Measurement of the flare and in-field linewidth variation due to the flare

Flare induced from the optical elements of exposure tools reduces the overlapped process margin and the contrast of Aerial images. As the line width of patterns shrinks with a higher speed, this flare will be more important in the near future. Thus, it is necessary to investigate the amount of flare in the optical elements of exposure tools and the effect of the flare on the microlithographic patterning. From this reason, the flare and the distribution of the flare across the slit position have been investigated with a specially designed photomask. And, also, the line width variations due to the flare have been thoroughly investigated. From our researches, two kinds of line width variations were observed on a wafer because of the flare and its distribution. First kind of the line width variation was induced from the pattern density. This kind of the line width variation would be sometimes observed in a device having the big difference of pattern densities. Second kind of the line width variation was induced from the horizontal distribution of the flare along the slit position. This kind of the line width variation would be mainly observed in a device exposed with a highly contaminated exposure tool. These kinds of line width variations could be well explained with an Aerial image calculation and predicted with a given pattern density and an amount of flare as well.