1. High-Vacuum Technology Course
Week 3
Paul Nash
HE Subject Leader (Engineering)

2. Vacuum Technology Final outstanding enrolments Recap on last week
Measuring Vacuum
Gauge types, ranges and costs
Active and Passive Gauges
Location of gauges
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 a variety of vacuum measurement techniques
To be able to select gauge types for a given range of vacuum
To explain the difference between Active & Passive gauges
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. Measuring Vacuum
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

5. Vacuum Gauges There are 3 phenomena used to measure vacuum: Mechanical
Vacuum Gauges There are 3 phenomena used to measure vacuum: Mechanical Displacement of materials Transport Movement of gases Ionisation Ion currents

6. Vacuum Gauges
Many different types of gauges are available because each only covers a limited range of pressures
Range of gauge utility

7. Schematic Circuit for a Pirani (hot wire) gauge
Pirani gauge
The Pirani is a dedicated low vacuum gauge device
The resistance of the hot wire changes with the rate of heat loss (conduction) to the gas
The Wheatstone bridge then measures the change in resistance of the hot wire
Pirani’s are rugged and generally reliable and rarely need attention
Schematic Circuit for a Pirani (hot wire) gauge

8. Pirani gauge

9. Correction Curve for Pirani Gauges
Pirani calibration
The calibration of a Pirani depends on thermal conductivity and so on the actual gas in the system
Correction Curve for Pirani Gauges

10. Pirani gauge Advantages
Low temp operating increases thermal stability by reducing thermal oxidisation of contaminants
Significantly better resolution in the range above 100 Torr
Long service life
Robust and stable under normal working conditions
Disadvantages
Cannot be used in high temp operations or located near heat sources
Results can vary depending on the orientation of the gauge (preferred vertical)
Can be easily contaminated particularly on installation

11. Penning (Cold cathode) Gauge
A Penning gauge measures the ion current flowing from the cathode to the anode
The magnetic field increases sensitivity by making the ions spiral as they travel to cause secondary ionization
Penning gauges require routine cleaning and testing

13. Penning (Cold cathode) Gauge

14. Capacitance Manometer
Gauge head on chamber
Controller and digital read-out

15. Capacitance Manometer
A = Annular electrode
D = Disk electrode
S = Substrate
G = Getter (in vacuum space)
Differential capacitance between annulus and disk depends on pressure difference between Test Chamber and “Getter”.

16. Ion gauges (Hot cathode)
Pressures lower than 10-5 Torr can be measured with ion gauges

17. Interpreting the output
The gauge output must be interpreted and converted into a vacuum measurement
This output may also be used to control activation of:
Pumps
Other gauges
Valves and process control

18. Passive & Active Gauges

19. Passive Gauges
Analogue
Digital

21. Active Gauges
Made possible by Surface Mount Technology on printed circuit boards
The gauge has an ID resistor to ‘tell’ the controller what type of gauge it is
Can also be interfaced to a PC Network for process control

22. Active Gauges
Multiple gauge inputs

23. Active Gauges
Multiple gauge inputs

24. Combined Gauges

25. Positioning of Gauge Heads

26. Positioning of Gauge Heads

27. Positioning of Gauge Heads