Standard Reference Materials: Antireflecting-Chromium Linewidth Standard, SRM473, for Calibration of Optical Microscope Linewidth Measuring Systems

摘要

The accurate measurement of feature dimensions on photomasks, such as those usedin the production of integrated circuits, becomes increasingly difficult as the dimensions approach the wavelength of the light used to make the measurement. The effects of optical diffraction obscure the location of the feature edges. Raggedness and nonvertical wall along the edges add to the uncertainty of the measurement. Standard Reference Material SRM 473 was developed for use in calibrating optical microscopes for measuring linewidths in the range of 0.5 to 30 um on antireflecting chromium photomasks. The SRM is described, and instructions on its use and precautions concerning its care and handling are given. The NIST linewidth measuring system and the procedures used to calibrate the SRM are discussed. The algorithm used for determining the line edge location incorporates a threshold criterion derived from analysis of microscope image profiles. The performance of this system is monitored by measuring line features on a control photomask before and after calibrating each.