Scanning Photoelectron Microscope Research Articles

Lithography with a Focused Soft X-ray Beam and a Monomolecular Resist

A zone-plate-focused soft X-ray microbeam was utilized for direct patterning of a monomolecular resist: aliphatic and aromatic self-assembled monolayers. The fabricated patterns were subsequently imaged and characterized by a scanning photoelectron microscope (SPEM) using the same microbeam as the excitation source. The observed contrasts could be explained in terms of specific beam-resist interactions. The spatial resolution of the X-ray patterning was about 0.5 μm, which was mostly determined by the current SPEM settings and can be noticeably improved.

A scanning photoelectron microscope for materials science spectromicroscopy at the Pohang Light Source

A Fresnel zone plate based SPEM (scanning photoelectron microscope) is in operation at the Pohang Light Source. Space resolution of the SPEM is typically ≤ 1 μm(0.4 μm in the best resolution) and the photon flux at the focused spot is ∼10 9 photons/ s. The SPEM is working in the energy range between 400 and 1,000 eV. In taking images and spectra, the SPEM detects photoelectrons from the focused spot using a hemispherical analyzer with 16-channel detection capability at energy resolution of ∼ o.5 eV. The SPEM also measures sample current, with which comparative x-ray absorption micro-spectroscopy is available in limited energy range with spectral resolving power (E/ΔE) of 3,000. The advantage of detecting sample current image and x-ray absorption spectrum at the Fe L III -edge is demonstrated for understanding the effect of electrochemically deposited Zn layer on Fe substrate.

Scanning photoelectron microscopy study of as-grown and heat-treated chemical vapor deposition boron-doped diamond films

The electronic structure of as-grown and high temperature (1625 °C) annealed chemical vapour deposition boron-doped (1–4 ppm) diamond films has been studied using a scanning photoelectron microscope with lateral resolution in the 1 μm range. The fresh surfaces have been obtained by cleaving free-standing films in situ at a pressure of 7×10−11 Torr. The major part of the contrast in photoelectron images is due to topography effect but grain structure (grain size 10–50 μm) can be also detected. The detailed study of separate grains shows that as-grown films demonstrate significant intensity in the vicinity of the Fermi level with a characteristic band tail which is believed to result from static and dynamic site disorder. In annealed films a sharp drop in Fermi level intensity is observed and samples show charging effects in scanning electron microscope measurements. As-grown films contain different types of defects which appear as electrically active trapping centers and give rise to the increased density of states at the Fermi level. The evolution of the defect structure and possible boron redistribution upon annealing explains the much lower photoemission signal around the Fermi level in heat-treated films.

Nondestructive probe of microstructures covered with a micrometer-thick insulating layer

We present an imaging technique which uses a scanning photoelectron microscope to image microstructures covered with a micrometer-thick insulating layer at submicrometer depth and lateral-space resolution. Line shifting in the photoelectron spectrum caused by local charging in the insulating surface layer provides depth information. This technique was used to nondestructively image micropatterns in a semiconductor device down to 3 μm beneath a surface insulating layer. The depth resolution was 0.2 μm, and the lateral-space resolution was 0.5 μm.

Performance of the SRRC scanning photoelectron microscope

A scanning photoelectron microscope has been constructed at SRRC. This SPEM system consists primarily of a Fresnel zone plate (ZP) with an order-selection aperture, a flexure scanning stage, a hemispherical electron analyzer, and sample/ZP insertion system. The flexure stage is used to scan the sample. A hemispherical analyzer with Omni V lens and a 16-channel multichannel detector (MCD) is used to collect photoelectrons. A set of 16 photoelectron images at different kinetic energies can be simultaneously acquired in one single scan. The data acquisition system is designed to collect up to 32 images concurrently, including 16 MCD signals, total electron yield and transmitted photon flux. The design and some initial test results of this SPEM station are presented and discussed.

Spectromicroscopy of interfaces with synchrotron radiation:: multichannel data acquisition

Probed length scales of sub-micrometer dimensions have been achieved in photoemission spectroscopy owing to the high flux and brightness of the soft X-rays provided by the third generation synchrotron sources and the progress in microfabrication of focusing elements for soft X-rays. The use of multichannel detectors in the recently constructed scanning photoelectron microscopes adds speed and flexibility in data acquisition. Here we present some results obtained with the scanning photoemission microscope at ELETTRA illustrating the importance of the multichannel data acquisition for the interpretation of the data.

SPECTROMICROSCOPY STUDIES WITH HIGH SPATIAL RESOLUTION

This paper reviews some recent achievements of synchrotron radiation XPS microscopy in the characterization of surfaces and interfaces of morphologically complex and multiphase materials. Using selected results obtained with the scanning photoelectron microscope built at the synchrotron light source ELETTRA in Trieste, the novel information provided by combining chemical sensitivity with submicron spatial resolution is presented.

Spectromicroscopy Studies with High Spatial Resolution

This paper reviews some recent achievements of synchrotron radiation XPS microscopy in the characterization of surfaces and interfaces of morphologically complex and multiphase materials. Using selected results obtained with the scanning photoelectron microscope built at the synchrotron light source ELETTRA in Trieste, the novel information provided by combining chemical sensitivity with submicron spatial resolution is presented.

Imaging the variation in band bending across a silicon pn junction surface using spectromicroscopy

We present a characterization of lateral silicon pn junction arrays fabricated on a Si(001) surface using a synchrotron-based scanning photoelectron microscope (SPEM). The Si 2p images show energy dependent contrast which varies continuously across the space charge region between regions of different doping. Combined with measurements of the changes in the Si 2p spectra across the pn junction, we demonstrate the capacity of SPEM in imaging variations in dopant concentration, the width of the charge depletion zone, and variations in band bending with oxide preparation.

Recent developments of the scanning photoelectron microscope at Elettra

Recent developments of the scanning photoelectron microscope at Elettra

Scanning photoelectron microscope with a laser-produced plasma X-ray source

Abstract We are developing a photoelectron microscope on a laboratory scale by using a laser-produced plasma X-ray source. It consists of a laser-produced plasma X-ray source, a monochromator with a toroidal mirror and a concave grating, a grazing incidence focusing mirror (Wolter type-I) and a hemispherical electrostatic electron energy analyzer. In this study, we intend to measure photoelectron spectrum images. The X-ray beam spot size was 9 μm×13 μm. An Au evaporated microchannel plate (MCP) was used as a sample.

Selective oxidation of surface grains in polycrystalline tin

Polycrystalline tin samples have been imaged during oxidation with molecular oxygen using the scanning photoelectron microscope on beam line 2.2 at the ELETTRA synchrotron. Chemical maps have been recorded by collecting the Sn 3d signal from the metal and oxide phases. The reactivity of surface grains, as indicated by the oxide signal, depended on the crystal plane exposed. In the early stages of oxidation studied here only SnO was formed. The reactivities of different grains judged from images and from the spectra taken on selected microspots have been used to suggest identifications for the crystal planes involved.

Calculations and engineering of dispersive energy analyzers for photoelectron microprobe

Bipotential (BP) electron optics elements, consisting of alternating, or reciprocally penetrated electrodes under two different potentials, which are used for creation of electrostatic fields similar to the field of Cylindrical Mirror Analyzer (CMA), as the energy analysing part of Scanning Photoelectron Microscope (SPEM), are described. Numerical analysis of different variants of CMA with BP elements was performed, the energy resolution being from 0.15% to 0.9%. The energy resolution of the simplest BP CMA, designed for AES, being of 0.3% with transmission about 10%. BP elements of energy analizators are manufactured with industrial methods - point welding through specially designed copper soldered ceramic insulators.

Esca Microscopy on Elettra: Chemical Characterization of Surfaces and Interfaces With Sub-Micron Spatial Resolution

ABSTRACTThe chemical sensitivity, spatial resolution and data acquisition rates achieved with the scanning photoelectron microscope built at ELETTRA, a third-generation synchrotron facility in Italy has made it an indispensable tool for surface analysis of laterally heterogeneous materials. The information on the composition and evolution of coexisting phases, mass transport and other surface processes occurring on a microscopic scale can be obtained by combining elemental and chemical mapping with core and valence level photoelectron spectromicroscopy with spatial resolution better than 0.15 μm and energy resolution better than 0.5 eV. Selected recent results will be presented to illustrate the capabilities and some of the possible applications of synchrotron radiation spectromicroscopy for characterization of complex spatially heterogeneous materials and studies of dynamic processes related to the interface chemical structure.

Metal-dielectric transition inBa0.6K0.4BiO3−ysingle crystals studied by scanning photoelectron microscopy

The electronic structure of Ba0.6K0.4BiO3-y single crystals has been studied using a scanning photoelectron microscope with a lateral resolution in the one micrometer range. It is possible to change the oxygen content (y) and convert the surface from the metallic to the dielectric state presumably by breaking the Bi-O bonds by using the focused zero-order light to irradiate the sample surface. The electronic states close to the Fermi level after such a treatment show a different doping dependence as compared to the case of potassium doping. By imaging the surface on the micrometer scale we find significant variations in the valence band intensity over the surface and observe a rather large intensity of the density of states close to the Fermi level. This will have a large impact on the discussions of dynamical lattice distortion and pseudogap behavior in the metallic phase. (Less)

Thermal desorption of oxides on Si(100): a case study for the scanning photoelectron microscope at MAX-LAB

A scanning photoelectron microscope, utilizing a focused beam of monochromatized photons in the energy range from 15 to 150 eV, has been used to study the thermal desorption of oxide layers on Si(100). The instrument can provide high-resolution photoelectron spectra from selected parts of the surface as well as images showing the lateral distribution (on a micrometer scale) of elements in different chemical states by monitoring the photoemission intensity of chemically shifted core levels. Both native (10-15 A) and thick (200-400 A) oxides have been studied. The desorption (at 840°C) of the native oxide proceeds through a phase of irregular (on a micrometer scale) and diminishing areas of dioxide until a clean surface is obtained. For the thick oxide, annealing to 1100°C creates circular voids in the oxide layer which grow linearly in diameter with annealing time. The surface in these voids mainly consists of clean silicon but a small amount of remaining SiO2 is observed. This remaining dioxide most probably consists of small clusters or particles. For both types of oxide, we find, during and after desorption, a surface-shifted component in the Si 2p core level spectra indicating that at least parts of the surface have an ordered structure which most probably is a 2 × 1 reconstruction. © 1997 Elsevier Science B.V. (Less)

Soft X-ray scanning photoelectron microscope using Wolter-type focusing mirror

The soft x-ray scanning photoelectron microscope has been developed and installed at a soft x-ray beamline of the Photon Factory (KEK-PF). The microscope uses a Wolter type-I grazing incidence mirror to form a soft x-ray microbeam. The mirror was fabricated more accurately than previous one by using a new replication method, allowing a 0.47-μm microbeam to be ahcieved. In addition, a high-precision x-y sample stage made it possible to obtain two dimensional photoelectron images. The microscope demonstrated a total-photoyield image of 0.3-μm-linewidth stripe patterns and an energy-selected photoelectron image of 2-μm-linewidth stripe patterns.

Scanning photoelectron microscope with submicron lateral resolution using a Wolter-type x-ray focusing mirror

The scanning photoelectron microscope is operated at a soft x-ray beamline (BL-8A) at the Photon Factory in the National Laboratory for High Energy Physics. The microscope uses a Wolter-type x-ray mirror as an x-ray focusing device for probe beam formation. The lateral resolution of the microscope is evaluated based on total photoyield imaging of Al stripes patterned on a SiO2 film. The 0.6- and 0.7-μm-wide stripes are detected with a modulation of 0.07–0.08 when a 150 eV soft x-ray microbeam with a sagittal beam size of 1.8 μm scans the stripes one dimensionally. The experimental results agree well with the changes in the photoelectron count rate expected from the beam intensity profile and from the arrangement of the stripe pattern. The highest lateral resolution attainable under current instrumental conditions is also predicted.

The vacuum ultraviolet scanning photoelectron microscope at MAX-LAB

The performance of a scanning photoelectron microscope at the MAX I storage ring in Lund is presented. The microscope utilizes undulator radiation in the energy range 15–150 eV and is comprised of a plane-grating monochromator with a Kirkpatrick–Baez objective and a gracing incidence ellipsoidal focusing mirror. The instrument with its high photon flux, 109–1010 photons/s, and narrow bandwidth, better than 0.2 eV, is excellently suited for high-resolution core-level spectroscopy and imaging of samples with lateral inhomogeneties in the micrometer range.

Ultrahigh lateral resolution spectromicroscopy beam line at ELETTRA (trieste)

AbstractThis report presents the project for the development of a combined facility consisting of a high spatial resolution soft x‐ray scanning photoelectron microscope (SPEM) and a scanning tunnelling microscope (STM) that is going to be built in an ultrahigh vacuum (UHV) station on one of the undulator beam lines at ELETTRA, Trieste. The photon microprobe for SPEM will be generated using a zone plate diffraction optic. A special design of a spherical grating monochromator will provide the source for illuminating the zone plate. The emitted photoelectrons will be detected and analysed using a high‐energy resolution hemispherical analyser with a large acceptance angle. The performance of the SPEM is projected to be as follows: (1) a photon spot size on the sample of ∼50 × 50 nm2; (2) a tunable photon energy range of 200–800 eV, with an energy resolving power of 3000 at the carbon K‐edge; (3) a photon flux in the spot that is > 109 photons s−1 (0.1% body wt.)−1. The projected performance of the STM instrument ensures a lateral resolution better than 2 Å. The combination of SPEM and STM techniques will enable chemical and structural mapping within the same microscopic areas of the sample surface. Descriptions of the main beam line components together with some examples of possible applications of this unique tool are included in the paper.