The intensity enhancement of transmission small angle x-ray scattering from nanostructures with a high aspect ratio

Transmission small angle x-ray scattering (tSAXS) has been developed as a metrology for the critical dimension (CD) measurements to facilitate integrated circuit (IC) chip fabrications. Synchrotron x-ray sources were used for their high brilliance and a wavelength less than one tenth of a nanometer was chosen for its high penetration power to enable transmission measurements through a silicon wafer with a nominal thickness of 0.7 mm. A major hold back preventing tSAXS from reaching wide applications in IC fabrication is the lack of high brilliance laboratory-based x-ray sources. Within the last few years, even without any major breakthrough in x-ray source technology, this tSAXS metrology has finally been used for 3D NAND and DRAM, i.e., memory chips with tall or high aspect ratio (HAR) architectures. The scattering intensities from HAR structures will be discussed quantitatively in terms of the sample height and the effective longitudinal coherence length of the incident x-ray.