Motorola makes EUV masks

Motorola, in a presentation at International Sematech's Next Generation Lithography Workshop, held in late August, announced the fabrication of extreme ultraviolet (EUV) photomasks capable of printing sub-100 nm features. Feature size on the 4X masks was 400 nm.

Joe Mogab, the director of advanced process development and external research at Motorola's DigitalDNA Lab, explained that the masks use standard Mo/Si multilayer blanks from Lawrence Livermore National Laboratory. These blanks are roughly 70% reflective at the 13 nm target exposure wavelength. Reflectance depends on wavelength, with peak reflectance occurring in a 0.4 nm band centered at 13 nm.

Reflectance and bandwidth characteristics are both sensitive to processing conditions. The molybdenum and silicon layers begin to mix at temperatures above 150°C. The optical surfaces are also sensitive to etching damage. Mogab reports that Motorola's mask process, using a wet chemical-etched chrome absorber layer, has avoided both these issues. The patterned masks had reflectance within a few tenths of a percent of the blank reflectance, and bandwidth within a few hundredths of a nanometer.

Though mask defectivity appears to be low, Mogab cautioned that actinic wavelength inspection tools do not yet exist. It is not yet clear how defects reported by DUV inspection tools will correlate with printable defects at the EUV wavelength.

Nor has Motorola yet printed wafers from these masks. It expects to use Livermore's EUV Engineering Test Stand to do so by early 2002. Though significant obstacles remain, Motorola plans to begin using EUV tools in production in 2006 or 2007. Lithography process development should begin by 2005.