Vacuum Technology
• Need for Vacuum Environment
• Vacuum processes used in
nano-manufacturing
• Vacuum and Gas Properties
• Measurement and creation of a
partial vacuum environment
Vacuum Fundamentals
Learning Objectives
• To develop an understanding of the
applications of vacuum technology in
nanomanufacturing.
• To be able to explain the basic behavior of
gases, based on the temperature,
pressure, volume and molecular density
present in the environment.
• To be able to define the basic units of
vacuum
Vacuum Fundamentals
What is a Vacuum?
• Ideal Vacuum
– A space totally devoid of all matter.
– Does not exist, even in outer space!
• Actual Vacuum (Partial Vacuum)
– A space containing gas at a pressure below
the surrounding atmosphere or atmospheric
pressure
• <760T @ sea level and 00 C with no humidity
Vacuum Fundamentals
Why Might We Need Vacuum?
• A vacuum provides a clean environment
– Devoid of possible contamination from other
gases that may be present from the
atmosphere
– Devoid of particles that may react with
physical processes that are intended to take
place
– Devoid of pressure that may limit restrict a
desired physical process
Vacuum Fundamentals
Common Uses of Vacuum
• Light Bulbs
– A vacuum pump removes oxygen from a light bulb so
that the filament won’t “burn out” (oxidation)
• Food Processing
– Vacuum sealing eliminates oxygen from food
containers to preserve the contents
• Plastics Manufacturing
– Vacuum-forming “draws” plastic sheets into shapes
such as “blister packs”
Vacuum Fundamentals
Where Do We Use
Vacuum in
Nanomanufacturing?
Vacuum Fundamentals
To Retain a Clean Surface
• Objective
– Clean surfaces
• Applications:
– Friction
– Adhesion
– Emission studies
– Materials testing for space
Vacuum Fundamentals
To Create Desired Features
• Objective
– Create Insulators
• SiO2
• SiN2
– Create Conductive
Layers
• Evaporative Coatings
• Sputtered Coatings
– To etch or remove
material
• Plasma Etch
• Reactive Ion Etching
Sputtering Coating System
http://www.teercoatings.co.uk
Vacuum Fundamentals
To Visualize Nano-features
• Objective
– View extremely small
Objects
• Scanning Electron
Microscopy
• Electron beam strikes
object being viewed
• Backscatter of electrons
is used to “image”
– Atmospheric
molecules present
may be “hit” by the
beam
http://en.wikipedia.org/wiki/Image:SEM_chamber1.JPG#file
Vacuum Fundamentals
Practice Questions
Click once for each question.
1. What is an Ideal Vacuum?
A space devoid of all matter.
2. What is one application of vacuum technology in
nanomanufacturing?
Sputtering or evaporative coating of metals or scanning
electron microscopy
Vacuum Fundamentals
The Basics of Vacuum and
Pressure
• Vacuum can simply be
thought of as a reduced
air pressure environment
– Atmospheric Pressure
comes from molecules of
oxygen, nitrogen, and other
gases present in air
– At sea level, this pressure
corresponds to 14.7 PSI or
760 torr (in honor of
Torricelli) which
corresponds to the number
of mm height of the
mercury column in the
barometer shown here.
Vacuum Fundamentals
The Basics of Vacuum and
Pressure
• In vacuum systems,
we remove the
atmospheric gases in
an enclosed area
– Fewer molecules of
gas result in lower
pressure
– Any pressure less
than or 760 torr can be
considered a partial
vacuum.
Vacuum Fundamentals
Ranges of Vacuum
Low or Rough
760 Torr to 1Torr
Vacuum
Medium Vacuum 1 Torr to 10-3
Torr
High Vacuum
10-3 to 10-7 Torr
Ultra-high
Vacuum (UHV)
Below 10-7 Torr
Vacuum Fundamentals
Typical Vacuum
Levels Required for Processing
Evaporative
Coatings
Light bulb
manufacturing
Scanning
electron
microscope
Electron Beam
Lithography
10-2 to 1 torr
10-3 to 10-1 Torr
10-4 to 10-7 Torr
Below 10-7 Torr
Vacuum Fundamentals
Gas Properties
• Gases consist of tiny particles called
molecules or atoms.
• Molecules are so far apart that any
attractive forces are ignored.
Vacuum Fundamentals
Four Qualities of a Gas
•
•
•
•
Volume (V)
Pressure (P)
Temperature (T)
Number of molecules (N)
Vacuum Fundamentals
Pressure and Molecular Density
• Pressure is a function of the number of
molecules present in a given volume.
Vacuum Fundamentals
Pressure and Molecular Density
• Molecules of gases tend to spread out, evenly applying force to the
containment chamber
• A larger volume, with the same number of molecules present, would
be at lower pressure than a smaller one
• Boyle’s Law - a relationship between pressure and volume
Vacuum Fundamentals
Pressure and Temperature
• As an equal number of molecules in an identical volume
is heated, the pressure increases (Guy-Lussac’s Law)
Vacuum Fundamentals
Kelvin Scale
C = .555 * (F – 32)
F = 1.8 * (C + 32)
K = (C + 273)
Vacuum Fundamentals
Charles’ Law
Volume and Temperature
Vacuum Fundamentals
Combined Gas Law
• The relationships between pressure,
temperature, and volume given in Boyle’s,
Charles’, and Gay-Lussac’s Law for a
constant number of gas molecules can be
taken together as the Combined Gas Law.
• This law can be used two of the 3
properties are known to find the third.
(P1 * V1) / T1 = (P2 * V2) / T2
Vacuum Fundamentals
Practice Questions
Click once for each question.
1. If the pressure in a 10L chamber is 50 torr, what
will the pressure for the same amount of gas be if
the chamber is 20L?
25 torr
2. The temperature of a sealed vacuum chamber at
10 torr increases 10 degrees. What will happen to
the pressure in the chamber?
The pressure will increase
Vacuum Fundamentals
Avogadro’s Law
• A volume of any gas containing 6.02 x 1023
(Avogadro’s number) atoms or molecules
is said to contain 1 mole.
• The special condition of a gas at one
atmosphere of pressure (760 Torr) and
273 K (0 C) is called standard temperature
and pressure (STP).
• At STP one mole of any gas occupies 22.4
liters (l), this is called molar volume.
Vacuum Fundamentals
Avogadro’s Law (2)
• Pressure is proportional to the number of
molecules at a constant temperature.
• Equal volumes of gas at the same
temperature and pressure contain the
same number of molecules (or moles, n).
P1 / n1 = P2 / n2
Vacuum Fundamentals
Ideal Gas Law
• The Ideal Gas Law can be used to calculate the
amount of gas (the molecular density) in a
known volume, with known pressure and
temperature.
• PV = nRT
–
–
–
–
–
P = pressure (Torr)
V = volume (liter)
n = amount of gas (moles)
T = temperature (K)
R = universal gas constant (62.4 Torr liter per
Vacuum Fundamentals
mole/K)
Click once for each answer.
• Given: P1 = 50 Torr, n1 = 0.5 mole, P2 = 2
Torr, if the volume and temperature remain
constant, what is n2?
• Solve for: 2
P1 / n1 = P2 / n2
2 = (2 Torr)*(0.5 mole)
50 Torr
2 = 0.02 mole
Vacuum Fundamentals
Vapor Pressure
Evaporation is the process
where a liquid changes to
a gaseous phase
In an open environment,
liquids continuously
evaporate
In a closed environment,
eventually an equilibrium
condition occurs where
evaporation and
condensation rates
become the same. This
occurs when the air
becomes saturated.
Vacuum Fundamentals
Vapor Pressure
We know that water
changes from a liquid to a
vapor state when we boil
it (temp above 100 deg
C) under normal
atmospheric conditions.
This occurs because at this
temperature, the vapor
pressure of the water
overcomes the
atmospheric pressure.
If we lower the pressure,
water boils at a lower
temperature.
Source:http://upload.wikimedia.org/
wikipedia/commons/2/25/Water_va
por_pressure_graph.jpg
Vacuum Fundamentals
Vapor Pressure
The vapor pressure of a substance in a
chamber is important for a number of
reasons.
• Possibility of vaporization of the substance
under low pressure
– May add to gas load of system
• Use of vaporization for processing
– Physical evaporative coatings
Vacuum Fundamentals
Vapor Pressure of Substances
Vacuum Fundamentals
Vapor Pressure
Vacuum evaporation can be
used to deposit metallic
coatings on surfaces.
The material is melted in a
heated crucible and goes
from solid to vapor state.
Vapor particles are
deposited on the surface
in straight line
trajectories.
CHA-600 Thermal Evaporator
Vacuum Fundamentals
Practice Questions
Click once for each question.
1. If a material in a vacuum environment has a vapor
pressure of 50mTorr, what will happen if the
chamber pressure is reduced to 5 m Torr?
The material will evaporate and become part of the gas
load.
2. The Vapor Pressure of Lubricant A is 10-4 Torr
and for Lubricant B it is 10-8 Torr. Which lubricant
would be best to use in a vacuum system and
why?
Lubricant B, since it is less likely to evaporate due to its
lower vapor pressure when the chamber is pumped
down
Vacuum Fundamentals
Molecular Density and Mean Free
Path
• Gas molecules collide with one another
• Lower pressure results in fewer molecules per unit volume.
Vacuum Fundamentals
Molecular Density and Mean Free
Path
• In the evaporative deposition system earlier described, a larger
mean free path means that there are fewer molecules of air present
to deflect the evaporated metal.
Vacuum Fundamentals
Practice Questions
Click once for each question.
1. If the pressure in a chamber drops from 1 millitorr
to 0.001 millitor, what happens to the mean free
path?
It increases.
2. What the condition where the rate of evaporation
and condensation in a closed container are equal
known as?
Saturation
Vacuum Fundamentals