The HYDRATM- APMI has been tailored to meet the requirements of Aerial Patterned Mask Inspection tools. This is achieved by the multiplexed operation of eight i-SoCoMoTM units where the goal is to be able to detect patterned mask defects at the 22 nm node and below. Mask pattern inspection is a process developed from projection lithography, requiring the analysis of critical dimension structures and in particular their line intensity profiles. It is important to be able to distinguish real line widths from variations due to randomness and in particular if a pattern defect becomes printable. This requires a good understanding of the systems sensitivity and response to particular types of defect to be found.