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Scanning electron microscopes (SEMs) are incredibly versatile instruments for millimeter to nanometer scale imaging and measurements of size and shape. New methods to improve repeatability and accuracy have been implemented on the so-called Reference SEMs at the National Institute of Standards and Technology (NIST). These methods include: 1) very fast digital imaging and real-time corrective composition of SEM images, showing superiority over both traditional fast or slow image collection methods; 2) high-precision sample stage with laser interferometry, providing traceability and compensation for stage drift and vibration with sub-nanometer performance; and 3) contamination and charging mitigation through hydrogen and oxygen plasma cleaning. These new methods can be applied in other SEMS as well to realize quantitative scanning electron microscopy.

This paper describes the design and implementation of a system for monitoring the performance of several major subsystems of a critical dimension measurement scanning electron microscope (CD-SEM). Experiments were performed for tests involving diagnosis of the vacuum system and column stability by monitoring of the following subsystems and associated functional parameters. These include: 1) Vacuum system with pressure as a function of time being recorded for the electron-optical column (gun chamber), the specimen chamber, and the sample-loading unit.2) The action of several components of the wafer handling system can be timed.3) The electron gun emission currents and other signals to monitor the characteristics of the condenser and objective lenses may be used to correlate with image quality. 4) Image sharpness, electron beam current, signal-to-noise ratio, etc. can be evaluated

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