With a sub-nanometric resolution required for nodes below 14 nm, according to the International Roadmap for Devices and Systems (IRDS), exploring new overlay characterization methods is key to drive further component size reduction and develop better-performing technologies. In this work, we present our first Small-Angle X-ray Scattering (SAXS) results of overlay measurements on stacks of silicon line gratings. Our method, novel for SAXS overlay measurements, is based on inverse problem resolution and reconstructs the in-depth profile (approximated as a stack of trapezoids) of the structure. We are thus able to extract overlay with SAXS with a very fine sensitivity, high precision and sub-nanometric resolution that suit the requirements for advanced technological nodes. We compared these results with those of Scanning Electron Microscopy (SEM) contour-based on product overlay. The reconstructed structures are compared to profiles obtained with Scanning Transmission Electron Microscopy (STEM). From the differences between these multi-scale techniques we can conclude on the high potential of SAXS to become a complementary to those existing, and assess its potential for advanced technology nodes.