Scanned Probe Metrology in the Presence of Surface Charge

Surface charge on insulating samples can be a significant source of error for scanning probe microscopes. We have found that it is possible to operate a scanning force microscope in a manner that makes it relatively immune to charge-induced forces while still allowing the probe tip to nopndestructively follow the surface topography. The need to maintain close charge balance n the sample is thus obviated. We have used this strategy to perform critical dimension measurements on optical photomasks with the Surface/Interface Stylus NanoProfilometer. This instrument incorporates a servoed force-balance sensor. Surface topography is determined by touching t he surface with contact forces between 0.1 and 1 micronewton.