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We report nanometer-sized silicon (Si) crystallites prepared by excimer laser ablation in constant pressure inert gas ambient. Size distribution of the Si ultrafine particles depends on the pressure of inert gas ambients. The relation between the average size and the ambient pressure can be explained by an inertia fluid model. It is verified that the size of the Si ultrafine particles is ∼3 nm and greater in diameter. Furthermore, crystallinity of the nanoscale ultrafine particles is crystalline similar to that of bulk Si.

Thick (20–30 µm) layers of highly pure GaN with device-quality smooth as-grown surfaces were prepared on freestanding GaN substrates by using our advanced hydride-vapor-phase epitaxy (HVPE) system. Removal of quartz parts from the HVPE system markedly reduced concentrations of residual impurities to below the limits of detection by secondary-ion mass spectrometry. Appropriate gas-flow management in the HVPE system realized device-quality, smooth, as-grown surfaces with an excellent uniformity of thickness. The undoped GaN layer showed insulating properties. By Si doping, the electron concentration could be controlled over a wide range, down to 2 × 1014 cm−3, with a maximum mobility of 1150 cm2·V−1·s−1. The concentration of residual deep levels in lightly Si-doped layers was in the 1014 cm−3 range or less throughout the entire 2-in. wafer surface. These achievements clearly demonstrate the potential of HVPE as a tool for epitaxial growth of power-device structures.

Optical properties of silicon (Si) nanocrystallites prepared by excimer laser ablation in constant-pressure inert gas have been studied in relation to the particle size. Visible photoluminescence (PL) bands in the red and green spectral regions appear at room temperature after an oxidation process. The red PL band is independent of the particle size and is stable without degradation by excitation light irradiation. It is concluded that the red PL is emitted from the surface states of the oxidized Si nanocrystallites. In contrast, the green PL band depends on the particle size. The green PL intensity decreases during excitation light irradiation in air, and then recovers in the subsequent vacuum evacuation. These results suggest that the origin of the green PL is associated with a quantum confinement effect of Si nanocrystallites.

The 193nm photoresist (ArF resist) degradation mechanism in dielectric etching was investigated by using an ultra-high-frequency electron-cyclotron-resonance plasma. This investigation focused on via-hole etching. It was found that the bottom-antireflection coating (BARC) etching condition is a critical factor in the reduction of striation and pitting after via-hole etching. X-ray photoelectron spectroscopy and scanning electron spectroscopy studies revealed that argon-less and low-incident-ion-energy conditions in BARC etching can keep the resist surface smooth and maintain a carbon-rich micromask-less state because decomposition of the C–H or OC–O bonds is suppressed. As a result, resist damage after via-hole etching is reduced remarkably. Furthermore, in the via-hole etching, it was also found that the characteristics of the fluorocarbon polymer, i.e., deposition rate and flourine-to-carbon ratio of the fluorocarbon polymer, stacked on the resist surface during etching strongly affect the ArF resist degradation. Low-sticking-coefficient radicals such as CF2 and a low amount of deposition thickness are suitable for damage-less etching. In regard to the formation of striations at the pattern corner, the sputtering effect was taken into consideration. As a result, in the case of via-hole etching, line-edge-roughness in the trench pattern was improved by about 50%, and a striation-less and pitting-less hole etched profile was obtained by using either an argon-and-xenon (20%) mixture as a dilution gas or a fluorocarbon gas at low flow rate under low gas pressure.

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In vertical devices containing GaN homoepitaxial layers on free-standing GaN substrates, damageless trench fabrication is a key issue in device processes. We used a free-standing GaN substrate with a dislocation density of 10 6 cm %2 and applied pulsed photo-electrochemical (PEC) etching to a homoepitaxially grown n % -GaN layer. Although the reported results of GaN-on-sapphire show poor etching uniformity caused by the high dislocation density in the range of 10 8 to 10 9 cm %2 , the etched surface of GaN-on-GaN obtained by pulsed PEC etching was almost flat at a low etching voltage. The photoluminescence intensity indicated that the etched surface does not have etching damage. Furthermore, we successfully obtained wet-etched mesa diodes with a high breakdown voltage of more than 3 kV and a high yield. These results indicate the applicability of pulsed PEC etching to the damageless trench fabrication of vertical GaN power devices using low-dislocation-density GaN substrates.