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Source: SEMICONDUCTOR MANUFACTURING HANDBOOK

CHAPTER 7

VACUUM TECHNOLOGY

Peter Biltoft
Lawrence Livermore National Laboratory
Livermore, California

7.1 VACUUM TECHNOLOGY OVERVIEW

7.1.1 What Is Vacuum

The environmental condition called vacuum is created when the pressure of a gas is reduced com-
pared to atmospheric pressure. On earth we typically create a vacuum by connecting a pump capa-
ble of moving gas to a relatively leak-free vessel. Through operation of the gas pump, the number of
gas molecules per unit volume is decreased within the vessel. As soon as one creates a vacuum, nat-
ural forces (in this case entropy) work to restore equilibrium pressure. The practical effect of this is
that gas molecules attempt to enter the evacuated space by any means possible. It is useful to think
of vacuum in terms of a gas at a pressure below atmospheric pressure. In even the best vacuum ves-
sels ever created, there are approximately 3,500,000 molecules of gas per cubic meter of volume
remaining inside the vessel. The lowest pressure environment known is in interstellar space where
there are approximately four molecules of gas per cubic meter.

7.1.2 A Very Brief History of Vacuum Technology
*
The recorded history of vacuum dates back to 150 B.C. Hero of Alexandria wrote Pneumatias in
which the function of siphons and pumps were discussed. Advances in the basic understanding of
the behavior of gases took place in Europe between A.D. 1500 and 1800. Notably, Galileo Galilei
studied the function of pumps, Evangelista Torricelli studied both pressure gauges (the barometer)
and gas pumps, and Otto von Guericke produced pumps specifically designed for creating vacuum.
The Englishman Robert Boyle published his scientific findings on the behavior of gases as a func-
tion of pressure. Devices invented in the nineteenth century such as the light bulb, x-ray tube, and
cathode ray tube required reliable methods for producing, measuring, and maintaining vacuum and
provided the motivation for the development of better vacuum equipment. As early as 1936 vacuum-
tube integrated circuits were built. The growing electronics industry, the Manhattan Project, and
exploration of outer space provided the drive for many of the advancements in vacuum technology
made between the 1930s and today, including the development of the turbomolecular pump, the ion
pump, and the partial-pressure analyzer.

* Source: www.avs.org/information/timeline.pdf

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