Effectiveness and confirmation of local area flare measurement method in various pattern layouts

It is well known that flare, which increases the background intensity and loses the image contrast, degrades the pattern fidelity and CD uniformity. Usually there is little mid and long-range flare at the initial exposure tool introduction except the short-range flare, so called, aberration. However, flare effect is observed in used exposure tools. To estimate the influence of flare, both lens quality of the exposure tool and mask pattern layout with various open ratios are important parameters to be considered. So it is very crucial to make a standard mask layout to measure the flare value as a tool specification. So far, CD variation of the long-range flare has been measured and reported. The long-range flare includes the average influence of the short and mid-range flare and affects more than several hundred- micron distances. Recently it is observed that lens contamination is a dominant component among sources of flare and induced by the pattern layout with its different open ratio. Being contaminated, the lens malfunctions with various types of scattering sources. These scattering sources make the mid and long range flare. This type of flare source has time dependence. If there are proper monitoring methods for the flare measurement, it is possible to maintain the lens quality within the limit of mid range flare. In addition, matching the flare value to CD distribution is not easy because there is no standard measurement method to distinguish the short and mid-range flare from the long-range one. In this paper a LOcal Area Flare Evaluation Reticle (LOAFER) method is suggested. The LOAFER is designed to measure the local area flare of the lens, that is, the short and mid-range flare and the local flare distribution of the exposure tool lens can be characterized. Then matching the result to the real device pattern will be introduced.