Fabs new and old save millions in contamination-control energy costs
BY HANK HOGAN
DALLAS, Texas - To hear Paul Westbrook tell it, the fab being built by Texas Instruments, Inc. (TI; www.ti.com) in Richardson, Texas, reflects his own personal experience. Westbrook, sustainable development manager for TI’s worldwide construction, has been involved in building cleanrooms for decades. He also lives in a self-designed active/passive solar home.
“Boy, wouldn’t it be grand if we could apply this principal on a very, very large scale?” Westbrook wonders.
TI is doing just that with a state-of-the-art 300 mm wafer fab scheduled for completion and tool installation next March. For an initial investment of less than $2 million, Westbrook predicts savings of greater than $3 million a year in fab operating costs, primarily in air-handling changes and water recycling and reuse.
But Texas Instruments isn’t alone in the effort to cut cleanroom energy and operating costs. The research consortium SEMATECH (www.sematech.org) sponsors regular industry meetings aimed at, among other things, cutting the energy and expense of fab operation. SEMATECH’s efforts target both new and existing semiconductor factories.
Texas Instruments’ new 300 mm fab being built in Richardson, Texas, is expected to result in a savings of $3 million a year in contamination-control energy costs.
“That [improving existing fabs] is a challenge because there isn’t as much incentive to go back and re-engineer things, unless it can be cost-effective,” notes Philip Naughton, project manager for SEMATECH’s environment, safety, and health (ESH) program.
Nonetheless, Naughton and Walter Worth, a SEMATECH Fellow in ESH technology development, report success. Through changes in air handling, the research consortium has helped member fabs save money to the tune of $1 million a year per fab while maintaining worker safety and product yields.
In the LEED
For the new TI fab, the company committed to meeting the criteria set forth in the United States Green Building Council’s Leadership in Energy and Environment Design (LEED) program. The fab will be the first in the industry to meet those requirements. According to TI’s Westbrook, the program is best suited for general construction, so when it came to the semiconductor cleanroom, the pioneering nature of the effort played a part in selecting which level-gold, silver, or bronze-to attempt to reach.
“For the fab, where there is certainly an interpretation challenge for us to make sure that we’re complying, we decided silver would be a very aggressive goal,” says Westbrook.
Based upon data collected at both TI and other SEMATECH member companies, almost 60 percent of the total energy consumption of a fab comes from facilities while the rest is from process tools. Of the facilities’ burden, 42 percent is chillers and the next largest category-air recirculation-consumes 18 percent. Exhaust contributes another 6.9 percent. By going to an ISO Class 5 turbulent airflow and reducing HEPA coverage to 25 percent, Westbrook notes that the air recirculation burden for the new fab will be reduced. Since the wafers will be in minienvironments or enclosed by front opening unified pods (FOUPs), the resulting higher particle counts aren’t a problem.
Because fab workers wear smocks, a certain amount of airflow has to be maintained to keep operators cool. So, the TI group is looking at what happens when smocks and protective gowning are made less heavy and cumbersome. Results from a series of tests are encouraging and could lead to lighter smocks when the factory is operational.
“We haven’t got the final okay, but we’ve got some pretty strong data,” says Westbrook.
Studies by SEMATECH have shown that cleanroom airflow velocity can be reduced 22 percent without impacting contamination control in fabs without FOUPs. So, existing fabs can, and probably will, follow the lead of TI and others to cut air velocity, thereby trimming air-handling and associated costs.
Other studies by SEMATECH have revealed that fab exhaust can also be reduced by nearly 30 percent, with resulting savings of as much as $1.5 million per fab per year. A facility’s exhaust sucks out harmful fumes and other unwanted manufacturing byproducts, such as particulates, but it also removes filtered and conditioned air. That lost air has to be replaced, which can be costly.
But reducing exhaust in an existing facility, such as by cutting airflow, has to be done carefully. Safety standards have to be met and product yield can’t suffer. According to SEMATECH’s Naughton, however, existing fabs can go through a qualification process in which one module is adjusted at a time. In this way, the factory can continue to produce product.
Beyond what can be done on the facility end, there are also semiconductor tools to consider. Here, the chief energy drain is another form of exhaust. “The vacuum pump is the largest single common component of energy,” says Naughton. “In other words, vacuum pumps represent 25 percent of the total amount of energy consumption in a wafer fab.”
The research consortium has worked with suppliers to create a standard to allow pumps, which can number a thousand in an older fab, to idle at a slower speed when controlled by software. Cutting the speed cuts the energy demand and can reduce operating expenses.
Aside from saving money and benefiting the environment, fabs are trying to save energy for another reason. The semiconductor industry is cyclical, with utilization for a given factory swinging from over 90 percent down to as low as 50 percent. As long as the amount of air moved has nothing to do with the number of wafers running through a fab, the industry will be faced with operating costs that don’t track utilization. That, says Naughton, is one reason why there’s so much focus on converting what are essentially fixed costs to variable ones.
SEMATECH’s Worth has seen the cycle of boom and bust more than a few times, and he doesn’t expect the nature of the industry to change. As he notes, “You bring out a bunch of new fabs and the price drops, and then you have an oversupply. Then you have to wait until the demand catches up with the supply.”