Influence of flare and NA error on lithography

More and more factors influence the lithography performance with the shrinkage of Critical Dimension (CD). CD error raised by litho tools imperfection cannot be ignored any more. Flare control and Numerical Aperture (NA) adjustment play a critical role in 90nm node dry lithography. In this paper, the respective and the joint impact of flare and NA error for 90nm dense line, semi-dense line and isolated line have been studied by simulation. The results show that the change of CD error is approximately linear with flare and NA error respectively. CD error and Depth of Focus (DOF) error for dense line are sensitive to the change of flare and NA error, especially the sensitivity of CD error to flare and NA error of dense line is larger than that of semi-dense line and isolated line. The placement error caused by flare and NA error is less than 10 -3 nm for these patterns. The joint impact of flare and NA error on lithography performance is not the linear sum of the results that two factors change respectively; there is a certain coupling effect between these two factors. For these patterns, the sensitivity of CD error to flare is larger than that to NA error, but a larger NA error can compensate the effect caused by flare. Therefore, the tolerance of flare can be relaxed by adjusting NA.