Vacuum%20Technology

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Vacuum Technology

• Need for Vacuum Environment
• Vacuum processes used in nano-manufacturing
• Vacuum and Gas Properties
• Measurement and creation of a partial vacuum
  environment

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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

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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
• lt760T _at_ sea level and 00 C with no humidity

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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

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Common Uses of Vacuum

• Light Bulbs
• A vacuum pump removes oxygen from a light bulb so
  that the filament wont 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

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Where Do We Use Vacuum in Nanomanufacturing?
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To Retain a Clean Surface

• Objective
• Clean surfaces
• Applications
• Friction
• Adhesion
• Emission studies
• Materials testing for space

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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
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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/ImageSEM_chamber1.JP
Gfile
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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
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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.

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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.

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Ranges of Vacuum
Low or Rough Vacuum 760 Torr to 1Torr
Medium Vacuum 1 Torr to 10-3 Torr
High Vacuum 10-3 to 10-7 Torr
Ultra-high Vacuum (UHV) Below 10-7 Torr
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Typical VacuumLevels Required for Processing
Evaporative Coatings 10-2 to 1 torr
Light bulb manufacturing 10-3 to 10-1 Torr
Scanning electron microscope 10-4 to 10-7 Torr
Electron Beam Lithography Below 10-7 Torr
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Gas Properties

• Gases consist of tiny particles called molecules
  or atoms.
• Molecules are so far apart that any attractive
  forces are ignored.

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Four Qualities of a Gas

• Volume (V)
• Pressure (P)
• Temperature (T)
• Number of molecules (N)

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Pressure and Molecular Density

• Pressure is a function of the number of molecules
  present in a given volume.

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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
• Boyles Law - a relationship between pressure and
  volume

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Pressure and Temperature

• As an equal number of molecules in an identical
  volume is heated, the pressure increases
  (Guy-Lussacs Law)

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Kelvin Scale

• ?C .555 (?F 32)
• ?F 1.8 (?C 32)
• K (?C 273)

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Charles LawVolume and Temperature
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Combined Gas Law

• The relationships between pressure, temperature,
  and volume given in Boyles, Charles, and
  Gay-Lussacs 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
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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
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Avogadros Law

• A volume of any gas containing 6.02 x 1023
  (Avogadros 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.

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Avogadros 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
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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
  mole/K)

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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
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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.

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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.

Sourcehttp//upload.wikimedia.org/wikipedia/commo
ns/2/25/Water_vapor_pressure_graph.jpg
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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

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Vapor Pressure of Substances
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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
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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
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Molecular Density and Mean Free Path

• Gas molecules collide with one another
• Lower pressure results in fewer molecules per
  unit volume.

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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.

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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