Shigeru Nomura

STRUCTURAL AND ELECTRICAL PROPERTIES OF CRYSTALLINE CEO2 FILMS FORMED BY METALORGANIC DECOMPOSITION

Titanium oxide (TiO2) thin films were formed on a Si substrate by metalorganic decomposition at temperatures ranging from 600°C to 1000°C. As-deposited films were in the amorphous state and were completely transformed after annealing at 600°C to a crystalline structure with anatase as its main component. During crystallization in oxygen atomosphere, a reaction between TiO2 and Si occurred at the interface, which resulted in the formation of a thin interfacial SiO2 layer. Capacitance-voltage measurement showed good dielectric properties with a maximum dielectric constant of 76 for films annealed at 700°C. For the crystallized TiO2 films, the interface trap density was 1×1011 cm-2eV-1, and the leakage current was 1×10-8 A/cm2 at 0.2 MV/cm. The modified structure of TiO2/SiO2/Si is expected to be suitable for the dielectric layer in an integrated circuit in place of SiO2 or Si3N4 films.

GE NANOCRYSTALS IN SIO2 FILMS

SiO2/Ge nanocrystal/SiO2 structures have been fabricated by deposition of Ge film on a SiO2 layer and subsequent oxidation of the structure at a temperature between 800 °C and 1000 °C. Secondary ion mass spectrometry results indicate that the Ge precipitates into the bulk SiO2 at a density of 1×1012 cm−2. Raman spectra show a sharp peak at 300 cm−1 for the nanocrystallized Ge. The nanocrystal diameter is determined to be 5 nm on average. In the metal–insulator–silicon structure, electron storage occurs in the SiO2/Ge/SiO2 potential well via electron tunneling into the oxide film. Capacitance-voltage measurements indicate that flatband voltage (VFB) shifts to 0.91 V after the electron injection. The VFB shift is attributed to the charge storing for a single electron per potential well.

Effects of additive elements on improvement of the dielectric properties of Ta2O5 films formed by metalorganic decomposition

Ta2O5-based composite thin films formed by metalorganic decomposition have been investigated with respect to their dielectric properties. The dielectric and insulating properties of composite (1−x)Ta2O5−xTiO2 and (1−x)Ta2O5−xWO3 thin films are found to be improved compared to those of pure Ta2O5 thin films. In particular, thin films with x=0.08 composition of additive TiO2 or WO3 to Ta2O5 exhibited superior dielectric and insulating properties. The maximum dielectric constant and charge storage density of composite films are about 20 and 53.6 fC/μm2, respectively, higher than those of pure Ta2O5 films (about 13 and 34.5 fC/μm2). The temperature coefficient of the dielectric constant of composite films dramatically decreases from 65 ppm/°C for pure Ta2O5 to less than 11 ppm/°C. The leakage current density of composite films is lower than 1×10−9 A/cm2 up to an applied electric field of 3 MV/cm. The dominant conduction is Poole–Frenkel conduction in the films according to the measurement temperature dependen...

Growth and characterization of Ge nanocrystals in ultrathin SiO2 films

Abstract Ge nanocrystals embedded in SiO 2 glassy matrices have been formed by the deposition of a Ge film on a SiO 2 layer and the subsequent thermal oxidation of the structure at a temperature between 800°C and 1000°C. Secondary ion mass spectrometry (SIMS) results indicate that the Ge precipitates into the bulk SiO 2 at a density of 1×10 12 cm −2 . Raman spectra show a sharp peak at 300 cm −1 for the nanocrystallized Ge. The average radius of the Ge nanocrystals in SiO 2 was determined to be about 5 nm by means of analysis of Raman spectra. In the metal-insulator-semiconductor (MIS) structure, electron storage occurs in the SiO 2 /Ge/SiO 2 potential well via electron tunneling into the oxide film. Capacitance–voltage ( C – V ) measurements indicate that the flatband voltage ( V FB ) shifts to 0.91 V after the electron injection. The V FB shift is attributed to the charge storing for a single electron per potential well. A step was observed in the current–voltage ( I – V ) characteristics. The precise simulation of quantum transport in a quantum size structure indicates that the step in the I – V curve is attributed to resonant tunneling in the SiO 2 /Ge/SiO 2 structure.

Structural and Electrical Properties of Crystalline CeO2Films Formed by Metalorganic Decomposition

Crystalline CeO2 films were formed on a Si (100) substrate by metalorganic decomposition at temparatures ranging from 600°C to 800°C. As-deposited films were in the amorphous state and were completely transformed to crystalline CeO2 above 600°C. However, during crystallization in oxygen atomosphere, a reaction between CeO2 and Si occurred at the interface, which resulted in the formation of a thin interfacial SiO2 layer. Capacitance-voltage measurement on these films showed good dielectric properties with a dielectric constant of 15, which is more than three times higher than that of SiO2. The modified structure of CeO2/SiO2/Si is expected to be suitable for the dielectric layer in an integrated circuit, in place of conventional dielectric films such as those of SiO2 or Si3N4.

Physical and electrical properties of Ge-implanted SiO2 films

Metal–oxide–semiconductor structures with a Ge nanocrystal embedded in SiO2 films were fabricated by Ge+ ion implantation and subsequent high-temperature annealing. The Raman spectra indicate the evidence of self-assembled Ge nanocrystals in the SiO2 films. The Ge size and its density were estimated to 3–5 nm and 1×1012/cm2, respectively. Photoluminescence spectra showed a strong blue–violet band around 400 nm and a weak near-infrared band around 750 nm, respectively. The several implantation-induced deficient centers are believed to be responsible for the blue-light luminescence. Capacitance–voltage characteristics exhibit the flatband voltage shifts of 1.02 V after the electron injection into the SiO2/Ge/SiO2 potential well. An anomalous leakage current was clearly observed in the current–voltage characteristics. The precise simulation of quantum electron transport in the SiO2 film indicates that the anomalous conduction is originated from resonant tunneling in the SiO2/Ge/SiO2 double-well band structure.

Growth kinetics of ultrathin silicon dioxide films formed by oxidation in a N2O ambient

The growth kinetics of ultrathin SiO2 films on silicon in a nitrous oxide (N2O) ambient have been investigated as a function of oxidation temperature and time. The results show that the overall growth follows the linear‐parabolic law proposed by Deal and Grove [J. Appl. Phys. 36, 3770 (1965)]. The data analysis indicates that although the oxidation proceeds by surface‐limited reaction in the initial stage, it rapidly changes into a diffusion‐controlled reaction. This behavior is evidenced from the fact that the reaction of the N2O molecule with the silicon surface produces an interfacial nitrogen‐rich layer which acts as a barrier to the oxidant passing through the SiO2/Si interface. From the Arrhenius equation for N2O oxidation, the activation energies for the linear rate constant B/A and for the parabolic rate constant B are determined to be 1.5 and 2.3 eV, respectively.

Highly sensitive MISFET sensors with porous Pt–SnO2 gate electrode for CO gas sensing applications

Abstract Novel devices based on a porous Pt–SnO2 metal–insulator–semiconductor field-effect transistor (MISFET) for carbon monoxide (CO) gas sensing have been proposed. The structure integrates the catalytic properties of porous Pt, a thin catalytic layer, and the spillover effect onto SnO2, a gas adsorptive oxide, with surface-sensitive MISFETs. The operation characteristics of the device for the detection of CO gas are presented as a function of CO gas concentration and operating temperature. The threshold voltage decreased rapidly with time when the device was exposed to CO gas depending on the operating temperature. It was possible to detect 54 ppm of CO gas with a response time of less than 1 min at 27°C. A model was proposed to explain the operation. The proposed sensing mechanism of the device is supported well by experimental data.

Effect of oxynitridation on charge trapping properties of ultrathin silicon dioxide films

The physical properties and charge trapping behavior of rapid thermal N2O-oxynitrided (RTON) and rapid thermal NH3-nitrided (RTN) ultrathin SiO2 films have been investigated. The results of secondary-ion-mass spectrometry and Fourier transform infrared reflection measurements indicate that although nitrogen atoms are incorporated into the RTON and RTN films, only the RTN film shows a large number of NH bonds in the bulk SiO2. Using an analytical model, the number of oxide charge traps, the capture cross section, and the charge trap generation rate for the RTON and RTN SiO2 films were determined. Under high-field stress, the RTON SiO2 film has a much smaller number of electron and hole traps and a lower electron trap generation rate, resulting in a larger charge-to-breakdown QBD value compared to that of pure SiO2 film. In contrast, a large number of electron traps which originate from NH and SiH bonds is present in the RTN film. The differences in the charge trapping phenomena and oxide breakdown characte...

Electrical Properties of (1-x)Ta2O5–xTiO2 Crystalline Thin Films Prepared by Metalorganic Decomposition

Polycrystalline (1-x)Ta2O5–xTiO2 thin films were formed on a Si substrate by metalorganic decomposition (MOD) at an annealing temperature of 900°C. Thin films with 0.92Ta2O5–0.08TiO2 (x=0.08) composition exhibited superior insulating properties compared to other compositions. The main reason for the improvement in the insulating properties could be the charge compensation of excess oxygen by the TiO2 additive. The leakage current density was lower than 1×10-9A/cm2 up to an applied electric field of 3 MV/cm. The bulk-limited Poole-Frenkel conduction dominates the current–voltage characteristics. capacitance–voltage characteristics of these films showed good dielectric properties with a maximum dielectric constant of 16 and a charge-storage density of 42.5 fC/µm2 at 3 MV/cm.