Investigation of Acoustic Cavitation in Aqueous Surfactant Solutions for Cleaning Applications
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Investigation of Acoustic Cavitation in Aqueous Surfactant Solutions for Cleaning Applications Mingrui Zhao1, Anfal Alobeidli2, Xi Chen3, Petrie Yam3, Claudio Zanelli3, Sharyl Maraviov4, Mona Nagel5, Farhang Shadman1 and Manish Keswani2, * 1
Chemical and Environmental Engineering, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721, U.S.A. 2 Materials Science and Engineering, University of Arizona, 1235 E. James E. Rogers Way, Tucson, AZ 85721, U.S.A. 3 Onda Corporation, 1290 Hammerwood Ave, Sunnyvale, CA 94089, U.S.A. 4 PCT Systems Inc., 49000 Milmont Dr, Fremont, CA 94538, U.S.A. 5 Carl Zeiss, Carl-Zeiss-Strasse 22, 73447 Oberkochen, Germany. * Corresponding author, E-mail: [email protected]; Fax: +1-520-621-8059 ABSTRACT Surfactants are commonly used as additives in cleaning formulations during acoustic cleaning of semiconductor surfaces. Since surfactants are surface active, they can affect cavitation characteristics and, therefore, influence cleaning efficiency and damage to the surface. In this work, stable and transient cavitation pressures were characterized in Triton“ X-100 containing aqueous solutions subjected to single frequency and dual-frequency sound fields using acoustic emission measurements. The hydrophone based technique allowed quantitative measurements of the absolute pressure values from stable and transient cavitation fields. The ratio of stable cavitation pressure to transient cavitation pressure under different conditions indicated that surfactants can play an important role in reducing feature damage while maintaining particle removal efficiency. Damage studies conducted on aluminum coated glass samples further confirmed these results. INTRODUCTION With advances in semiconductor technology and continuous dimension shrinkage of transistors, acoustic cleaning has become increasingly important in integrated circuit (IC) industry for surface cleaning and preparation due to its high effectiveness and easy implementation [1-2]. Although effective particle removal can be achieved at high power density, it can also cause feature damage [3]. Both stable and transient cavitation and streaming contribute to cleaning, whereas damage is mainly caused by transient cavitation. Stable cavitation refers to oscillation of bubbles, which generates microstreaming. By contrast, transient cavitation is the growth and eventual collapse of bubbles that results in extremely high temperatures and pressures and formation of shock waves and microjets that damage the surface [4]. The relative extent of stable and transient cavitation is controlled by tuning of various sound field and solution variables including transducer operating frequency and power density, dissolved gases, solution temperature, and use of additives such as surfactants. Leong et al. demonstrated the growth of bubbles in solutions containing sodium dodecyl sulfate (SDS) [5]. In their study, a microscope combined with a camera was used to capture the
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