Spectroscopic imaging of buried layers in 2+1D via tabletop ptychography with high-harmonic EUV illumination

We use EUV coherent microscopy to obtain high-resolution images of buried interfaces, with chemical specificity, in 2+1 dimensions. We perform reflection mode, ptychographic, coherent diffractive imaging with tabletop EUV light, at 29nm, produced by high harmonic generation. Our damascene-style samples consist of copper structures inlaid in SiO2, polished nearly flat with chemical mechanical polishing. We obtain images of both an unaltered damascene as well as one buried below a 100nm thick layer of evaporated aluminum. The aluminum is opaque to visible light and thick enough that neither optical microscopy, SEM, nor AFM can access the buried interface. EUV microscopy is able to image the buried structures, non-destructively, in conditions where other techniques cannot.