(August 31, 2010) — In this video interview, Jürgen M Lobert, Ph.D., director, analytical services, at Entegris, sits down with editorial director Peter Singer. Lobert discusses airborne molecular contamination (AMC) tools and process protection in micro lithograhy. AMC chemical filters, purifiers and measurement are also covered.
AMC concerns have changed over time: what were chip makers and exposure tool OEMs concerned about 10 years ago and now, with 248nm, 193nm, and 192 immersion processes?
Contamination concern used to be ammonia salt formation on optical surfaces, then was added acid AMC and condensable organic AMC. Ammonia is an AMC that every human produces, making contamination control difficult in the clean room. 193i started looking at more silicon-containing and other “refractory” compounds that can affect apertures. Current focus is on low molecular weight (LMW; also low boiling point / volatile or non-condensable) organic AMC.
LMW organic AMC is difficult to capture, difficult to measure, difficult to clean from optical surfaces (silicon contamination) and difficult to control. All of that is exacerbated by the mandate to control and measure AMC at the low ppt level. At this level, analytical methods are at their limits; material outgassing and non-linear low-concentration effects become real challenges. Scanners are extremely costly and must be run at maximum uptime. Contamination can cost hundreds of thousands of dollars in wafer fab.
Are there solutions for LMW AMC? None specific, exclusive or targeted, says Lobert. The industry roadmaps (SEMI, ITRS) are behind in AMC standards, there is no alignment with OEM concerns. Highest concern requirements come from OEMs who try to balance process need and analytical reality. This is a transitional area with some AMC being captured well, some others not at all. The analytical dilemma: the trapping technology is essentially a small version of AMC chemical filters, prone to the same limitations. AMC removal solutions consist of providing more material of the old kind or creating new, specific AMC removal media for specific AMC molecules. All limited by the same old boundaries such as pressure drop and flow. Both packaging and materials science will need to be employed to tackle this problem and provide the best comprehensive solution (all organics, acids and bases).
AMC removal solutions can be more effectively created when combining the development of AMC removal products with analytical expertise. Entegris’ GMC business unit employs the “See it. Control it. paradigm: see AMC by measuring it, control it through removal solutions.” That combination provides confidence in product specifications, products developed with lowest-level AMC removal in mind and with robust and realistic product validation (filter testing facility), applications expertise and support from the filter vendor, and the AMC filter/purifier supplier also supplies AMC analytical services for product development as well as in-field validation, says Lobert.