The minimum pressure for viscous flow in a 1 inch diameter pipe is approximately 5 Torr. At 5 Torr, the mean free path is 0.2 cm. The Knudsen number is then: Kn = MFP/d = 0.2 cm / 2.54 cm = 0.078 Since Kn < 0.01, the flow will be viscous at or below 5 Torr pressure.

1. VACUUM AND THIN FILM
TECHNOLOGY
ELET 250
Dr. Fred Strnisa
f.strnisa@hvcc.edu

2. CLASS ACTIVITIES
• Lectures
• Demonstrations
• Homework
• Laboratory exercises and reports
• Quizzes and exams
• Visit a local clean room facility

3. GRADES
Weekly quizzes, exams, homework 50%
Lab 25%
Final Exam 25%

4. 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.

5. TEXT (required)
• Hata, David, Introduction to Vacuum
Technology, Pearson Prentice Hall,
2008
• Recommended:
– Vacuum Technology and Coating
www.vactechmag.com

6. COURSE OBJECTIVES
Study vacuum and plasma generation
techniques used in microelectronic, thin film
and nanotechnology applications

7. 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.

8. 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

9. 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

10. 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

11. 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

12. Clean Environment - Less Matter
Lower Molecular Interference
Low Friction
Thermal Insulation
Promote Evaporation
Unique Electrical Properties
"Suction"
Application
of Force
To Vacuum PumpBeneficial Properties
of Vacuum

13. Silicon Wafer with Integrated Circuits

14. Wafer with Scale

15. How Small ?
Human Hair (cross section) 100 microns
Lower Limit of visibility (naked eye) 40 microns
Smog, Tobacco Smoke 10 microns
Bacteria 2 microns
Virus 0.5 microns
1 micron = 0.001 mm
Devices <0.5 microns

16. Eight Basic Steps to
Form Semiconductor Device
1. Start with Bare Silicon wafer
2. Oxidize wafer (form SiO2 Layer)
3. Apply photo resist
4. Expose resist through a mask
5. Develop and remove resist
6. Remove exposed SiO2
7. Dope wafer to form pn junction
8. Metallization to form electrical contacts

22. Eight Basic Steps to
Form Semiconductor Device
1. Start with Bare Silicon wafer
2. Oxidize wafer (form SiO2 Layer)
3. Apply photo resist
4. Expose resist through a mask
5. Develop and remove resist
6. Remove exposed SiO2
7. Dope wafer to form pn junction
8. Metallization to form electrical contacts

23. 3-D Integration

24. COMPLEX PROCESS
10 -15 processes per layer
>60 layers per wafer
>900 processes per wafer
COSTLY
Facility: $1-10 Billion
Process time per wafer: weeks
High Yield is Necessary
VACUUM IS A CRITICAL PART OF
THE PROCESS

25. Semiconductor Applications
• Crystal growth
• Oxidation
• Etching
• Doping
– Diffusion
– Ion Implantation
– Epitaxy
• Film deposition
– Evaporation
– Sputtering
– Chemical Vapor Deposition

26. VACUUM

27. 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”

28. 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

29. “Common” Pressure Units
Pascal, 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 – Torr
Europe – bar or mbar
Japan - Pascals

30. 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

32. 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
10
5
3.3 x 10
3
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 Pascal
Torr "Traditional"
AVS
Vacuum Ranges

33. Distance
Between
Molecular
Collisions
Rough
Medium
High
Ultra
High
Hg
20
360 100
20
-40
Water
Zn
250
Fe, Cu
Al
>650
Effective
Thermal
Insulator
Thermal
Conductivity
Varies with
Pressure
Thermal
Conductivity
Constant
Self
Sustaining
Glow
Discharge
Effective
Electrical
Insulator
Collective
Behavior
Complex
Behavior
Molecules
Behave as
Individuals
microns
mm
meters
km
10,000s
of km
Fraction
of a
Second
Several
Seconds
Hours
Days
Vaporization Temperature
(Degrees C)
Thermal
Conductivity
Electrical
Conductivity
Molecular
Behavior
Time to
Contaminate
a Surface
Some Properties Related to the Vacuum Environment
-120
Molecules
in 1 liter
(0 Deg. C)
2.7 x 10
22
3.5 x 1019
3.5 x 1016
3.5 x 1011
3.5 x 107
450
280
Mg
130

34. Questions
• Which of these characteristics would
determine the degree of vacuum
required for:
– Thermos bottle
– Freeze dryer
– Surface science
– Large particle accelerators

35. 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)

36. 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?

37. 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)

40. Key Developments in the Early 20th Century
Langmuir's Umbrella
Diffusion Pump
1916
Gaede's
Box Pump
1910

41. 2 - Stage
Oil
Sealed
Rotary
Pump
Liquid
Ring
6 Stage
3 Stage
1 Stage
Sorption
Pump
Roots
Blower
Hot (Bayard - Alpert)
and Cold Cathode
Ion
Capacitance
Manometer
Piston &
Dry Pumps
Gas Storage &
Delivery
Steam
Ejector
Molecular
Drag
Pump
High and Ultra-High
Vacuum Pumps:
Turbo-Molecular
Diffusion
Cryogenic
Ion
Ti 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 Etch
LPCVD
Ashing
Neon
Ion Sources
Base
Pressures
for
Backfilled
Applications
Neon
CVD
Sputter
RIE
Molecular Distillation
Freeze Drying
Sputter Deposition
Dewars
Vacuum Metallurgy
Lamps
Evaporated Films
Mass Spectrometers
Electron Microscopes
Surface Physics
Particle Accelerators
Electron Tubes
Torr Production Measurement Application
100 km
200 km
300 km
Altitude Above
the Earth
SRG
Pirani
Thermo-
couple
McLeod
Bourdon
Convection
Pirani

42. Behaviors and Characteristics of Gases
The Properties of Gases as:
Compressible Fluids
Collections of Individual Molecules

43. 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 Law
Under equal conditions of
temperature and pressure, a given
volume will contain the same
number of molecules regardless
of the type of gas.
22.4
liters
6.02 x 10 molecules
23
He 4 gms
O 32 gms
Xe 131 gms
2
T = 0 C
P = 760 Torr
o
One mole of a substance will have a mass, in grams,
equal to the atomic mass of the substance

44. ½
1 2
Pressure
Pressure results from molecules hitting a
surface. It equals force per unit area and
is related to molecular mass and velocity.
Equal numbers of molecules of any type in
a given volume at the same temperature
will exert the same pressure.

45. 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)
Heavier
Cooler
Lighter
Warmer
Nitrogen at
20 °C
500
Velocity Distribution of Gas Molecules

46. 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.

47. 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

48. 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?

49. Discussion
• Pressure is a measure of number
density (number molecules / unit
volume)

50. 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 Liters
T = Temperature in K
n = Amount of Gas in Moles
R = Universal Gas Constant
½
1 2
K

51. Question
• Describe some mechanisms that would
result in a reduction of pressure in the
vessel on the previous slide
• Hint: PV=nRT

52. 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 the
major 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 the
constituent gases.
Partial
Pressure
Total
Pressure

53. 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 Path
The Mean Free Path (MFP) is the average
distance traveled by molecules between
collisions. For air at standard temperature:
MFP =
5 x 10
-3
PTorr
(cm)

54. 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

55. Viscous Flow
Motions of
Individual
Molecules Net Motion of Gas
Velocity
Distribution
Region of
Higher
Pressure
Viscous - Laminar
Flow
Turbulent
Flow
Region of
Lower
Pressure
Mean Free Path is
Substantially Smaller than
the Line or Chamber Diameter

56. Viscous Flow - The Knudsen Number
Pressure
(Torr)
Mean Free Path or d (cm)
The Knudsen Number (K ) is the
relationship 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

57. Example
• Calculate minimum pressure for viscous
flow in a pipe 1 inch (2.54 cm) in
diameter
• d=2.54 cm, Kn<0.01
torr
MFP
P
cmcmdKMFP n
1
2
33
2
)10(0.2
)10(54.2
)10(5)10(5
)10(54.2)54.2(01.0

58. Molecular Flow
Higher
Pressure,
Higher
Impingement
Rate
Lower
Pressure,
Lower
Impingement
Rate
?
Mean Free Path is
Larger than the
Line or Chamber Diameter

59. Molecular Flow
• MFP>chamber diameter
• Calculate maximum pressure for
molecular flow in 1 inch pipe
torr
MFP
P 3
33
)10(0.2
54.2
)10(5)10(5

60. 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 Flow
Regime
Transition
Region
Viscous Flow
Regime
Flow Regimes
d

61. Conductance
The Ability of a Gas to Pass
Through the Various
System Elements
P1
P2
Simple Line
P1
P2
Valve
P1
P2
P1
P2
> >
P1
P2
<P1
P2
Pump

62. Conductance as Volumetric Flow
1 liter
1 per sec.
Volumetric Flow is defined as the volume of gas, at
the 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

63. Q = PS
• Q = Throughput
– Torr-Liters/sec
• P = Pressure
– Torr
• S = Speed
– Liters/sec

64. Conductance in Viscous Flow
½
1 2
½
1 2
d
L
For Laminar - Viscous Flow in a Long Tube
with Nitrogen at Room Temperature:
ave
C = 188 x x P
d
4
L
P1
P2
liters / sec

65. Conductance in Molecular Flow
We saw previously that the flow of a gas that is in the molecular
regime through a tube is related to the impingement rate.
The impingement rate varies with the molecular density of the gas
which, in turn, varies with the pressure.
Since these factors go hand in hand, it turns out that pressure
does not play a factor in the conductance of tubes in the
molecular flow regime.
For nitrogen at room temperature:
C = liters / sec
L
12.3 x d
3

66. 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 molecular
flow, individual molecules will be traveling in both directions
through the tube.

67. Some Common Joining Methods
Elastomer Sealed Connectors
Metal Sealed Connectors

68. ISO- KF Flanges Clamping Ring
Flange
Metal Center Ring
with O-Ring

69. Compression Set
Fresh O-Ring,
Uncompressed
O-Ring in Use,
Maximum Compression
O-Ring After Use,
with Permanent Set
Normal Compression
Set

70. Other Common Applications
of O-Ring Seals
Valve Face Seal -
O-Ring Captured in
Trapezoidal Groove
Compression Connector
for Round Tubing Rotating Shaft Seal Through
Vacuum Wall

71. 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

72. CF Flanges
Knife Edge Flange
Copper Gasket
Mechanism For Providing
Spring Force to Seal Area

73. Issues and Practices for High Vacuum
Gas Load & Base Pressure
Mass Quantity & Throughput
Cleanliness
Materials
Construction

74. Enemies of Vacuum & Cleanliness
Backstreaming
Virtual Leaks
Permeation
Real Leaks
Particulates
Elastomer Seal on
Baseplate
Metal
Vacuum
Wall
Diffusion
Permeation
Vaporization
Desorption
Vacuum
Environment
AmbientCondensates
Grime
Rough
Medium
High
Ultra
High
Condensation
Particulate Generation
Large Leaks
Gross Contamination
Volume & Loosely
Bound Water
Elastomer Outgassing and
Permeation
Surface Desorption
Diffusion Through Metal
Permeation Through Metal
Vaporization
Admittance of
Room Air
Backstreaming

75. Next Time
• Gauges
– Thermal Conductivity
– Capacitance Manometer
• Rotary pumps

76. Vacuum Gauging
Ranges and Operating Principles
of Common Vacuum Gauges
Indirect Gauges
Direct Gauges

77. Rough
Medium
High
Ultra
High
Thermal
Conductivity
of Residual Gas
Ionization of Residual Gas Drag Induced by
Residual Gas on
Moving Object
Force Applied
to Surface
Hot &
Cold
Cathode
Ion
Gauges
Residual
Gas
Analyzer
Gas
Composition
Analysis
System
Total
Pressure
Measurement
Spinning
Rotor
Gauge
Capacitance
Manometer
Ranges of Vacuum Gauges
Thermo-
couple &
Pirani
Gauges
Convection
Pirani
Atm
100
10-3
10
-8

78. Medium Vacuum
System Pressure
Readout
Mechanical Pumps
Time Constant
Problems and Solutions
System Pressure Profile
Simple System Diagnostics
Time
Rough
Medium
Isolation &
Soft Pump Valves
Trap
Pump Isolation
& Vent Valves
Chamber
Vent Valve
Chamber
Gauge
Pump

79. 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?