Lithographic effects of mask critical dimension error

Magnification of mask dimensional error is examined and quantified in terms of the mask error factor (MEF) for Line and hole patterns on three types of masks: chrome-on-glass (COG), attenuated phase-shifting mask (PSM) and alternating PSM. The MEF is unity for large features, but increases rapidly when the critical dimension (CD) is less than 0.5 lambda/NA for line-space patterns and 0.75 lambda/NA for contacts. In general dark-field spaces exhibit higher sensitivity to mask dimensional error than light-field lines. Sensitivity of attenuated PSMs is similar to COG masks, even for applications in which attenuated PSMs provide benefits in process latitude. Alternating PSMs have the lowest MEF values. Although the MEF has only a slight dependence on feature nesting for contacts, dense lines and spaces exhibit markedly higher MEF values than isolated features. The MEF of a 0.35 lambda/NA isolated line is 1.6 whereas that of a dense line of the same dimension is 4.3! Annular illumination is effective in reducing the mask error sensitivity of dense lines. Dose variation causes changes in the MEF of contacts but has little effect on line-space features; focus error degrades (increases the value of) the MEF of both pattern types. A high diffusion and low contrast photoresist process also worsens the MEF Consequences of mask CD error amplification include tightening of mask specification, design grid reduction, shift in optimal mask bias and enhanced defect printability.