METHOD FOR MEASURING ALIGNMENT RATIO OF WAFER

摘要

PURPOSE: A method is provided to prevent an intensity of wafer alignment signal weakening caused by reduction of a step coverage of wafer alignment mark in a flattening process. CONSTITUTION: An alignment light(35) is divided by two lights through a beam splitter(30), which one(36) is for a wafer alignment mark(17) and the other(38) for a reflection mirror(25). A reflected light(39) from a mirror interferes with a light(37) reflected from a wafer alignment mark. Passages of reflected lights are symmetric to each other so phases of the ones are same. Then an intensity of an interfered light(40) turns to be double and a measuring sensitivity of a wafer alignment signal is increased as much.