Chap 6 2 Wafer cleaning 6 Contamination Control

Chap 6 -2. Wafer cleaning

6. Contamination Control in Wafer Fabs RCA clean > SC-1 and SC-2 > Piranha mixture…… DHF NH 4 OH H 2 O 2 DIW HCl H 2 O 2 DIW H 2 SO 4 H 2 O 2 HF Megasonic, spray and scrubbing Rinse and drying Dry cleaning

What is cleaning ? To reduce the surface contamination to a minimum level during semiconductor manufacturing processes in order to achieve higher yield. Pre-Cleaning Post-Cleaning Contamination Cleaning process for subsequent process. Ex) surface preparing, cleaning before CVD and furnace To remove the contamination induced in previous process. Ex) post-CMP cleaning, Post PECVD

Importance of Cleaning It must be added after each process in semiconductor processes Decrease of device dimensions Reduction of electrical characteristics Yield

Classification of Cleaning < Mechanical Type > Wet Scrubber Dry Megasonic Single-wafer spin Aerosol SCF Noncontact Contact < Chemical solution > APM (SC-1) HPM (SC-2) SPM DHF BOE Ozonated / water Metal Heavy organic Oxide Film Metal Particle Metal

Cleaning Solution < SC-1 ; APM> Lift off Au, Ag, Cu, Ni, Cd, Zn, Co, Cr Etching the particles Prevention of readhesion < SC-2 ; HPM> Dissolution HCl : H 2 O 2 : DIW = 1: 1: 5 at 75~85℃ Heavy metal, Alkali ions, Metal hydroxides Hydrophilic after the cleaning

HF & BOE < HF > Oxide film Metal except noble metal as Cu, Au Impurity in oxide film < BOE > ; Buffered Oxide Echant NH 4 F + HF Stable etch rate by buffer High chemical wettability with surfactant

O 3 / HF(SCROD) Particle removal Ozonated water Si. O 2 + HF H 2 O + Si. F 4 Oxide removal Oxide By oxide film removal Si + O 3 Si. O 2 +O Metal removal Particles removal DHF

Development of Cleaning Eco-friendly Reduction of process time < IMEC > Little light Chemistry

Scrubbing Total Interaction Energy = van der Waals Energy (Hamaker constant +Particle ssize) ) - Attractive + Electrostatic Energy (Zeta Potential) - Repulsive/Attractive Noncontact : Hydrodynamic drag force Contact : Rotation torque of brush Brush force > Total interaction force Remove !

< Readhesion > + Physical force Brush + Brush out Brush + + Zeta potential < with surfactant > Physical force Brush - Brush - - Brush out

Megasonic Cavitation Acoustic streaming Radiation force Megasonic energy(1000 -15500 k. Hz)

Application of megasonic

Single wafer spin < SEZ Spin Etcher > Lower chemical and water High efficiency and short process time Lower scratch by particles With O 3 / DHF / N 2 < Single wafer spin >

Cryogenic Aerosol-based Cleaning Technology Physical force of Aerosol No surface tension Conventional gas : CO 2, Ar Damage of pattern in semiconductor N 2 Gas is more light than CO 2, Ar

SCF (Super Critical Fluid) cleaning Damage of pattern in Wet cleaning by surface tension Environment problem Dry process SCF Cleaning CO 2 (31℃, 7. 3 MPa) Super critical fluid : Surface tension is zero