Metasurface-enabled optical alignment with nanometer accuracy

We report a holographic alignment system for the precise alignment of 3D semiconductor devices and compound flat optics. The system uses cascaded metasurfaces to project two holographic patterns, and by interfering the patterns in the far field, small misalignments can be measured without the need for a high-resolution microscope. Operating at 850nm, the technique achieves lateral and axial accuracies of 1 nm and 1 µm, respectively, surpassing the lateral diffraction-limit accuracies of microscopic imaging methods by two orders of magnitude. The technique has potential applications in high-precision alignment detection and registration of multilayer patterns and separate samples and wafers.