As development of stacked Nanosheet Gate All-Around (GAA) transistor continues as the candidate technology for future nodes, several key process points remain difficult to characterize effectively. With the GAA device strategy, it is critical to have an inline solution that can provide a readout of physical dimensions that have an impact on the threshold voltage (VT) and yield. Metrology challenges for obtaining these metrics arise from increasingly dense arrays coupled with both high aspect ratios, high numbers of correlated parameters, and increasingly complex 3D geometries. Large area metrology structures can be used for 3D parameters’ process monitoring through techniques such as scatterometry and xray diffraction (XRD) which deliver averaged results over that area, but variation impacting specific devices cannot currently be understood without destructive cross-section. Prior work to characterize the dimensions of these GAA devices has primarily featured optical metrology, X-ray metrology, and critical-dimension scanning electron microscopy (CDSEM), but these techniques have their own challenges at the critical process points. Atomic force microscopy (AFM) had not been utilized due to the aspect ratios and small trench widths which were inaccessible to conventional techniques. However, due to recent advances in scanning and novel probe technologies, AFM is well-suited now to solve these local, three-dimensional challenges. Through this study, we demonstrate AFM characterization of a key process point in the GAA process flow for multiple structures with varying channel lengths, after epitaxial (epi) growth along the Si sidewall. The AFM scan results are compared to CDSEM images for top-down corroboration of topography and to other reference metrology for height correlation. The impact of measured variations in epi height to device performance is also reviewed.
EUV resist characterizations for line and space patterning as a function of dose and illumination conditions for varying pitches down to 28 nm are discussed. The unintentional resist line top loss (LTL) after development has been monitored and analyzed for all experimental conditions. Furthermore, line top roughness (LTR) is introduced, which is a 3 stochastic metric characterizing in-plane roughness related to the top of the resist lines. The main characterization technique employed for this study is atomic force microscopy (AFM) with novel probing algorithms as well as novel tips with diameters down to 5 nm and aspect ratios of 10:1. Additionally, results acquired by critical dimension scanning electron microscopy and optical critical dimension scatterometry are presented. It was found that the unintentional LTL is resist- and pitch-dependent and can be higher than 9 nm at 16 nm half-pitch but does not correlate with line break defect density results. However, LTR measurements of small area scans at dense line/space pitches may be used to draw conclusions about line break defect densities and hence yield. The resist specific metrics, LTR and LTL, allow for fast and early-on evaluation of new chemical formulations and help to forecast pitch- and dose-dependent performance. Furthermore, the results can be used to improve resist model accuracy for optical proximity correction calculations.