Patent ID: 6727989
Filing Date: 2004-04-27
Classification: G03F

Abstract:
In an overlay measurement mark comprising an inner box and an outer box located at a predetermined area on a mask through which patterns are formed on a semiconductor device, the improvement of an enhanced overlay measurement mark that extends the overlay measurement range to overcome the limitations of overlay measurement marks that give an overlay shift range comparable to the measurement tools uncertainty and gives only stepper or scanner mechanical alignment errors but fails to provide accurate image placement error information due to stepper or scanner exposure conditions comprising:in-focused marks means printed at an optimal or ideal focal plane level from an illumination source; de-focused marks means located at a different focus level from the optimal focal plane to provide image placement shift of said de-focused marks larger than that of said in-focused marks means to enable measurement of the shift of de-focused marks not attributable to a mechanical alignment error to be determined with greater accuracy; and different feature size marks means placed across reticle field locations to provide estimations of actual device feature image placement errors.