ZEISS
3 Product and Functional Description | 3.2 Main Components
7
Objective lens
Focuses the electron beam on to the
specimen surface.
8
Scanning coils
Deflect the beam across the specimen
surface in what is usually referred to as
a raster scan.
9
Specimen
Sup
Suppressor voltage
Extractor voltage
Acceleration voltage
B
Liner tube voltage
Gun
A Schottky field emitter serves as gun
1
. The filament is heated by applying the filament cur-
rent. Electrons are emitted from the heated filament while an electrical field, called extractor volt-
age (U
Ext
), is applied. To suppress unwanted thermionic emission from the shank of the Schottky
field emitter, a suppressor voltage (U
Sup
) is applied as well.
EHT
The emitted electrons are accelerated by the acceleration voltage (U
EHT
), for example 10 kV.
Beam Booster
The beam booster is a feature of the electron optical column and has the following functions:
§
It minimizes beam widening that may occur due to stochastic electron-electron interactions.
Consequently there is almost no loss in beam brightness, even at low acceleration voltages.
§
It enhances protection against external stray fields.
Anode
3
and liner tube are connected mechanically and electrically and form the beam
booster. A booster voltage (U
, liner voltage) of +8 kV is applied to the beam booster in addition
to the acceleration voltage, so that a high beam energy is maintained throughout the entire col-
umn. The function of the beam booster depends on the acceleration voltage U
:
§
EHT ≤ 20 kV: liner tube/beam booster is connected to +8 kV
§
EHT > 20 kV: liner tube/beam booster is connected to ground, i.e. is switched off
Because of the danger of arcing, the beam booster function is not available in variable pressure
(VP) mode.
Apertures
The electron beam passes through the anode aperture
3
first, afterwards through the multi-
hole aperture
5
.
The anode aperture defines the maximum possible probe current.
The multihole aperture is the final beam limiting aperture. It is decisive for the probe current. The
standard is the 30 μm aperture hole that is the central aperture. Other aperture sizes are se-
lectable to meet the requirements of a wide range of applications.
For the Gemini 1 column, two types of multihole aperture are available:
§
20 nA high resolution configuration
Anode aperture di-
ameter
Multihole aperture
type
Probe current
Typical application
40 μm
7 hole aperture
30, 7, 10, 15, 20,
60, 120 μm
3 pA to 20 nA
High resolution
§
100 nA high current configuration
Anode aperture di-
ameter
Multihole aperture
type
Probe current
Typical application
90 μm
6 hole aperture
30, 10, 20, 60, 120,
300 μm
6 pA to 100 nA
High current
Instruction Manual ZEISS SIGMA series | en-US | Rev. 7 | 352102-9344-006
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