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AMU Abbreviation for Automatch Unit. This is a self-controlling variable capacitor,
which is connected between an electrode (to which it is normally close-coupled)
and the discharge power supply. Its purpose is to shift the voltage and current
waveforms to maximise the power transfer. It also transforms the load
impedance to 50Ω.
Rotary pump A pump downstream of the chamber (See also Rotary pump)
Baratron
See CM gauge. Baratron is a trade name.
Base pressure The lowest pressure attainable by a high vacuum pump. Alternatively, the
pressure, which should be attained before starting a process.
Clean gas This refers, in fact, to 'cleaning gas'. It is a gas which, when converted to a
plasma, removes contamination from the walls of the chamber and from the
electrodes.
CM gauge (Baratron) Capacitance manometer gauge in which gas pressure deflects a membrane and
thus a measured capacitance. Measures absolute pressure down to
approximately 10
-5
Torr. Not affected by corrosive gases. Does not need a
correction factor for different types of gas.
Electrode One of two metal plates within the process chamber, which form part of the
electrical discharge system. The lower electrode is sometimes referred to as the
'table'. They are fabricated from aluminium alloy or stainless steel, and may
either be heated by integral electrical resistance elements, or cooled by chilled
water pipes.
Gas ballast Inert gas introduced into a port on a rotary pump to improve its ability to pump
condensable vapours.
Gas factor Ion gauges, Pirani gauges, Penning gauges and mass flow controllers need to be
adjusted when run on different gases, to prevent them from being inaccurate.
This 'gas factor' depends on the gas and also the type of instrument.
Gate valve A high vacuum valve with a stainless steel shutter having linear motion. It may
be used for high vacuum isolation and also for pressure control.
ICP An abbreviation for Induction Coupled Plasma.
Interlock A safety device (either software or electrically implemented) that allows a piece
of apparatus to function only when predetermined conditions are fulfilled.
Ion gauge
(Bayard-Alpert gauge)
This gauge uses a glowing cathode to emit electrons. Any positive ions created
by collisions with gas molecules are collected on a thin central ion collection
wire. The ion current varies with the gas density. Used for checking very low
base pressures down to 10
-10
Torr. It needs to be calibrated to the gases being
measured (see Gas factor). The filament lifetime will be limited in reactive gases.
Process Information (Information contained in this document is confidential)
Printed: 08 October 2007 11:00 Page 11 of 14 Issue 1: August 07
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