Katsutoshi Izumi

High Speed C-MOS IC Using Buried SiO2 Layers Formed by Ion Implantation

Buried SiO2 layers were formed by oxygen-ion(16O+) implantation into silicon. The impurity distribution of the oxygen-implanted silicon substrate was analyzed by Auger spectroscopy. The properties of the buried SiO2 layers were investigated by infrared spectra, C-V characteristics, dielectric strength, dielectric constants, and refractive indices. The epitaxially-grown silicon layer on the buried SiO2 layer showed a good monocrystalline state. MOS devices were fabricated using the epitaxial silicon layer, and the field effect mobilities of holes and electrons were 240 and 610 cm2/V s, respectively, for 5 V gate bias. 21-stage C-MOS ring oscillators with effective channel length of 3.1 µm were fabricated. The propagation delay time and the dissipation power were 0.83 ns/stage and 0.33 mW/stage, respectively, for 5 V operation of the oscillators.

Challenge to 200 mm 3C-SiC Wafers Using SOI

200 mm wafer with 3C-SiC/SiO2/Si structure has been fabricated using 200 mm siliconon- insulator (SOI) wafer. A top Si layer of 200 mm SOI wafer was thinned down to approximately 5 nm by sacrificial oxidization, and the ultrathin top Si layer was metamorphosed into a 3C-SiC seed layer using a carbonization process. Afterward, an epitaxial SiC layer was grown on the SiC seed layer with ultra-high vacuum chemical vapor deposition. A cross-section transmission electron microscope indicated that a 3C-SiC seed layer was formed directly on the buried oxide layer of 200 mm wafer. The epitaxial SiC layer with an average thickness of approximately 100 nm on the seed was recognized over the entire region of the wafer, although thickness uniformity of the epitaxial SiC layer was not as good as that of SiC seed layer. A transmission electron diffraction image of the epitaxial SiC layer showed a monocrystalline 3C-SiC(100) layer with good crystallinity. These results indicate that our method enables to realize 200 mm SiC wafers.

Circuit designs and fabrication of swarm-intelligence LSIs based on modeling foraging behaviors of ants

Novel functional LSIs based on swarm intelligence of ant colony have been proposed. An ant colony is a highly organized society, though individual ants themselves act only according to simple behavioral patterns. Focusing on a foraging pattern among them, the modeled function was integrated on one LSI chip. To verify the function, the fabricated LSI was applied to solve a quasi-traveling salesman problem. Simulation results indicated that a designed LSI has swarm intelligence due to pheromone communication. This work suggests the possibility of fabricating swarm intelligence LSIs with our design method, based on modeling the foraging behaviors of ants.

Simulation Method for Buried Oxide Formation of Separation by Implanted Oxygen Structure during Post-Implantation Thermal Annealing

We have developed a simulation method for buried oxide layer formation of separation by implanted oxygen (SIMOX) structures during thermal annealing after oxygen implantation into Si. The SiO2 precipitation in oxygen-implanted Si substrates is numerically simulated, introducing the Cahn-Hilliard equation for the evolution of oxygen concentration distribution in a Si matrix. We have found that different initial depth profiles of oxygen cause different types of profiles of domain structures distinguished as a continuous oxide layer, an array of discontinuous oxide islands, and an oxide layer including Si islands. Our simulation well reproduces the SIMOX structures observed experimentally for different oxygen doses. Also, the dynamic simulation results agree well with experimental ones. These results indicate that our simulation method enables to extract the dose window for continuous oxide layer formation as well as to study the formation mechanism of the buried oxide layer of the SIMOX substrate by post-implantation thermal annealing.

High-Precision Analysis of Oxygen Depth Profile in 16 O + -Implanted Silicon Substrates by Spectroscopic Ellipsometry

A precise method of analyzing oxygen depth profiles in oxygen-ion ( 16 O + )-implanted Si substrates by spectroscopic ellipsometry has been developed. The specimens were formed by 16 O + -implantation into Si(lll) with oxygen doses ranging from 3 to 10 X 10 17 /cm 2 at 180 keV. The optical characteristics such as the amplitude ratio angle (ψ) and phase difference angle (Δ) vs. wavelength (λ) of the specimens were measured by spectroscopic ellipsometry. The 16 O + -implanted Si layer was modeled as a transition layer, which was composed of crystalline Si and SiO 2 , and the composition ratio of crystalline Si to SiO 2 was assumed to change continuously in a direction toward depth, In the model the Ψ-λ and Δ-λ spectra were calculated reversely by using the effective medium approximation analysis method. In the simulation fitting was performed to correlate the measured characteristics. The simulated oxygen depth profile and the modeled layer structure were compared with actual results obtained by Rutherford backscattering spectroscopy and cross-sectional transmission electron microscopy. This method can obtain oxygen depth profiles in 16 O + -implanted Si substrates easily and nondestructively with a higher precision compared to conventional techniques.

Hetero-Epitaxial Growth of GaN onto SiC-on-SIMOX Substrates

1.Introduction A plan to develop electron-photon merged devices has been revealed as one of the next generation, post Si devices [1]. In the devices, electrons undertake the operation or calculation, and light undertakes signal transmission, respectively. In order to realize super high-speed ULSIs applying the synergetic effects, the devices consist of Si LSIs and GaN photo-device arrays. SOI is introduced as a basic technology to fabricate both of these devices monolithically. We had previously developed a 200 mm diameter SiC-on-insulator substrate [2]. The top SiC layer works as a buffer layer for GaN epitaxial growth [3]. In this paper, we report on the hetero-epitaxial growth of GaN onto a 50 mm diameter SiC-on-SIMOX substrate which had been cut out from an 200mm diameter substrate.