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Vacuum coating questions about Torr and Argon


I am researching the "how to" of vacuum deposition coating of aluminum on plastics and metals. I have purchased the Handbook of Deposition Technologies for Films and Coatings [affil link on Amazon] as you suggested, and have 2 academic questions. If I am currently at 29.92 in Hg and need to get to 10-6 Torr. What is a Torr? and What is it equivalent to in in Hg? Second can the process be done in an inert gas such as Argon? Thank you very much in advance for your help. Mark

Mark Robidoux
- Malvern, Pennsylvania

First of two simultaneous responses--


1 Torr is equal to 1 mm of Hg. Therefore 29.92 in Hg is equal to 760 mm Hg or 760 Torr, which is atmospheric pressure at sea level. 1 x 10-6 Torr is 0.000001 Torr.

Vacuum deposition of aluminum can be done in a number of different physical vapor deposition methods. First is evaporation which does not require an argon atmosphere. Second is cathodic arc which does not require argon. Third is sputtering which does require an argon atmosphere. Forth is Ion Vapor Deposition, which I believe does use argon.

Typically, when argon is used in a vacuum gasses are pumped out of the vacuum chamber until a pressure in the 10-6 Torr range is reached. Then argon is backfilled into the chamber until a pressure of 10-4 to 10-2 is reached. The argon is usually used to create some kind of plasma. Argon is specifically used because it is a noble gas and doesn't react with the material being deposited. Similarly, helium, neon, krypton and xenon can be used.

Hope this helps.

John Davis
John Davis
- Berthoud, Colorado, USA

Second of two simultaneous responses--

Here, you need to go to the metric system. The ideal air pressure at sea level is 760 mm Hg = 760 Torr. You need to evacuate the chamber using a mechanical pump and then a diffusion pump to go down to 10E-6 Torr or 10E-3 milliTorr (mT). This process cannot be done at atmospheric pressures if that is what you are implying about argon. This is because most metals do not vaporize at these high pressures. The metals will just keep boiling in the molten pool. Typically, this process will not provide desirable coatings above 10E-1 Torr or 100 mT.

Mandar Sunthankar
- Fort Collins, Colorado


You might be interested in my book Handbook of Physical Vapor Deposition (PVD) Processing [affil link on Amazon].

Table of Contents 1. Introduction 2. Substrate ("Real") Surfaces and Surface Modification 3. The Low-Pressure Gas and Vacuum Processing Environment 4. The Low-Pressure Plasma Processing Environment 5. Vacuum Evaporation and Vacuum Deposition 6. Physical Sputtering and Sputter Deposition ("Sputtering") 7. Arc Vapor Deposition 8. Ion Plating and Ion Beam Assisted Deposition 9. Atomistic Film Growth and Some Growth-Related Film Properties 10. Film Characterization and Some Basic Film Properties 11. Adhesion and Deadhesion 12. Cleaning 13. External Processing Environment

Appendix 1. Reference Material Appendix 2. Transfer of Technology from R&D to Manufacturing Glossary of Terms

Donald M. Mattox
Society of Vacuum Coaters
Albuquerque, New Mexico
Donald is the author of: Handbook of Physical Vapor Deposition (PVD) Processing and The Foundations of Vacuum Coating Technology [affil links]

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