Nondestructive nanoparticle removal from sub-micron structures using megasonic cleaning
Ahmed A. Busnaina
Jin-Goo Park, Yung Joon Jung, Mehmet R. Dokmeci
Date of Award
Doctor of Philosophy
Department or Academic Unit
College of Engineering. Department of Mechanical and Industrial Engineering
engineering, mechanical, nanoparticle, megasonic
The removal of nanoparticles from patterned wafers is one of the main challenges facing the semiconductor industry. As the size of structures shrinks with each new generation of devices, it becomes more difficult to remove nanoscale particles. Nanostructures (specially, poly silicon lines) were found to be vulnerable to damage as a result of cavitation when megasocnic cleaning is utilized. Megasonics utilizes acoustic streaming to reduce the acoustic boundary layer and utilize the generated pulsating flow to remove nanoscale particle from trenches and other structures on the wafer. Although Megasonics is believed to be a solution for many of these cleaning challenges, it has been shown to cause severe damage to nanoscale device structures such as poly-silicon lines.
Nanoparticle removal from nano size silicon trenches was investigated using polystyrene latex (PSL) particles. Submicron and nano size trenches were fabricated in silicon. Removal of 100nm and 200nm PSL particles from the nano size trenches was achieved using megasonic cleaning. Results indicate that megasonic power has more influence on the particle removal efficiency than cleaning time specially for large trenches.
The cause of damage in megasonics cleaning was investigated. Our damage mechanism hypothesis is that cavitation damage does not occur at megasonic frequencies as shown by many over the last 3-4 decades but rather, secondary frequencies as low as 40 KHz exist in megasonic tanks with sufficiently high power to generate ultrasonic cavitation responsible for damage. Frequency and amplitude (power) measurements also show that traditional megasonic tank transducers generate many frequencies as low as 40 kHz at high amplitude (power). Elimination all of the low frequencies (using a narrow band transducer) demonstrated that damage does not occur even at high power once the low ultrasonic frequencies (with high amplitude) are eliminated. Effective damage free removal of nanoscale particles was demonstrated at high amplitude (power). This shows that damage in a traditional megasonic tank is the result of these low frequencies and that by eliminating these low frequencies (with high amplitude) damage can be eliminated without sacrificing effective cleaning.
Karimi, Pegah, "Non distructive nanoparticle removal from sub-micron structures using megasonic cleaning" (2009). Mechanical Engineering Dissertations. Paper 9. http://hdl.handle.net/2047/d20000671
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