Advanced semiconductor devices are moving toward three-dimensional (3D) geometries due to scaling demands and performance requirements. Non-destructive metrology necessary for process control of 3D structures must be advanced to facilitate their transition from technology development to high-volume manufacturing. Thin film metrology using Mueller matrix spectroscopic ellipsometry (MMSE) and X-ray diffraction (XRD) film metrology, as well as patterned structure metrology using optical critical dimension (OCD) and X-ray fluorescence (XRF) techniques, have proved capable of measuring the Si/Si1−xGex superlattices and gate-all-around transistor test structures. Because these techniques are indirect, their limitations associated with superlattice device structures need to be further understood. To understand these limitations, a four-superlattice layer Si/Si1−xGex structure was measured at four process steps: as an unpatterned film stack, after anisotropic column etch, and at low and high levels of cavity etch. Thin film samples were analyzed with XRD and MMSE, and patterned samples were analyzed using OCD, as well as XRF. A model was developed describing the primary and secondary process effects on the structure. This was evaluated for consistency on datasets collected at different measurement azimuth angles. Square error–based methods were evaluated to quantify OCD model detectability of fit variable step deviations, as well as sensitivity relative to the model to measurement error. OCD and XRF results were compared with reference scanning transmission electron microscopy (STEM) images of nanowire test structure lamellae. Dual-azimuth fit OCD models were found to be within 0.3 nm of the STEM reference mean.
Advanced semiconductor devices are moving toward 3D geometries due to scaling demands and performance requirements. The non-destructive metrology necessary for process control for high volume manufacturing of 3D structures must be advanced to facilitate their transition from technology development to high volume manufacturing. Optical Critical Dimensions (OCD) techniques based on Mueller Matrix Scatterometry (MMSE) as well as XxRay Diffraction (XRD) have proved capable of measuring the Si/Si1-xGex few layer superlattices used to fabricate Gate All Around (GAA) transistor device test structures. The limitations of these techniques associated with superlattice device structures needed to be further understood. To understand the limits of MMSE Scatterometry and XRD, a four superlattice layer Si/Si1-xGex structure was measured as a film stack, a column etched sample, and at two levels of cavity etch. XRD was used to determine individual layer thicknesses and compositions of the film stack, and electron microscope data was used to verify initial structure dimensions for OCD models. First, film stack characterization and metrology for both ellipsometry and x-ray characterization were explored. OCD modeling and measurement strategies were evaluated to address the challenge of fitting the superlattice thicknesses in the stack at different etch levels. We demonstrate the characterization of relevant test structure dimensions, including cavity etch using MMSE-Scatterometry. We also demonstrate an alternate technique, x-ray fluorescence for determining cavity etch on the same structures.
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