Hideyuki Noda

SR-stimulated etching and OMVPE growth for semiconductor nanostructure fabrication

Abstract Synchrotron radiation- (SR-)stimulated etching and selective area growth by organometallic vapor phase epitaxy were performed to form an ordered array of InP crystals on SiO 2 -patterned InP (001) substrate. The SR-stimulated etching was used to pattern the SiO 2 film, because photochemical reaction using SR was expected to provide smooth surfaces, vertical side walls and fine patterning. In the first place, we investigated the basic properties of the SR-stimulated etching by using a mm-size pattern of SiO 2 mask. The etched depth was observed to increase linearly with the irradiation dose. It was found that the etching depth was controlled very accurately. Next, we used μm-size patterns of SiO 2 masks for fabricating the ordered array of InP crystals. In a atomic force microscope image of the sample after etching, a steep side wall was observed. However, the etched surface was not smooth, contrary to our expectation. Moreover, some dust were observed on the surface. From this dust it was found that the SR-stimulated etching had a resolution of ≤100 nm at most.

Water-based high-volume stress-free ultra-thin powder-chip method

We propose fabrication and subsequent packaging processes for ultra-small and ultra-thin (75×75×7.5 µm) radio frequency identification (RFID)-chips (called “RFID powder chips”). To fabricate a chip with no chipping and micro-cracks and to increase the chip yield per wafer, self-etch-stop thinning and 5-µm narrow dicing were performed using anisotropic dry etching in a SOI-wafer based process. Consequently, a damage-less 7.5-µm-thick RFID powder chip with an Au-coated double-surface electrode structure was obtained. The structure of the surface electrodes has the advantage that, when mounting the powder chip on an external antenna film for the packaging process, the chips are just placed in a relatively large electric-contact area on the antenna without the need for highly accurate positioning, orientation, and side surface controls. A technological issue for the packaging process is how to handle the powder chip. Because the chips not only form aggregated structures from electrostatic and van der Waals forces in a dry environment, but also are mechanically brittle, the conventional pick-up technique is unfeasible. Accordingly, we have developed a new water-based, stress-free chip handling technique. In this technique, the chips are kept dispersed by liquid stirring, and only a single chip is captured and manipulated using a micropipette. The water-based chip capturing process strongly depends on dispersion and mobility controls of the chips. Yield rates for various liquid solutions and stirring speeds were investigated. Addition of 0.5% non-ionic surfactant to the powder chip stock solutions effectively prevented chips from sticking together. Also, high capture rates above 90% were obtained with stirring speeds ranging from 1000 to 1200 rpm. The positioning accuracy of the chip placing process was also investigated. Using robotic actuators with repeatable positioning accuracies of above +/− 50 µm in chip manipulation, a 100% success rate was obtained in the case of the square placing-area of 300 µm. During pick-up and place operation, no chip breakage was observed.

Hydrogen Diffusion and Chemical Reactivity with Water on Nearly Ideally H-terminated Si(100) Surface

A nearly ideally H-terminated condition for a Si(100) 2×1 surface is determined from the dependence of the peak intensity and the linewidth of the coupled monohydride symmetric stretching vibration on the hydrogen exposure and exposure temperature, which has been investigated with infrared reflection absorption spectroscopy (IRRAS) using CoSi2 buried metal layer substrate. Even for nearly ideally H-terminated surfaces, the linewidth significantly changes depending on the hydrogen exposure and the exposure temperature. The concentration of deuterium atoms incorporated in the Si bulk is measured by temperature programmed desorption, and it is concluded that hydrogen diffusion into the subsurface of Si has a significant influence on the linewidth broadening. The chemical reactivity with water on the H-terminated Si surface is also investigated.

Attomol-level ATP bioluminometer for detecting single bacterium: ATP calibration curve is linear from 0 to 5 amol

We have developed an automated high-sensitive ATP bioluminometer for detecting single bacterium. The apparatus consists of a tube rack for setting reagents and samples, two washing baths for preventing sample carry-over from dispenser nozzle, and x-, y-, z- actuators for moving the dispenser, and an high-sensitive optical system. The reaction tube was selected to reduce the background signal intensities for the ATP bioluminescence measurement. The background signal intensity of the reaction tube was 18 RLU, which is almost the same as the dark counts of the photomultiplier (16 RLU). The ATP calibration curve was linear from 0 to 5 amol (its slope = 22.4 RLU/amol and 3.3 SD of the blank sample signal = 17.9 RLU), and the detection limit of 0.8 amol was obtained. The relationship between intracellular ATP and CFU in Escherichia coli (ATCC25922) was kept linearity from 0 to 20 CFU, and the intracellular ATP (amol) per CFU was calculated to be 3.3 amol/CFU (R2 = 0.9713). Moreover, the relationship between intracellular ATP and CFU in Staphylococcus aureus (ATCC25923) was also kept linearity from 0 to 30 CFU, and the amol/CFU was calculated to be 1.6 amol/CFU (R2 = 0.9847). The automated ATP bioluminometer has ultra-high sensitivity and will be a powerful tool for measuring ATP luminescence derived from small number of bacteria.

DNA hybridization feature on “Bead-array” — DNA probes on beads arrayed in a capillary

We present a DNA analysis platform named “Bead-array”, where 100-μm-diameter beads are lined with determined order in a capillary, and its hybridization detection features. Model hybridization experiments revealed that as little as 1 amol of fluorescent-labeled oligo DNA was detected and hybridization reaction was completed in one minute irrespective of the amount of target DNA. When the number of target molecules was smaller than that of the probe molecules on the bead, 10 fmol, almost all targets were captured on the bead. “Bead-array” enables reliable and reproducible measurement of the target quantity. This rapid and sensitive platform is very promising for various genetic testing tasks.