Hybrid metrology for non-destructive lateral cavity etch measurements of 8-superlattice layer nanowire test structures (NWTS) using optical Mueller matrix spectroscopic ellipsometry (MMSE), x-ray diffraction (XRD), and x-ray reflectivity (XRR)

Lateral gate-all around (LGAA) transistor structures are on the IEEE IRDS logic roadmap for sub-3 nm nodes, with scaling being enabled in part by utilizing increased numbers of Si/Si(1-x)Ge(x) superlattice layers to form the structures. A key manufacturing step is the lateral cavity etch process, which is required for the indent etch and gate release steps. After anisotropic etch through the superlattice, the cavity etch step selectively etches the Si(1-x)Ge(x) layers, resulting in device geometries that are cannot be measured with traditional top-down scanning electron microscope (CDSEM) critical dimension metrology. Accurate, non-destructive metrology is necessary to enable high volume manufacturing of LGAA devices. A set of 8-superlattice layer samples containing nanowire test structure (NWTS) targets were processed at three levels of cavity etch. A hybrid metrology approach was explored which combined three techniques for accurate measurements. High-resolution X-ray Diffraction (HRXRD) determined individual layer thickness measurements, which were fed forward into an Optical Critical dimension (OCD) model for a nanowire test structure (NWTS). The OCD-determined cavity etch parameter was verified using X-ray Fluorescence (XRF) measurements of overall germanium volume. Transmission electron microscope (TEM) reference measurements were taken of lamellae prepared using focused ion beam (FIB) milling of the sample. The destructive TEM measurements were used as a reference to determine the accuracy of the non-destructive hybrid metrology. Sub-nanometer matching to STEM was achieved with the nondestructive hybrid XRD/OCD and XRF feed forward method.