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One-monolayer deposition characteristics have been investigated for Ge on the Si(1 0 0) surface and Si on the Ge(1 0 0) surface by using a co-axial impact collision ion scattering spectroscopy. A subtracted spectrum method has been proposed for the detailed analysis of the interface structure. Incident angle dependence of the signal intensity shows that both Ge/Si and Si/Ge hetero-interfaces are atomically abrupt without intermixing and surface segregation.

Optimization has been done theoretically for the phase-modulated excimer-laser annealing method to grow highly packed large grains in the Si film, where the divergence of the laser light beam plays an important role. Generalized optimum annealing conditions were given graphically as a function of the maximum-to-minimum light intensity ratio. Theoretical results were verified also experimentally by growing grains as large as 7 μm with 10 μm-pitch using a single shot of excimer-laser light pulse. It is pointed out that there is a room for improving the packing density to almost 100% by simply shortening the pitch of the phase shifters.

Silica films with various types of alkyl groups were grown from the liquid phase, at room temperature, using alkyl tri-alkoxy silane compounds. From Fourier transform infrared (FTIR) absorption measurements, a majority of Si-alkyl bonds in the source molecules were found to remain in the grown film, while Si-alkoxy bonds were completely removed. Electrical and thermal properties have been measured comparatively for various films having dense alkyl groups. The films with the methyl group are promising for silicon production in ultra large-scale integrated circuits (Si-ULSIs) and the film having the vinyl group for non-heat-tolerant compound-semiconductor large-scale integrated circuits (LSIs).

Chemical vapor deposition parameters have been investigated for low (∼200°C) temperature deposited and hydrogen-free SiO 2 films from a mixture of tetra-iso-cyanate-silane and various kinds of tertiary-alkyl-amine. Di-methyl mono-ethyl amine was found the most suitable partner gas for H free low temprature CVD source gas mixture. Addition of small amount of H 2 O (0.5% of tertiary-alkyl-amine) was effective for decreasing the deposition temperature up to 50°C without serious drawbacks on the film properties such as hydration and electric properties. The deposition rate increased to higher temperatures by using those best partner gases, di-methyl mono-ethyl amine, with tetra-iso-cyanate-silane. The resistivity defined at 1 MV cm −2 was >10 16 Ω cm, and breakdown field strength at 1 μA cm −2 was >6 MV cm −2 . The fixed-charge density and interface sate density near midgap were ∼4 × 10 12 cm −2 and ∼10 12 eV −1 cm −2 respectively.

An advanced excimer-laser annealing method, named phase-modulated excimer-laser annealing method, has been reviewed for large-grain growth in Si thin-films. The laser-light intensity is modulated two-dimensionally on the Si film surface that triggers a lateral motion of the melt–solid interface, resulting in the lateral grain growth. The intensity distribution can be designed well by a phase-shift concept. Large grains were grown at pre-designed positions at 500°C, and are expected to possibly be aligned with less than 30 μm in pitch. The method seems attractive for high-performance and quasi single-crystal thin-film devices, which include thin-film transistors, silicon-on-insulator-based ULSIs, solar-cells and porous Si photonic devices.

Reaction process has been studied for an atomic hydrogen-induced abstraction of methyl groups on the Ge surface. The reaction rate estimated from experiments had a very large activation energy and depended on a surface coverage of methyl groups; they are not expected for a `pure' Eley–Rideal mechanism. The process can be explained by the `modified' Eley–Rideal mechanism or the `precursor' mechanism based on two-dimensionally bound hydrogen atoms on the surface.

We achieved the atomic-layer-deposition of SiO2 with an extremely low H content for the first time by using Si(NCO)4 and N(C2H5)3. The deposition rate was independent of the exposure times of both sources. The saturated deposition rate was about 1.2 A/cycle at 150°C. AFM observation revealed that the increase of roughness after 50 deposition cycles was only about 0.4 A in root mean square. The FT-IR spectra showed that the deposited film was SiO2 without Si–H, Si–OH or NCO bond.

Atomic-layer-epitaxy (ALE) of germanium has been analyzed by a kinetic model and a thermodynamic model. Chlorogermanes are found to be unsuitable since they cannot satisfy the self-limiting adsorption condition due to quick thermal desorption of HCl from the surface. On the other hand, the ideal growth rate of one monolayer per cycle is expected for dimethylgermane. This is because there exists no recombinative desorption reaction between surface methyl groups and H that will break the self-limiting adsorption condition. It has also been confirmed, from thermodynamic considerations, that the elemental chemical reactions used in this ALE, i.e., self-limiting adsorption and reduction of surface methyl groups by atomic hydrogen, are spontaneous.

Atomic layer etching of Ge has been investigated experimentally based on the surface chemistry that Cl can adsorb on the clean Ge surface at room temperature and desorb thermally as GeCl 2 at high temperatures. The ideal etching rate of one monolayer per cycle has been achieved. The critical Cl 2 dosage for the saturated etching rate was about 7.2×10 6 L. Increase of the surface roughness after etching of 100 cycles was about 3.5 monolayers.

A kinetic model has been presented for atomic layer epitaxy of Si using cyclic exposures of SiH 2 Cl 2 and atomic hydrogen. This model is based on the surface reaction of adsorbates formed by gas-phase reaction of SiH 2 Cl 2 . The ideal growth rate of one monolayer per cycle is achieved only when the dominant precursor is SiHCl. Limiting factors of the ALE window are also discussed.

Self-limiting monolayer adsorption of Ge has been demonstrated on Si(100) at 520°C using dimethylgermane as a self-limiting molecular precursor. This opens a way for hetero-ALE of Ge on the Si surface.

Atomic layer epitaxy of germanium has been demonstrated successfully by alternating exposures of atomic hydrogen, which acts as a reactant for extracting hydrocarbon from the surface, and of dimethylgermane as a self-limiting molecular precursor. The ideal growth rate of one monolayer per cycle has been achieved with a wide ALE temperature window between 420°C and 528°C.

Based on the first result of the layer-by-layer deposition of silicon dioxide films by a cyclic exposure of water and tetra isocyanate silane, Si(NCO) 4 , new isocyanate compounds preferable to Si(NCO) 4 have been proposed for ideal layer-by-layer deposition characteristics. Preliminary results are also presented for one of the substances.

Novel atomic layer epitaxy (ALE) methods have been proposed for Ge, where the elemental kinetics of the chemical vapor deposition method are divided into two sequential phases, i.e., a monolayer adsorption phase and a subsequent desorption phase for the surface-terminating species. Ge-ALE has been achieved, for the first time, with an ideal growth rate of one monolayer per cycle, under constant substrate temperature conditions. The detailed ALE method and growth characteristics have been presented. Furthermore, atomic hydrogen exposure is shown to be effective for widening the Ge-ALE window.

Two ALE methods of Si are successfully demonstrated, where H atoms play an essential role. In the first method, H atoms are used as self-limiting species over the grown layer. Si3H8 was used as source gas and the substrate temperature was modulated in order to switch two steps, i.e. an adsorption step and a desorption step, in an ALE cycle. When the temperature was lower than 380°C in the adsorption step and higher than 520°C in the desorption step, the grown layer thickness per cycle was saturated at 0.8 ML/cycle, closer to the ideal value than in the SiH4 or Si2H6 cases. In the second method, atomic H is used as an active reducer of the self-limiting species. SiH2Cl2 as source gas and atomic H were irradiated to the surface, alternately. An ideal monolayer growth per cycle was obtained with the substrate temperature over 540°C, much lower than in the case of the molecular H2 reducer.

SiO2 films were deposited layer by layer from a new silicon source gas, i.e. tetra-iso-cyanate-silane (Si(NCO)4). An average growth rate of about 0.17 nm per cycle was achieved by a cyclic process of alternating reaction of the substrate surface with Si(NCO)4 and H2O respectively. The detailed deposition characteristics together with chemical and physical properties of the deposited film were evaluated with ellipsometry, Fourier transform IR spectroscopy, X-ray photoelectron spectroscopy and Auger electron spectroscopy.

We have found that an undesirable SiNH component is reduced drastically from the low-temperature-deposited SiN surface by intense ArF excimer-laser irradiation on the low-temperature-deposited SiN film. This pre-annealing of the SiN film is very effective in forming an abrupt Si/SiN interface, and thus plays a very important role in high-performance excimer-laser-crystallized poly-Si/SiN thin-film transistors aiming at high-quality liquid-crystal displays. Annealing characteristics are also presented for the various SiN film thickness and for both the ArF and KrF excimer-laser lights.

Atomic H is proposed for the reducer gas in the atomic layer epitaxy (ALE) of Si. Its high reactivity makes it possible to remove surface-terminating adsorbates, which cause the self-limitation of unwanted successive deposition of Si compounds, at low temperature. The ALE growth was attempted by the alternating exposure of the Si(111) substrate to SiH 2 Cl 2 and H. Ideal monolayer growth was obtained and the growth rate was independent of the gas volumes and the substrate temperature. The lower ALE limit of the substrate temperature was 540 °C, about 250 °C lower than the case of H 2 as the reducer gas.

Hydrogenated amorphous-silicon bipolar transistors have been investigated for the first time. A novel device structure suitable for transistor operation is described in detail, and its fabrication process and the experimental results are also presented. The common-emitter current gain β exceeded 2.

The dynamic as well as static characteristics of molybdenum/hydrogenated amorphous-silicon Schottky barrier diode were investigated. We obtained the rectification ratio of 10 9 and steady current densities of up to 1.5A/cm 2 at ±2V bias voltage. The breakdown voltage was more than 20V. Switching operation was observed even at 10MHz without appreciable distortion. It was estimated that the charge-up time and charge-decay time of a liquid crystal pixel with 1mm×1mm area in series with a diode having a junction area of 15μm×15μm were less than 1μsec and 100sec, respectively.

A new approach for improving a-Si:H transistors has been proposed. The concept is based on the size effects and quantum mechanical effects that will appear in an ultra-thin a-Si:H layer. Experimental results including those on a 10nm-thick transistor performance are described, and a two-step deposition method suitable for ultra-thin a-Si:H film is proposed.

Charge-transfer characteristics of hydrogenated amorphous-silicon charge-coupled devices (a-Si:H CCDs) have been investigated theoretically by taking diffusion and self-induced drift of electrons into account. Theoretical results were then compared with experimental results obtained from a group of ultra-thin a-Si:H CCDs having various physical dimensions. The maximum efficiency measured experimentally was 99.9%.

Theoretical and experimental studies in the application of a-Si:H to charge-coupled devices (CCDs) are summarized and recent results are presented. The device operates in a new mode where transient signal electrons are stored in the accumulation state of the a-Si:H/insulator interface. Taking multitrapping effects of electrons by localized states into account, charge transfer characteristics have been analyzed. It is shown that the clock frequency can be increased without degradation of the transfer efficiency by shortening the transit time of conduction electrons. The first a-Si:H CCD operation has been confirmed experimentally by an insulator/a-Si:H/insulator structure sandwiched between staggered transfer electrodes. Then, the improved device structure with resistively connected transfer electrodes has been developed. The device operated with the transfer efficiency of more than 99%/ transfer at clock frequencies between 1kHz and 200kHz.

A numerical program to obtain the impurity profile within a semiconductor material from the measured spreading resistance data was developed. In the program, an image method was applied to calculate the spreading resistance of the multilayered structure, which consisted of a stack of layers, each of homogeneous resistivity, with thicknesses equal to the spacing of the spreading resistance data. The solution adopted in the present program is described in this paper. Converting results from the spreading resistance data to the impurity profile of an implanted and diffused sample and buried channel are also shown.