Monitoring of submicrometer linewidths using diffraction gratings

Abstract

For a typical fabrication facility, linewidth control is done after the patterning and etch processes by means of a scanning electron microscope (SEM). Several techniques using diffraction gratings have been proposed as in-line or in situ replacements for the SEM linewidth measurement. One such system was developed for use in the Microelectronics Manufacturing Science and Technology (MMST) mini- factory. The system used in the MMST factory was capable of measuring the critical dimensions needed for factory control. This critical dimension diffraction measurement system consists of optics and processing algorithms necessary to measure a series of gratings in an etch processor or directly after processing in a metrology chamber. The optics allow the measurement of a full diffraction pattern with one image. The processing algorithms convert this image to a list of diffraction orders and intensities for each grating in the set. These are then used by the pattern matching algorithms to determine grating linewidth.