MODEL AND SIMULATION OF SCANNING TUNNELING MICROSCOPE TIP SEMICONDUCTOR INTERACTIONS IN PN JUNCTION DELINEATION

Scanning tunneling microscopy (STM) is an electrically sensitive technique with atomic resolution, making it a viable candidate for use in shallow junction delineation. It has been demonstrated that STM can be used to distinguish between n- and p-type semiconductors, yet the effects of STM tip and sample biases on the electronic structure of the silicon and, hence, on the tunneling current have not been extensively explored. A tunnel diode model has been proposed coupled with classical band bending to simulate these effects. The scanning of the tip across the junction was simulated using structure defining algorithms in PISCES, a two dimensional device simulator. The tip electrode was moved incrementally across the silicon surface at a set height. PISCES was called at each new tip location to produce a new structure file. The Poisson equation was solved by PISCES at each tip location to determine band bending. Silicon surface potentials were extracted from the simulation and incorporated into the tunneling current calculations. Tunneling currents in the model depend on the density of empty states in the electron-receiving material, on the density of filled states in the electron-supplying material, and on the tunneling probability across the tip-to-semiconductor gap. The tunneling currents were then compared to experimental results.