ISO 14291:2012

INTERNATIONAL ISO
STANDARD 14291
First edition
2012-07-15
Vacuum gauges — Definitions and
specifications for quadrupole mass
spectrometers
Manomètres à vide — Définitions et spécifications des spectromètres
de masse quadripolaires
Reference number
©
ISO 2012
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ii © ISO 2012 – All rights reserved

Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Terms and definitions . 1
2.1 Definitions of components. 1
2.2 Definitions of physical parameters . 5
3 Symbols and abbreviated terms . 8
4 Principle of QMS . 9
5 Specifications for a QMS to be provided by manufacturers . 9
5.1 Mass range . 9
5.2 Type of ion source . 9
5.3 Type of ion detector . 9
5.4 Mass resolution .10
5.5 Mass number stability .10
5.6 Sensitivity .10
5.7 Linear response range .10
5.8 Minimum detectable partial pressure .10
5.9 Minimum detectable concentration .10
5.10 Maximum operational pressure .10
5.11 Scanning parameter .10
5.12 Signal output . 11
5.13 Potentials . 11
5.14 Detector specifications . 11
5.15 Set point . 11
5.16 Maximum bake-out temperature . 11
5.17 Nominal operating conditions. 11
5.18 Warm-up time . 11
5.19 Filament material . 11
5.20 Electron emission current . 11
5.21 Filament exchange . 11
5.22 Detector exchange . 11
5.23 Fitting to chamber .12
5.24 Mounting orientation .12
5.25 Dimensions .12
5.26 Internal volume .12
5.27 Mass of sensor head and electronic unit .12
5.28 Input power of electronic unit .12
5.29 Cable .12
5.30 Software .12
5.31 Interface .12
5.32 Storage and transportation condition.12
6 Optional specifications for QMS to be provided by manufacturers .13
6.1 Mass resolution .13
6.2 Fragmentation or cracking pattern .13
6.3 Temperature coefficient of sensitivity .13
6.4 QMS sensor cleaning .13
6.5 Degassing .13
6.6 Degassing power .13
6.7 Photographs .13
6.8 Inspection record .13
6.9 Outgassing rate .13
Bibliography .14
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International
Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 14291 was prepared by Technical Committee ISO/TC 112, Vacuum technology.
iv © ISO 2012 – All rights reserved

Introduction
Quadrupole mass spectrometers (QMSs) are nowadays used not only for leak detection and residual gas
analysis in vacuum but also as instruments to provide quantitative analysis in processes and control processes
such as physical and chemical vapor deposition, and etch processes.
Total pressure, composition of the gas mixture, QMS settings, environment conditions, etc., have a significant
influence on the measured signal, its uncertainty and interpretation. For this reason, it is not possible to calibrate
QMS for all its possible applications. Instead, it has either to be calibrated for the particular conditions of use
or for a standardized condition.
There is also some need for standardization in order to enable QMS users to compare devices of different
manufacturers and to use the QMS properly.
In continuation of efforts of TC 112 during the 1990s, this International Standard takes a first step towards
establishment of a standardized calibration procedure for QMS by defining the terms and parameters.
INTERNATIONAL STANDARD ISO 14291:2012(E)
Vacuum gauges — Definitions and specifications for
quadrupole mass spectrometers
1 Scope
This International Standard defines terms relevant to quadrupole mass spectrometers (QMSs) and specifies
the parameters required for specification by QMS manufacturers necessary for proper calibration and for
maintaining the quality of partial pressure measurement.
This International Standard applies to QMSs with an ion source of the electron impact ionization type. Such
QMSs are designed for the measurement of atomic mass-to-charge ratios m/z typically <300. QMSs with other
ion sources, such as those of the chemical ionization, photoionization, and field ionization types, as well as the
measurements of m/z above 300, which are mainly used to specify organic materials, lie outside the scope of
this International Standard.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1 Definitions of components
2.1.1
quadrupole mass spectrometer
QMS
mass spectrometer in which ions are injected axially into a quadrupole lens consisting of a system of four
electrodes, usually rods, to which radio frequency and d.c. electric fields in a critical ratio are applied, so that
only ions with a certain mass/charge ratio emerge
[2]
[SOURCE: ISO 3529-3:1981, 3.5.2.2]
Note 1 to entry Such a QMS consists of a sensor head and electronic unit.
2.1.2
sensor head
analyser tube
sensor
sensor unit
sensing head
gauge head
equipment consisting of an ion source, quadrupole mass filter, and ion detector in one enclosure
2.1.3
ion source
part of the QMS in which ions of gas molecules and atoms are produced
Note 1 to entry For the production of positive ions, the ion source generally uses an electron impact ionization process.
2.1.3.1
open ion source
ion source with a high conductance to the surrounding vacuum environment, often designed as an open grid structure
Note 1 to entry All of the operational components of this ionization hardware are exposed to the same vacuum region.
2.1.3.2
closed ion source
enclosed ion source
differential pressure ion source
ion source that uses a nearly sealed container to ionize the gas to be analysed with openings only for passing;
sample gas; energetic electrons (for impact ionization); and exciting ions
Note 1 to entry This type of ion source permits ionization at pressures that are higher than the mass filter and detector.
It should be used in a sample pressure reduction system with a high vacuum pump on the mass filter.
2.1.3.3
molecular beam ion source
crossed beam ion source
ion source that accepts a focused beam of neutral gas molecules directed at the ion formation region without
interference from any ion source components
Note 1 to entry The molecular beam traverses the ion formation region and is usually at right angles to the electron
beam and mass filter axes.
Note 2 to entry For molecular beam epitaxy, the crossed beam ion source is also designed to accept molecular beams
at various acceptance angles. Some molecular beam ion source designs include a protective shroud around the ion
source with an aperture to the ion formation region. As the molecular beam exits the ion source, it may be trapped or
pumped to minimize contribution to background from scattered molecules.
2.1.4
quadrupole mass filter
device consisting of four parallel conductive rods arranged in a square array with opposite rods connected
electrically in parallel
Note 1 to entry A quadrupole mass filter separates the ions coming from the ion source on the basis of their mass-to-
charge ratios by a critical ratio of radio frequency (r.f.) and direct current (d.c.) electrical fields applied to the rods. The rod
pairs are driven with opposite r.f. phase and d.c. polarity.
2.1.5
ion detector
ion collector
device collecting the positive ions that have passed through the mass filter to measure the ion current
Note 1 to entry Two types of ion detectors are common: Faraday cup and secondary electron multiplier (SEM).
2.1.5.1
Faraday cup
metal plate or open cylinder or similar on which the ions from the mass filter are collected
Note 1 to entry An actual Faraday cup ion detector is illustrated in Figure 1 a). However, a metal plate, Figure 1 b), open
cylinder, Figure 1 c), or similar on which the ions from the mass filter are collected is usually called a Faraday cup-type
ion detector. A Faraday cup generally has a gain of unity, i.e. for each ion collected, one electron flows from the detecting
electrometer.
2.1.5.2
secondary electron multiplier
SEM
detector in which the ions from the mass filter strike the entrance surface and release electrons
Note 1 to entry The released electrons are accelerated and strike another surface of the SEM resulting in multistage
amplification of the electron current. SEMs can use discrete dynodes or a continuous dynode surface with a potential
gradient to increase the electron current and microchannel plate electron multiplier.
2 © ISO 2012 – All rights reserved

a)  Faraday cup type b)  Metal plate type c)  Open cylinder type
Figure 1 — Faraday cup type ion detector
2.1.5.2.1
discrete dynode electron multiplier
secondary electron multiplier that uses discrete dynodes between which secondary electrons are accelerated
Note 1 to entry The voltages applied to each dynode establish the potential gradients that accelerate the secondary
electrons and lead to increased numbers of electrons at each stage. Figure 2 is a schematic diagram of a discrete dynode
electron multiplier.
Key
1 ammeter
2 electron
3 negative high voltage
Figure 2 — Discrete dynode electron multiplier
2.1.5.2.2
1)
continuous dynode electron multiplier
CEM
type of secondary electron multiplier with a continuous dynode, often with a horn-like channel
Note 1 to entry See Figure 3.
Note 2 to entry The applied voltage from entrance to exit of the channel establishes the potential gradient along the
channel which accelerates secondary electrons and leads to increased numbers of electrons from entrance to exit.
® ®
1) One of the original CEMs is known as Channeltron . Channeltron is the trademark of a product supplied by Burle.
This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of
the product named.
Key
1 ammeter
2 electron
3 negative high voltage
Figure 3 — Continuous dynode electron multiplier (CEM)
2.1.5.2.3
microchannel plate electron multiplier
MCP electron multiplier
type of secondary electron multiplier which consists of a large number of small, parallel continuous-dynode
channels (typically 5 µm to 25 µm in diameter), in a planar array, or “plate”
2.1.6
electronic unit
unit consisting of a radio frequency source and several regulated power supplies and amplifiers which operate
the ion source and mass filter as well as measure detected ion current
Note 1 to entry The electronic unit usually incorporates a microprocessor and firmware to control the electronics and
usually pass data to an external computer. Electronic units may be integrated or separate.
2.1.6.1
integrated type
electronic unit mounted directly on sensor head
Note 1 to entry See Figure 4.
2.1.6.2
separated type
electronic unit separated from the sensor head but connected to it via one or more cables
Note 1 to entry See Figure 5.
Key
1 electronic unit
2 computer
Figure 4 — Integrated electronic unit
4 © ISO 2012 – All rights reserved

Key
1 electronic unit
2 computer
Figure 5 — Separated electronic unit
2.2 Definitions of physical parameters
2.2.1
sensitivity
S
ratio of the change in spectrum peak height (ion current), I - I , to the corresponding change in partial
pressure, p - p
II−
Sp =
()
pp−
()
(1)
where
I is the ion current measured at partial pressure p;
I is the ion current measured at residual pressure p
0 0
Note 1 to entry Sensitivity is expressed in amperes per pascal.
[4]
Note 2 to entry Sensitivity is defined differently in ISO 27894:2009 for an ionization gauge with an emissive cathode.
The sensitivity of a hot-cathode ionization gauge is defined as
II−
c 0
S = (2)
Ip − p
()
e 0
where
I is the ion current measured at pressure p;
c
I is the ion current measured at residual pressure p ;
0 0
I is the emission current.
e
2.2.2
relative sensitivity factor
r
x
sensitivity S for a specified gas species, x, divided by sensitivity S for nitrog
...