Tetsuya Nishiguchi

High-quality SiO2 film formation by highly concentrated ozone gas at below 600°C

Highly concentrated (>93 volu200a%) ozone (O3) gas was used to oxidize silicon for obtaining high-quality SiO2 film at low temperature. Compared to O2 oxidation, more than 500u200a°C lower temperature oxidation (i.e., from 830 to 330u200a°C) has been enabled for achieving the same SiO2 growth rate. A 6 nm SiO2 film, for example, could be grown at 600u200a°C within 3 min at 900 Pa O3 atmosphere. The temperature dependence of the oxidation rate is relatively low, giving an activation energy for the parabolic rate constant of 0.32 eV. Furthermore, a 400u200a°C grown SiO2 film was found to have satisfactory electrical properties with a small interface trap density (5×1010u2009cm−2/eV) and large breakdown field (14 MV/cm).

Reactive oxygen beam generation system using pulsed laser evaporation of highly concentrated solid ozone

A reactive oxygen beam generation system is described for the formation of high-quality and high-precision films. This system utilizes pulsed laser evaporation of highly concentrated solidified ozone (O3). The equipment for safely generating and handling a large amount of high-purity liquid and solid O3 was also developed for this purpose. The beam is characterized by its high concentration of oxygen atoms in an excited state [O(1D)], constant flux per laser shot (4×1017u2009moleculesu200acm−2u200ashot−1), appropriate level of kinetic energy (KE) for enhancing the surface reaction (mean KE of 0.4 eV, maximum KE of 2 eV) and small angular spread (6°). These characteristics enabled us to precisely control the SiO2 film thickness by the number of laser shots, and achieve an enhanced Si oxidation rate and new local oxidation process.

Rapid Oxidation of Silicon Using UV-Light Irradiation in Low-Pressure, Highly Concentrated Ozone Gas below 300 °C

A low-temperature, damage-free process for growing ultrathin (<6 nm) silicon dioxide (SiO2) films was successfully developed. The excitation of low-pressure, highly concentrated O3 gas using photons with energies less than 5.6 eV led to rapid growth rates of 2 and 3 nm within 1 and 5 min, respectively, even when the process temperature was as low as 200 °C. The enhanced oxidation rate was due to an increased supply of O(1D) atoms at the Si surface. Transmission electron microscope images revealed that the SiO2 film formed with a uniform thickness and a smooth, distinct SiO2/Si interface. Capacitance–voltage and current–voltage measurements showed that 200 and 300 °C as-grown films had a satisfactorily low density of mobile ions and trap charges as well as ideal insulating properties.

Advantage of Highly Concentrated (≥90%) Ozone for Chemical Vapor Deposition SiO2 Grown under 200 °C Using Hexamethyldisilazane and Ultraviolet Light Excited Ozone

We have compared the UV-light-excited ozone chemical vapor deposition (CVD) process conditions and the film quality for the cases where either highly concentrated (≥90%: HC) or 7% ozone and either hexamethyldisilazane (HMDS) or tetraethoxysilane (TEOS) are used. The SiO2 film deposited using HMDS and UV-excited HC ozone with an optimized flow rate has the highest quality in terms of leakage current density, etching rate, and deposition rate which are comparable or superior to those of the conventional thermal TEOS SiO2 grown at 620 °C. These results lead to a conclusion that it is preferable to use HC ozone for UV-light-excited-ozone CVD to deposit the high quality SiO2 films at a practical rate at a temperature as low as 200 °C.

Improvement in Chemical-Vapor-Deposited-SiO2 Film Properties by Annealing with UV-Light-Excited Ozone

Ultraviolet-enhanced, highly concentrated (>90 vol %) ozone gas annealing was carried out at 200 °C to fabricate as-deposited tetraethoxysilane chemical vapor deposited SiO2 film (TEOS-CVD films) applicable as a gate dielectric material for thin-film transistors. As a result of this annealing, the leakage current density, fixed charge density, and dielectric constant of the films decreased to those of thermally grown silicon oxide. The relative dielectric constant, for example, was reduced from 5.4 to 4.0. The films resistance to wet-etching solution was also improved, particularly within the region located 3–5 nm from the films surface. In the region, the reduction in the amount of the excess positive charges of Si and the increase in the density of an ideal Si–O bonding network were confirmed from X-ray photoelectron spectroscopy measurements. These results suggest that oxygen atoms are incorporated into the film, while impurities contained in the film such as OH are out gassed by the diffusion of oxygen atoms generated from the photo dissociation of ozone in the gas phase. The annealing effects with and without oxygen atom supply were compared and the mechanism of the annealing is discussed.

Photochemical Reaction of Ozone and 1,1,1,3,3,3-Hexamethyldisilazane: Analysis of the Gas Reaction between Precursors in a Photochemical Vapor Deposition Process

The photochemical reaction of 1,1,1,3,3,3-hexamethyldisilazane (HMDS) and ozone (O3) in the gas phase was analyzed as the side reaction in the photochemical vapor deposition (photo-CVD) process irradiated by ultraviolet light: the analysis was conducted by Fourier-transform infrared absorption spectroscopy (FT-IR) and mass spectrometry (MS). The final products of this photochemical reaction between HMDS and O3 are CO2, N2, and H2O, although this reaction is initiated at the Si–N–Si bond of HMDS with O3 and ultraviolet (UV) light, thus producing, as a reaction intermediate, a compound with carbonyl and/or carboxylic group followed by Si–N–Si scission.

Rapid and Uniform SiO2 Film Growth on 4 inch Si Wafer Using 100%-O3 Gas

We have developed a lamp-heated cold-wall chamber that can process a large Si wafer using a highly concentrated (>90 vol.%) ozone gas to achieve rapid and uniform oxidation at a lower temperature than that used in conventional thermal oxidation. Uniform SiO2 formation with a film thickness uniformity of within 0.2 nm was achieved. The SiO2 growth rate, however, was not markedly accelerated compared with that achieved using conventional low (i.e., 10 vol.%)-concentration O3 gas. This was considered to originate from the decomposition of O3 gas in the gas phase before arriving at a heated surface as determined from the local ozone concentration measurements we performed. By increasing gas flow velocity so as to reduce the area of the thermal boundary layer on the heated surface in which decomposition of O3 to molecular oxygen is enhanced, SiO2 growth rate was actually improved.