Mask inspection technologies for expanding EUV lithography

The demand for EUV mask qualification by inspection and metrology techniques continues with the technology node shrink. Smaller node products contain a higher number of masks that require EUV exposure. Semiconductor industries have developed a variety of inspection and metrology tools to accommodate these needs. The progress of these techniques provides well-qualified semiconductor devices. Blank manufacturing is the initial step of the mask-making process. Nanometer-scale bumps and pits on the substrate, uniformity of multilayer stack, and particle-induced wafer printing defects must be controlled during the blank-making process. Both optical mask inspection and actinic blank inspection (ABI) are widely used as effective qualification methods to detect a defect of interest. Patterned mask inspection is an essential process step for mask making. The optical pattern inspection operating at DUV wavelengths near 193nm, Actinic Patterned Mask Inspection (APMI) that uses EUV 13.5nm wavelength, and EB inspection are the presently used patterned mask inspection technologies. APMI plays a key role in EUV mask inspection due to its high-resolution imaging. The introduction of reliable database mode inspection capability added more usability for the latest single die configuration masks. To manage all the printing defects, actinic solutions have the capability to realize fast and reliable results. EUV pellicles are already in use with EUV masks. Thus, the actinic solution is considered a required inspection method for patterned mask qualification for pellicle mounted mask too. Multiple APMI systems have already been installed in mask industries for through-pellicle inspection purposes. We will report the current progress of patterned mask inspection technologies, applications, and the future roadmap for high NA EUV.