Method and system for measuring pattern placement error on a wafer

摘要

A method for measuring pattern placement error (PPE) on a wafer includes receiving a photomask pattern. One or more unit cell patterns are added to the photomask pattern. Each of the unit cell patterns includes at least one reference design pattern and at least one PPE check design pattern. A photomask is fabricated from the photomask pattern with the one or more unit cell patterns added thereto. A wafer is patterned using the fabricated photomask. A microscope image of the patterned wafer is acquired. Pattern placement error is measured as a displacement between the at least one reference design pattern and the at least one PPE check design pattern.