The application of high pressure or environmental microscopy techniques is not new to scanning electron microscopy. However, application of this methodology to semiconductor metrology is new because of the combined need for implementation of high resolution, high brightness field emission technology in conjunction with large chamber and sample transfer capabilities. This methodology employs a gaseous environment to help neutralize the charge build-up that occurs under irradiation with the electron beam. Although potentially very desirable for the charge neutralization, this methodology has not been seriously employed in photomask or wafer metrology until now. This is a new application of this technology to this area, but it shows great promise in the inspection, imaging and metrology of photomasks in a charge-free operational mode. For accurate metrology, this methodology affords a path that minimizes, if not eliminates, the need for charge modeling.