Magnification Errors in the SEM

Abstract

Test and inspection instrumentation requirements are becoming more stringent, as evidenced by the International Standards Organization ISO-9001 certification. To qualify for certification it will be mandatory to calibrate and maintain calibration on laboratory instrumentation. The semiconductor industry also requires accuracies in the sub-micrometer range. However, “the SEM does not always tell the truth”. This work addresses magnification accuracy.Magnification accuracy in the scanning electron microscope (SEM) is affected by the instruments design, manufacture, calibration, and its operating environment. In order to check and calibrate the instrument a standard is required. The only currently available NIST (National Institute of Standards and Technology) magnification standard for the SEM (SRM-484) measures in one dimension and only at higher (> 1000X) magnifications. Recognizing that microscopy is by nature two-dimensional we need to calibrate SEMs in both the X & Y dimensions. A suitable standard has been developed which is usable at least over the normal range of SEM accelerating voltages (200eV and higher) and magnifications (10X to 50,000X).