Kohei Sakaike

Direct observation of grain growth from molten silicon formed by micro-thermal-plasma-jet irradiation

Phase transformation of amorphous-silicon during millisecond annealing using micro-thermal-plasma-jet irradiation was directly observed using a high-speed camera with microsecond time resolution. An oval-shaped molten-silicon region adjacent to the solid phase crystallization region was clearly observed, followed by lateral large grain growth perpendicular to a liquid-solid interface. Furthermore, leading wave crystallization (LWC), which showed intermittent explosive crystallization, was discovered in front of the moving molten region. The growth mechanism of LWC has been investigated on the basis of numerical simulation implementing explosive movement of a thin liquid layer driven by released latent heat diffusion in a lateral direction.

Layer Transfer and Simultaneous Crystallization Technique for Amorphous Si Films with Midair Structure Induced by Near-Infrared Semiconductor Diode Laser Irradiation and Its Application to Thin-Film Transistor Fabrication

A novel layer transfer and simultaneous crystallization of amorphous silicon (a-Si) films induced by near-infrared semiconductor-diode-laser (SDL) irradiation has been investigated. The a-Si films supported by narrow quartz columns on a starting quartz substrate and a counter substrate [glass and poly(ethylene terephthalate)] were in face-to-face contact, and an SDL irradiated the a-Si films with midair structure. After SDL irradiation, the Si films were completely transferred and crystallized simultaneously on the counter substrates. In-situ monitoring revealed that the layer transfer took place either in the solid phase or the liquid phase followed by phase transformation in the cooling period. High performance polycrystalline Si thin-film transistors were successfully fabricated on the transferred Si films, which showed a high on/off ratio of more than 105 and a field-effect mobility as high as 268 cm2 V-1 s-1.

Fabricating metal-oxide-semiconductor field-effect transistors on a polyethylene terephthalate substrate by applying low-temperature layer transfer of a single-crystalline silicon layer by meniscus force

A low-temperature local-layer technique for transferring a single-crystalline silicon (c-Si) film by using a meniscus force was proposed, and an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET) was fabricated on polyethylene terephthalate (PET) substrate. It was demonstrated that it is possible to transfer and form c-Si films in the required shape at the required position on PET substrates at extremely low temperatures by utilizing a meniscus force. The proposed technique for layer transfer was applied for fabricating high-performance c-Si MOSFETs on a PET substrate. The fabricated MOSFET showed a high on/off ratio of more than 108 and a high field-effect mobility of 609 cm2 V−1 s−1.

Melting and solidification of microcrystalline si films induced by semiconductor diode laser irradiation

Rapid thermal annealing of microcrystalline Si (µc-Si) films induced by cw semiconductor diode laser (SDL) irradiation has been investigated. Owing to the higher absorption coefficient of µc-Si than that of amorphous Si (a-Si), 1.2-µm-thick µc-Si films are melted and recrystallized within 3 ms, whereas no phase transformation of a-Si films is observed under the same annealing condition. The annealed Si films show a high crystalline volume fraction of 97% and [111] preferential orientation. Characteristic triangle surface structures aligned to the laser scanning direction, which suggests that the lateral solidification from molten Si is observed.

Low-temperature layer transfer of midair cavity silicon films to a poly(ethylene terephthalate) substrate by meniscus force

A single-crystalline-silicon (c-Si) layer (supported by columns on a starting Si-on-insulator wafer) and a counter-poly(ethylene terephthalate) (PET) substrate were placed in close face-to-face contact, and pure water was sandwiched in between the c-Si layer and the PET substrate. The samples formed in this manner were heated on a hot plate at 80 °C. By the meniscus force generated during the evaporation of the sandwiched water from the samples, the c-Si films were completely transferred to the PET substrate. A (100)-oriented c-Si thin film that shows good adhesion was successfully formed on PET substrates at low process temperatures.

Leading Wave Crystallization Induced by Micro-Thermal-Plasma-Jet Irradiation of Amorphous Silicon Films

The crystalline grain growth of silicon induced by micro-thermal-plasma-jet irradiation has been directly observed using a high-speed camera. An oval-shaped molten region (MR) was formed after the solid phase crystallization (SPC), and it was clearly observed that laterally large grains grew perpendicular to the liquid–solid interface. Leading wave crystallization (LWC), which showed intermittent grain growth with a liquid–solid interface velocity as high as 4500 mm/s, was discovered in between the MR and SPC region. From numerical calculation, it has been clarified that the explosive lateral growth of LWC is triggered by the formation of a thin liquid layer and the explosive propagation of the layer is driven by released latent heat.

Fabrication of N-channel single crystalline silicon (100) thin-film transistors on glass substrate by meniscus force-mediated layer transfer technique

We propose a novel low-temperature layer transfer of single crystalline silicon (100) to glass substrate using meniscus force and midair cavity structure. Local transfer of thermally-oxidized silicon-on-insulator (SOI) layer to glass was successfully carried out at 80 °C. N-channel thin-film transistor (TFT) fabricated on glass at 300 °C showed a field-effect mobility of 1097 cm2 V−1 s−1, a threshold voltage of 1.1 V and a subthreshold swing value of 78 mV/dec. Raman scattering analysis suggests such a high mobility of TFT is originated from tensile strain introduced after gate SiO2 film deposition.

Formation of silicon-on-insulator layer with midair cavity for meniscus force-mediated layer transfer and high-performance transistor fabrication on glass

We attempted to transfer a phosphorus ion (P+)-implanted oxidized silicon-on-insulator (SOI) layer with a midair cavity to a glass substrate using meniscus force at a low temperature. The SiO2 column size was controlled by etching time and the minimum column size was 104 nm. The transfer yield of the implanted sample was significantly improved by decreasing the column size, and the maximum transfer yield was 95% when the implantation dose was 1 × 1015 cm−2. The causes of increasing transfer yield are considered to be the tapered SiO2 column shape and the hydrophilicity of the surface of oxidized samples with implantation. N-channel thin-film transistors (TFTs) fabricated using the films on glass at 300 °C showed a field-effect mobility of 505 cm2 V−1 s−1, a threshold voltage of 2.47 V and a subthreshold swing of 324 mV/dec. on average.

A technique for local area transfer and simultaneous crystallization of amorphous silicon layer with midair cavity by irradiation with near-infrared semiconductor diode laser

A technique for local layer transfer and simultaneous crystallization of amorphous silicon (a-Si) films with midair cavity induced by near-infrared semiconductor diode laser (SDL) irradiation is demonstrated. After SDL irradiation, the silicon (Si) films were completely transferred and crystallized simultaneously on counter substrates. Electron backscatter diffraction pattern maps confirmed that the maximum grain size of the transferred Si films is 20 µm. High-performance polycrystalline Si thin-film transistors (TFTs) were successfully fabricated on the locally transferred Si films. These TFTs showed a high on/off ratio of more than 106 and a field-effect mobility as high as 492 cm2 V−1 s−1.

Fabrication of High Performance Single-Crystalline Silicon Thin Film Transistors on a Polyethylene Terephthalate Substrate

A single-crystalline-silicon (c-Si) layer (supported by columns on a starting Si-on-insulator wafer) and a counter polyethylene terephthalate (PET) substrate were placed in close face-to-face contact, and pure water was sandwiched in between the c-Si layer and the PET substrate. The samples formed in this manner were heated on a hot plate at 80°C, and the SOI layer is transferred to PET by the meniscus forces. By applying the proposed transferred technique, high performance c-Si thin-film transistors (TFT) were successfully fabricated on the PET substrate, which showed a field-effect mobility as high as 552 cm 2 V -1 s -1 .