Method for performing an alignment measurement of two patterns in different layers on a semiconductor wafer

摘要

In an alignment or overlay measurement of patterns on a semiconductor wafer (1) an error ocurring during performing a measurement in one of a predefined number of alignment structures (20) in an exposure field (2) of a corresponding predefined set of exposure fields (10) can be handled by selecting an alignment structure (21b) in a substitute exposure field (11). This exposure field (11) needs not to be part of the predefined set of exposure fields (10), i.e. an inter-field change (101). Thus, the number of alignment measurements on a wafer remains constant and the quality is increased. Alternatively, when using another alignment structure (21a) in the same exposure field (10, 11), i.e. an intra-field change (100), the method becomes particlularly advantageous when different minimum structure sizes are considered for the substitute targets (21a). Due to the different selectivity in e.g. a previous CMP process, such targets (21a) might not erode and do not cause an error in a measurement, thus providing an increased alignment or overlay quality.