Hank Hogan
MOUNTAIN VIEW, CA—Shock waves from the September earthquake in Taiwan were widespread. Some of them were even felt, in more ways than one, on the West Coast of the United States. As a result, Mountain View, CA-based Semiconductor Equipment and Materials International (SEMI) dispatched a team of experts to assess the damage.
Led by Stacy Bartoletti, an associate with structural engineering concern Degenkolb Engineers (San Francisco), and Brian Sherin, managing principal of Environmental and Occupational Risk Management (EORM) Inc. (Sunnyvale, CA), the team has just finished its evaluation and submitted a report to SEMI. This is only one sign of the interest semiconductor players in the U.S. have in the Taiwan tremor and earthquake disaster recovery. However, that interest may or may not translate into action.
“We are always looking to improve our processes, but I cannot say the quake specifically resulted in any change. We have a plan. It is designed to handle emergencies on the scale of a major earthquake,” says Bill Calder, a spokesman for Intel Corp. (Santa Clara, CA) which has facilities throughout the western United States.
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Bartoletti:Tools can be restrained.
“We took the safest route of all. We just recently closed down our last West Coast fab. So we have no fabs here on the West Coast at all,” remarks Paul Murphy, vice president of wafer fab manufacturing at National Semiconductor Corp. (Santa Clara, CA).
Murphy goes on to say that the threat of seismic activity had very little to do with the decision to shut down National’s West Coast operations in the summer of 1999. Nevertheless, he notes that the company’s remaining semiconductor cleanroom manufacturing facilities in Texas, Maine and the United Kingdom should be relatively safe from earthquakes.
Lacking a solid anchor
What the SEMI team found in Taiwan has a bearing on U.S. facilities, although just how much isn't clear. The standard measure of how powerful an earthquake is at a location is as a percent of gravity. A 100 percent reading would mean that the acceleration was equal to the pull of the Earth. This measure is affected by the strength of the earthquake, of course, but it's also strongly influenced by how far away the epicenter of the tremor is, local soil conditions and other factors.
Near the epicenter accelerations can be 90 to 100 percent. Further away, the number drops markedly. For instance, in the Taiwan quake, the semiconductor facilities in the Hsinchu Science Park were about 70 miles (110 kilometers) from the epicenter. As a result, accelerations at ground level were 10 to 15 percent for most of the buildings. That attenuation was important both for the structures themselves and for the equipment within them.
“For some of the tools in the building themselves to start moving, it's going to take an earthquake that produces maybe about 20 percent of gravity acceleration,” comments Bartoletti of Degenkolb.
That 20 percent is an estimate made by looking at equipment on higher floors. There tools that weighed thousands of pounds moved as a result of the building swaying. An important point is that although the tools can begin to move at such accelerations, they don't have to. The tools can be restrained by being anchored to the building. In this way, the tool doesn't move relative to the building or any of the process plumbing. Unfortunately, such tactics weren't uniformly employed in Taiwan.
“Almost none of the equipment was either anchored or anchored correctly,” notes Sherin of EORM.
Broken glass
For US facilities, however, this may be less of a problem because of tighter guidelines and inspections. According to Sherin, the recommended SEMI practice is for hazardous material handling equipment to be designed to survive 96 percent of gravity acceleration. Local requirements, such as those found in Santa Clara county in California, govern the anchoring of such equipment. Depending on soil conditions and other factors, those numbers can be quite high. Sherin believes that facilities in the US have adhered to these guidelines; however, neither he nor anyone else can guarantee that all tools are anchored properly.
In addition, Sherin also says that the regulations have recently undergone a revision. Such changes have been made over the years, and not all will necessarily be reflected in all semiconductor cleanrooms. This is particularly true for older wafer fabs—those operating for a decade or so with no major redesign. These are the locations that Sherin is worried about.
“There may be some problems,” he says.
There is also a somewhat related concern. Vertical furnaces save precious floor space by using vertical quartz tubes for high temperature processing steps. Such tools are 12 to 14 feet tall with a base that's 4 to 6 feet wide. Therefore, the top of the furnace can undergo considerable movement, much like a skyscraper would, during an earthquake. According to Sherin, some Taiwanese facilities reported that 90 percent of their vertical diffusion tubes cracked or broke. That, says Sherin, may be important information.
“Let's figure out how to better protect these types of tools. For example, maybe you not only anchor them at the bottom, but you also anchor them at the top,” he says.
No change in plans
For the most part, however, any information from the Taiwan earthquake has not yet been incorporated into plans by U.S. facilities,
“We have not made any changes or updates in light of the Taiwanese earthquake, but our crisis plan already includes earthquakes as part of our natural disaster possibilities,” says Grant Jones, a spokesman for Micron Technology, Inc. (Boise, ID).