US Patent 7250235 Focus monitor method and mask

A focus monitor method comprising preparing a mask comprising a first and second focus monitor patterns and an exposure monitor pattern, the focus monitor patterns being used to form first and second focus monitor marks on a wafer, and the exposure monitor pattern being used to form exposure meters on the wafer, obtaining a exposure dependency of a relationship between a dimensions of the focus monitor marks and the defocus amount, forming the focus monitor marks and exposure monitor mark on the wafer, measuring a dimension of the exposure monitor mark to obtain an effective exposure, selecting a relationship between the dimensions of the focus monitor marks and the defocus amount corresponding to the effective exposure, measuring a dimensions of the first and second focus monitor marks, and obtaining a defocus amount in accordance with the measured dimensions of the focus monitor marks and the selected relationship.