In this study, overall critical dimension (CD) error budget analysis procedure is proposed to estimate the source of CD
error. Until now, local CD variation has been treated as noise or uncertainty, since it has been considered not real, and it
is difficult to be measured. However, the actual measurement result shows the local CD variation occupies a significant
portion of overall CD variation. We included the local variation into overall CD budget analysis, and performed the
budget break-down of the local CD variation. This analysis was performed on the layers of a sub-50nm DRAM device.
We calculated local CD uniformity from CD SEM measurement data having multi-point measurement on each frame.
Metrology error of wafer CD SEM and mask CD SEM was measured, and local CD uniformity (CDU) of mask was also
measured. To estimate the impact from the mask local CDU, we performed simulation with a virtual mask shape which
has the same level of local variation with real mask. The remaining budget, except metrology and mask induced budget,
is treated as a process roughness. To predict the budget caused by process roughness, a randomly varying threshold map
was applied. In this approach, the local CD variation of 2-dimensional patterns is considered as an extension of the LWR