Vacuum Technology

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

2. 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

3. 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

4. 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

5. 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”

6. Where Do We Use Vacuum in Nanomanufacturing?

7. To Retain a Clean Surface • Objective • Clean surfaces • Applications: • Friction • Adhesion • Emission studies • Materials testing for space

8. 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

9. 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

10. 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

11. 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.

12. 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.

13. Ranges of Vacuum

14. Typical VacuumLevels Required for Processing

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

16. Four Qualities of a Gas • Volume (V) • Pressure (P) • Temperature (T) • Number of molecules (N)

17. Pressure and Molecular Density • Pressure is a function of the number of molecules present in a given volume.

18. 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

19. Pressure and Temperature • As an equal number of molecules in an identical volume is heated, the pressure increases (Guy-Lussac’s Law)

20. Kelvin Scale C = .555 * (F – 32) F = 1.8 * (C + 32) K = (C + 273)

21. Charles’ LawVolume and Temperature

22. 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

23. 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

24. 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.

25. 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

26. 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)

27. 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

28. 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.

29. 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_vapor_pressure_graph.jpg

30. 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

31. Vapor Pressure of Substances

32. 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

33. 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

34. Molecular Density and Mean Free Path • Gas molecules collide with one another • Lower pressure results in fewer molecules per unit volume.

35. 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.

36. 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