1. High-Vacuum Technology Course
Week 5
Paul Nash
HE Subject Leader (Engineering)

2. Vacuum Technology Recap on last session
Progress on assignments to date
This activity presents fundamental information on vacuum. The principles of vacuum are related to a basic set of properties that relate to gases. Some of the processes that take place in the top-down nanomanufacturing environment require vacuum conditions in order to proceed correctly or to avoid contamination. The measurement of the level of vacuum present in the process is important, as the levels required vary for each type of process.
To be able to understand the various concepts involved with vacuum technology, it is important that the basic concepts of vacuum and its associated terminology be discussed.
The Vacuum Fundamentals Module covers the basic concepts of pressure, gas laws, and gas characteristics .
These topics are fundamental to the understanding of vacuum systems.
MATEC M097SS01.ppt

3. Learning Objectives
To be able to describe the properties of a variety of materials in a vacuum environment
To be able to select materials for use in a vacuum environment
Describe activities and what to expect
The learning objectives of this activity include developing a basic understanding of what a vacuum is. Since vacuum defines the absence of molecules, and gases are usually what need to be removed from an environment, the knowledge of gas behaviors is essential. The units of vacuum are presented in terms of pressure, as any vacuum can be described as the absence of pressure.
MATEC M097SS01.ppt

4. Vacuum Pumps Work from previous session ……..

5. Throughput
By stating the flow in terms of pressure times volume flow rate, the variation in gas density with pressure is allowed for
This gives a flow unit that relates directly to the actual quantity of gas in the flow:

6. Vacuum Pump Types Low and medium vacuum. Rotary Vane
Vacuum Pump Types Low and medium vacuum Rotary Vane Mechanical Booster High and Ultra-High vacuum Diffusion pump Turbomolecular pump Cryogenic pump Ion pump

8. Vacuum Pump Accesories
Foreline Traps For prevention of pump oil vapour migrating back into the system at low pressures from rotary pumps

9. Vacuum Pump Accesories
Dust Filters For prevention of dust being carried from the process into the pump. Increases pump life by reducing wear, but reduces pumping speed by 10 – 25%. Chemical Filters For prevention of aggressive chemical vapour dust being carried from the process into the pump. Usually activated charcoal.

10. Vacuum Pump Accesories
Dust Filters For prevention of dust being carried from the process into the pump. Increases pump life by reducing wear, but reduces pumping speed by 10 – 25%.

11. Vacuum Pump Accesories
Oil Mist Filters For trapping pump oil carried out in exhaust gases from rotary pumps.

12. High to Ultra-high Pump Comparisons

13. High to Ultra-high Pump Comparisons

14. High to Ultra-high Pump Comparisons

15. High to Ultra-high Pump Comparisons

16. Materials
In nanomanufacturing, several applications of vacuum technology are used to support basic operations. Vacuum alone does not perform the operation, but without it, the processing attempted would not be successful.
MATEC M097SS01.ppt

17. Materials for use in a vacuum
General requirements: Very low rates of outgassing Tolerant to bakeout temperatures (can be up to 450oC) Requirements are more stringent as we head to higher vacuum levels

18. Materials for use in a vacuum
Specific risks: Materials may sublimate in vacuum (transition from solid to gas) Gases can be released from porous materials or cracks/crevices Traces of lubricants and residues from machining may be present on surfaces

19. Materials to avoid Cadmium Zinc
Often present in the form of plating (fasteners etc.) or in some brazing alloys
Zinc
A problem in high vacuum and high temperatures. Present in some alloys like brass (some electrical fittings)

20. Materials to avoid Magnesium PVC
Low melting point (650oC at atmosphere). Contains free hydrogen gas
PVC
Often found in wire insulation, dust caps etc.

21. Materials to avoid Paints Polymers Many have an affinity to water
Especially plastic tapes. Mould release residue can be an issue too. Polymers may generate a static charge attracting dust
Nylon has a high outgassing rate

22. Materials to use - Metals
Stainless Steel
Most common choice in HV and UHV systems
304 - common
304L – Low carbon variant of 304 especially in UHV systems
321 – for when low magnetic permeability is required
BUT…. Avoid 303 grade – contains sulphur and tends to outgas

23. Materials to use - Metals
Mild Steel
Can be used above 10-6 Torr
Can be nickel plated to reduce outgassing
BUT…. Can pass hydrogen and has a strong tendency to rust

24. Materials to use - Metals
Aluminium & Al Alloys
Low outgassing
Easy to machine
Low weight and lower cost than S/S
BUT…
Some alloys contain a high proportion of zinc
Must NOT be anodised
Poor strength at high temperatures
Not easy to weld

25. Materials to use - Metals
Nickel
Relatively low cost
Easy to machine
Can be spot-welded
High melting point (1455oC)
Resistant to corrosive fluids and atmospheres
BUT…
Ferromagnetism restricts applications that would be affected by magnetic fields

26. Materials to use - Metals
Copper (Oxygen-free) C10100 & C10200
‘Oxygen-free’ type is widely used
Easy to machine
Impermeable to hydrogen and helium
Low sensitivity to water vapour
BUT…
Normal copper is difficult to outgas fully
Tends to oxidise and form scale
Strength falls above 200oC and vapour pressure is an issue over 500oC

27. Materials to use - Metals
Tungsten
Can be used at high temperatures
Can be used for filaments
BUT…
Becomes brittle when work-hardened

28. Materials to use - Metals
Indium
Can be used in wire form for demoutable seals
Gold
Can be used in wire form for demoutable seals in UHV systems

29. Materials to use - Metals
Beryllium
Can be used for X-Ray windows
High resistance to vacuum
BUT…Toxic in dust form
Zirconium
Low production of secondary electrons
Can be used for Neutron windows
Can be used as a molecular capture medium
BUT….Expensive and relatively rare

30. Materials to use - Polymers
PTFE
Good electrical insulator
Tolerant to high temperatures
Low outgassing
BUT…
Cannot be used as a barrier between vacuum and atmosphere as it is permeable to gases

31. Materials to use - Polymers
Kapton
Good electrical insulator
Tolerant to high temperatures
Very low outgassing
Available in tape and film form

32. Materials to use - Polymers
PEEK – Polyether ether ketone
Excellent mechanical & chemical resistance
Suitable for UHV applications
Very low outgassing
BUT…
Has a melting point of 343oC

33. Materials to use - Polymers
Nitrile rubber
Used for demountable seals (‘O’ rings etc.)
Good electrical insulator
BUT…
Poor chemical resistance
Can dry out and crack

34. Materials to use - Polymers
Viton
Used for demountable seals (‘O’ rings etc.)
Can also be used as a seating face in valves
Good electrical insulator
Good chemical resistance
Bakeable to 200oC

35. Materials to use - Ceramics
Borosilicate glass
Used for viewports
Can be machined and joined with metals
Low coefficient of thermal expansion – resistant to thermal shock

36. Materials to use - Ceramics
Porcelain and Alumina
Excellent electrical insulation
Non-porous if fully vitrified
Low coefficient of thermal expansion – usable to 1500oC
BUT…
Alumina can be dimensionally unstable during vitrification

37. Materials to use – Lubricants & adhesives
Vacuum Greases
Low outgassing
Adhesives for use in vacuum
Low outgassing, stable at high temperature
‘Torr Seal’
‘Vacseal’
Vacuum Greases
Low outgassing
Adhesives for use in vacuum
Low outgassing, stable at high temperature
‘Torr Seal’
‘Vacseal’