<title>Calibration of scanning electron microscope magnification standards SRM484</title>

Abstract

Standard Reference Material (SRM) 484 is an artifact for calibrating the magnification scale of a scanning electron microscope. Since 1977 the National Institute ofStandards and Technology (MST) has produced seven issues of SRM484 amounting to approximately 1 150 samples in all. The standards are fabricated by electroplating alternate layers ofnickel and gold onto a substrate of a Monel sheet metal. The plate is then diced, and the individual pieces are mounted on edge in a holder. Each sample is metallographically polished to obtain a smooth surface and to reveal gold lines. The samples are calibrated using a scanniig electron microscope incorporated with a laser interferometer. A piezo flexure stage carries the sample across the stationary electron beam. A backscattered electron detector detects an intensity peak at each location where the electron beam interacts with a gold line. The displacement ofthe traveled stage between lines is monitored by the interferometer. A computer program records the intensity peaks and displacement information and determines the distance (spacing) between any two peaks. The spacing is measured from a peak-to-peak algorithm rather than an edge-to-edge algorithm in order to avoid the determination ofline edge positions. Properties ofthe SRM484 and the measurement system result in recent expanded uncertainties (at the level oftwo standard deviations) of approximately 4% for 0.5 jim spacings and 0.5% for 50 tm spacings. Key words: Interferometer, Measurement uncertainty, Scanning Electron Microscope, SEM magnification, Standard Reference Material.