Hajime Watakabe

Electrical and structural properties of poly-SiGe film formed by pulsed-laser annealing

Electrical and structural properties of polycrystalline silicon germanium (poly-SiGe) films fabricated by pulsed-laser annealing were investigated. Observation of laser-induced melt-regrowth of SiGe films using transient conductance measurement revealed that the melt depth and the crystallization velocity increased as Ge concentration increased. The increase of the crystallization velocity resulted in increase of the average size of crystalline grains from 66 to 120 nm at the laser energy density of 360 mJ/cm2 with increasing Ge concentration from 0 to 60%. The crystalline volume ratio obtained by reflectivity spectra in the ultraviolet region also increased from 0.83 to 1.0. Numerical analysis revealed that the density of electrically active defects decreased from 3.5×1018 to 1.1×1018 cm−3 as Ge concentration increased from 0 to 80%. The density of defect states of Si0.8Ge0.2 films were reduced from 3.5×1018 to 1.9×1018 cm−3 by 13.56-MHz hydrogen plasma treatment at 250 °C, 30 W, and 130 Pa for 30 s. How...

Application of Plasma Jet Crystallization Technique to Fabrication of Thin-Film Transistor

The crystallization of a-Si films on glass substrates using the plasma jet crystallization (PJC) technique and its application to thin-film transistor fabrication were studied. Amorphous Si (a-Si) films deposited by plasma-enhanced chemical vapor deposition (PECVD) of 50% SiH4 diluted with H2 were crystallized by thermal plasma jet under the power of 1.6 to 2.6 kW input to the plasma source and the substrate scan speed of 170 to 1000 mm/s. The crystallinity of the films was improved by treating the films at a higher input power for a longer duration. Thin-film transistors (TFTs) fabricated using the crystallized films showed good electrical characteristics. By increasing the input power from 1.86 to 2.29 kW in the crystallization, the average field-effect mobility was increased from 42 to 61 cm2V-1s-1, and the threshold voltage was decreased from 4.0 to 3.4 V. These results indicate that the PJC technique is a very promising low-temperature process technology.

High-Pressure H2O Vapor Heat Treatment Used to Fabricate Poly-Si Thin Film Transistors

High-pressure H2O vapor heat treatment was applied to reduction of defect states of silicon films and SiOx/Si interfaces in the fabrication of n-channel polycrystalline silicon thin film transistors (poly-Si TFTs). A carrier mobility of 170 cm2/Vs and a low threshold voltage of 2.4 V were achieved by heat treatment at 260°C with 1.3×106 Pa H2O vapor for 3 h applied to 25-nm-thick silicon films crystallized by the irradiation of a 30-ns-pulsed XeCl excimer laser at 280 mJ/cm2. Additional high-pressure H2O vapor heat treatment after TFT fabrication further improved them to 620 cm2/Vs and 1.7 V, respectively.

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.

Defect Reduction Treatment for Plasma-Tetraethylorthosilicate-SiO2 by High-Pressure H2O Vapor Heat Treatment

Improvements in the electrical and structural properties of tetraethylorthosilicate (TEOS) SiO2 films fabricated by plasma-enhanced chemical vapor deposition (PECVD) method were investigated using high-pressure H2O vapor heat treatment. The density of interface trap states was reduced from 3.3×1012 (initial) to 5.1×1010 cm-2 eV-1 by 1.3×106 Pa H2O vapor heat treatment at 260°C for 9 h. The density of fixed charges was also reduced from 6.1×1011 to 1.3×1011 cm-2. The full width at half-maximum (FWHM) of the optical absorption band corresponding to vibration of Si–O–Si bonding was reduced from 82.9 to 78.1 cm-1. Narrowing in FWHM of the Si 2p core level peak measured by X-ray photoelectron spectroscopy (XPS) was also observed. The reduction in the FWHM probably results from improvement of the Si–O bonding network.

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.

Formation of polycrystalline-silicon-germanium films by pulsed laser-induced rapid annealing

Pulsed laser rapid annealing of silicon-germanium (SiGe) films on quartz glass substrate was investigated. Laser-induced melt-regrowth properties were analyzed by the transient conductance measurements. The maximum electrical conductivity of the germanium films associated with the maximum melt depth was increased from 370 to 4420 S/cm as laser energy density increased from 130 to 200 mJ/cm2. The complete melting of the films was observed at laser energy density above 200 mJ/cm2. The electrical conductivity of the silicon films was increased from 340 to 4480 S/cm as laser energy density increased from 280 to 530 mJ/cm2. The melt duration of germanium films slightly increased from 73 to 81 ns as the laser energy density increased from 130 to 180 mJ/cm2. On the other hand, the melt duration of the silicon films was increased from 56 to 120 ns as laser energy density increased from 330 to 500 mJ/cm2. In the complete melting condition, they were furthermore increased to 117 and 145 ns for germanium and silicon, receptivity. The average size of crystalline grain was increased from 66 to 120 nm as germanium concentration increased from 20 to 60%. The crystallization to the lateral direction induced by the deep melting and rapid solidification increased the grain size.