Patent Description:
The present invention, in some embodiments thereof, relates to particle beam manipulation and, more particularly, but not exclusively, to particle beam manipulation employing phase modulation.

A scanning electron microscope (SEM) and a scanning transmission electron microscope (STEM) are combined with an electron optical device such as an electron lens to form an extremely small electron beam crossover (hereinafter, will be referred to as a beam probe) on the plane of an observed sample. Transmission scattered electrons, reflected electrons, secondary electrons, or derived X-rays from a small region irradiated by the beam probe are measured to obtain information on the structure and composition of the small region. The electron microscope two-dimensionally scans the beam probe on the plane of a sample by means of an electromagnetic electron beam deflector, obtaining a two-dimensional image.

The resolution of a high-resolution electron microscope is far from being optimal, mainly due to the spherical aberration of the objective lens. Attempts have been made over the years to correct these aberrations. Known in the art are techniques which include taking a series of images of the object under variable objective focus conditions [<NPL>)], and holographic techniques [<NPL>)]. Also known are techniques that employ quadrupole-octopole [<NPL>)] or hexapole [<NPL>)] electromagnetic correctors Further reference is made to "<NPL>, which reports on profiled phase plates for imprinting an aberrated electron beam with sherical aberration of the equal magnitude but opposite sign, thereby cancelling it.

According to an aspect of some embodiments of the present invention there is provided a method of manipulating an electron or ion beam as defined in claim <NUM>.

The method comprises transmitting the beam through a phase mask selected to spatially modulate a phase of a wavefront of the beam over a cross-section thereof.

According to the invention the phase modulation is selected to at least partially compensate for aberrations generated by a beam focusing system.

According to the invention the method comprises applying a multipole electromagnetic field to the beam.

According to the present invention there is provided a system for manipulating an electron or ion beam as defined in claim <NUM>, comprising a phase mask selected to spatially modulate the phase front of the beam over a cross-section thereof.

According to the invention the system comprises a beam focusing system, wherein the phase modulation is selected to at least partially compensate for aberrations generated by the beam focusing system.

According to the invention the system wherein the beam focusing system is positioned behind the phase mask.

According to some embodiments of the invention the system is configured as a transmission electron microscope system.

According to some embodiments of the invention the system is configured as a scanning electron microscope system.

According to some embodiments of the invention the system is configured as an electron beam tomography (EBT) system.

According to some embodiments of the invention the system is configured as an electron beam lithography system.

According to some embodiments of the invention the system is configured as spectroscopy system.

According to some embodiments of the invention the system is configured as a mass spectroscopy system.

According to some embodiments of the invention the system is configured as a free electron laser system.

According to some embodiments of the invention the system comprises an electrostatic lens.

According to some embodiments of the invention the aberrations comprise spherical aberrations.

According to some embodiments of the invention the aberrations comprise chromatic aberrations.

According to some embodiments of the invention the phase mask is discrete.

According to some embodiments of the invention the phase mask is continuous.

As used herein the terms "about" and "approximately" refer to ± <NUM> %.

Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings and images.

The present invention relates to particle beam manipulation and, more particularly to particle beam manipulation employing phase modulation.

<FIG> is a flowchart diagram of a method suitable for manipulating a particle beam.

It is to be understood that, unless otherwise defined, the operations described hereinbelow can be executed either contemporaneously or sequentially in many combinations or orders of execution. Specifically, the ordering of the flowchart diagrams is not to be considered as limiting. For example, two or more operations, appearing in the following description or in the flowchart diagrams in a particular order, can be executed in a different order (e.g., a reverse order) or substantially contemporaneously. Additionally, several operations described below are optional and may not be executed.

According to the invention, the particle beam is an ion or an electron beam. Phase modulation of other particle beams is also contemplated, but not forming part of the present invention. Representative examples of such other beams include, without limitation, a neutral particle beam (e.g., a beam of C<NUM> molecules, or a beam of particles selected from the group consisting of I<NUM>, SF<NUM>, CFCl<NUM>, WF<NUM>, F, Cl and perhallogenated carbon compounds).

The method can be employed in many applications. In preferred embodiments, the method is employed for reducing or eliminations aberration caused by a focusing system such as an electrostatic or electromagnetic lens.

One type of aberration that can be reduced or eliminated by the method of the present embodiments is spherical aberration. In conventional electron lenses, electrons that enter the lens' field at a distance from the lens axis are deflected more strongly than in proportion to this distance. Thus, the intersection of these electrons with the lens axis occurs at different points, causing what is commonly termed spherical aberration.

Another type of aberration that can be reduced or eliminated by the method of the present embodiments is chromatic aberration which results from the fact that electrons of different energies are deflected by different amounts by the focusing system. The method of the present embodiments can reduce or eliminate both longitudinal chromatic aberration and transverse chromatic aberration. In longitudinal chromatic aberration, electrons of different energies are brought to focus on different planes in the image space, which gives a blurring effect. Thus, longitudinal chromatic aberration arises due to the focal length varying with the electron energy. In transverse chromatic aberration, electrons of different energies from a single point are brought to focus to different points on the same image plane, resulting in a lateral shift of the image. Thus, transverse chromatic aberration can be seen as an effect due to magnification varying with electron energy.

Other types of aberration that can be reduced or eliminated by the method of the present embodiments include astigmatism and trefoil.

The particle beam (e.g., electron beam), manipulated by the method of the present embodiments, is preferably a substantially coherent particle beam. The degree of coherence of a particle beam can be quantified by a quantity known as the visibility that can be extracted from an intensity profile of an interference pattern generated by the beam. Denoting by Imax the intensity at the highest peak of the profile and by Imin the intensity of the valleys next to the highest peak, the visibility can be defined as V=(Imax-Imin)/(Imax+Imin).

As used herein, "substantially coherent particle beam" refers to a particle beam characterized by visibility of at least <NUM> or at least <NUM> or at least <NUM>.

The particle beam can be generated by any system employing particle beam, e.g., electron beam. Representative examples including, without limitation, a transmission electron microscope (TEM) system, a scanning electron microscope (SEM) system, an electron beam tomography (EBT) system, an electron beam lithography system, a spectroscopy system, a mass spectroscopy system, electron energy loss spectroscopy (EELS) system, auger electron spectroscopy (AES) system, an electron beam ion trap (EBIT) spectroscopy system, a free electron laser system, and the like. Such systems are collectively referred to herein as electron beam analysis systems.

The method begins at <NUM> and optionally and preferably continues to <NUM> at which a particle beam, such as, but not limited to, electron beam, is generated, for example, by a particle beam analysis system employing particle gun, such as an electron gun or the like. At <NUM> the particle beam is focused by a beam focusing system, such as an electromagnetic or electrostatic lens. According to the invention, the beam passes first through a phase mask <NUM>, but according to embodiments not covered by the present invention, the method continues to <NUM> at which the particle beam is transmitted through a phase mask. The phase mask is selected to spatially modulate a phase of the beam over a cross-section of the beam. The phase modulation is selected to compensate, at least partially, for aberrations generated by the beam focusing system. According to the invention, the beam passes through the focusing system after it is transmitted through the mask. It is appreciated that it is not necessarily for the mask to be placed in the focal or image plane of the focusing system. It is additionally appreciated that when there are several focusing systems a mask can be used for each focusing system. Alternatively or additionally, a mask can be used to for compensating, at least partially, accumulated aberrations generated during the passage of the beam through two or more focusing systems.

Further, the mask can be spaced apart from the focusing system or it can be integrated with the focusing system, wherein the latter option is not covered by the present invention.

In the present invention, the method continues to <NUM> at which an electromagnetic and/or electrostatic field is applied to the beam. The electromagnetic and/or electrostatic field is a multipole field (e.g., quadrupole, hexapole, octapole, etc.).

The multipole field can be used as an active aberration corrector which is complementary to the phase mask. That is the combination of the effect caused by the phase mask and the effect caused by the multipole field reduces or eliminates the aberration. For example, the phase mask can be selected to reduce or eliminate spherical aberration and the multipole field can be selected to reduce or eliminate chromatic aberration. Another example is a configuration in which the mask provides aberration correction along a first axis and the multipole field provides correction along a second axis, wherein both axes are preferably perpendicular to each other and to the particle beam's axis (also referred to in the literature as the optical axis). An additional example is a configuration in which the mask causes a converging effect along the first axis, and the multipole field causes a diverging effect along the second axis, and an opposite configuration in which the multipole field cause a converging effect along the first axis, and the mask causes a diverging effect along the second axis.

It was found by the present inventors that such a combination of an active corrector and a phase mask can provide performance that is impossible to get otherwise.

<FIG> is a schematic illustration of a particle beam system <NUM>, including some components that are also part of the present invention. System <NUM> can be electron beam analysis system, such as, but not limited to, a TEM system, a SEM system, an EBT system, an electron beam lithography system, a spectroscopy system, a mass spectroscopy system, an EELS system, an AES system, an EBIT system, and a free electron laser system.

System <NUM> comprises a particle beam source <NUM> configured for generating a particle beam <NUM> and a particle beam manipulation system <NUM>. In some embodiments of the present invention system <NUM> also comprises a beam focusing system <NUM>, such as, but not limited to, an electrostatic or electromagnetic lens, that is configured to focus beam <NUM> onto a sample <NUM>.

Particle beam manipulation system <NUM> comprises a phase mask <NUM> selected to spatially modulate a phase of beam <NUM> over a cross-section of beam <NUM>. In the present invention phase mask <NUM> modulates the phase of beam <NUM> so as to at least partially compensate for aberrations generated by focusing system <NUM>. In the schematic illustration of <FIG>, mask <NUM> is shown positioned behind focusing system <NUM>. However, this option does not form part of the claimed invention according to which the mask <NUM> is positioned in front of focusing system <NUM>. Other options not forming part of the claimed invention also contemplate configurations in which focusing system <NUM> is integrated with mask <NUM>.

Particle beam manipulation system <NUM> optionally and preferably also comprises an electromagnetic or electrostatic lens <NUM>. Lens <NUM> applies an electromagnetic and/or electrostatic field, which is a multipole field (e.g., quadrupole, hexapole, octapole, etc.). Lens <NUM> can serve as an active aberration corrector complementary to mask <NUM>, as further detailed hereinabove.

Various types of phase masks are contemplated to be used by the method and system of the present embodiments. Generally, the phase mask provides a predetermined pattern (e.g., a phase pattern, an intensity pattern) at a predetermined plane. Though not forming part of the claimed invention, the predetermined plane can be, for example, the image plane or the diffraction plane of the focusing system of the particle, e.g., electron beam analysis system.

As used herein "image plane" refers to a plane defined by a plurality of points wherein each such point is an intersection point of two or more particle trajectories passing through the same point of a sample.

As used herein "diffraction plane" refers to a plane defined by a plurality of points wherein each such point is an intersection point of two or more particle trajectories passing through respective two or more different points of the sample.

The phase mask is typically formed of a solid material having a non-uniform thickness. In various exemplary embodiments of the invention, the thickness is selected such that at least <NUM>% of the particles successfully pass through the solid material. The spatial distribution of the thickness over the area of the phase mask is described by a thickness function that can be discrete or continuous.

A continues distribution of the thickness can be embodied as a thickness that gradually varies across the mask.

A discrete distribution of the thickness can be embodied as a pattern of spaced apart spatial features, wherein the thickness of the solid material between spatial features is different from the thickness of the solid material at the spatial features. The spatial features can be of one or more of: dots, linear segments, curves, two-dimensional regions and the like. Typically, the spatial features are characterized by a grid of coordinates which can be a rectangular grid or a non-rectangular grid. For example, when the spatial features are dots, they can form a lattice of dots over the grid which may be periodic, quasi-periodic or a-periodic. Typically, but not necessarily, the solid material between two adjacent spatial features is thicker than at those spatial features. Thus, for example, the spatial features can form a groove pattern.

In some embodiments the thickness function varies according to the fourth power of a distance from the center of the mask. These embodiments are useful for correcting spherical aberration, and are particularly useful for relatively small angular aperture (e.g., less than <NUM> radians or less than <NUM> radians or less than <NUM> radians or less than <NUM> radians).

In some embodiments the thickness function over the phase mask is selected such as not to exceed a critical point at which the accumulated phase equals a predetermined threshold. These embodiments are also useful for correcting large aberration values, or imposing large phase changes with minimal material thickness, and are particularly useful for larger angular aperture (e.g., above <NUM> radians). A suitable accumulated phase threshold is, for example, about 2π.

In some embodiments the thickness function of the phase mask is binary. Such thickness function describes a phase mask having only two thickness values across the mask.

Representative examples of various types of thickness functions suitable for the present embodiments are provided in the Examples section that follows.

The phase mask can be made of any material that is transmissive to the particle beam, e.g., electron beam. Representative examples including, without limitation, silicon, silicon nitride (SiN), silicon carbide (SiC), silicon oxide (SiO2), boron nitride (BN), carbon, aluminum, gold, silver and diamond. Preferred thickness of the mask, at regions of highest thickness, is less than <NUM>.

The term "consisting essentially of' means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

In light optics, using matter's refractive index to control light is known. In electron microscopy and materials science, deliberate manipulation of the electron beam by custom fabrication of thin masks is almost non-existent or sought-after. Lately, there has been a growing number of publications on manipulation of electron beams using binary (amplitude) masks, rather than phase masks. It was found by the present inventors that phase masks offer a higher energy throughput and larger bandwidth than binary gratings.

This Example relates to the manipulation of coherent electron-beams using diffractive-electron-optics elements (DEOE). A coherent free-electron beam source such as the Field Emission Gun used in the Transmission Electron Microscope (TEM) is optionally and preferably employed. Samples for observation in TEM can be placed on a grid or a membrane such as, but not limited to, any of the standard <NUM>-diameter grids or membranes. In some embodiments of the present invention thin Silicon-Nitride (SiN) membranes ranging from <NUM> to <NUM> in thickness are used. The advantage of these membranes is that they have low scattering and are mechanically robust. Much like light waves passing through glass and acquiring a phase-shift dependent on the material's refractive index, an electron passing through a SiN membrane similarly accumulates a phase factor directly related to the thickness of the interacting material according to [<NPL>] <MAT> where A is the electron's wavelength, E<NUM> = m<NUM>c<NUM> and E = eU are the electron's rest and kinetic energy, respectively, where the kinetic energy is given by the acceleration voltage U and the electron's charge e. The remaining quantities are the thickness t and the material's inner potential Ui, which comprises the electron-optical refractive index n(E).

The DEOE according to some embodiments of the present invention is fabricated employing a Focused Ion Beam (FIB) to mill through the SiN membrane, creating a desired spatial variance of thicknesses which is designed using holographic algorithms. An example of a fabricated hologram and the obtained electron beam are shown in <FIG>. The DEOE can be phase-based and/or amplitude-based, and may have any number of levels. In some embodiments of the present invention the DEOE has only two levels. Such DEOE is referred to herein as a binary DEOE.

In some embodiments of the present invention the DEOE is used for the correction of spherical aberrations of electron lenses.

The de-Broglie wavelength of the electron in the standard TEM (acceleration voltage in the <NUM><NUM>[V] range) is approximately <NUM> picometers. According to Abbe's principle, this enables measurements with picometer resolution. However, the resolution of a high-resolution TEM is almost <NUM> times worse than that (about <NUM> nanometers), due to the spherical aberration of the objective lens. This is a well-known problem with which prominent scientists have struggled starting from the early days of the TEM, back in the <NUM>. Methods for aberration correction do exist nowadays, but they are very complex and expensive. For example, correction can be done by taking a series of images of the object under variable objective focus conditions [<NPL>)], or by holographic techniques [<NPL>)]. In recent years, aberration correction was implemented by adding quadrupole-octopole [<NPL>)] or hexapole [<NPL>)] electromagnetic correctors. These, however, are complicated elements which make the microscope much more expensive.

The present inventors found that the aberration of the electron lenses can be corrected by adding a thin film whose shape and thickness are controlled using nano-fabrication techniques, such as focused-ion beam milling. This film can be a patterned phase plate for the electron that shapes its wavefront in order to balance the distortion of the electron lenses.

The electrons are focused in the TEM using magnetic lenses. These lenses consist of a coil through which current is injected. This coil is held inside a metal shield that has a hole in the middle through which the electrons pass and get focused. This lens creates a bell-shaped magnetic field along the optical axis. More complicated lenses are quadrupole lenses that are constructed from four poles of opposite polarity, as well as hexapole and octopole lenses that consist of either six or eight poles, respectively. Most of the high-resolution TEMs operate with standard polepiece lenses. Advanced electron microscopes also include combinations of hexapole or quadrupole and octopole lenses that are used to correct lens aberrations.

It was found by the present inventors that conventional magnetic lenses are far from perfect, and suffer from severe aberrations. An example is spherical aberration wherein electron rays that pass farther away from the optical axis have shorter focal length, as shown in <FIG>. As a result of this aberration, the rays are not focused to a point at the focal plane, but to a circular spot of a finite size.

Owing to this aberration, the smallest diameter that can be observed in a specimen is dnin = <NUM>Csα<NUM> , where Cs is the lens spherical aberration constant and α is the angular spread of the electron beam. The spherical aberration constant is typically in the range <NUM>-<NUM>. Hence, for Cs = <NUM>mm, α = <NUM>mrad the smallest diameter that can be observed in a specimen is dmin = <NUM>nm, which is already twice larger than the diffraction limit for the same angular aperture.

The effect of the aberration can also be described in terms of wavefront distortion. An ideal lens converts a planar wavefront to a spherical wavefront which later converges to the image point. However, owing to spherical aberrations, the wavefront beyond a lens is more strongly curved in the outer zones of the lens, with respect to the ideal spherical wave, and therefore the outer part of the beam focuses at a shorter distance with respect to the part that is close to the optical axis. Let ΔS be the optical path difference between the ideal spherical wave and the actual wave that is obtained from the lens, and let W be the corresponding phase difference (also known as wave aberration) <MAT>.

In the case of spherical aberration and assuming that there is no defocusing: <MAT>.

This means that the spherical aberration results in wavefront distortion that scales as the fourth power of the conical angle θ, which is also the fourth power of the aperture radius r ≈ θf, where f is the lens focal length.

In addition to spherical aberrations there are other aberrations, such as distortion, axial astigmatism, coma and chromatic aberrations. Usually, the spherical aberration is dominant.

Aberration of the magnetic lenses in the high-resolution TEM is limiting its resolution to ~<NUM>, which is approximately <NUM> times larger than the de-Broglie wavelength of the electrons in the TEM. Scientists have struggled to overcome this limitation already from the early days of the TEMs, in the <NUM>. It was shown already in <NUM> by Otto Scherzer that spherical and chromatic aberrations cannot be eliminated in rotationally symmetric electron lenses [<NPL>)]. Scherzer proposed various ways for correcting chromatic and spherical aberrations [<NPL>)]. Among them is the proposal to use electrostatic or magnetic multipole elements for correcting chromatic and spherical aberrations, as well as some other suggestions, such as use of charge foils, mirrors, high frequency lenses, etc. Dennis Gabor proposed the concept of holography as a method of overcoming the limits of aberrations [<NPL>)]. The implementation of these concepts proved to be very challenging, and it took <NUM> years until Haider et al published the first images obtained using a TEM that included hexapole elements for aberration correction [<NPL>)], following an approach proposed by Rose. Krivanek et al showed correction of spherical aberration of using a quadrupole-octopole system [<NPL>)]. These multipole correctors provided nearly a factor of two improvement in resolution, from <NUM> to <NUM>. State of the art commercial aberration-corrected TEMs provide nowadays a slightly better resolution of -<NUM>. However, the multipole correctors cannot be simply added to an existing TEM, the design and implementation is quite delicate, and the cost of aberration corrected microscope is about twice than that of a high resolution TEM (e.g. -<NUM> MEuro for Cs-corrected Titan G2 vs. -<NUM> MEuro for high-resolution Tecnai F20). Moreover, the resolution is still quite far from the electron wavelength.

The present inventors discovered that the DEOE can be used for aberration correction. The DEOE is fabricated by nano-fabrication, and the present inventors showed that the DEOE can control the wave-front of the electron wave-function. Rather than applying electromagnetic forces, the electron is controlled by modulating its wave-front in the nano-fabricated element. In some embodiments of the present invention thin films whose shape and thickness are controlled by focused ion beam milling are prepared, so that the electron wavefunction undergoes a different phase shift at each of at least some points of the film. This space-dependent phase is designed according to some embodiments of the present invention to cancel the aberrations that are added by the electron lens.

In order to illustrate the technique of the present embodiments, a spherical aberration is considered. This aberration is equivalent to a wavefront deviation from the ideal spherical wave which scales r<NUM>, where r is the radial coordinate at the aperture. Hence, if the electron beam passes through a plate whose thickness also scales as r<NUM> before entering the lens, it accumulates a space-dependent phase shift that exactly cancels the aberration of the lens, as illustrated in <FIG>. Assuming lens focal length of <NUM> and electron wavelength of <NUM> pm (which is obtained with a voltage of <NUM> kV), the shape of the wavefront distortion is given by <MAT>.

The highest distortion is obtained at the largest radius of the aperture, θƒ ≈ <NUM>µm, and is equal to approximately π radians. In silicon for example, the accumulated phase with respect to air in a layer of thickness t is given by <MAT>.

This means that a thickness of <NUM> generates a phase shift of π. The phase shift corrector can therefore be of variable thickness of the form d(r) = d<NUM> + d<NUM>r<NUM>, with a thickness that is <NUM> thicker in the edge of the plate with respect to its center, as shown in <FIG>. Assuming the thickness at the center is d<NUM> = <NUM>nm, it becomes <NUM> at the edges, still smaller than the typical mean free path in silicon, which is more than <NUM>. The present inventors showed the transmission of electrons through a plate fabricated according to some embodiments of the present invention, which already shows the r<NUM> dependence.

While this type of phase plate is suitable, for example, for a lens with a small numerical aperture (e.g., <NUM> mrad or less), the resolution can be improved by operating with lenses having larger numerical aperture, whose diffraction limit λ/(<NUM> sin θ) is therefore smaller. This translates to larger apertures, and hence to larger spherical aberration, wherein thicker compensating films can be used. To avoid or reduce scattering, a "zone-plate" type of compensators can be used. In these embodiments, the thickness function optionally and preferably does not exceed a critical point in which the accumulated phase is 2π. Beyond this point, the thickness is set back to the minimum value, as shown in <FIG>.

In some embodiments a binary phase plate that has only two possible values of the thicknesses is employed. In these embodiments, a high frequency carrier modulation for imposing amplitude and phase information can be used.

An example is shown in <FIG>. This allows obtaining a corrected image at the first diffraction order.

In some embodiments of the present invention a hybrid corrector is employed. The hybrid corrector combines nano-fabricated phase plate with a multipole electromagnetic lens. This allows splitting the tasks of aberration compensations between the two types of correctors. It was found by the present inventors that such a hybrid corrector can provide performance that is impossible to get otherwise.

Several samples have been fabricated to test the ability of the present embodiments to properly shape the thickness of the phase plate. Amorphous silicon film of <NUM> thickness was placed on top of a TEM grid. The film was then thinned by milling circles in FIB, using a 35kV Galium beam with 20pA current. <NUM> concentric circles with different radii were milled, each one milling ~<NUM>/<NUM> of the total film thickness. The radius of each circle was determined by the R<NUM> function. The circles were milled starting with the smaller central circle and the subsequent circles were then milled outwards from the center with a step size of <NUM>. The films were then inserted into the TEM and images of the electron beam that passes through them were recorded. An example is shown in <FIG>. In these thin films, the brightness of each area in the image is nearly linearly proportional to the thickness of the film. By analyzing the brightness of the image as a function of the radial coordinate the profile of the shape after the milling process is estimated. Using this analysis, films whose recorded intensity patterns show the required R<NUM> dependence have been obtained, as shown in <FIG>.

A "zone-plate" corrector according to some embodiments of the present invention is shown in <FIG>. Such a corrector can be fabricated using high resolution FIB, electron beam nano-lithography and the like. Electron beam nano-lithography was applied to fabricate Fresnel lenses for electrons [<NPL>)]. The potential advantage here is the ability to compensate for much larger wave-front deviations, with respect to the simpler variable thickness corrector.

A binary thickness corrector is shown in <FIG>. This corrector has two possible thicknesses: the original thickness of the sample, and the milled thickness determined by the FIB. A binary thickness corrector can be used to correct many types of wavefront distortions. In some embodiments, binary thickness corrector is used to compensate for the chromatic aberration [<NPL>)], and spherical aberration.

A DEOE according to some embodiments of the present invention can also be fabricated by means of nano-fabrication other than a FIB. Representative examples include, without limitation, e-beam lithography, optical lithography and later mass-production by nano-imprinting. The free-electron source and lens setup can be TEM, or any other electron source and lens setup. Representative examples include, without limitation, scanning electron microscopes, free-electron lasers and any device that creates or manipulates electron beams. Specifically, electron lenses may be magnetic or electric.

The DEOE of the present embodiments can be discrete (for example, characterized by a rectangular lattice composed of distinct dots), or characterized by a non-rectangular lattice or be continuous. The DEOE can, in some embodiments of the present invention, be composed of shapes other than dots. The DEOE can, in some embodiments of the present invention, include sub-lattices. DEOE can, in some embodiments of the present invention, be arranged as entirely continuous shapes with any desired topographical mapping of heights that result in a desired pattern in the diffraction plane or the image plane of the lens system.

The DEOE can be made of any material that can facilitate phase modulation, once patterned. Typically, a low-scattering material is used so that only the phase of the electrons is controlled and energy throughput is maximal. However, for some applications variance of amplitude may be desired and appropriate materials may be chosen for this case. Also, DEOEs may be made by coalescing several different materials or alternately depositing some upon others to achieve the required phase and amplitude manipulation.

DEOEs may also be constructed in three-dimensions by planar techniques: depositing and spatially altering a layer of material, then repeating the process to yield any number of layers each of which with its own geometrical or material composition.

Aside from generic, elemental materials such as gold, silver, silicon etc., DEOEs may be based on composite structures such as carbon-based structures or nano-fabricated electronics, or elements that respond to external stimulation such as laser light, temperature change, etc..

Claim 1:
A method of manipulating an electron or ion beam propagating along an optical axis, the method comprising:
generating the beam (<NUM>) by a beam source (<NUM>);
transmitting the beam through a phase mask (<NUM>) positioned in front of a beam focusing system (<NUM>) with respect to the direction of propagation, said phase mask being selected to spatially modulate a phase of a wavefront of the source beam over a cross-section thereof, to at least partially compensate for aberration generated by said beam focusing system; and
applying a multipole electromagnetic field (<NUM>) to the beam so as to also at least partially compensate for said aberrations;
wherein said compensation by said multipole electromagnetic field is complementary to said compensation by said phase mask.