Standard Reference Material (SRM) 484 is an artifact for calibrating the magnification scale of a scanning electron microscope. Since 1977 the National Institute of Standards and Technology (NIST) has produced seven issues of SRM484 amounting to approximately 1150 samples in all. The standards are fabricated by electroplating alternate layers of nickel 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 scanning 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 of the 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 of line edge positions. Properties of the SRM 484 and the measurement system result in recent expanded uncertainties (at the level of two standard deviations) of approximately 4% for 0.5 um spacings and 0.5% for 50 um spacings.
Proceedings Title: Proceedings of SPIE, Metrology, Inspection, and Process Control for Microlithography X, Susan K. Jones, Editor
Conference Dates: March 11, 1996
Conference Location: Santa Clara, CA
Conference Title: Scanning Probe Metrology
Pub Type: Conferences
interferometer, measurement uncertainty, scanning electron microscope, SEM magnification, Standard Reference Material