Lab-based multi-wavelength EUV diffractometry for critical dimension metrology

The industry is developing extreme-ultraviolet wavelength (EUV) techniques to measure critical dimensions (CDs) in logic fabrication. As nascent approaches are unveiled, evaluations against reference metrologies are essential to motivate development at higher speeds using industrially relevant length scales. The parametric geometries determined from EUV diffractometry data using a tabletop coherent high-harmonic generation (HHG) source are compared against dimensions from synchrotron-based CD small angle x-ray scattering (CD-SAXS) for four line-space arrays with CDs below 50nm. An EUV imaging reflectometer captures the 0th order reflection and the 1st order diffraction intensities as functions of grazing angle. The 1st order intensities are functions of five wavelengths from the spectral comb of this HHG source. Fits to these data using rigorous couple-wave analysis (RCWA) electromagnetic simulations yield parametric values and uncertainties. EUV diffractometry simulations match well in general with the measured data after accounting for cross-sectional geometry and experimental conditions. EUV diffractometry line widths correlate well against those of CD-SAXS at the mid-height of the latter. These promising results were obtained using a general-purpose prototype coherent EUV reflectometer. Routes for further enhancing the sensitivity and accuracy are presented and are in progress.