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Probe position control for enhanced resolution of electrostatic force microscopy

Electrostatic force microscopy (EFM) testing is an extremely useful tool for non-contact internal function and failure analysis of high-speed integrated circuits. Internal circuit voltages are measured by sensing the local electrostatic force on a small micromachined probe that is held in close proximity to the circuit measurement point. Since electrical forces are longrange in nature, the tip-to-sample spacing is usually the determining factor for the EFM instrument spatial resolution and is typically the same order as the spacing. To significantly improve the EFM instrument spatial resolution and voltage sensitivity, a position feedback system, based on controlling the capacitance gradient, is presented to maintain the tip-to-sample spacing to approximately 100 nm. For such small separations, the feedback system prevents the tip from crashing into the surface due to either environmental disturbances or snapping into the surface due to the electrical force gradient.