Potentials for high-pressure/environmental SEM microscopy for photomask dimensional metrology

Binary and phase-shifting chromium on quartz optical photomasks have been successfully investigated with high-pressure/environmental scanning electron microscopy. The successful application of this methodology to semiconductor photomask metrology is new because of the recent availability. of a high-pressure SEM instrumentation equipped with high-resolution, high-signal, field emission technology in conjunction with. large chamber and sample transfer capabilities. The high-pressure SEM methodology employs a gaseous environment to help diminish the charge build-up that occurs under irradiation with the electron beam. Although very desirable for the charge reduction, this methodology has not been employed much in photomask or wafer metrology until now. This is a new application of this technology to this area, and it shows great promise in the inspection, imaging and metrology of photomasks in a charge-free operational mode. This methodology also holds the potential of similar implications for wafer metrology. For accurate metrology, high-pressure SEM methodology also affords a path that minimizes, if not eliminates, the need for charge modeling. This paper presents some new results in high-pressure SEM metrology of photomasks.