Burdick sheets - Hydrodynamics of Micron-Scale Particle...

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Hydrodynamics of Micron-Scale Particle Removal from Surfaces Gretchen Burdick Arizona State University Department of Chemical and Materials Engineering Tempe, AZ 85287
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Particles and Semiconductor Device Manufacturing » Cleanliness crucial to device fabrication • Uniform electrical characteristics • High reliability » Particulate contamination an ever-present problem • Produces killer defects in device and interconnect structures • Results in high losses » Chemical mechanical polishing (CMP) a major source of particulate contamination » Cleaning process must • Remove all particles, including particles less than 1 micron in diameter • Not roughen wafer surface excessively » Brush scrubbing and megasonic cleaning have potential for removing small particles » Cleaning processes have problems with • Resource consumption • Lack of understanding of cleaning mechanism • Inefficient and unreliable processes
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Hydrodynamic Removal Model – Objective z x Surface Particle Flow characteristics Adhesion model prediction Removal mechanism Re pc (X) Predict particle removal Re p (Flow) Assess mechanism(s) of micron-scale particle removal from surfaces using a critical particle Reynolds number approach
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Adhesion Model Predicts van der Waals interactions for particles on surfaces Couples computer simulation with adhesion model Accounts for particle and surface: composition, geometry, morphology, and deformation 0 0.01 0.02 0.03 0.04 0.05 0.06 116 146 176 206 236 266 296 Removal Force (nN) Frequency of Occurence Average Observed Force = 176 nN Range of Observed Force = 139 - 201 nN 0 50 100 150 200 250 300 350 0 2 4 6 8 10 12 Particle Radius ( m m) Removal Force (nN) Experimental Data (average of 50 measurements) Model Predictions (average of 5000 predictions) s + s Removal Force = Adhesion Force PSL spheres in contact with a silicon substrate DI H 2 O 3 m m alumina particle (contact radius = 350 nm) in contact with a silicon substrate in DI H 2 O Cooper. Ph.D. Thesis, Arizona State University (2000).
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Relevant Forces μ ρ = p p V d Re Lever arms are functions of geometry, morphology, and deformation Rolling Removal Criterion F A = Adhesion force F L = Lift force M D = External moment of surface stresses F D = Drag force = Points around which rolling can occur 2 A 2 L 1 D D l F l F l F M + + p D Re d M p p D Re ) 1 (Re F < p 2 d L Re dz du d F Horizontal lever arm Vertical lever arm d F A F L M D Particle α F D 2a Surface δ l z x V p l 1 l 2
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Assessing Particle Removal At a given flow condition » Removal occurs when Re p (Flow) Re pc (Rolling) » Ideal system of smooth, deformable spherical particles of identical radius adhering to a smooth, flat, deformable surface Single adhesion force Single value of Re pc All or none of the adhering particles should be removed » Real system of deformable particles with non-uniformly distributed roughness and a finite size distribution adhering to a
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Burdick sheets - Hydrodynamics of Micron-Scale Particle...

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