F10 lec01 overview

VACUUM AND THIN FILM TECHNOLOGY

ELET 250

Dr. Fred Strnisaf.strnisa@hvcc.edu

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

Wafer with Scale

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?