ADAPTIVE METROLOGY - AN ECONOMICAL STRATEGY FOR JUDGING THE ACCEPTABILITY OF A MASK PATTERN

Size and placement of all features in a mask used for semiconductor in tegrated circuit manufacture must be within specified ranges for the m ask to be acceptable. However the decision on whether the mask meets t hese specifications is usually based on a limited set of measurements: less than 1 in 10(6) of all possible sites. Conventional variance ana lysis on such measurements is inadequate and often misleading because mask pattern errors have significant systematic components. Here we de scribe a more efficient metrology approach for determining whether a m ask meets specifications, ''adaptive metrology'' where the results obt ained as the measurements proceed are used to decide how many, and whe re, more measurements are needed. The process is continued until there is sufficient information to make a decision whether or not the mask is acceptable. In this way the systematic component of the mask errors can be exploited either to increase the accuracy of decisions or to s horten the average measurement time for a given decision accuracy. (C) 1995 American Vacuum Society.