Aerial Image Measurement System (AIMS): This is an optical technique developed to evaluate the printability of features in a lithographic system. It is required to monitor the quality of the masks used in wafer fabrication, analysing the effect of potential defects, the effectiveness of mask repairs and the properties of mask features that are used to enhance the printing of certain aspects of the pattern information. AIMS negates the need to print the mask pattern using a stepper printer and makes use of sophisticated algorithms to interpret the properties of the mask from the aerial images that are captured.