Nobuyuki Andoh

Rapid crystallization of silicon films using electrical-current-induced joule heating

Melt-regrowth properties of 60-nm-thick silicon films were characterized in the case of electrical-current-induced joule heating. The electrical energy accumulated at a capacitance caused melting of the silicon films via joule heating with a maximum intensity at 1.5×106 W/cm2. The melt-regrowth duration increased from 6 to 75 μs as the capacitance increased to 0.05–1.5 μF. Crystalline properties of the silicon films were also investigated. 7 μm long crystalline grains with the (110) preferential crystalline orientation were observed using a transmission electron microscope. The tensile stress at 3.4×108 Pa remained in the films. The analysis of electrical conductivity resulted in a density of defect states of 3.5×1016 cm−3 in the films. The product of the generation efficiency, the carrier mobility and the average carrier lifetime was estimated to be ∼10−3 cm2/V.

Heating Layer of Diamond-Like Carbon Films Used for Crystallization of Silicon Films

Rapid thermal crystallization of silicon films with a heating layer of diamond-like carbon (DLC) films is reported. DLC films 200 nm thick have an optical absorbance higher that 0.7 for wavelengths shorter than 1000 nm. They are also heat resistant to about 5000 K. A crystalline volume ratio of 0.85 is achieved for silicon films through heat diffusion from DLC heated by 30-ns-pulsed XeCl excimer laser irradiation at 200 mJ/cm2 for 100 nm DLC/5 nm SiO2/25 nm Si/quartz, while it is only 0.4 for 25 nm Si/quartz because of high reflection loss. Crystallization of silicon films is also achieved by 1064 nm YAG laser heating of the 200 nm DLC layer overlying the silicon films.

Activation behavior of boron and phosphorus atoms implanted in polycrystalline silicon films by heat treatment at 250°C

The activation behavior of boron and phosphorus implanted into laser-crystallized silicon films were investigated. The ratio of recrystallization of an ion-doping-induced amorphous region by heat treatment at 250°C was 0.35 for a boron concentration lower than 6.4×1019 cm-3 and 0.5 for a phosphorus concentration lower than 2.5×1019 cm-3. This ratio decreased as dopant concentration increased. High electrical conductivities of 1.1×102 S/cm and 7.3 S/cm were achieved by oxygen plasma treatment at 250°C for 1 h in the cases of 3.2×1020-cm-3 boron and 5.0×1019-cm-3-phosphorus doping, respectively. Numerical analysis of the electrical conductivity revealed that the electrical conductivity was governed by recrystallization ratio and the density of the intrinsic defects of polycrystalline films.

Characterization and control of defect states of polycrystalline silicon thin film transistor fabricated by laser crystallization

Abstract Improvement of characteristics of polycrystalline silicon thin film transistors (poly-Si TFTs) was achieved by defect reduction methods of oxygen plasma at 250 ° C and at 30 W and 1.25×106-Pa high-pressure H2O vapor heat treatments at 270 ° C . Numerical analysis of transfer characteristics revealed that the combination of oxygen plasma for 40 min with the high-pressure H2O vapor annealing for 3 h effectively reduced the densities of deep level states from 1.4×1018 (as crystallized) to 1.6×10 17 cm −3 and the densities of tail states from 9.2×1018 (as crystallized) to 2.7×10 18 cm −3 , respectively. The threshold voltage of transfer characteristics was reduced from 4.1 to 1.3 V through the defect reduction.

Activation of Silicon Implanted with Phosphorus Atoms by Infrared Semiconductor Laser Annealing

We activated silicon implanted with phosphorus atoms by infrared semiconductor laser annealing with a diamond-like carbon (DLC) optical absorption layer. The silicon samples implanted with phosphorus atoms at 10 and 70 keV with concentrations of 5×1014, 1×1015, and 2×1015 cm-2 were coated with 200-nm-thick DLC films. The samples were annealed by irradiation with a 940 nm continuous wave laser at 70 kW/cm2 with a beam diameter of 180 µm. The laser beam was scanned using a moving stage at 3–20 cm/s, which gave an effective dwell time of 0.9–6.0 ms. The amorphized surface regions were recrystallized by laser annealing longer than 1.2 ms. The in-depth profile of phosphorus concentration hardly changed within 5 nm for laser annealing for 2.6 ms. The sheet resistance markedly decreased to 106 and 46 Ω/sq for the samples implanted with phosphorus atoms at 10 and 70 keV by laser annealing at a dwell time of 2.6 ms, respectively. Phosphorus atoms were effectively activated with a carrier density near the phosphorus concentration for implantation at 70 keV. A low carrier generation rate was observed for implantation at 2×1015 cm-2 and 10 keV. An intermediate SiO2 layer effectively blocked carbon incorporation to a level below 1017 cm-3.

Infrared semiconductor laser crystallization of silicon thin films using diamond-like carbon as photoabsorption layer

We report the crystallization of silicon thin films using a continuous wave (CW) infrared semiconductor laser with the assistance of diamond-like carbon (DLC) as a photoabsorption layer. A beam of a 940-nm-wavelength CW semiconductor laser was irradiated to samples of 400-nm-thick DLC/50-nm-thick Si/glass with a laser power density of 7.4–24.7 kW/cm2. The beam was scanned on the samples at a speed of 15–100 cm/s. The DLC layer was heated to a temperature above the melting point of silicon by effective absorption of laser light. Thus, the underlying 50-nm-thick silicon films were crystallized by the heat defused from DLC. It was found that the threshold energy density for the crystallization of silicon films decreased as the laser power density increased. The maximum crystallinity factors estimated from Raman scattering spectral data of silicon films were 1 and 0.78 for laser power densities of 24.7 and 7.8 kW/cm2, respectively. Electron backscattering diffraction pattern (EBSD) measurements revealed that crystalline grains were randomly oriented with an average size of 3 µm.

Rapid joule heating of metal films used to fabricate polycrystalline silicon thin film transistors

We report fabrication of p-channel polycrystalline silicon thin film transistors (poly-Si TFTs) at a low temperature using a rapid crystallization joule heating method. Fifty-nm-thick silicon films were crystallized via 300-nm-thick SiO2 intermediate layers by heat diffusion from joule heating induced by electrical current flowing in chromium strips. The maximum grain size was about 100 nm. Oxygen plasma of 13.56 MHz at 100 W, 130 Pa and 250°C was applied for 5 min for defect reduction in the polycrystalline silicon films. Heat treatment at 200°C with 1.3×106-Pa-H2O vapor was applied for 3 h to improve electrical properties of SiOx gate insulator. TFTs had a high carrier mobility of 204 cm2/Vs and a low threshold voltage of -2.1 V.

Characterization of high-quality a-SiC : H films prepared by hydrogen-radical CVD method

High-quality a-SiC : H films have been prepared by using a hydrogen-radical CVD method. Si2H6 and C2H2 were used as source gases, and C2H2 was introduced by decomposing with microwave plasma. Consequently, carbon content and optical band gap could be controlled well by C2H2 the flow rate. It was confirmed that very stable a-SiC : H films can be produced by this technique.

Activation of Implanted Boron Atoms in Silicon Wafers by Infrared Semiconductor Laser Annealing Using Carbon Films as Optical Absorption Layers

We report continuous wave (CW) IR semiconductor laser annealing for the activation of boron atoms implanted into an n-type Si wafer with diamond-like carbon (DLC) films as optical absorption layers. Boron atoms were implanted at 10 keV at doses of 5?1014, 1?1015, and 1.5?1015 cm-2. The depth at the boron concentration of 1018 cm-2 was 50 nm. Samples were annealed by irradiation at 66.5?80.5 kW/cm2 and 2.6 ms. The sheet resistance of the sample markedly decreased to 531 ?/sq for implantation at 1.5?1015 cm-2 by laser annealing. Boron atoms were almost completely activated at a carrier density near the boron concentration for implantation at 10 keV. The largest diffusion length of boron atoms was 3 nm.

Pulsed Laser Annealing of Thin Silicon Films

The 30 ns pulsed XeCl excimer laser annealing of silicon films with an average thickness of 2.2 nm formed on quartz substrates is reported. Crystallization occurred at laser energies between 150 and 170 mJ/cm2. Raman scattering spectra revealed the mixed states of small crystalline grains, and nanocrystalline and disordered amorphous regions. The amorphization of the silicon films was observed for laser irradiation above 180 mJ/cm2. Photoluminescence was observed around at approximately 3 and 2 eV from 18 to 130 K for the films annealed at 260 °C for 3 h in 1.3 ×106 Pa H2O vapor after laser irradiation at 170 mJ/cm2.