A lifetime study of EUV masks

Extreme Ultraviolet Lithography (EUVL) offers the promise of dramatically improved resolution at the price of introducing a complex web of new lithographic challenges. The most conspicuous departure from DUV lithography is that exposure the wavelength is reduced from 193 to 13.5nm. Under exposure at this short EUV wavelength, all materials absorb. Consequently the scanner optics and masks must be reflective and wafer exposure occurs in vacuum without a pellicle to protect the mask. This represents a dramatic shift from the current DUV mask use case. For example, the mask will have to be cleaned after exposure to remove contamination accumulated instead of being protected for its lifetime by a transparent pellicle. The impact of cycling through the exposure tool and being cleaned multiple times will be studied using particle inspection, scatterometry, reflectometry and AFM measurements. The results will be used to identify contamination modes and to propose best practices for EUVL mask exposure.