IBM Reveals Carbon Nanotube Air Filters for Semiconductor Manufacturing Processes
May 4, 20100
International Business Machines Corporation (Armonk, NY) developed carbon nanotube filters. The filter includes a filter housing; and chemically active carbon nanotubes within the filter housing, the chemically active carbon nanotubes comprising a chemically active layer formed on carbon nanotubes or comprising chemically reactive groups on sidewalls of the carbon nanotubes; and media containing the chemically active carbon nanotubes, according to inventors Steven J. Holmes, Mark C. Hakey, David V. Horak and James G. Ryan in U.S. Patent 7,708,816.
In advanced semiconductor manufacturing, airborne contaminants can cause degradation of photoresist layers and optical elements of advanced photolithography systems such as immersion lithography tools, wherein airborne molecules can polymerize when exposed to the very high energy light beams of advanced lithography tools. The resultant polymer can then coat the optics degrading the image quality of the tool and coat the tooling causing degraded alignment tolerances. Additionally contaminant molecules can be adsorbed by the photoresist layer, interfere with the photochemistry and cause photoresist defects. Conventional filters are unable to remove much of these airborne molecules. Similarly, contaminant molecules can exist in the gas streams used for purging and operating of various components of the tool.
Therefore there is a need for an advanced chemical and particulate filter for applications requiring extremely low levels of contaminants in the filtered air and/or gas streams. IBM’s carbon nanotube filter meets that need.
The filter utilizes carbon nanotubes having a chemically active layer or carbon nanotubes having chemically reactive groups on the sidewalls of the carbon nanotubes as a filter media. The small size of carbon nanotubes provides a large surface area and the chemically active layer or chemically reactive groups provides sites for attracting, binding or chemically reacting with contaminant molecules in the air or gas streams being filtered.
FIG. 13 is a flowchart of the method of making chemically active nanotube filters according to the present invention. In step 600, a substrate is provided. In step 605 a catalytic layer is formed on the substrate. The catalytic layer may be optionally patterned. In step 610, CNTs are formed on the catalytic layer. As an alternative to steps 600, 605 and 610, steps 615 and 620 may be performed. In step 615 a CNT precursor and CNT catalyst are provided. In step 620, a CNT mat is formed. In step 615, the CNTs on the substrate from step 610 or the CNTs in the CNT mat from step 620 are chemically activated by either forming a reactive layer on the CNTs or forming reactive groups on the sidewalls of the CNTs. In step 630, the substrates with chemically active CNTs or the chemically active CNT mat are placed in a filter housing.