Vacuum Fundamentals • Need for Vacuum Environment • Vacuum processes used in nano-manufacturing • Vacuum and Gas Properties • Measurement and creation of a partial vacuum environment Vacuum Technology
Feb 12, 2016
Vacuum Fundamentals
• Need for Vacuum Environment • Vacuum processes used in
nano-manufacturing• Vacuum and Gas Properties• Measurement and creation of a
partial vacuum environment
Vacuum Technology
Vacuum Fundamentals
• 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
Learning Objectives
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
• 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
Why Might We Need Vacuum?
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 Systemhttp://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
1. What is an Ideal Vacuum? Click once for each question.
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
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
Ranges of Vacuum
Vacuum Fundamentals
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
Typical VacuumLevels Required for Processing
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’ LawVolume 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
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?
Click once for each question.
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 mole/K)
Vacuum Fundamentals
• 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
Click once for each answer.
Vacuum Fundamentals
Vapor PressureEvaporation 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 PressureWe 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_vapor_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 PressureVacuum 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
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?
Click once for each question.
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
1. If the pressure in a chamber drops from 1 millitorr to 0.001 millitor, what happens to the mean free path?
Click once for each question.
It increases.
2. What the condition where the rate of evaporation and condensation in a closed container are equal known as?
Saturation