Photomask Defectivity and Cleaning: A New Milieu

Photomasks are conceptually simpler than wafers: fewer levels, fewer process steps, and larger main features. However, mask optical proximity correction (OPC) features are about the same size as a wafer's printed features. A single wafer defect affects one die, while a single mask defect affect...

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Bibliographic Details
Published in:Semiconductor International 2007-09, Vol.30 (10), p.41
Main Authors: Kalk, Franklin, Gordon, Joseph, Chan, David
Format: Magazinearticle
Language:English
Subjects:
Cleaning
Customer feedback
Cutting tools
Defects
Manufacturers
Production planning
Semiconductors
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Summary:Photomasks are conceptually simpler than wafers: fewer levels, fewer process steps, and larger main features. However, mask optical proximity correction (OPC) features are about the same size as a wafer's printed features. A single wafer defect affects one die, while a single mask defect affects every die. Mask defects are detected optically, so even minor optical fluctuations on the mask render it defective. Thus, the historical mask cleaning challenge has been to provide a mask perfectly free of microscopic contamination without altering its physical properties or damaging the masking layers. ArF (193 nm) lithography tools have introduced a new defect class known as haze. All variants of haze share two attributes: they are often detected only after the mask is exposed in the wafer scanner, and the source is molecular contamination near the mask surface. Classic mask cleaning techniques, effective at removing microscopic contamination defects, can actually contribute to one type of haze. Eliminating haze requires a collaborative effort between mask manufacturers, wafer manufacturers and tool and materials suppliers. Focusing primarily on haze, this article describes our most recent understanding of mask defects, their detection and elimination, and methods for maintaining a defect-free mask throughout its useful life in the wafer fab.
ISSN:0163-3767