Application of High Pressure/Environmental Scanning Electron Microscopy to Photomask Dimensional Metrology

Abstract

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.

Review of current progress in nanometrology with the helium ion microscope

“…Photomasks can be very difficult to image in the SEM due to charge build-up in the quartz. Postek et al (2003) successfully used variable pressure SEM to dissipate the charge build-up for the imaging and metrology of chromium photomasks [31]. The HIM can also be successfully employed in the imaging and metrology of these samples (figure 7).…”

Modeling for accurate dimensional scanning electron microscope metrology: then and now

“…Clearly, coating the sample with a very thin, but conductive layer of osmium, gold, or carbon can minimize that problem, but that is not always possible. Another possibility for charge reduction is the use of a variable‐pressure SEM that in low‐pressure gaseous environment around the sample diminishes the charge build‐up (Postek and Vladár, 2003). In addition, the application of retarding or accelerating electric fields around the sample also can reduce the effects of sample charging.…”