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BOC Edwards' gift to MassNanoTech stirs supercritical memories |
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Feb 23, 2007 at 12:18 PM |
A recent press release from BOC Edwards about the donation of a dense fluid processing system to MassNanoTech stirred up some supercritical memories.
Remember the serious push a few years ago to develop supercritical carbon dioxide (scCO2) as a possible surface cleaning/prep/drying solution for nanometer-scale chipmaking? I sure do.
I spent quite a bit of time investigating scCO2 and talking to many of the technology's principal proponents (and a few prescient naysayers). I visited the TEL Supercritical Systems unit's scCO2 test bed near Phoenix and other facilities, and discussed the technology's prospects with chipmakers, IMEC, Sematech, and a variety of suppliers, including Praxair and BOC Edwards.
MICRO published several scCO2-related news stories and technical features, including an early 2004 article coauthored by BOC and its technology partner, Micell Integrated Systems, which listed "process steps in which scCO2 is thought to be particularly advantageous." These included "lithographic image development; postdevelop photoresist drying; postetch and postash cleaning of high-aspect-ratio structures and porous low-k structures; cleaning, postclean drying, postclean lubrication, and etching of MEMS devices; barrier layer and seed layer metal deposition; porous ultra-low-k film formation; and compound semiconductor device metal lift-off."
For a technology cycle or two, it seemed like scCO2 might be a contender.
Then, despite millions of dollars of investment, the prospects for scCO2 went south and most work stopped. TEL pulled the plug on its project and the other players pushed scCO2 to the back burner---or off the R&D stove entirely. For one thing, other surface treatment approaches, especially the wet ones, were found to be more extendable down the technological roadmap than previously thought. There were the nagging difficulties of not only how to integrate scCO2 into the process flow but how to convince skeptical fab managers that their facilities could safely and efficiently accommodate the high-pressure systems. There was also the dilemma of whether a sustainable scCO2 infrastructure could be nurtured and flourish.
But don't count out scCO2 just yet. There are still ongoing research projects, such as the one at MassNanoTech, recent recipients of BOC's DFP-200 system. I contacted Jim Watkins, a professor of polymer science and engineering at the University of Massachusetts at Amherst and director of the National Science Foundation Center for Hierarchical Manufacturing and codirector of MassNanoTech. He sent me the following info on how the DFP tool will be used there.
"Supercritical fluids offer unique opportunities for materials chemistry and processing for the semiconductor and related industries. At UMass, we have developed a new approach to the preparation of well-ordered ultra-low k dielectric mesoporous silicate films that involves the 3-D replication of preorganized block copolymer templates in supercritical carbon dioxide. The process involves spin coating a template film, followed by infusion and phase-selective condensation of organosilicate precursors within the template using supercritical CO2 as the carrier. The resultant films exhibit excellent mechanical properties and dielectric constants below 2.2.
"Separation of template formation from infusion and deposition of the precursors offers an additional advantage. The process can be used to produce directly patterned dielectric films by using templates that can be patterned using photolithography prior to infusion of the organosilicate precursors.
"The donation of the BOC DFP-200 to the Center for Hierarchical Manufacturing at UMass will enable the scale up to 200-mm wafers for process development and film evaluation using a tool platform that has been engineered for integration into existing process flows."
Research such as this suggests there still might be a place for supercritical carbon dioxide in nanoscale devicemaking's future.
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