Hiroshi Kuwano

Solid-phase crystallization behaviors of in situ phosphorous-doped amorphous silicon films deposited using Si2H6 and PH3

The solid-phase crystallization of in situ phosphorous-doped amorphous silicon films deposited by low-pressure chemical vapor deposition using disilane is studied for various P concentrations and annealing temperatures. The nucleation rate is found to follow a power law with respect to the annealing time. The power index is 1.3 for P concentrations up to about 5×1019 cm−3 and decreases slightly at higher P-doping levels. The grain growth rate is enhanced as the P concentration increases, particularly above 1×1019 cm−3. The activation energy of the grain growth rate is 2.6 eV regardless of the P concentration. The final grain size in the crystallized films increases markedly for a P concentration over 1×1019 cm−3, but is almost independent of the annealing temperature. The crystallization behavior and final grain size can be represented by equations extended from those of Avrami–Johnson–Mehl using the time-dependent nucleation rate.

Properties of platinum‐associated deep levels in silicon

The diffusion of platinum into n‐ and p‐type silicon has been carried out at temperatures ranging from 850 to 1000 °C and for times ranging from 1 to 50 h. Three deep levels associated with platinum were detected by the deep‐level transient spectroscopy technique: two acceptor levels of Ec−0.23 and Ec−0.52 eV and a donor level of Ev+0.36 eV. The Ec−0.23 and Ev+0.36 eV levels are produced by platinum occupying the substitutional sites of silicon lattice. The Ec−0.52 eV level has not been characterized but is probably associated with some interstitial platinum‐oxygen or other defect complex. Diffusion profiles of the substitutional platinum show that platinum diffuses into silicon mainly via the so‐called kick‐out mechanism.

Energy distribution of trapping states at grain boundaries in polycrystalline silicon

A method to obtain the energy distribution of traps at grain boundaries in polycrystalline silicon films from the activation energy of resistivity measured as a function of doping concentration is proposed. The energy distribution of trapping states in the energy gap for plasma‐hydrogenated and nonhydrogenated polycrystalline silicon films doped with boron are determined: nonhydrogenated films have a Gaussian distribution with a peak at the midgap, and after plasma hydrogenation the peak at the midgap has diminished. The validity of the monoenergetic trap model applied to the conduction in nonhydrogenated and plasma‐hydrogenated polycrystalline silicon films is discussed.

Conduction mechanism of high‐resistivity polycrystalline silicon films

The electrical properties of polycrystalline silicon films deposited by low‐pressure chemical vapor deposition and doped by boron, phosphorus, or arsenic with ion implantation, are investigated, and it is found that the resistivity versus donor concentration curve has a peak point for the completely depleted samples. An improved conduction model for the high‐resistivity polycrystalline silicon films is proposed. The theoretical results are in reasonable agreement with experiment. It is shown that the trap level located at the grain boundary exists at 0.51 eV above the valence‐band edge and that the hole current dominates the whole current through the films for all of the lightly doped samples, even for the donor‐doped samples.

Determination of the Energy Distribution of Grain Boundary Traps in Polycrystalline Silicon Films

The energy distribution of grain boundary traps in polycrystalline silicon films is determined from the activation energy of resistivity measured as a function of boron and phosphorus doping concentrations. The energy distribution is expressed as the Gaussian distribution with its center located at 0.10 eV under the midgap and the standard deviation of 0.18 eV.

Injected carrier lifetimes and double‐injection currents in semiconductors with a single impurity level

Theoretical analyses of the lifetimes of injected electrons and holes, and the double‐injection currents in long p‐i‐n diodes with a single impurity level, are treated by evaluating the space‐charge density formed by the injection of the minority carrier lifetimes and the current‐voltage characteristics are obtained in a low‐ and a high‐injection regime, and approximately in an intermediate‐injection regime, when the physical parameters of the i region and the dependence of the equilibrium majority‐carrier density upon temperature have been measured beforehand.

Annealing effect on the resistivity of polycrystalline silicon films passivated with plasma‐deposited silicon‐nitride films

The thermal annealing effect on resistivity is investigated for polycrystalline silicon films passivated with plasma‐enhanced chemically vapor deposited silicon‐nitride (p‐SiN) films. The resistivity in the heavily doped polycrystalline silicon films has a minimum value at an annealing temperature of approximately 500 °C, and the resistivity in the lightly doped films monotonically increases with the increase of annealing temperature. The dependence of the resistivity on annealing temperature is explained in terms of the variations of the density and the energy level of the traps at the grain boundaries, which are caused by the adsorption or the decomposition of hydrogen atoms. These conclusions are obtained by comparing the dependence in the polycrystalline silicon films with  p‐SiN films with that in the plasma‐hydrogenated polycrystalline silicon films without  p‐SiN films.

Recystallization characteristics of polycrystalline silicon films amorphized by germanium ion implantation

Abstract The recrystallization characteristics of polycrystalline silicon (poly-Si) films amorphized by germanium ion (Ge + ) implantation on a SiO 2 layer are studied by TEM analysis, and the possibility of enlarging the final grain size is investigated. Also, the characteristics of Ge + implanted films with phosphorus doping are reported and discussed. The nucleation and growth rates of undoped Ge + implanted films are lower and higher, respectively, than those of silicon ion (Si + ) implanted films, so that the former films achieve grain sizes about 2–3 times larger than the latter films, depending on annealing temperature. Phosphorus doping in Ge + implanted films effectively enhances the grain size, because of the retardation of random nucleation and the enhancement of grain growth. An average grain size of 12 μm is obtained in doped Ge + implanted films with a phosphorus concentration of 1 × 10 20 ions/cm 3 after annealing at 650°C for 5 h, which is about four times larger than that in undoped Ge + implanted films.

Control of Resistivity of Polycrystalline Si Films by Solid-Phase Recrystallization (SPR)

The effect of the grain size after solid-phase recrystallization (SPR) on the resistivity of polycrystalline Si (poly-Si) films was investigated in detail. SPR poly-si films were obtained by amorphization by Si ion implantation and by subsequent recrystallization by low-temperature furnace annealing. Resistivity could be precisely controlled by choosing the doping concentration and by full amorphization and recrystallization at a fixed temperature. This was due to the controlled increase in grain size and the decrease in trapping state density per unit volume. An advanced model on the resistivity was proposed in which the resistivity dependence on the dopant concentration was well explained. It was indicated that the grain boundary of SPR poly-Si films exhibits the same electrical characteristics as that of as-deposited films.

Platinum as Recombination-Generation Centers in Silicon

The general equations of steady-state lifetime in semiconductors with multiple deep impurity levels are derived based on the recombination theory. From the obtained equations the six capture cross sections of three Pt-induced levels in silicon are experimentally determined. The behaviors of minority carrier lifetime and leakage current in Pt-diffused devices are also discussed. It is found that the minority carrier lifetime is influenced by the three Pt-related levels and that the major contribution to the leakage current arises from the level of E c-0.52 eV.