Yoshito Jin

Using electron cyclotron resonance sputtering in the deposition of ultrathin Al2O3 gate dielectrics

The gate-dielectric characteristics of an ultrathin Al2O3 film deposited by electron cyclotron resonance sputtering are investigated. The sputtering process is classified as operating in either of two deposition modes: a metal mode and an oxide mode. Characteristics of the deposited films, such as their surface morphology, uniformity of thickness, and degrees of interlayer-oxide formation, are presented for both modes. The electrical characteristics of metal-mode Al2O3 films after annealing in a high vacuum (around 10−4 Pa) are looked at in detail. The metal-mode condition and high-vacuum annealing prevents the formation of interlayer oxide and reduces the flat-band voltage (VFB) shift but also produces a rather large capacitance–voltage (C–V) hysteresis loop. A small equivalent oxide thickness of 1 nm, low values for leakage current of around 2×10−3 A/cm2, and a fixed negative-charge density of 7×1010 cm−2 are demonstrated for the metal-mode films. The large C–V hysteresis loop is reducible by oxidation.

Anisotropic Etching of Si and WSiN Using ECR Plasma of SF6–CF4 Gas Mixture

The characteristics of Si etching with electron cyclotron resonance (ECR) plasma of SF6–CF4 are studied in order to improve anisotropy in dry etching using fluoride gases. Si undercutting is decreased by increasing the amount of CF4. Si patterns with vertical sidewalls are obtained with an etch rate of 40 nm/min. Oxygen addition to SF6–CF4 increases Si/SiO2 etching selectivity to more than 10, but does not cause any undercutting. It is concluded that carbon (C) that decomposes from CF4 protects the pattern sidewall from undercutting by fluorine radicals. These results are applied to the anisotropic etching of WSiN as the gate material for GaAs metal-semiconductor field effect transistors (MESFETs). WSiN patterns are more vertical when the chamber inner wall exposed to SF6–CF4 ECR plasma is stainless steel rather than quartz. This is attributed to the reduction of the amount of CO, which possibly forms volatile tungsten-carbonyl [W(CO)6] and, along with fluorine radicals, causes undercutting. It is confirmed that the stainless steel inner wall does not cause serious wafer contamination by metallic elements when WSiN patterns are almost vertically etched.

Generation of Electron Cyclotron Resonance Neutral Stream and Its Application to Si Etching

A low-energy (10–20 eV) neutral stream generated by charge exchange reactions in an electron cyclotron resonance (ECR) plasma stream is extracted by eliminating charged particles and used for Si etching. The formation of a cusp magnetic field over the substrate eliminates charged particles because electrons are led outside the substrate by the magnetic field. In addition, residual ions are repelled by a positive voltage supplied to the substrate, and it becomes possible to irradiate the etching samples with only the neutral stream. The etch rate for Si is about 100 A/min with a gaseous mixture of Cl2 and a small amount of SF6, and a microwave power of 400 W. We confirm that neutral stream etching allows us to attain anisotropic etching shapes without distortion, and that it can be used for delineating fine patterns.

Low-Temperature Silicon Oxidation with Very Small Activation Energy and High-Quality Interface by Electron Cyclotron Resonance Plasma Stream Irradiation

Oxidation using electron cyclotron resonance (ECR) plasma stream provides a large silicon dioxide growth rate at the initial growth stage (>6 nm/min), a very small activation energy of 0.02 eV for oxidation, and a high-quality interface with interface trap density of 3×1010 cm-2·eV-1. The plasma stream was extracted by a divergent magnetic field from the ECR region and irradiated on a single-crystalline silicon substrate with ion energies of 10–30 eV. The high-quality interface was obtained by oxidation without substrate heating and only postoxidation annealing at 400°C in hydrogen ambient.

Characterization of Metal Insulator Metal Electrical Properties of Electron Cyclotron Resonance Plasma Deposited Ta2O5

The electrical properties of tantalum pentaoxide (Ta2O5) films deposited by an electron cyclotron resonance (ECR) plasma sputtering have been investigated using metal–insulator–metal (MIM) capacitor structures. The deposition conditions of Ta2O5 films and the bottom electrode materials of the MIM have been examined from the point of view of both the low leakage current and the high capacitance. On the TiN bottom electrode, additional postdeposition plasma irradiation on the first thin Ta2O5 layer was effective in ensuring a high breakdown strength of the MIM, because of the stabilization of the interlayer between the Ta2O5 film and the TiN bottom electrode film. However, the MIM using a Ru bottom electrode, which shows the characteristics of conductive films even for oxides, showed the high breakdown characteristics of approximately 4.5 MV/cm for as-deposited Ta2O5 in metal-mode deposition in ECR sputtering. In both cases, the dielectric constant of Ta2O5 was approximately 25, so that a high capacitance of approximately 3 fF/µm2 was for frequencies of up to 1 MHz for a MIM with a Ru bottom electrode and 20-nm-thick Ta2O5 film.

Electron-cyclotron-resonance sputtering apparatus for multilayered optical bandpass filters applicable to wavelength division multiplexing

A new apparatus for fabricating narrow-bandpass multilayer filters applicable to wavelength-division multiplexing and the development of this apparatus are described. Electron-cyclotron-resonance (ECR) sputtering with two plasma sources is used in the apparatus. The plasma is produced from a mixture of Ar and O2 gas and, with a metallic target, generates stable “metal-mode” deposition. That is, the target is sputtered in a metallic state, and this is followed by oxide-film formation, which is enhanced by exposure of the substrate to the ECR plasma. SiO2 and Ta2O5 films formed by ECR sputter-deposition in metal-mode are suitable for optical multilayer filters because this form of deposition provides surface smoothness, low loss, and stability of refractive index. Uniformity of deposition is good, with variations in thickness over a 200mm diameter within ±0.43% for SiO2 and ±0.27% for Ta2O5. The refractive indices of the SiO2 and Ta2O5 films are 1.46 and 2.10 at a wavelength of 1550nm. Surfaces are very smo...

Reduction of effective dielectric constant of gate insulator by low-resistivity electrodes

On metal–oxide–semiconductor capacitors, the effective dielectric constant (keff) values extracted from high-frequency capacitance–voltage measurements were found to decrease when gate electrodes of very low resistivity were used. The equivalent-oxide thickness increase reaches about 1 nm with the low-resistivity electrodes. We examined gate insulators of SiO2, Al2O3, and HfO2 and gate electrodes of Al, TiN, Au, Cr, and TaN. The equivalent-oxide thickness increase can be prevented by inserting a high-resistivity metal film only 0.3 nm thick between the very low-resistivity metal and the insulator. The present results suggest that keff is reduced by the screening of ionic insulators with free electrons of the metal due to a quantum effect.

Atomic Layer Epitaxy of GaAs Using GaCl3 and AsH3

It was demonstrated that the atomic layer epitaxy (ALE) of GaAs could be performed by using GaCl3/H2 and AsH3/H2. The GaCl3 is a powder at room temperature and can be supplied from outside the reactor, and is essentially carbon free. The ALE growth temperature was from 200°C to 500°C. The growth temperature of 200°C is the lowest ever reported in GaAs ALE. The fact that the ALE was performed at 200°C indicates that Ga was supplied as GaCl3, suggesting the possibility of AlGaAs ALE using AlCl3, GaCl3 and AsH3.

Neutral Stream Extraction from Electron Cyclotron Resonance Plasma by Using Parallel Magnetic Field

A low-energy neutral stream is generated by charge exchange reactions between the accelerated ions in an electron cyclotron resonance plasma stream and the background molecules and atoms. This stream is extracted using a parallel magnetic field to eliminate charged particles. Etched Si profiles demonstrate that this neutral stream has high directionality.

Vapor Phase Epitaxy of AlGaAs by Direct Reaction between AlCl3, GaCl3 and AsH3/H2

AlAs and AlGaAs were successfully grown by a directly reacting of AlCl3, GaCl3 and AsH3 for the first time. The AlCl3 and GaCl3 were contained in stainless steel evaporators (60°C–120°C), and supplied by He carrier gas. The AsH3 (10% in H2) was supplied directly to the deposition zone by H2 carrier gas during the growth. The AlAs layers could be grown in the temperature range from 550°C–700°C, and a maximum growth rate of 3.5 µm/h was obtained. The AlGaAs was grown at 600°C, with a typical growth rate of about 2 µm/h. The Al content was controlled in the entire composition range but was not linearly proportional to the Al content in the supplied gas. These results suggest the possibility of new carbon-free gas sources for the chemical beam epitaxy (CBE) and atomic layer epitaxy (ALE).