Aerial Pattern Mask Inspection (APMI): Once a blank mask has been inspected and accepted it has to be patterned with the required details for the particular lithographic stage it is required for. The next generation of masks for the EUV wavelengths will need to make use of reflective structures based upon multi-layer mirror technology for the patterning process, to allow efficient reflection of the radiation on to the substrate for pattern transfer. These multi-layered masks are more complex and more vulnerable to defects, environmental effects and general damage and therefore a high degree of mask integrity has to be insured before they are committed to the high volume production process, which is what the APMI process aims to achieve.