A dynamic analysis on the contaminant particles’ removal mechanism in cryogenic carbon dioxide (CO 2 ) cleaning process Dept. of Mechanical Engineering Chung-Ang University Nano-System Dynamics Lab. Seonghoon Lee, Pilkee Kim, Jongwon Seok

Contents ■Motives & Objectives ■Cleaning methods for the removal of fine particles ■Theories of CO 2 snow cleaning ■Modeling of particle detachment mechanism ■Simulation for particle detachment mechanism : Rebounding ■Discussion & Remaining issue

Motive & Objectives ■Motive - Weak point : Adhesion and removal mechanism among the particles - Requirement : Optimization of CO 2 snow cleaning method by adopting reasonable adhesion model ■Objectives - Adhesion mechanism between substrate & contaminant particle, CO 2 snow particle & contaminant particle - Dynamic modeling and simulation - Optimization of CO 2 snow cleaning method for high PRE (Particle Removal Efficiency)

 Megasonic cleaning method Wet cleaning Dry cleaning  Chemical fluid application - APM (Ammonia peroxide mix) - HPM (Hydrochloric peroxide mix) - SPM (Sulfuric peroxide mix) - DHF (Diluted hydrofluoric acid)  Sputtering  Chemical dry-cleaning  UV/O 3 cleaning  Laser Cleaning  Cryogenic Cleaning Cleaning methods for the removal of fine particles Cleaning methods

■ The principal mechanisms - Phase transition : gas & solid CO 2 (2 phase) - Nucleation process - Particle removal mechanism  Phase transition 1 phase CO 2 ( about 60 bar, -80 ℃ ) Gas CO 2 + Solid CO 2 (about 1bar, -80 ℃ ) Adiabatic expansion process Theories of CO 2 snow cleaning Container

 Nucleation process - For gas CO 2 source (Build-up process) 45 % for liquid source >> 8 % for gas CO 2 Liquid CO 2 Gas CO 2 Solid CO 2 - For liquid CO 2 source (Break-down process) Dry ice snow yield Theories of CO 2 snow cleaning

 Particle removal mechanism - Momentum transfer by solid CO 2 - Drag force by gas CO 2 - Thermophoresis Removal force Adhesion force (40%) (50%) (10%) : Rebounding, Rolling, Sliding, Lifting Theories of CO 2 snow cleaning Adhesion forces Removal forces - Van der waals force - Electric double layer force - Capillary force - Hydrogen bond  detachment

■ Contact model Hertz model JKR model GT-JKR model Hertz model : Model considering contact and deformation for external force JKR model : adhesion force + Hertz model GT-JKR model : surface roughness + JKR model  Contact between CO 2 snow & contaminant particle  Hertz model  Contact between substrate & contaminant particle  JKR model Modeling of Particle Detachment Mechanism

y 1, y 2 x1x1 x2x2 d1d1 d2d2 ■ Particle detachment Modeling of Particle Detachment Mechanism Dynamic modeling of rebounding by vertical collision among particles d 1 : displacement of CO 2 snow, d 2 : displacement of contaminant v

■ Assumption  Perfect-elastic bodies without plastic deformation for each materials  Shape of particles : Spherical contaminant / Spherical dry-ice  Contact model : Hertz model, JKR model  Removal mechanism : Rebounding by vertical collision  No gravity effect Silica substratePTFE contaminantDry-ice Young’s modulus (GPa) Poisson’s ratio Density (kg/m 3 ) Adhesion energy0.024 (J/m 2 ) ■ Material properties Modeling of Particle Detachment Mechanism

 Contaminant radius : 0.1 ㎛  Snow radius: 1 ㎛ (a) Initial Collision velocity : 3 ㎧ (b) Initial collision velocity : 5 ㎧ (c) Initial collision velocity : 8 ㎧ (d) Initial collision velocity : 10 ㎧ Collision velocity ↓ : Insufficient momentum ■ Dynamic characteristics according to collision velocity Contaminant remain Contaminant removal Simulation for particle detachment mechanism : Rebounding Contaminant displacement Dry-Ice displacement

Radius ↓ : Adhesion force increase, Radius ↑ : Insufficient momentum ■ Dynamic characteristics according to contaminant radius Contaminant displacement Dry-Ice displacement Simulation for particle detachment mechanism : Rebounding  Snow radius : 1 ㎛  Snow velocity : 1 ㎧ (a) Contaminant radius : 0.1 ㎛ (b) Contaminant radius : 0.5 ㎛ (c) Contaminant radius : 1 ㎛ (d) Contaminant radius : 2 ㎛ Contaminant removal Contaminant remain

Conclusion & Remaining Issue ■ Conclusion Finally, we concluded that the results of this simulation are similar to general tendencies of fine particles in the cleaning process.  Elasto-plastic material  Surface roughness  Sliding, rolling & lifting ■ Remaining Issue  First simulation shows that the insufficient momentum of snow induces the particle contaminant to remain on the substrate.  Also it is found that the fine particle is difficult to remove from the substrate surface as known generally

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