Apparatus and method for inspecting a surface of a sample

The invention relates to an apparatus and method for inspecting a sample. The apparatus comprises a generator for generating an array of primary charged particle beams (33), and a charged particle optical system with an optical axis (38). The optical system comprises a first lens system (37, 310) for focusing all primary beams (33) into a first array of spots in an intermediate plane, and a second lens system (313, 314) for focusing all primary beams (33) into a second array of spots on the sample surface (315). The apparatus comprises a position sensitive backscattered charged particle detector (311) positioned at or near the intermediate plane. The second lens system comprises an electromagnetic or electrostatic lens which is common for all charged particle beams. Preferably the second lens system comprises a magnetic lens for rotating the array of primary beams (33) around the optical axis (38) to position the second array of charged particle spots with respect to the first array at an angle.ImPhys/Imaging PhysicsApplied Science

De Philips EM300 Elektronenmicroscoop

Een elektronenmicroscoop is een apparaat waarin met behulp van een elektronenbundel een klein voorwerp vergroot kan worden afgebeeld. Zoals een lichtbundel gefocusseerd kan worden door lenzen van glas, kan een elektronenbundel gefocusseerd worden door elektrostatische of magnetische velden. Elektronen worden uit een materiaal in het vacuüm gebracht door een gloeidraadje zo warm te maken dat de elektronen “er uit koken”, of een zodanig sterk elektrisch veld op een scherpe naald te zetten dat de elektronen uit het materiaal “getrokken” worden. Door deze elektronenbron op een negatieve hoogspanning ten opzichte van aarde te zetten, versnellen de elektronen tot bijna de snelheid van het licht en vormen een bundel. Een magneetlens bestaat in essentie uit een grote spoel koperdraad en een magneet-ijzercircuit, dat het magneetveld op de as van de microscoop concentreert. De vergrote afbeelding van een preparaat wordt op een fluorescentiescherm zichtbaar gemaakt. Al in 1878 was aangetoond dat het scheidend vermogen van een microscoop wordt bepaald door de golflengte van de gebruikte straling. Rond 1920-1925 ontstond het inzicht dat elektronen zich ook als golven kunnen gedragen. Aangezien de golflengte van elektronen aanzienlijk korter is dan die van licht, kunnen in een elektronenmicroscoop veel kleinere details zichtbaar gemaakt worden dan in een lichtmicroscoop.ImPhys/Charged Particle Optic

Lithography system

Lithography system comprising a light source producing a light beam directed to a mask (3) located in a mask level and an optical demagnifier (4-6) for demagnifying by a factor and focusing the beam. The light beam is focused on a converter element (8) for converting said beam in a further beam having a smaller wavelength than UV light. The beam at the mask level has a transversal size smaller than the desired resolution at the object level multiplied by the demagnifying factor.Applied Science

Scanning transmission electron microscope

The invention relates to a scanning transmission electron microscope comprising an electron source, an electron accelerator and deflection means for directing electrons emitted by the electron source at an object to be examined, and in addition a detector for detecting electrons coming from the object and, connected to the detector, a device for processing the detected electrons so as to form an object image, wherein a beam splitter is provided for dividing the electron beam from the electron source into beamlets to be directed at the object to be examined, and wherein the detector is designed for the detection of separate electron patterns that correspond to said beamlets.Applied Science

Reliability Study of RTV 566 for Its Application as a “Spring”

This paper reports the preliminary feasibility study of room temperature vulcanization (RTV) 566 for its application as a “spring” for in situ height adjustment in our proposed design for an array of Schottky emitters. The reliability of the RTV 566 is tested in terms of its viscoelastic properties for thicknesses of 95, 142, and 195 ?m. The shear modulus varied a little with the thickness. Although the RTV 566 shows a very little hysteresis, it shows a clear sign of viscoelastic behavior, rendering it unsuitable for the application. The viscoelastic behavior of the RTV 566 is modeled with the Findley model.Imaging Science and TechnologyApplied Science

Effect of the electric field on the form stability of a Schottky electron emitter: A step model

The stability of the physical shape of an electron emitter (co)determines the stability of the performance of electron-beam equipment. A typical short-term instability of the Schottky electron source is the instability of the (100) facet at the tip end known as “collapsing rings.” This instability causes probe instabilities, but it is known from experiments that this can be prevented by applying high enough extraction voltages. The phenomenon of collapsing rings can be explained with a step-flow model, which is based on variations in equilibrium concentrations of adatoms on the surface. The effect of the extraction voltage can be incorporated by acknowledging the redistribution of the surface charge associated with adatom formation. For operation at constant extraction voltages the adatom formation energy becomes a function of the local charge density. The charge-density distribution on the emitter surface as a function of the applied extraction voltage can be calculated with boundary-element methods. It is shown that, provided the relevant material properties are known, it can be predicted if, for a given tip shape, a collapse is to be expected.IST/Imaging Science and TechnologyApplied Science

Reversible shape changes of the end facet on Schottky electron emitters

The Schottky electron source is predominant in today’s focused electron-beam equipment, but its properties are still not fully understood. Generally, its performance is predicted, assuming its tip end geometry is known and stable. In this work, it is shown that the size of the end facet (slowly) shrinks upon reduction in the extraction voltage and (more rapidly) grows upon restoration of the original voltage. Furthermore, the shape of the end facet could be made to change from more circular to octagonal or more squarish. These changes affect the properties of the beamlet that will be cut from the facet beam for practical applications. Better knowledge of the in situ shape of the emitter allows for a better prediction of its performance and stability.IST/Imaging Science and TechnologyApplied Science

Electron microscope

An electron microscope provided with an electron source; an energy-dispersive element; an accelerating tube; a plate mounted between the energy-dispersive element and the specimen, in which a selection slit is provided at right angles to the dispersive direction of the dispersive element; source imaging electron optics for obtaining an image of a source in the plane of the plate comprising the selection slit.Applied Science

Optimization of focused ion beam performance

The authors have analyzed how much current can be obtained in the probe of an optimized two-lens focused ion beam (FIB) system. This becomes relevant, as systems become available that have the potential to image and/or fabricate structures smaller than 10 nm. The probe current versus probe size curves were calculated for a commercial gallium-FIB, the nano-FIB system, and the helium microscope, using partly published, partly estimated system parameters. The current in sub-10 nm probes in the Ga systems turns out to be limited by the reduced brightness of the source and the chromatic aberration of the objective lens. In probes larger than 40 nm the current is limited by the angular current density and the spherical aberration of both lenses. The He system is limited at all probe sizes by the angular current density of the source and the chromatic aberration of both lenses in sub-5 nm probes and the spherical aberration of both lenses at probes larger than 10 nm. As the emission current of the He source is much smaller than that of the Ga source, the statistical Coulomb interactions in the gun lens region do not contribute to the total probe size, as is the case for the Ga systems.IST/Imaging Science and TechnologyApplied Science