New Application of Variable-Pressure/Environmental Microscopy to Semiconductor Inspection and Metrology
Michael T. Postek, Andras Vladar
Variable-pressure/environmental scanning electron microscopy has been used for successful investigation binary and phase-shifting chromium on quartz optical photomasks. This methodology was also applied to patterned 193 nm photoresist structures. The application of this methodology to semiconductor metrology is new because of the recent availability of variable-pressure scanning electron microscopy (SEM) instrumentation equipped with high-resolution, high-signal, thermally assisted field emission technology in conjunction with large chamber and sample transfer capabilities. The variable-pressure SEM methodology employs a gaseous environment around the sample to help diminish the charge build-up that occurs under irradiation with the electron beam. Although very desirable for the charge reduction in many biological, pharmaceutical, and food applications, this methodology has not been employed for semiconductor photomask or wafer metrology until now. This is a new application of this technology to this area, and it shows great promise in inspection, imaging, and metrology in a charge-free operational mode. For accurate metrology, variable-pressure SEM methodology also affords a path that minimizes, if not eliminates, the need for charge modeling. This paper presents some of the early results in the variable-pressure SEM metrology of photomask and photoresist structures.
critical dimension, environmental microscopy, high-pressure, metrology, scanning electron microscopy, SEM