Wet Bench materials scrutinized after fires
03/01/1998
Wet bench materialsscrutinized after fires
Spurred on by new fire safety protocols from the insurance industry, and by the recent rash of devastating fab fires in Taiwan, chipmakers and equipment suppliers are taking a hard look at wet bench safety issues, and seeking ways to reduce the benches` fire hazard. Also, concerns are being raised about possible cost increases for the unglamorous but crucial wet processing stations.
Wet bench safety is a long-standing issue; the catastrophic 1996 blaze at a Winbond fab was linked to a quartz cleaning bench. Factory Mutual Research Corp. estimates that wet processing tools were involved in more fab incidents over the past 20 years than any other tool type. But the issue is now one of SEMATECH`s top priorities in 1998, and work is underway to coordinate efforts with the Semiconductor Industry Association (SIA) and SEMI to find solutions that will lower risks. Over the next few months, meetings are scheduled between these and other groups to discuss the risk of fires in wet benches, and minimize those risks and damages when blazes do occur.
The industry`s insurance companies, including major underwriter Factory Mutual, are pressing chip companies to create an inherently safe cleanroom, and do one of two things: either install fire detection/suppression systems in existing benches or, for new benches, replace materials that pose high fire risks with newer plastics that meet the insurance companies` flammability protocols.
Steve Burnett, SEMATECH`s ESH best practices manager, said the idea of the inherently safe fab may be the best approach, but noted, "There`s a point where it`s not practical. What we need to do first is evaluate what the real risk is," he said. "We want to have a logical approach to this. There`s a lot of focus on this issue, and we don`t want to have duplicate efforts. We see this as a genuine global issue."
Any cleanroom fire can put personnel at risk, damage facilities, equipment, and work in process, and result in lost production time, but toolmakers and chipmakers are taking a cautious approach to the proposed changes, especially because this is not the first time they`ve been asked to make a change for safety`s sake.
With the exception of stainless steel solvent tools, many wet benches are currently manufactured using a fire retardant polypropylene material, or (primarily among Asian companies) PVC-type material. Fire retardant polypropylene was introduced to replace polypropylene, but when the fire retardant materials do burn, they release high amounts of smoke and corrosives.
Mike Burke, VP and chief engineer for Factory Mutual`s Allendale Insurance, said a bench fire controlled with ceiling level sprinkler systems can cause upwards of $25 million in damages; the stakes are much higher in fabs without sprinkler protection.
For new benches, the list of potential alternative materials includes modified versions of PVC, and fluoropolymer derivatives. For the installed base of benches, fire detection/suppression system options include fine water spray, CO2 and FM200, a replacement for Halon. Burke said these systems have the capability to stop a fire before it reaches the size of a thumb. "We now have dozens of customers who`ve installed these systems," he said.
Both of these risk-reducing options, however, have their drawbacks. Many chip companies have a real concern about the suppression systems, which they fear could do more harm than good, especially if accidentally activated. In addition, retrofits or redesigns will require downtime for the tool, and lost business time for the chipmaker. New materials may come at a higher cost and require new fabrication techniques. Bob Kampia, product safety engineer for wet bench supplier SubMicron Systems, Allentown, PA, roughly estimates that some proposed materials could cost 50% more than current materials - and increases could go as high as 600% for materials that meet the flammability standards and are fully chemical compatible.
To aid the process, SEMATECH is planning to develop materials compatibility tests and will set up a database on the new materials as they relate to flammability, mechanical properties, ease of construction, cost, and availability. The end result will be a list of best materials meeting flammability standards and processing requirements.
Burnett is also planning to better define SEMATECH`s approach to the issue of fire suppression systems on benches at the SIA`s committee meeting on wet bench safety.
"Everybody`s aware of the issue. We`re now getting ready to get the momentum going," said Burnett. "It`s very important that this is all coordinated. If we can sit down and come up with a common set of best practices, we can then sit down with the insurance companies and say `this is what we think is the right way to go`." - Christine Lunday, WaferNews