If you have an ISO quality-control program, you already have the infrastructure in place for S20.20. You just have to add the technical elements,” Steinman says. “ISO certifiers will be able to certify to the S20.20 standard, as well.”

The S20.20 document is already available in English, Chinese and Spanish, and is being rapidly adopted by organizations across the globe. “When things are standardized, people don’t have to make decisions about whether they should do it or not,” Steinman says. “It becomes something that everyone has to do and they understand that. It’s a way for everyone in the electronics food chain to do the right thing to make sure they all use the right level of ESD protection.”

The ESD Association currently offers an ESD program documentation review service, through which the ESD Association’s Facility Certification committee will review a manufacturer’s ESD program documentation and compare it to the requirements listed in ANSI/ESD S20.20-1999. A report is provided that describes the areas that need to be improved in order for documentation to be compliant with ANSI/ESD S20.20-1999.

“This service should be considered a must for any company that is preparing for facility certification based on ANSI/ESD S20.20-1999,” Newberg says. “Getting this certification enables companies to prove to their clients that they are meeting industry standards.” For some groups, such as the military and NASA, S20.20 certification is already a requirement of doing business.

Material choices

Along with ionization and traditional grounding tools for equipment and personnel, manufacturers are also taking a hard look at the materials being used in the cleanroom and how they relate to ESD.

Electrostatic charges on materials are the result of a transfer of electrons caused by the sliding, rubbing, or separating of a material, which is a prime generator of electrostatic voltages. Plastics, fiberglass, rubber and textiles can all collect these charges. When this happens to an insulating material, which does not allow for the flow of electrons across or through its bulk, the built-up charge tends to remain in the localized area of contact. This electrostatic charge on the insulator can induce a charge on nearby conductors, such as a person or a microcircuit, which can then discharge via an arc or spark when the conductor comes in contact with a body at a sufficiently different potential.

“Disk drive manufacturers are reducing the potential for ESD events with the use of advanced polymers that can replace metal carriers with static-dissipative thermoformed or CNC ceramic/ICP parts,” says Bob Vermillion, president of RMV Technology Group (Clayton, Calif.), an ESD solution provider. “These polymers reduce rapid discharge by exhibiting surface resistance, volume resistance or two-point resistance readings.”

When evaluating ESD protective materials, the most common property to test is surface resistivity or surface resistance of a material, since that provides a measure of how well the material dissipates electrical charge in contact with its surface.

Cleanroom operators and tool manufacturers are implementing more ESD-resistant materials to meet client needs. Conductive materials, such as shielded bags, foils, and metal, are popular because they have low electrical resistance-generally less than 1 x 105 ohms/sq (surface resistivity) and 1 x 104 ohm-cm (volume resistivity)-and allow electrons to flow easily across their surfaces or through their volumes. When a conductive material becomes charged, the charge (i.e., the deficiency or excess of electrons) is uniformly distributed across the surface of the material. If the charged conductive material makes contact with another conductive material, the electrons will easily transfer between the materials. If the second conductor is grounded, the electrons will flow to ground and the excess charge on the conductor will be neutralized. Conductive materials are usually carbon-particle- or carbon-fiber-filled throughout.

Static dissipative materials used to prevent electrostatic discharge to and from humans generally have a resistivity between 106 and 109 ohms/sq. They have an electrical resistance between insulative materials and conductive materials. There can be electron flow across or through the dissipative material, but it is controlled by the surface resistance or volume resistance of the material.

For static-dissipative materials, like all materials, charge can be generated triboelectrically. However, like the conductive material, the static-dissipative material will allow the transfer of charge to ground or other conductive objects. The transfer of charge from a static-dissipative material will generally take longer than from a conductive material of equivalent size. Slowing the charge transfer is one way to prevent ESD damage. Charge transfers from static-dissipative materials are significantly faster than from insulators and slower than from conductors.

There are many kinds of antistatic or static-dissipative materials, but not all can be used in a cleanroom to reduce the risk of ESD because there may be contamination issues. For example, plastics that are surface-coated with quaternary ammonium salts, amidoamines, or salts of octanoic acid to impart nonpermanent ESD properties cannot be used in the cleanroom. ESD-control materials for the cleanroom must pass the same tests for particle generation, outgassing, and the presence of chemical residues that are applied to all materials used in the cleanroom.

The future

Looking ahead over the next couple of years, cleanroom operators should expect more of the same. The good news is that, since the disk drive industry has figured out how to control static electricity down almost to zero levels, there is a roadmap to follow.

And while semiconductor manufacturers are heading in the same direction, they are fortunate to have already automated many of their processes, removing humans-the biggest ESD risk factor in the cleanroom-from the equation. But there’s still much to be done, says Steinman. “For the semiconductor industry, there’s a wafer-level ESD problem coming that people need to think about,” he says. “The important thing to remember is that you don’t want to solve an ESD problem. That’s too expensive. It’s much more cost-efficient to prevent one from happening in the first place.”

ESA-A problem for bio/pharmaceuticals and medical devices as well

“ESD control in a cleanroom environment goes hand-in-hand with controlling electrostatic attraction (ESA) and the build-up of charge on wafers, disk drives, MR heads, microprocessor-driven devices or components,” says RMV’s Vermillion. ESA is the accelerated deposition of particles onto a surface due to the presence of an electric field created by excess electrical charge on a surface.

If surfaces are charged, ESA attracts and holds particles that would otherwise remain airborne in the cleanroom laminar airflow. Submicron-sized particles cause defects in semiconductor production in much the same way that dust on a photographic negative or print paper causes a visual defect.

“As technology changes lead to smaller feature sizes in semiconductor devices, the size of the killer particle also decreases,” says MKS’s Steinman. “Smaller particles are more easily attracted-and more difficult to remove-because of static charge on surfaces, and once they’re bonded to a charged surface, it’s very difficult to remove the contamination.”

ESA has also become a problem for pharmaceutical and medical device manufacturers who face biological contaminants in the cleanroom. Even though the allowable particles in a pharmaceutical environment are much bigger than in a semiconductor manufacturing facility, the stakes are much higher when a particle becomes charged and attracts to critical materials that could affect anything from the sterility of a tool to the viability of a pacemaker or stent, explains River’s Edge’s Newberg. “You can’t afford any failures there.”

An ionization system releases the charge on these particles so they remain in the airflow and can be swept back into the air filter systems.

Newberg has seen more and more pharmaceutical and medical device manufacturers looking into ionization systems as they come to understand the damage that ESA can cause.

By Al Brown, C.Eng, Rushbrook Consultants Ltd.

It’s been 10 years since Factory Mutual, or FM Global as they are now known, substantially revised and reissued their loss prevention guideline for semiconductor manufacturing fabrication facilities. A lot of changes have taken place since then, many driven by The FM Global Loss Prevention Data Sheet 7-7 (2003) and by the insurance companies that recommend that wafer fabs be protected to that standard.

Fire retardant polypropylene ductwork failing during an FM 4922-based fire test. Photo courtesy of Rushbrook Consultants Ltd.Click here to enlarge image

The main factor that drove the revision to FM7-7 was a growing realization by FM that the value of property and business interruption had increased rapidly but protection criteria had not kept pace. The result was that, although fires in a fab protected to the old FM7-7 were no larger in physical terms, the value of losses that resulted were increasing.

S14 and fire risk assessment

While FM7-7 was being revised, the SEMI Fire Protection Task force began to develop SEMI S14-0200, Safety Guideline for Fire Risk Assessment for Semiconductor Manufacturing Equipment. Industry consensus was finally achieved in 2000 and the resulting document is now regularly used by the industry to evaluate the fire risk associated with equipment destined for semiconductor fabrication cleanrooms.

The real benefits of SEMI S14, however, depend very much on how the equipment manufacturers and end users employ it. The greatest benefits are obtained by incorporating fire risk assessment into the design and development of a machine, helping designers to achieve a cost-effective and practical implementation of fire mitigation measures. But even six years after its introduction, S14 is still regarded by many equipment manufacturers and third parties as a compliance step to be overcome, and in many cases this results in an evaluation of the equipment very late in the design process, often just before shipment, presenting little opportunity for changes to be made cost effectively and without impact on delivery or installation of the machine.

Protecting legacy plastic wet benches

FM7-7 introduced the industry to the Cleanroom Material Flammability Test Protocol (FM4910) aimed at reducing the fire hazard of new manufacturing equipment. At the same time, FM7-7 provided guidelines for existing plastic wet benches, process liquid heating systems and the use of flammable liquids.

Since the late 1990s, many fabs have faced increasing pressure to replace or protect existing plastic wet benches and plastic ductwork. Many companies have simply accepted the recommendations of the insurers and installed carbon dioxide or fine water mist, following the guidelines in FM7-7 and providing full protection to the plastic wet benches. For insurers and risk managers applying a deterministic approach, this route to providing protection gives a comfortable feeling that the risks have been successfully mitigated, although it is arguably a costly approach. Others have adopted a risk-based approach, starting with a detailed fire risk assessment, before developing a risk mitigation strategy for their company as a whole and then entering the implementation phase.

The advantage of the fire risk assessment approach is that the protection criteria can be tailored to the company’s risk profile and risk management objectives, while still providing an adequate level of protection for most insurers and reinsurers. The difference in approach is like one company asking the insurance company if they will be happy with full protection and another asking if the insurance company will accept a targeted investment in a package of engineering controls, fire detection and fire suppression. The insurance company will always say yes to full protection-they have no reason not to-but in many cases they will also say yes to a well-designed and well-implemented risk mitigation program. The benefit for the end users of the risk assessment approach is that they remain in control of the process, including the cost and pace of implementation, ensuring that they fully understand and target higher risks first.

The risk-based approach ensures that fire suppression systems are applied where the risk of a fire occurring will result in injury to personnel, significant property damage, production interruption, or environmental damage. However, if the risk is assessed to be lower, then a mixture of fire detection and engineering controls, or engineering controls alone, may be more appropriate. There are two main differences with this approach. First, life safety is explicitly considered as part of the assessment, something that is typically omitted from the insurance company assessments. Secondly, the omission of fire suppression from some tools of plastic construction, such as those using unheated DI water, can be justified. These are required to be protected if the FM guidelines are strictly followed.

A note of caution, however: Such risk-based approaches should only be employed if the end user is willing to invest significant effort in detailed risk assessment by qualified personnel and they can ensure that management of change is strictly controlled, preventing a low fire-risk tool from becoming a higher risk tool due to uncontrolled changes to the process. The approach does not simply ignore specific hazards, but recognizes that the risk presented by some wet benches may be no higher than other equipment or hazards within the cleanroom that have already been judged acceptable by the insurer or Authority Having Jurisdiction (AHJ).

Plastic ductwork-The fuse running through fabs

A similar approach can be applied to the mitigation of exposures from plastic ductwork. Plastic fume-exhaust ductwork has been involved in most, if not all, of the major fab and cleanroom fires in the last 30 years. From fires in Scotland in 1977, to the Taiwan fires in 1996 and 1997, to fires in France and the Netherlands in 2002 and 2003, to the most recent fires in Asia in 2005-in each case plastic ductwork allowed the fire to spread through the construction material of the ductwork or to spread smoke to areas of the cleanroom and equipment that were unaffected by fire. Such fires have cost the industry and its insurers well in excess of a billion dollars over 30 years, all because of design decisions to use low-cost combustible ductwork and to omit sprinkler protection from within the ductwork.

Beginning in early 1996, with FM’s focus on reducing plastic usage in cleanrooms and ensuring that ductwork was replaced or protected, have continued to the present day. At SEMICON Europa in 2005, Philips Semiconductors reported the success of its approach to plastic ductwork risk mitigation. The company reported successful implementation of major projects in Europe and Asia where not only installation of sprinklers into existing ductwork, but replacement of ductwork in operating wafer fabs was accomplished. Once again, this was a risk-based approach supported by detailed fire risk assessments and the development of a strategy for risk mitigation.

The risk mitigation strategy was based on an S14-style assessment looking at the likelihood of a fire occurring and an assessment of the extent of damage that would follow, taking into account life safety, property protection, business interruption and environmental impact. Where the risk was judged to be slight, a decision was usually taken not to protect or replace ductwork, but where the risk was high or critical, ducts would typically be replaced, with medium-risk ductwork being replaced or protected with sprinklers. Such an approach can often justify the use of unapproved materials for short sections of ductwork, such as hook-up ducts in PVDF, based on the evaluated fire risk.

The development of this risk-based approach also enabled the evaluation of the practicality of protection and replacement. In cases where risk mitigation was found to be impractical, the risk assessments were used to document the deviation from the corporate strategy. But in many cases the detailed analysis carried out during the risk assessment helped facility project engineers to find imaginative alternative solutions that sometimes made risk mitigation easier than first envisaged, often allowing functional improvements to the fume exhaust system or improved cleanroom space utilization.

By enabling some ductwork to be left in place and not protected, particularly that associated with low or slight fire risk equipment, it is estimated that many millions of dollars can be saved in a typical risk mitigation project, while leaving a residual risk level that is no greater than that presented by other equipment or connected equipment in the fab. Once again, caution is urged in the use of this approach, which should only be applied using experienced and knowledgeable fire risk engineers in communication with all stakeholders, including insurers and AHJs, to ensure that an acceptable and sustainable protection scheme is developed.

New challenges

In the detail of projects to protect wet benches or ductwork, it is often forgotten that the primary aim is to control the value of potential losses. One means of doing this is to reduce the use of unnecessary plastics, particularly traditional plastics, which propagate fire and release large quantities of polluting smoke. It is ironic, therefore, that while many companies in Asia-Pacific are investing in ductwork replacement and protection programs and installing fire-safe ducts for new projects, there has been increased use in the last few years of other plastics in cleanrooms. In particular, there has been an increase in the use of acrylic and polycarbonate vision panels for the creation of minienvironments and for the separation of areas within the cleanroom. Whereas previously the use of such plastic was typically restricted to vision panels at eye level, many cleanrooms are now using such panels from floor to ceiling in fabs with ceiling heights in excess of 5 meters.

These clear plastic walls have helped in many cases to turn cleanrooms with very low combustible loading into ones where, once again, the potential exists for a spreading fire involving plastics, with further potential for significant smoke development. The irony is that, in many cases, building designers have chosen these materials to save money on construction costs, due to their light weight and ease of erection, only to create a hidden, ongoing cost for the insurance programs, which will be carried in many cases throughout the life of the cleanroom.

The challenges that were identified in 1996 when FM revised 7-7 have largely been addressed. However, due to changes in the industry, much of the development today is focused in Taiwan, Japan, Korea and more recently China. This creates a number of issues for risk managers and insurers. Firstly, a new generation of designers has the responsibility for large cleanroom projects and, in many cases, they are unaware of the hazards that were extensively discussed and debated in the 1990s in North America and Europe.

Secondly, new industries have emerged without a strong connection to the U.S., including TFT-LCD and plasma display screen fabrication, both of which are now fabricated in cleanrooms many times the size of the ones that were envisaged when FM7-7 was revised in 1996. Although the processes are essentially similar in some respects to silicon wafer fabrication, particularly through the use of chemical vapor deposition (CVD) using silane, metallization and photolithography processes, the major difference is one of scale. The largest silicon wafer currently in general use is only 300 mm in diameter with a surface area of 0.07 m2, whereas the largest glass substrate used for LCD fabrication is the ‘Gen 7,’ which measures 1,870 m x 2,200 mm (or 4.11 m2). This increased surface area results in a vast increase in the size of equipment and in the quantity of chemicals and gases being applied for each substrate, including silane.

The demand for high flows of silane has led to the installation of increasing numbers of bulk silane systems using ISO modules holding 6,000 liters of the pyrophoric gas, which has been linked to many deaths and injuries over the life of the semiconductor industry. Although FM was instrumental in developing guidance for the safe use of silane, many of its findings are not being implemented at wafer fabs and LCD fabs around the world.

Despite the fatal explosion and fire in Taiwan in 2005, designers and installers continue to disregard some of the basic safeguards of silane use, including the use of restrictive flow orifices and the location of bulk silane ISO modules in well-ventilated, outdoor locations. In fact, some installations have even been placed indoors and the facility connection to the ISO module has been made to the fill port instead of the consumer connection to maximize the flow rates.

All of this demonstrates that, while a significant amount of progress has been made in the last ten years, there are still many challenges ahead for fire safety engineers and risk consultants. It is also important to recognize that if standards such as FM7-7, NFPA 318 and SEMI safety standards are to remain relevant and of value to the global industry in the future, then they will need to rapidly evolve to address the new challenges created by the Asia-Pacific cleanroom operations being constructed on a truly amazing scale and at a pace never seen in North America or Europe.

Al Brown is a registered professional engineer in the U.K. and managing director of Rushbrook Consultants (Strathaven, Scotland, U.K.; www.rushbrook.com), which specializes in fire safety engineering, risk assessment and occupational health and safety consulting for advanced cleanroom manufacturing industries including semiconductor, MEMS, FPD and PDP. Rushbrook has offices and consultants in U.K., France and China. Mr. Brown has 21 years of risk engineering experience and serves on NFPA 318 and NFPA 75 technical committees. He is co-chair of the SEMI Fire Protection Task Force and European EHS Committee. He can be reached at [email protected].

The author would like to dedicate this article to Roger Benson, who inspired a generation of fire risk engineers and consultants with his knowledge and passion for the semiconductor industry.