MICROCHIP MANUFACTURING by S. Wolf

Transcription

1 MICROCHIP MANUFACTURING by S. Wolf Chapter 8: CONTAMINATION- CONTROL & CLEANING TECHNOLOGY for ULSI APPLICATIONS 2004 by LATTICE PRESS

2 CHAPTER CONTENTS Contamination-Types in IC Fabrication Sources of Contamination in Chip Manufacturing Effects of Contamination on ULSI Devices Contamination-Prevention in Wafer Fabs Wafer-Cleaning Techniques Particle-Removal from Wafer Surfaces Rinsing & Drying Wafers Particle-Detection on Wafer Surfaces MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-2

3 8-3 Chapter 8: Contamination Control & CONTAMINATION TYPES IN IC-FABRICATION Clean wafer-surfaces are critical for: device-performance, reliability, & yield Wafer-Contamination: Particles Si & Atmospheric Dust Clothing Lint Skin Flakes Bacteria in UP-Water Films Solvent-Residues Oil-Films Trace-Quantities of Metals & Ions MICROCHIP MANUFACTURING EXAMPLES OF PARTICLE- TYPES ON IC-WAFERS SOURCES OF CONTAMIN- ATION IN IC S - FROM 1980 TO by LATTICE PRESS Sunset Beach CA

4 SOURCES OF CONTAMINATION IN CHIP-MANUFACTURING Process-Equipment Liquid & Gaseous Chemicals Ultra-Pure Water Polymeric Photo- Resist Liquids Containers of Chemicals (& Cassettes that hold Wafers) Humans (& the Clothes they wear) Ordinary Air MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-4

5 EFFECTS OF CONTAMIN- ATION ON ULSI DEVICES Films Impair Adhesion Inhibit Cleaning Trace-Metals Degrade Devices Harm Gate-Oxides Ionic Contaminants (Na) MOSFET Instability Gate-Oxide Breakdown Particles Disrupt Feature Patterns Pinholes MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-5

6 CONTAMINATION-PREVENTION MEASURES Control Environment in Which Wafers are Processed Wafer-Fab & Cleanroom Cleanroom Protocols Gowning of Workers Ultrapure-Chemicals & Process-Materials Ultrapure-Water Optimized Tools & Processes MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-6

7 REMOVING AIR-PARTICLES & KEEPING RESIDUAL AIRBORNE-PARTICLES FROM WAFER-SURFACES Continuous Air-Circulation thru HEPA-Filters Laminar, Ceiling-to-Floor Flow in Wafer-Workspaces Cleanroom/Chase - Tools Behind Bulkhead High- Efficiency Particle- Attenuation (HEPA) Filter 8-7 MICROCHIP MANUFACTURING Tool Bulkhead Installation 2004 by LATTICE PRESS Sunset Beach CA

8 MINIENVIRONMENTS, SMIF, & FOUPs To keep wafers free of particles during transport between tools - carry them in SMIF-boxes SMIF - Standard Mechanical Interface (Bottom- Opening) 300-mm wafers use FOUPs FOUP - Front-Opening Unified Pod MINI- ENVIRONMENTS SMIF Boxes 8-8 MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA FOUPs

9 QUANTIFYING AIR-CLEANLINESS IN FABS Defined by US-Govt: in terms of Federal-Standard How many particles are allowed per unit-volume of air? Cleanliness is characterized by the term CLASS CLASS-X means that in each cubic-ft of air there are less than X total particles larger than 0.5-µm CLASS-10: Fewer than 10-particles/ft µm CLASS-1: Fewer than 1-particle/ft µm MICROCHIP MANUFACTURING Cleanroom Class-Limits according to Fed-Std 209E (Right-set of plots) 2004 by LATTICE PRESS Sunset Beach CA

10 Chapter 8: Contamination Control & GOWNING GOWNING is used to reduce particles shed by humans from reaching wafers Cleanroom Attire includes Body-Suit Gloves Booties Hood Face-Mask Cleanroom-Fabric does not shed particles (monofilament) Cleanroom-Protocols must be strictly followed by LATTICE PRESS Articles of Cleanroom Attire Cleanroom Fabric (top) Street-Clothing Fabric (Bot)

11 CLEANROOM PROTOCOLS Many rules must be strictly followed by fab-workers Wafers are batch-transported tool-to-tool in Cassettes Single-wafers are manually moved with vacuum-wands No smoking in the fab Workers cannot wear makeup, perfume, contact-lenses Do not stirup particles MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Wafer Cassettes Vacuum-Wand 8-11

12 Chapter 8: Contamination Control & WAFER CLEANING: RCA-CLEAN Wafer-Cleaning Removes: Particles Films Metals & Ions PhotorResist Etch-Residues Front-End Cleans use aggressive chemicals: RCA-CLEAN Standard-Clean-1 (SC-1) NH 4 OH:H 2 O 2 :H 2 O Standard-Clean-2 (SC-2) HCl:H 2 O 2 :H 2 O Back-End Cleans use solvents MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA FRONT-END VS BACK-END CLEANING- PROCESSES RCA-CLEAN SEQUENCE 8-12

13 Chapter 8: Contamination Control & Cleaning Technology PARTICLE-REMOVAL Particles arrive on wafers from: Air Liquid-Chemicals Particles adhere to wafer byvan-der-waals force Methods to Remove Particles from Wafers Chemical Removal Electrical-Repulsion Mechanical- Dislodgement Particle-Removal Processes RCA-Clean 8-13 Megasonic-Vibration MICROCHIP MANUFACTURING Particle-Removal-Mechanism Model Drawing of a Megasonic Cleaning-Tank 2004 by LATTICE PRESS Sunset Beach CA

14 Cleaning Technology for ULSI PARTICLE REMOVAL BY BRUSH-SCRUBBING Brush-Scrubbing is performed after several-processes to remove particles from wafers: CMP Sawing Lapping Water-Jet sprays wafer & a soft brush (made from poly-vinyl alcohol - PVA) is rotated over wafer-surface. Liquid being sprayed usually has ph > 7 Double-Sided Brush-Scrubbing is especially effective Double-Sided Brush Scrubber MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-14

15 DI-WATER WAFER-RINSERS Cleaning-Chemicals are removed by rinsing wafers in ultra-pure water (UPW) in Rinsers Water flowed until effluent is 18-MΩ resistivity OVER- FLOW RINSER CASCADE RINSER DUMP- RINSER MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-15

16 WAFER DRYERS Spin-Dryers Remove Water 1. Physically (Spin-Wafers) 2. Thermally (Hot-Gas) Isopropyl-Alcohol (IPA) Dryers 1. Heated IPA-Vapor Displaces Water 2. IPA Evaporates SPIN- DRYER IPA-DRYER MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-16

17 PARTICLE-DETECTION ON WAFER SURFACES Particle-Detection Tools Optical Microscopes Scanning-Electron Microscopes (SEMs) Laser-Scanners Particles-per-Wafer-per-Pass Automatic Particle-Counters Scans UnPatterned-Wafers Laser-Beam scatters off particles on wafer-surface Integrated Light-Detector collects any scattered-light Wafer-Map shows particles Concept of Particles-per-Waferper-Pass (PWP) Automatic Particle-Detection Tool MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-17

18 SUMMARY OF KEY CONCEPTS Unprecedented Cleanliness must exist during ULSI Chip-Manufacture Each of the hundreds of Processing Steps can introduce contamination Many techniques are used to prevent such contamination from reaching wafers Other methods are used to remove any contamination that cannot be prevented Cleaning Techniques Rinsing & Drying Wafers Wafers are continuously monitored to detect presence of contamination MICROCHIP MANUFACTURING 2004 by LATTICE PRESS Sunset Beach CA 8-18