Characterization of correlated line edge roughness of nanoscale line gratings using small angle x-ray scattering

To meet the challenges in dimensional metrology as the minimum feature size in semiconductor devices approaches sub-35 nm length scales, we have been developing a nondestructive method using x rays termed critical dimension small angle x-ray scattering (SAXS). Its capacity to quantify the dimension of linewidth, pitch, line height, and sidewall angle of line gratings has been demonstrated. In this work, we have further extended its capabilities to quantify the correlated line-edge roughness (LER) and linewidth roughness (LWR). Model line grating patterns with controlled LER and LWR were prepared and measured using x ray, their results were analyzed with model calculations. The magnitude of LER/LWR deduced from x-ray results compares favorably with the scanning electron microscopy results obtained from the same samples. An apparent Debye-Waller factor, which can be deduced from the SAXS data without any detailed model-based calculations, is found to be a convenient parameter to quantify the amplitude of LER/LWR.