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.
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
4. Effects of Static Charge on
High Technology Manufacturing
Particle
attraction &
bonding to
charged surfaces
Robotic Damage to
lockup product
5. Contamination Study
A Particle Contamination Study
200 mm wafer in a Class 1 Mini-Environment
Wafer at 0 V Wafer at 2000 V
class 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. 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
7. 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.
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. 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. 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 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/
11. How Small is 22 nm?
Size of Small Objects
100
10
Size (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. Corona Ionizers and their
Contamination Mechanisms
The invisible contaminant
13. 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
14. Beyond Erosion, All Corona Ionizers
Turn AMC gasses into Solid Particles
This is Called Agglomeration
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 www.simco.com, www.ion.com, www.desco.com, www.meech.com
16. Specifying a Corona Ionizer at 0.5 m
Made 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. 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. 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%
19. 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!
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
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. To Understand the Advantages of
AlphaBoost®, Examine how these
Particles are Made:
There are lots of organic vapors in a semiconductor cleanroom.
Cyclohexasiloxane
These chemicals are “cooked” by corona ionizers.
24. ANY Corona Ionizer in Fab Air will be
Effected 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. 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 up
charge from emitter Particle is repelled
point from emitter point
26. As the Tiny Particle Crosses the Plasma
(Twice) it Picks up Free Radicals from
the Soup
28. Agglomeration in the Macro World:
Watch water droplets
slide down the
outside side of a cold
glass of beer
Hail Falling From the clouds
29. 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
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. AlphaBoost – the Advantages of
Corona Without the Tradeoffs
The invisible contaminant
32. 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
33. 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.
34. The Alphas Collide with Air
Atoms and Ionize Them
ion
ion ion ion
ion
ion ion
ion
ion ion
The process continues as long as the source is active ((1-2 years)
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. Ordinary Alpha Ionizers In Laminar Airflow may
not Discharge an Entire EFEM
ULPA
No Ions Here!
Ions Recombine Before they Reach the Target
37. 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!
38. The Product is Compact and Easy
to Mount in an EFEM
The ionizing element is the
size of a coin
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. 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
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
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. 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. 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
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. Semiconductors at the 25 nm Node and
Beyond Require Alphaboost® to Fab
Chips Cleanly and Economically
60
Critical Dimension (nanometers)
50
40
30
20
10
0
2005 2010 2015 2020 2025
Year
Editor's Notes
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