It's time to reclaim and reuse cleanroom consumables
by Robert P. Donovan
Generally, capital costs and labor expenditures dominate the operating costs of most cleanroom manufacturing operations. In semiconductor manufacturing especially, the capital costs associated with the many multimillion-dollar tools that rapidly age and require frequent updating or replacement are by far the largest cost component of doing business.
Consumables' costs, however, can sometimes also be significant or even dominating. Consumables are items or materials that are used up in the process of manufacturing a product. Among many other materials or items, cleanroom consumables in semiconductor manufacturing include ultra-pure water, process gases, photoresist CMP slurries, wipers and gloves. Understandably, with the exception of gloves, expensive CMP slurries constitute the most costly component of CMP cost of ownership.
Workers in a semiconductor cleanroom manufacturing facility wear gloves to protect products from contamination during handling and to protect themselves from exposure to chemicals used in semiconductor processing. Many of these gloves are disposable; they're simply discarded after one use, with the worker donning a fresh pair of gloves each time gloves are removed for any reason.
Workers typically go through up to 4 pair of gloves per shift, at a cost of about a dollar per shift per worker. With more than a million semiconductor workers worldwide, disposable cleanroom gloves cost the industry more than a billion dollars a year, and usually represent a semiconductor manufacturer's costliest consumable that is not part of the product or the materials directly used to process product.
Nitrile's resistance and strength
The most commonly used disposable cleanroom glove is made of nitrile. Nitrile polymers consist of three monomers: acrylonitrile, butadiene and a carboxylic acid. Acrylonitrile provides resistance to hydrocarbon oils, fats and solvents; butadiene provides rubber-like properties to the finished glove; and the carboxylic acid adds tensile strength and abrasion/tear resistance.
Workers don a pair of nitrile gloves as the last gowning step before entering the cleanroom from the gowning area. The nitrile gloves can be worn over a gowning glove, put on before entering the gowning area from the outside and worn throughout the gowning procedure, or can simply be exchanged with the gowning glove and worn directly on the bare hand without any liner. In any case, the nitrile glove becomes disposable waste after use.
What the semiconductor industry really needs is an economical, practical process for converting used, discarded nitrile cleanroom gloves into a useful by-product or a valuable, reusable resource—a reuse role for these gloves that results in an income generator for the semiconductor operator and avoids the waste and costs of landfill disposal.
Using the discarded gloves as feedstock for making fresh nitrile gloves is an obvious possibility, as is laundering used gloves for reuse. Neither of these options is presently practiced; no doubt, for sound economic reasons.
Reusing CMP slurries is an even more pressing economic need, especially with the growing use of newer and more expensive slurries for CMP operations with copper, and the fragile, low-dielectric constant layers forecast to be needed in future semiconductor production. Happily, slurry reuse is receiving some attention.
Reference 1 reports "regeneration" of used slurry that performs as well as normal slurry, and cites a 1997 patent that incorporates a blending of used and fresh slurry to achieve "a significant savings in fresh slurry usage" with "substantially the same performance as 100 percent fresh slurry."²
In addition, the 2001 International Technology Roadmap for Semiconductors forecasts that their task entitled "Develop CMP slurry recycling" will reach the qualification/pre-production stage this year.
Reusing consumables, rather than discarding them, offers a win-win situation—the industry achieving cost reductions while offering another step toward a greener environment,
ROBERT P. DONOVAN is a process engineer assigned to the Sandia National Laboratories and is a monthly columnist for CleanRooms magazine. He can be reached at: firstname.lastname@example.org
1. Park, J-G, K-J Lee and M-S Kim, "In-Situ Recycle of Used Oxide Slurry for Production", Abs. 914, 204th Meeting of the Electrochemical Society, Inc., 2003
2. U. S. Patent 5,664,990, "Slurry Recycling in CMP Apparatus" (to Integrated Process Equipment Corp.) Adams, J. A, G. A. Krulik and C. R. Harwood, Sept 9, 1997