Critical Dimension Calibration Standards for ULSI Metrology

NIST and International SEMATECH are developing single‐crystal reference materials for use in evaluating and calibrating critical dimension (CD) metrology tools. Primary calibration of these reference materials uses a high‐resolution transmission electron microscopy (HRTEM) image of the cross section of the feature at sufficient magnification to resolve and count the individual lattice planes; the transfer calibration is provided by complementary metrology techniques. In previous work, electrical test structure metrology served as the transfer metrology. Recent work has centered on evaluating the performance of these CD reference materials in the metrology tools which we expect will comprise the bulk of their usage: the critical dimension scanning electron microscope (CD‐SEM) and atomic force microscope (AFM). In particular, a critical dimension AFM (CD‐AFM) is particularly useful. This technique uses flared tips and two‐dimensional feedback to allow scanning of near‐vertical sidewalls. It is currently expected that CD‐AFM will serve as an additional transfer calibration technique. Additionally, since earlier samples showed a high variability in the appearance of the samples, additional screening using the CD‐SEM and AFM will provide significant improvement to verify that each device meets minimal uniformity characteristics.