Method of measuring the aberration of a projection lens

摘要

A new inspection method is provided for testing lens aberrations during production of semiconductor wafers in projection apparatus such as wafer steppers or scanners. It is checked for lens degradation by measuring aberration specific measurement pattern structures (3) preferrably being arranged in fields of a test mask, and then projected to corresponding measurement pattern structures (8) on the wafer. A signal is issued, if threshold values (2) representing a corresponding aberration such as spherical aberration, astigmatism, coma or three-leaf-clover are exceeded. For the latter measurement symmetric DT-like pairs of rectangles (303) are provided in order to compare left-to-right-differences in critical dimension with threshold values (2). Also, structures combining sagittal and tangential lines into, e.g., waggon wheel-like structures (304) are provided. As a result of the signal (1) issued, a tool dedication strategy such as to reduce tool specifications can be initiated. <IMAGE>