A deep UV Fourier ptychographic microscope for microstructural characterization

Characterization of surface topography is a crucial step in device manufacturing and material design that requires high resolution, 3D maps of large areas. Optics are limited to either optimizing for field-of-view (FOV) or resolution. Fourier ptychography (FP) surpasses this limit by combining the k-spaces of multiple, low resolution measurements at different illumination angles to produce a higher resolution image. By solving for the amplitude and phase of the object, FP also reconstructs topography. Moreover, shorter imaging wavelengths are capable of resolving finer features. We present a novel deep UV Fourier ptychographic microscope design for microstructural characterization. A large space bandwidth product (SBP) is achieved by using dual-axis galvanometer (galvo) mirrors to steer the illuminating beam to implement Fourier ptychography and translation stages to image a large area. Use of Fourier ptychography improved system resolution from 0.25 μm to 0.20 μm and accurately reconstructed the surface topography of a test indentation. Scanning a copper sample over 225 positions effectively increased the FOV 75× from 2.6 × 10−2mm2 to 1.9mm2. The DUV FP microscope’s innovative design is advantageous to material and device manufacturing by enabling high resolution topographic imaging over large areas and thus facilitating accurate, large scale characterization of sample surfaces.