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Cleanroom air-ionization-in-a-nano-world

Cleanroom air-ionization-in-a-nano-world






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  • It is important to state that micro contamination in semiconductor and LCD panels manufacturing Is the most important reason to use ionization in the cleanroom In other areas, like semiconductor back end for semiconductor manufacturing and for cell and final assembly for LCD manufacturing microcontamination sensitivity is not the first concern,
  • Ion bars placed in the load chamber of a 300 mm process tool. This is called the EFEM or Equipment Front End Module.
  • Ionizers stop particles in the EFEM from settling on the wafer due to electrostatic attraction. We will show that a corona bar is not good enough for 2011 manufacturing.
  • ITRS=International Technology Roadmap for SemiconductorsThis is a document that all of the fabs use as their bible.
  • Define killer particle as one large enough to potentially make a die non functional if the particle lands on the die in the processing process. The particle may simply fall off or it may land on a part of the die where the it does no harm but for smaller particles, this is not an issue.
  • Emitter points wear out and the material they loose can land on the wafer. All corona points wear out in time due to the corona process. All corona ionizer manufacturers state a recommended time to replace the points.
  • Agglomeration is a physical process in which particles pick up more material to grow larger. The material comes from solvents in the air (called Airborne Molecular Contaminants or AMCs). The energy to drive the process comes from the corona itself which is a plasma around the emitter tips.
  • This is actual data of the number of particles per cubic foot for two state of the art ionizers in production today. The number of small particles is surprisingly large and cannot be ignored. It looks like ionizers replace large particles with smaller ones. It is a net improvement but there comes a time when the killer particle size will become small enough that the number of particles made by an ionizer will be unacceptableShow the .01 micron (10 nm )location on the horizontal axis and read the number of particles from the graph: 600,
  • This reads the particle count value from the graph on slide 16 calculates the number of particles that pass over the 300 mm wafer. State that this is the number of particles that pass close to a wafer due to the ionizer in a single step of the manufacturing process.
  • Using statistical analysis and commonly accepted probabilities, this is the yield loss due to ionizer induced microcontamination. Not a terrible impact when you consider the good that the ionizer does.
  • Later this year people will start printing 25 nm structures and the particles that can kill get smaller. The yield is no longer acceptable.
  • We have shown that ionizers stop airborne particles from being pulled down to the surface by neutralizing the wafer.Now we have shown that ionizers add charged particles to the environment that are also electrostatically attracted to the wafer. At 25 nm, the number of particles saved and the number of particles added is a poor tradeoff. With a corona ionizer.
  • How do corona ionizers create particles? They build them out of the organic junk in the air of the fab. The organic junk is there because the processes require those chemicals.
  • Imagine a tiny particle in the corona’s plasma. It is attracted to the tip. The force is called the dielectrophoretic force and it always attracts the particle to the emitter point..—The particle moves through the soup picking up material as it goes. This is just like dipping a wick into a vat of melted wax to make a candle.When the particle reaches the emitter, it picks up charge and is expelled through the soup picking up more material.Note that the particle leases the soup charged so it is really dangerous from a microcontamination standpoint. If it gets near the wafer, it WILL stick even if the wafer is neutral.
  • This process is called agglomeration
  • Examples to help the end user see the concept
  • What about the particles that do not leave the soup? They grow fuzz. This leads to a requirement to clean and adjust each emitter. In a fab this meansShutting down the toolOpening the mini environmentCleaning each emitterBringing in an ionizer and setting the balance and discharge speed of each ionizerClosing the minienvironment and waiting for the cleanliness level to recover. This might be 15-30 minutes.All in all, this could cost a full hour of tool unavailability and 60-90 man minutes per tool to do the job. These both are costly.
  • The arguments areAt 25 nm node, particle count per wafer with corona ionizers is a net lossEven for this generation of semiconductors and flat panels, the tool unavailability (up to 6o minutes per week) is a terrible expense.Even for a fab running at 70% where tool availability is not an issue, personnel time for maintenance is.
  • An alpha source continuously makes a balanced stream of ions with no need for electrical power to generate themIt just runs and does not deviate in performance for a full year
  • Alphas for Po210 move only 4 cm through the airAfter they stop, they are completely benign, just like a child’s balloonNothing is required to cause them to make ions. They just do.
  • The alpha bumps into air molecules and ionizes them at each collision. When they give up all of their energy, they find two electrons and become neutral helium atoms.The process makes ions efficiently for more than one year.
  • Alphas are a unique ray. They are very heavy and slow moving. They move through matter like a bull in a china shop causing damage to molecules as they go.They barley move through air before they give up all of their energy. If they strike a person, they do not have enough energy to penetrate the dead skin layer that covers each of us.You need to keep the source out of your body. So do not eat a source and do not burn it and inhale the fumes.
  • An alpha ionizer works well within 10 cm but beyond that, the ions all recombine so it will not work well in a mini environment by itself.
  • We use a relatively low voltage to push the ions away from the source. The field map of a 2 cm disk at voltage is very different than the field map of a shape emitter point. The fields extend further so that the ions are pushed down electrostatically and by laminar flow.AlphaBoost pushes the ions well enough that a mini environment can be ionized efficiently.
  • The product uses a Po210 button and it is mounted in a plastic housing. The housing delivers the pusher voltage to the product and for some applications, it also provides a connection to drive ions with air flow.
  • Look at ON periods a.nd OFF periods. There is not difference. No particles
  • Same thing with 10 nm particles. None!
  • Typical values for performance in an EFEM
  • Typical close in performance such as at a wafer aligner
  • Benefits list
  • Corona is going to go away just like coal plants which generate electricity and smoke
  • We are rushing into the future. You will not be able to use old technology

Cleanroom air-ionization-in-a-nano-world Cleanroom air-ionization-in-a-nano-world Presentation Transcript

  • Transforming Technologies Presents
    ALPHABOOST™The Next Generation of Ultra-Clean Air Ionization
  • Outline
    Microcontamination, Electrostatics and High Tech Manufacturing
    Corona Ionizers and their Contamination Mechanisms collide with the 25nm node
    Alphaboost® The Advantages of Corona without the Tradeoffs
  • Micro-Contamination in High Technology Manufacturing
  • Effects of Static Charge on
    High Technology Manufacturing
  • Contamination Study
    200 mm wafer in a Class 1 Mini-Environment
    Wafer at 0 V
    class 1 mini environment for 6 weeks
    Wafer at 2000 V
    class 1 mini environment for 6 weeks
    Data from Frank Curran, MS thesis, "The Effects of Static Charge on Silicon Wafers in the Semiconductor Industry," The Engineering Council of England, Nov. 1997
  • Electrostatic Attraction Defeated by Mini-Environment Ionizers
    “Implementing a Static Control Program to Increase the Efficiency of Wet Cleaning Tools” Micro Magazine June 2001. Long, CW, Peterman, J and Levit, L.B. http://www.micromagazine.com/archive/06/01/long.html
  • In 1990 Corona Ionization Was the State of the Art
    Corona Ion Bars were available with Sub Class 1 Cleanliness
    This was absolutely acceptable for semiconductor manufacturing
    Fed Std 209E Class 1 requires less than one 500 nm particle/cubic foot of fab air.
  • The CD Compared to 500 nm Particles
    CD circa 1990
    500 nm
    • Ionizer Performance can no longer be judged by Fed Std 209E.
    • Ionizer performance must be related to KILLER Particles!
  • Semiconductor Front End Processing
    2009 ITRS Roadmap
  • Semiconductor Fab: What Particle Size Causes Yield Loss?
    For the present 45 nm node (DRAM 1st Level Metal ½ Pitch)*
    45 nm
    90 nm
    45 nm
    Either of these contaminating particles can kill the die!
    Define killer particle size as a ≥ ½ * 45 nm
    for this 45 nm technology (allow for uneven pitch)
    * 2009 Intl. Technology Roadmap for Semiconductors Update, http://www.itrs.net/
  • How Small is 22 nm?
    110 mm
    60 mm
    3 mm
    100 nm
    22 nm
    2 nm
  • Corona Ionizers and their Contamination Mechanisms
    The invisible contaminant
  • Corona Ionizers Use Sharp Points to Generate an Intense Electric Field
    • In time the plasma at the tips erodes the points.
    • Where did the material go?
    • This erosion is the main source of large particles and you pay extra to get points that do not erode easily.
    • But they still erode.
    • Even silicon points must be replaced every two years due to erosion.
    Photograhs from http://www.ion.com/documents/technical/EmitterMaintenance.pdf
  • Beyond Erosion, All Corona Ionizers Turn AMC gasses into Solid Particles
    This is Called Agglomeration
  • Range of Agglomerated Particle Emissions from High Technology Air Ionizers
    Particles Per Cubic Foot
    Particle Size (Microns)
    Data based upon a survey or readily available published results. E.G. see www.simco.com, www.ion.com, www.desco.com, www.meech.com
  • Specifying a Corona Ionizer at 0.5 mm Made Sense in 1990 but NOT in 2011!
    Particles Per Cubic Foot
    Particle Size (Microns)
    Extrapolation based upon normalized 1/x3 distribution accepted by the industry
  • What is the Impact of These Tiny Particles? For Particles from the Cleanest Corona Ionizer…
    • Particle Density, r(r)=12 particles/ft3 @ 22.5 nm or greater
    • Laminar flow rate in Mini-environment, v= 60 ft/min
    • Wafer Residence Time in EFEM, t= 1 minute
    • The Number of Particles moving over a wafer :
    • Take d=300 mm, N=(12part/ft3)p(d/2)2vt=
    • 267 particles 22.5 nm or greater!
  • Particles from Ionizers are Charged so Most (~50%) Will Stick!
    • For a 45 nm process with 22.5 nm as a killer particle size,
    • Particle Load/wafer~2700/2=267 particles @22.5 nm orgreater.
    • Assume 2% actually kill a die.
    • Assume 500 die per wafer, 400 process steps.
    • Particle Limited Yield=98.67%
    • Particle Limited Yield (1000 die/wafer)=99.27%
  • What Happens at the 25 nm Node?
    • For a 25 nm process with 10 nm as a killer particle size,
    • Particle Load/wafer~2700/2=1350 particles.
    • Assume 2% actually kill a die.
    • Assume 500 die per wafer, 400 process steps.
    • Particle Limited Yield=94%!
    • Particle Limited Yield (1000 die/wafer)=96%!
    This yield loss cannot be tolerated!
  • Are You an Adrenaline Junkie?
  • Which do You Want?
    Fab Contamination Particle Load
    Ionizer Contamination Load?
    We have found a way to allow neither!
    It’s Called AlphaBoost®
  • To Understand the Advantages of AlphaBoost®, Examine how these Particles are Made:
    • There are lots of organic vapors in a semiconductor cleanroom.
    • These chemicals are “cooked” by corona ionizers.
  • ANY Corona Ionizer in FabAir will be Effected by these AMCs.
    The corona process generates heat at the very tip of the emitter
    =5 mA*10kV
    =50 mW of heat
    The heat disassembles the AMCs into radicals and cooks the “soup”.
  • A Free Radical Soup in an Electric Field will Grow Particles!
    High Voltage On Point Creates Strong Electric Fields
    Particle is drawn in by
    dielectrophoretic force
    + -
    + -
    + -
    Particle picks up charge from emitter point
    Particle is repelled from emitter point
  • As the Tiny Particle Crosses the Plasma (Twice) it Picks up Free Radicals from the Soup
  • Agglomeration: Molecules to Nano-Clusters to Micro-Clusters
  • Agglomeration in the Macro World:
    Watch water droplets slide down the outside side of a cold glass of beer
    Hail Falling From the clouds
  • Maintenance of Corona Ionizers Dealing with the Fuzz
    Emitter points must be cleaned every few months and the ionizer must be rebalanced with a CPM
  • Summary:
    • Corona Ionizers ALL Make Sub Micron Particles
    • Most also make larger Particles
    • Corona Ionizers all Must be Cleaned and Re-Balanced every 1-3 months – this is expensive and time consuming.
    • AlphaBoost® Eliminates all of these Issues
  • AlphaBoost – the Advantages of Corona Without the Tradeoffs
    The invisible contaminant
  • Alpha Emitter Technology – the Engine in AlphaBoost®
    Alpha Technology Uses
    No High Voltage (kV)
    No Emitter Points
    No Electrical Power
    Alpha Technology Requires
    No Cleaning
    No Adjusting
  • Alpha Emitter Technology Employs Po210, a 5.3 MeV Alpha Source
    • Alpha particles move up to 4 cm from the source and stop
    • They become Helium atoms and drift away harmlessly
    • As they Travel, each one makes ~250,000 ion Pairs`
    • No electricity is required to make ions
    • Ion output is automatically balanced with no adjustments.
  • The Alphas Collide with Air Atoms and Ionize Them
    The process continues as long as the source is active ((1-2 years)
  • Is the Alpha Source Safe?
    Safety Rules:
    Alpha particles are stopped by
    a sheet of paper
    or by the dead skin covering your body
    Once they stop, Alpha particles become harmless helium atoms
    Don’t eat alpha sources
    Don’t smoke alpha sources!
    Return them after they are spent
    They convert into lead
  • Ordinary Alpha Ionizers In Laminar Airflow may not Discharge an Entire EFEM
    No Ions Here!
    Ions Recombine Before they Reach the Target
  • Alphaboost™ Separates Ion Polarities and Push Ions down Electrostatically in Waves
    ±300 - 500 V
    Height of EFEM
    Half Cycle ~
    Laminar Flow Velocity
    Ions move 1+ m!
  • The Product is Compact and Easy to Mount in an EFEM
    The ionizing element is the size of a coin
  • AlphaBoost Has
    No KiloVolt voltages
    No Need for Balance Adjustment
    No Corona
    No Sharp Points to Wear Out
    No Fuzz Ball Creation Mechanism
    No Gas to Particle Agglomeration Mechanism
  • Ionizer LPC Cleanliness Study *
    94.2±4 particles/ft3 with ionizer ON and 95.5±3 particles/ft3 with ionizer OFF
    *Robert Wilson, ESDA Symposium 1987, A Novel Nuclear Ionization Source Employing a Pulsed Electric Field
  • Ionizer CNC Cleanliness Study *
    1.25.2±0.9 particles/ft3 with ionizer ON and 3.3±0.15 particles/ft3 with ionizer OFF
    *Robert Wilson, ESDA Symposium 1987, A Novel Nuclear Ionization Source Employing a Pulsed Electric Field
  • AlphaBoost® Discharge Performance
  • Operation of AlphaBoost® in an EFEM
    80 fpm air flow
    • Typical Discharge Performance 1 m below the ionizer :
    • Discharge times ± 25 seconds
    • Voltage Swing +15 V
    • Set to ±500 V Bias Swing
    • Frequency 2.0 Hz
  • Operation of AlphaBoost® Adjacent to a Wafer Aligner
    80 fpm air flow
    • Typical Discharge Performance 25 cm below the ionizer :
    • Discharge times ± 7 seconds
    • Voltage Swing +5 V
    • Set to ±300V Bias Swing
    • Frequency 4.0 Hz
    75 cm
    25 cm
  • AlphaBoost® Benefits
    Fast Discharge time
    Balanced by Physics, not by Adjustment
    Inherently Stable
    No Fuzzball to Clean Off
    No points to Replace
    No CPM Balance Adjustment
    Same Delivery Efficiency as Corona Technology
  • AlphaBoost – Conclusions
  • Conclusions
    Records went from the phonograph cylinder to 78 RPM hard plastic to Vinyl High Fidelity Recordings and
    Underwent Constant Improvement of the Same Technology
    But they Eventually they Became Obsolete – limited life, sensitivity to handling & to dust
    Cameras went from the pin-hole to lens to multi element lenses but it took digital photography to satisfy today’s photographers.
    Corona Ionizers underwent Technology boosts
    from Tungsten to Titanium to Silicon points and
    from AC to DC to Pulsed DC to Complex Waveforms
    But Technology has passed them by
    Electricity was Generated by Burning Dirty Coal in 1900. Now Clean Solar Electrical Power is Coming on Line rapidly!
  • Semiconductors at the 25 nm Node and Beyond Require Alphaboost® to Fab Chips Cleanly and Economically