Cleanroom air-ionization-in-a-nano-world-2


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Alpha ionization is an inherently clean and balanced technology that eliminates all particle concerns associated with corona ionization. Alpha technology eliminates airborne molecular contamination (AMC) particle agglomeration risks caused by corona ionizers.

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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-2

    2. 2. 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 Summary
    3. 3. Micro-Contamination in High TechnologyManufacturing
    4. 4. Effects of Static Charge onHigh Technology Manufacturing Particle attraction & bonding to charged surfaces Robotic Damage to lockup product
    5. 5. Contamination Study A Particle Contamination Study 200 mm wafer in a Class 1 Mini-Environment Wafer at 0 V Wafer at 2000 Vclass 1 mini environment for 6 weeks 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 5
    6. 6. 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.
    7. 7. In 1990 Corona Ionization Was the State of the ArtCorona 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.
    8. 8. The CD Compared to 500 nm Particles CD circa 1990 1995 500 nm 2000 2005 2010 2 0 •Ionizer Performance can no longer be judged by Fed Std 209E. •Ionizer performance must be related to KILLER Particles!
    9. 9. Semiconductor Front End Processing 2009 ITRS 2009 ITRS Roadmap Roadmap 60 50 Critical Dimension (nm) 40 30 DRAM stagger-contacted Metal 1 (M1) ½Pitch (nm) Flash Uncontacted Poly Si ½ 20 Pitch (nm) 10 0 2005 2010 2015 2020 2025 Year
    10. 10. Semiconductor Fab: What Particle Size Causes Yield Loss? For the present 45 nm node (DRAM 1st Level Metal ½ Pitch)* Metal 1 45 nm 90 nm 45 nmEither 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,
    11. 11. How Small is 22 nm? Size of Small Objects 100 10Size (um) 1 0.1 0.01 0.001 dollar hair germ virus killer DNA bill Size (um) 110 m 60 m 3.00E+0 m nm nm nm 1.00E-0 2.20E-0 2.00E-0
    12. 12. Corona Ionizers and theirContamination MechanismsThe invisible contaminant
    13. 13. Corona Ionizers Use Sharp Points toGenerate 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 largeparticles and you pay extra to get points that donot erode easily.But they still erode.Even silicon points must be replaced everytwo years due to erosion. Photograhs from
    14. 14. Beyond Erosion, All Corona IonizersTurn AMC gasses into Solid ParticlesThis is Called Agglomeration
    15. 15. Range of Agglomerated Particle Emissions from High Technology Air Ionizers 10000 Particles Per Cubic Foot 1000 100 10 1 0.01 0.1 1 0.1 Particle Size (Microns)Data based upon a survey or readily available published results. E.G. see,,,
    16. 16. Specifying a Corona Ionizer at 0.5 mMade Sense in 1990 but NOT in 2011! Corona Ionizer 1 100 Particles Per Cubic Foot 10 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.1 Particle Size (Microns) Extrapolation based upon normalized 1/x3 distribution accepted by the industry
    17. 17. What is the Impact of These Tiny Particles?For Particles from the Cleanest Corona Ionizer…Particle Density, 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=( part/ft3) d/2)2vt=267 particles 22.5 nm or greater!
    18. 18. Particles from Ionizers are Charged so Most (~50%) Will Stick!For a 45 nm process with 22.5 nm as a killer particlesize,Particle Load/wafer~2700/2=267 particles @22.5nm 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%
    19. 19. What Happens at the 25 nm Node?For a 25 nm process with 10 nm as a killer particlesize,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!
    20. 20. Effect of Particle Load on Yield 7 6 5 4 yield enhancement from electrostatic micro 3 contamination control% Yield Loss 2 yield degradation from corona ionizer particles 1 Net Yield Improvement 0 1990 1995 2000 2005 2010 2015 -1 Year -2 -3
    21. 21. Are You an Adrenaline Junkie?
    22. 22. Which do You Want? Fab Contamination Particle Load Ionizer Contamination Load? Neither?We have found a way to allow neither!It’s Called AlphaBoost®
    23. 23. To Understand the Advantages ofAlphaBoost®, Examine how theseParticles are Made:There are lots of organic vapors in a semiconductor cleanroom. CyclohexasiloxaneThese chemicals are “cooked” by corona ionizers.
    24. 24. ANY Corona Ionizer in Fab Air will beEffected by these AMCs.The corona process generates heat at the very tip of the emitter 25oC W=iV 100oC =5 A*10kV 500oC 750oC mW of heat =50 The heat disassembles the AMCs into radicals and cooks the “soup”.
    25. 25. A Free Radical Soup in an Electric Field will Grow Particles! High Voltage On Point Creates Strong Electric Particle is drawn in by dielectrophoretic force Fields + - + - + -Particle picks upcharge from emitter Particle is repelledpoint from emitter point
    26. 26. As the Tiny Particle Crosses the Plasma(Twice) it Picks up Free Radicals fromthe Soup
    27. 27. Agglomeration: Molecules toNano-Clusters to Micro-Clusters
    28. 28. Agglomeration in the Macro World:Watch water dropletsslide down theoutside side of a coldglass of beer Hail Falling From the clouds
    29. 29. Maintenance of Corona Ionizers Dealing with the FuzzEmitter points must be cleaned every fewmonths and the ionizer must be rebalancedwith a CPM
    30. 30. 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
    31. 31. AlphaBoost – the Advantages ofCorona Without the TradeoffsThe invisible contaminant
    32. 32. Alpha Emitter Technology – theEngine in AlphaBoost ® Alpha Technology Uses  No High Voltage (kV)  No Emitter Points  No Electrical Power Alpha Technology Requires  No Cleaning  No Adjusting
    33. 33. Alpha Emitter Technology EmploysPo210, 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.
    34. 34. The Alphas Collide with Air Atoms and Ionize Them ion ion ion ion ion ion ion ion ion ionThe process continues as long as the source is active ((1-2 years)
    35. 35. Is the Alpha Source Safe?Yes! Safety Rules: Alpha particles are stopped  Don’t eat alpha sources by  Don’t smoke alpha sources!  a sheet of paper  Return them after they are  or by the dead skin covering your body spent  They convert into lead Once they stop, Alpha particles become harmless helium atoms
    36. 36. Ordinary Alpha Ionizers In Laminar Airflow may not Discharge an Entire EFEM ULPA No Ions Here! Ions Recombine Before they Reach the Target
    37. 37. Alphaboost™ Separates Ion Polarities and Push Ions down Electrostatically in Waves 300 - 500 V Height of EFEMHalf Cycle ~ Laminar Flow Velocity Ions move 1+ m!
    38. 38. The Product is Compact and Easyto Mount in an EFEM The ionizing element is the size of a coin
    39. 39. 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
    40. 40. 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 aPulsed Electric Field
    41. 41. 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
    42. 42. AlphaBoost® Discharge Performance
    43. 43. Operation of AlphaBoost® in an EFEM ULPA 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
    44. 44. Operation of AlphaBoost®Adjacent to a Wafer Aligner ULPA 80 fpm air flow Typical Discharge 75 cm Performance 25 cm below the ionizer : Discharge times 7 seconds Voltage Swing +5 V Set to 300V Bias Swing 25 cm Frequency 4.0 Hz
    45. 45. 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
    46. 46. AlphaBoost – Conclusions
    47. 47. 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!
    48. 48. Semiconductors at the 25 nm Node andBeyond Require Alphaboost® to FabChips Cleanly and Economically 60 Critical Dimension (nanometers) 50 40 30 20 10 0 2005 2010 2015 2020 2025 Year