Corning's Extreme ULE glass debuts for next-gen High-NA EUV chipmaking

Corning has introduced its new ultra-low expansion (ULE) material that is designed to withstand ever increasing power of upcoming Low-NA (Numerical Aperture) and High-NA EUV lithography systems. The new Extreme ULE material is projected to be used for next-generation photomasks and lithography mirrors that will be used with next-generation fab tools. 

A key feature of the Extreme ULE material is its extremely low thermal expansion, which provides exceptional consistency for photomask use. In addition, its superior flatness helps to minimize "photomask waviness", reducing unwanted variability in chip production. These properties enable the application of advanced pellicles and photoresists to boost yields and performance. 

As extreme ultraviolet lithography tools attain higher performance in terms of wafer per hour (WPH) processing, they adopt more powerful light sources, and the more powerful light sources expose photomask pellicles, photomasks, and ultimately resists and wafers to higher dosage of EUV radiation and heat.  

In an EUV tool, the plasma source that generates EUV light emits a lot of heat, but the heat is mostly confined to the source chamber, which is separated from the photomask. The light is carried by a set of lithography mirrors that are susceptible to heat. As for the photomask itself, it is made of multilayer reflective materials designed to reflect EUV light. While these layers are highly reflective, some absorption still occurs, leading to a slight heating of the mask. Considering how intricate modern circuits are, even a slight deformation or inconsistency could lead to yield-killing defects or performance variabilities. 

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