Page 7 - Kratos AXIS Nova

HIGH SPATIAL RESOLUTION XPS IMAGING XPS FROM SELECTED AREAS ION SPUTTER DEPTH PROFILING
As well as impressive spectroscopic performance, the AXIS MULTI-TECHNIQUE CAPABILITIES Selected area spectroscopy is performed by inserting an The AXIS Nova can be configured with a
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Nova incorporates a spherical mirror analyser (SMA) for high Whilst the AXIS Nova is primarily designed for high aperture into the electrostatic lens column, forming a virtual standard floating column monoatomic
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spatial resolution XPS imaging. In parallel imaging mode the throughput high performance XPS additional analytical probe at the surface of the sample. Spectra are acquired from Ar ion source or the Gas Cluster Ion Source
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spatial distribution of the photoelectrons is retained as they are capabilities can be added without compromising the defined selected areas down to 15 μm diameter with improved (GCIS) depending on the type of sample to be
projected onto the 2-dimensional delay-line detector. Stigmatic, performance. An ultraviolet He-discharge lamp can be performance over the first generation instrument. Multipoint profiled. With either ion source ESCApe software allows
parallel images can be collected in a matter of seconds offering added to allow collection of ultraviolet photoemission spectra can be acquired from any position within the field of compucentric rotation during sputtering to minimise ion induced
shorter acquisition times and higher spatial resolution than spectra (UPS) for valence band and work function view using an electrostatic deflection system. A simple mouse sample roughening during etching.
sequential rastered beam or stage mapping approaches. measurements. click is used to define the analysis position from an image +
An attribute of the SMA is that it operates in fixed analyser deflecting the virtual probe using electrostatic scan plates. This The standard monatomic Ar ion source (Minibeam 4) provides
transmission mode ensuring that the energy resolution of Ion scattering spectroscopy (ISS) can be configured as approach removes the need to move the sample and hence continuously variable beam energies between 4 keV and 50 eV.
photoelectron images is constant for all kinetic energies. This is an additional technique for elemental characterisation uncertainties introduced with repeated sample translation. The ion column has a bend to suppress energetic neutrals as
of particular importance for quantitative imaging applications. of the outermost surface of the sample. Both the well as the capability to operate in floating mode for high ion
Parallel images may also be acquired at lower pass energies to Minibeam 4 and 6 ion sources can be configured beam current density at low ion energies. Float mode gives the
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improve the energy resolution, analogous to spectroscopy mode, for use with low energy He ions and the advantage of improved interface resolution and fast etch rates
allowing chemical state imaging where necessary. analyser polarity reversed to achieve this even at low ion acceleration voltage.
acquisition mode simply through the
The low spherical aberration of the electron optics ensures that ESCApe User interface. The multi-mode GCIS (Minibeam 6) is capable of generating
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the image of the surface can be magnified onto the detector Ar clusters consisting of hundreds or even thousands of Ar
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with very little distortion. This ensures high spatial resolution atoms as well as monatomic Ar ions for depth profiling and
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images. Parallel imaging at the highest magnification gives a He for optional ion scattering spectrometry (ISS). The use of
guaranteed spatial resolution of 3 μm. cluster ions allows the successful depth profiling of ‘soft’ organic
polymers with retention of chemistry. The energy per projectile
R1 SPECTRUM
atom, or partition energy, can be as low as a few electron volts.
It has been shown that these cluster ions sputter material from
the near-surface, causing very little sub-surface damage so
that excellent interface resolution can be maintained through
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multilayer depth profiles of several microns. Ar cluster mode
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Overlaid chemical state images of silicon depth profiling is also finding application to inorganic depth
Counts per second aluminium (red) from a micro-patterned cause less preferential sputtering than conventional monatomic
dioxide (blue) elemental silicon (green) and
profiling where small (n=500) clusters accelerated to 20 keV
device. The optical microscope image
(inset) shows the area analysed using XPS
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Ar ions when etching inorganic materials.
imaging. Areas on the XPS image indicate
where 15 μm diameter selected area Si 2p
core level spectra were acquired. Pre-defined ion source operating conditions provided in a look-
up table allow easy use of either ion source. Automation extends
to the argon gas supply for the ion source which can be turned
on and off as required during unattended operation, pressure in
Binding Energy / eV monatomic mode being controlled by an automatically regulated
piezoelectric valve.
ANALYSIS AREA 1

Spectromicroscopy data acquired at 80 eV pass energy through the R2 SPECTRUM
spherical mirror analyser of Al pattern on Si wafer. The image shows Counts per second
the Al (blue) and Si (red) over the 400 μm field of view. Spectra, (right)
demonstrating the excellent energy resolution, were reconstructed by
summing the pixels as a function of energy from the regions indicated
on the image.

SPECTROMICROSCOPY Concentration (%)
A series of fast images can be acquired as a function of Binding Energy
energy allowing the extraction of spectra from images ANALYSIS AREA 2
(spectromicroscopy data with over 65,500 spectra over Counts per second
the defined field of view). Such datasets are ideally suited
to multivariate analysis which can be used to partition the
data from noise and reconstruct spectra form single pixels.
After extracting the spectra, components may be fitted Counts per second
using conventional peak fitting approach with the significant
advantage that the components may then be used to Etch time (s)
reconstruct quantitative chemical state images that would not Binding Energy / eV
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be possible in conventional parallel imaging XPS. 4 kV Ar depth profile of alternating layers GaAs / Al Ga As, a model single
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1-x
Binding Energy / eV photon LED device, expanded to show the emitter region corresponding to
layers 15 – 19.
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