Far more energy and chemicals than previously suspected are required to produce semiconductors, according to the first comprehensive life cycle analysis of the tiny silicon chips. The analysis, which was published by an international team of researchers and recently posted to ES&T’s Research ASAP site, also provides compelling evidence that the U.S. Toxics Release Inventory (TRI) significantly underestimates the semiconductor industry’s emissions.

“The environmental weight of semiconductors far exceeds their small size,” write the paper’s authors, Eric Williams of United Nations University in Tokyo, Robert Ayres of the INSEAD business school in Fontainbleau, France, and Miriam Heller of the U.S. National Science Foundation. According to their calculations, at least 1272 grams of fossil fuel and chemicals are needed to produce a 32-bit DRAM memory chip, and another 400 grams of fossil fuel are required to produce the electricity required to operate it over its lifetime. In essence, these embodied materials and energy inflate the weight of the 2-gram chip by 630-fold to 1.7 kilograms, the authors calculate. The analysis puts semiconductors at the top end of the materials intensity scale, Williams says. “No other product is as organized.”

Barb Karn, an environmental scientist at the U.S. EPA’s Office of Research and Development, calls the research a “wonderful classical industrial ecology study,” adding that the semiconductor industry has long had the undeserved reputation of being clean.

Williams says that the results surprised him. “We had an inkling the number would be big, but I didn’t think that when translated into mass it would be as big as it is, especially when contrasted with traditional products.” For example, the ratio of fossil fuel and chemical inputs to the weight of a newly manufactured automobile is 2 to 1, according to the researchers. “Of course the fuels needed to operate an automobile over its lifetime far exceed the weight of the car,”Ayres adds.

The only other products likely to have as high of a ratio of indirect to direct materials as silicon chips are drugs, solar cells, and nanoscale materials like carbon nanotubes, according to Ayres and Heller.

The environmental weight estimate for semiconductors is conservative, the paper stresses. Because very little process-level data are available, the researchers relied on recent data from an anonymous industry source. With the exception of silicon itself, they were unable to unearth any information that could be used to precisely estimate the amount of energy required to produce semiconductor-grade chemicals, which must be extremely pure, and packaging materials. The estimates also don’t consider the fuels needed to transport the materials to manufacturing sites, Heller says.

On the basis of available data, the paper’s authors assert that they “believe that TRI significantly undercounts emissions.” The information collected by the U.S. EPA about the country’s domestic semiconductor industry stands out for being far lower than any other comparable data source, they argue. The Electronics Industry Association of Japan’s emissions value is 10 times that of the TRI, for example, although the size of the two countries’ industries is comparable. The United Nations Environment Program and the United Nations Industrial Development Organizations characterizes chemical use by the semiconductor industry as being 500 times higher per square centimeter of silicon as does the TRI, which is only concerned with toxic chemicals.

“Every single study I know of suggests that the TRI captures less than 10% of the actual emissions. . . . usually much less,” Ayres says. The number of chemicals covered by the TRI are but a small fraction of the numbers that are used, explains Ted Smith of the Silicon Valley Toxics Coalition, an industry watchdog group. The study could be improved by factoring in the relative hazardousness of the chemicals used to create semiconductors, he adds. The European Union’s Restriction on Hazardous Substances directive is driving manufacturers away from some of the most hazardous substances, like lead, cadmium, and brominated flame retardants, he says.

Smith stresses that the calculations of microchips’ environmental weight would be even higher if they took into consideration end-of-life issues such as how both the chips themselves and the solvents used to create them are ultimately disposed. “The end-of-life process issues have always been of major concern,” he says. In Taiwan, for example, chlorinated solvents used to produce semiconductors are burned as fuel for cement kilns, creating dioxins, he explains. Even in the United States, two firms that were founded to recycle solvents are now reselling them as fuel, he adds.

Williams estimates that microprocessors, the “brains” inside today’s personal computers, could require 4 times as much material per square centimeter as memory chips. However, the detailed data required to analyze processors such as Intel’s Pentium are not yet available, he says.

The Semiconductor Industry Association did not return phone calls for this article. —KELLYN S. BETTS