Operating Procedures
:
Optimizing Imaging
C O N F I D E N T I A L – FEI Limited Rights Data
5-16
Accelerating Voltage and Beam Currents
The choice of accelerating voltages – in the UI named High Voltage (HV) – and
Beam Currents for the active display is possible via the toolbar dropdown list
boxes and depends on the active beam type:
•
For the
electron
beam, HV and current are independent, so any change of the voltage will not influence the
current.
•
For the
ion
beam, currents available are dependent on the HV selected; for example at 30 kV the current is 100
pA, however, the current reduces to 13 pA when the HV is set to 5 kV, even when used ion beam aperture
remains the same.
Changing High Voltage
Besides a normal list box behaviour an intermediate value can be
entered into the toolbar editable HV text box or set by the
Column
module /
High Voltage
adjuster on the Beam control page. This
provides a calculated range of beam current / spot values.
Default values in the list box are set in the
Preferences
dialog /
Presets
section.
Electron Beam Current
This is one of the basic operating parameters. In other way it is represented as the function of the electron beam
diameter (usually presented as the
Spot
size, expressed by a relative number from 1 to 20 in the
Standard
Use case
(depending also on the accelerating voltage) and from 2 to 18 in the
OptiPlan
and
OptiTilt
column Use cases), the
final lens aperture diameter and its opening angle set by the condenser. It is considered to be close to ideal when
spot edges just touch the neighbouring one. If it is too large, overlaps occur and the image appears out of focus. If it
is too small, electronic noise appears in the image.
A suitable beam current value for a particular magnification can be determined easily, when good focus and
astigmatism correction is achieved.
Changing Electron Beam Current
Either electron
Beam Current
or
Spot Size
can be shown within the User Interface. This can be set
in the
Preferences
dialog /
General
section or by right-clicking on the toolbar text box and
selecting the desired context menu proposal.
An intermediate value can be set by the
Column
module /
Beam current
/
Spot size
adjuster on the
Beam Control page. Default values in the list box are set in the
Preferences
dialog /
Presets
section.
Table 5-2
Spot sizes and recommendation of their use
SEM Column Use Case
Spot size
Best Use
Standard / OptiTilt / OptiPlan
1–4
Very low currents, charging and sensitive samples
Standard / OptiTilt / OptiPlan
4–6
High resolution
Standard / OptiTilt / OptiPlan
6–12
Standard imaging
Standard / OptiTilt / OptiPlan
12
and more
High current imaging, X-ray analysis with SDD detectors
Summary of Contents for Scios 2
Page 1: ...User Operation Manual Edition 1 Mar 2017 ...
Page 103: ...Alignments I Column Alignments C O N F I D E N T I A L FEI Limited Rights Data 4 19 ...
Page 110: ...Alignments 254 GIS Alignment option C O N F I D E N T I A L FEI Limited Rights Data 4 26 ...
Page 170: ...Operating Procedures Patterning C O N F I D E N T I A L FEI Limited Rights Data 5 60 ...
Page 178: ...Maintenance Refilling Water Bottle C O N F I D E N T I A L FEI Limited Rights Data 6 8 ...