Pushing toward Green Manufacturing

Requirements Should Be Met during Process R&D Stage

Bijan Moslehi, PhD, is chief technology officer and senior vice president, semiconductor technology research, for The Noblemen Group, a boutique investment banking, strategic advisory, and business development firm. Moslehi has 20 years' experience working in the semiconductor and semiconductor equipment industries. He can be reached at bmoslehi@noblemengroup.com.

Despite its critical importance, the semiconductor industry has been somewhat conservative in implementing large-scale environmental initiatives, mainly because of the complexity of the manufacturing processes. With a few exceptions, the industry has not treated this issue as seriously as other technical roadmap challenges.

The industry traditionally has accepted change, as long as it is cost effective and does not present the slightest risk in the fab or to the product, alter processes of record, or require requalification. However, the introduction of several major environmental protection regulations and protocols has triggered a more accelerated adoption of "green manufacturing" practices in the semiconductor industry.

In a global economy, any environmental regulation, such as the two far-reaching directives enacted by the European Union (EU), fully affects all semiconductor manufacturers that market and sell their products worldwide. These two EU directives are known as Waste from Electrical and Electronic Equipment (WEEE) and Restrictions on the Use of Hazardous Substances (RoHS).

WEEE is considered a major source of heavy metals and organic pollutants. The WEEE directive is designed to prevent waste and improve disposal requirements through promotion of prevention, reuse, recycling, and recovery techniques. When it takes effect in August, the directive will hold manufacturers and suppliers of 10 categories of equipment—including electrical and electronic equipment—responsible for collection, recycling, and end-of-life disposal of their products.

The RoHS directive addresses health issues and is intended to reduce leaching of hazardous substances out of landfills into ground and surface waters, and to lower the emission of incinerated toxic chemicals into the air. Starting in July 2006, the directive will ban lead, mercury, cadmium, hexavalent chromium, and the polybrominated biphenyl flame retardants PBB and PBDE.

In Japan, the "Pollutant Release and Transfer Register" (PRTR) laws control and report the extent of certain chemicals and substances released into the environment and promote the improved management of them. The U.S. Environmental Protection Agency has lowered the maximum allowable lead threshold in products. China is adopting pollution control measures for electronic products that are similar to the EU RoHS directives. The Montreal Protocol restricts chlorofluorocarbons and other ozone-depleting chemicals, while the Kyoto Protocol aims at reducing greenhouse gas emissions (including carbon dioxide) that lead to global warming. Perfluorinated compounds (PFCs), which are used in semiconductor process equipment chamber cleaning and etch processes, are very stable greenhouse gases. The World Semiconductor Council has set goals for reduced PFC emissions by 2010.

In response to RoHS, a major worldwide effort has been under way to eliminate lead entirely from the packaging and assembly manufacturing processes. Following years of effort, lead-free solder pastes (such as silver-tin-oxide) have been developed and introduced. Many issues have been resolved, such as whisker growth and challenge of a narrower process window caused by the higher melting point and different thermal and reflow profile. Green products, in addition to meeting RoHS requirements, are free of chlorine, bromine, and antimony, and do not use any red phosphorus.

ISO 14001, the International Standards Organization (ISO) environmental standards series, addresses the environmental management of businesses and green manufacturing practices. The standards provide guidelines and controls for energy consumption, waste handling and treatment, and other activities that affect natural resources and the environment. ISO 14001 evaluates the environmental impact of a company and its products. It is designed to help set targets to meet requirements, develop and prioritize environmental response plans, document environmental policy and procedures, implement ongoing measurements against targets, and provide guidelines for internal audits.

True green manufacturing goes well beyond ISO 14001. The life cycle assessment (LCA) technique quantitatively analyzes and assesses the environmental impact of a product throughout its life, starting from the raw material stage, continuing through manufacturing, all the way through its transport, usage, and disposal. A useful tool, LCA supports the manufacturing of green products with minimum amounts of atmospheric emissions, aqueous effluents, and solid wastes. By reducing air, water, and land pollution and improving air and water quality, this leads to improved health and safety through better protection of the ecosystem.

Environmentally friendly products also reduce energy consumption levels, use recyclable components, and offer proper disposal procedures. During product manufacturing, the elimination, reduction, recycling, and reuse of chemicals and water, combined with proper waste control and treatment of those chemicals, should be major areas of focus. Conservation practices would further reduce the usage of energy, electric power, water, and paper.

One example from the semiconductor industry is the critical environmental and toxicological challenge of wafer- cleaning chemicals and solvents. Environmentally friendly manufacturing considerations have generated strong interest, including reduced chemical and water usage, development of more-benign chemistries and, where possible, elimination of liquid solvents and chemicals. In wet wafer-cleaning tools, chemical usage can be reduced through the use of dilute chemistries, increased bath lives, decreased operating temperatures, reprocessing, the use of bath lids and covers, and the adoption of small, single-tank systems. Improvements in vapor-phase Marangoni drying have led to huge reductions in isopropyl alcohol consumption.

Despite major improvements over the years, the reduction of pure water usage has been more difficult. More recently however, the use of ozonated DI water and small, single-tank systems have helped reduce water consumption. By replacing sulfuric acid/hydrogen peroxide mixture (or piranha solution) with ozonated DI water, as well as replacing the popular RCA cleans (SC-1 and SC-2) and HF solutions with highly dilute chemistries, a typical high-volume production fab would cut its annual chemical expenditures by millions of dollars. An additional benefit of these actions would be improved yields.

The use of wafer-cleaning solvents presents many challenges to materials suppliers and their customers. For example, the EU has banned the replacement for hydroxylamine-based chemistries, which are used in back-end-of-line resist strip. These solutions have been developed in recent years at great expense, and potential stripping alternatives may not be as effective. This case shows that a broader perspective and approach is needed, one that leads to more-successful technical and financial results across the entire supply chain while also meeting the intended environmental targets throughout a product's life cycle.

Creative formulas must be found for establishing effective communication forums among customers, manufacturers, suppliers, and regulators, beginning in the early phases of research and product development and continuing throughout a product's implementation. It would also be more economical to follow a uniform set of global standards. Improved communication combined with better standardization would help contain and reduce costs, which would otherwise be passed on to the end-users.

In many cases, environmentally benign manufacturing techniques and practices are economically beneficial, provided that the concepts of design for environment (DFE) are strictly followed. Potential risks must be addressed and implementation costs minimized. Therefore, it is critical to evaluate and introduce DFE methods correctly and in a timely fashion, right from the onset of the research and process and product development phases. The entire sequence of each process module, as well as the interactions among the various process steps, must be fully optimized for the environment. In addition, green manufacturing concepts must be followed throughout the entire supply chain.

The National Science Foundation/ Semiconductor Research Corp. (NSF/ SRC) Engineering Research Center for Environmentally Benign Semiconductor Manufacturing (led by the University of Arizona in Tucson) has emerged as a major research contributor to these green chipmaking efforts. The center's stated objectives include "creating new and effective environmentally benign manufacturing processes" and "demonstrating the positive impact of design for environment on all aspects of semiconductor manufacturing."

Historically, the semiconductor industry has been very slow in reacting to change, including the implementation of environmental initiatives. However, experience has shown that environmental benefits and economic gains are not mutually exclusive. Cost savings can be achieved through reduced energy consumption, improved health and safety, better efficiency and productivity, waste minimization, and more-effective waste treatment and disposal. Even insurance premiums may be lowered because of better compliance with safety regulations. Companies that recognize these facts can enjoy an enhanced image as a socially responsible corporation and a competitive edge in marketing, as well as many other potential economic benefits.