Ichiro Nakamichi

Low-temperature oxidation of silicon in dry O2 ambient by UV-irradiation

The mechanism of thermal oxidation of silicon in dry O2 ambient with UV-irradiation has been discussed. The dependence of SiO2 thickness on oxidation time follows the model proposed by Cabrera and Mott for relatively short oxidation time. Such dependence follows the model by Deal and Grove for longer time. The main oxidizing species is ozone (O3) or some other reactive species generated from O3 at lower temperatures and this gradually changes to O2 with an increase in temperature. The SiO2 film formed at 500°C for 1 h by the present technique has a similar quality to that of SiO2 formed at high temperatures in dry O2 ambient, as evaluated from Fourier Transform-Infrared (FT-IR), Auger Electron Spectroscopy (AES) and Capacitance-Voltage (C-V) characteristics.

Low-Temperature Thermal Oxidation of Silicon in N2O by UV-Irradiation

A new thermal oxidation method using UV-irradiation has been proposed. Silicon dioxide of 3.5–4.0 nm thickness can be formed in 0.5 h at 200–500°C under N2O flow with UV-irradiation. Oxide formed by the present method is determined to be silicon dioxide. The fixed charge density at the Si/SiO2 interface is relatively low for 500°C oxidation. It is estimated to be about 2×1011 cm-2 without any thermal annealing.

The enhanced diffusion of low-concentration phosphorus, arsenic and boron in silicon during IR-heating

The diffusion of P, As and B in silicon during IR-heating has been investigated quantitatively under low-concentration conditions. A spin-on source was used for the diffusion of the dopants. The diffusion coefficient was determined by fitting the measured concentration profile to the complementary error function. Enhanced diffusion was obtained for these three impurities. The degree of the enhancement became larger in the order of As, P and B. The cause of the enhancement was found to be the generation of excess self-interstitials during IR-heating.

The Diffusion of Bismuth in Silicon

The diffusion of bismuth into silicon from a spin-on source has been investigated at a temperature range of 1050–1200°C. The concentration profile of bismuth agrees with the complementary error function, and its diffusion coefficient shows a value similar to the values of phosphorus and boron. Its activation energy is estimated to be 2.50 eV. That is much smaller than the values of phosphorus, boron and arsenic.

Enhanced thermal oxidation of silicon by UV-irradiation

Silicon can be thermally oxidized at low temperatures under dry O2 or N2O flow with UV-irradiation. The oxide thickness is about 9.0 nm in 4 h at 500°C on dry O2+UV oxidation. The oxide formed by dry O2+UV is thicker than that formed by N2O+UV at a relatively long oxidation time. The main oxidation species are ozone for dry O2+UV and excited-state 1D oxygen atoms for N2O+UV. The quality of oxide film formed by dry O2+UV is equal to that formed by common oxidation in dry O2 without UV.

Oxidation-Retarded Diffusion of Bismuth in Silicon

The effect of thermal oxidation of silicon on the diffusion of bismuth in silicon has been investigated quantitatively. The diffusion coefficients of bismuth during drive-in are determined by adopting the best-fitted parameters in the numerical simulation of the experiments. The diffusion of bismuth is retarded by the thermal oxidation of silicon. The degree of retardation is less than that of antimony. The oxidation time dependence of the retardation is more marked than that of antimony. These contradictions suggest that the diffusion mechanism of bismuth in silicon may not be a simple dual mechanism.

Enhanced thermal oxidation of silicon in steam ambient by UV-irradiation

Thermal oxidation of silicon can be markedly enhanced by UV-irradiation in steam ambient. The typical thickness of the oxide is about 65 nm at 500°C for 90 min. This value is nearly equal to that of usual oxidation in dry O2 at 1000°C, and is much thicker than those produced by other oxidation techniques at relatively low temperatures, such as by dry O2+UV and using oxygen plasma. The characteristics of the oxide films obtained by the present technique are similar to those of usual dry O2 oxidation performed at high temperatures.

Enhanced-Nitridation of Silicon by UV-Irradiation

Silicon can be directly nitrided at relatively low temperature under NH3 flow with UV-irradiation from a low-pressure mercury lamp. The typical thickness of film is 6.2 nm for nitridation of 1 h at 800°C. The thickness is saturated with an increase in nitridation time. The Auger electron intensity of nitrogen is about two times larger than that of oxygen at the surface of the film. The apparent peak of IR absorption by the Si-N bond is seen at a wave number of 835 cm-1.

The Effect of Thermal Oxidation of Silicon on Boron Diffusion in Extrinsic Conditions

Boron diffusion during extrinsic conditions in silicon has been investigated under both oxidizing and inert atmospheres for different temperatures (950–1100°C) and times. Oxidation-enhanced diffusion (OED) was found. This result is opposite to the oxidation-retarded diffusion of arsenic case.

The enhanced and suppressed electroless plating of copper by UV-irradiation

The effect of irradiation of ultraviolet (UV) light from a low pressure mercury lamp on the copper electroless plating process has been investigated. Both enhancement of the plating rate and the opposite effect of suppression are obtained. It is possible to make copper film pattern by these effects with resolving power of 50 µm.