Ahmed A. Busnaina

Wall deposition of aerosol particles in a turbulent channel flow

Abstract Motion of small suspended particles in a turbulent channel flow is studied. The mean flow field is simulated using a two-equation κ-e turbulence model. Trajectories of aerosol particles in the channel are evaluated by solving the corresponding Lagrangian equation of motion, which includes the effects of Brownian motion and turbulence fluctuations. Simulations are carried out for aerosol particles (of various sizes) released at different locations across the channel. Depositions of particles on the channel wall for several flow Reynolds numbers and different inlet turbulence intensity are evaluated. The results show that turbulence fluctuations dominate the particle dispersion and deposition processes. The deposition rate is shown to increase as the flow Reynolds number or the inlet flow turbulence intensity increases. The Brownian effects become significant for particles smaller than 1 μ.

REMOVAL OF PARTICULATE CONTAMINANTS USING ULTRASONICS AND MEGASONICS: A REVIEW

Sonic cleaning is a commonly used technique for removal of particles from surfaces. The theory of particle removal using ultrasound is reviewed. Effects of cavitation and acoustic streaming are discussed. Experimental results using ultrasonics and megasonics (ultrasonic cleaning near 1 MHz) from the literature are reviewed. Emphasis is placed on removal of fine particles from silicon surfaces for semiconductor manufacturing applications.

The adhesion-induced deformation and the removal of submicrometer particles

Adhesion-induced deformations of submicrometer polystyrene particles on silicon substrates were observed as a function of time using scanning electron microscopy. The contact area between the particle and the substrate was found to increase with time for a period of approximately 72 hours before reaching a constant value. The ratio of the final contact radius to the particle radius was ~ 0.4. The time dependence of this deformation appears similar to the creep phenomenon in bulk polymers. These results are related to the studies of particle removal conducted for different time periods, using hydrodynamic and centrifugal removal forces. The removal efficiency was found to decrease with time. This correlates well with the increase in the adhesion force on the particles with time as observed from the SEM measurements. The effect of the particle diameter on the removal efficiency and the correlation between the time dependent adhesion-induced deformation and particle removal efficiency is discussed.

Assessment of finite difference approximations for the advection terms in the simulation of practical flow problems

Abstract An assessment of seven discretization schemes for the advection terms of the transport equation to reduce numerical diffusion in practical flow problems has been established. The schemes have been evaluated using three test cases for laminar flow problems. The test cases consist of the transport of a scalar step in a uniform velocity field, two interacting parallel streams, and a slot jet. The performance of the schemes is evaluated for advection-dominated flows in transient and steady-state solutions. The considered schemes include four that have not been evaluated before for practical flow problems. In general, schemes which produced less numerical diffusion suffered from more numerical dispersion or oscillations. Two bounding techniques considered in the study were effective in significantly elliminating numerical dispersion.

Interfacial and Electrokinetic Characterization of IPA Solutions Related to Semiconductor Wafer Drying and Cleaning

In this study, the interfacial and electrokinetic phenomena of mixtures of isopropyl alcohol (IPA) and deionized (DI) water in relation to semiconductor wafer drying is investigated. The dielectric constant of an IPA solution linearly decreased from 78 to 18 with the addition of IPA to DI water. The viscosity of IPA solutions increased as the volume percentage of IPA in DI water increased. The zeta potentials of silica particles and silicon wafers were also measured in IPA solutions. The zeta potential approached neutral values as the volume ratio of IPA in DI water increased. A surface tension decrease from 72 to 23 dynes/cm was measured when the IPA concentration increased to 30 vol %. The surface excess of IPA at the air-liquid interface reached a maximum at around 20 vol % IPA. The adhesion forces of silica particles on silicon wafers were measured using atomic force microscopy in IPA solutions. The adhesion force increased as the volume percent of IPA in water increased. Lower particulate contamination was observed when the wafers were immersed and withdrawn from solutions containing less than 25 vol % IPA.

ROLES OF CAVITATION AND ACOUSTIC STREAMING IN MEGASONIC CLEANING

Despite wide use of megasonics in the semiconductor industry, the physics of megasonic particle removal remains largely unexplained. Mechanisms of particle removal in sonic baths are discussed, including the effects of operating parameters such as frequency, temperature, and power density. Experimental results are related to the theory, showing both cavitation and acoustic streaming as important components of the megasonic process.

Measurement of the adhesion and removal forces of submicrometer particles on silicon substrates

In this study, the magnitude of the applied removal force and its relationship to the theoretical adhesion force is determined. The removal is done through the application of known hydrodynamic drag and lift forces on submicrometer particles. The hydrodynamic removal forces are then correlated with the removal percentage and the adhesion forces. A useful correlation that can be used to determine the adhesion force from the known applied removal force and the removal percentage is presented. Below 90% removal, the data indicate a linear relationship between the removal force and the removal percentage. The effects of time on the adhesion force and particle deformation are also presented.

The Effect of Relative Humidity on Particle Adhesion and Removal

Abstract The removal of small particles is vital for contamination-free manufacturing. In humid environments liquid can condense between the particle and substrate and give rise to a very large capillary force, which increases the total force of adhesion. The removal and adhesion forces of polystyrene latex (PSL) particles and pigmented coating chips were measured on silicon, polyethylene terephthalate, metallized and polyester coating substrates as a function of humidity. The results indicate that the capillary force is significant at a relative humidity above 50% and dominates at a relative humidity above 70%. At relative humidity below 45%, the electrostatic force becomes significant. The adhesion forces varied depending on the particles and substrates used, but the trend of high adhesion at high and low relative humidity was observed for all PSL particles/substrate systems. The pigmented coating chips/substrate system however, exhibited high adhesion at high relative humidity and low adhesion at low relative humidity.

The effect of time, temperature and particle size on submicron particle removal using ultrasonic cleaning

Ultrasonic cleaning is an established method for removing micron-size particles or larger from hard substrates. This paper presents the effect of the ultrasonic frequency and time functions on submicron particle removal effectiveness. The effect of the particle size, concentration and the cleaning liquid temperature is also investigated. The removal efficiency is shown to be dependent on the ultrasonic time and frequency functions. The liquid temperature is shown to have a major effect on the ultrasonic cleaning process. The removal efficiency is shown to decrease with decreasing particle diameter. The results show that the ultrasonic cleaning technique can effectively remove particles of sizes 0.3 μm and larger.

Analysis of Scratches Formed on Oxide Surface during Chemical Mechanical Planarization

Scratch formation on patterned oxide wafers during the chemical mechanical planarization process was investigated. Silica andceria slurries were used for polishing the experiments to observe the effect of abrasives on the scratch formation. Interleveldielectric patterned wafers were used to study the scratch dimensions, and shallow trench isolation patterned wafers were used tostudy the effect of polishing parameters, such as pressure and rotational speed head/platen . Similar shapes of scratches chattertype were observed with both types of slurries. The length of the scratch formed might be related to the period of contact betweenthe wafer and the pad. Large particles would play a significant role in increasing the number of scratches. The probability ofscratch generation is more at higher pressures due to higher friction force and removal rate. The optimization of the head to platenvelocity could decrease the number of scratches.© 2009 The Electrochemical Society. DOI: 10.1149/1.3265474 All rights reserved.Manuscript submitted August 10, 2009; revised manuscript received October 26, 2009. Published December 15, 2009.