Electron holographic characterization of electrostatic potential distributions in a transistor sample fabricated by focused ion beam

A cross-sectional sample of a silicon-metal-oxide semiconductor field-effect transistor, which was directly cut from an integrated circuit wafer, has been prepared carefully using a focused-ion-beam technique and examined by means of off-axis electron holography. In the reconstructed phase image, heavily doped source, and drain regions are revealed clearly as bright contrast, from which an n-channel transistor is identified. In addition, two-dimensional phase distributions around both source and drain regions show a core area with relatively high phase in the heavily doped region, which may be attributed to the effect of doping atoms and residual defects and strains remaining after implantation. The electrostatic potentials across the core area and depletion layer are estimated and discussed. This work demonstrates the feasibility of using a focused-ion-beam technique to prepare electron holographic sections of a wide range of semiconductor devices.