Osamu Ishihara

Low ion energy electron cyclotron resonance etching of InP using a Cl2/N2 mixture

The low‐energy (about 30 eV) ion etching of InP with an excellent vertical sidewall profile, smooth surface, and a high etch rate (more than 1000 A/min) has been demonstrated in an electron cyclotron resonance plasma using a Cl2/N2 mixture. Surface analysis by x‐ray photoelectron spectroscopy and plasma diagnostics by optical emission spectroscopy suggest that the etching mechanism is dominated by the reduction of Cl neutral radical density by N2 dilution and the formation of InN and P3N5 due to the reaction between the atomic nitrogen in the Cl2/N2 plasma and the InP substrate. The success of this technique appears to be based on a new InP dry etching concept which controls the volatility of PClx (x=1–5) products, thus balancing the desorption rate of InClx (x=1–3) products, in contrast to the conventional reactive ion etching method which enhances the desorption of nonvolatile InClx products by high‐energy ion bombardment.

Analysis of Gate Lag in GaAs Metal-Semiconductor Field-Effect Transistor Using Light Illumination

We have developed a novel method for analyzing the gate lag effect in gallium arsenide (GaAs) metal-semiconductor field-effect transistor (MESFET) using light illumination. It is estimated that the density of trapped electrons at the surface of an active channel layer is above 6×1011 cm-2 from the dependence on photon flux density. Photon energy dependence shows that the electrons are mainly trapped at the GaAs surface. Angle-resolved analysis indicates that the trapped electrons at the active channel layer between the gate and the drain mostly account for the gate lag effect. Temperature dependence of the transconductance (g m) dispersion shows that the activation energy of this trap is 0.33 eV. Two-dimensional device simulation demonstrates the similar transient characteristics of the drain current, which originates from the electrons trapped at the GaAs surface.

Selective Epitaxial Growth of GaAs from the Liquid Phase

Selective epitaxial growth of GaAs from the liquid phase was investigated. The epitaxial layer was grown on a (100) plane of a GaAs substrate with Sn-melt. In order to improve wettability of the melt to the substrate surface, Ni film was deposited onto the substrate surface. The substrate was selectively etched by the melt-etching technique and the etched holes were refilled with the epitaxial material. It was found that the shapes of the etched holes and the growth layers depend on the orientation of the windows with regard to the substrate orientation. When the sides of the square windows are oriented parallel to the direction, the sides of the etched holes and those of the growth layers become (111) planes and the shape of the growth layers accurately follow the mask pattern.

Effect of shifter edge angle and lens aberration on the pattern profile in the edge-line phase-shift method

Origin of asymmetrical resist patterns, which had been observed in the edge-line phase shift lithography, has been investigated by simulations and experiments concerning the affects of shifter edge angle and stepper lens aberration. It has been found that the asymmetry of resist patterns has been caused by coma aberration of stepper projection lens and enhanced as the shifter width becomes narrower. Furthermore, the effect of shifter edge angle has been proved equivalent to the effect of narrowing the shifter width.

High Power, High Reliability p-n Junction GaAs IMPATT Diodes for J-Band

p-n junction GaAs IMPATT diodes with Hi-Lo structure were studied for high output power, high efficiency and high reliability. High output power over 10 W was obtained with average efficiency of 20% with good yield by optimizing the carrier profile and investigating multi-chips operation. The maximum output power and efficiency were 11 W at 5.7 GHz and 23.3% at 6.5 GHz, respectively. Median failure time over 106 h at 200°C was deduced by an activation energy of 1.85 eV in diodes metallized with Au–Ge by accelerated life tests.

Effect of lens aberration on resist pattern profiles in edge-line phase-shift method

In edge-line phase-shift lithography, asymmetrical resist patterns formed by both sides of shifter edges have been observed in the case of a narrow shifter. The effect of phase error, shifter width and shifter edge angle on resist pattern profiles has been investigated by simulations and experiments. It has been confirmed that the asymmetry of resist patterns is mainly due to the coma aberration of the stepper projection lens and is enhanced as the shifter width becomes narrower. The effect of decreasing the shifter edge angle has proved to be equivalent to the effect of narrowing the effective shifter width.