Microcontamination and Cleanroom Control PDF

Microcontamination Control Microcontamination is any micro foreign material or energy that has a detrimental effect on a product or process. For example, Particles (Solids) Vibration (Energy) Ions (in Liquids) Electromagnetic Interference or Radiation (E...

Microcontamination Control Microcontamination is any micro foreign material or energy that has a detrimental effect on a product or process. For example, Particles (Solids) Vibration (Energy) Ions (in Liquids) Electromagnetic Interference or Radiation (Energy) Molecular (Gases) Electrostatic Discharge (Energy) Microcontamination control measures in Wafer Fabrication: Clean Room Ultra Pure Water ESD Control  Microcontamination Effects Product or Process: Yield Performance Reliability Particle Related Failures HEAD Short circuits &/or ESD damaged devices DISK PARTICLE 0.5um  Microcontamination and Yield (Y) Y Poisson postulates that: Yield is exponentially inversely proportional to Area of Product. Y= e-AD Yield is exponentially inversely proportional to Defect Density AD The larger the size of a product the easier probabilistically it is subject to contamination by particles. Defect Density is a measure of the cleanliness of the environment. Both means that Yield is directly affected by Microcontamination Control. The smaller the size (the smaller the surface area, the more difficult probabilistically speaking to get contaminated by particles, notwithstanding technologically & machine capability) & the cleaner the environment, the higher the production yield. Device yield should improve as things get smaller according to Poisson, that’s how important he attributes failures to contamination causes.  Particulate Contaminants Size & Characteristics Under ordinary Illumination Human hair 75-100um 0.3um 10um visible particles ~ 35µm. Not to scale for illustration only In microcontamination control of particulates, the contaminants size (0.01 to 100µm) & therefore their characteristics we are dealing with: Invisible Airborne (because of their weightlessness)  Contaminants Size Comparison & Chart Spittle marks, Finger prints & Smoke particles are all Invisible Aerosols Smoke & Dust are Invisible & Airborne Metallurgical Dust (Aerosols) Tobacco Smoke Human Hair Diameter Insecticide Dust 10,000 0.001 0.005 5,000 1000 0.01 0.05 100 500 0.1 0.5 10 50 1 5  Cleanroom A room in which the concentration of airborne particles is controlled and which has one or more clean zones. Cleanroom Class The number of particles >0.5um that can be found in 1 cubic foot. Class 1000 clean room will have less than 1000 particles >0.5um in 1 cubic foot.  Cleanroom Operation Filtration Airflow Control Filtration Mechanism: Gravity (large) Inertial Impaction (large) Direct Interception (large) Electrostatic (small) Diffusion (small) Worst case overall efficiency occurs at a specific size for HEPA & ULPA: HEPA Filter: High Efficiency Particulate Air efficiency 99.997 % @0.3µm diameter. ULPA Filter: Ultra-Low Particulate Air efficiency 99.999997 % @ 0.12 µm diameter.  Cleanroom Operation Airflow Control: 70 to 110ft/min or 0.35 to 0.45m/s HEPA Filters Laminar Flow in ceiling Raised Floor & Balancing To remove Standing Recirculating Air (see next slide) HEPA filters to be changed: Raised Floor When airflow speed decreases Return Air Plenum To minimize Energy Consumption  Cleanroom Operation HEPA Filters HEPA Filters in ceiling in ceiling Grade Level Grade Level Floor Return Air Return Air Floor Return Air Return Air Grill Near Grill Near Grill Near Grill Near Floor Floor Floor Floor  Cleanroom Operation Closed Floor Tiles Center of Room Closed Floor Tiles Mostly Closed Floor Tiles Mostly Closed Floor Tiles Mostly Open Floor Tiles Mostly Open Floor Tiles Fully Open Floor Tiles Air Flow Balancing of Raised Floor in Cleanroom  Cleanroom Practice People are the major source of contaminants (Skin, Sweat & Saliva): Cleanroom Apparel (Gowning: Face Mask, Hairnet, Jumpsuit, Booties & Gloves). Cleanroom Skills (Education & Training) Personal Hygiene (Education & Training) Tools are also sources of contaminants: Tables (Perforated or Not depending on how it affects the airflow).  Temporary storage (Perforated).  Work Table (Solid: Not perforated) Chairs (Always perforated). Machines & others (Cleaning schedule required).  Cleanroom Practice Perforated table tops causes particles Horizontal obstructions force air to move from the human body to move towards horizontally on solid table. Take advantage the product. of this and direct air flow toward operating personnel. Cleanroom Level (of Cleanliness): As defined in MIL STD 1246, the size in µm at which no more than one particle will be found per square foot of surface area (example for gloves, table or chairs). Not just Cleanroom Class compatibility when making decisions of purchase.