f10 lec01 overview
TRANSCRIPT
CLASS ACTIVITIES
• Lectures• Demonstrations• Homework• Laboratory exercises and reports• Quizzes and exams• Visit a local clean room facility
GRADES
Weekly quizzes, exams, homework 50%
Lab 25%Final Exam 25%
Late assignments (lab reports and homework)
• Late assignments will not be accepted without a written medical excuse.
• 0ne letter grade will be deducted for each day an assignment is late.
• All assignments must be turned in at the beginning of the class for which they are due.
• Your lowest lab grade and assignment grade will be dropped.
TEXT (required)
• Hata, David, Introduction to Vacuum Technology, Pearson Prentice Hall, 2008
• Recommended:– Vacuum Technology and Coating
www.vactechmag.com
COURSE OBJECTIVES
Study vacuum and plasma generation techniques used in microelectronic, thin film and nanotechnology applications
MAJOR TOPICS• Gas flow• Pressure regimes • Gas laws • Out gassing • Vacuum production • Leak & contamination detection• Residual gas analysis (RGA) techniques• Thin film deposition technologies• Safety concerns involved in the
installation, maintenance and operation of vacuum and thin film equipment.
Why Vacuum ?
Vacuum is critical to most semiconductor fabrication processes
Understand the hardware
Understand how it works as a system
If you don’t know how it works you can’t use it intelligently
In many real cases, what you do with or to a vacuum systems has just as much effect on performance as the hardware
What is Vacuum ?
Any gas at sub-atmospheric pressure
Vacuum is really the absence of gas
Vacuum is not absolute, but a continuous range of conditions covering 15 orders of magnitude in common usage (103 to 10-12 Torr)
Vacuum technology involves moving and removing gases
How / Why do we use Vacuum ?• Produce a cleaner environment
– Remove contaminants that can cause unwanted reactions
• Increase mean free path (MFP)– Allow sputtering, evaporation and ion
implantation• Control number of surface collisions
– Sputtering of metal layers– Control rate of film growth in chemical
vapor deposition• Lower molecular density
– Reduce unwanted contaminants– Allow plasma– Increase evaporation rate without
increasing temperature (freeze drying)– Reduce heat conduction
How / Why do we use Vacuum ? (continued)
• Create a force– Hold wafers in place– Move solids or liquids through pipes
• Reduce heat flow– Reduced pressure reduces collisions between
molecules and hence heat transfer decreases– Different gasses have different thermal
conductivities• Increase vaporization
– Fewer molecules impacting surface or knocking vaporized molecules back to surface
• Protect materials from reactive molecules– Pump out reactive molecules and backfill with
inert gas
Clean Environment - Less MatterLower Molecular Interference
Low FrictionThermal Insulation
Promote EvaporationUnique Electrical Properties
"Suction"
Application of Force
To Vacuum PumpBeneficial Properties of Vacuum
Silicon Wafer with Integrated Circuits
How Small ?Human Hair (cross section) 100 micronsLower Limit of visibility (naked eye) 40 micronsSmog, Tobacco Smoke 10 micronsBacteria 2 micronsVirus 0.5 microns
1 micron = 0.001 mm
Devices <0.5 microns
Eight Basic Steps to Form Semiconductor Device
1. Start with Bare Silicon wafer2. Oxidize wafer (form SiO2 Layer)3. Apply photo resist4. Expose resist through a mask5. Develop and remove resist 6. Remove exposed SiO2
7. Dope wafer to form pn junction8. Metallization to form electrical
contacts
Eight Basic Steps to Form Semiconductor Device
1. Start with Bare Silicon wafer2. Oxidize wafer (form SiO2 Layer)3. Apply photo resist4. Expose resist through a mask5. Develop and remove resist 6. Remove exposed SiO2
7. Dope wafer to form pn junction8. Metallization to form electrical
contacts
3-D Integration
COMPLEX PROCESS10 -15 processes per layer>60 layers per wafer>900 processes per wafer
COSTLYFacility: $1-10 Billion Process time per wafer: weeks
High Yield is Necessary
VACUUM IS A CRITICAL PART OF THE PROCESS
Semiconductor Applications
• Crystal growth• Oxidation• Etching• Doping
– Diffusion– Ion Implantation– Epitaxy
• Film deposition– Evaporation– Sputtering– Chemical Vapor Deposition
VACUUM
How to Characterize Vacuum• Just like we characterize a gas
• Pressure: ( force/area)– Force exerted is not really a useful concept
• Volume:– Volume of container
• Temperature:– Temperature of the walls (almost always)
• Number Density: ( number of molecules per unit volume )– Related to Pressure– A more useful quantity than actual
“pressure”
Units of Pressure Pressure is Force
per Unit Area• Pounds/sq. in• Newtons / sq.meter• Tons/ sq. angstrom
Atmospheric Pressure
• 14.7 pounds/sq. in.• 105 Newtons/sq.
meter• 760 Torr• about 1 ton/sq ft
SI UNITS:• Pascal = 1 Newton/
sq. meter• 1 atm = 105 pascals
Non-Si Units: (common units)
• Torr, milliTorr• Bar, millibar
Torr is widely used and understood
• Avoiding it is difficult
“Common” Pressure UnitsPascal, Torr, Bar
Basic unit is mm Hg (1mm Hg = 1 Torr)
Vacuum begins at atmospheric pressure,approximately 760 mm Hg = 760 Torr
1 bar = 100,000 bar = 750 Torr (NOT 760 Torr)1 mbar = 0.75 Torr = 100 Pa
Units:US – TorrEurope – bar or mbarJapan - Pascals
Standard Atmospheric Pressure
• 760 Torr • 1.01325 x 105 Pascal• 1.10325 bar• 1013.25 mbar• 101.325 kPa
• 1 Bar = 105 Pascals = 750 Torr
760
10-3
1
10-8
750
25
7.5 x 10-4
7.5 x 10-7
7.5 x 10-10
7.5 x 10-13
105
3.3 x 103
10-1
10-4
10-7
10-10
Low
Medium
High
Very High
Ultra High
Extreme Ultra High
Rough
Medium
High
Ultra High
25
Torr PascalTorr "Traditional"
AVS
Vacuum Ranges
DistanceBetweenMolecularCollisions
Rough
Medium
High
UltraHigh
Hg
20
360 100
20
-40
Water
Zn
250
Fe, CuAl
>650
EffectiveThermalInsulator
Thermal ConductivityVaries withPressure
Thermal Conductivity
Constant
Self Sustaining
GlowDischarge
EffectiveElectricalInsulator
CollectiveBehavior
ComplexBehavior
MoleculesBehave asIndividuals
microns
mm
meters
km
10,000sof km
Fractionof a
Second
SeveralSeconds
Hours
Days
Vaporization Temperature(Degrees C)
ThermalConductivity
ElectricalConductivity
MolecularBehavior
Time toContaminate
a Surface
Some Properties Related to the Vacuum Environment
-120
Moleculesin 1 liter
(0 Deg. C)
2.7 x 1022
3.5 x 1019
3.5 x 1016
3.5 x 1011
3.5 x 107
450
280
Mg
130
Questions
• Which of these characteristics would determine the degree of vacuum required for:– Thermos bottle– Freeze dryer– Surface science– Large particle accelerators
Questions (answers)
• Which of these characteristics would determine the degree of vacuum required for:– Thermos bottle (thermal conductivity)– Freeze dryer (vaporization temperature)– Surface science (time to contaminate
surface)– Large particle accelerators (mean free path)
Questions
• What are some materials that should be avoided in high or ultra-high vacuum systems?
• Why might these materials be satisfactory for medium vacuum levels?
Questions (answers)
• What are some materials that should be avoided in high or ultra-high vacuum systems? (Mg, Zn, Hg)
• Why might these materials be satisfactory for medium vacuum levels? (low vapor pressure at room temperature)
"Torricellian Vacuum"
An Early VacuumExperiment - 1667
Barometer(Torricelli)
1640s
760 mm(Variable and Less
on the Tops ofTall Mountains)
Discovery of Vacuum
von Guericke's Experimentsat Magdeburg - 1647 - 1657
?Piston AirPump
Evolution of VacuumScience & Technology
Incandescent Lamp
Thermionic Vacuum TubeVacuum EvaporationPirani GaugeIon Gauge
X-Ray Tube
"Canal Ray" Tube
Particle AcceleratorIon SourceMass SpectrometerIon ImplanterCathode Ray Tube
Crookes' Experimentswith Electrical Discharges
in Vacuum - 1870s
SprengelPump - 1865
Traps+
+
Fluorescent LampNeon Sign
Key Developments in the Early 20th Century
Langmuir's UmbrellaDiffusion Pump
1916
Gaede's Box Pump
1910
2 - StageOil
SealedRotaryPump
LiquidRing
6 Stage
3 Stage
1 Stage
SorptionPump
RootsBlower
Hot (Bayard - Alpert)and Cold Cathode
Ion
CapacitanceManometer
Piston &Dry Pumps
Gas Storage &Delivery
SteamEjector
MolecularDragPump
High and Ultra-HighVacuum Pumps:Turbo-Molecular
DiffusionCryogenic
IonTi Sublimation
To 10& Lower
-10
10
10
10
10
10
10
10
10
10
10
10
10
10
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
>> Atm.
To 10& Lower
-10
Epitaxial Film Growth
Vacuum Distillation"Suction"
Plasma EtchLPCVDAshingNeon
Ion Sources
BasePressures
for Backfilled
Applications
NeonCVD
Sputter
RIEMolecular Distillation
Freeze DryingSputter Deposition
DewarsVacuum Metallurgy
Lamps
Evaporated FilmsMass SpectrometersElectron Microscopes
Surface PhysicsParticle Accelerators
Electron Tubes
Torr Production Measurement Application
100 km
200 km
300 km
Altitude Abovethe Earth
SRG
Pirani
Thermo-couple
McLeod
Bourdon
ConvectionPirani
Behaviors and Characteristics of Gases
The Properties of Gases as:
Compressible Fluids
Collections of Individual Molecules
HeH
NeFONC
Si P S Cl Ar
Br Kr
Xe
1.0 4.0
14.012.0 16.0 19.0 20.2
28.1 31.0 32.1 35.5 39.9
79.9 83.8
131.3
Avogadro's LawUnder equal conditions of
temperature and pressure, a given volume will contain the same
number of molecules regardlessof the type of gas.
22.4liters
6.02 x 10 molecules23
He 4 gmsO 32 gmsXe 131 gms
2
T = 0 CP = 760 Torr
o
One mole of a substance will have a mass, in grams,equal to the atomic mass of the substance
½
1 2
Pressure
Pressure results from molecules hitting asurface. It equals force per unit area andis related to molecular mass and velocity.
Equal numbers of molecules of any type ina given volume at the same temperature
will exert the same pressure.
HeH
NeFONC
Si P S Cl Ar
Br Kr
Xe
1.0 4.0
14.012.0 16.0 19.0 20.2
28.1 31.0 32.1 35.5 39.9
79.9 83.8
131.3
Number
Speed (m/s)
HeavierCooler
LighterWarmer
Nitrogen at 20 °C
500
Velocity Distribution of Gas Molecules
Question
• Some vacuum gauges work on the principle of inferring pressure from a gas’ thermal conductivity.
• Describe some disadvantages that arise from using this principle.
Discussion• Different gases have different thermal
conductivities
• Pressure reading depends on thermal conductivity of gas– Light gases move faster & have higher
thermal conductivity (He, H2)– Heavier gases move slower & have lower
thermal conductivity (Ar, Xe)
Must calibrate thermal conductivity gauge with the gas it will measure
Question
• Some gauges work on the basis of measuring true pressure as expressed in force per unit area. What is a major advantage of this approach?
Discussion
• Pressure is a measure of number density (number molecules / unit volume)
The Ideal Gas Law
Defines the Relationship Between Pressure, Volume, Temperature and
Type & Amount of Gas
PV = (nR)T
P = Pressure in Torr V = Volume in LitersT = Temperature in Kn = Amount of Gas in MolesR = Universal Gas Constant
½
1 2
K
Question
• Describe some mechanisms that would result in a reduction of pressure in the vessel on the previous slide
• Hint: PV=nRT
10 -3
10 -2
10 -1
10 0
10 1
10 2
10 3
Kr, H ,N O,Xe, O ,CH
2 2
3 4
He, Ne
CO2
Ar
H O2
2O
2N
Dalton's Law of Partial Pressures
Cumulative partial pressures of themajor constituents of room air (in
Torr) at 50% relative humidity
In a mixture of gases, the total pressure is the sum of the pressures
exerted by each of theconstituent gases.
PartialPressure
TotalPressure
0.1 0.5 1.0 5 10 50 100
10 -6
10
1
0.1
0.01
0.001
10
10
-5
-4
10 -7
Pressure (Torr)
Mean Free Path (cm)
Mean Free PathThe Mean Free Path (MFP) is the averagedistance traveled by molecules between
collisions. For air at standard temperature:
MFP =5 x 10
-3
PTorr
(cm)
Flow• So far we have discussed the properties
of gases contained in a bound volume
• In most applications a gas is flowing through a system of pipes, chambers and pumps
• Depending on the pressure, the flow characteristics of gases can change dramatically
Viscous Flow
Motions ofIndividualMolecules Net Motion of Gas
VelocityDistribution
Region ofHigher
Pressure
Viscous - LaminarFlow
TurbulentFlow
Region ofLower
Pressure
Mean Free Path isSubstantially Smaller than
the Line or Chamber Diameter
Viscous Flow - The Knudsen Number
Pressure (Torr)
Mean Free Path or d (cm)
The Knudsen Number (K ) is therelationship between Mean Free Path(MFP) and the controlling dimension(d) of a system element.
n
K =n
MFP
d
When K <0.01, the flow will be viscous.
n
0.1 0.5 1.0 5 10 50 100
10 -6
10
1
0.1
0.01
0.001
10
10
-5
-4
10 -7
MFP
Viscous Flow Regime
Example• Calculate minimum pressure for
viscous flow in a pipe 1 inch (2.54 cm) in diameter
• d=2.54 cm, Kn<0.01
torrMFP
P
cmcmdKMFP n
12
33
2
)10(0.2)10(54.2
)10(5)10(5
)10(54.2)54.2(01.0
Molecular Flow
HigherPressure,
HigherImpingement
Rate
LowerPressure,
LowerImpingement
Rate
?
Mean Free Path is Larger than the
Line or Chamber Diameter
Molecular Flow
• MFP>chamber diameter• Calculate maximum pressure for
molecular flow in 1 inch pipe
torrMFP
P 333
)10(0.254.2
)10(5)10(5
Pressure (Torr)
Mean Free Path or d (cm)
0.1 0.5 1.0 5 10 50 100
10 -6
10
1
0.1
0.01
0.001
10
10
-5
-4
10 -7
Molecular FlowRegime
TransitionRegion
Viscous FlowRegime
Flow Regimes
d
Conductance
The Ability of a Gas to PassThrough the Various
System Elements
P1
P2
Simple Line
P1
P2
Valve
P1
P2
P1
P2> >
P1
P2
<P1
P2
Pump
Conductance as Volumetric Flow
1 liter
1 per sec.
Volumetric Flow is defined as the volume of gas, atthe prevailing pressure, that is transported in a given
amount of time through a conducting element.
The commonly used units are liters per second.
Volumetric Flow does not indicate the quantity(mass or number of molecules) of gas
being transferred.
Conveyor Conductance = 1 liter per second
Q = PS• Q = Throughput
– Torr-Liters/sec
• P = Pressure – Torr
• S = Speed – Liters/sec
Conductance in Viscous Flow
½
1 2
½
1 2
d
L
For Laminar - Viscous Flow in a Long Tubewith Nitrogen at Room Temperature:
aveC = 188 x x P
d4
L
P1
P2
liters / sec
Conductance in Molecular Flow
We saw previously that the flow of a gas that is in the molecularregime through a tube is related to the impingement rate.
The impingement rate varies with the molecular density of the gaswhich, in turn, varies with the pressure.
Since these factors go hand in hand, it turns out that pressuredoes not play a factor in the conductance of tubes in the molecular flow regime.
For nitrogen at room temperature:
C = liters / secL
12.3 x d3
Things to Remember About Conductance
Lines should be as short and fat as possible.
It is better to be fat than short.
A tube in molecular flow will have a lower conductance than that of the same tube in viscous flow.
Although there is a net flow direction for gases in molecularflow, individual molecules will be traveling in both directionsthrough the tube.
Some Common Joining Methods
Elastomer Sealed Connectors
Metal Sealed Connectors
ISO- KF FlangesClamping Ring
FlangeMetal Center Ring
with O-Ring
Compression Set
Fresh O-Ring,Uncompressed
O-Ring in Use,Maximum Compression
O-Ring After Use,with Permanent Set
Normal Compression
Set
Other Common Applications of O-Ring Seals
Valve Face Seal -O-Ring Captured inTrapezoidal Groove
Compression Connectorfor Round Tubing Rotating Shaft Seal Through
Vacuum Wall
Requirement Acceptable Not Acceptable
General Chem. Resistance Viton, Teflon, Kalrez, Kel-F Silicone, Polyurethane
Ozone Resistance Viton, Propyl Buna-N
Temp to 150 C, Low Set Viton E-60C, Silicone Teflon, Viton A, Buna
Temp above 150 C, Low Outgassing
Polyimide, Kalrez Viton
Moderate/Low Outgassing at 20 C after 150 Bake
Viton Any Material with Low Temperature Limit
Low Permeation Kel-F, Viton, Butyl Silicone
Radiation Resistance Polyimide, Polyurethane Teflon, Butyl, Viton
General Purpose, Low Cost Buna-N Kalrez
Elastomer Selection
CF Flanges
Knife Edge Flange
Copper Gasket
Mechanism For ProvidingSpring Force to Seal Area
Issues and Practices for High Vacuum
Gas Load & Base Pressure
Mass Quantity & Throughput
Cleanliness
Materials
Construction
Enemies of Vacuum & Cleanliness
BackstreamingVirtual Leaks
Permeation
Real Leaks
Particulates
Elastomer Seal onBaseplate
MetalVacuum
Wall
Diffusion
Permeation
Vaporization
Desorption
VacuumEnvironment AmbientCondensates
Grime
Rough
Medium
High
UltraHigh
CondensationParticulate GenerationLarge LeaksGross ContaminationVolume & Loosely
Bound Water
Elastomer Outgassing andPermeation
Surface Desorption
Diffusion Through Metal
Permeation Through Metal
Vaporization
Admittance ofRoom Air
Backstreaming
Next Time
• Gauges – Thermal Conductivity– Capacitance Manometer
• Rotary pumps
Vacuum Gauging
Ranges and Operating Principlesof Common Vacuum Gauges
Indirect Gauges
Direct Gauges
Rough
Medium
High
UltraHigh
ThermalConductivity
of Residual Gas
Ionization of Residual Gas Drag Induced byResidual Gas onMoving Object
Force Appliedto Surface
Hot &Cold
CathodeIon
Gauges
ResidualGas
Analyzer
GasComposition
Analysis
SystemTotal
PressureMeasurement
SpinningRotorGauge
CapacitanceManometer
Ranges of Vacuum Gauges
Thermo-couple &
PiraniGauges
ConvectionPirani
Atm
10 0
10 -3
10 -8
Medium VacuumSystem
PressureReadout
Mechanical PumpsTime ConstantProblems and SolutionsSystem Pressure ProfileSimple System Diagnostics
Time
Rough
Medium
Isolation &Soft Pump Valves
TrapPump Isolation& Vent Valves
ChamberVent Valve
Chamber
Gauge
Pump
Assignment (due next lecture)
• Text – page 7, Problem 6• Text – Read chapter 2• Prepare for quiz on today’s lecture
– 10 semiconductor manufacturing steps
– MFP calculation– Other?