Masks for 0.25-μm lithography

Specifications for photomasks to be used to print 0.25 micrometers structures have to be much tighter than mask specifications for today's most advanced 0.5 micrometers technologies. As optical lithography works closer to its resolution limit, line shortening, increased susceptibility to errors in mask manufacturing, and enhanced printing of mask defects has to be taken into account. Phase shift masks improve the process window of lithography and provide therefore more room for selective mask biasing. However, the additional parameters inherent to particular phase shift mask types (phase shift, transmission uniformity for attenuated phase shift masks, rim uniformity for rim-phase shift masks) contribute to the total error budget and need therefore to be controlled to very tight tolerances, too.