Atsushi Kenjo

Low-temperature formation (<500°C) of poly-Ge thin-film transistor with NiGe Schottky source/drain

Poly-Ge thin-film transistors (TFTs) with Schottky source/drain (S/D) contacts were fabricated on glass by low-temperature (<500°C) processing. First, the annealing characteristics of Ni/crystal-Ge stacked structures were examined. The results indicated that NiGe∕n-Ge Schottky contacts (ϕBn=0.51eV, n=1) with flat interfaces and low reverse leakage current [(2–5)×10−2A∕cm2] could be obtained by choosing an appropriate annealing temperature (200–300°C). Based on this result, p-channel TFTs were fabricated with poly-Ge formed on glass by solid-phase crystallization at 500°C. TFTs showed relatively high hole mobility (about 140cm2∕Vs) with very low S/D parasitic resistance and no kink effect. The potential capability of the proposed devices for high-performance TFTs was demonstrated.

Ni-imprint induced solid-phase crystallization in Si1−xGex (x: 0–1) on insulator

Position control of solid-phase crystallization in the amorphous Si1−xGex (x: 0–1) films on insulating substrates was investigated by using Ni-imprint technique. Crystal nucleation at the imprinted positions proceeded approximately 2–20 times, depending on Ge fraction, faster than the conventional solid-phase crystallization, which was due to the catalytic effect of Ni. As a result, large SiGe crystal regions (∼2μm) were obtained at controlled positions. On the other hand, the growth velocity did not changed, which suggested that grown regions contained few residual Ni atoms.

Atomically controlled molecular beam epitaxy of ferromagnetic silicide Fe3Si on Ge

Low-temperature (60°C) molecular beam epitaxy (MBE) of Fe3Si layers on Ge substrates was investigated. From x-ray diffraction and transmission electron microscopy measurements, it was shown that Fe3Si layers including the DO3 type were epitaxially grown on Ge(110) and Ge(111), while polycrystal Fe3Si was formed on Ge(100). Although the Fe3Si∕Ge(110) interface was slightly rough (∼1nm), the Fe3Si∕Ge(111) interface was atomically flat. Such atomically controlled MBE of Fe3Si on the Ge(111) substrate can be employed to realize Ge channel spin transistors, which can be integrated with Si large-scale integrated circuits.

Ge-fraction-dependent metal-induced lateral crystallization of amorphous-Si1−xGex (0≦x≦1) on SiO2

Metal-induced low-temperature (≦550 °C) crystallization of amorphous-Si1−xGex (0≦x≦1) on SiO2 has been investigated. In the case of low Ge fraction (0≦x≦0.2), Ge-doping enhanced plane growth was observed. This achieved strain-free poly-Si0.8Ge0.2 with large grains (18 μm). On the other hand, dendrite growth became dominant in the case of intermediate Ge fractions (0.4≦x≦0.6). By optimizing the growth conditions (x: 0.4, annealing: 450 °C, 20 h), very sharp needle-like crystal regions (width: 0.05 μm, length: 10 μm) were obtained. These polycrystalline SiGe films on SiO2 should be used for the system-in-display, three-dimensional ultralarge scale integrated circuits, and novel one-dimensional wires.

DEEP LEVEL OF IRON-HYDROGEN COMPLEX IN SILICON

Deep levels related to iron in n-type silicon have been investigated using thermally stimulated capacitance (TSCAP) combined with minority carrier injection. The TSCAP measurement reveals two traps of EV+0.31 and EV+0.41 eV. The trap of EV+0.41 eV is a donor due to interstitial iron. The trap of EV+0.31 eV, due to a complex of interstitial iron and hydrogen, is observed in the sample etched chemically with an acid mixture containing HF and HNO3 and annihilates after annealing at 175 °C for 30 min. It is demonstrated that interstitial 3d transition metals such as vanadium, chromium, and iron tend to form complexes with hydrogen in n-type silicon, and the complexes induce donor levels below the donor levels of the isolated interstitial species. This trend is related to the interaction between the metals and hydrogen in the complexes.

Ion-beam stimulated solid-phase crystallization of amorphous si on SiO2

Abstract Influences of ion-beam irradiation on solid-phase-crystallization of a-Si on SiO 2 were studied in the temperature range between 200 and 700°C. Significant enhancement of crystal nucleation was observed under ion irradiation (25 keV, 1×10 16 Ar + cm −2 ). As a result, nucleation at a temperature lower than that of the softening of soda-lime glass (450°C) becomes possible. In addition, nuclei growth along the [111] and [110] directions was detected using X-ray diffraction methods. These are a big advantage for the fabrication of high-quality and low-cost thin-film transistors on glass substrates.

Epitaxial Growth of Ferromagnetic Silicide Fe3Si on Si(111) Substrate

Epitaxial growth of the ferromagnetic silicide Fe3Si on Si substrates was investigated using molecular beam epitaxy. X-ray diffraction (XRD) measurements revealed that the Fe3Si phase was formed at 60–300 °C, and the FeSi phase was formed at 400 °C. From the results of XRD and transmission electron microscopy measurements, it was found that the Fe3Si(111) layers were epitaxially grown on Si(111) substrates, while random poly-crystal Fe3Si layers were formed on Si(100) substrates. Detailed XRD measurements showed that a small amount of DO3-type Fe3Si was formed together with the B2-type Fe3Si. Vibrating sample magnetometer measurements revealed that Fe3Si(111) layers on Si(111) substrates have in-plane magnetic anisotropy with a period of 180°.

Modified metal-induced lateral crystallization using amorphous Ge∕Si layered structure

Modified metal-induced lateral crystallization (MILC) using a‐Ge∕a‐Si∕Ni∕SiO2 layered structures has been investigated. MILC growth velocity in the a‐Ge∕a‐Si layered structures was enhanced by three times compared with that in the a‐Si single layers. As a result, poly-Si films with large areas (∼10μm) were obtained in a short time annealing (<5h) at 550°C. It is speculated that crystal nucleation in the a‐Ge layers stimulated the bond rearrangement in the a‐Si layers, which enhanced the MILC velocity. This will be a powerful tool for realizing large poly-Si areas on insulating films for future system-in-displays.

Metal-Induced Solid-Phase Crystallization of Amorphous SiGe Films on Insulator

The metal-induced low-temperature (≤550°C) crystallization of a-Si1-xGex (0 ≤x ≤1) on SiO2 has been investigated. A Ge-fraction-dependent crystal growth was observed. In the case of a low-Ge fraction, plane growth dominated, the velocity of which was enhanced by 80% with increasing Ge fraction from 0 to 20%. This produced strain-free poly-SiGe with large grains (18 µm). On the other hand, dendrite growth became dominant in the case of intermediate Ge fractions (40–60%). By optimizing the growth conditions (x: 0.4, annealing: 450°C, 20 h), very sharp needlelike crystals (width: 0.05 µm, length: 10 µm) were obtained. These new polycrystalline SiGe films on insulator should be used for system-in-display, three-dimensional ultra large-scall integrated circuits, and novel one-dimensional wires.

Ge-Channel Thin-Film Transistor with Schottky Source/Drain Fabricated by Low-Temperature Processing

The fabrication of Ge-channel thin-film transistors (TFTs) with Schottky source/drain (S/D) contacts was investigated. First, the annealing characteristics of Ni/c-Ge stacked structures were examined. NiGe/n-Ge Schottky contacts (Bn=0.51 eV, n=1) with a low reverse leakage current [(2–5)×10-2 A/cm2] were obtained at 200–300 °C. Second, the electrical characteristics of Al/SiO2/c-Ge metal–oxide–semiconductor (MOS) structures were investigated, in which SiO2 films were formed by plasma-enhanced chemical vapor deposition at 250 °C. The MOS structures were proven acceptable for device operation. On the basis of the obtained results, TFTs with NiGe Schottky S/D contacts were fabricated using poly-Ge/quartz substrates. The maximum processing temperature was 500 °C in the solid-phase crystallization of a-Ge films. The TFTs showed good p-channel operation characteristics with a mobility of ~100 cm2 V-1 s-1 without showing kink effects. This is a great advantage for the realization of high-performance TFTs for system-in-displays.