Tomo Ueno

Low-Temperature and Low-Activation-Energy Process for the Gate Oxidation of Si Substrates.

A low-temperature and low-activation-energy process for the gate oxidation of Si substrates has been proposed. Using the energy-controlled excited oxygen generated in rare-gas and O2 molecule mixture plasma, the enhancement of the oxidation rates was achieved. In addition, the oxidation rates and kinetics drastically change with the type of mixed rare gas in the plasma. Using Kr as the mixed rare gas, the interface trap density near the mid gap [Dit(mid)] of the SiO2/Si interface grown at 500°C was 2.6×1011/cm2/eV, which was comparable to that of the as-grown one using conventional thermal oxidation at a higher temperature. For this process, the oxidation rates were shown to be hardly dependent on the substrate temperature, and the activation energy of B, which is the parabolic rate constant, was found to be low, 0.14 eV.

Characterization of Pb(Zr, Ti)O3 Thin Films on Si Substrates Using MgO Intermediate Layer for Metal/Ferroelectric/Insulator/Semiconductor Field Effect Transistor Devices

Pb(Zr, Ti)O3(PZT)/MgO/Si(001) stacked structures, one of the potential components of ferroelectric-gate field effect trnsistors, have been fabricated and characterized. According to the electrical characterization of MgO/Si structures, MgO thin films prepared on Si substrates at a low growth rate showed a small leakage current of ~10-8 A/cm2 order in an electric field of 1 MV/cm. In C-V measurements of as-grown MgO/Si interfaces, injection-type hysteresis was observed because of crystal defects in the MgO film adjacent to the interface. After oxygen annealing at 400°C, however, it showed no hysteresis and a low interface trap density of the order of 1011 cm-2eV-1 was achieved with no formation of a low-dielectric layer at the MgO/Si interface. These results indicate that MgO thin films are applicable as gate insulators of FETs. After a PZT film was deposited on the MgO/Si structure, the C-V characteristic of the stacked structure showed a ferroelectric hysteresis curve and a low interface trap density of 5×1011 cm-2eV-1. A maximum memory window width of 1.2 V was obtained for the PZT thin film on Si substrate with a MgO intermediate layer.

Process dependence of the SiO2/Si(100)interface trap density of ultrathin SiO2 films

The interface trap density of states Dit of ultrathin SiO2 film has been investigated as a function of process variables. The process parameters used were oxidation temperature (1000–1200 °C), oxide thickness (4–10 nm), and annealing condition, including ambient (deuterium, argon, and in vacuum), temperature (500 and 900 °C), and time (10–120 s). Analysis of as‐grown SiO2 films showed that the Dit decreases with increasing oxidation temperature and/or oxide thickness. With annealing in argon or in vacuum at 900 °C, the Dit decreases exponentially at the initial stage, then starts to increase linearly with increasing time. Similar behavior was observed for 900 °C deuterium annealing. Deuterium annealing at 500 °C was more effective in the reduction of the Dit, whereas argon annealing at the same temperature did not affect the density at all. A possible model for annealing kinetics is proposed to explain the experimental results.

Radiative Transition with Visible Light in Electrochemical Anodized Polycrystalline Silicon

Radiative transition with visible light was observed by means of a porous layer made from polycrystalline silicon (poly-Si). Photoluminescence (PL) spectra were characterized as a function of initial poly-Si materials. For poly-Si formed by the casting method, a PL spectrum with the peak energy of 2.00 eV and the fullwidth at half maximum (FWHM) of 0.42 eV were obtained. For poly-Si formed by thermal CVD, the peak energy and the FWHM were 1.84 eV and 0.57 eV, respectively. On the basis of these findings, the structure of a highly developed display system, which contains TFT and luminous regions in the same poly-Si layer, was also proposed.

Evaluation of GeO desorption behavior in the metal/GeO2/Ge structure and its improvement of the electrical characteristics

The relation between germanium monoxide (GeO) desorption and either improvement or deterioration in electrical characteristics of metalGeO(2)Ge capacitors fabricated by thermal oxidation has been investigated. In the metalGeO(2)Ge stack, two processes of GeO desorption at different sites and at different temperatures were observed by thermal desorption spectroscopy measurements. The electrical characteristics of as-oxidized metalGeO(2)Ge capacitors shows a large flat-band voltage shift and minority carrier generation due to the GeO desorption from the GeO(2)Ge interface during oxidation of Ge substrates. On the other hand, the electrical properties were drastically improved by a postmetallization annealing at low temperature resulting in a metal catalyzed GeO desorption from the top interface.

Low-temperature fabrication of ultrathin ZrO2/Si structure using metal deposition followed by oxygen annealing

Metal deposition followed by oxygen annealing has been carried out for the fabrication of ZrO2/Si structures. Using this method, 200°C oxygen annealing enables the oxidation of Zr metal and 220°C annealing enables the surface potential control of Si in metal–insulator–semiconductor (MIS) structures, even if the dielectric constant of ZrO2 has been shown to be 11.8. High-quality ZrO2 films with a dielectric constant of ~20 can be achieved by 300°C annealing with an interfacial layer of 0.9 nm thickness. For these films, no degradation of leakage characteristics was observed after the thermal budget corresponding to that of impurity activation at 850°C for 30 min. Consequently, using this method, a high-quality ZrO2/Si structure that has good chemical stability under a high thermal budget could be fabricated at a low temperature.

Fabrication of c-Axis Oriented Pb(Zr, Ti)O3 Thin Films on Si(100) Substrates Using MgO Intermediate Layer

Tetragonal perovskite Pb(Zrx Ti1-x )O3 (PZT) ferroelectric thin films with single c-axis orientation were successfully fabricated on Si(100) substrates using an intermediate layer of MgO thin film. The (100) oriented MgO intermediate layers can be prepared on Si(100) substrates with low growth rate during RF magnetron sputtering at a substrate temperature of 300° C. On the (100) oriented MgO intermediate layer, PZT can be deposited using a digital Metalorganic chemical vapor deposition (MOCVD) method at 480° C. By analysis of cross sections of the PZT/MgO/Si(100) stacked structure using focused ion beam observation, it is clearly shown that a uniform MgO layer causes the deposited PZT film to consist of a uniform tetragonal perovskite phase. However, a nonuniform MgO layer causes the PZT film to contain an additional phase because of direct contact between PZT and the Si substrate.

Solid State Reaction of Mo on Cubic and Hexagonal SiC

Mo/3C-SiC and Mo/6H-SiC interfaces have been investigated by Auger electron spectroscopy, Rutherford backscattering spectroscopy, X-ray diffraction, and transmission electron microscopy. High temperature annealing at 1200°C for 1 hour caused a reaction at the interfaces, resulting in forming a Mo2C/Mo5Si3/SiC multilayer. We have found that SiC poly-typism (3C or 6H) and Mo deposition process (evaporation or sputter deposition) make no influence in forming the multilayer. The diffusion mechanism at the Mo/SiC interface will be discussed.

HfO2/Si and HfSiO/Si Structures Fabricated by Oxidation of Metal Thin Films

Hafnium metal deposition followed by oxidation, either on bare silicon or SiO2/Si substrates, was performed for the fabrication of high-k/Si gate stacks with small equivalent oxide thickness values. HfO2/Si structures were fabricated without substrate heating but with the electron cyclotron resonance (ECR) plasma oxidation of Hf metal deposited on bare Si substrates by DC magnetron sputtering. These HfO2/Si structures have ideal abrupt interface without interfacial layer (IL)-SiO2 and silicide layers, as determined by an X-ray photoelectron spectroscopy (XPS) measurements. A direct stacking was induced by the characteristic film growth of ECR plasma in a buried interfacial region. On the other hand, on SiO2/Si substrates, the HfSiO/Si structures were successfully fabricated by thermal treatment for both the interdiffusion of Hf metal and SiO2, and the oxidation of the layer. The HfSiO/Si structures show small leakage currents because of high barrier heights and have no hafnium silicide layer.

Electrical properties of germanium oxynitride and its interface with germanium prepared by electron-cyclotron-resonance plasma oxidation and nitridation

We report on the electrical properties of germanium oxynitride and its interface with germanium prepared by nitriding the germanium oxide/germanium surface by irradiating a nitrogen plasma stream generated by an electron-cyclotron-resonance plasma source without substrate heating. Excellent leakage current characteristics were obtained for a metal–insulator–semiconductor capacitor with a gate stack consisting of a silicon nitride sputter-deposited on germanium oxynitride with an interface trap density of ~2×1011 cm-2eV-1. Moreover, the equivalent oxide thickness of the germanium oxynitride was found to be about 30% smaller than that of germanium oxide. The reported germanium oxynitride is suitable as a beneficial interlayer between high-dielectric-constant gate insulators and germanium.