Observation of Water-Droplet Impacts with Velocities ofO(10 m/s) and Subsequent Flow Field

Abstract

A two-fluid spray cleaning technique has been gaining popularity as a cleaning process in the semiconductor industry. The most essential physical process in this technique is the impact of droplets with a velocity of O(10 m/s) on a solid surface. This study aims to experimentally and numerically investigate water-droplet impacts with velocities of up to 50 m/s and their subsequent flow fields, especially the gas flow field in the strictly limited area in the vicinity of the contact line. First, we experimentally evaluated the velocity of the splash and numerically calculated the gas velocities. Comparison of these velocities supported our assumption that the maximum gas velocity may be on approximately the same order as the velocity of the splash. Therefore, we concluded that the gas velocity field of the order of 500 m/s indeed develops at the impact of droplet with a velocity of the order of 50 m/s. Moreover, we determined that the gas pressure was of the order of 1.0 MPa by numerical analysis. Such a high pressure leads to shock wave propagation, which can contribute to the cleaning process in semiconductor production. To manufacture semiconductors, cleaning techniques that use physical action, such as megasonic agitation, are generally employed 1 together with those using chemical action to enhance the cleaning efficiency. A deionized water/gas-mixture jet spray cleaning technique, in other words, a two-fluid spray cleaning technique, is also gaining popularity.1-4 The advantage of this technique over megasonic agitation is the magnitude of the physical action generated by a highspeed droplet impacting a solid surface. However, most cleaning techniques that use physical action tend to cause structural damage and pattern collapse; therefore, the particle removal force should be quantitatively understood and measured. 5,6 The development of advanced spray technology offers the possibility of preventing this damage by controlling both the sizes and velocities of the droplets with extremely high accuracy. 7,8 It should be emphasized here that the most essential physical process in this two-fluid spray cleaning technique is the droplet impact upon the solid surface with a velocity of several tens of meters per second. Until recently, the velocities of liquid droplets in most experimental studies on liquid-droplet impacts were restricted to the range of several meters per second, 9-11 mainly due to the difficulties associated with high-speed observation. On the other hand, Mehdizadeh et al., 12 Pan et al., 13 and Visser et al. 14 reported on experimental studies that utilized droplet impacts at velocities of the order of 10 m/s. Mehdizadeh et al.12 observed the impacts of water droplets with radii of about 1 mm on stainless steel surface mounted on the end of a rotating arm whose linear velocities of up to 50 m/s. They measured the number of fingers and maximum diameter of the droplet after spreading. Pan et al. 13 observed the collision between a solid plate and a droplet with a radius of about 0.5 mm and a speed...

Effect of wall surface wettability on collective behavior of hydrogen microbubbles rising along a wall

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Pressure generated at the instant of impact between a liquid droplet and solid surface

“…We numerically investigated the liquid droplet impact pressure rise on a solid surface. We analysed the pressure generation at droplet impact by solving the two-dimensional axisymmetric compressible Euler equations [22,50]. To close the Euler equations, we implemented the stiffened-gas equation of state (2.8) in our numerical analysis; hence, we compare the pressure rise due to the liquid droplet impact obtained by numerical analysis with the stiffened-gas pressure rise Δ P sg (2.10).…”

“…Impact velocity V was set to 100 m s −1 because this order of magnitude of impact velocity can be typically observed in cleaning technologies for semiconductor device processes [23,50,58,59], in single water droplet impact experiments [11,60,61] and in numerical simulations of liquid droplet impact [9,26]. Note that the difference between c 0 and s is hardly noticeable if the value of V is much smaller, and the stiffened-gas equation of state (2.8) is not applicable if the value of V is much larger.…”

A phenomenological analysis of droplet shock-induced cavitation using a multiphase modeling approach

“…Shock-induced cavitation within a droplet, upon impact or interaction with a shock wave, occurs in wide range of applications, as a desired or adverse effect, ranging from raindrop impact on aircraft, 6 to combustion and detonation of multiphase mixtures, 7 through ink-jet printing or liquid jet-based physical cleaning, 8,9 to name but a few. The comprehension of the bubble dynamics within the droplet is thus of major importance to evaluate the erosion efficiency of the bubblecompounded droplet, related to the collapse and jetting processes of the cavitation bubbles.…”