Non‐Destructive X‐Ray Imaging of Patterned Delta‐Layer Devices in Silicon

The progress of miniaturization in integrated electronics has led to atomic and nanometer‐sized dopant devices in silicon. Such structures can be fabricated routinely by hydrogen resist lithography, using various dopants such as P and As. However, the ability to non‐destructively obtain atomic‐species‐specific images of the final structure, which would be an indispensable tool for building more complex nano‐scale devices, such as quantum co‐processors, remains an unresolved challenge. Here, X‐ray fluorescence is exploited to create an element‐specific image of As dopants in Si, with dopant densities in absolute units and a resolution limited by the beam focal size (here ≈1 µm), without affecting the device's low temperature electronic properties. The As densities provided by the X‐ray data are compared to those derived from Hall effect measurements as well as the standard non‐repeatable, scanning tunneling microscopy and secondary ion mass spectroscopy, techniques. Before and after the X‐ray experiments, we also measured the magneto‐conductance, which is dominated by weak localization, a quantum interference effect extremely sensitive to sample dimensions and disorder. Notwithstanding the 1.5 × 1010 Sv (1.5 × 1016 Rad cm−2) exposure of the device to X‐rays, all transport data are unchanged to within experimental errors, corresponding to upper bounds of 0.2 Angstroms for the radiation‐induced motion of the typical As atom and 3% for the loss of activated, carrier‐contributing dopants. With next generation synchrotron radiation sources and more advanced optics, the authors foresee that it will be possible to obtain X‐ray images of single dopant atoms within resolved radii of 5 nm.