Low-level currents in ion-implanted MOSFET

Low-level currents in ion-implanted MOSFET are of special importance in the design of low-voltage MOSFET circuits. In this paper, low-level currents in MOSFET with single and double layer implanted impurities are discussed. A single boron layer in n-channel MOSFET causes positive threshold shift and less steep log nSF(surface electron density)-VG(gate voltage) curves compared with unimplanted MOSFET. Single phosphorus implantation gives rise to negative-threshold shift, but residual current occurs. By compensating for the distribution tail of the main impurity by the opposite type impurity, the log nSF-VGcurves shift in an almost parallel manner. Double-layer implantation, which consists of a phosphorus layer just below the surface of silicon and an equal dose of boron layer inside the silicon substrate, causes less steep log nSF-VGcurves with negligible threshold shift.