EUVL is a significant departure from the lithography used today, but reducing mask defects is key to its viability. Fred Conroy, Tiger Optics, describes a new AMC detector that could help in this aim.
On-line analysis of airborne molecular contamination (AMC) in semiconductor manufacturing cleanrooms has taken on added significance of late. As the industry prepares to migrate to extreme ultraviolet (EUV) lithography to shrink the size of chip designs, the requirements to reduce airborne contamination and to monitor the contamination levels in real-time grow ever more stringent.
To that end, semiconductor manufacturers have shifted to new, more sensitive AMC detectors, reliant upon techniques such as Continuous Wave Cavity Ring-Down Spectroscopy (CW CRDS) and Ion Mobility Spectroscopy (IMS).
Notably, with previous generations of lithography tools, contamination issues have been well documented, based upon varying methods in place to monitor the contamination events. Airborne acid contamination results in corrosion issues and airborne contamination due to bases leads to “T-top” formations (a large, T-shaped insoluble head on a photoresist feature) as well as a haze that forms on the back of the reticle, known as reticle hazing.
Acids in the ambient air, specifically low concentrations of hydrogen fluoride (HF), can attack the HEPA filters and accelerate the release of boron, which can result in crystal salt formations, creating a reservoir for permanent low-level contamination. Another acid-induced wafer defect occurs when hydrochloric acid (HCl) makes the photoresist soluble, engendering hole-type defects on the photoresist.
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