Masayuki Jyumonji

Optimum Light Intensity Distribution for Growing Large Si Grains by Phase-Modulated Excimer-Laser Annealing

Characteristics have been investigated for both KrF excimer-laser light and KrF excimer-laser crystallization of Si thin films. The results were applied to design an optical system for growing densely packed and large grains. A high-resolution beam profiler confirmed that the laser light intensity distribution on the sample surface had a nearly ideal triangular form with a maximum-to-minimum intensity ratio of approximately 2, as designed. This distribution could grow 5-µm-long grains with a packing efficiency close to 100% by a single laser light pulse.

Characterization of high-performance polycrystalline silicon complementary metal-oxide-semiconductor circuits

Polycrystalline silicon (poly-Si) complementary metal–oxide–semiconductor (CMOS) circuits have been fabricated by using an advanced excimer-laser annealing method and a plasma-oxidation method. The 1-µm-long thin-film transistors (TFTs) were fabricated on arrays of laterally grown long and narrow grains, so that the majority of carriers were free from scattering at grain boundaries during propagation through the channel. The propagation delay time measured by a 21-stage ring oscillator was 175 ps and a power-delay product of 9×10-13 J/gate was obtained at a supply voltage of 3.3 V. The obtained propagation delay time was almost the same as those of bulk Si devices having the same gate length. Furthermore, we expect that 1-µm-long CMOS TFT circuits on glass will have a performance superior to that of 1-µm-long bulk Si devices when the short channel effect and threshold voltage fluctuation are controlled well.

Characterization of Novel Polycrystalline Silicon Thin-Film Transistors with Long and Narrow Grains

Excellent characteristics of polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with long and narrow grains aligned one-dimension have been experimentally clarified for the first time. The field effect mobility and on-off transition slope of n-channel and p-channel devices were as high as 685 cm2 V-1 s-1 and 190 mV/decade and 145 cm2 V-1 s-1 and 104 mV/decade, respectively. Fluctuations of characteristics were considerably reduced by widening the channel, and uniform characteristics were observed when there were approximately twenty long grains within the channel. These results were obtained when the TFT channel was formed within a region free from grain boundaries formed by head-on collision of laterally growing grains and seeds used to initiate lateral grain growth. Material properties are discussed from the viewpoint of device characteristics.

An Advanced Sample Structure for Large-Grain Growth by Excimer Laser Crystallization

We have developed an advanced sample structure for large-grain growth by excimer-laser crystallization of Si. More than 10 μm long grains were grown laterally in a 50 nm thick Si layer by phase-modulated excimer-laser annealing. A photosensitive SiO x capping layer prepared using a conventional plasma-enhanced chemical vapor deposition apparatus enables this longer lateral growth with lower irradiated intensity of laser light than those with the conventional SiO 2 capping layer.

Rapid formation of arsenic-doped layer more than 1.0 μm deep in Si using two KrF excimer lasers

Sequential irradiation by two KrF excimer lasers (λ=248 nm) has been used to activate arsenic atoms implanted into Si substrates. The 1st laser pulse having 34 ns pulse width followed by the 2nd laser pulse of 23 ns after a time delay was irradiated to the sample. Laser fluences of the 1st laser pulse and the 2nd laser pulse were set at 2.4 J/cm 2 and 0.5 J/cm 2 , respectively. The substrate was heated to 700°C. From Rutherford backscattering spectroscopy (RBS) analysis, the depth of the doped layer is confirmed to be 1.0 μm. Severely rippled surface was observed by atomic force microscope (AFM) for the sample irradiated without the 2nd laser pulse, but the surface morphology can be improved by the sequential irradiation of two pulses. For a time delay of 150 ns, the minimum values of χ min (4.61%) and sheet resistance (41.43 Ω/ □) were obtained.

Mechanism of silicon implant-deposition for surface modification of stainless steel 304 using KrF-excimer laser

Simultaneous implantation and deposition of Si by KrF-excimer-laser (248 nm) irradiation in an ambient silane (SiH4) gas realize the surface modification of stainless steel (SUS) 304 at room temperature. This process is referred to as the Laser Implant-Deposition (LID). Depth profiles of Si concentration in the modified layers and the total quantities of supplied Si (Si dose) are analyzed by Rurtherford Backscattering Spectroscopy (RBS) measurements. The Si supply mechanism of LID is discussed with variations of the Si dose as a function of laser fluence, gas pressure, and the number of laser pulses. The calculation of temperature along the depth during the LID process suggests that the Si atoms diffuse into the SUS304 in a liquid phase. Fitting of the calculated depth profile to the experimental data, using the interdiffusion theory, gives an interdiffusion coefficient between Si and SUS304 as high as ≈ 2.8×10−6 cm2/s. A simplified model for simulation, by which well agreed depth profiles of Si can be simulated for various experimental conditions, is proposed.

Computer simulation of deeply doped layers in Si using double-pulse excimer lasers

A deeply doped layer in Si with high crystalline quality and a smooth surface can be obtained by sequential irradiation of two KrF excimer lasers (A = 248 nm). This novel technique, referred to as double-pulse irradiation, involves high-speed diffusion of dopant and recrystallization of the molten layer induced by laser irradiation. At the typical 1st laser fluence of 2.4J/cm 2 and the 2nd laser fluence of 0.5J/cm 2 , the numerical simulations of thermal diffusion in the Si substrate during the laser irradiation reveal that the suppression of the surface roughness by the double-pulse irradiation is mainly caused by the re-heating induced by the 2nd pulse. In addition, the simulations also indicated that the average resolidification velocity of the double-pulse irradiation was estimated to be ∼3.7 m/s, which was smaller than that of single KrF excimer laser irradiation of 4.8 m/s. This result corresponds to the improvement of the crystalline quality of the sample irradiated by double-pulse lasers.

Importance of pure Si films in pulsed-laser-induced lateral growth

We have investigated the effects of impurities in starting silicon films on excimer-laser-induced lateral growth characteristics. The films should have a low concentration of impurities to achieve long lateral growth, since impurities, such as carbon, nitrogen, oxygen, and fluorine, in the films were found to affect the lateral growth characteristics severely. A stacked structure with a capping layer is also considered essential for maintaining pure molten Si during lateral growth.

P‐50: Distinguished Poster Paper: Arrays of Large Si Grains Grown at Room Temperature for x‐Si TFTS

Arrays of large Si grains have been grown by phase-modulated excimer-laser annealing at room temperature. Home-plate- and square-shaped grains could be grown over the whole irradiated substrate area. These results indicate that the fabrication of x-Si TFTs on glass is a realistic development target.

Deposition of Pure Hydrogenated Amorphous Silicon by Plasma-Enhanced Chemical Vapor Deposition for Polycrystalline Silicon Thin Film Transistors

A high-purity hydrogenated amorphous silicon film has been successfully deposited using an advanced plasma-enhanced chemical vapor deposition system that is available for mass-production use. Oxygen and carbon concentrations in the film were as low as 1.3×1017 and 2.6×1016 atoms/cm3, respectively, i.e., about hundredth part of the typical values achieved using a recent large-area deposition system and as low as those in CZ-Si wafers. The film was characterized as a function of SiH4 gas flow rate and outgas rate from the reaction chamber, and the results suggest that oxygen and carbon in the film comes predominantly from H2O and CO2 out-gassing from the chamber wall, respectively.