Two Dimensional Dopant Profiling by Scanning Tunneling Microscopy

Recent progress in two-dimensional doping profile measurements on silicon with scanning tunneling microscopy and spectroscopy (STM/STS) is presented. STM spectroscopy modes described are constant-current imaging, onset voltage profiling, vacuum-gap modulation spectroscopy and resonant-electron-tunneling spectroscopy with a marker molecule. These modes employ dependence of tunneling current on dopant type and concentration through the band bending induced by the metal STM tip at the surface. The combination of multiple spectroscopy modes and complimentary simulations makes the STM/STS as a powerful instrument for Si device characterization with the ability to observe the surface potential and location of individual dopant atoms on flat and electrically inert Si surfaces. Actual measurements are demonstrated for both the oxidized surfaces and the hydrogen-terminated Si(111) surface. Carrier concentration maps of small Si devices are shown. The mechanism of the measurements is discussed.