Characterization of a 100-nm 1D pitch standard by metrological SEM and SFM

Abstract

We report on investigations including calibration of a 100 nm pitch structure, the NanoLattice by VLSI Standards, with a special metrological scanning electron microscope (SEM) and a scanning force microscope (SFM). The SEM used is called electron optical metrology system (EOMS) and basically consists of a dedicated low voltage e-beam column which is mounted on top of a large vacuum chamber with an integrated, laser-controlled precision 2D stage. The key feature of this instrument is the advantage to combine sub-nm-resolution object position measurement by vacuum laser interferometry with a high resolution e-beam probe of about 5-10 nm. Correlation methods combining the laser interferometer and secondary electron intensity profile data are used to analyze global pitch as well as local pitch deviations. The EOMS measurements confirm an excellent pitch uniformity. Preliminary estimations yield sub-nanometric mean pitch uncertainties for the 100 nm grating period over the whole active area of 1 mm x 1.2 mm. Additional SFM investigations were performed by a modified NanoStation III (SIS GmbH, Germany) which has been especially adapted for high stability measurements. In this way, the instrument allows to determine pitch homogeneity and line edge roughness (LER) of the structures with high reproducibility. Preliminary results show a good agreement with EOMS measurements.