Electron cyclotron resonance plasmas have been used to produce the most effective, shortest time plasma hydrogenation of thin-film polycrystalline silicon transistors yet reported. We demonstrate that significant improvement in device characteristics can be achieved with these plasmas using exposure times of the order of only 1 min and that 5 min exposures give saturated characteristics of a 2 V threshold voltage, a 65 cm2/V s mobility, and a 107 on/off ratio. We also explore the pressure and power level dependence of this passivation, as well as the effects of shielding with a grid, and show that the more efficient and more stable electron cyclotron resonance hydrogen exposures are at lower pressures.

Reactive ion etching and magnetically enhanced reactive ion etching with CHF3/O2 are employed to remove SiO2 from boron-doped Si substrates. Etch-induced gap states in the substrate are monitored using deep-level transient spectroscopy. The dominant state is found to be a donor with a hole binding energy of 0.36 eV. The state has been identified as that of the carbon-interstitial oxygen-interstitial pair. The depth profile of the pair is determined by two competing mechanisms: the pair generation and its electrical deactivation by atomic hydrogen. The latter process is especially prevalent in the presence of a magnetic field.

In this study we explore the silicon substrate damage produced by CI 2-and HBr-based reactive ion polycrystalline silicon overetches used in the definition of polycrystalline Si / SiO, [ single-crystal Si structures. The damage-caused traps, examined by means of deep-level transient spectroscopy, in the p-type Si are found to have concentrations that can exceed one tenth that of the boron dopant, and are detectable as far as -10 pm from the SiO, / Si interface. The concentration and depth of these traps are shown to depend on the polycrystalline Si overetch selectivity, initial oxide thickness, and on the magnetic field strength as well as the presence of hydrogen.

We compute string scattering amplitudes in an orbifold of Minkowski space by a boost, and show how certain divergences in the four point function are associated with graviton exchange near the singularity. These divergences reflect large tree-level backreaction of the gravitational field. Near the singularity, all excitations behave like massless fields on a 1+1 dimensional cylinder. For excitations that are chiral near the singularity, we show that divergences are avoided and that the backreaction is milder. We discuss the implications of this for some cosmological spacetimes. Finally, in order to gain some intuition about what happens when backreaction is taken into account, we study an open string rolling tachyon background as a toy model that shares some features with R 1,1 /Z.

Hydrogen plasmas generated by electron cyclotron resonance currently provide the most efficient plasma exposure technique available for passivating the grain boundaries of polycrystalline silicon. In this report, we show that careful optimization may be required when using this passivation approach on polycrystalline silicon gated, polycrystalline silicon thin film transistors fabricated using low temperature oxides. Optimization is found to be necessary for thin film transistors (TFTs) with polycrystalline Si gates in order to prevent the onset of high leakage currents which can develop when exposures are too long. The effects of exposure time, substrate temperature, microwave power level, pressure, and plasma dilution with an inert gas are examined to determine the conditions for optimal improvement in electrical performance. A model is also presented to explain this need for optimization of the electron cyclotron resonance hydrogen plasma passivation of poly-Si TFTs.