Automatic in-situ focus monitor using line-shortening effect

A new focus monitoring method, AIFM has been developed. Specially designed box-in-box was drawn on conventional Cr binary mask and investigate. The box-in-box were drawn to enlarge the line end shortening effect in this new method. There is a lateral shift between inner and outer box in printed feature, and it can be measured quickly at a number of locations across the field and across the wafer with a common overlay measurement system. AIFM provides a means of evaluating focus effects such as field curvature, astigmatism, and field tilt like other focus measurement method. This method has another advantage of in-situ process condition monitoring by drawing focus monitor patterns in real product masks. Experiments were performed to evaluate the effects of pattern geometry and exposure dose on the sensitivity of the focus monitor. AIFM data shows good correlation with conventional focus measurement using SEM line width measurement.