Inline x-ray metrology for complementary field-effect transistors (CFET)

This paper demonstrates the relevance of X-rays for inline metrology and process control of complementary field-effect transistors (CFET). After briefly reviewing the stringent metrology needs of CFET, we focus on the starting epitaxial SiGe/Si multilayer and demonstrate that inline X-ray diffraction (XRD) allows the accurate measurement of every individual thickness and composition of this complex stack. Further, we compare to the performance of inline X-ray reflectivity (XRR), which beyond providing individual thicknesses in angstrom-level agreement with XRD also gives access to elusive information about the roughness of the SiGe/Si interface. Moving along the integration flow, we explore the profiling capabilities of inline grazing-incidence small-angle X-ray scattering (GI-SAXS) after inner spacer lateral recess through simulation and preliminary experiments. As we demonstrate, GI-SAXS provides independent information about width, height and inner spacer cavity depth but would necessitate deeper probing depths and smaller beam footprint to enable CFET metrology. Moving to incident energies lower than the currently used Cu K might solve this issue.