Ways to improve contamination control and wafer cleaning, plus some futuristic technology such as fuel cells for portables, were highlights of the Materials Integrity Management Symposium in Santa Clara, CA, June 3-4.
Aside from some in-depth technical presentations, the attendees also were rewarded with dramatic images and inside stories of the first successful non-stop around-the-world balloon flight, as well as a glimpse into how the Biosphere project was turned from being the butt of late-night jokes to a successful multi-dimensional research program aimed at learning about the earth's mesocosms.
Brian Jones, co-pilot with Bertrand Piccard, showed breath-taking images and told gripping stories of their trials and tribulations in a huge helium balloon that carried the two adventurers from Switzerland around the earth to a landing in an Egyptian desert 20 days later.
The early Biosphere project in Tucson, AZ, ran over its $40 million, 4-year target by $110 million and two extra years, then failed because microbes in the rich rainforest soil created too much CO2, changing the atmosphere and disrupting other experiments. Christopher Bannon, senior VP and chief of staff for Columbia University's Biosphere 2 Center, explained how the university was turning the venture into a wide array of experiments, including a million gallon living salt water ocean and coral reef. Studies of forests, rainforests, coral calcification, and hydrodynamic boundary layers continue, with thousands of student visitors and participants living in dorms. A new energy initative has been launched there, Bannon said, including wind, solar, fuel cell, and other new technologies.
As dimensions shrink, airborne molecular contaminants (AMCs) are becoming an increasing problem, both from the atmosphere and from ambient sources such as acids and bases, dopants, and metals, according to Ray Martin of Asyst and Kirk Mikkelsen of Entegris. Wafers spend over 80% of their fab life in queuing, transport, and storage, and a systematic program is needed to minimize contamination at each process step. Preventing contamination is more effective than removal for both particles and AMC, particularly as thermal budgets are going down, they concluded. Multiple techniques will become important, including gas purges and choices of materials. Standards may help, particular one for clean dry air (XCDA). Every part of the chain for wafer processing must be involved, from materials and equipment suppliers to facilities and process engineers as well as contamination control specialists.
The traditional RCA clean is no longer suitable for many of the materials now going into processing, according to Steven Verhaverbeke of Applied Materials. Hydrogen peroxide will remove the tungsten from local interconnects, for example, and short chemical exposures are required. Single wafer cleaning, with a single clean rather than the two-step cleaning in the RCA approach, combined with full-coverage megasonics, is the approach developed by Applied for its Oasis cleaning system. Using surfactant particle removal techniques speeds particle removal and prevents redeposition, according to Verhaverbeke.
Thin wafer handling is another increasing problem addressed by Steffen Keilbach of PROTEC Group AG, Germany. Chucks have evolved from the stationary to the transfer electrostatic chuck, using polymers, glass, and ceramic materials. The company has developed what it calls smart-carrier technology to reduce stresses in thin wafers with a reversible clamping system and tapeless front-side protection, he explained.
Tracking and handling thousands or reticles in a modern fab is another growing problem addressed by the bare reticle stockers described by John Davidson of Brooks Automation. While there are several approaches to reticle storage, the bare reticle approach, using no carriers, offers very high storage density. But to make it work, a specially designed robot is needed for clean transfer, and an integrated cleaning system removes any contamination before each use in the Brooks Automation approach, according to Davidson. More advanced inspection and quality measurements may be needed before each use in future bare reticle handling systems, he indicated.
Several types of miniature fuel cells being developed to power portable electronic equipment were described by Philip Cox of PolyFuel. These include proton exchange membrane (PEM) types, alkaline fuel cells (AFCs) that can use methanol or ethanol, and solid oxide fuel cells that can use other hydrocarbons. Cox suggested that direct methanol PEMs are the best choice because of unlimited, unplugged run times and no recharge capacity degradation. AC adapters are not needed, and these fuel cells can outperform lithium ion batteries in long run time applications, according to Cox. He discussed work on an array of technical challenges to make these miniature fuel cells commercially competitive.— B. H.