Minori Shirota

Formation of a submillimeter bubble from an orifice using pulsed acoustic pressure waves in gas phase

The mechanism of a bubble production method using pulsed acoustic pressure waves in gas phase is investigated using high-speed photography. The acoustic characteristics of the present bubble generator are also investigated. We found out the optimal acoustic waveform for producing only one bubble per one action; the bubble detachment radius is accurately controlled by first applying the positive onset-assistance acoustic pressure wave and then the negative detachment-assistance acoustic pressure wave with an accurately controlled time lapse. From an orifice with a radius of 0.09mm submerged in water, bubbles with radii in the range of 0.28–0.78mm with an extremely small standard deviation of less than 1μm are obtained. The shrinking and pinch-off motions of a capillary bridge connecting the bubble and orifice at the time of bubble detachment are observed in detail. The balancing force on a growing bubble, which is based on a spherical bubble formation model is also estimated. As a result, we reveal that wh...

Resist Stripping and Surface Cleaning Technique Using High Speed Steam-Droplet Mixture

A novel resist stripping and surface cleaning technique is proposed. We have improved wet vapor resist stripping technique (Ojima & Ohmi) using high-speed steam and purified water droplets mixture. Relatively low pressure steam (0.1MPa∼0.2MPa) is mixed with purified water in front of the nozzle, and sprayed to Si wafer with resist. Using this new technique, we are able to strip resist without chemicals very quickly and also to clean a wafer surface, i.e., to eliminate some particles. This technique has an advantage not only in reducing some processes of semiconductor manufacturing but also in maintaining chemical-free environment. Both droplet velocity and diameter distributions were measured by Phase Doppler Anemometer (PDA). Resist stripping was observed with a high-speed video camera and the fringes of the removed resist region were observed with a digital microscope. Mechanism of this resist stripping process is discussed.Copyright