Takashi Mashiko

Parametric Study on the Physical Action of Steam--Water Mixture Jet: Removal of Photoresist Film from Silicon Wafer Surfaces

We performed experiments to elucidate the physical action of a steam–water mixture jet, which we have proposed as a promising, environmentally friendly tool for cleaning surfaces. Photoresist-coated silicon wafers were adopted as the target and the jet performance of resist removal was evaluated, with several parameters being varied. We found that the resist-removal performance improves as the thickness or the mechanical strength of the resist film decreases, resist–wafer adhesivity decreases, or jet duration increases. The results imply that the essential part of the resist removal by the jet is a physical process including peel-off, in contrast to the established techniques such as the batch cleaning method utilizing chemical reactions. The results also indicate that the physical impact of the jet can be controlled, which will be a significant advantage in applying the jet as a cleaning technique.

The Flip-Side of Academic English (AE)

While we reported positive changes in class atmosphere in “Flipping Out in Japan” at iA2017 in Iasi, Romania, questions regarding empirical evidence of language improvement were lacking. Also, the control and experimental groups were not adequately demarcated. Our evaluations were subjective and impressionistic. With the addition of a third partner who advised a final testing protocol, we hope to address both of these criticisms with replicable test results. In this article, we re-examine our premises and the goals of our research. The “flipped classroom,” or experiential learning, is all about context, and because both control and experimental groups did well last year in the class with a decidedly improved atmosphere, we decided this year to maintain the “flipped” format for both groups. With the enhancements of a senior student “mentor” and visitors to the experimental group, and two native English speakers teaching the control group, we are relying on a series of quizzes structured on the relevant material in each module of the class, with the final exam based on those quizzes, to provide robust empirical data which will convince peers of the approach’s utility.

Thermal Convection of a Phase-Changing Fluid

To investigate the effect of phase transitions of the fluid on thermal convection, we are conducting experiments of thermal convection of the mixture of a thermosensitive gel and water. The gel absorbs water and swells below a certain critical temperature, while it discharges water and contracts above the critical temperature. The swelling ratio, as well as the critical temperature, can be controlled, which enables us to investigate the effect of phase transition in a series of experiments, where the critical temperature is set between the top and bottom boundary temperatures and the swelling ratio is systematically changed. In flow visualization, we have observed temporally stable and spatially fixed low-velocity regions which are surrounded by distinct high-velocity regions. Such a phenomenon is not observed in thermal convection of a single-phase fluid like water or air, and peculiar to the phase-changing fluid. Also, we have measured the rheological properties of the fluid and found, for example, the shear-thinning behavior, with which we try to explain the observed convection behaviors.

Measurement of Adhesion Force of Resist to Wafer by Using SAICAS: Characteristics of Lift-Off of Resist by Steam-Water Mixed Spray

We performed two experiments on resist-coated wafers. In the measurement of the resist-wafer adhesivity, we confirmed that it is significantly increased by an HMDS layer in between. In the resist-removal experiment using steam-water mixed spray, we found that the area of resist removal is limited within the area of spray application if HMDS is used, otherwise the former can be larger than the latter. These results suggest that the resist removal from a wafer surface by steam-water mixed spray is essentially a peel-off process.

Order Estimation of Physical Processes in Dynamics of Steam-Water Mixed Spray Cleaning Technique

We have been developing an innovative ultra-low environmental load cleaning technique by the use of steam-water mixed spray. We showed that this technique is quite effective in both cleaning and photo-resist stripping. We also found that the physical force associated with steam-water mixed spray is greater than that with air-water mixed spray; hence we proposed that the condensation plays an important role in this cleaning technique. In order to discuss further this mechanism, we perform the order estimation of physical processes in dynamics of liquid droplet moving in vapor flow impacting on a solid interface in this study. Results show that droplet impact velocity can be reduced while the droplet approaches to the solid surface. However, the vapor in the gap can condensate to either the liquid droplet or the solid surface with the velocity whose order of magnitude cannot be negligible compared to the impact velocity; hence the amount of vapor that should be pushed out from gap can be drastically reduced, This condensation results in the significant reduction of viscous force. This reduction of force with the existence of condensation reduces the impact velocity deceleration. Consequently significantly large impact pressure is generated.